4: Atomic Structure Flashcards
why are some nuclei unstable?
they are large in size; the protons and neutrons within them are out of balance
how do nuclei become more stable?
they will decay - give off radiation
what is the definition of activity?
the rate at which a source of unstable nuclei decays (Bq)
what is the definition of count-rate?
the number of decays recorded each second by a
detector (eg Geiger-Muller tube) (Bq)
is activity or count-rate always higher and why?
activity - not all decays will be recorded
what is electron emission?
when electrons emit energy as photons, causing it to lose energy and drop down an energy level (closer to the nucleus)
what is electron absorption?
when electrons gains/absorbs energy, causing it to go up an energy level (further away from the nucleus
what are alpha particles?
helium nucleus - 2 protons and 2 neutrons
what are beta particles?
high energy electrons emitted from the nucleus when a neutron turns into an electron and a proton
what are gamma rays?
high energy electromagnetic waves - always emitted alongside alpha and beta particles
put the three radiations in order of penetrative ability (least to most)
alpha, beta, gamma
what are the three radiations stopped by?
alpha - paper; beta - few mm of aluminium; gamma - several inches of lead
put the three radiations in order of their range of air (shortest to longest)
alpha - around 5cm; beta - around 50cm; gamma rays - infinite as it is not absorbed by air, though it does get less intense w distance
put the three radiations in order of ionising ability (most to least)
alpha, beta, gamma
what is the half-life?
the time taken for the activity of the number of original nuclei to drop to half of its initial value
how can we work out half-lives from initial and final activity, and time?
figure out how many times you have to halve the initial activity to get to the final activity -the number of half-lives that have passed; divide the time by the number of half-lives to figure out the value of one half life
what is irradiation?
exposing a material to alpha, beta or gamma radiation - the material will not become radioactive
what is contamination?
when radioactive material get on a material
which is more harmful - irradiation or contamination?
contamination - can cause far more harm, due to the continuous exposure to radiation that it will produce
what precautions should be taken to prevent contamination and irradiation?
areas where radioactive sources are used should be routinely checked for contamination and sources themselves should be checked for any signs of leakage
what precautions should be taken to keep workers who work around radioactive sources safe?
Workers - routinely monitored to check the levels of radiation that they are exposed to, strict limits are placed on what they can receive/ the amount of time they can spend using radioactive materials; barriers can be placed between the worker and the source in order to absorb the radiation
why is it important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review?
often takes time for the harmful effects of radiation to emerge; they were not understood well; so it is vital that scientists share their findings with other scientists around the world to increase understanding
what are sources of background radiation?
rocks - minerals that give off radon gas; cosmic rays from space; fallout from nuclear weapons testing and nuclear accidents; hospitals
levels of background radiation can vary significantly from place to place
what are the dangers of a short half life?
the nuclei will decay very quickly; will emit a lot of radiation in a short amount of time; the levels of radiation emitted could make handling the source extremely dangerous
what are the advantages of a short half life?
if only a small amount of the isotope is used, short half-life can be advantageous, as the material will quickly lose its radioactivity
