Unit 10 - Radioactivity

isotope

atoms of the same element with equal numbers of protons while different numbers of neutrons. Chemical properties remain the same but physical properties may differ.

radioactivity decay

spontaneous process by which an unstable atomic nucleus loses energy by emitting radiation. it transforms the original atom into a different atom or different states of the same atom

activity

rate at which a radioactive source decays.

unit of activity

Becquerel (Bq)

1 Bq = 1 delay/s

how to measure radioactivity

using a geiger-muller (GM) tube with a counter to measure the number of counts of radiation reaching it in 1 second

using photographic films

more radiation, darker it becomes

sources of radioactivity

natural and artificial

natural radioactivity

radiation from naturally occuring sources

cosmic rays, radioactive rocks, soil, human body

artificial radioactivity

radiation from human activities

medical imaging, nuclear power, industrial uses

ionization

process by which an atom or molecule gains or loses electrons forming charged particles called ions. this can occur due to exposure to high radiation, collisions or through electric fields

types of radiation

alpha, beta, gamma, neutron

alpha (a) radiation

made of 2 protons and 2 neutrons and releases heavy, positively charged particles

they are highly charged and relatively slow

it has low penetration

highly ionizing

formula thingie for alpha radiation

X → Y + d

mass number subtracts by 4

atomic number subtracts by 2

beta (b) radiation

made of electrons that emits the beta particle.

moderate speed and charge

medium penetration, stopped by a few aluminium layers

moderately ionising

formula thingie for beta radiation

X → Y + B-

atomic number adds by 1

gamma (y) radiation

electromagnetic waves (no mass or charge)

very high penetration

weakly ionising

parent nucleus X releases energy as gamma rays after alpha or beta decay

neutron radiation

made of neutrons

high speed, no electric charge

high penetration can pass through several layers

weakly ionising directly

half-life

time it takes for half the nuclei in a sample to decay

uses of each type of radiation

alpha: smoke detectors

beta: foil thickness monitoring

gamma: cancer treatment

dangers of radioactivity

damage or kill living cells leading to burns, radiation sickness or cancer

alpha: dangerous if ingested or inhaled

beta and gamma': can penetrate the body causing internal damage

nuclear fission

splitting a large unstable nucleus into smaller nuclei releasing energy and neutrons. it happens in nuclear power plants to generate electricity. produces radioactive waste and can start a chain reaction

in nuclear power plants to produce electricity

uranium 235

nuclear fusion

combining two small nuclei to form a large nucleus releasing energy. it happens in the core of stars like the sun. produces more enery than fission. requires extremely high temperature and pressure. no long living radioactive waste.

sun

nuclear power stations

nuclear power stations convert energy from nuclear reactions (fission) into electricity

key components and functions of nuclear power stations

reactor, fuel elements, moderator (water that slows down neutrons to trigger more fission reactions), control rods

energy transformation

nuclear energy, thermal energy in reactor, kinetic energy of steam turnign turbines, electrical energy in generator