Ionizing radiation penetrating power

Gamma radiation has a very high penetrating power. A small fraction of the original stream will pass through several feet of concrete or several meters of air. The specific ionization of a gamma is low compared to that of an alpha particle, but is higher than that of a beta particle. 

Gas Ionization Counters A common gas ionization counter is the Geiger-Muller counter where the electronic pulses derived from the ionization process are registered as counts. The instrument can be adjusted to detect only radiation with a desired penetrating power. 

The emission of nuclear particles or radiation from an isotope during its disintegration is commonly referred to as radioactivity. These emissions are classified as of the three basic types a, 0 and y. a-Particles, which are helium nuclei, have only weak penetrating power and may be stopped by 5-10 cm of air or thin metallic sheets. They are, however, highly energetic, ranging from 4 to 10 MeV. Thus they have a high ionization capacity... 

The intensity and penetrating power of the mercury radiation projected in the direction of motion of the electrons and also perpendicular to it have been measured by means of the ionizing effects produced inside of the ionization chamber. These experiments have been made in order to determine whether or not the beams of rays are homogeneous, and, also, to compare the penetration with that to be expected according to certain theoretical distributions of energy in the spectrum of radiation due to the impacts of electrons of given velocity. The material used to de-... 

Fig. 5.16. Penetrating powers of ionizing radiations a-particles can be stopped by paper, p-particles can be stopped by aluminum, y-radiation is weakened by lead, but is never greatly totally blocked neutrons will pass through lead, but will be stopped by thick wax or concrete.

Fig. 5.17. Penetrating powers of ionizing radiation in tissue y and n radiation penetrates easily P-particles penetrate a few centimetres at max. a-particles do not penetrate the dead layer of the skin.

A common gas ionization counter is the Geiger-Miiller counter (Figure 26-5). Radiation enters the tube through a thin window. Windows of different stopping powers can be used to admit only radiation of certain penetrating powers. 

Neutrons - neutrons are emitted during nuclear fission and have very great penetrating powers. They can cause intense ionization. Bremsstrahlung - electromagnetic radiations produced by the slowing down of a p particle. They can have considerable penetrating powers. 

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