Topic 4: Atomic physics

Radiation/ radioactive decay

Given out by unstable atomic nuclei to become stable

Alpha decay

• highly ionising

• Weakly penetrating

• Can be stopped by ~5cm of air

Beta decay

• medium ionising

• Medium penetrating

• Stopped by ~50cm of air or a piece of paper

Gamma ray

• low ionising

• Highly penetrating

• Stopped by very far in the air or a few cm of lead

Equation for alpha decay

4/2He

Equation for beta decay

0/-1e

Equation for gamma decay

doesn’t change the mass or charge

Half life

Time taken for half the nuclei in a Sample to decay

Short half life

• prevents less of a long term risk and doesn’t remain strongly radioactive

Long half life

• Remains weakly radioactive for a long period of time

Calculating net decline of radioactive nuclei

Initial number- number after x lives/ initial number

Contamination

• long period of time

• Source of radiation is transferred to an object

• Unwanted presence of radioactive atoms on other materials (hazard decaying of contaminated atoms releases radiation)

Irradiation

• Short time period

• Source emits radiation which reached object

Background radiation

Weak radiation that can be detected from natural/ external sources

examples of background radiation

• cosmic rays

• Radiation from underground rocks

• Nuclear fallout

• Medical rays

Tracers in medicine

• technetium has half life of 6hrs

• decays into safe isotope to be excreted

• Injected or swallowed and has enough time to flow through the body and be detected without damaging the body due to radiation

• Gamma emitter, passes through body tissue without being absorbed

Chemotherapy (uses of decay)

• emitting gamma rays, directed onto certain area of the body with cancerous cells, absorbs the energy and dies to control the disease

• Hard to direct accurately and surrounding healthy cells to be irradiated too

Nuclear fission

Splitting of a large and unstable nucleus , releases energy

• chain reaction when it collided with another radioactive nucleus and that nucleus splits

Nuclear fusion

When two small nuclei fuse to form a heavier nucleus, releases a lot of energy

• more efficient at releasing energy than fission