Gamma rays ionization effects

The interaction between beta rays and matter is a more complex problem than the corresponding one for gamma rays. Three effects need to be considered they are in order of importance atom displacements, bremsstrah-lung, and ionization. 

Relative Biological Effectiveness (RBE)—The RBE is a factor used to compare the biological effectiveness of absorbed radiation doses (i.e., rad) due to different types of ionizing radiation. More specifically, it is the experimentally determined ratio of an absorbed dose of a radiation in question to the absorbed dose of a reference radiation (typically 60Co gamma rays or 200 keV x rays) required to produce an identical biological effect in a particular experimental organism or tissue (see Quality Factor). 

When using an ionization chamber for detecting neutrons, beta particles can be prevented from entering the chamber by walls thick enough to shield out all of the beta particles. Gamma rays cannot be shielded from the detector therefore, they always contribute to the total current read by the ammeter. This effect is not desired because the detector responds not only to neutrons, but also to gamma rays. Several ways are available to minimize this problem. 

Some substances, known as fluors or scintillants, respond to the ionizing effects of alpha and beta particles by emitting flashes of light (or scintillations). While they do not respond directly to gamma rays, they do respond to the secondary ionization effects that gamma rays produce and, as a result, provide a valuable detection system for all emissions. 

A unit of dose equal to the amount of ionizing radiation that produces in humans the same biological effect as one rad of X-rays or gamma rays. One rem is equal to 0.01 sievert. 

Irradiation by ionizing radiation and its effect on milk lipase activity have also been studied (Tsugo and Hayashi 1962). Irradiation doses of 6.6 x 104 rads destroyed 70% of the activity. The udders of lactating cows, when exposed to 60 Co gamma rays, gave milk with decreased lipase and esterase activity (Luick and Mazrimas 1966). 

The primary interaction of gamma rays with matter is the production of ionization or excitation. The three processes of interaction are the photoelectric effect, the Compton effect, and pair production. The predominance of each of these effects is determined by the energy of the gamma ray and the atomic number, Z, of the absorber. The photoelectric effect is favored for low energies, the Compton effect for intermediate energies, and pair production for high energies... 

Since gamma rays are electrically neutral particles, they are not deflected by electric or magnetic fields and they do not have an ionizing effect. 

Explain why, although gamma rays are far more penetrating than alpha particles, the latter are more likely to cause damage to an organism. Which type of radiation is more effective at causing ionization of biomolecules ... 

The moderator slows the neutrons to increase the efficiency of the fission reaction. The control rods absorb neutrons to slow or halt the fission reaction. 39. Even though gamma rays penetrate human tissue very deeply, they are very small and cause only occasional ionization of biomolecules. Alpha particles, because they are much more massive, are very effective at causing ionization of biomolecules and produce a dense trail of damage once they get inside an organism. 

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