Beta-gamma emission

Am is produced when 239Pu is exposed to neutrons, such as may occur in nuclear reactors. (239Pu, it should be noted, is produced when uranium 238 [238U], is exposed to neutrons.) The reaction sequence involves the successive absorption of neutrons and emission of gamma rays, written as (n,y) and the emission of a beta particle, (3. ... 

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. 

Radioactive isotopes that decay by the emission of alpha or beta radiation undergo a change in the nature of their nuclei and are converted into isotopes of other elements. The emission of gamma rays, on the other hand, does not change the nature of the nuclei of the radioisotopes from which the rays are emitted. Gamma rays are a form of dissipation of nuclear energy. 

EXAMPLE 22.7. When a 2 1 nucleus disintegrates, the following series of alpha and bela particles is emitted alpha, beta, beta, alpha, alpha, alpha, alpha, alpha, beta, alpha, beta, beta, beta, alpha. (Since emission of gamma particles accompanies practically every disintegration and since gamma particles do not change the atomic number or mass number of an isotope, they are not listed.) Show that each isotope produced has a mass number that differs from 238 by some multiple of 4. 

Make sure that in alpha, beta, gamma, and positron emission the particle being emitted is on the right-hand side of the reaction arrow. In electron capture, the electron should be on the left side of the arrow. 

There are five main types of emissions alpha emission, beta emission, positron emission, electron capture, and gamma emission. Four of these produce changes in the elements undergoing decay, and the end result is a more stable atomic structure. 

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. 

How is gamma radiation produced in a radioactive decay When a radioactive nucleus emits an alpha or beta particle, the nucleus is often left in an unstable, high-energy state. The relaxation of the nucleus to a more stable state is accompanied by the emission of gamma radiation. 

Internal transition involves the emission of electromagnetic radiation in the form of gamma (y) rays from a nucleus in a metastable state and always follows initial alpha or beta decay. Emission of gamma radiation leads to no further change in atomic number or mass. 

Figure 3 Measured vs predicted efficiencies for radionuclides decaying by high energy beta emission and beta/gamma emission.

Because gamma rays are massless, the emission of gamma rays by themselves cannot result in the formation of a new atom. Table 4-3 summarizes the basic characteristics of alpha, beta, and gamma radiation. 

Lutetium-177 is increasingly being viewed as a potential radionuclide for use in in vivo therapy because of its favourable decay characteristics. Lutetium-177 decays with a half-life of 6.73 d by emission of beta particles with maximum energies of 497 keV (78.6%), 384 keV (9.1%) and 176 keV (12.2%) to stable Hf. The emission of gamma photons of 113 keV (6.4%) and 208 keV (11%) with relatively low abundances provides advantages that allow simultaneous... 

Explain why gamma rays often accompany alpha emission, beta emission, positron emission, and electron capture. 

Bart et al. (62) have described the enclosure of a Mettler TA-1 thermoanalyzer in a sealed system in order to permit the examination of samples containing alpha and beta/gamma emissions. Samples containing plutonium and uranium may be studied by TG with no radiation hazard to the operator. All balance components could be reached through glove ports. 

Radioactive nuclei, formed by neutron activation, disintegrate by beta-, gamma-, or -exceptionally - alpha-emission in biomedical neutron activation analysis, only the first and the second are of practical impedance. 

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. 

A gamma ray is short wavelength electromagnetic radiation emitted from the nucleus. Nuclei which have undergone transmutation by alpha or beta decay or by capture of a neutron often return to the ground state by emission of gamma radiation. Addition of a neutron changes the atomic mass or isotope number of the element but not the atomic number, as seen by the formation of plutonium-242 from plutonium-241. 

This is the last chapter in Part I of the general chemistry review. In this chapter, we will discuss the different aspects of radioactivity. Radioactivity is a nuclear phenomenon. It results from natural nuclear instability or externally induced nuclear instability. We will limit our discussion of nuclear chemistry to the basic aspects of radioactivity involving radioactive emissions such as alpha emission, beta emission, gamma rays, positron emission, and electron capture. We will also review other ideas such as the half-lives of radioactive substances and the mass-energy equation. 

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