What is the source of emitted delayed neutron during the decay of 87Br?

 

Pl see the ‘full’ decay scheme of 87Br and 94Br.

 

In case of Br-87, it decays by 2 simultaneous β-.  

1. 87Br (β-)87mKr
2. 87Br (β-)87Kr

 

87mKr decays to 86Kr by neutron emission i.e.  

87mKr (n) 86Kr (Stable)

 

^87mKr₃₆  à ⁸⁶Kr₃₆ + ¹n₀

Where as 87Kr undergoes several β- decay and finally decays to stable 87Sr.

 

So basically neutron emission followed by β- decay is an alternative to gamma deexcitation which happens after β- decay. Most of the radionuclides formed by neutron fission are β- emitter. One category deexcites to ground state directly without any further emission e.g. 99Tc, second category by gamma emission e.g. 137Cs and third category by neutron e.g. 87Br.

 

1^st category: Excited Nuclide (β-) à Stable Nuclide

2^nd category: Excited Nuclide (β-) à Unstable Nuclide* (γ) àStable Nuclide

3^rd category: Excited Nuclide (β-)  à Unstable Nuclide* (n) àStable Nuclide.

 

Ref: Akyurek, T., and Shoaib Usman. "Spent fuel interrogation using delayed fast neutron spectrum at Missouri University of Science and Technology Reactor." Progress in Nuclear Energy 85 (2015): 525-540.. [https://www.sciencedirect.com/science/article/abs/pii/S0149197015300512]

 

Similar example can be seen for 94Br decay also. The neutron decay should be drawn as straight line as shown for 87Br, since there is no change in Z.

Ref: Michael F. L'Annunziata,Chapter 20 - The Atomic Nucleus,Radioactivity (Second Edition),Editor(s): Michael F. L'Annunziata, Elsevier, 2016, Pages 679-728, ISBN 9780444634894, https://doi.org/10.1016/B978-0-444-63489-4.00020-4.

 Few more examples of 3^rd category radionuclides

 

So the source of neutron is 87mKr nucleus.  

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