PATTERNS OF NUCLEAR STABILITY

The significance of these numbers for nuclear stability is similar to the numbers of electrons associated with the very stable noble gases (i.e., 2,10,18,36, 54, and 86 electrons). 

Of the two stable isotopes of antimony mentioned in rule 1, both have even numbers of neutrons lSb and pSb. 

There are more stable nuclei containing 2,8,20,50,82, or 126 protons or neutrons than there are containing other numbers of protons or neutrons. For example, there are 10 stable isotopes of tin (Sn) with the atomic number 50 and only 2 stable isotopes of antimony (Sb) with the atomic number 51. The numbers 2. 8. 20.50. 82. and 126 are called magic numbers. 

There are many more stable nuclei with even numbers of both protons and neutrons than with odd numbers of these particles (Table 20.2). 

All isotopes of the elements with atomic numbers higher than 83 are radioactive. 

The principal factor that determines whether a nucleus is stable is the neutron-to-proton ratio (n/p). For stable atoms of elements having low atomic number ( 20), the n/p value is close to 1. As the atomic number increases, the neutron-to-proton ratios of the stable rmelei also increase. This deviation at higher atomic numbers arises because more neutrons are needed to counteract the strong repulsion among the protons and stabilize the nueleus. The following rales are usefiil in gauging whether or not a particular nucleus is expected to be stable  

TABLE 20.2 Number of Stable Isotopes with E cn and Odd Numbers of Protons and Neutrons 

No single rule allows us to predict whether a particular nucleus is radioactive and, if it is, how it might decay. However, several empirical observations can help us predict the stability of a nucleus. 

Some nuclides, such as and are stable, whereas others, such as are unstable and undergo fission. Why is it that some nuclides are stable but others that may have only one more or one fewer neutron dxe not No single rule allows us to predict whether a particular nucleus is radioactive and, if it is, how it might decay. However, several empirical observations ctm help us predict the stabiUty of a nucleus. 

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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. 

Stability and Nuclear Structure The oddness or evenness of N and Z values is related to some important patterns of nuclear stability. Two interesting points become apparent when we classify the known stable nuclides ... 

In a similar maimer, patterns of nuclear stability, results of nuclear reactions and spectroscopy of radiation emitted by nuclei have yielded information which helps us develop a picture of nuclear structure. But the situation is more complicated for the nucleus than for the atom. In the nucleus there are two kinds of particles, protons and neutrons, packed close together, and there are two kinds of forces - the electrostatic force and the short range strong nuclear force. This more complex situation has caused slow progress in developing a satisfactory model, and no single nuclear model has been able to explain all the nuclear ph omena. 

PATTERNS OF NUCLEAR STABILITY We see that nuclear stability is determined largely by the neutron-to-proton ratio. For stable nuclei, this ratio increases with increasing atomic number. All nuclei with 84 or more protons are radioactive. Heavy nuclei gain stability by a series of nuclear disintegrations leading to stable nuclei. 

Nuclear Stability Patterns of Nuclear Stability Nuclear Binding Energy ... 

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