Alpha particles penetration

SCR protons and alpha-particles penetrate only a very few cm into solid matter. Therefore, SCR-produced cosmogenic nuclides are normally not expected to be observed in meteorites, because their outermost few cm usually were ablated in the Earth s atmosphere. SCR nuclide concentration profiles therefore mostly have been calculated for the Moon, i.e., for samples with lunar chemical composition irradiated at 1 AU from the Sun. Most of the recent work has been done by R.C. Reedy and coworkers (e.g., Rao et al. 1994 Reedy 1998a,b) and R. Michel and coworkers (Michel et al. 1996 Neumann... 

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. 

Americium toxicity results primarily from the damage done by the alpha particle emitted during radioactive decay. This alpha particle has very limited penetration in tissue, and hence, the cellular damage (including damage to genomic material) occurs only in the immediate vicinity of the sequestered americium. 

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. 

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. 

C—Alpha particles are the least penetrating, and gamma rays are the most penetrating. 

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. 

Weak beta radiation and alpha particles often cannot penetrate the covering material but the use of a scintillant, which, together with the sample, will dissolve in a suitable solvent, enables a similar technique to be used. Liquid scintillation counters usually consist of two light-shielded photomultiplier... 

Ideally, measuring radioactivity in water assets in the field would involve minimal sampling and sample preparation. However, the physical properties of specific types of radiation combined with the physical properties of water make evaluating radioactivity in water assets in the field somewhat difficult. For example, alpha particles can only travel short distances and they cannot penetrate through most physical objects. Therefore, instruments designed to evaluate alpha emissions must... 

Beryllium is an excellent source of alpha particles, which are the nuclei of helium atoms. Alpha particles (radiation) are not very penetrating. These particles travel only a few inches in air and can be stopped by a sheet of cardboard. Alpha particles are produced in cyclotrons (atom smashers) and are used to bombard the nuclei of other elements to study their characteristics. 

---