the atom and radioactivity Flashcards
what is an isotope?
sotopes of an element have the same number of protons, but a different number of neutrons.
describe unstable isotopes
The unstable ones tend to be isotopes with a different number of neutrons than the ‘original’[2]. The nuclei of unstable atoms/isotopes are interesting because they can decay - they magically turn into a different element, and release ionising radiation in the process.
what are the three forms of radiation?
alpha, beta and gamma rays
Describe alpha particles
-Alpha particles are Helium nuclei (2 protons and 2 neutrons).
-They have the smallest range (~ a few cm)
-They are the most ionising form of radiation (because they have a +2 charge, and so they can easily drag electrons away from things –> ionisation)
-They are blocked by almost everything, including paper and skin.
Describe beta particles
-Beta particles are high speed electrons (and therefore have mass 0 and charge -1)
-They have a medium range (up to 1m)
-They have medium ionising power (their -1 charge isn’t quite as good as Alpha’s +2 charge at knocking electrons off atoms)
-They are blocked by aluminium.
describe gamma rays
-Gamma rays are photons, and therefore have a charge of 0 and a mass of 0.
-They have the longest range (they can travel much, much more than 1m)
-They are the least ionising (in order for a gamma ray to knock an electron off, it needs to hit the electron directly and give it so much energy that it leaves the electron shell. This is unlikely).
-They are blocked by big sheets of lead or other high-atomic-number heavy materials.
Why can ionising radiation be dangerous when exposed too much?
you can develop cancer as it damages the DNA
what are the uses of ionising radiation?
-Alpha particles can be used in smoke detectors. A small bit of a substance that gives off alpha radiation is put near two electrodes and the ionisation allows a current to flow. -Smoke absorbs the radiation, breaking the current and causing the alarm to go off.
-Beta radiation can be used to test the thickness of paper (how exciting) by measuring how much is blocked.
-Beta or gamma radiation with a short half-life can be used in medicine to test how a certain organ is functioning.
-Gamma radiation can be used to sterilise tools for surgery.
half life definition
Half-Life is the average time it takes for the number of nuclei in a radioactive sample to halve.
what is background radiation caused by?
cosmic rays, rocks beneath the earth’s surface
How does alpha decay occur?
take your original element, subtract 2 from the proton number (z) and subtract 4 from the mass number (n) to get your new element, and stick a Helium nucleus on the other side of the equation.
How does beta decay occur?
element X decays into element Y. Element Y has the same mass number, but its proton number has increased by 1. A beta particle (with a charge of -1 and a mass of 0) is emitted.
How does gamma decay occur?
A nucleus just changes from a high energy state to a lower energy state, releasing a gamma photon in the process. The mass number and atomic numbers don’t change.
