Radioactivity Flashcards
Define activity.
Number of decays per second.
Define decay constant.
The probability of a nucleon decaying per unit time.
Describe the spontaneous and random nature
of radioactive decay of unstable nuclei.
It is spontaneous because it happens with no external influence - it cannot be induced. It is random because we cannot predict which nucleon will decay next.
Describe the nature, penetration and range of
alpha-particles.
Strongly ionising, slow, absorbed by paper or a few cm of air, have a charge of +2 and a relative mass of 4.
Describe the nature, penetration and range of
beta-particles
Weakly ionising, fast, absorbed by about 3mm of aluminium, have a charge of -1, a negligible mass and are equivalent to an electron.
Describe the nature, penetration and range of gamma-rays.
Very weakly ionising, speed of light, absorbed by many cm of lead, or several m of concrete. No charge or mass.
How do we calculate the activity of a sample?
Decay constant x number of nuclei.
Define half-life.
The average time it takes for number of undecayed atoms to halve.
How do we calculate the decay constant?
ln2/half-life
State the similarities and differences between the discharge of a capacitor and the decay of a radioactive substance.
They both have the same decay equations, where the letters represent the amount of charge and number of nuclei remaining. We use both of these equations in the same way. 1/decay constant is the equivalent to the time constant (CR), and the half-life of both of them is equivalent to ln2 multiplied by these values.
Describe the uses of radioactive isotopes in smoke alarms.
Smoke alarms contain a weak alpha-particle emitter close to two electrodes. The radiation ionises the air, and a current flows between the electrodes. In the event of a fire, the smoke absorbs the radiation, breaking the current and sounding the alarm.
Describe the technique of carbon dating.
Living organisms absorb the radioactive isotope carbon-14. When they die, the activity of the carbon-14 falls. We can compare the activity in a substance to a similar, living substance to see how long ago the organism died.
