Negatrons, radioactivity

Beta Particle—An electron that is emitted from the nucleus of an atom during one type of radioactive transformation. A beta particle has a mass and charge equal in magnitude to that of the electron. The charge may be either +1 or -1. Beta particles with +1 charges are called positrons (symbolized (3+), and beta particles with -1 charges are called negatrons (symbolized (3 ). 

BETA DECAY. The process that occurs when beta particles are emitted by radioactive nuclei. The name beta particle or beta radiation was applied in the early years of radioactivity investigations, before it was fully understood what beta particles are. It is known now, of course, that beta particles are electrons. When a radioactive nuclide undergoes beta decay its atomic number Z changes by +1 or —1, but its mass number A is unchanged. When the atomic number is increased by 1, negative beta particle (negatron) emission occurs and when the atomic number is decreased by 1, there is positive beta particle (position) emission or orbital electron capture. 

The term antineutrino usually denotes an antiparticle whose emission is postulated to accompany radioactive decay by negatron emission, such as, for example, in neutron decay into a proton p+, negatron e and aiiliiieulnno IT, expressed by the equatiuii n p+ + e + vj. Capture of a neutrino by the neutron, ve + n - p+ + e would be an equally good description of the process. Positron emission is accompanied by a neutrino,... 

Examples 1 C, 1 C and gC are three of the isotopes of carbon. About 98.9% of naturally occurring carbon is in the stable JC form. 1 is also a stable isotope but it only occurs at 1.1% natural abundance. Trace amounts of radioactive 1gC are, found naturally this Is a negatron-emitting radioisotope (see Table 35.2). 

Two types of p particles can be created by radioactive decav. Negatrons (/3 ) are electrons that form when one of the neutrons in the nucleus is converted to a proton. In contrast, the positron ( ), also with the mass of the electron, forms when the number of protons in the nucleus is decreased by one. The positron has a transitory existence, its ultimate fate being annihilation in a reaction with an electron to yield two 0.51 l-MeV photons. 

If a nucleus has a NIZ ratio too high for stability, it is said to be neutron-rich. It will undergo radioactive decay in such a manner that the neutron to proton ratio decreases to approach more closely the stable value. In such a case the nucleus must decrease the value of N and increase the value of Z, which can be done by conversion of a neutron to a proton. When such a conversion occurs within a nucleus, 8 (or negatron) emission is the consequence, with creation and emission of a negative /3-particle designated by 8 or e (together with an anti-neutrino, here omitted for simplicity, see Ch. 4). For example ... 

Most of the radioisotopes used as isotopic labels in activation analysis decay with beta (positron and negatron) radiations and/or gamma rays. By convention, beta-emitting radionuclides are usually measured by gas-filled or gas-flow proportional counters or Geiger counters. Sometimes, liquid scintillation counters are used to complete a beta-ray measurement. The more conventional method for gamma-ray measurements involves the use of a gamma-ray spectrometer equipped with either a scintillation or solid-state detector. Stevenson (918) discusses the characteristics of radioactive decay and gives details on the methods and instruments used to detect emitted radiations. 

The various decay processes are listed in Table 1. Radioactive nuclides emit either nucleons (alpha particles, very rarely protons or neutrons) or electrons (negatrons, positrons). As an alternative to the emission of a positron, a proton may capture an electron of the K-shell (K-capture). By the emission of an alpha particle the mass number and the atomic number are reduced by the emission of electrons either the number of neutrons (jS -decay, negatron emission) or the number of protons ()S -decay, positron emission) is reduced. By K-capture also the number of protons is reduced. Due to the missing electron in the K-shell, characteristic X-rays of the newly produced atomic species are emitted. 

Any radioactive decay process in which the atomic number Z changes but the mass number A does not is classified as fi decay. Three types of p decay are encountered negatron emission, positron emission, and electron capture. Examples of the three processes are the following ... 

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