Beta particles penetration

Neutron activation reactions have also been considered for mine detection. Here a radioactive element is produced in the mine which in the process of decay, emits nuclear radiation, either alpha or beta particles or yrays or two of these or all three in combination. For buried mines the penetrating 7iays are of most in-... 

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. 

This metal chamber serves to shield the plates from outside electric fields and to contain the air or other gas. Gamma rays have very little trouble in penetrating the metal walls of the chamber. Beta particles and alpha particles, however, are stopped by the metal wall. For alpha and beta particles to be detected, some means must be provided for a thin wall or "window." This window must be thin enough for the alpha and beta particles to penetrate. However, a window of almost any thickness will prevent an alpha particle from entering the chamber. 

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). 

Radionuclides that do not emit beta particles likely emit alpha particles. An alpha particle is, in effect, a helium atom (two protons and two neutrons) ejected from an unstable nucleus. An alpha particle can only travel a few inches in air and cannot penetrate the outer layers of dead skin cells. Therefore, alpha particles are not external hazards and produce tissue damage only if alpha-emitting radionuclides are ingested, inhaled, or injected. 

Beta particles are normally faster than alpha particles and not as easy to stop. For this reason, they are able to penetrate light materials such as paper and clothing. They can penetrate fairly deeply into skin, where they have the potential for harming or killing cells. They are not able to penetrate deeply into denser materials, however, such as aluminum. Beta particles, once stopped, become part of the material they are in, like any other electron. 

Alpha particles are the least-penetrating form of radiation and can be stopped by a sheet of paper. Beta particles readily pass through paper but not through a sheet of aluminum. Gamma rays penetrate several centimeters into solid lead. 

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

Why would you expect alpha particles to be less able to penetrate materials than beta particles ... 

Alpha particles are, first of all, much bigger in size than beta particles, which makes them less able to pass through the pores of materials. Second, alpha particles are enormously more massive than beta particles. So if beta particles have the same kinetic energy, they must be moving considerably faster. The faster-moving and smaller beta particles are therefore more effective in penetrating materials. 

Shaw also describes two techniques that now make it possible to analyze particles without removing them from collection filters. To determine the mass of a sample, technicians insert the particle-laden filter between a source that emits beta particles and a detector that counts them. As the mass increases, the number of particles that can penetrate the sample decreases. To determine the atomic elements in a specimen, laboratory workers may also separately carry out x-ray fluorescence spectroscopy. X-rays passed through the sample cause each element to emit charactenstic x-rays. The energy levels of the rays reveal the identity of the elements the intensity of the x-rays (number emitted) reflects the concentrations. 

Because of their relatively large mass, a particles move slowly (up to only one-tenth the speed of light) and can be stopped by a few sheets of paper or by the top layer of skin. Beta particles, because they are much lighter, move at up to nine-tenths the speed of light and have about 100 times the penetrating power of... 

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