Physics - Topic 11 - Nuclear Radiation

nuclear decay is spontaneous and random. what do these two terms mean?

• random - cannot identify which atom/nucleus will be the next to decay

• spontaneous - external factors cannot influence when a nucleus will decay

what is the law of radioactive decay?

rate of decay is directly proportional to the number of unstable nuclei present.

A = ? (in terms of number of unstable nuclei present)

• A = λN

• A is the activity in Bq

• λ is the decay constant, measured in s⁻¹ or min⁻¹

• N is the number of unstable nucle, unitless

dN/dt = ?

dN/dt = -λN

λ = ?

λ = ln2/t₁/₂

A = ?, N = ?

• A = A₀e^-λt

• N = N₀e^-λt

write an equation for the nuclear decay of an unstable parent nuclide X into a daughter nuclide Y via alpha decay.

write an equation for the nuclear decay of an unstable parent nuclide X into a daughter nuclide Y via beta minus decay. write another equation to show which sub-atomic particle is being converted.

write an equation for the nuclear decay of an unstable parent nuclide X into a daughter nuclide Y via beta plus decay. write another equation to show which sub-atomic particle is being converted.

define nuclear binding energy and state its associated equation

• nuclear binding energy is the energy needed completely separate the individual nucleons in the nucleus

• BE/ΔE = Δmc²

• Δm is the mass deficit - calculated by finding initial mass - final mass

• c is the speed of light in a vacuum

how do nuclear fusion and fission cause a change in binding energy per nucleon?

• fusion - increase

• fission - increase

• fusion involves an increase in binding energy (per nucleon) as the number of nucleons increases

• fission involves as increase in binding energy (per nucleon) as the number of nucleons decreases

• if binding energy per nucleon increases energy is released in the process

• the rate of decay depends upon the number of unstable nuclei in the sample (A = λN)

• radium has a large half-life, so unstable nuclei are present in the sample for a long time

• when a nucleus decays there is a (small) decrease in mass Δm

• energy is released according to ΔE = Δmc²

• Δm is small but c is large, so a significant amount of energy is released

• energy released by the decay becomes kinetic energy of the atoms in the sample (hence the sample is above the temperature of the surroun