Gamma attenuation

Clifford, C. E., and Mauney, T. H., Gamma Attenuation Heasurements Through Water in the MTR Mock-Up. ORNL CF-SO-8-85, November 3, 1950. 

The front, rear, sides and top thermal shield are surrounded by the biological shield. The six old reactors, except for the top shield at C Reactor have laminated biological shields with alternate layers of 3-3/4" steel and 4-1/2" masonite for a total thickness of slightly over four feet, four inches. The steel provides a heavy material for gamma attenuation, neutron capture, and inelastic scattering. The masonite provides hydrogen for elastic scattering. 

Tungsten, incorporated into the shield, provides best gamma attenuation... 

The SNPP reactor induced radiations would subject the spacecraft and the l C electrical and electronic components to radiation exposures larger than normally found in terrestrial nuclear applications, but they would be expected to be quite moderate compared to the Jovian radiation levels. In addition, the reactor gamma interactions at the outer surface of the reactor could knock electrons off the surface of the reactor to form an electron cloud that could travel around the shadow shield to the remainder of the spaceship. The existence of this electron radiation had not been confirmed, but needs to be evaluated for reactors which do not have significant amounts of gamma attenuation around the reactor, as would be the case with shadow shields as applied on the JIMO spaceship. 

One solution to the penetration problem for thick parts or dense materials is to convert the electrons to X-rays. Fig. 3 shows the attenuation of gamma rays... 

Unlike X-rays and gamma rays, electrons are rapidly attenuated. The maximum range of a 1-million-volt electron is about 4 m in air and about 5 cm in water. In... 

These coefficients must be multiplied by the density of air and tissue, respectively. Figure 15.7.2-1 depicts a radiation fallout field. Let C be the curie activity/m. The radiation into a unit area receptor at z = 1 m above the ground. The area is emitting C r dr d0 gammas/s. These are attenuated in the air as exp(-p, R) and geometrically as l/(4 7t R). The radiation received by the receptor is given by equation 15.7.2-1 which becomes 15.7.2-2 by a change of... 

Compton Effect—An attenuation process observed for x- or gamma radiation in which an incident photon interacts with an orbital electron of an atom to produce a recoil electron and a scattered photon whose energy is less than the incident photon. 

Kim JH, Kim HY, Kim S, Chung JH, Park WS, Chung DH. Natural killer T (NKT) cells attenuate bleomycin-induced pulmonary fibrosis by producing interferon-gamma. Am J Pathol 2005 167(5) 1231-1241. 

There are three methods of attenuating (reducing the energy level of) gamma-rays photoelectric effect, compton scattering, and pair production. 

Pearse, R.N., Kawabe, T., BoUand, S., Guinamard, R., Kurosaki, T., and Ravetch, J.V., 1999, SHIP recruitment attenuates Fc gamma RllB-induced B ceU apoptosis. Immunity, 10 6753-6760. 

In addition to the 9.17 MeV photon transmission, the NRA approach needs a background gamma measurement to assist in compensating for the mass-dependent attenuation (non-resonant absorption) of the photons in the cargo. Prototype NRA... 

Another approach is the whole-killed or inactivated vaccine. These vaccines are derived from the pathogen itself, rather than a weakened form, as are live attenuated vaccines. Chemical (e.g., formalin, ether, and beta-propiolactone) or physical (e.g., heat, ultraviolet, and gamma irradiation) means, or combinations thereof, are used to inactivate the pathogen. Notable examples of this type of viral vaccine include the inactivated polio vaccine... 

Density, level, and thickness measurements all depend upon the determination of the number of radiations per unit time penetrating the sample and producing a measurable signal in the radiation detector. When the amount of matter between the source and the detector increases, there usually is a decrease in the signal. The following relationship demonstrates the exponential natme of the attenuation of beta oi gamma radiation ... 

Beta radiation has a finite range, whereas in theory x- and gamma rays are exponentially attenuated. It should be noted that x-radiation of each energy exhibits sharp changes in absorption coefficients for certain absorbers. 

Smythies, L.E., Coulson, P.S. and Wilson, R.A. (1992) Monoclonal antibody to Interferon-gamma modifies pulmonary inflammatory responses and abrogates immunity to Schistosoma mansoni in mice vaccinated with attenuated cercariae. The journal of Immunology 149, 3654-3658. 

Qin, L., Ding, Y., Pahud, D.R., Chang, E., Imperiale, M.J. and Bromberg, J.S. (1997) Promoter attenuation in gene therapy interferon-gamma and tumor necrosis factor-alpha inhibit transgene expression. Hum. Gene Then, 8, 2019-2029. 

It must be noted that the resolution changes with the size of the object being scanned due to different attenuation of the gamma rays. However, the obtained resolutions should be adequate for a column of 30.5-cm-diameter. 

If the emulsion does not contain solids, then the determination of water and oil can usually be easily and accurately determined by Karl Fischer titration [66,107]. Other, less accurate, methods include [66] conductivity, capacitance, and gamma-ray or microwave [108] attenuation. 

Desreumaux, P., Dubuquoy, L., Nutten, S., Peuchmaur, M., Englaro, W., Schoonjans, K., Derijard, B., Desvergne, B., Wahli, W., Chambon, P., Leibowitz, M. D., Colombel, J. F., et al. (2001). Attenuation of colon inflammation through activators of the retinoid X receptor (RXR)/ peroxisome proliferator-activated receptor gamma (PPARgamma) heterodimer. A basis for new... 

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