p6.2

Question 1

what is the difference between small and large nuclei when they are unstable?

Answer 1

small nuclei = radioactive decy (emit alpha, beta, gamma radiation)

large nuclei = nuclear fission
(break apart into two nuclei)

Question 2

define nuclear fission

Answer 2

the splitting of a large parent nucleus into two smaller daughter nuclei, with the release of energy and neutrons

Question 3

what causes most nuclear atoms to undergo fission

Answer 3

usually hit with a neutron + the unstable nucleus absorbs a neutron

Question 4

why does radioactive decay not occur with large unstable nuclei?

Answer 4

as it would not make the nucleus stable

Question 5

what does the term fissile mean?

Answer 5

when an atom can be made to undergo fission

Question 6

how do nuclear power stations prevent a nuclear meltdown?

Answer 6

have control rods which absorb surplus neutrons so energy is generated at a steady rate
(so only one neutron from each fission event can produce another fission event)

Question 7

what is a nuclear chain reaction?

Answer 7

process in which neutrons released during a fission event go on to produce further fission events

Question 8

what happens during an uncontrolled chain reaction? (and give an example when that happens)

Answer 8

• every neutron from each fission event goes on to produce further fission events
• energy released at exponential rate
• nuclear bomb

Question 9

what are fissionable isotopes of an element?

Answer 9

isotopes which can be made unstable, but they themselves are stable

Question 10

if you add neutrons to any heavy nuclei, will it become unstable?

Answer 10

no, they must be fissionable isotopes (so can be made unstable)

Question 11

give one example of a fissionable material

Answer 11

uranium-235

Question 12

why must there be a material that absorbs neutrons in a nuclear reactor?

Answer 12

• no material to absorb neutrons = an uncontrollable reaction occurs
• energy released at exponential, increasing rate
• very dangerous, lead to an explosion

Question 13

define what nuclear fusion is

Answer 13

the joining of two small parent nuclei into a larger daughter nucleus, with the release of energy

Question 14

where does nuclear fusion occur?

and how

Answer 14

in stars

- 2 light nuclei (ie. hydrogen) forced together at high speeds + form heavier nuclei (ie. helium)

Question 15

advantages of nuclear fusion? 4

Answer 15

• no radioactive waste produced (forms stable nuclei)
• fuel needed is available in water (ie. hydrogen - from electrolysis)
• fusion produces a lot more energy than fission
• no greenhouse gases produced

Question 16

disadvantages of nuclear fusion?

Answer 16

• building reactors is very difficult/not viable

Question 17

why is nuclear fusion currently not viable?

Answer 17

more heat energy is required to make nuclei overcome repulsive forces + fuse than is released from fusion

Question 18

why are stars able to carry out fusion easily?

Answer 18

have very high temperatures + very high pressures

high pressure due to strong gravitational pull

Question 19

why is nuclear fusion so hard?

Answer 19

all nuclei have the same positive charge, and so they repel each other (very hard for them to join)

Question 20

why are high temperatures and pressures needed for nuclear fusion?

Answer 20

temp = nuclei moving at high speeds

pressure = keeps nuclei close enough to fuse

Question 21

where does the energy come from in nuclear fusion?

Answer 21

• when two smaller nuclei fuse, the mass of the larger one is slightly smaller than the total mass of the smaller nuclei
• so the ‘missing mass’ is transformed into energy (by the equation e = mc^2)
• and released as radiation

Question 22

how does nuclear fusion release so much energy?

Answer 22

as the speed of light is very large, and when substituted into the equation e=mc^2, it can produce a huge amount of energy

Question 23

similarities of nuclear fusion and fission

Answer 23

• both produce more energy than fossil fuels

- both involve the use of nuclei

Question 24

differences of nuclear fusion and fission

Answer 24

FUSION

• two small nuclei to a larger one
• more energy released than in fission
• no dangerous waste is produced
• needs high pressure + temp

FISSION

• large unstable nuclei break apart
• only needs a neutron to start reaction
• produces dangerous radioactive waste as by-product

Question 25

what is the difference between contamination and irradiation?

Answer 25

contamination - radioactive material is injested/taken in

irradiation - when you are exposed to radiation from an external source

Question 26

how do doctors use radiation?

Answer 26

inject patients with radioactive isotopes (to see if objects functioning correctly)

• radiation is detected by a gamma camera

Question 27

is contamination or irrigation more dangerous?

Answer 27

contamination, as it lasts for a longer period of time (more ionising radiation)

Question 28

why are radioactive materials dangerous to the body, but low radiation is not?

Answer 28

as the body can repair itself from small doses of radiation

ie. everyday due to background radiation

Question 29

what kind of half life must a tracer have in medicine?

Answer 29

not too short = decay before using gamma camera

not too long = tracer emits radiation for a long time + harms body cells greatly

Question 30

what can a gamma knife be used for?

Answer 30

gamma radiation onto a cancer tumour only (healthy cells = low dose)

Question 31

why do doctors use gamma radiation instead of alpha or beta radiation?

Answer 31

as it has the least ionising power (from within the body), and would pass straight through the atom, and pose the least harm to the patient

Question 32

why is alpha radiation the most dangerous if contaminated with it?

Answer 32

as it is strongly ionising, and so would damage body cells greatly

Question 33

what forms of radiation are the most dangerous if from an external source?

Answer 33

gamma and beta, as they have a longer range and can penetrate the skin and damage cells

Question 34

hazards of contamination?

Answer 34

cannot remove radioactive material from inside you

Question 35

does using radioactive cosmetics contaminate or irridate you?

Answer 35

contaminate as it is on your skin, and is absorbed (later is inside your body)

Question 36

how do the hazards assocaited with radioactive material differ according to the half-life involved?

Answer 36

• longer half life
• means it releases radiation for longer
• so can ionise cells repeatedly + damage them