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Gamma X

Alexandre_Volta · SF

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Gamma X

Gamma Radiation

Gamma radiation (7.5Gy) resulted in a significant decrease in body weight, tissue weight, testis: body weight ratio (the gonadosomatic index (GSI)) and tubular diameter up to 15 days of irradiation.

From: Polyphenols in Human Health and Disease, 2014

Related terms:

Nested Gene

Neutron

Photon

Positron

Ionizing Radiation

X Ray

Positron Emission Tomography

Single Photon Emission Computed Tomography

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Gamma radiation

Tim Sandle, in Sterility, Sterilisation and Sterility Assurance for Pharmaceuticals, 2013

4.1 Introduction

Gamma rays are a form of electromagnetic radiation, whereby gamma radiation kills microorganisms by destroying cellular nucleic acid [1]. The use of gamma irradiation is relatively widespread and was first described in the British Pharmacopeia in 1963 and in the United States Pharmacopeia in 1965 (17th edition). The use of gamma radiation became more widespread in the 1980s, following concerns with the ecological and toxicological risks associated with ethylene oxide. However, it is only in recent years that the use of gamma irradiation has increased within the healthcare sector and the pharmaceutical industry. This arises from the use of gamma radiation to sterilise consumables and single-use technologies used for aseptic operations. The use of single-use disposable technologies has advanced, because organisations have moved away from equipment that needs to be sterilised or consumables that are recycled. This has established gamma radiation as the most widely-used method for sterilisation [2].

Whilst gamma radiation is very suitable for plastic materials, it cannot be used for aqueous drug products and pharmaceuticals with a proteinaceous component, because the process can degrade such products. This chapter outlines the application of gamma radiation, discusses the way in which it works, and describes the important aspects of validation.

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Sterilisation considerations for implantable sensor systems

S. Martin, E. Duncan, in Implantable Sensor Systems for Medical Applications, 2013

8.3.4 Sterilisation by exposure to radiation

Methods of sterilising medical devices using radiation include X-rays, gamma rays, and electron-beam (ISO 11137-1, 2006). Their suitability for the sterilisation of implantable sensor systems depends on compatibility with the sensor materials and on the volume of product.

High-energy X-rays are a form of ionising energy suitable for irradiating large volumes of product. Their penetration is sufficient to treat multiple pallet loads of low-density packages while maintaining a uniform dose across all of the product. As well as benefitting from quantity, X-ray sterilisation is a 'clean' electricity-based process not requiring chemical or radioactive material. Commercial use for medical devices began in the mid-1990s, though adoption has been slow. The current availability of high-power accelerators may increase the market share (Stichelbaut et al., 2006).

Gamma rays are very penetrating and are used for the sterilisation of about one-third of medical devices, especially for disposable medical equipment, such as syringes, needles, cannulas and intravenous sets. The disadvantages of this method are that gamma radiation can affect some materials and involves an isotope, usually Cobalt-60, meaning that operators require bulky shielding and storage of the isotope presents a hazard for the facility (Technical information, Cobalt5).

Electron-beam (E-beam) processing is less frequently used for medical device sterilisation but is increasingly popular with manufacturers for whom it is suitable. Unlike gamma radiation, E-beams use an on-off technology and provide a much higher dosing rate than gamma or X-rays. Another advantage is that owing to the higher dose rate, less exposure time is needed, lowering the potential for degradation to polymers. A limitation is that electron beams are less penetrating than either gamma or X-rays.

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Imaging and Adenoviral Gene Therapy

Jillian R. Richter, ... Kurt R. Zinn, in Adenoviral Vectors for Gene Therapy (Second Edition), 2016

2.1 Nuclear (Gamma-Ray) Imaging

Gamma rays are the highest energy photons (shortest wavelength, highest frequency), arising out of nuclear events during radioactive decay. For in vivo applications, the best gamma rays are of low energy (100–511 keV) because they can penetrate tissues. Gamma rays in this energy range can also be efficiently stopped, and therefore measured by external detectors. Most human imaging procedures with radioactivity are accomplished using 99mTc, which emits a 140 keV gamma ray during decay. 99mTc has a 6 h half-life and is continuously available from generators at hospitals or at regional nuclear pharmacies. It is the decay product of 99Mo (half-life = 66 h) and is eluted daily from the 99Mo/99mTc generator system, and therefore available at very high specific activity and low cost. 99mTc can be chelated (complexed) with various compounds that have different biological characteristics, or it can be attached to proteins.

99mTc is typically imaged with a gamma camera that includes a collimator, a lead gamma-ray attenuator that is placed between the imaging subject and the gamma-ray detector. There are various types of collimators, some specific for low energy gamma rays, whereas others are thicker and designed for higher energy gamma rays. Examples of collimators are the parallel-hole collimator and the pinhole collimator. The parallel-hole collimator allows passage of gamma rays that are perpendicular to the plane of the collimator. In contrast, the pinhole collimator has a small round hole at the end that allows projection of the gamma rays onto the detector crystal, thus forming an image like a pinhole camera. Figure 1 presents images of an Ad5 vector encoding luciferase that was radiolabeled with 99mTc and injected intravenously in four mice. Each mouse was positioned below the pinhole collimator at 10 min after injection, and a static gamma camera image was collected. The gamma rays emitted from the animal were stopped by the detector crystal and visible light photons were emitted. These photons were captured by the photomultiplier tubes adjacent to the crystal, and converted to a voltage pulse. The X,Y location of the interaction event was recorded, as well as the magnitude of the voltage pulse (Z, pulse height), which was proportional to the energy of the gamma ray that was stopped. The 2D gamma camera image in this example showed the expected liver pattern of the Ad5 vector distribution.

Figure 1. Gamma camera imaging of 99mTc-labeled Ad5 encoding luciferase following intravenous injection in 4 mice.

Proteins can be radiolabeled with 99mTc for imaging applications. Most often, the 99mTc is attached to proteins with a bifunctional chelator. With this system the chelator is first attached to the protein, then the 99mTc in complexed to the chelator in a separate step. An example was the 99mTc-labeling of Ad5 knob.1 Besides 99mTc, other radionuclides that are used for imaging include 67Ga, 111In, 123I, 125I, and 131I (see Table 2). These radionuclides have different gamma-ray emissions; therefore, simultaneous imaging with 99mTc is possible.

Table 2. Common PET and SPECT Radionuclides Used in Imaging

PET IsotopesHalf-lifeDecay Modes (% Abundance)Energy of Emissions Relevant for Imaging, keV (% Abundance)Source11C20.4 minβ+ (100%)385.7 β+ (99.8%)Cyclotron511.0 γ (199.5%)13N10.0 minβ+ (100%)41.8 β+ (99.8%)Cyclotron511.0 γ (199.6%)15O2.0 minβ+ (100%)735.3 β+ (99.9%)Cyclotron511.0 γ (198.8%)18F1.8 hβ+ (100%)249.8 β+ (96.7%)Cyclotron511.0 γ (193.75%)64Cu12.7 hβ− (38.5%)278.2 β+ (17.6%)Cyclotronε (61.5%)511.0 γ (35.2%)68Ga1.1 hε (100%)836.0 β+ (87.9%)Generator511.0 γ (178.3%)86Y14.7 hε (100%)394.1 β+ (1.1%)Cyclotron454.2 β+ (1.9%)509.4 β+ (1.3%)535.4 β+ (11.9%)681.1 β+ (5.6%)767.8 β+ (1.7%)883.3 β+ (3.6%)1436.8 β+ (2.0%)307.0 γ (3.5%)382.9 γ (3.6%)443.1 γ (16.9%)511.0 γ (64%)89Zr3.3 daysε (100%)395.5 β+ (22.7%)Cyclotron511.0 γ (45.5%)124I4.2 daysε (100%)366.8 β+ (0.3%)Cyclotron687.0 β+ (11.7%)974.7 β+ (10.7%)511.0 γ (45.0%)SPECT isotopes67Ga3.3 daysε (100%)91.3 γ (3.1%)Cyclotron93.3 γ (38.8%)184.6 γ (21.4%)209.0 γ (2.5%)300.2 γ (16.6%)393.5 γ (4.6%)99mTc6.0 hIT (99.99%)140.5 γ (89.1%)Generator111In2.8 daysε (100%)171.3 γ (90.7%)Cyclotron245.4 γ (94.1%)123I13.2 hε (100%)159.0 γ (83.3%)Cyclotron131I8.0 daysβ– (100%)284.3 γ (6.1%)Reactor364.5 γ (81.5%)

The image presented in Figure 1 is a planar image that represents a 2D projection of the 99mTc-Ad5 at 10 min after intravenous injection. SPECT is also possible with specialized gamma cameras that are routinely available in small animal imaging cores and nuclear medicine departments. SPECT is accomplished by collecting multiple images (or projections) at various angles around the subject; the detectors move while the subject remains static. A tomographic image of the distribution of the radioactivity is produced following reconstruction of these projections.

Gamma camera imaging is differentiated from PET as PET can image only 511 keV gamma rays that arise from positron decay. PET is a 3D imaging technique for the indirect detection of positrons. Positrons are positively charged electrons that are emitted from a proton-rich nucleus during radioactive decay. The lifetime of positrons is relatively short since they undergo annihilation by combining with an electron, giving rise to two 511 keV gamma rays at opposite (180°) orientations. The 511 keV gamma rays are actually detected in PET, not the positrons. PET scanners have a circular array of detectors that are designed to detect photons in coincidence, and the exact time of detection can be recorded. This means that during analyses it can be precisely known when two detectors at opposite orientations simultaneously detect the 511 keV gamma rays, arising from the positron annihilation event. Since various 511 keV pairs of photons strike different opposite pairs of detectors, the location of the actual decay events can be determined when the image is reconstructed. PET scanners do not require collimators, since the coincidence detection method accomplishes the same objective. There have been many recent advances in SPECT and PET hardware.2

Radionuclides that are used in PET imaging are proton rich and produced at cyclotrons using charged-particle reactions. A list of common PET radionuclides is included in Table 2. Most PET radionuclides have short half-lives; therefore, production must be in close proximity to where imaging will be done. In addition, PET radionuclides such as 11C, 13N, and 15O are suitable as intrinsic labels for many molecules, thereby enabling imaging studies of the actual molecule of interest. For example, fatty acid metabolism could be imaged with the 11C-labeled fatty acid, where the 11C replaced the normal 12C in the molecular structure. Intrinsic labeling of this type cannot be accomplished with 99mTc, since the radionuclide is not part of the molecule. A bifunctional chelate would be required for the 99mTc to attach it to the fatty acid, and due to the size of the chelator the 99mTc-labeled fatty acid might have different in vivo uptake and elimination characteristics than the natural fatty acid.

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Irradiation of Blood Products

Richard O. Francis MD, PhD, in Transfusion Medicine and Hemostasis (Third Edition), 2019

Sources of Irradiation

γ-rays, X-rays, and PI technologies can be used to irradiate blood products and cause adequate T-lymphocyte inactivation at the doses described. Usually, γ-rays originate from cesium 137 or cobalt 60 while X-rays are generated from linear accelerators or stand-alone units.

Since the September 11, 2001 attacks, there has been increased regulation of blood irradiators by the US Nuclear Regulatory Commission (NRC). One initiative through the Energy Policy Act is to find alternative technologies that do not use radionuclides, such as electricity, or use lower-risk sources. Therefore, there has been increasing use of X-ray irradiators.

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Nuclear Geology

Michel Cuney, in Encyclopedia of Geology (Second Edition), 2021

Gamma radiation

Gamma radiation is an electromagnetic radiation with considerable penetration in air, enabling its use for airborne measurements, but easily attenuated by a relatively thin shield of solid material.

The smallest unit of radioactivity is the Becquerel (Bq), which correspond to a rate of one disintegration per second (dps). The Curie (Ci) is equal to 3.7 × 1010 Bq (or dps), which corresponds to the radioactivity of 1 g of 226Ra.

The particles or radiations emitted during a nuclear reaction, have characteristic emission energies. The energies of nuclear radiations range from several electron-volts (eV) to more than 10 MeV. Nuclear reactions and the resulting radiation can be either of natural or artificial origin. The activity of radioactive particles and radiation decreases with time during their transmission in a given matrix (atmosphere, water, or solid earth materials). Alpha and beta particles will be only detected in close proximity of the radiation source, whereas gamma radiations can be detected from some distance away. For this reason gamma radiation is measured in order to detect U, Th and K concentrations in the Earth's crust using airborne surveys.

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Borehole Geophysics

Pierdominici Simona, Kück Jochem, in Encyclopedia of Geology (Second Edition), 2021

Natural radioactivity

The naturally occurring gamma radiation of the formation around the borehole is measured by two sonde types, both using scintillation crystals to detect the incident gamma rays. The total gamma ray sonde (GR) measures the natural radioactivity by counting all gamma rays. The sonde calibration translates these gamma counts to the standardized unit gamma-API [gAPI], which allows a comparison of readings of different GR sondes. (API stands for American Petroleum Institute.)

The spectral or spectrum GR sonde (SGR) sonde in addition analyses the energy spectrum of the incident gamma rays. A best fit algorithm matches the measured GR spectrum, finally yielding the weight contents of Potassium 40K [%], Thorium 232Th [ppm], and Uranium 238U [ppm]. These three elements and their decay-products produce all naturally occurring radioactivity. Total and spectrum GR can be measured through steel casings.

An important application of the total GR log is for depth matching. A total GR log is generally measured alongside with all other sondes for depth matching amongst several individual logging runs within one hole section. SGR and GR logs are applied for instance for lithostratigraphy construction (Fig. 7), cyclostratigraphic analysis, identification of sandstone and clay layers, and the calculation of natural heat production.

Fig. 7. Downhole logging measurements in sedimentary and crystalline rocks. The logs show different values depending on the type of rock. High values in total gamma and spectrum gamma ray in rocks with high clay content, while intermediate and low values for other rock types. Density and neutron porosity logs show high values, suggesting high compactness and low porosity in rocks such as granite, gneiss and basalt. F, fracture.

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Basic Principles in Gynecologic Radiotherapy

Catheryn M. Yashar MD, FACR, FACRO, in Clinical Gynecologic Oncology (Ninth Edition), 2018

Sources of Radiation

Gamma rays are the photons emitted from the atomic nuclear decay of radioactive isotopes—for example, 137Cs (cesium) or 60Co (cobalt). X-rays are photons electrically generated by bombarding a target such as tungsten with electrons (how a linear accelerator works). When these fast-moving electrons approach the tungsten nuclear field, they are attracted to the nucleus and thus veer from their original path. This change in direction causes deceleration and kinetic energy is converted to x-rays in the form of bremsstrahlung photons. These emitted x-rays, or photons, vary in energy from zero to a maximum determined by the kinetic energy of the bombarding electrons. Machines such as the betatron and linear accelerator generate electrons with high kinetic energy and thus produce high-energy x-rays. In addition to bremsstrahlung photons, characteristic photons are also produced as atoms seek to fill electron orbital vacancies (see later discussion). Gamma rays and x-rays can be collectively called photons, and what is of medical importance is the energy and delivery of the photon, not the source.

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Introduction to Emission Tomography

MILES N. WERNICK, JOHN N. AARSVOLD, in Emission Tomography, 2004

4 Noise in Emission Tomography Data

In addition to the factors just mentioned, all ET data are corrupted by noise, which is usually the factor that most limits the image quality obtainable by ET. To understand noise in ET, we must look more closely at the detection process.

Gamma rays are photons and thus are governed by the laws of quantum physics and the randomness that this entails. Therefore, to be precise, we should think of the projection image at the face of the gamma camera as a probability density function governing the photon detection process. Specifically, the probability that any given event will take place within a given region of the image (e.g., a pixel) is proportional to the average rate of gamma-ray arrivals within that region.4 Thus, on average, more events will be recorded in bright areas of the projection image than in dark areas during any given time interval.

However, the actual number of events recorded within a region of the image during any fixed time interval is a random number. Therefore, if we were to image the same object again and again, we would each time obtain a slightly different result. This variation, which is manifested as a speckled appearance within each projection image, is called noise. The noise in ET images is called photon noise because it arises from randomness inherent in the photon-counting process. Photon noise is also called Poisson noise, because the number of events recorded in any fixed interval of time obeys the well-known Poisson probability distribution, which is commonly associated with counting processes.5

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Compton Cameras for Nuclear Medical Imaging

W.L. ROGERS, ... A. BOLOZDYNYA, in Emission Tomography, 2004

3 Polarization

Single gamma rays emitted from a nucleus are unpolar-ized. That is, all orientations of the electric vector are equally likely. When an unpolarized beam undergoes Compton scattering it becomes partially linearly polarized orthogonal to the scattering plane because the scattering cross section for the perpendicular and parallel components is not the same (Klein and Nishina, 1929). The degree of polarization is a function of scattering angle and initial gamma-ray energy as illustrated by Eq. (9) (McMaster, 1961) and Figure 6:

FIGURE 6. Gamma-ray polarization as a function of scattering angle at three primary gamma-ray energies.

(9)p=sin2θ1+cos2θ+(E0−E1m0c2)(1−cosθ1)

Moreover, a subsequent Compton scattering of this partially polarized beam will produce an azimuthally asymmetric intensity in the scattered gamma rays that depends on the angle between the incident gamma-ray polarization, e1, and the scattered gamma-ray polarization, e2. Kamae et al., (1987) have described an application of this method to measuring the energy, direction, and polarization of incident gamma rays.

Polarization influences two aspects of Compton camera performance. First, gamma rays that scatter in the patient will be partially polarized. Those scattered gamma rays that cannot be rejected by energy windowing will have an asymmetric azimuthal scattering distribution in the first detector and should therefore be back-projected using a weighted azimuthal distribution. Because the initial scattering plane is unknown, there is no frame of reference for the asymmetry, so these events must be modeled using a uniform azimuthal distribution. The effects of this mismodeling have not been evaluated. Second, polarization effects can be used to reduce the conical ambiguity for gamma rays that have not been scattered in the patient. For gamma rays that undergo two or more scatters in a Compton camera, Dogan (1993; Dogan et al., 1992) has shown that it is possible to determine an azimuthal weighting function for the conical back-projection that reduces the ambiguity. One must first determine the sequence of interactions. Methods for sequencing have been described by Kamae and Hanada (1988), Dogan (1993; Dogan et al., 1990, 1992), and Durkee (Durkee, Antich, Tsyganov, Constantinescu, Fernando, et al., 1998; Durkee, Antich, Tsyganov, Constantinescu, Kulkarni, et al., 1998) and essentially consist of determining which set of energies and scattering angles calculated for each of the postulated sequences best fits the data. For n interactions, there are n! sequences to test, so untangling more than three interactions could be very time consuming.

Figure 7 illustrates the probability of Compton double scattering as a function of azimuthal angle. Results are shown for 150-keV gamma rays and two different initial scattering angles (Dogan et al., 1992). Polarization effects have been included in a system design study by Chelikani et al (2004), but the effect of this added information on improving image quality for Compton imaging has not been completely investigated to our knowledge. However, it appears from Figure 7 that one can substantially reduce the ambiguity in azimuth for low-energy gamma rays for the larger scattering angles.

FIGURE 7. Azimuthal probability of conical distribution derived for double Compton scattering for 150-keV incident gamma rays. θ1 is the first scattering angle, and Φ is the azimuthal angle around the cone measured with respect to the second scattering plane.

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Gamma Radiation

Gamma rays are electromagnetic waves of the same nature as light, having much shorter wavelength, and consequently much higher frequency and energy.

From: Encyclopedia of Soils in the Environment, 2005

Related terms:

Proton

Shale

Radioactive Isotope

Neutron

Photon

Alpha Radiation

Irradiation

Uranium

X Ray

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Well Logging

John R. Fanchi, in Shared Earth Modeling, 2002

Gamma Ray Logs

Gamma rays are photons (particles of light) with energies ranging from 104 ev (electron volts) to 107 ev. Gamma ray logs are used to detect in situ radioactivity from naturally occurring radioactive materials such as potassium, thorium and uranium. In general, shale contains more radioactive materials than other rock types. Consequently, the production of gamma rays by radioactive decay is greater in the presence of shale. A high gamma ray response implies the presence of shales, while a low gamma ray response implies the presence of clean sands or carbonates.

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Exploration Technique

A.M. Dayal, ... A.K. Varma, in Shale Gas, 2017

5.3.1 Introduction

Gamma ray measurement is the most important part of any shale gas exploration because shale with high organic content has high gamma ray intensity. A gamma ray survey can be carried out in an unexplored sedimentary basin to get a broad picture about the presence of organic shale. The geochemical analysis of organic shale shows the high content of potassium, uranium, and thorium, which are high gamma ray material. A gamma ray survey for a shale formation of Cretaceous and Mesozoic age is not useful. For that purpose, another geophysical exploration like resistivity and porosity work is necessary. The association of natural gas in shale formations is as free gas and adsorbed gas. Some of the natural gas may be present in the form of kerogen in a shale formation.

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Quasars

B.M. Peterson, ... M. Vestergaard, in Encyclopedia of Physical Science and Technology (Third Edition), 2003

III.A.1 Gamma Rays

Strong γ-ray emission is detected in blazars only. Gamma-ray emission is strongly correlated with radio emission and radio variability. The γ-rays are almost certainly relativistically beamed emission that arises in jets (Section II.C), and therefore are seen only when the jet is directed towards the observer. The γ-ray emission is also highly variable. Gamma rays are probably the result of inverse-Compton upscattering of lower energy photons. The origin of the seed photons is not known, but might be either the low-frequency synchrotron photons or photons from the accretion disk.

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Source Rock Evaluation

Harry Dembicki, Jr., in Practical Petroleum Geochemistry for Exploration and Production, 2017

Gamma Ray

The gamma ray signal detected in wireline logs is derived primarily from the naturally occurring radioactive elements uranium, potassium-40, and thorium. It has been long known that source rocks are often "hot" zones on gamma ray logs. The high gamma ray response associated with source rocks comes from the uranium content of the sediments. Uranium compounds are water soluble when the sediment's Eh is oxidative, but under reducing conditions, uranium compounds precipitate and become fixed in the sediments. Organic matter in sediments can cause reducing conditions to develop which in turn precipitates uranium from natural waters (Fertl and Chilingar, 1988), and the amount of uranium in the sediments is often directly proportional to the amount of organic matter present. Increases in gamma ray response with organic matter content are frequently detected in the bulk gamma ray signal. However, an increase in bulk gamma ray may also be in response to increases in potassium-40 and/or thorium in the sediment. A better indicator of increased organic matter content with increasing gamma ray signal can be obtained using only the uranium signal derived from spectral gamma ray logs (Fertl and Rieke, 1980). Gamma ray logs used for source rock studies must be corrected for borehole size.

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Practical Petrophysics

Martin Kennedy, in Developments in Petroleum Science, 2015

4.5.5 Spectral Gamma Ray

The gamma-ray tools described in the previous sections measure the total gamma-ray count-rate regardless of the gamma-ray energies. But in fact the energy of the individual gamma rays can be measured using the scintillator-photo-multiplier detector at the heart of nearly all modern gamma-ray tools. This is useful information because the energy of the gamma ray produced by the decay of an unstable nucleus is a characteristic property of the nucleus. For example, when K-40 decays it emits a gamma ray with an energy of 1.46 MeV. The number of 1.46 MeV gamma rays detected at a particular depth can thus be related to the number of potassium atoms in the volume of investigation of the tool.

The scintillator is a cylinder of dense transparent material that emits a flash of light when a gamma ray is absorbed. The photo-multiplier is an electronic device that converts light to an electrical pulse. Dense materials are preferred for the scintillator because they are most likely to absorb the incoming gamma ray completely and they have to be transparent in order for the flash of light to be detected. For many years the standard scintillator was a single crystal of sodium iodide doped with thallium but in the 1990s alternative materials began to appear that were more efficient gamma-ray absorbers (the density of NaI is 3.67 g/cm3, BGO one of materials that is replacing it, has a density of 7.13 g/cm3!). Regardless of what the scintillator is made from, it turns out that the intensity of the light is proportional to the energy of the gamma ray. The photo-multiplier in turn converts the light flash to a voltage pulse whose magnitude is proportional to the light intensity so the net effect is that the electrical signal gives the energy of the incoming gamma ray.

In practice the measurement is complicated by the fact that the energy recorded by the tool is not necessarily the energy of the original primary gamma ray. In fact the majority of gamma rays arriving at the tool will have much lower energy because of scattering either in the formation, mud or the tool itself. Even if the gamma ray arrives at the detector without being scattered it may not be completely absorbed, so in the case of a K-40 decay the tool actually records an energy of less than 1.46 MeV. The net effect is that the primary gamma rays that can be related to the concentrations of uranium, potassium and thorium make up only a small fraction of the total count-rate recorded by the tool (one in a thousand or less). In order to get statistically meaningful count-rates spectral gamma-ray tools use scintillators that are many times larger than those used in a standard gamma-ray tool. Even then some sophisticated signal processing is used to try and extract more information from the scattered gamma rays.

Furthermore, the measurement becomes less accurate at high temperatures. It is also more difficult to build a spectral tool in LWD form because the large amount of steel in the tool absorbs and scatters most of the primary gamma rays. The recent improvements in detector technology however, have allowed at least one contractor to offer an LWD spectral gamma-ray service.

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Active Faults of Sea Area

Ye Yincan et al, in Marine Geo-Hazards in China, 2017

1.3.6 γ Ray Measurement

γ Ray measurement can also be used for submarine active fault survey. The Atmosphere and Ocean Research Institute, The University of Tokyo (AORI), has used the "Pale blue" ship to conduct γ ray measurement experiments at Yokosuka offshore and Sagami Bay; Japanese scholars Hiroshi Wakita et al. put the radioactive detector in the bottom of the sea tug and used an optical fiber transmission determination system to speculate the submarine fault location according to the different ray intensity. Experimental results show that the submarine can be completely measure γ ray, and can infer its concentration to help judge the existence and position of sea active faults.

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Introduction to Well Logging

C. Richard Liu, in Theory of Electromagnetic Well Logging, 2017

1.3.1 Gamma ray log

Gamma rays are basically short bursts of high-frequency EM waves emitted by the atomic nuclei. Such emission may happen when a nucleus is collided by another particle, or naturally unstable. Some elements contained in the earth spontaneously emit gamma rays: potassium-40, thorium, uranium, and the radioactive families of the last two. These elements mainly exist in shales, which are thus more radioactive than any other formations. Therefore the formation radioactivity is detected by the Gamma Ray logging tool, and used for bed definition and correlation.

Two types of gamma ray detectors are used in the logging tools: the Geiger–Mueller (G-M) counter and the Scintillation counter. The G-M counter consists of a gas chamber and a power-fed electrode, and detects the voltage pulses caused by the gas ionization when a gamma ray enters. The scintillation counter uses a sodium iodide crystal, which gives off a tiny flash of light whenever penetrated by a gamma ray. Such flashes are then converted into electrical pulses by a photomultiplier tube. Generally, the Scintillation counter has a superior sensitivity, and often preferred in modern logging tools. However, it is usually more expensively made, and cannot stand very high temperature as well as the G-M counter.

In addition to the total gamma rays, the tools today can also record the gamma ray spectrum emitted by different minerals, and quantitatively analyze the contributions of each element. This method can be used in clay type identification, or evaluating the source rock potential.

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CHERENKOV COUNTING

MICHAEL F. L'ANNUNZIATA, in Handbook of Radioactivity Analysis (Second Edition), 2003

X. GAMMA-RAY DETECTION

Gamma radiation can produce Cherenkov photons indirectly through gamma-ray photon-electron interactions as the gamma radiation travels through a transparent medium. The number of photons emitted by a Cherenkov detector is generally only approximately 1% of the number emitted by a good scintillator for the same gamma-ray energy loss (Sowerby, 1971). Although the Cherenkov detection efficiencies of gamma radiation are low, unique applications of the Cherenkov effect for the analysis of gamma radiation exist, and the effect plays an important role as a source of background in various methods of radioactivity analysis. One should always be aware of the potential for gamma radiation to produce Cherenkov photons.

The transfer of gamma-ray photon energy to an atomic electron via a Compton interaction produces a Compton electron with energy, Ee, within the range between zero and a maximum defined by

(9.34)0<Ee≤Eγ−Eγ1+2Eγ/0.511

where Eγ is the gamma-ray photon energy in MeV and the term Eγ –(Eγ/(1 + 2 Eγ/0.511)) defines the Compton-electron energy at 180° Compton scatter according to equations previously defined in Chapter 1. To produce Cherenkov photons the Compton electron must possess energy in excess of the threshold energy, Eth, defined by Eq. 9.5 previously in this chapter. For example, the threshold energy for electrons in water (n = 1.332) according to Eq. 9.5 is calculated to be 263 keV. A Compton electron must possess, therefore, energy in excess of 263 keV to produce Cherenkov photons in water. In this case, however, the gamma-ray photon must possess an energy in excess of 422 keV calculated according to the inverse of Eq. 1.109 or

(9.35)Eγ=Ee+Eγ'+φ

where Ee is the Compton electron energy, E′γ is the energy of the Compton-scattered photon, and ϕ is the electron binding energy. The electron binding energy is negligible and can be ignored. Thus, Eq. 9.35 can becomes

(9.36)Eγ=Ee+Eγ1+2Eγ/0.511

For example, if we take Ee to be 0.263 MeV, the threshold electron energy for Cherenkov production in water, and E′γ as the scattered-photon energy at 180° Compton scatter, Eq. 9.36 becomes

(9.37)Eγ=0.263MeV+Eγ1+2Eγ/0.511

where Eγ = 0.422 MeV is the threshold gamma-ray energy for the production of Cherenkov photons in water. Threshold energies will vary according to the index of refraction of the medium, and these are provided graphically in Fig. 9.13 for gamma radiation and electrons or beta particles.

FIGURE 9.13. Threshold energy for Cherenkov radiation as a function of index of refraction of the detector medium for gamma rays and electrons or beta particles. The threshold energies for electrons or beta particles are calculated according to Eq. 9.5, and the gamma-ray threshold energies are calculated according to Eq. 9.36 as the gamma rays that yield electrons of the threshold energy via 180° Compton scatter.

Although Cherenkov detection efficiencies for gamma radiation are low, the phenomenon is applied to create threshold detectors. A variety of media, which vary significantly in refractive index, can be selected to discriminate against gamma radiation of specific energy. For example, silica aerogels of low refractive index (n = 1.026) can be used to discriminate against gamma rays of relatively high energy (2.0 MeV) while a transparent medium of high refractive index such as flint glass (n = 1.72) can serve to discriminate against relatively low-energy gamma radiation (0.25 MeV). Figure 9.13 illustrates the potential for gamma-ray energy discrimination according to refractive index of the detector medium.

Another application of gamma-ray detection is the Cherenkov verification technique used in nuclear safeguards to verify the authenticity of irradiated nuclear fuel, which is one of the important tasks performed by the International Atomic Energy Agency (IAEA). The IAEA nuclear safeguards program audits the national declarations of fuel inventories to insure that no illicit diversion of nuclear material has occurred. High levels of gamma radiation are emitted by fission products in irradiated nuclear fuel. The irradiated fuel stored under water will produce Cherenkov light as a result of Compton scattering in the water surrounding the fuel. A Cherenkov Viewing Device containing a UV-transmitting lens coupled to a UV-sensitive charge-coupled device (CCD) and image monitor enables the real-time imaging of the UV light portion of the Cherenkov radiation in the presence of normal room lighting (Attas et al., 1990, 1992, 1997; Attas and Abushady, 1997; Kuribara, 1994; Kuribara and Nemeto, 1994, Lindsey et al., 1999). The presence of fission products and the nature of their distribution, as indicated by the Cherenkov glow, is used as evidence of fuel verification.

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Gamma-Ray Astronomy

J.Gregory Stacy, W.Thomas Vestrand, in Encyclopedia of Physical Science and Technology (Third Edition), 2003

III.B.1 Atmospheric Gamma Rays

Gamma rays are produced in copious quantities in the upper atmosphere of the Earth as a consequence of cosmic-ray interactions. Balloon experiments rely typically on the "growth curve" technique to estimate the contribution of atmospheric gamma rays to the observed event count rate. In this method, the total count rate of the detector is determined as a function of the residual atmosphere remaining above the balloon-borne instrument as it rises to float altitude. Since the downward vertical atmospheric gamma-ray flux is assumed to be zero at the top of the atmosphere, all remaining event counts are assumed to be truly cosmic in nature (or locally produced within the experiment itself, see following). Both Monte Carlo calculations and semiempirical models are employed to test the reliability of such measurements.

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Physics of Terrestrial Planets and Moons

P. Falkner, R. Schulz, in Treatise on Geophysics (Second Edition), 2015

10.23.4.7 Gamma-Ray Spectrometer

Gamma-ray spectroscopy (GRS) is used for determining the surface elemental composition of planetary bodies either from orbit or directly on planetary surfaces. In situ measurements on surfaces are preferable since they are less prone to atmospheric effects or other disturbing contributions. Direct surface measurements can provide ground truth for orbital measurements but are in most cases limited to local measurements only.

The detected gamma rays arise from two sources: (1) gamma rays emitted spontaneously by naturally occurring radioactive elements like K, Th, and U and (2) cosmic ray-induced gamma rays emitted by elements like H, C, O, Si, and Fe. Each chemical element produces a unique set of gamma-ray lines, and gamma spectroscopy allows for distinctive identification of these fingerprints and determination of the relative abundance of a specific chemical element. The ambient cosmic-ray flux produces neutron-induced reactions on elements in the planetary surface, which in turn produce the characteristic γ-rays that are used to determine the elemental concentration. A scintillator (e.g., cesium iodide (CsI), LuAP, or LaBr3) is used to convert the γ-ray into light emission, which is detected by sensitive large photodiodes. The background provided by cosmic rays and by the spacecraft is a source of noise. Mars Odyssey GRS, for example, was mounted on a 6 m boom to reduce the S/C background for the measurements (Boynton et al., 2004). Anti-Compton shielding is used to improve the GRS spectra quality to rejection of γ-rays from cosmic-ray interactions with the spacecraft material or other unwanted sources (Meyer et al., 1996). Important instrument factors are the precision of the scintillator material, sensitivity to radiation damage, quantum efficiency of the readout photo diodes, and the capability to suppress background counts. Since the γ-ray spectrometer sensitivity increases with the square root of the integration time, the expected integration times range from several orbits for the natural radio nuclides to several months for the cosmic ray-induced events. Of course, the sensitivity is also a strong function of the efficiency and energy resolution of the instrument.

Surface compositions finally are deduced from a comparison between the γ-ray spectra emitted by an area of the planetary surface with simulations based on calculated fluxes of assumed surface composition. By applying an iterative process, it is possible to derive a chemical composition that best fits the measured in-orbit fluxes.

Examples of γ-ray spectrometers based on either Ge detectors or scintillators are the γ-ray and neutron spectrometer on Messenger (Burks et al., 2004) or the Mercury gamma-ray and neutron spectrometer (Kozyrev et al., 2006) on the BepiColombo mission to Mercury.

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Gamma Radiation

Gamma radiation allows for the immediate release of the product after processing, through a procedure known as "dosimetric release."

From: Clinical Engineering Handbook, 2004

Related terms:

Dow Chemical

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Elongation at Break

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Polyolefins

Laurence McKeen, in The Effect of Sterilization on Plastics and Elastomers (Third Edition), 2012

8.1.5 Ultrahigh Molecular Weight Polyethylene

Sterile applications: UHMWPE is used as the wear-bearing surface of hip and knee arthroplasty and total joint replacement.

Gamma radiation resistance: Gamma radiation has been a common sterilization method for UHMWPE used in total joint replacement. The products are sterilized by gamma radiation from a Cobalt-60 source. Gamma radiation can lead to extensive oxidation in PE. Gamma radiation improves cross-linking of UHMWPE resulting in an interpenetrating network of HMW polyethylene chains with the potential benefit of increased strength, thus increasing resistance to wear. However, sterilization in air may be particularly harmful because it may initiate a long-term oxidative process that has a negative impact on the implant's mechanical properties.

Ethylene oxide (EtO) resistance: EtO sterilization does not cause oxidative degradation.

Data for UHMWPE plastics are found in Table 8.16 and Figs 8.10–8.12.

Table 8.16. Volumetric Wear of Sterilized Ultrahigh Molecular Weight Polyethylene5

Sterilization MethodWear Cycles in MillionsVolumetric Wear (mm3)UnagedAgedEthylene oxide15892120513–86Gamma158512871703–220

Figure 8.10. Effect of gamma radiation dose on the maximum strength of ultrahigh molecular weight polyethylene.6

Figure 8.11. Effect of gamma radiation dose on the elongation ultrahigh molecular weight polyethylene.6

Figure 8.12. Wear rate versus radiation dose for ultrahigh molecular weight polyethylene UHMWPE used in total knee replacements.7

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Out-of-seam dilution: Economic impacts and control strategies

Joseph C. Hirschi, Y. Paul Chugh, in Advances in Productive, Safe, and Responsible Coal Mining, 2019

9.4.2.1 Natural gamma radiation (NGR)

NGR is the most advanced CID technology with more than 150 units employed around the world [20]. This method works on the principle that shale, clay, silt, and mud have higher levels of naturally occurring radioactivity than coal due to their containing small quantities of radioactive potassium (K-40), uranium, and thorium. Measured NGR decreases exponentially as a function of coal thickness; thus, attenuation of the NGR sensor toward coal can be used to measure coal thickness between the sensor and the rock interface. NGR technology has many features that make it a viable option in automated mining operations. It can measure coal thicknesses from 1.0 to 20 in. (2.5–50 cm). The unit is compact and easily mounted on mining machines. It has a display panel that is easy to read by operators using remote control devices. The most prevalent applications to date have been on longwall units. There are a few inherent weaknesses that arise from distribution of radioactive material in the coal seam. For example, NGR levels vary from seam to seam requiring units to be calibrated for each seam in which they will be used. A related issue is that NGR levels can vary within a seam depending on levels of radioactive constituents present at the time of geologic deposition. Also, rock partings (in-seam dilution) can show false seam boundaries. The applicability of NGR systems in Illinois may be limited since black shale is a typical immediate roof layer and it has radiation properties that are similar to coal.

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Polymer-on-Polymer Structures Based on Radiation Grafting

Celestino Padeste, Sonja Neuhaus, in Polymer Micro- and Nanografting, 2015

2.3.4 Gamma Radiation

Gamma radiation is usually defined as radiation with photon energies above 200 keV. Radiation grafting using γ-radiation—for example, from 60Co sources—is a relatively old technique that was investigated, for instance, for the production of graft membranes for fuel cell applications using the simultaneous grafting approach [22]. The radioactive sources are advantageous in that they are independent of electrical equipment; in turn, due to the high photon energy and the concomitant risks, an extremely high level of protective measures is required for safety reasons. In addition, radiation of such high energy shows very high penetration through any material and particularly through polymers. Most of the radiation will therefore not interact with the sample. As a result, long exposure times are required to induce the desired effect, and processes are generally inefficient. Furthermore, the absorption of radiation by materials used to produce masks is rather low at such high photon energies. Therefore, the thickness of absorption masks for structured grafting using γ-radiation would be unreasonably high.

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Radiation

Bill Collum, in Nuclear Facilities, 2017

2.4.3 Gamma

Gamma radiation needs materials such as lead, steel, or concrete to halt its travel, so is definitely the one with characteristics most commonly associated with radiation. It differs fundamentally from both alpha and beta, in that gamma radiation does not come in the form of particles but is instead pure energy. So it is from the same family as radio waves, visible light, ultraviolet light, and so on that we see on the electromagnetic spectrum. Typical gamma emitters include iodine-131, barium-137m, cobalt-60, and radium-226. It has tremendous penetrating power, travels at the speed of light, and in some cases can cover hundreds or even thousands of meters through the air.

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Sanitation

Lúcio Flávio de Magalhães Brito, Douglas Magagna, in Clinical Engineering Handbook, 2004

Gamma Radiation

Gamma radiation is pure energy generated by the spontaneous decay of radioisotopes. Exposure to gamma rays sterilizes the product by disrupting the DNA structure of microorganisms on or within the product, thereby eliminating the ability to reproduce life sustaining cells. The ionizing energy produced by gamma rays is deep penetrating, thus making it an ideal solution for products with various densities and product packaging types. No area of the product, its components, or packaging is left with uncertain sterility after treatment. Even high-density products, such as pre-filled syringes, can be readily processed and used with confidence. The gamma process is repeatable and easy to use, with a proven track record. Its deep penetrating capabilities make it a viable solution for a wide range of packaged products. Accompanying dosimetric-release procedures allow for the immediate shipment of products after sterilization processing.

Gamma radiation has been recognized as a safe, cost-competitive method for the sterilization of health care products, components, and packaging since the 1950s and has gained in popularity over the years, due to its simplicity and reliability. Gamma radiation effectively kills microorganisms throughout the product and its packaging, with little temperature effect. Benefits of gamma radiation are precision dosing, rapid processing, uniform-dose distribution, system flexibility, and the immediate availability of the product after processing.

Gamma radiation of single-use, disposable medical devices for the purpose of sterilization is being used by an ever-increasing percentage of the health care industry. Gamma radiation, which once accounted for only 5% of the sterilization market, has grown to nearly 50%. Although cost and reliability have been identified as contributing factors to the industry's conversion to gamma radiation, there are other key elements to be considered.

Packaging remains intact with gamma processing. As there is no requirement for pressure or vacuum, seals are not stressed. In addition, gamma radiation eliminates the need for permeable packaging materials. Packaging and raw materials suppliers have recognized the shift to radiation and are continuing to develop products that are specifically formulated for radiation stability. Tough, impermeable packaging materials are available to provide a strong, long-term, sterile barrier.

Gamma processing, is a highly reliable procedure, mostly due to its simplicity. Because time is the only variable to control, the possibility of deviation is reduced to a minimum. Gamma radiation allows for the immediate release of the product after processing, through a procedure known as "dosimetric release." This procedure is accepted by the U.S. Food and Drug Administration (FDA) due to the inherent reliability of the radiation process and is outlined, in detail, in the standards document ANSI/AAMI/ISO 11137-1994, Sterilization of Health Care Products-Requirements for Validation and Routine Control-Radiation Sterilization.

Dosimetric release is a product release mechanism, based solely on the dosage of radiation delivered to the product. This measurement, usually identified in kiloGrays (kGy), is obtained using dosimeters, which are placed on product containers during processing. Upon completion of the gamma process, the dosimeters are removed from the product containers and are read, using a specialized instrument to verify the minimum and maximum dosages received by the product. Once the delivered dose is verified, the product is released for shipment.

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Polyvinyls and Acrylics

Laurence McKeen, in The Effect of Sterilization on Plastics and Elastomers (Third Edition), 2012

9.5.1 Homopolymer

Manufacturers and trade names: Altuglas International Plexiglas, Novacor, and Evonik Industries Acrylite®.

Sterilization resistance: Wet ethylene oxide and steam sterilization methods are not recommended for acrylic.12

Gamma radiation resistance: Plexiglas SG-7 exposed to 5.0 Mrad of gamma radiation experiences virtually no yellowing or discoloration. Properties such as impact, tensile, and flexural strength, modulus of elasticity, and percent elongation are constant.13 Gamma sterilization has a tendency to yellow most acrylics. This yellowing is often temporary and recovery can be complete, with the parts retaining their original integrity. The higher the radiation dosage, the greater the yellowing and the longer the required recovery time. Current techniques have cut recovery time to a week for some grades.12

E-beam radiation resistance: Plexiglas maintains constant impact, tensile, and flexural strength, modulus of elasticity, and percent elongation properties.13

Ethylene oxide (EtO) resistance: Acrylics and impact-modified acrylics are compatible with ethylene oxide gas and can be EtO sterilized without adversely affecting the medical device.

Data for acrylic homopolymer plastics are found in Tables 9.13–9.16 and Fig. 9.21–9.28.

Table 9.13. Effects of Gamma Radiation on Altuglas International Plexiglas SG-7 and Plexiglas SG-10 Radiation-resistant Grade Acrylic14–16

Exposure Conditions Radiation dose (Mrad)Unexposed5Unexposed5Properties RetainedTest method Tensile strength (MPa)493737ASTM D638 Elongation at break (%)4.36.96.7– Flexural modulus (MPa)240017601790– Flexural yield strength (MPa)805960ASTM D790 Izod impact (J/cm)0.30.50.4ASTM D256 Charpy impact (J/cm2)6.39.74.4ASTM D256Optical Properties HazeMax 2%ASTM D1003 Transmission, visible92%ASTM D1003

Table 9.14. Effect of Gamma Radiation Sterilization on Yellowness Index of Novacor Acrylic Resin17

Exposure Conditions Radiation dose (Mrad)1.272.83.555.431.272.83.555.43Postexposure Conditioning Time (h)0840Surface and Appearance Yellowness index noteYellowDark yellowDark yellowYellow orangeLight yellowLight yellowLight yellowDark yellow

Table 9.15. Effect of Gamma Radiation Sterilization on Yellowness Index of Acrylic17

Material NoteTransparent, General-Purpose GradeTransparent, Impact ModifiedExposure Conditions Radiation dose (Mrad)3535Postexposure Conditioning Tensile strength8058100100 Modulus100100100100 Notched Izod impact––9689Surface and Appearance Δ Yellowness index2024.51419

Table 9.16. Qualitative Review of Effects of Low-Temperature Hydrogen Peroxide Gas Plasma (LTHPGP) Sterilization on Cyro Industries' Acrylite H15-003 Acrylic Resins20

TypeUnexposedLTHPGP SterilizedProperties RetainedTest Method Tensile strength (MPa)80.2578.6ASTM D638 Tensile modulus (MPa)32403261ASTM D638 Elongation at break (%)10.35.5ASTM D638 Elongation at yield (%)5.75.5ASTM D638 Notched Izod impact (fppi, 1/8 in)0.360.31ASTM D256Optical Properties Gloss, 60 °C137138ASTM D523 Haze (%)0.70.9ASTM D1003 Refractive index1.491.49ASTM D542 Transmittance (%)9393ASTM D1003 Yellowness index0.40.3ASTM D1003

Figure 9.21. Gamma radiation dose versus yellowness index of Altuglas International Plexiglas V-Grade acrylic resin.18

Figure 9.22. Gamma radiation dose versus yellowness index of Altuglas International Plexiglas DR-G Grade acrylic resin.18

Figure 9.23. Gamma radiation dose versus yellowness index of Altuglas International Plexiglas HFI-10 G acrylic resin.18

Figure 9.24. Beta radiation dose versus tensile strength of acrylic resin.19

Figure 9.25. Beta radiation dose versus tensile modulus of acrylic resin.19

Figure 9.26. Beta radiation dose versus notched Izod impact strength of acrylic resin.19

Figure 9.27. Beta radiation dose versus yellowness index of acrylic resin.19

Figure 9.28. Post-beta radiation exposure time versus yellowness index of acrylic resin.19

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CHERENKOV COUNTING

MICHAEL F. L'ANNUNZIATA, in Handbook of Radioactivity Analysis (Second Edition), 2003

X. GAMMA-RAY DETECTION

The transfer of gamma-ray photon energy to an atomic electron via a Compton interaction produces a Compton electron with energy, Ee, within the range between zero and a maximum defined by

(9.34)0<Ee≤Eγ−Eγ1+2Eγ/0.511

(9.35)Eγ=Ee+Eγ'+φ

(9.36)Eγ=Ee+Eγ1+2Eγ/0.511

For example, if we take Ee to be 0.263 MeV, the threshold electron energy for Cherenkov production in water, and E′γ as the scattered-photon energy at 180° Compton scatter, Eq. 9.36 becomes

(9.37)Eγ=0.263MeV+Eγ1+2Eγ/0.511

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The Nature of Isotopes and Radiation

PETER B. VOSE, in Introduction to Nuclear Techniques in Agronomy and Plant Biology, 1980

Attenuation of γ-radiation

γ-radiation is absorbed exponentially, and the absorbing power of a substance increases with atomic number and density. The attenuation of γ-radiation by matter can be described mathematically, and is defined by the linear absorbtion coefficient µ′, measured in cm−1, and which is the fractional decrease in radiation intensity per unit of distance, its value depending on the nature of the material.

When µ′ is the linear absorbtion coefficient and Io the intensity of an incident γ-beam, then the intensity I of the radiation after passing through absorbing matter of thickness T is given by

(10)I=Ioe−μ′T

This is exactly the same form as equation (6) relating to radioactive decay, and is shown graphically in Fig. 1.6.

FIG. 1.6. Determination of the linear absorbtion coefficient, µ′. Log radiation beam intensity versus absorbing material thickness.

The mass absorbtion coefficient, µ, is the fractional decrease in radiation intensity per unit of surface density (cm2g−1) and is of most practical importance. It is defined as −μ′ρ, where ρ is the density of the absorbing matter.

Some practical applications of gamma attenuation theory and the determination of mass absorbtion coefficients are considered further on pages 342–344 of Chapter 14.

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Sterilisation and cleaning of metallic biomaterials

S. Lerouge, in Metals for Biomedical Devices, 2010

13.3.1 Overview of sterilisation processes

Gamma radiation and ethylene oxide are still the main industrial sterilisation processes of medical devices but several other processes, such as moist heat (steam autoclave), dry heat, electron beam radiation and, more recently, low-temperature hydrogen peroxide gas plasma, ozone or peracetic acid are available and are increasingly used in healthcare facilities. Process principles and inactivation mechanisms, as well as main advantages and disadvantages, of each of these processes will be described in the following section. Main parameters, as well as advantages and disadvantages are reviewed in Table 13.1.

Table 13.1. Parameters, advantages and limits of the main sterilisation processes

TechniqueMain parametersAdvantagesLimitsSteam sterilisation (autoclave)121 °C, 5–20 min

High humidity level

Options:

Flash autoclave 134 °C, 3–6 min in vacuum with steam pulses Low temperature steam (110–115 °C, 35–40 min)Simple, safe, rapid and efficient

Good penetrability

Easy to monitor

No toxic residues

Can sterilise liquids

Low cost

Rapid

Allows sterilisation of more heat sensitive materialsHigh temperature and moisture

Incompatible with many thermosensitive polymers.

Metals may corrode

Requires breathable packaging

Incompatible to many materials due to very

high temperature and moisture

Longer exposure

Efficiency subject to some controversyDry heat160–170 °C

1–2 hoursGenerally avoids metal corrosionLonger exposure than steamGamma radiations10–40 kGy (most common 25 kGy)

Ambient temperature

A few hoursExcellent penetrability, efficiency and reliability

Dosimetric release

Large product volumes

Cost effective

Compatible with many materials

No residues

Environmentally safe, except for the disposal of radioactive wasteIsotope containment requires costly

facilities for safety reasons

Only available in a few industrial centres

Some polymer damage, increasing with increased doses

Limited to single industrial sterilisationElectron-beam11–40 kGyVery rapid (seconds/minutes) Compatible with more materials than gamma raysLower penetrability than gamma rays

Less penetration than gammaEthylene oxide (EO)25–65 °C (generally 55 °C)

High humidity

EO: 400–1500 mg/L

2–4 hours + aerationCompatible with most materials Efficiency, relatively good penetrabilityLong cycle and safety risks

EO toxicity and mutagenicity: Safety risks

for sterilisation personnel

Toxic EO residues and reaction products in

polymers: requires aeration

EO may be banned by regulations

Difficult to monitor

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Pretreatment Strategies for Biochemical Conversion of Biomass

Hongzhang Chen, Lan Wang, in Technologies for Biochemical Conversion of Biomass, 2017

3.3.2.3 High-energy Radiation Treatment

γ-Radiation (ionizing radiation) is commonly used to destroy straw cell walls and other agricultural waste composition (Al-Masri & Zarkawi, 1994). It is also very efficient in decreasing the polymerization degree of fibers or the removing lignin (Sandev & Karaivanov, 1979). Ionizing radiation is of benefit to the depolymerization (Focher, Marzetti, & Cattaneo, 1981) of cellulose. It can also loosen the structure of cellulose; it affects the structure of cellulose, thereby increasing the activity and accessibility of the cellulose. Thus, in the production of viscose fibers, radiation treatment can dissolve the pulp, and enhance the ability of cellulose to convert into viscose. For example, Fischer, Rennert, and Wilke (1990) used a 1 MeV electron accelerator to generate high-energy electrons for the radiation treatment of sulfite pulp. The results showed that the pulps treated with high-energy electron showed better uniformity and the reaction capacity with carbon disulfide. γ rays generated by 60Co has similar treatment effect with high-energy accelerated electrons (Focher et al., 1981; Stepanik, Rajagopal, & Ewing, 1998).

Treatment with high doses of radiation can reduce the content of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid-insoluble lignin (ADL), and reduce sugar in the cell walls of straw, thereby increasing the digestibility of straw (Baer, Leonhardt, & Flachowsky, 1980; Leonhardt, Baer, & Hennig, 1983; Gralak, Krasicka, & Kulasek, 1989; Al-Masri & Guenter, 1993). Low doses of radiation can be used for sterilizing agricultural byproducts; Kume, Ito, and Ishigaki (1990) reported that a dose of 15 kGy was enough to kill all aerobic strains. A dose of 5–6 kGy can reduce fungi on the shell of the compressed fibers bed under the detection level. Malek, Chowdhury, and Matsuhashi (1994) reported that γ-rays from 30 kGy are needed to kill the aerobic bacteria in the straw. Kim, Yook, and Byun (2000) also found that 5–10 kGy γ radiation can effectively reduce microbial contamination in herbs.

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