11. Radioactivity

fission with excitement!

radioactivity

the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation

Henri Becquerel (1896)

put uranium salts on a photographic plate wrapped in black paper, called the process radioactivity, described uranium as radioactive

Marie & Pierre Curie (1898)

extracted and discovered polonium and radium from an ore of uranium called pitchblend

types of radiation

alpha particles, beta particles, gamma radiation

what are alpha particles?

2 protons and 2 neutrons, same as helium nucleus

alpha particles occur when…

'pieces' of the nucleus are thrown out of the unstable nucleus as it changes to a more stable nucleus

alpha particles - speed at which they travel

relatively slowly

alpha particles - charge

positive

alpha particles - effect on electric field

attracted to negatively charged plate

alpha particles - penetrating power

stopped by paper/few cm of air

what are beta particles?

high energy electrons

beta particles occur when…

formed when a neutron in an unstable nucleus is changed into a proton and an electron

beta particles - speed at which they travel

fast moving

beta particles - charge

negative

beta particles - effect on electric field

attracted to positively charged plate

beta particles - penetrating power

stopped by 5mm aluminium sheet

what is gamma radiation?

high energy waves

gamma radiation occurs when…

an unstable nucleus emits gamma radiation to lose surplus energy

gamma radiation - speed at which they travel

travel at the speed of light

gamma radiation - charge

neutral

gamma radiation - effect on electric field

no effect

gamma radiation - penetrating power

several cm of lead

how can radiation be detected?

geiger-muller tube/geiger counter

example of alpha particle emitter

americium-241

example of beta particle emitter

carbon-14

example of gamma ray emitter

cobalt-60

in chemical equations…

same elements in reactants and products

in nuclear equations…

elements themselves change

nuclear reaction

a process that alters the composition, structure, or energy of an atomic nucleus

chemical reaction vs nuclear reaction difference 1

involves electrons rather than nucleus - nuclei stay the same vs changes take place in the nucleus - electrons not involved

chemical reaction vs nuclear reaction difference 2

no new element is formed vs new element is formed

chemical reaction vs nuclear reaction difference 3

no release of nuclear radiation vs nuclear radiation is released

chemical reaction vs nuclear reaction difference 4

chemical bonds broken and formed vs no chemical bond breaking or bond formation involved

alpha particle decay nuclear reaction

mass number decreases by 4, atomic number decreases by 2, new element formed + helium nucleus

beta particle decay nuclear reaction

mass number stays the same, atomic number increases by 1, new element formed + electron

the loss of gamma radiation does not create new atoms/elements…

energy is simply lost from the nucleus

radioisotope

a radioactive isotope

commonly used radioactive substances

americium-241 used in smoke detectors, carbon-14 used in carbon dating, cobalt-60 used in cancer treatments

why is there a degree of natural/background radiation?

radioactive gas radon in earth's crust, testing of nuclear weapons, accidents at nuclear power plants

half-life of an element

the time taken for half of the nuclei in a sample to decay

what is the purpose of knowing the half-life of an element?

it allows us to compare radioactive substances and their rates of decay