Discussion
In the fission of U-235 nuclei, it is observed that the fission fragments decay by emission of negatively charged beta particles and attain state of stable nuclei.
The reason for emission of negatively charged beta particles is that the fission fragments :
Answer: D
The fragments emit β− particles because they are rich in neutrons.
U-235 has a neutron-to-proton ratio of about 1.55. The fission fragments, of mass number roughly 90 to 145, inherit nearly that ratio, but stable nuclei of that size have a ratio of only about 1.2 to 1.4. Each fragment therefore has too many neutrons, and it moves toward stability by a chain of β− decays, in each of which a neutron becomes a proton.
Proton-rich nuclei decay by positron emission or electron capture, not β−. Prompt neutron emission does happen, but it only partly relieves the excess and is not the cause of beta decay, and spin has no bearing on the sign of the beta particle.
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