Atomic structure Flashcards
What is the radius of an atom and a nucleus in relation to this?
1 * 10^-10.
A nucleus is around 1/10000 of this.
How has the model of the atom developed over time?
- Indivisible.
- Plum pudding model, JJ Thomson, ball of positive charge with negative electrons embedded in it.
- LOOK IT UP
Compare activity, count rate and half lifes.
Activity is the rate of decay (becquerels, count rate is the number of decays per second (measured on a Geiger-Muller tube) and a half life is the length of time it takes for the number of nuclei of an isotope to halve.
Compare alpha, beta, gamma radiation based on penetration, range in air and ionising power.
Alpha: helium nucleus,
Beta: electron from neutron turning into proton,
Gamma: nucleus cools down by emitting energetic electromagnetic wave gamma,
Neutron: absorption of cosmic rays or Chadwick or fission,
Alpha α Skin/paper High < 5 centimetre (cm)
Beta β 3 mm aluminium foil Low ≈ 1 metre (m)
Gamma γ Lead/concrete Very low > 1 kilometre (km)
Can you form nuclear equations for alpha and beta radiation?
With alpha, the atomic number decreases by 2 and the mass number decreases by 4.
With beta, the atomic number is constant as a neutron is turned into a proton and the mass number increases by 1.
Where can background radiation come from?
Natural sources like rocks and cosmic rays from space. Man made sources like nuclear weapons and nuclear accidents.
Explain in full nuclear fission.
It may be spontaneous or caused by a large nuclei absorbing a neutron. This nucleus splits into two smaller, roughly equal in size nuclei, plus gamma rays and two or three neutrons. All the products have KINETIC ENERGY so ENERGY is released. In an uncontrolled setting, neutrons will continue being absorbed and triggering more decay exponentially, not at a 1:1 rate.
Explain in full nuclear fusion.
Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.
What are the uses of irradiation? What are the considerations medically? What are the positives and negatives?
Sterilising fruit and sterilising surgical instruments.
Gamma knife are aimed from many directions converging so the largest dose is delivered to a cancerous tumour while the surrounding healthy tissue is fine, you must consider the nature of decay, half-life and toxicity.
Positives include sterilisation without high temperatures so objects don’t melt. Negatives include not killing all bacteria and exposing people to danger.
What are the uses of contamination? What are the considerations medically? What are the positives and negatives?
Contamination can be used medically as the radioactive sources (isotopes)(technetium-99) are tracked by a gamma camera or x-ray to show what is occurring within the body soft tissues. For example kidneys or the blood vessels to check for blockages, as changes in gamma emitted will indicate. The radioactive materials used for contamination must be not poisonous and have a short half-life to keep the dose low.
The advantages in medical uses are: exposure can be limited by using isotopes with low half-lifes; and screenings can replace invasive procedures. The disadvantages are: radioisotopes may go where they aren’t wanted; they may not be fully removed; and exposure can damage healthy cells.
Contamination can also be used to check for leaks. A gamma emitter is introduced to the system and where the leak is there will be a build up of gamma emissions that can be detected by a Geiger-Muller tube. The isotope used must be gamma for its penetration, it must not be poisonous and it must have a half-life of at least a few days to allow the gamma emissions to build up in the soil.
The advantages are: medical and industrial tracing; exposure can be limited by using isotopes with low half-lifes; and screenings can replace invasive procedures. The disadvantages are: radioisotopes may go where they aren’t wanted; they may not be fully removed; and exposure can damage healthy cells.
What are the effects of radiation on the human body?
Eyes High doses can cause cataracts.
Thyroid Radioactive iodine can build up and cause cancer, particularly during growth.
Lungs Breathing in radioisotopes can damage DNA.
Stomach Radioactive isotopes can sit in the stomach and irradiate for a long time.
Reproductive organs High doses can cause sterility or mutations.
Skin Radiation can burn skin or cause cancer.
Bone marrow Radiation can cause leukaemia and other diseases of the blood.
Radiation causes cell death and mutation.
What precautions can be taken to lower risk ( the likelihood of cell damage )?
keep radioactive sources like technetium-99 shielded (preferably in a lead-lined box) when not in use
wear protective clothing to prevent the body becoming contaminated should radioactive isotopes leak out
avoid contact with bare skin and do not attempt to taste the sources
wear face masks to avoid breathing in materials
limit exposure time - so less time is spent around radioactive materials
handle radioactive materials with
tongs
in order to keep a safer distance from sources
monitor exposure using detector badges, etc
