Beta particle emission decay

Lead-210 has a half-life of 20.4 years. This isotope decays by beta particle emission. A counter registers 1.3 X 104 disintegrations in five minutes. How many grams of Pb-210 are there ... 

There are three common ways by which nuclei can approach the region of stability (1) loss of alpha particles (a-decay) (2) loss of beta particles (/3-decay) (3) capture of an orbital electron. We have already encountered the first type of radioactivity, a-decay, in equation (/0). Emission of a helium nucleus, or alpha particle, is a common form of radioactivity among nuclei with charge greater than 82, since it provides a mechanism by which these nuclei can be converted to new nuclei of lower charge and mass which lie in the belt of stability. The actinides, in particular, are very likely to decay in this way. 

In 1899 he identified two forms of radioactivity, which he called alpha and beta particles. As we saw earlier, he deduced that alpha particles are helium nuclei. Beta particles are electrons - but, strangely, they come from the atomic nucleus, which is supposed to be composed only of protons and neutrons. Before the discovery of the neutron this led Rutherford and others to believe that the nucleus contained some protons intimately bound to electrons, which neutralized their charge. This idea became redundant when Chadwick first detected the neutron in 1932 but in fact it contains a deeper truth, because beta-particle emission is caused by the transmutation ( decay ) of a neutron into a proton and an electron. 

The two fission-produced radio-strontium isotopes of interest in environmental samples are 90Sr and 89Sr. Sr-90 has a fission yield of 5.8 %, a half-life is 28.78 a, and the radioactive daughter 90Y with a half life of 2.67 d, to which it decays by beta-particle emission. Sr-89 has a fission yield of 4.7%, a half life of 50.52 d, and decays to the stable daughter89 Y. The decay schemes given in Figure 13.1 show that these two radio-strontium isotopes for practical purposes can only be measured by beta-particle counting. 

There are three main types of radioactive decay alpha particle emission, beta particle emission, and the emission of gamma radiation. When an unstable isotope undergoes radioactive decay, it produces one or more different isotopes. We represent radioactive decay using a nuclear equation. Two rules for balancing nuclear equations are given below. 

Beta particle emission—A neutron turns into a proton and an electron. The new proton stays in the nucleus and the electron is emitted from the atom, and the electron is called a heta particle. Another subatomic particle, known as an antineutrino, is also produced. An example is the decay of carhon-14 into nitrogen. 

Beta particles A beta particle is a very fast-moving electron that is emitted when a neutron in an unstable nucleus converts into a proton. Beta particles are represented by the symbol (3 or e. They have a 1 — charge. Their mass is so small compared with the mass of nuclei involved in nuclear reactions that it can be approximated to zero. Beta radiation consists of a stream of fast-moving electrons. An example of the beta decay process is the decay of iodine-131 into xenon-131 by beta-particle emission, as shown in Figure 24.4. Note that the mass number of the product nucleus is the same as that of the original nucleus (they are both 131), but its atomic number has increased by 1 (54 instead of 53). This change in atomic number occurs because a neutron is converted into a proton, as shown by the following equation. 

Positron emission occurs only when the energy difference between the parent radionuclide and the products exceeds 1.02 MeV (the energy equivalent of the sum of the masses of an electron and a positron). The atom s recoil, as for beta-particle emission, is a few electron volts. At lesser energy differences, a proton in the nucleus can be converted to a neutron by electron capture, i.e., the capture by the nucleus of an atomic electron from, most probably, an inner electron shell (see discussion below of CEs). The process of electron capture parallels positron emission and may occur in the same isotope. It is accompanied by emission of a neutrino and characteristic X rays due to the rearrangement of atomic electrons. Electron capture may also be signaled by the subsequent emission of gamma rays. Examples of these decays are given in Sections 9.3.4 and 9.3.6. 

The decay scheme of the naturally occurring radionuclide (see Fig. 9.6) is 89.1% by beta-particle emission, 10.9% by electron capture, and 0.001% by positron decay. The 1311-keV maximum-energy beta-particle decay is to the ground state of " °Ca. Electron-capture decay is followed instantaneously by emission of a 1461-keV gamma ray from the excited state of °Ar to its ground state. Electron capture decay to the ground state is 0.2% per disintegration. 

The naturally occurring radioactive decay series that begins with IfU stops with formation of the stable Pb nucleus. The decays proceed through a series of alpha-particle and beta-particle emissions. How many of each type of emission are involved in this series ... 

A radioactive decay series that begins with oTh ends with formation of the stable nuclide Pb. How many alpha-particle emissions and how many beta-particle emissions are involved in the sequence of radioactive decays ... 

The isotope is known to undergo a series of five successive alpha-particle emissions before ending up as the isotope slPb (at which point the isotope undergoes a series of beta-particle emissions before finally reaching stability). Write nuclear equations for the series of alpha emissions undergone by as it decays to slPb. 

Nuclei that have a neutron-proton ratio which is so high that they lie outside the belt of stable nuclei often decay by emission of a negative electron (a beta particle) from the nucleus. This effectively changes a neutron to a proton within the nucleus. Two examples are... 

Beer s law The absorbance of electromagnetic radiation by a sample is proportional to the molar concentration of the absorbing species and the length of the sample through which the radiation passes, beta (P) decay Nuclear decay due to fi-particle emission, beta (P) particle A fast electron emitted from a nucleus in a radioactive decay. 

The numerical combination of protons and neutrons in most nuclides is such that the nucleus is quantum mechanically stable and the atom is said to be stable, i.e., not radioactive however, if there are too few or too many neutrons, the nucleus is unstable and the atom is said to be radioactive. Unstable nuclides undergo radioactive transformation, a process in which a neutron or proton converts into the other and a beta particle is emitted, or else an alpha particle is emitted. Each type of decay is typically accompanied by the emission of gamma rays. These unstable atoms are called radionuclides their emissions are called ionizing radiation and the whole property is called radioactivity. Transformation or decay results in the formation of new nuclides some of which may themselves be radionuclides, while others are stable nuclides. This series of transformations is called the decay chain of the radionuclide. The first radionuclide in the chain is called the parent the subsequent products of the transformation are called progeny, daughters, or decay products. 

Beta (—) decay ( ). When we consider 146C, we see that the nucleus contains six protons and eight neutrons. This is somewhat "rich" in neutrons, so the nucleus is unstable. Decay takes place in a manner that decreases the number of neutrons and increases the number of protons. The type of decay that accomplishes this is the emission of a (3 particle as a neutron in the nucleus is converted into a proton. The (3 particle is simply an electron. The beta particle that is emitted is an electron that is... 

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