ATOMIC STRUCTURE

The structure of an atom

  • Neutrons have a mass number of 1, and no charge

  • Protons have a mass number of 1, and +1 charge - they determine the element

  • Electrons have a -1 charge, and a very very very very small mass

  • The mass number of an element is the total number of neutrons and protons

  • The atomic number is the total number of protons ( and therefore electrons)

  • Isotopes have the same number of protons and a different number of neutrons, so a different mass number

    • Only about half of an elements isotopes are stable - unstable isotopes decay into other elements by emitting radiation (radioactive decay)

  • Electrons are arranged in shells and can jump up energy levels if they have enough energy - get ‘excited’

    • The energy needed comes from electromagnetic radiation

    • Soon after, electron will fall back to the previous shell and emit energy as electromagnetic radiation

  • Ionisation is when an electron leaves the outer shell of an atom and becomes a + ion

  • Ionising radiation is radiation that is able to knock electrons of the outer shells of atoms

Nuclear radiation

  • Only a few of an element’s isotopes are stable

    • unstable isotopes undergo radioactive decay, where they emit something (neutron, proton, waves or electrons)

  • Alpha radiation \alpha

    • 2 protons and 2 neutrons are emitted (He nucleus)

    • 2+ overall charge

    • Relatively large, so it can’t penetrate very far into other materials

    • Can only travel a few cm in air and is absorbed by a single sheet of paper

    • Is strongly ionising (can easily knock off electrons)

  • Beta particles \beta

    • Electrons are emitted

    • Charge of -1 and very little mass

    • They aren’t electrons emitted from shells, but instead a neutron splits into a proton and an electron, which is emitted at high speed

    • It is moderately ionising

    • Penetrates moderately far - several metres in air and is absorbed by a few mm of aluminium

  • Gamma rays \gamma

    • Waves of electromagnetic radiation

    • Is often emitted after alpha or beta radiation

    • There is no mass or charge

    • Is weakly ionising

    • Penetrates really far in air - a few km and is only absorbed by thick lead

  • Emission of a neutron

    • If an isotope has too many neutrons, it can emit one to become more stable

Half lives and radioactive decay

  • Unstable isotopes can emit radiation to become stable - radioactive materials

  • This decay process is random, so you can’t tell when an isotope is going to decay

  • Activity is the overall rate of decay of all isotopes in a sample

  • A becquerel is 1 decay per second

  • Half-life is the time taken for the number of nuclei in a radioactive sample to halve or the time taken for the number of decays to half, which are both correlated

  • For example, if the activity was 600, then 300 and then 150 every 2 hr (halving), the half life would be 2 hours

  • Activity can be recorded by a Geiger-muller tube and counter, which records all the decays that reach it per second (includes background radiation - very small) - known as the count rate

Radioactive contamination

  • Irradiation is the process by which objects are exposed to radiation, but doesn’t continue to ionise when you leave the area

    • It can be ionising or not (like ultraviolet)

    • Any radiation reaching you is irradiating you

  • Contamination is when radioactive particles are on or in other objects

    • If you are contaminated, the radioactive isotope is more likely to decay and therefore irradiates you

  • Ionising radiation is the most dangerous as it can enter other cells and interact with the molecules inside - can ionise DNA and causes mutations, developing cancer

  • Alpha is the most harmful in/on the body and then Bata, then Gamma

  • Out of the body, Beta and Gamma are the most dangerous as they can penetrate skin easily

  • Dosage depends on how far you are from the source, how long the exposure is and how radioactive it is

  • Precautions include wearing protective, lead lined clothing, storing in a lead lined box and using tongs to handle it.

  • ONLY CONTAMINATION IS HARMFUL TO OTHERS

Uses of radiation

  • Medical

    • Sterilisation of surgical instruments

    • Gamma rays to kill cancerous tumours - They are aimed at the tumours, so it gets the highest dose and attacks the cells

    • Beta radiation can be put directly in the body next to the cancer/ in it, and is more damaging, but it can’t travel as far

    • Potential side effects could be that healthy cells are killed or damaged

  • Domestic and industrial

    • Smoke alarms use Alpha radiation, and is absorbed by smoke when present, which breaks circuit and sets it off

    • Thickness monitoring with Beta radiation

Nuclear fission

  • Nuclear fission is the splitting of a large, unstable nuclei into smaller nuclei while releasing energy

  • It can be spontaneous and split by itself, unforced - rare

  • Or it can happen by absorbing a neutron

    • This splits a nucleus

    • It is used in nuclear reactors

  • Usually uranium 235 is used as it is a large, unstable nucleus

  • A neutron is fired at it, causing the nucleus to split into two smaller nuclei, and also releases a few more neutrons and lots of energy

  • When this happens, the neutrons released fire at more uranium 235 and cause a continuous chain reaction (what happens in a nuclear reactor and a nuclear bomb - when uncontrolled)

  • In nuclear reactors, the rate of fission has to be carefully controlled

    • Done by control rods which are lowered into the reactor to absorb neutrons and stop the chain reaction

    • The energy released can be used to heat up water, to create steam and drives turbines to power generators and create electricity

    • PROS - Uranium or Plutonium fuel is relatively cheap

      • It creates a large and steady amount of energy

      • It is clean energy

    • CONS - Nuclear power plants are expensive to build

      • Nuclear waste is expensive to remove

      • Risks of major disaster

Nuclear fusion

  • Nuclear fusion is two nuclei fusing together to create a larger one, and releases energy

  • For example, 11 H + 12 H \rightarrow 32 H , and loads of energy is released (and a neutron)

  • This is the process used to fuel stars

  • Some of the mass from original nuclei is converted into energy

  • PROS - Produces no radioactive waste

    • Can easily make hydrogen for fuel

  • CONS - It can only happen at really high temperatures and pressure (10000000 degrees c), so we can’t currently do it on earth

Nuclear Equations for Fission & Fusion - GCSE Physics Notes

Background radiation

  • Everyone experiences and is exposed to a low level of radiation everyday

    • From natural and man-made sources

  • It can be from - buildings, radon gas from the ground (50%), food and drink and artificial sources (12% - 90% of which are medical, and nuclear and weapon testing makes up less than 5%)

  • The level you experience can depend on where you live, your job, etc.

    • This most be taken into account in experiments 

  • Generally irradiation, but some contamination in foods 🍌

  • A becquerel (Bq) is 1 activity per second

  • A sievert (Sv) is the unit to measure radiation dosage

    • The amount of damage that would be caused by absorption of 1J in each kg of body mass

    • For example, eating a banana is 0.000098 mSv and a fatal dose is 10000mSv

Nuclear equations

  • Alpha is a helium nucleus (2 protons and 2 neutrons)

    • Mass number changes by -4, and atomic number changes by -2

  • Beta is the loss of an electron from a neutron

    • +1 to the atomic number (no mass change as so small)

  • Gamma has no change as it is pure energy

DONE!!!