GCSE Physics - P4 Atomic Structure

atoms and EM Radiation

when electrons change orbit (move closer or further from nucleus)

when electrons move to a higher orbit (further from the nucleus) the atoms has absorbed EM radiation

when the electrons falls to a lower orbit (closer to th nucleus) the atoms has emitted EM radiation

if an electron gains enough energy it can leave the atom to form a positie ion

radius of an atom

1 × 10^-10

relative mass of:

proton

neutron

electron

1

1

very small

relative charge of:

proton

neutron

electron

+1

0
-1

electron arrangement

electrons lie at different distances from the nucleus at different energy levels.

radiation

some atomic nuclei are unstable, the nucleus gives out radiation as it changed to become more stable. this is a random process called radioactive decay

forms of decay

alpha (helium nucleus)

gamma (radiation)

neutrons

beta minus (electron)

alpha decay

• highly ionising

• weakly penetrating

  (5cm of air)

beta decay

• medium ionising

• medium penetration

  50cm of air, sheet of paper

gamma decay

• low ionising

• highly penetration

  very far in air, few cm of lead

nuclear equations

alpha ⁴₂He

beta 0 -1 e

half life

• the time taken for half the nucleu in a sample to decay. this process is random

shot half life

• source presents less of a risk as it does not remain strongly radioactive

• so initially it is very radioactive but quickly dies down s presents less of a long term risk

long half life

• source remains weakly radioactive for a long period of time

alpha particles in smoke alarms

• contains americium and it doe not reach far because alpha is weaky penetrating

• if smoke reaches alarm, the amount of alpha particle in the air drops

• causing alarm to sound

• it is suitable because it will not need to be replenished and its weak activity eans it won’t be harmful to anyone

net decline

calc the ratio of net decline of radioactive nucleu after x half lives

half the intial number of nucleii and keep doing so ‘x’ number o times

net decline = initial number - number of x half lives/ initial number

contamination

• lasts for long periods of time

• source of radiation is transferred to an object

• the unwanted presence of radioactive atoms on other materials - the hazard is the decaying of the contamination atoms releasing radiation

irradiation

• lasts only for short period of time

• the source emits radiation which reaches the object

• exposing an object to nuclear radiation but does not make it radioactive

• medical items are irradiated to kill bacteria on the surface

background radiation

weak radiation that can be detectd from natural/external sources

the level of background radiation and radiation dose may be affected by occupation and or location

measurement for radiation dose is siverts (Sv)

examples of background radiation

• cosmic rays

• underground rocks

• medical rays

tracers

• technitium is a medical tracer

• half life of 6hrs

• decays into a safe isotope that can be exreted by the body

• injected or swallowed and there is enough time for it to flow through the body and be detected before it decays away but is only present for a short time to minimise any harm from radiation

• gamma emmiter so it can pass through the body tissue without being absorbed

chemotherapy

gamma emitters are used to emit gamma rays which are directed onto certan areas of the body with cancerous cells which absorb the energy and die controlling the disease

used to cotrol unwanted tissue

as it is hard to direct accurately, surround health cells may also be irraded and their destruction causes unhealthy side effects