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DSE Physics: Radioactivity and Nuclear Energy — Practice Questions & Answers
The nuclear atom and radioactive decay, alpha, beta and gamma radiation, half-life, fission and fusion, radiation uses and hazards, and mass-energy equivalence.
240 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
The half-life of a radioactive nuclide is the time for the activity of a sample to fall to
one half of its initial value
zero
one quarter of its initial value
double its initial value
Tap an answer to check it.
Why After one half-life the activity halves.
2
Multiple choice · Medium
A radioactive isotope X has a half-life of 20 hours. After a time of 10 hours, the approximate fraction f of the sample remaining is
3/4 > f > 1/2
f = 1/2
1/4 <= f <= 1/2
f > 3/4
Tap an answer to check it.
Why 10 h is half a half-life, so f = (1/2)^0.5 = 0.71, i.e. between 1/2 and 3/4.
3
Multiple choice · Hard
A sample contains 8.0 x 10^10 undecayed nuclei and has a half-life of 12 hours. The number remaining after 2.0 days (48 hours) is
5.0 x 10^9
1.0 x 10^10
2.0 x 10^10
2.5 x 10^9
Tap an answer to check it.
Why 48 h = 4 half-lives; 8.0e10 x (1/2)^4 = 8.0e10/16 = 5.0 x 10^9.
4
Fill in the blank · Easy
Radioactive decay is both random and
Check answer
Answer:
spontaneous
Why Decay is spontaneous.
5
Fill in the blank · Medium
A nuclide has a half-life of 8 hours. After 24 hours the fraction of the original nuclei remaining is
Check answer
Answer:
1/8 / 0.125
Why 24 h = 3 half-lives; (1/2)^3 = 1/8.
6
Fill in the blank · Hard
A source of half-life 30 minutes has an initial activity of 6.4 x 10^4 Bq. After 2.0 hours its activity is
Check answer
Answer:
4 / 4.0
Why 2.0 h = 4 half-lives; 6.4e4/16 = 4.0 x 10^3 Bq.
7
Multiple choice · Hard
Radium-226 (²²⁶₈₈Ra) undergoes alpha decay to radon (Rn). The correct nuclear equation is
²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He
²²⁶₈₈Ra → ²²⁴₈₆Rn + ⁴₂He
²²⁶₈₈Ra → ²²²₈₈Rn + ⁴₂He
²²⁶₈₈Ra → ²²²₈₆Rn + ⁰₋₁e
Tap an answer to check it.
Why Alpha decay: ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He, conserving nucleon number and charge.
8
Multiple choice · Medium
In writing a nuclear equation, the sums that must be equal on both sides are the
nucleon numbers and the proton numbers
masses in grams
neutron numbers only
half-lives
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Why Both the total nucleon numbers and the total proton (charge) numbers must balance.
9
Multiple choice · Easy
An alpha particle carries a charge of
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Why An alpha particle (2 protons) has a charge of +2e.
10
Fill in the blank · Medium
In the alpha decay of radium-226, the daughter nucleus radon has a nucleon number of
Check answer
Answer:
222
Why 226 − 4 = 222.
Key terms in Radioactivity and Nuclear Energy
Nucleon: A particle found in the nucleus of an atom, namely a proton or a neutron.
Proton number: The number of protons in a nucleus, also called the atomic number, which identifies the element.
Nucleon number: The total number of protons and neutrons in a nucleus, also called the mass number.
Isotope: Atoms of the same element with the same proton number but different numbers of neutrons.
Radioactivity: The spontaneous and random emission of radiation from unstable nuclei.
Alpha particle: A helium nucleus of two protons and two neutrons emitted by some radioactive nuclei.
Beta particle: A fast-moving electron emitted from a nucleus when a neutron changes into a proton.
Gamma ray: High-energy electromagnetic radiation emitted from a nucleus, with no charge or mass.
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