The proton number of uranium is 92 and the proton number of radon is 88 - AQA - A-Level Physics - Question 10 - 2021 - Paper 1
Question 10
The proton number of uranium is 92 and the proton number of radon is 88.
Which series of decays turns a uranium nucleus into a radon nucleus?
Worked Solution & Example Answer:The proton number of uranium is 92 and the proton number of radon is 88 - AQA - A-Level Physics - Question 10 - 2021 - Paper 1
Step 1
A: α + β + β + α + α
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Answer
To evaluate this option, we note that the uranium nucleus must lose four protons to transform into radon. Each alpha decay (α) reduces the proton number by 2, while beta decay (β) keeps the mass number the same but changes one neutron to a proton.
If we apply this combination:
Two α decays decrease the proton number by 4 (from 92 to 88).
The β decays do not change the proton number but could balance the neutron count if necessary.
Thus, this sequence would effectively create radon from uranium, making this option correct.
Step 2
B: β + β + α + β + α
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Answer
This sequence starts with two beta decays (each maintaining the proton number) and follows with two alpha decays (decreasing the proton number). Since it begins with a stable number of protons, it does not lead to radon effectively.
Step 3
C: α + α + α + β + β
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Answer
This option indicates three alpha decays, reducing the uranium proton number by 6, which overshoots the necessary count to reach radon (88 protons). Therefore, this option is incorrect.
Step 4
D: β + β + β + β + α
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Answer
In this case, four beta decays do not alter the proton number when starting from uranium and then one alpha decay reduces it. This path also fails to achieve the necessary configuration to form radon.
