Positron penetrating power

Due to the penetrating power of the emitted SllkeV gamma photons, which can pass through several millimetres of stainless steel, detection is possible from within steel reactors or process vessels. The coincident detection of photons is the principle of techniques such as Positron Emission Tomography (PET), Positron Emission Particle Tracking (PEPT), and Positron Emission Profiling (PEP), which are discussed below. 

The nucleons consist mainly of photons, electrons, and positrons, and compose about 10 percent of the cosmic radiation at sea level. A fraction of muons and nucleons are absorbed while traversing the atmosphere. Variations in absorber thickness (air mass) are proportional to variations in barometric pressure. The absorption length for cosmic-ray muons at sea level in the atmosphere is 4,000 g/cm (Cocconl, 1951), and for cosmic nucleons, 120 g/cm (Hayakawa, 1969). Thus, it is clear that muons have significantly higher penetrating power than nucleons, about 33 times in the air. The probability of absorption rapidly increases with the atomic number, Z. In terms of lead shielding, these muons can penetrate a meter or more, while nucleons can be stopped in several inches of lead. 

Beta Particles A beta particle is an electron (negative charge) or positron (positive charge) separated from the nucleus of an atom. Smaller than alpha particles, beta particles travel at higher speeds and have enough penetrating power to pass through nearly 14 in. of human tissue. 

The identity and symbol of the daughter nuclide of any positron emission is determined in a manner similar to alpha and beta decay, as shown in Example 17.3. Positron emission is similar to beta emission in its ionizing and penetrating power. Table 17.1 summarizes the different kinds of radioactivity that we have covered in the chapter. 

Positrons, emitted from atomic nuclei when protons change into neutrons. Positrons have the same mass as electrons but opposite charge, and so are represented by the symbol +V- They have intermediate ionizing power and intermediate penetrating power. 

How do the ionizing power and penetrating power of positrons compare to other types of radiation ... 

Rank alpha particles, beta particles, positrons, and gamma rays in terms of (a) increasing ionizing power (b) increasing penetrating power. 

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