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Physics > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

1
Q

history of atom

A

-Democritus proposed all matter was made up of lumps called atomos
-jj thompson created plum pudding model

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2
Q

Rutherford experiment

A

1909, stream of alpha particles from radioactive source hit thin sheet of gold foil
and strike a fluorescent screen surrounding it

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3
Q

rutherford experiment conclusions

A

-atoms must be mostly empty space
-nucleus must have large positive charge
-most of the mass is concerntrated at the nucleus
-nucleus is very tiny

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4
Q

initial Ek equation

A

Qnucleus x q alpha / 4pi εo r

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5
Q

how to estimate radius of nucleus

A

rutherford scattering experiment, some particles are deflected 180
the alpha particle does this when Ep = initial Ke

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6
Q

electron diffraction

A

electrons are leptons that dont interact with the SNF
more accurate for measuring the radius

lambda = hc / E

E = energy of atom

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7
Q

radius of atom

A

0.05nm ( 5 x 10^-11)

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8
Q

radius of smallest nucleus

A

1fm (1 x 10^-15

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9
Q

sin theta

A

1.22 lambda / 2R

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10
Q

nuclear radius equation

A

R = Ro A^1/3

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11
Q

Ro

A

1.4fm (1.4 x 10^-15)

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12
Q

nuclear density equation

A

A m-nucleon/(4/3)pi (Ro A^1/3)^3

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13
Q

alpha radiation

A

strongly positive
can easily pull electrons off atoms

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14
Q

why alpha particles have ashort range

A

ionising atoms requires energy from the alpha partcile
the alpha particle quicly ionises many atoms ( about 10000 ionisations per mm of air for each alpha particle) and loses all their energy very quickly

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15
Q

alpha radiation uses

A

smoke detectors

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16
Q

beta radiation

A

lower mass and charge than alpha particle but higher speed
means it can still knock electrons off atoms
each beta particle will ionise around 100 atoms per mm of air

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17
Q

beta particle uses

A

can be used to measure the thickness of materials, like aluminium wood, etc.

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18
Q

gamma radiation uses

A

used to diagnose patients without the need for surgery
a radioactive source with short half life is eaten or injected and PET scanner is used to detect emitted gamma rays

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19
Q

background radiation

A

weak level of nuclear radiation found everywhere

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20
Q

how to measure background radiation

A

take 3 readings of the count rate using at greiger counter without a radioactive source present and find mean

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21
Q

sources of background radiation

A

-air(alpha radiation gas released from rocks)
-grounds and buildings (rocks)
-cosmic radiation
-living things
-man-made radiation

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22
Q

decay constang

A

constant of proportionality
the probability of a specific nucleus decaying per unit time and is a measure of how quickly an isotope will decay

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23
Q

activity equationS (3)

A

A = lambda x N
A = -N / t
A = Ao e^-lambda t

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24
Q

equation for N (2)

A

N = n Na
N = No e^-lambda x t

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25
Q

half life

A

average time it takes for the number of unstable nuclei to halve

or activity to halve ( how to measure as you cant accuratly measure number of unstable nuclei too small )

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26
Q

half life equations (3)

A

0.5No = No e^-lambda T0.5
ln0.5 = -lambda x T0.5
T0.5 = ln2 / lambda

27
Q

radioactive dating

A

carbon-14 is used
living plants take in CO2 from the atmosphere during photosynthesis along with carbon-14
when they die the activity of carbon-14 starts to fall
half life is roughly 5730 years

28
Q

medical diagosis

A

Technetium-99m widely used in medical tracers
tracer swallowed / injected and moves through body to point of interest
radiation emitted is recorded and an image is produced
gamma radiation with half life of 6 hours is suitable

29
Q

a nucleus is unstable if

A

-too many neutrons
-too few neutrons
-too many nucleons - heavy
-too much energy

30
Q

above line of stability

A

nuclei have too many neutrons
beta minus decay

31
Q

below line of stability

A

nuclei have too many protons
beta plus dceay

32
Q

very heavy nuclei

A

too many nucleons
alpha decay

33
Q

beta minus decay

A

neutron rich nucleus

34
Q

beta plus decay

A

proton rich nucleus

35
Q

gamma emission

A

after beta and alpha decay they have excess energy and are in an excited state therefore it must undergo gamma emission

36
Q

mass defect

A

difference of the mass of the nucleus and the added up mass of the individual nucleon constituents

37
Q

einstein equation

A

e = mc^2

38
Q

lost mass

A

as nucleons join together mass decreases
the lost mass is converted into energy and released
the energy released is equal to the mass defect

39
Q

binding energy

A

energy needed to separate all of the nucleons in a nucleus
equal to mass defect

40
Q

1u is roughly equal to…

A

931.5 MeV

41
Q

average binding energy per nucleon

A

binding energy / nucleon number

42
Q

fission sources

A

uranium 235 and plutonium 239

43
Q

fission

A

large nuclei are unstable and some can randomly split into two smaller nuclei
energy is released and the new smaller energy have a higher average binding energy per nucleon

44
Q

fission reaction

A

neutron fired at unstable nucleus
the unstable nucleus fissions into two smaller nuclei and a few neutrons and also releases energy

45
Q

fusion

A

two light nuclei join together to create a larger nucleus
a lot of energy is released as new heavier nuclei have much higher average binding energy per nucleon

46
Q

fusion energy required

A

all nuclei are positive
therefore electrostatic force of repulsion between them
nuclei can only fuse together if if they overcome this force and get close enough for the attractive SNFto hold them together
roughly 1MeV of Ke needed

47
Q

how to calculate energy released for fission or fusion

A

e = change m c^2
where m is total diffrence in mass between initial and final nuclei

48
Q

chain reaction

A

nuclear reactors use rods of uranium as fuel for fission reactors
these are placed into the reactors
this fission reaction produce more neutrons which induce other nuclei to fission

49
Q

moderator

A

fuel rods need to be placed in a moderator (e.g. water) to slow down / and/or absorb neutrons
you need a moderator that will slow down some neutrons enough so they can cause further fission, keeping the reaction going at a steady rate

the moderator slows down neutrons through elastic collisions with the nuclei of the moderator material
when nuetrons collide with particles of a similar mass, theyre are slowed down more efficiently

50
Q

why is water commonly used as moderators

A

wtaer is used as it contains hydrogen which has a similar mass to a neutron

51
Q

moderator by elastic collision

A

assuming the collison is perfectly elastic both Ke and momentum is conserved
assuming the moderator particle is stationary at first then conservation of momentum = mn x vn = mn vn’ + mm vm’

52
Q

conservation of kinetic energy moderator

A

0.5mn vn^2 = 0.5mn vn’^2 + 0.5mm vm’^2

53
Q

final velocity of neutron (vn’)

A

(mn - mm)/(mn + mm) X vn

54
Q

final velocity of moderator

A

vm’ = 2mn / (mn + mm) X vn

55
Q

if mass of moderator particle = mass of neutron

A

final mass of neutron would be 0 and all of Ke and momentum woukd be transferred to moderator particle

56
Q

critical mass

A

the amount of fuel needed for a fission chain reaction to continue at a steady rate on its own

57
Q

if less than critical mass

A

sub-critical mass and reaction will just peter out

58
Q

supercritical mass

A

nuclear reactors use a supercritical mass of fuel and control the rate of fission using control rods

59
Q

control rods

A

control the chain reaction by limiting the number of neutrons in a reactor
they absorb neutrons so that the rate of fission is controlled
control rods are made up of boron that can absorb neutrons and can be inserted by varying amounts to control the reaction rate

60
Q

coolant

A

sent around the reactor to remove heat produced by fission
material used should be a liquid or gass at room temperature and be efficient and transferring heat
often the coolent is the same water that is being used as the moderator
the heat from the reactor can be used to make steam which can be used to power the letrcity generating turbines

61
Q

reactor shielding

A

nuclear reactor usually surrounded by a thick concrete case which acts as shielding preventing the radiation from reaching any of the workers

62
Q

emergency shut down

A

in an emergency the reactor can be shut down remotely by the release of control rods
control rods are lowered fully into the reactor which slows down the reactions as quickly as possible

63
Q

handling and storing waste products

A

unused uranium fuel rods only emit alpha radiation so its easy to contain
spent duel rods are more dangerous as since fission waste products usually have a larger proportion of neutrons than nuclei
fission waste usually emits beta and gamma which is strongly penetrating

when material is removed its very hot and placed into cooler ponds until it colls down and placed in a sealed container until its activity drops

64
Q

how waste products can be used

A

can be used in practical applications like tracers in medical diagnosis

Physics (15 decks)

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