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Physics > RADIOACTIVITY Year 13 > Flashcards

RADIOACTIVITY Year 13 Flashcards

1
Q

What was Thomson’s idea of an atom?

A

He put forward the plum pudding model in which an atom is a positively charged sphere containing tiny negatively charged electrons stuck in it.

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2
Q

How did the golden foil alpha particle experiment disprove the plum pudding model?

A

The alpha particles were expected to deflect by a very small amount by the electrons if the model was true.However,most of the particles went straight through but some were deflected by more than 90 degrees.

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3
Q

What is a head on collison?

A

This is when an alpha particle collides with the centre of a nucleus and is deflected back by an angle of 180 degrees.

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4
Q

What is the relationship between an alpha particles closeness to the head on direction?

A

The closer a particles inital path is to the head on collison the greater its angle of deflection is likely to be.This is because the electrostatic repulsion between the particle and nucleus is more due to the decreased distance between them.

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5
Q

What is the charge of a nucleus?

A

It is +Ze where z is atomic number and e is charge of an electron.

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6
Q

What is the size of a nucleus relative to the atom it is in?

A

d=D/10000

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7
Q

What could be concluded from the Rutherford experiment?

A

Most of an atom is empty space as a lot of particles passed straight through.The centre nucleus must be positively charged as some of the alpha particles were deflected by a large angle.Most of the mass of the atom is concentrated in the centre as the alpha particles with the most momentum were deflected back.The nucleus is small as very few particles were deflected back.

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8
Q

What is the effect of a magnetic field on the 3 types of radiation?

A

A magnetic field deflects both alpha and beta radiation in different directions.However, it has no effect on Gamma radiation.

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9
Q

What absorption test can you use to measure beta radiation?

A

Use a source, absorber, geiger tube and counter.Start off by measuring the background count rate.Then position the source in front of the tube and record the count rate over a given period.Then put the absorber in front of the tube and measure the count rate while using different thicknesses of absorbers.You can plot a graph of count rate against thickness of absorber to see results.

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10
Q

What are the ranges of the different types of radiation in the air?

A

Alpha is a few cm the ke and range is the same for each particle emitted from the same source.
Beta has a range up to a metre,the range of Beta particles from the same source vary some may be maximum so can travel slightly further.
Gamma radiation has an unlimited range in the air.However,the count rate decreases with distance from the source as the radiation spreads out in different directions.

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11
Q

What stops each radiation and what is the distribution of energy from the source?

A

Alpha is stopped by thin paper,Beta is stopped by 5mm of aluminium and gamma is stopped by thick concrete or lead.Alpha is constant, beta varies up to a maximum and gamma is constant.

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12
Q

What is intensity?

A

It is the radiation energy per second passing through a unit area.

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13
Q

What are the harmful effects of exposure to ionising radiation?

A

Human exposure to ionising radiation can cause the cells in the body to die or start to divide uncontrollably due to the release of free radical ions.This is caused by damage to the dna and this can be passed on to future generations.

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14
Q

What does the severity of the damage done to the cells by radiation depend on?

A

This depends on the type of the radiation and the dose received.

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15
Q

What is background radiation?

A

It is radiation due to cosmic rays and from radioactive materials such as rocks and buildings.We are always exposed to it.

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16
Q

List 5 sources of background radiation?

A 
Air(radon gas)
Medical industry
Buildings and rocks
Food and drink
Cosmic rays
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17
Q

How should radioactive materials be stored?

A

They should be stored in lead lined boxes as most sources emit gamma rays.The aim of this is to reduce the gamma level to the background rate.In addition a lock and key box is required to store them in,

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18
Q

What should you do when using radioactive sources?

A

If the source is solid use tongs and make sure they hold the radiation as far away as possible to stop alpha and beta radiation travelling.If the source is in liquid or gas form it should be kept in a sealed box to prevent inhalation.Sources should be used for a short time to limit exposure.

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19
Q

What is the half life of a radioactive isotope?

A

It is the time taken for the mass of the isotope to half.

This is the same as the time taken for the nuclei to half.

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20
Q

What is a decay curve?

A

Its an exponentially decreasing curve of mass against time.

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21
Q

What type of process is radioactive decay?

A

It is a random process as it is unpredictable.

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22
Q

What is the activity of an isotope and how is it measured?

A

The activity is the number of radioactive nuclei that disintegrate per second.Activity is measured in bq.=1 disintegration per second.

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23
Q

What is activity proportional to?

A

It is proportional to the mass of the isotope as they both decrease exponentially with time.And the nukber of unstable nuclei in a sample.

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24
Q

What is the formula for the power of a source?

A

P=AE where A is activity and E is energy of photons.

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25
Q

What is the formula for the rate of disintegration?

A

deltan/deltat=-lambda n.Lambda is the decay constant.

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26
Q

What are the equations for remaining nuclei,activity,count rate and mass.

A

N=No*e^/lambdat same for others.

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27
Q

What is the decay consant?

A

It is the probability of an individual nucleus decaying per second

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28
Q

What is the formula for half life?

A

Half life=ln2/lambda

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29
Q

Describe uses of radioactivity?

A

It can be used to carbon date as all living organisms have carbon 14 in them.

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30
Q

Describe the types of radiation on a NZ graph

A

Up until z=20 the light isotopes follow a straight line trend graph.As z increases beyond 20 stable nuclei have more neutrons than protons.Alpha emitters occur beyond z=60.These have more neutrons than protons.B minus and alpha emitters are on the left of the stable belt.While B plus emitters are on the right of the belt.So is electron capture

31
Q

What happens in a series decay?

A

Depending on the position of the isotope relative to the stability belt it will decay.

32
Q

What happens if a daughter nucleus is formed in an excited state?

A

It will release a gamma photon from its meta stable state to its ground state.

33
Q

What is the formula for the first minimum seen in electron diffraction?

A

sintheta=1.22lambda/2R r is radius of nucleus.

34
Q

What is the formula for the radius of a nucleus?

A

R=R0*A^1/3 A is atomic number and r0=1.05fm

35
Q

What is the method of closest approach?

A

An alpha particle deflected through 180 degrees will reverse its direction at the point where Ek=Ep.You can find the radius by using Qgold Qalpha/4pie0r

36
Q

What is binding energy?

A

It is the work done to separate a nucleus into its constituent protons and neutrons.

37
Q

What is the mass defect of a nucleus?

A

It is the difference in mass between the separated nucleons and nucleus.It is equal to the binding energy of the nucleus

38
Q

Why is there a mass defect in nucleus?

A

The strong nuclear force has to do work to bring protons and neutrons together.This process releases some energy.Therefore the mass of the nucleus is less than the mass of the separated constituents.

39
Q

What is the formula for mass defect?

A

Mass of proton + mass of neutrons - mass of nucleus.

40
Q

What is the formula for the binding energy of a nucleus?

A

E=mdc^2. mass defect in Mev=Binding energy.

41
Q

What is the binding energy per nucleon in a nucleus?

A

It is the average work done per nucleon to remove all the nucleons from a nucleus.Therefore it is a measure of nuclear stability.

42
Q

What is nuclear fission?

A

This is when an unstable nucleus collides with a neutrons and forms two equal stable daughter nuclei.

43
Q

What are fission neutrons?

A

Fission neutrons are neutrons releases as a result of nuclear fission.These neutrons are able to cause chain reactions by colliding with other uranium nuclei which in turn release more fission neutrons.

44
Q

What is the energy released from a fission reaction equal to?

A

It is equal to the change in binding energy of the daughter nuclei.The fragment nuclei are smaller and as a result are more tightly bounded to each other so have greater binding energy.

45
Q

What is nuclear fusion?What happens to the binding energy of the product?

A

Is the process of fuses two light nuclei to form a heavier nucleus.The binding energy of the product rises as the nucleons are more closely packed together.As a result energy is released.Which is equal to change in binding energy.

46
Q

What condition must be met for nuclear fusion to take place?

A

The two nuclei must collide at high speeds to overcome electrostatic repulsion and allow the strong nuclear force to pull them closer together.

47
Q

What is the function of fuel rods and what do they contain?

A

Their function is to collide with the thermal neutrons and undergo nuclear fission.They contain uranium isotopes enabling them to do this.

48
Q

What are the function of control rods and what are they made of?

A

Their function is to limit the rate of fission by absorbing excess neutrons.The aim is for one fission neutron per fission to be released.They can be adjusted to increase or decrease the rate of fission.

49
Q

What is the function of the moderator and what is it made from?

A

Its job is to slow down fission neutrons in order for chain reactions to occur and it is made out of water.It does this by elastic collisions with the neutrons.The hydrogen atoms in the water.The moderator should be of similiar mass to a neutron.

50
Q

What is critical mass?What mass do nuclear reactors use?

A

It is the amount of fuel needed to maintain a steady chain reaction of fission.They use supercritical mass to allow several more fissions to occur.

51
Q

How do moderators slow down fast moving neutrons?

A

Fast moving neutrons collide elastically with the atoms of the moderator.Collisions of particles with the same mass are more efficient at slowing the neutrons down.

52
Q

Describe the reactor core safety feature?

A

It is a thick steel vessel able to withstand the high temperature and pressure of fission.Also it can absorb some beta, neutrons and gamma radiation.

53
Q

Describe the safety feature of the building the core is in?

A

The building the core is in is surrounded by thick concrete walls that can absorb any neutrons or gamma radiation that escapes from the reactor vessel.

54
Q

What feature do reactors have in case of an emergency?

A

They have an emergency shut down system which inserts the control rods fully to stop fission.

55
Q

How is high level radioactive waste stored eg spent fuel rods?

A

Spent fuel rods are highly radioactive so they are stored in underground cooling ponds for up to a year.Then the radioactive material is removed from them and the rest of the material is stored underground in steel casks.Most countries store high level waste underground.

56
Q

Where is intermediate and low level waste stored?

A

Intermediate waste with low activity is stored in steel cases and placed in special buildings with walls of reinforced concrete.Low level waste is put in metal drums and buried in trenches.

57
Q

Describe rutherford’s alpha particle scattering experiment?

A

It consisted of firing alpha particles at thing gold foil and then these particles would hit a fluorescent screen causing a flash of light.

58
Q

How to find the nucleus radius using closest approach method.

A

At a point where the particles is deflected 180 degrees by the nucleus its kinetic energy will transfer to its electric potential energy.1/2mv^2=Qq/4pie0r.

59
Q

How to find nuclear radius using electron diffracton?

A

Fire a beam of high energy electrons towards a screen with a low wavelength.Each high speed electron is diffracted by an individual nucleus.

60
Q

Formula to find radius of nucleus from high speed electron diffraction?

A

sin theta=1.22lambda/2R.First minimum appears here.

61
Q

Describe the diffraction pattern of the electron?

A

Bright central maximum followed by declining maxima.As angle of diffraction increases.

62
Q

What is the typical value for the radius of a nucleus?

A

About 1-1.05 fm.

63
Q

What is a use of alpha radiation?

A

Alpha radiation can be used in a smoke alarm as it ionises the air and allows a current to flow between the electrodes.However,the smoke will absorb the alpha particles preventing a current from flowing.

64
Q

What is the use of beta radiation?

A

It can be used to test the thickness of paper.Fire a source of beta radiation at paper and have a reciever beneath the paper.If the paper is too thick the count rate will drop and the the rollers must come together.

65
Q

What is the use of gamma rays?

A

Due to its weakly ionising and highly penetrating properties it can be used in medical tracers to help diagnose or kill cancer cells.

66
Q

Describe the inverse square law of gamma radiation?

A

Gamma rays are emitted in all directions from a source.As these rays start to spread out the further away from the source they are,their intensity drops significantly.I=k/x^2.

67
Q

How to experimentally measure the inverse square law for gamma rays?

A

Use a geiger tube connected to a geiger counter and align it with the start of the ruler.Record the background count rate and take an average.Then place a radioactive source at distance d,2d,3d,4d…. and take an average of the count rates at these readings.Then plot a graph of intensity against distance and you should see an exponential decay graph.Makes sure to take the corrected count rates.

68
Q

What is the formula for the activity of a sample?

A

A=lambdaxN.Where lambda is the decay constant.

69
Q

Why might a nucleus be unstable?

A

It either has too few or too many neutrons.It has too much energy or it has too many nucleons all together.

70
Q

Describe the types of decay with respect to the line of stability?

A

Beta minus occurs above the line of stability as there are too many neutrons.Beta plus occurs below the line of stability as there are two many neutrons.Alpha occurs below the line of stability at the top as there are too many nucelons.

71
Q

What happens in beta minus decay?

A

This is when an electron and antineutrino are ejected from a nucleus causing a neutron to change into a proton.

72
Q

How are gamma rays emitted from the nucleus?

A

Either by electron capture or after alpha/beta decay as the nucleus may be in an excited state?

73
Q

What happens in electron capture?

A

This is when a nucleus absorbs one of its orbiting electrons which causes a proton to convert into a neutron.

74
Q

How can you tell whether a nucleus should under go fission or fusion?

A

By looking at the graph of average binding energy against nucleon number.Those elements on the left of iron should under go fusion and those on the right should undergo fission based on the change of average binding energy with nucleon number

Physics (19 decks)

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