radioactivity Flashcards
1
Q
what is the mass number also known as?
A
the nucleon number
2
Q
what is the mass number?
A
n. of protons & neutrons
3
Q
what is the atomic number also known as?
A
the proton number
4
Q
what is the atomic number?
A
n. of protons
5
Q
what are isotopes?
A
atoms with the same number of protons but different number of neutrons
6
Q
why is a radioisotope unstable?
A
it has too many neutrons- decays and emits radiation randomly
7
Q
radioisotopes randomly emit alpha or beta particles or gamma radiation to form what?
A
a new atom with a different number of protons
8
Q
where is radiation emitted from?
A
the nucleus of an unstable atom
9
Q
radiation happens…
A
randomly
10
Q
radiation from a nucleus can take what 3 forms?
A
- alpha
- beta
- gamma
11
Q
what is an alpha particle?
A
- a helium nucleus
- 2 protons, 2 neutrons
12
Q
what charge does an alpha particle have?
A
+2 charge
13
Q
are alpha particles fast or slow?
A
quite slow
14
Q
are alpha particles big or small?
A
massive (relatively)
15
Q
what does radium become when it decays?
A
radon
16
Q
what is a beta particle?
A
- a very fast electron emitted from the nucleus
17
Q
what is the charge on a beta particle?
A
-1 charge
18
Q
are beta particles fast or slow?
A
fast
19
Q
do beta particles have a big or small mass?
A
very small mass
20
Q
what is a gamma wave?
A
- an electromagnetic wave- very short wavelength, very high frequency
21
Q
do gamma waves have a charge?
A
no charge
22
Q
are gamma waves slow or fast?
A
extremely fast- speed of light (3 x10 to the power of 8)
22
Q
what is the mass of an alpha particle?
A
4u- heavy (massive)
23
Q
what is the mass of a beta particle?
A
- 1/1850
- very small
24
what is the mass of a gamma wave?
0
25
what is the penetrating power like for alpha particles?
- low
26
why is penetrating power low for alpha particles?
- cannot get through materials easily
- stopped by 5cm of air & by thin aluminium
27
what is the penetrating power like for beta particles?
mid power
28
why do beta particles have medium penetrating power?
stopped by mm of aluminium
29
what is the penetrating power like for gamma waves?
high
30
why is the penetrating power high for gamma waves?
- stopped by thick lead or concrete
- can travel long distances in air
31
what is ionisation?
the process of adding or removing electrons from atoms
32
do alpha and beta have lots of kinetic energy?
yes- they are moving fast
33
what is half life?
the time taken for half the radioactive nuclei to decay
34
why do we measure half life?
- the decaying process is random
- we can't measure the whole life of a radioactive material
- so we have to measure half life
35
how is the beta electron formed?
when a neutron in the nucleus splits into a proton and an electron
36
the beta electron (negative) is always...
0
-1
37
how is a positive ion left behind?
the radiation provides energy to allow outer shell electron to escape the pull of the nucleus- leaving a positive ion behind
37
the beta proton is always...
0
+1
38
what is activity?
number of decays per second in Becquerels (Bq)
38
why is alpha less penetrating than beta & gamma?
- alpha- large mass & a 2+ charge
- large mass: more chance to interact with atoms in material it travels through- more chance of ionisation- transfer of energy
- 2+ charge: attracts negative charge (electrons)- helping ionisation
39
beta has a negligible mass & a 1- charge- what does this mean in terms of ionisation?
- negligible mass: less chance of interaction with atoms-less ionisation
- 1- charge: repel negative electrons- dont help ionisation
40
is gamma a strong or weak ioniser?
very weak ioniser
41
which is the most dangerous inside the body?
alpha- weak penetrator- cannot get out- has strong ionising power- loses all energy inside the body
42
which is the least dangerous inside the body? -
gamma is least dangerous- has weak ionising power
43
which is the most dangerous outside the body?
gamma- strong penetrator
44
what does penetrate mean?
the ability of each radiation to pass through material
45
what does the more material the radiation can pass through mean?
- the greater the penetration power
- the more dangerous they are
46
what 3 factors do we need to consider when choosing which source of radiation we want to use?
- type of radiation needed
- penetrating power
- half life
47
what type of radiation is used for sterilising medical equipment?
gamma
48
what type of half life does gamma radiation have when sterilising medical equipment?
long
49
what type of radiation is used when killing cancer cells?
gamma radiation
50
what type of half life does gamma radiation have when killing cancer cells?
short half life
51
what type of radiation is used when gauging thickness in paper or sheet metal factories?
beta
52
what type of radiation is used for tracers- to find water leaks in underground pipes?
gamma
53
what type of half life is used for gamma radiation for tracers to find water leaks in underground pipes?
short
54
what type of radiation is used for medical tracers in the body?
gamma
55
what type of half life does gamma radiation have for medical tracers in the body?
short half life
56
what type of radiation is used for nuclear fission & fusion?
alpha
57
what type of half life is used for alpha radiation for nuclear fission & fusion?
long
58
what is nuclear fission?
splitting of a heavy unstable nucleus (U235) to release energy
59
what is nuclear fusion?
the joining of 2 light nuclei to release energy
60
what does adding a neutron do to a molecule?
makes it more unstable
61
what happens in terms of energy when nuclear fission happens?
lots of energy is released from the nucleus- from the nuclear store
62
what does nuclear fission involve?
a nucleus splitting into two large fragments
63
what are the products of nuclear fission called?
daughter nuclei
64
what do most isotopes need to split?
most need to be induced to split by absorbing another particle- usually a neutron
65
what are the isotopes most used in nuclear reactors?
uranium 235 and plutonium 239
66
the fission of 235U- fast neutron?
fast neutrons pass through the uranium nucleus, without causing it to split
67
the fission of 235U- slow neutron?
slow neutrons are absorbed by the 235U nucleus, becoming an unstable 236U which then splits into 2 smaller nuclei and 3 fast neutrons
68
why do we need slow neutrons in nuclear fission?
we need slow neutrons so they can be absorbed
69
uncontrolled chain reaction- what happens if the mass of uranium is too large?
- the rate of the fission reaction increases very rapidly
- the temperature rises by thousands of degrees in a fraction of a second and a nuclear explosion results
70
controlled chain reaction- what happens if the mass of uranium is a little lower?
- if the mass is a little lower and a material is used to absorb excess neutrons, then the rate of fission can be controlled
- this means the uranium can be kept hot (few hundred degrees) for years
71
what type of chain reaction do we have in nuclear power stations?
controlled chain reaction
72
what does an uncontrolled chain reaction result in?
a nuclear bomb
73
what is needed to make use of the energy from nuclear fission?
- fuel rods
- control rods
- a moderator
- some means of transferring the heat generated into electricity
- shielding
74
what are the fuel rods enriched with?
U-235
75
what are the control rods made out of?
boron
76
what do the control rods do?
absorb neutrons
77
what does the moderator do?
slows down fast neutrons so they can keep the reaction going
78
what does shielding do?
protects the environment and us from harmful radiation
79
what is the shielding made out of?
thick concrete
80
what does the fuel rods being lowered and raised mean?
- lowered- fuel rods cool down
- raised- fuel rods heat up
81
the energy released goes into what store?
nuclear store- KE- thermal- KE- electricity
82
how does fission happen?
fire a neutron at U235 to split it
83
how does fusion happen?
H&H join to make a heavier nucleus
84
what conditions does fission require?
need to be moderated to a slower speed
85
what conditions do fusion require?
high temperatures and pressure to overcome repulsive forces between 2 positive hydrogens
86
what particles does fission produce?
- 2 daughter nuclei and a small number of radioactive neutrons
87
what particles does fusion produce?
helium nucleus
88
why is energy released in fission?
the kinetic energy of all the fission products
89
why is energy released in fusion?
released energy comes from a loss of mass of the smaller nuclei
90
where does fission happen?
in nuclear reactors used to generate electricity
91
where does fusion happen?
in the stars- it is a star's source of energy
92
fission only happens if the neutron colliding with U235 is....
slow
93
fusion does not happen at...
low temperatures & pressures
94
key sources of background radiation?
- cosmic rays from space
- the ground- particular rocks
- gases- e.g. radon gas
- food- organic food has carbon 14
