topic 4 - atomic physics (flashcards)

isotopes

atoms that have the same number of protons, but different number of neutrons

plum pudding model

• JJ Thompson

• ball of positive charge with electrons embedded in it

• overall, the atom had a neutral charge

alpha scattering

• Rutherford

• fired alpha particles at a thin piece of gold foil

• nucleus is very small and positively charged

• atom is mostly empty space

nuclear model

• Rutherford concluded that the nucleus of the atom is very small and positively charged

• electrons orbit the nucleus

• most of the atom is empty space

background radiation

• there are many naturally-occurring isotopes; some have isotpes which decay over time, releasing radioactive particles or waves into the surroundings

sources of background radiation

natural:

• radon in atmosphere

• food and drink

• cosmic rays

artificial:

• medical usage

• fallout from weapon tests

• nuclear powr discharges

why are people at higher altitudes more likely to receive a higher dosage of background radiation?

more cosmic rays reach them as the atmosphere is less dense/thinner at higher altitudes

alpha radiation

• helium nucleus - 2 protons and 2 neutrons

• penetration - stopped by paper

• highly ionising

beta radiation

• electrons

• penetration - stopped by 2-3mm of aluminium

• medium ionising

gamma radiation

• electromagnetic wave

• penetration - stopped by several centimetres of lead

• low ionising

half-life

the time taken for the number of radioactive nuclei in a sample to halve

• the shorter the half life, the faster the decay

• isotopes with longer half-lives are typically more dangerous as they stay radioactive for longer

• decay is a random event

irradiation

occurs when there is exposure to ionising radiation from the radioactive source

contamination

occurs when the radioactive source itself is spread (e.g. by an explosion)

nuclear fission

the splitting of a large nucleus

a neutron is fired at the large nucleus in order to split it into two smaller nuclei

releases energy and a few stray neutrons

control rods

made from a substance (e.g. cadmium) that will absorb neutrons

nuclear fusion

the joining together of two small, light nuclei

requires huge amounts of energy

reaction forms a helium nucleus, releases a spare neutron and lots of energy

benefits of nuclear fusion as an energy source

(deuterium-tritium)

• fuels are relatively abundant- available

• renewable source of energy

• not a chain reaction - reaction will stop safely is there is a problem

disadvantages of nuclear fusion

• reaction requires very large amounts of energy to start

• temperatures in excess of 10,000,000°C needed