Radioactive decay predicting mode

Protons and neutrons are called nucleons. A nuclide is any nucleus with specific numbers of each type of nucleon. A plot of number of neutrons (N) versus number of protons (Z) for all nuclei shows a narrow band of stability. Unstable nuclei undergo various modes of radioactive decay. The mode can often be predicted from a nuclide s mass relative to the atomic mass and N/Z ratio. 

The pattern of nuclear stability can be used to predict the likely mode of radioactive decay neutron-rich nuclei tend to reduce their neutron count proton-rich nuclei tend to reduce their proton count. In general, only heavy nuclides emit a particles. 

The first four modes of radioactive decay can be plotted on a single diagram (Fig. 10.3), which allows for a prediction of the nature of the daughter nucleus from a parent subject to any one of the above processes. 

There are four stable isotopes of iron with mass numbers 54, 56, 57, and 58. There are also two radioactive isotopes iron-53 and iron-59. Predict modes of decay for these two isotopes and write a nuclear reaction for each. (See Table 21.2.)... 

In the preceding section we have described three methods of determining nuclear spin — one optical and two magnetic. The nuclear spin plays a central role in forming the nuclear energy states. It is therefore to be expected that it also should be of importance in nuclear reactions and in radioactive decay. Let us consider some rules for the lifetimes of unstable nuclei, for their permitted modes of decay, and for the role of nuclear spin. Knowing these rules, it is, for example, possible from a decay scheme to predict the spin states of levels which have not been measured. 

SECTION 21.2 The neutron-to-proton ratio is an important factor determining nuclear stability. By comparing a nuclide s neutron-to-proton ratio with those in the band of stability, we can predict the mode of radioactive decay. In general, neutron-rich nuclei tend to emit beta particles proton-rich nuclei tend to either emit positrons or im-dergo electron capture and heavy nuclei tend to emit alpha particles. The presence of magic numbers of nucleons and an even number of protons and neutrons also help determine the stability of a nucleus. A nuclide may undergo a series of decay steps before a stable nuclide forms. This series of steps is called a radioactive series or a nuciear disintegration series. 

A stable nucleus remains intact indefinitely, but the great majority of nuclei are unstable. An unstable nucleus exhibits radioactivity, emission of radiation due to its spontaneous disintegration. In Section 23.2, you ll see that each type of unstable nucleus has its own characteristic rate of radioactive decay. In this section, we cover important terms and notation for nuclei, define the types of emission, and desalbe various modes of radioactive decay and how to predict which occurs for a given nucleus in the process, you ll learn how to write nuclear equations. 

Predicting the Mode of Decay An unstable nuclide generally decays in a mode that shifts its N/Z ratio toward the band of stability. This fact is illustrated in Figure 23.2B, which expands a small region of Figure 23.2A to show all of the stable and many of the radioactive nuclides in that region, as well as their modes of decay. Note the following points, and then we ll apply them in a sample problem ... 

New forms of radioactivity were reported. Proton emission from ground states, predicted as the simplest decay mode of proton-rich nuclei and long searched for, was observed in 1982 for Lu (81 ms) produced by a heavy-ion reaction (Hofinann et al. 1982). Unusual large nuclear radii were found for some very light nuclei (Tanihata et al. 1985) and later attributed to neutron haloes, e.g., for Li (8.5 ms) to a halo of two neutrons around a i core. Even a new kind of natural radioactivity was discovered in 1984 (Rose and Jones 1984) emission of nuclei fi-om Ra (lid) leading to Discoveries of other rare decay modes involving the emission of a variety of fragments from very heavy nuclei soon followed. 

Predict the mode of decay of (a) plutonium-239 (b) indium-120. Keep in mind that our guidelines don t always work. For example, thorium-233, Th, which we might expect to undeigo alpha decay, actually undeigoes beta decay. Furthermore, a few radioactive nudei actually lie within the belt of stability. Both e d and Nd, for example, are stable and lie in the belt of stability. Nd, however, which lies between them, is radioactive. 

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