Radioactivity Flashcards
Define the mass defect
The difference between the mass of the nucleus and the total mass of the nucleons infinitely separated
Define binding energy
The energy required to separate the nucleons to infinity.
define fusion
Two smaller nuclei join together to form one larger nucleus.
Define radioactive decay
It is the spontaneous emission of radiation from an unstable nucleus.
What does it mean when radioactive decay is said to be random?
Random means that you can’t predict when a nucleus will decay.
What does it mean when radioactive decay is said to be spontaneous?
Spontaneous means that it is not affected by any external factors.
Define the activity of a sample.
The number of decays per unit time.
Why does the activity of a sample decrease as the sample decays.
Every nucleus has the same probability of decay. AS time passes there are fewer undecayed nuclei remaining, so fewer will decay per unit time. This explains why activity decreases with time.
Equation relating Activity, decay constant, and number of nuclei.
A = λ* N
Why can the count rate of a radioactive sample be more than expected.
The daughter nucleus might also be unstable.
What is meant by the decay constant of a sample? λ
The decay constant of a sample is the probability of decay of a nucleus per unit time.
State the equation relating the decay constant and the half-life of a sample.
t1/2 = ln(2) / λ
Define half-life
It is the time taken for the activity of a sample to halve.
What is the instrument used to measure the count rate.
A geiger muller tube
Why is the mesaured count rate of a sample alwyas smaller than the actual count rate of a sample? (min 3-max 5)
-Sample emits in all directions but detector only captures emissions in one direction.
-Some emissions are absorbed before reaching the detector.
-Some emissions are scattered within the sample.
-Simultaneous arrival of multiple particles only registers once.
-Some particles may reach the detector but not cause ionisation .
