(b) radioactivity

structure of an atom (7.2)

the nucleus contains protons and neutrons and the shell contains electrons. ¹⁴₆C

atomic (proton) number (7.3)

the number of protons in the nucleus of an atom

mass (nucleon) number (7.3)

the number of protons + the number of neutrons in the nucleus of an atom

isotope (7.3)

two isotopes of the same element have the same number of protons but a different number of neutrons

alpha (α) particles (7.4 / 7.5 / 7.7)

alpha radiation is a type of ionising radiation, meaning it is emitted from unstable nuclei in a random process.

• an alpha particle is a helium nucleus

  • two protons, two neutrons (⁴₂He)

  • this means that when emitted, the atomic number goes down by 2 and the mass number goes down by 4

• it has a large mass and a strong positive charge

• alpha radiation is the least penetrative and can be stopped by a sheet of paper, skin or a couple centimetres of air

beta (β^-) particles (7.4 / 7.5 / 7.7)

beta radiation is a type of ionising radiation, meaning it is emitted from unstable nuclei in a random process.

• a beta particle is a fast moving electron

  • this means that there is no change to the atomic or mass numbers when beta radiation is emitted

• it has a very small mass and a negative charge

• beta radiation is more penetrating than alpha radiation, so it can pass through skin, air and paper but is absorbed by a few centimetres of body tissue or a few millimetres of aluminium

gamma (γ) rays (7.4 / 7.5 / 7.7)

gamma radiation is a type of ionising radiation, meaning it is emitted from unstable nuclei in a random process.

• gamma rays are high-energy electromagnetic waves caused by changes in nucleus

  • this means that there is no change to the atomic or mass numbers when gamma radiation is emitted

• part of the electromagnetic spectrum (shortest wavelength) so it travels at the speed of light

• there is no mass and no charge

• gamma rays are very penetrative, easily penetrating body tissue and can only be stopped by a few centimetres of lead or a metre of concrete

investigate the penetration powers of different types of radiation using either radioactive sources or simulations (7.6)

do this with a geiger müller tube

ionising radiation detectors (7.9)

photographic film and geiger-müller detectors

sources of background (ionising) radiation (7.10)

radon gas from the ground, buildings and the ground, cosmic rays, food and drink, artificial sources (medical (x-rays, cancer treatment), nuclear power and weapons testing etc.)

the activity of a radioactive source …? (7.11)

decreases over a period of time and is measured in becquerels

half-life (7.12 / 7.13)

half life is time time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate (number of decays recorded each second by a detector) to halve.

uses of radioactivity in industry and medicine (7.14)

x-rays and cancer treatment

contamination (7.15)

having radioactive atoms on something

irradiation (7.15)

exposure

dangers of ionising radiations (7.16)

mutations, can damage cells + tissue