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Grade: 12


nucleus is stable only when n/p ratio is greater than 1. why???

nucleus is stable only when n/p ratio is greater than 1. why???

11 years ago

Answers : (1)

Askiitians Expert Bharath-IITD
23 Points

Dear Praharsha,


It has been found that the stability of nucleus depends upon its neutron to proton (n/p) ratio. A plot of N (the neutron number) against Z (atomic number or number of protons) show that for stable nuclides upto Z = 20, N = 20 i.e., the relationship can be represented by a line with a slope of 45°. "'2 Thus maximum stability is attained when N = Z.

fig 11.1 -A plot of number of neutrons (N) against the atomic number (Z) for a range of stable nuclei From the plot it is evident that

(i) light nuclei (A < 20) have n/p ration dose to unity.

(ii) for heavy nuclei (A > 20) the n/p ratio increases progressively due to dominance of number of neutrons. Thus stable nuclei (non-radioactive) have n/p ratio between 1 -1.6. These lie in the shaded region of the plot which is also called stability belt or stability zone.

The elements whose nuclei do not fall within the stability zone are said to be unstable. The unstable nuclei, whose n/p ratio is either less than 1 or greater than 1.6, disintegrate giving out a, b, g rays in their attempt to attain stability. The process of disintegration continues till the n/p ratio falls within the stability

The explanation for the stability of the nuclei for the limits mentioned can be explained through meason theory which is of high conceptual level.

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Adapa Bharath

11 years ago
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