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Sunday, March 11, 2018

A 23892U nucleus decays in two stages to a 23491Pa nucleus. What was emitted in these two stages?



Question 4
A 23892U nucleus decays in two stages to a 23491Pa nucleus.

What was emitted in these two stages?
A α + β          B α + γ          C β + β          D β + γ





Reference: Past Exam Paper – November 2008 Paper 1 Q40





Solution:
Answer: A.

During the decay: 23892U        - - >             - - >  23491Pa + ???

For any decay, the proton number and mass number must be conserved.
Proton number: 92 = 91 + x
Mass number: 238 = 234 + y

Thus, x = 92 – 91 = 1              and y = 238 – 234 = 4


3 types of radiation can be emitted during radioactive decay: alpha, beta (minus) and gamma. We know that alpha particle is 42α and beta particle is 0-1β. Gamma is an EM wave and does not have a mass or proton number.


We need to identify which of the combinations provided in the multiple choice would give an overall proton number of +1 and overall mass number of 4.

Consider choice A:     [α and β]
Proton number = 2 + –1 = +1
Mass number = 4 + 0 = 4

So, A is correct

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