Skip to main content

Back to the full dot-point answer

NSWPhysicsQuick questions

Module 8: From the Universe to the Atom

Quick questions on Radioactive decay and half-life: HSC Physics Module 8

8short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is alpha decay?
Show answer
A heavy nucleus emits an alpha particle (24^4_2He, two protons and two neutrons). The atomic number decreases by 2, mass number by 4.
What is beta-minus decay?
Show answer
A neutron in the nucleus converts to a proton, emitting an electron (the beta particle) and an electron antineutrino. Atomic number increases by 1, mass number unchanged.
What is gamma decay?
Show answer
The nucleus is left in an excited state after an alpha or beta decay (or after a nuclear reaction). It drops to a lower state by emitting a high-energy photon (gamma ray). No change in ZZ or AA.
What are balancing nuclear equations?
Show answer
In any decay equation, two conservation laws must hold:
What is the decay law?
Show answer
If N(t)N(t) is the number of undecayed nuclei at time tt, the rate of decay is proportional to NN:
What is q1?
Show answer
Distinguish between alpha, beta-minus and gamma decay in terms of the change to mass number AA and atomic number ZZ. [3 marks]
What is q2?
Show answer
A sample contains 8.0×10128.0 \times 10^{12} atoms of 32^{32}P (T1/2=14.3 dT_{1/2} = 14.3 \text{ d}). Calculate the activity in Bq. [3 marks]
What is q3?
Show answer
226^{226}Ra decays by α\alpha-emission with T1/2=1600 yrT_{1/2} = 1600 \text{ yr}. (a) Write the nuclear equation. (b) Calculate the fraction of the original 226^{226}Ra remaining after 4800 yr4800 \text{ yr}.

All PhysicsQ&A pages