Atomic physics Flashcards
Atomic structure
- Atoms are made of electrons, protons and neutrons
- Protons and neutrons are in nucleus and electrons orbit the nucleus in shells
- Equal number of protons and electrons
Mass number
Number of protons + neutrons
Atomic number
Number of protons and electrons
Number of neutrons
Mass number - atomic number
Nuclear radiation
- Too many or too few neutrons will make nucleus unstable. These unstable isotopes are radioisotopes
- Unstable nuclear eventually decays giving out ionising radiation to achieve stability
- Ionising radiator = uncharged atoms lose electrons, turning them into ions
Three types of radiation
Alpha, Beta and Gamma
range and penetration
Can be investigated with different materials with different thicknesses and density. Penetrating effect shows how well it is able to pass through different materials . Range describes how far they can travel.
Radiation frequently with atoms along its path losing its energy more quickly
Charge, mass and energy
These properties can be investigated by the effect that a magnetic field has on each type of radiation
Gamma has no charge 0
Alpha has a positive charge +2
Beta has a negative charge -1
Alpha has more mass than beta and alpha and beta move faster with more energy
Alpha mass is 4, Beta mass is 1/1800 and gamma is 0
Alpha stopped by mm of paper, Beta stopped by mm of aluminium, Gamma is stopped by cm of lead
Radioactive decay
Process undergone by radioisotope to make the arrangement of its nucleus more stable (random process, no prediction)
Uses of nuclear radiation
- Medical tracers (Gamma)
- Radioactive isotopes used to help doctors identify diseased organs, chemical compound that emits gamma radiation
- Either swallowed or injected. Its passage around the body can be traced using gamma ray cameras
- Different compounds chosen for different diagnostic tasks e.g. isotope iodine-123 is absorbed by the thyroid gland in the same way as the stable form of iodine
- Isotope decays and emits gamma radiation, camera can be used to form a clear image of the thyroid gland. The half life of iodine is 13 hours
- A short half life is important as it means the activity of the tracers decreases to a very low level in a few days
Non medical tracers
- Gamma rays can be used to track flow of liquids in industrial process. Complete piping systems like heat exchanged in power stations
- tracers with short half lives are used so radiation levels return to background levels quickly after trace is finished
- Alpha and beta emitters would not be suitable as they wouldn’t penetrate the ground and be detected by the detector
Radioactive carbon dating
- Fixed proportion of the carbon found in atmospheric CO2 is radioactive carbon-14
- All living things contain carbon-14 as plants absorb it during photosynthesis. Whilst the organism is active, carbon-14 is decaying but being replaced either by eating or photosynthesis
- When organism dies, amount of carbon-14 decreases as it decays to nitrogen
- Half life is 5600 years
Thickness quality control
- In paper mills, thickness of paper can be controlled by measuring how much radiation passes through paper to the Geigher counter
- Counter controls pressure of the rollers to give correct thickness
- Beta emitter used as alpha particles would not penetrate paper and gamma rays would pass through unaffected
- Source requires a long half life so lots of paper can be monitored
irradiation
- Ionising radiation used to kill micro-organisms on surgical instruments and other medical equipment to sterilise them
- Some food products are treated in a similar way to make sure they are free from any bacteria that will cause food poisoning
Radiotherapy
- Cobalt-60 is a radioisotope often used in radiotherapy to treat cancerous tumours
- A beam of gamma radiation emitted by the sample of cobalt-60 is focused precisely on the tumour thereby minimising damage to the healthy cells that surround it
- Cobalt 60 has relatively long-half life (compared to other medical users) of about 5 years so can be used for multiple therapy sessions
