4- Atomic Structure & Radioactivity

Question 1

Define Radioactive decay

Answer 1

when nuclear radiation is emitted by an unstable nucleus so that it can become more stable -random process -can knock electrons out of an atom in a process called ionisation

Question 2

Properties of an alpha particle

Answer 2

2 protons+2 neutrons
highest ionising power
travel a few cm in air
stopped by 1 sheet of paper

Question 3

Properties of a beta particle

Answer 3

fast moving electron
high ionising power
travels ~ 1cm in air
stopped by few mm of aluminium

Question 4

Properties of a gamma ray

Answer 4

-short wave-length, high frequency EM radiation
-low ionising power
-(almost) unlimited range in air
-stopped by lots of cm of lead/ metres of concrete

Question 5

what is the activity of a radioactive source equal to

Answer 5

the rate of decay of an unstable nucleus

Question 6

what is activity of radioactive source measured in

Answer 6

becquerel / Bq

Question 7

what does 1 Bq mean

Answer 7

1 decay per second

Question 8

What do detectors record

Answer 8

a count rate eg geiger counter

Question 9

define half-life

Answer 9

-time for half of number of unstable nuclei to decay
-time for count rate/activity of a source to half

Question 10

count rate after n half lives=

Answer 10

initial count rate / 2^n

Question 11

net decline=

Answer 11

reduction in activity / original activity

Question 12

to find the reduction in activity after a given number of half lives:

Answer 12

1- calculate activity after each half life
2- subtract final activity from original activity

Question 13

define irradiation

Answer 13

when an object is exposed to nuclear radiation

Question 14

define contamination

Answer 14

when atoms of a radioactive material are in/on an object

Question 15

how do irradiation and contamination both cause harm

Answer 15

through ionisation

Question 16

how to prevent irradiation

Answer 16

shield/remove/move away source of radiation

Question 17

how long does an object stay contaminated for

Answer 17

-object remains exposed to radiation as long as it is contaminated
-can be very difficult to remove

Question 18

protection against irradiation and contamination (give 3)

Answer 18

1-maintain distance from radiation source
2-limit time near source
3-shield from the radiation

Question 19

what should happen to studies on effects of radiation (and why)

Answer 19

should be published, shared with other scientists and checked by peer review (because they are important for human health)

Question 20

what does ionising radiation do to living cells

Answer 20

can damage them

Question 21

what does the risk of ionising radiation depend on

Answer 21

-half-life of the source
-type of radiation

Question 22

is alpha radiation dangerous inside or outside body

Answer 22

dangerous inside body because it affects all surrounding tissue
only affects skin/eyes outside body because it cannot penetrate further

Question 23

is beta/gamma radiation dangerous inside or outside body

Answer 23

dangerous inside or outside body because they can penetrate into tissues

Question 24

what is radiation dose measured in

Answer 24

sieverts (Sv)

Question 25

radiation dose

Answer 25

-measures health risk of exposure to radiation -depends on type/amount of radiation

Question 26

background radiation

Answer 26

radiation that is around us all the time always present but levels are sometimes higher in some locations /jobs

Question 27

where does background radiation come from

Answer 27

1.natural sources (eg rocks & cosmic rays) 2.nuclear weapons & nuclear accidents

Question 28

radiation in medicine (give 2 examples)

Answer 28

1. exploration of internal organs 2.control/destruction of unwanted tissue

Question 29

exploration of internal organs is where..

Answer 29

gamma-emitting tracers injected / swallowed by patient, gamma cameras can then create an image showing where tracer has gone.

Question 30

when exploring internal organs using gamma radiation, how long should the half life of tracer be

Answer 30

short enough so most of nuclei will decay shortly after image is taken (limits patients radiation dose)-normally 6 hrs

Question 31

control/destruction of unwanted tissue is where…

Answer 31

narrow beams of gamma radiation can be focused on tumour cells (to destroy) (gamma is used because it can pentrate outside of body) OR beta/gamma emitting implants placed surgically inside/next to tumour (half lives must be long enough to be effective but short enough not to irradiate patient after treatment)

Question 32

define nuclear fission

Answer 32

when a large unstable nucleus absorbs an extra neutron and splits into 2 daughter nuclei, releasing gamma radiation, 2-3 neutrons and lots of energy

Question 33

what are nuclear explosions (how are they prevented in power stations)

Answer 33

uncontrolled chain reactions (chain reactions controlled in power stations by absorbing neutrons)

Question 34

what is spontaneous fission

Answer 34

when an unstable nucleus splits without absorbing a neutron

Question 35

define nuclear fusion

Answer 35

when 2 light nuclei join together to form a heavier nuclei, releasing large amounts of energy and gamma radiation

Question 36

define nuclear fusion

Answer 36

when 2 light nuclei join together to form a heavier nuclei, releasing large amounts of energy and gamma radiation