Alpha particles penetrating power

The nuclear reactor also must be shielded against the emission of radioactive material to the external environment. Suitable radiation controls include both thermal and biological shielding systems. Radiation from alpha particles (a rays) and beta particles ((3 rays) has little penetrating power, but gamma rays have deep penetration properties. Neutron radiation is, however, the primary area of risk. Typically, extremely thick concrete walls are used as a neutron absorber, but lead-lined concrete and special concretes are also used. 

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. 

Neutrons have no electrical charge and have nearly the same mass as a proton (a hydrogen atom nucleus). A neutron is hundreds of times larger than an electron, but one quarter the size of an alpha particle. The source of neutrons is primarily nuclear reactions, such as fission, but they are also produced from the decay of radioactive elements. Because of its size and lack of charge, the neutron is fairly difficult to stop, and has a relatively high penetrating power. 

Gamma rays (y) have high penetrating power and are not deflected by electric or magnetic fields. Beta particles ( 3) have a lower ionizing power and greater penetrating power than alpha particles (a). 

In order to handle radioisotopes safely it is necessary, among other things, to define fairly carefully the penetrating power of the radiation emitted by any isotope. Alpha particles, having only a relatively limited number of energy levels, are absorbed by contact with other atoms. The absorbing power of a material is referred to in terms of its equivalent thickness. The thickness required can be calculated by dividing the equivalent thickness by the density of the material. 

Which has the greatest penetrating power—alpha particles, beta particles, or gamma rays ... 

As they penetrate through matter, alpha particles produce large amount of ions, but their penetrating power is so low that they can easily be stopped by a sheet of paper. 

Beta particles are very small. They are fast moving electrons that are shot out of the nucleus of a radioactive element. They are easily stopped by a few sheets of paper, a thin sheet of metal or about 20 cm of air. Even the most energetic beta particle can only travel a metre or so in air before it is stopped. It has a penetrating power 100 times greater than alpha particles. You do not keep a radioactive element giving off this radiation in your pocket ... 

Alpha (a) particle It is a double positive charge carrying helium nucleus He2+) released spontaneously from a high-atomic mass radioactive element. It has low penetration power and can be stopped by a thin sheet of paper or a layer of air. Has no external hazards has internal hazards. 

Emitted by heavy atoms, such as uranium, radium, radon, and plutonium (to name a few), alpha particles are helium nuclei, making them the most massive kind of radiation. Alpha radiation can cause a great deal of damage to the living cells it encounters, but has such a short range in tissue (only a few microns) that external alpha radiation cannot penetrate the dead cells of the epidermis to irradiate the living cells beneath. If inhaled, swallowed, or introduced into open wounds, however, alpha radiation can be very damaging. In nature, alpha radiation is found in rocks and soils as part of the minerals, in air as radon gas, and dissolved in water as radium, uranium, or radon. Alpha emitters are also found in nuclear power plants, nuclear weapons, some luminous paints (radium may be used for this), smoke detectors, and some consumer products. Objects and patients exposed to alpha radiation may become contaminated, but they do not become radioactive. 

The discussion in this section is primarily based on Lind s book. Much of the early work in radiation chemistry was done either with radium sources and/or radon sources. These sources produced primarily alpha rays and weak beta rays. The lack of penetrating power of these particles made early experiments very difficult. 

Alpha (a) Thin sheet of plastic scintillator or zinc sulfide embedded in a transparent tape Phosphors are wrapped in very thin aluminized mylar foil to exclude light. a-Particles, because of low penetrating power, lose all their energy to scintillators. P- and y-Particles produce only smaller pulses and by adjustment of appropriate setting of the discriminator, a-Particles alone can be counted. 

Compare the penetrating powers of alpha particles, beta particles, and gamma rays. 

The three types of radiation vary in their penetrating power. Alpha particles are stopped by even a thin sheet of paper, but beta particles require thicker shields, such as a dense piece of wood. The energetic gamma rays are stopped only by thick blocks of lead or concrete. 

Radioactive decay is a process whereby unstable nuclei change into more stable ones by emitting particles of different kinds. Alpha, beta and gamma (a, P and y) radiation was originally classified according to its different penetrating power. The processes involved are illustrated in Fig. 1. 

Figure 23.7 Penetrating power of radioactive emissions. Penetrating power is often measured in terms of the depth of water that stops 50% of the incoming radiation. (Water is the main component of living tissue.) Alpha particles, with the highest mass and charge, have the lowest penetrating power, and 7 rays have the highest. (Average values of actual penetrating distances are shown.)...

In contrast to alpha emission, beta emission is characterized by production of particles with a continuous spectrum of energies ranging from nearly zero to some maximum that is characteristic of each decay process. The jS particle is not nearly as effective as the alpha particle in producing ion pairs in matte r because of its small mass (about /7(XK) that of an alpha particle), At the same time, its penetrating power is substantially greater than that of the alpha particle. Beta-particle energies are frequently related to the thickness of an absorber, ordinarily aluminum, required to stop the particle. 

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