P7- Radioactivity

Alpha (a) + charge                              

• like helium = 2 protons, 2 neutrons
• alpha radiation emitted from nucleus
• absorbed by paper, travel few cm in air
• stongly ionising (due to size)
• large particles, lots of collisions
• used in smoke detectors

Beta (B) -- charge

• fast moving electron from nucleus
• no mass
• absorbed by aluminium, few m in aair
• every beta particle emitted, neutron turns to a proton
• used to test thickness of wood

Gamma (Y)

• waves of electromagnetic radiation released by nucleus
• short wave length
• absorbed by lead, few m concrete, unlimited in air
• weakly ionising, mostly passes through atoms

Radioactive substance always contains an unstable nuclei, it is an atom that naturally decays and can give off alpha, beta particles or gamma radiation.

Plum pudding model (PPM) --> Nucleur model because gold foil and alpha particles experiment

PPM rejected because some alpha particles were deflected back, realise most mass in centre, so nucleus have a positive charge , since (+) alpha repelled, and rest went through empty space.

Chadwick proved neutron, which explained inbalance between atomic mass and number.

Nucleur model accepted because of alpha particle scatter experiment.

isotope- atoms that naturally (of an element) with a different number of neutrons.

unstable isotopes decay into other elements and give out radiation to become more stable (radioactive decay)

nucleus loses 2 protons and 2 neutrons in alpha

nucleus gains 1 proton (changed from neutron) loses a neutron and 1 high speed electron. in beta

DANGER

• alpha - not unless digested/inhaled
• beta - penetrate skin, energetic enough to be ionising
• gamma - mess up cells DNA, cause mutations and cancer

Count rate = number of counts per second detecteed by a geiger counter

radioactive isotope decays = count rate decreases ( count rate decreases as activity decreases)

%= final activity / initial

When graph starts to go flat, it's because it is nearly completely decayed, its any background radiation.

Half-life = average time it takes for original nuclei to decay to half it's original level

Medical tracers: Small radiation in body, detector around body, to detect (B&Y) passing through, can't stay active in body for long - short half life chosen

Medical treatments:

• gamma rays focus on tumour, try not to damage other cells
• Electromagnetic waves inactivate viruses, kill bacteria - used to sterilise equiptment

nucleur fission = splitting of a large unstable nucleus

• releases energy
• makes smaller, lighter atoms that are the same size and with some kinetic energy
• rarely happens unforced
• 2-3 neutrons releases, but are slow, so can be absorbed into another nucleus (chain reaction)
• energy carried away by gamma rays
• can be used to heat water, turn turbines or generators

Nucleur fusion = join small nuclei

• two light nuclei collide at high speed, fuse, make larger heavier nucleus
• hydrogen can make helium
• some mass turns to energy - which is released as radiation
• Very high temperature and pressure

• control rods - lowered into core, absorb neutrons to control chain reactions and energy released
• fuel rods - contain nucleur fuel
• moderator - reduces speed of fast neutrons
• coolant - maintain pressure and remove heat