e.g. carbon-12: 6 protons, 6 neutrons, 12C
m = atomic mass unit = 1/12 mass of C-12
"A chemical element is a substance that cannot be broken down into anything simpler"
"An atom is the smallest identifiable part of a chemical element"
1. Scintillation screen
Emits a pulse of light when ionising radiation falls on it- electronic from called scintillation counter is very accurate
2. Cloud chamber
Ionisation leaves a trail of droplets in supersaturated ethanol vapour
3. Ionisation chamber
Ionised air molecules form a current between the outer casing and the central electrode (needs amplifying)
4. Geiger-Müller tube
As above but contains a gas in which the avalanche effect occurs
5. Bubble chamber
Superheated liquid boils to form bubbles along the path of high-energy subatomic particles
The activity of a source is the rate of disintegration of it with time. One disintegration per second is one Bequerel (Bq). The energy absorbed is the dose in grays (Gy). The dose equivalent in sieverts (Sv) represents the potential damage to living tissues by radiation.
Background radiation must always be taken into account for experiments into radioactivity.
dN = -lN where l is the decay constant
The solution is:
N = N0e-lT
If t = t½, N = N0/2
N = 1 = e-lt
Since ln(½) = -ln2
t½ = ln2
Nuclear emission carries energy away from an atom, making it more stable. The change from one element to another is called transmutation. A second emission, especially gamma, often follows the first, producing a decay series.
The binding energy of a nucleus is the energy that would be released if the nucleus were brought together from infinity. The binding energy is carried away by a reduction in mass called the mass defect.
D E = D mc2
½mv2max = hf-f
l = h/p where h is Plank's constant and p the momentum of the electron.