Nuclear instability (A-level only) Flashcards – AQA A-level Physics (7408)

What does an $N$–$Z$ graph plot for nuclei?

Neutron number $N$ against proton number $Z$.

What region of an $N$–$Z$ graph do stable nuclei occupy?

A band, rather than an arbitrary range of neutron-to-proton ratios.

How do neutron and proton numbers compare in light and heavy stable nuclei?

For light nuclei, $N$ is generally close to $Z$; for heavier nuclei, $N$ is generally greater than $Z$.

What can happen to nuclei outside the stable band on an $N$–$Z$ graph?

They are unstable and can decay towards greater stability.

How is a nucleus judged to be neutron-rich or proton-rich on an $N$–$Z$ graph?

By comparing it with stable nuclei in the same region of the graph.

What happens in alpha decay, and what is the emitted particle?

An unstable nucleus emits an alpha particle: a helium-4 nucleus containing two protons and two neutrons.

How do the proton number, neutron number and mass number change in alpha decay?

Proton number decreases by 2, neutron number by 2, and mass number by 4.

What is the general nuclear equation for alpha decay of $^{A}_{Z}X$?

$^{A}_{Z}X \rightarrow {}^{A-4}_{Z-2}Y + {}^{4}_{2}\alpha$

Which two quantities balance across an alpha-decay equation?

Mass number and charge.

What happens to a neutron in an unstable nucleus during beta-minus decay?

It changes into a proton, emitting an electron (the beta-minus particle) and an electron antineutrino.

How do the proton number $Z$, neutron number $N$ and mass number $A$ change in beta-minus decay?

$Z$ increases by 1, $N$ decreases by 1, and $A$ remains unchanged.

What is the general nuclear equation for beta-minus decay?

${}^{A}_{Z}X \rightarrow {}^{A}_{Z+1}Y + {}^{0}_{-1}e + \bar{\nu}_e$

What happens to a proton during beta-plus decay, and which particles are emitted?

It changes into a neutron, emitting a positron (the beta-plus particle) and an electron neutrino.

How do $Z$, $N$ and $A$ change in beta-plus decay?

$Z$ decreases by one, $N$ increases by one, and $A$ remains unchanged.

What is the general nuclear equation for beta-plus decay?

${}^{A}_{Z}X \rightarrow {}^{A}_{Z-1}Y + {}^{0}_{+1}e + \nu_e$

What happens during electron capture?

An unstable nucleus captures an inner-shell electron. A proton combines with it to become a neutron, emitting an electron neutrino.

How does electron capture change the atomic number $Z$, neutron number $N$ and mass number $A$?

$Z$ decreases by 1, $N$ increases by 1, and $A$ is unchanged.

Write the general nuclear equation for electron capture by $^{A}_{Z}X$.

$^{A}_{Z}X + {}^{0}_{-1}e \rightarrow {}^{A}_{Z-1}Y + \nu_e$

What is an excited nuclear state?

A nuclear state with more energy than the ground state.

What equation relates the energy of an emitted gamma photon to the nuclear energy-level difference and photon frequency?

$E_\gamma = \Delta E = hf$

What does a downward arrow between levels on a nuclear energy-level diagram represent?

A transition to a lower nuclear energy level with emission of a photon whose energy equals the level difference.

How does gamma emission affect a nuclide’s proton and neutron numbers?

Neither number changes, so the nuclide remains the same.

What is technetium-99m, and what does it become when it emits gamma radiation?

It is a metastable excited nuclear state that transitions to technetium-99.

How is technetium-99m used in medical diagnosis?

Its emitted gamma radiation is detected to obtain information about its distribution in the body.