Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 42 - Nuclear Physics - Exercises and Problems - Page 1275: 44

Answer

No.

Work Step by Step

From the mentioned graph, the binding energy per nucleon for $ ^{56}\text{Fe} $ is about $ 8.8 \, \text{MeV} $. So, the total binding energy $ B_{\text{Fe}} $ for the $ ^{56}\text{Fe} $ nucleus is: $$ B_{\text{Fe}} = \text{Binding energy per nucleon} \times \text{Mass number} $$ Substitute the values: $$ B_{\text{Fe}} = 8.8 \, \text{MeV} \times 56 = 493 \, \text{MeV} $$ The binding energy per nucleon for $ ^{28}\text{Al} $ is about $ 8.4 \, \text{MeV} $ from the graph. So, the total binding energy $ B_{\text{Al}} $ for a single $ ^{28}\text{Al} $ nucleus is: $$ B_{\text{Al}} = \text{Binding energy per nucleon} \times \text{Mass number} $$ Substitute the values: $$ B_{\text{Al}} = 8.4 \, \text{MeV} \times 28 = 235 \, \text{MeV} $$ And hence, $$ B_{\text{2Al}} = 2 \times B_{\text{Al}} = 2 \times 235 \, \text{MeV} = \bf 470 \rm \, {MeV} $$ Now we need to Compare the Binding Energies. The total binding energy of the original $ ^{56}\text{Fe} $ nucleus is $ 493 \, \text{MeV} $, which is higher than the combined binding energy of the two$\; ^{28}\text{Al} $ nuclei. $$ (B_{\text{Fe}} = 493 \, \text{MeV}) > (B_{\text{2Al}} = 470 \, \text{MeV}) $$ Since the binding energy of the $ ^{56}\text{Fe} $ nucleus is greater, this means the $ ^{56}\text{Fe} $ nucleus is more tightly bound than the two $ ^{28}\text{Al} $ nuclei. So, to force $ ^{56}\text{Fe} $ to fission into two $ ^{28}\text{Al} $ nuclei, an energy input is required. Therefore, the $ ^{56}\text{Fe} $ nucleus$\underline{\color{red}{\text{ cannot}}}$ spontaneously fission into two $ ^{28}\text{Al} $ nuclei because its binding energy is higher, indicating it is more stable.
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