Physics - 07 Radioactivity Flashcards
What is the mass/ nucleon number?
The number of protons + number of neutrons
What is the atomic/ proton number?
The number of protons
What is an isotope?
Different atoms of an element with the same number of protons + electrons but different numbers of neutrons
What are the protons in the nucleus held together by?
Strong nuclear force which is strong enough to hold the nucleus together despite the protons trying to repel each other
What happens if there are too few/ many neutrons?
The balance of these forces is affected and the nucleus will become unstable.
What will eventually happen to an unstable nucleus?
An unstable nucleus will eventually decay - this is where it gives out energy + may also give out alpha and beta particles.
What is ionising radiation?
Ionising radiation causes atoms to gain/ lose electric charge, forming ions
Describe the process of random decay.
When unstable nuclei decay, they give out ionising radiation.
Unstable nuclei decay at random: we cannot predict which nucleus will decay or when it will decay.
We can only measure the probability that a certain proportion of radioactive material will decay in a certain time.
What are the three basic types of ionising radiation?
Alpha, beta, gamma.
What is alpha radiation?
An alpha particle is a helium nucleus (I.e, no electrons) ejected from an unstable nucleus.
Alpha particles have a relatively large mass - they are made of 4 nucleons (2 protons and 2 neutrons), and have a charge of +2.
They have a very short range - they can be stopped by a few cm of air.
They are very strongly ionising.
Describe beta radiation.
Beta particles are very fast moving electrons ejected from the nucleus.
Beta particles are very light and have a relative charge of -1.
They have a larger range than alpha particles, travelling long distances through air, passing through paper and are stopped by a few mm of aluminium.
Describe gamma radiation
Gamma rays are EM waves with a very short wavelength and very high frequency.
They have no mass and no charge and are therefore very weakly ionising but very penetration - it takes several cm of lead or 1m of concrete to stop them.
Gamma rays are emitted in “packets” of energy called photons.
What is the unit of radioactivity?
The becquerel (Bq)
What is the becquerel a measure of?
The number of decays per second. 1 Bq = 1 decay per second.
It’s very small so we tend to use kBq or MBq.
What is half life?
The half life of a radioactive element is the average time that it takes half the nuclei in a sample to decay.
(As time goes on, fewer and fewer radioactive atoms remain. This means that the number of atoms decaying in a given time decreases and so the amount of radiation detected (the count rate) also decreases!)
