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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