4: Atomic Structure

Question 1

why are some nuclei unstable?

Answer 1

they are large in size; the protons and neutrons within them are out of balance

Question 2

how do nuclei become more stable?

Answer 2

they will decay - give off radiation

Question 3

what is the definition of activity?

Answer 3

the rate at which a source of unstable nuclei decays (Bq)

Question 4

what is the definition of count-rate?

Answer 4

the number of decays recorded each second by a

detector (eg Geiger-Muller tube) (Bq)

Question 5

is activity or count-rate always higher and why?

Answer 5

activity - not all decays will be recorded

Question 6

what is electron emission?

Answer 6

when electrons emit energy as photons, causing it to lose energy and drop down an energy level (closer to the nucleus)

Question 7

what is electron absorption?

Answer 7

when electrons gains/absorbs energy, causing it to go up an energy level (further away from the nucleus

Question 8

what are alpha particles?

Answer 8

helium nucleus - 2 protons and 2 neutrons

Question 9

what are beta particles?

Answer 9

high energy electrons emitted from the nucleus when a neutron turns into an electron and a proton

Question 10

what are gamma rays?

Answer 10

high energy electromagnetic waves - always emitted alongside alpha and beta particles

Question 11

put the three radiations in order of penetrative ability (least to most)

Answer 11

alpha, beta, gamma

Question 12

what are the three radiations stopped by?

Answer 12

alpha - paper; beta - few mm of aluminium; gamma - several inches of lead

Question 13

put the three radiations in order of their range of air (shortest to longest)

Answer 13

alpha - around 5cm; beta - around 50cm; gamma rays - infinite as it is not absorbed by air, though it does get less intense w distance

Question 14

put the three radiations in order of ionising ability (most to least)

Answer 14

alpha, beta, gamma

Question 15

what is the half-life?

Answer 15

the time taken for the activity of the number of original nuclei to drop to half of its initial value

Question 16

how can we work out half-lives from initial and final activity, and time?

Answer 16

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

Question 17

what is irradiation?

Answer 17

exposing a material to alpha, beta or gamma radiation - the material will not become radioactive

Question 18

what is contamination?

Answer 18

when radioactive material get on a material

Question 19

which is more harmful - irradiation or contamination?

Answer 19

contamination - can cause far more harm, due to the continuous exposure to radiation that it will produce

Question 20

what precautions should be taken to prevent contamination and irradiation?

Answer 20

areas where radioactive sources are used should be routinely checked for contamination and sources themselves should be checked for any signs of leakage

Question 21

what precautions should be taken to keep workers who work around radioactive sources safe?

Answer 21

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

Question 22

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?

Answer 22

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

Question 23

what are sources of background radiation?

Answer 23

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

Question 24

what are the dangers of a short half life?

Answer 24

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

Question 25

what are the advantages of a short half life?

Answer 25

if only a small amount of the isotope is used, short half-life can be advantageous, as the material will quickly lose its radioactivity