5. Nuclear physics Flashcards
Name a piece of equipment that is used to detect background radiation
Geiger muller tube
Types of radiation
Which is most ionising and penetrating
Alpha
Beta
Gamma
Alpha - most ionising
Gamma - most penetrating
Charge of a particle
Alpha
Beta
Gamma
Alpha = 2+
Beta = +/- 1e (depending on whether it’s an electron or a positron)
Gamma = No charge
What is the particle?
Alpha
Beta
Gamma
Alpha = Helium nucleus
Beta = Positron or electron (usually an electron)
Gamma = High energy photon or EM wave
Range in air?
Alpha
Beta
Gamma
Alpha = 1-5cm
Beta = 10-100cm
Gamma = Infinite (obeys the inverse square law)
Range in other materials?
Alpha
Beta
Gamma
Alpha = Stopped by paper
Beta = Stopped by thin sheets of aluminium
Gamma = Slowed down by thick blocks of lead
Define half life
Half life is the time it takes for half of the nuclei to decay. It’s a constant
What are the 3 types of ionising radiation?
Alpha, Beta and gamma
Emitted randomly
What is alpha radiation?
2 protons and 2 Neutrons
(Helium nuclei)
The nucleus loses 2 protons and 2 neutrons
This means the madd number decreases by 4 and the atomic number decreases by 2
What is beta radiation?
A fast moving electron emitted by the nucleus
Inside the nucleus, a neutron turns into a proton
This means the atomic number increases by 1 and the mass number stays the same (you haven’t lost a nucleon)
What is gamma radiation?
Electromagnetic wave- therefore no particles, less force exerted on electrons, doesnt lose as much energy, travels further
The nucleus loses some energy
The atomic and mass number don’t change
What is the relative mass of alpha radiation?
4 (2 protons and 2 neutrons)
What is the relative mass of beta radiation?
1/1836 (this is because beta radiation is a fast moving electron)
What is the relative mass of gamma radiation?
0
What is the relative charge of alpha?
+2
What is the relative charge of beta?
-1
What is the relative charge of gamma?
0
What material absorbs alpha?
Paper/skin/few cm of air
What material absorbs beta?
Few mm of aluminium or about 1m of air
What material reduces gamma?
Few cm of lead or several metres of concrete
What is ionisation?
when radiation collides with an atom
causes the atom to lose electrons
atom becomes an ion
What is ionising power?
The force exerted on atoms when radiation collides with them
Radiation with more charge will interact with atoms with a larger force so it has a larger ionising power
Radiation with more ionising power loses energy faster, (larger force, passes on more energy) as it doesn’t have more energy it just ionises atoms more quickly
It doesnt penetrate as far
What is penetrating power?
How far radiation can travel before losing all its energy
What type of radiation has the highest penetrating power?
Gamma, followed by beta then alpha
What type of radiation has the highest ionising power?
Alpha, followed by beta then gamma
Alpha has the highest charge and mass
Why does beta have a higher penetrating power than alpha?
alpha has higher mass and charge
larger force between alpha and electrons
energy of the alpha lost quicker
alpha cannot penetrate as far
Describe the method for alpha beta and gamma practical
Measure the background count for 2 minutes using Geiger Muller tube, counter and stop clock.
Place the radioactive source near the Geiger Muller tube and measure the amount of ionising radiation that it detects in a fixed time with no absorbing materials.
Place paper, aluminium and lead between the tube and source and repeat
Why is it important to repeat the measurements?
For reliability and to calculate the average
What could cause the measurements to be different?
The detector might not detect all the radiation and as radiation is a random process levels can fluctuate
What problems would be caused if we measured how much radiation was detected in 1 second or 10 seconds instead of 1 or two minutes?
This would cause smaller values and the fluctuation will be quite large, making the results harder to compare
Safety precautions?
Radioactive sources should be kept in a lead lined box
Should be picked up using long handled tongs
Don’t point them at people and keep your distance
Reduce exposure time by not keeping the sources in the room for very long
Why should you measure the background radiation?
To check whether all the radiation has been absorbed, and detect whether the value remaining is due to the source or background radiation
How do you find out the type of radiation emitted by the source?
Look at the big drops in the values
If there was a big drop when paper was put in front, then its alpha etc.
Why is the distance between detector and source the same for each experiment?
Control variable as distance affects the exposure to radiation and could decrease or increase the count
What happens to alpha in an electric field?
Attracted to the place of opposite charge
What happens to beta in an electric field?
Attracted to the place of opposite charge and deviated to the greatest extent due to lower mass
What happens to gamma in an electric field?
Not deviated at all since it has no charge
What is background radiation?
Alpha beta and gamma radiation that is all around us
Where does background radiation come from?
The air (radon gas)
Medical uses
The ground (rocks, eg granite)
Food and drink (eg bananas)
Cosmic
What is half life?
The average time it takes for the number of radioactive nuclei in a sample to halve (decay)
What is activity?
The number of decays every second
What does the unit Bq stand for?
Becquerels
- the unit of activity
How can you measure activity?
With a Geiger muller counter
How do you work out activity?
No. Decays/time (s)
What should you always do when finished with your paper?
Highlight the units and check everything has been converted eg minutes to seconds
Why does radioactivity decrease over time?
The number of nuclei that could decay decreases over time
— as there are fewer nuclei remaining, fewer are able to decay
— therefore the activity also decreases
— the activity halves after every half life
What are the problems in carbon dating an object less than the half life (5730 years) off carbon 14? And what about an object that has an age much larger than this?
1.Too few c-14 nuclei would have decayed
— it would not be possible to measure this
2. Nearly all of the c-14 would have decayed - nothing to measure
How is alpha radiation used in smoke alarms?
Alpha particles pass through two charged plates and ionises the atoms in the air.
The ions flow towards the oppositely charged plate. This causes a current to flow .
If smoke is present it will absorb some of the alpha particles resulting in less ionisation, which means a smaller current flows, so the alarm sounds.
Why is alpha used in smoke alarms?
It has a low penetrating power so it will be absorbed by the smoke and also it is absorbed by a few cm of air, so as long as the detector is high up on a wall it is safe for humans to be in the same room.
Why is a source with a long half life used for the smoke detector?
So that the smoke detector does not have to be replaced too frequently
How is beta used in gauging?
Aluminium is placed between a radioactive source and a detector, and the thicker the sheet, the lower the count rate since more beta is absorbed
What would happen if alpha particles were used for gauging?
Have a low penetrating power so would be absorbed by the aluminium, there will be no change in the cam reading so you can’t determine the thickness
How is gamma radiation used in crack detection?
Gamma emitter injected into pipeline downstream, so it flows
As gamma has a high penetrating power, it can be transmitted by rocks and earth surrounding the pipe
Where there is a crack in the pipe, gamma radiation will penetrate more easily, and collect outside the pipe, and more radiation will be detected at that point
What would happen if alpha particles were used for crack detection?
Low penetrating power, so the radiation would not make it to the surface and be detected
Why would a source with a half life of several hours or days be used?
Too long- environmental damage
Too short- not long enough for experiment
How is beta and gamma radiation used as a medical tracer?
1) beta and gamma penetrate the skin and tissue
2) source injected, penetrates skin and tissues
3) the source’s movement in the body is detected and monitored on a computer
4) used to see if there are any bodily issues
Why does the source have a short half life for a medical tracer?
So that the initial levels are high enough to be detected, but then decrease quickly so as not to cause too much damage to healthy tissues
Why would you not use alpha for a medical tracer?
Wouldn’t be able to penetrate organs and tissues
High ionising power makes it harmful if it is inside you
How is gamma radiation used to kill cancerous cells?
Beam of gamma radiation is rotated around the body with the tumour as the focus
where gamma rays intersect = high dose of radiation
but doesn’t damage healthy tissue, low dose
How can gamma rays be used to sterilise food and equipment?
food can be irradiated to kill bacteria and to keep it fresh, doesnt involve high temps so fresh fruit can be sterilised without being damaged
medical equipment can be sterilised
What is the difference between contamination and irradiation?
Irradiation -> exposed to ionising radiation, not dangerous as not EMITTING ionising radiation
contamination -> when some of radioactive isotope has been transferred to object IT WILL CONTINUE TO EMIT IONISING RADIATION it is dangerous to us
Why is radiation dangerous when it ionises the cells in our body?
damages DNA of cells causing cell mutations that lead to cancer or destroy the cells
What sources are most dangerous outside the body and why?
Beta and gamma
can penetrate the skin and muscle tissue and reach organs to do damage
less dangerous inside though- low ionising power
What source is the most dangerous inside the body?
Alpha
high ionising power, does all its damage in more localised area
Less dangerous outside as less likely to reach healthy cells
What are safety precautions that you can take?
Wearing lead lined aprons
Working behind lead glass screens
Reducing the exposure time to the radiation
Radiation detector badges - photographic film which when developed shows amount of radiation the worker has been exposed to
What is nuclear waste?
Radioactive material that has no use
Why is nuclear waste difficult to dispose of?
Dangerous - emits a, b, g, radiation
need to wait several half lives until it is safe to handle (could be hundreds, thousands of years)
very expensive
hard to find suitable places to bury it
How can you dispose of nuclear waste?
Put it in steel drums
Bury it underground under concrete - it might leak out and contaminate water sources
Might have to use robots
What is the energy transfer process in fission?
Store of nuclear energy in the parent nucleus is transferred to the store of kinetic energy of the daughter nuclei and neutrons and some gamma radiation
Will also release heat energy
What happens in a chain reaction?
When a nucleus splits it releases more neutrons which can cause more fission reactions to occur
What happens if a chain reaction is very uncontrolled?
Heat builds up very quickly
Can cause a meltdown or explosion
How do nuclear weapons work?
Use uncontrolled chain reactions
What is the role of the control rods in a nuclear reactor?
to slow the rate of reaction
boron control rods absorb neutrons, ensuring that an uncontrolled chain reaction does not occur
control rods can be lowered to absorb more neutrons and slow the reaction further
What is the role of the graphite moderator?
slows down the neutrons by absorbing some of their kinetic energy
makes them slow enough to be absorbed by nuclei, and increases rate of reaction
What is the role of shielding in a nuclear reactor?
Concrete or lead shielding is used to protect workers from ionising radiation released during the fission reaction process
What is the coolant?
Water that is passed through the reactor to absorb some of the thermal energy, which is turned into steam to turn turbines and generate electricity
Why do some atoms emit radiation?
Because they have unstable uncle that can only stabilise by emitting radiation.
3 types of radiation
Alpha
Beta
Gamma
Relative mass of protons
1
Relative mass of neutrons
1
Relative mass of electrons
1/2000
Alpha Radiation
α
2 protons + 2 neutrons.
Relative mass of 4
Stopped by paper
5 cm range in air
Greatest ionising power
Beta Radiation
B
Relative mass of 0
Charge of -1
A neutron in the nucleus changes into a proton and an electron. The electron is expelled from the atom but the proton stays.
Stopped by aluminium
1m range in air
Medium ionising power
Gamma Radiation
Y
Uncharged and has no mass- is a form of electromagnetic radiation.
Doesn’t change the element etc.
stopped by lead.
Unlimited range in air.
Least ionising power.
Half Life
The time it takes for the number of nuclei of the isotope in a sample to halve.
What halves every half life?
The no. of atoms of a radioactive isotope
+
The count rate.
Nuclear Fission
The process in which certain nuclei (uranium-235 and plutonium 239) split into two ‘fragment’ nuclei as a result of absorbing a neutron, releasing energy and two or three neutrons as a result. (chain reaction).
Fission Neutrons
Neutrons released during fission, which travel at high speed and also catalyse other Fission Reactions.
What three things are produced by Nuclear Fission?
> Fragment Nuclei
Fission Neutrons: 2-3.
Energy in the form of radiation, and the kinetic energy of the fission neutrons and fragment nuclei.
Nuclear Fission Reactor
> A reactor that releases energy steadily due to the fission of a suitable isotope such as Uranium-235.
This isotope is suitable because exactly one Fission Neutron from each reaction goes on to catalyse another reaction, keeping the rate of energy production steady.
Features of the inside of a Nuclear Reactor
> Water is added as a moderator (to slow down the uranium atoms so that they can cause further fission) and a coolant (to absorb kinetic energy from the neutrons and feel rods).
Control Rods: Absorb surplus neutrons (keeps the chain reaction under control).
Reactor Core: Made of thick steel to withstand high temps and pressures. Surrounded by concrete shield to absorb any escaping radiation.
Fission
Splitting.
What is the mass number?
Number of protons and neutrons in the nucleus
What is the atomic number?
Number of protons/electrons in an atom
What are isotopes?
Are atoms of the same element which have a different mass number
What does 23Na stand for?
23 is the mass number
Give an example of natural nuclear reaction
Nuclear decay
Define nuclear decay
It is the process where part of unstable nuclei disintegrated from it and it is emitted as radiation
Give examples of artificial nuclear reactions
Fusion and fission
Define nuclear fusion
It is the process where two atomic nuclei combine
Define fission
It is the process where atomic nucleus splits to other fragments
How is radioactivity measured?
In becquerels
In alpha decay what happens to the atomic number and mass number?
Mass number decreases by four
Atomic number decreases by 2
What is produced in alpha decay?
Helium
What is radioactivity?
A random process
What is background radiation?
The low intensity present in the Earth’s atmosphere.
Give sources of background radiation
Radiation from the earth’s crust
Radiation from outer space
Emission from nuclear experiments and power stations
Building materials
Radon gas
How does radioactivity form ions?
When alpha, beta particles or gamma rays collide with a material they knock off an electron
What is an ion?
Any atom that has lost or gained electrons
What are uses of ionising radiation?
A smoke detector
What is the relative charge of alpha particles?
+2
What is the speed of alpha?
0.1 speed of light
What is the ionizing effect of alpha particles?
Highest ionisation due to frequent collision with gas molecules since they are massive
What is the ionizing effect of alpha particles?
Highest ionisation due to frequent collision with gas molecules since they are massive
What is the penetrating effect of alpha particles?
Stopped by a sheet of paper or skin
What are beta particles?
High energy electrons emitted from the nucleus
What is the relative charge of beta particles?
-1
What is the ionising effect of beta particles?
Much less ionisation than alpha rays
What is the penetrating effect of beta particles?
Stopped by a few mm of aluminium
What is gamma rays?
High energy-frequency electromagnetic radiation
What is the relative charge of gamma rays?
0
What is the ionising effect of gamma rays?
least ionisation effect
What is the speed of gamma rays?
Speed of light
What is the penetrating effect of gamma rays?
Very high penetration effect can only be stopped by a thick sheet of lead
When the current is going down( positive is up, negative is down) what happens when alpha particles are being shot through it?
They will be slightly deflected down
When the current is going down( positive is up, negative is down) what happens when beta particles are being shot through it?
They are deflected more up
When the current is going down( positive is up, negative is down) what happens when gamma rays are being shot through it?
Nothing happens
When the current is going up( positive is down, negative is up) what happens when alpha particles are being shot through it?
They will slightly deflect up
When the current is going up( positive is down, negative is up) what happens when beta particles are being shot through it?
They are deflected greatly down
What happens in beta radiation?
A neutron in the parent nucleus changes to proton and electron
What happens to the mass number and atomic number in beta decay?
The atomic number increases by one
What is the half life?
Average time for half of the atoms in a given sample to be decayed or average count rate reduced to half of the original counts
What happens in a graph showing count rate?
It decreases
What is decay series?
It is one element turning into another which turns into another
What are uses of radioactivity?
Gamma rays are used to kill bacteria- sterilization
Smoke detector
Monitor thickness
Carbon dating- find the age of living organisms
Dating rocks
Find leaks/blockages in pipes
Tracers to investigate a patient’s body
Treatment of cancer
Which radiation is the most dangerous if the radioactive source is inside the body?
Alpha radiation because it is easily absorbed by cells
Which radiation is the most dangerous if the radioactive source is outside the body?
Beta and gamma because they can penetrate through skin
What is at the centre of every atom?
A nucleus
What does the nucleus contain?
Protons and neutrons - they make up most of the mass of the atom but take up virtually no space
What charge are electrons?
Negatively charged - very small
What do electrons do?
Move around the outsize of the atom - there path takes up a lot of space giving the atom its overall size
What do the number of protons equal?
The atomic number
What do the protons and neutrons equal to?
The mass number
What are isotopes?
Atoms with the same number of protons but different number of neutrons
What are the two isotopes of carbon?
Carbon-12 and Carbon-14 (Carbon-14 has two more neutrons than ‘normal’ Carbon-12)
What number do the top and bottom numbers of an element represent (when drawing an isotope)
Top - mass number
Bottom - atomic number
Usually each element has one or two stable isotopes. What are the other isotopes?
Unstable - they tend to be radioactive so decays and emits radiation (eg Carbon-14)
What kind of process In radioactive decay?
A random process - each nucleus decays spontaneously and is completely unaffected by physical conditions like temperature
What does a nucleus split into when it decays?
Three types of radiation - alpha, beta and gamma - in the process the nucleus often changes into a new element
Give examples of background radiation
Rocks/Soil/Food/Air
Cosmic rays
Fallout from nuclear explosions
Nuclear waste
What happens to a sample of radioactivity over time?
It decreases
What happens each time an alpha or beta or gamma particle is given out?
One more radioactive nucleus has disappeared
What happens as the unstable nuclei all disappears?
The activity as a whole decreases as the older the sample gets, the less radiation it will emit
What is the problem with trying to measure how quickly the activity drops off?
It varies for some isotopes and the activity never reaches zero which is why we use to idea of a half life
What is a half life?
The time it takes for half of the radioactive atom to decay
What does a short and long half-life means?
Short half life - activity falls quickly because lots of nuclei decay quickly
Long half life - activity falls more slowly because most of the unstable nuclei dont decay for a long time
How can you measure the half life of a sample using a graph?
Can only be done by talking several readings of a source activity usually using a Geiger-Muller detector
How is the half life found from a graph?
Find the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis
What should you do with the background radiation that also enters the GM detector?
First measure the background radiation then subtract it from every reading you get
What happened in 1804?
John Dalton agreed with Democritus that matter was made of tiny sphere (“atoms”) that couldn’t be broken up
He reckoned that each element was made up of a different type of “atom”
What happened 100 years later?
J J Thomson discovered that electrons could be removed from from atoms (so Daltons theory wasn’t quite correct)
Thomson suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them like plums in a plum pudding
Why didn’t the “plum-pudding” theory not work?
In 1909 Hans Geiger and Ernest Marsden tried firing alpha particles at thin gold foil.
Most of the particles went straight through and where detected when they hit the zinc sulfide screen and gave off a tiny flash of light. The odd alpha particles came straight back which was a shock
Who came up with the nuclear model of the atom?
Ernest Rutherford, boss of Geiger and Marsden, uses their results to come up with it
If the plum pudding was right, what should happen to the alpha particles?
They should pass straight through the gold foil
What was concluded from the fact that some of the alpha particles bounced back?
Inside the atoms there must be small positively charged nuclei which repel the passing alpha particles
What does Rutherfords model of the atom show?
Most of mass concentrated at the centre
Most of an atom is empty space
Nucleus must be small since since very few alpha particles are deflected by much
The nucleus must be positive to repel the positively charged alpha particles
The faster an alpha particle travels…
The less it will be deflected by a nucleus
The more positively charged a nucleus is (the higher the atomic number)…
The more an alpha particle will be deflected
The closer an alpha particle passes to the nucleus…
The more it will be deflected
What do you need to remember when your balancing a nuclear equation?
The total atomic number and mass number has to be equal on both sides
What do you need to remember about the different ionising radiation?
Alpha emission - mass number decreases by 4, atomic number decreases by 2
Beta emission - mass number stays the same but atomic number increases by 1
Gamma emission - mass number and atomic number stays the same
What are the three type of ionising radiation?
Alpha, beta and gamma
What does nuclear radiation cause?
Ionisation - by bashing into atoms and knocking electrons off
What happens to atoms with no overall charge during ionisation?
They are turned into ions (which are charged)
The further the radiation can penetrate before hitting an atom and getting stopped…
The less damage it will do along the way so the less ionising
How can you detect ionising radiation?
Photographic film or Geiger-Muller detector
What are alpha particles?
Helium nuclei - (4H)
2
What are alpha particles made up of?
2 protons and 2 neutrons - they are big, heavy and slow moving
Do alpha particles penetrate far into materials?
No - they are stopped quickly
What makes alpha particles strongly ionising?
There size which means they bash into a lot of atoms and knock off electrons before they slow down, which creates a lot of ions
What makes alpha particles strongly ionising?
There size which means they bash into a lot of atoms and knock off electrons before they slow down, which creates a lot of ions
Why are alpha particles deflected by electric and magnetic fields?
They are positively electrically charged
Why are alpha particles deflected by electric and magnetic fields?
They are positively electrically charged
What does emitting an alpha particle decrease?
The atomic number by 2 and the mass number by 4
What are beta particles?
Electrons - emitted when a neutron turns into a proton and an electron
What happens to the atomic and mass numbers in a beta particle?
The atomic number increase by 1 and the mass number stays the same (0 e-)
-1
Give 3 facts about beta particles?
They move quite fast (quite small)
They penetrate moderately
They are moderately ionising
They are negatively charged so deflected by an electric/magnetic field
What are gamma rays?
EM waves with a very short wave that have no mass and are just energy
How far can gamma rays penetrate?
A long way through materials without being stopped so they are weakly ionising because they tend to pass through rather than collide with atoms
How comes gamma rays are not deflected by electric or magnetic fields?
They have no charge
When do gamma emissions happen?
After beta or alpha decay
Do gamma rays have an effect on atomic and mass numbers?
No - if a nucleus has excess energy, it looses this energy by emitting a gamma ray
How can you identify the type of ionising radiation?
By its penetrating power
Alpha particles are stopped by…
Paper, skin or a few centimetres of air
Beta particles are stopped by…
Thin metal like aluminium
Gamma rays are stopped by…
Thick lead or very thick concrete
What makes beta and gamma suitable for medical tracers?
They penetrate the skin and other body tissues
How do medical traces work?
A source that emits beta or gamma radiation is injected into the patient.
The radiation penetrates the body tissue which can then be detected externally by a computer which converts the readings on he screen
Why does the radioactive source need to have a short half life?
So you can use less of the radioactive source but still get a reading on your detector
Why would you never use an alpha particle for medical tracers?
It would be useless - alpha particles are stopped by body tissues so your would never detect it externally
Also strongly ionising so can be really harmful if it gets inside of you
What else can gamma be used for?
Industrial traces - said
Name a piece of equipment that is used to detect background radiation
Geiger muller tube
Types of radiation
Which is most ionising and penetrating
Alpha
Beta
Gamma
Alpha - most ionising
Gamma - most penetrating
Charge of a particle
Alpha
Beta
Gamma
Alpha = 2+
Beta = +/- 1e (depending on whether it’s an electron or a positron)
Gamma = No charge
What is the particle?
Alpha
Beta
Gamma
Alpha = Helium nucleus
Beta = Positron or electron (usually an electron)
Gamma = High energy photon or EM wave
Range in air?
Alpha
Beta
Gamma
Alpha = 1-5cm
Beta = 10-100cm
Gamma = Infinite (obeys the inverse square law)
Range in other materials?
Alpha
Beta
Gamma
Alpha = Stopped by paper
Beta = Stopped by thin sheets of aluminium
Gamma = Slowed down by thick blocks of lead
Define half life
Half life is the time it takes for half of the nuclei to decay. It’s a constant
What is the nature of alpha?
2 protons and 2 neutrons
What is the nature of beta?
and electron from the nucleus
What is the nature of gamma?
an electromagnetic wave
What is the charge of alpha?
+2
What is the charge of beta?
-1
What is the charge of gamma?
0
What is the penetrating power of alpha?
Low
What is the penetrating power of beta?
Medium
What is the penetrating power of gamma?
High
What is the ionising power of alpha?
High
What is the ionising power of beta?
Medium
What is the ionising power of gamma?
Low
What is a use of alpha?
Smoke detectors
What are two uses of beta?
Aluminium foil thickness testing and filling washing powder boxes.
What are three uses of gamma?
Testing for holes in pipes, cancer treatment, tracer.
What is contamination?
When a radioactive substance had been absorbed into and object it emits the radiation itself.
What is irradiation?
When an object has been exposed to some radiation. It does not emit radiation and has not absorbed any radiation.
Which is dangerous?
Contamination
What is nuclear fusion?
When two small nuclei join together to form one large nuclei, resulting in lots of energy being released.
What is nuclear fission?
Induced nuclear fission is when a slow moving neutron is injected into a large unstable nucleus, splitting it into two daughter nuclei and 2 or 3 neutrons.
What is a chain reaction?
A reaction where the products of a reaction become a reactant in another.
Why must fission occur at high temperature and pressure?
In order to overcome the strong forces of repulsion.
What reaction occurs in nuclear power stations?
Fission
What is the function of control rods?
They are made of neutrons and absorb neutrons to control the rate of fission.
What is the function of fuel rods?
They contain uranium for fission
What is the function of the moderator?
It slows down neutrons allowing fission to occur
Name 3 advantages of nuclear power stations.
releases less CO2
high energy density
reliable and not weather dependant
Name 3 disadvantages of nuclear power stations.
expensive to build and maintain
dangerous
hard to obtain fuel
social and aesthetic concerns
Equation for alpha:
mass number: 4
atomic number: 2
Equation for beta:
mass number: 0
atomic number: -1
Equation for gamma:
mass number: 0
atomic number: 0
State three sources of background radiation
Any fromrocks/radon gasspace/ cosmic rays/sunmedical sourcescarbon atoms in living things
A nucleus of radon-222 has 86 protons. How many protons are there is a nucleus of radon-220?
86
A nucleus of radon-222 has 136 neutrons. How many neutrons are there in a nucleus of radon-220?
134
The number of nucleons in a carbon-14 nucleus is
14
The number of neutrons in a carbon-14 nucleus is
8
The number of electrons in a carbon-14 atom is
6 - same as protons
What are the three types of ionising radiation/radioactivity?
Alpha, beta and gamma
What is an alpha particle?
A helium nucleus
Is an alpha particle positively charged, negatively charged or neutral?
positively charged - has 2 protons and 2 neutrons
What is a beta particle?
An electron
Is a beta particle positively charges, negatively charged or neutral?
negatively charged
How is a beta particle produced?
A neutron splits into a proton and an electron. The electron is ejected.
Is gamma radiation a particle?
No - it is an electromagnetic wave, it has no mass
Is gamma radiation positively charged, negatively charged or neutral?
It has no charge
What are isotopes?
Atoms with the same number of protons are the same element. Isotopes are the atoms of the same element with different numbers of neutrons.
What peice of equipment can be used to detect beta particles?
Geiger-Muller tube Photographic film
An isotope has a half-life of 3 days. How long would it take for a sample of the isotope to decay to one eighth of the original value?
9 days
A sample of an isotope has a count rate of 200. Forty days later the count rate has dropped to 25. Calculate the half-life of the isotope.
13.33 days
If an isotope has a half-life of 20 seconds then how long will it take for its activity to drop from 1000 to 125?
60 seconds
Explain what is meant by the term half-life.
The amount of time it takes for half of the atoms in a radioactive substance to decay.
Explain what is meant by unstable nuclei.
It could decay at any time.
The activity of a radioactive source is the number of ioninsing particles it emits per second. This is measured in what?
Becquerels Bq
Carbon-14 has a half-life of 5700 years.A sample of cloth contains 6.0 g of carbon-14.What mass of carbon-14 will remain in the cloth after 11 400 years?
1.5 g
Why are some isotopes described as stable?
Stable isotopes do not emit ionising radiation.
Explain what is meant by background radiation?
Background radiation is radiation produced by radioactive material in the Earth and in the Earth’s atmosphere. It should be measured and taken into account when measuring the activity of radiation from a particular source.
Explain the difference between natural background radiation and artificial radiation?
Natural background radiation is due to the decay of naturally occurring radioactive isotopes in the Earth that were formed when the Solar System was created. Natural radiation also results from high-energy particles that bombard the Earth. Artificial background radiation comes from
man-made sources, rather than from the rocks that make up the Earth.
Give three examples of sources of BR?
Uranium in rocks in the Earth’s crust (natural). Radioactive materials that have escaped into the environment from nuclear power stations (artificial). Fallout from atmospheric nuclear weapon
testing in the 1950s and 1960s (artificial).
Explain simply, the principle of the GM tube?
Ionising radiation causes ionisation of a low-pressure gas inside the tube. The ionised gas allows a current to flow between two electrodes, and the current is detected by an electronic circuit.
What does a rate meter measure in a GM tube?
A rate meter gives an indication of the number of decays occurring per second.
Rate meter is calibrated at kBq. How is this unit defined?
A bequerel is a rate of decay of one disintegration per second. 1 kBq is 1000 disintegrations per
second.
Define what is meant by the half life of a radioactive material?
The half-life of a radioactive sample is the average time taken for half the unstable atoms in the sample to undergo radioactive decay.
Radioactive decay is a random process. Explain this?
Random means that the decay of an individual atom is unpredictable; we cannot say when any particular atom will undergo decay.
A student wants to measure the half life of a radioactive isotope. He is told that is has a half life of between 10 and 20 minutes.
What measurements should he take?
How should he use the measurements to find the half life?
Students should measure the background radiation. They should then measure the radioactivity of the sample using a GM tube and rate meter at regular intervals of, say, 5 minutes for a period
of 30–40 minutes.
The readings of the activity of the sample should be corrected by subtracting the average background radiation count. The corrected readings should then be plotted on a graph of count rate against time. The time taken for the
initial activity to fall to half can then be measured from the graph.
Explain why a particles half life of 6 hours and decay by emission of low energy gamma and beta particles is good in medicine?
It has a short half-life, so its activity drops to a negligible level in a day or two. Beta particles and low energy gamma rays penetrate soft tissue easily, so the progress of the isotope through the body can be monitored easily. The emitted radiation is not strongly ionising, so the risk of
tissue damage is acceptably small. (It is also relatively easy to produce.)
How can an isotopes’ progress in the body be monitored?
By using a detector such as a GM tube.
What can cause an isotope to decay to another isotope of a different element with the same mass no?
Beta decay. The process involves a change in element but with a negligible change in mass.
How can iodine isotope be used to identify an over-active thyroid gland?
Iodine-131 is taken up by the thyroid gland in the same way as ordinary iodine. An overactive thyroid concentrates more iodine – if the concentration of I-131 is greater than normal, this can be detected by measuring the activity and comparing it with the expected take-up from a normal thyroid gland.
How can iodine isotope help to treat an over-active thyroid?
I-31 is a high-energy beta-emitter. The radiation is sufficiently ionising to destroy cells in the thyroid, reducing its activity.
Explain the advantages of ionising radiation for sterilizing surgical equipment
Surgical instruments may be sealed into wrappers and then sterilised using radiation. The radiation passes through the wrapper, destroying any organisms on the instrument, which then remains sterile within its wrapper.
How can you use ionizing radiation to check the thickness of paper during production?
type of radiation
how it will be used to measure paper thickness
what checks should be made to make sure measurements are accurate
safety procedures
Beta radiation is used. It can pass through paper (unlike alpha particles) but the thicker the paper, the greater the amount of beta radiation absorbed.
A beta-emitting source is placed above the paper as it emerges from the rollers used to press it to
the required thickness and a detector is placed beneath the paper in line with the source. The count rate will decrease as the thickness of the paper passing between the emitter and the
detector increases.
To ensure accuracy, the background radiation count should be taken regularly so that the reading from the detector can be corrected. The half-life of the beta-emitting source needs to be quite long (so that the count rate does not fall significantly over short intervals), but the apparatus will need to be recalibrated regularly using paper of known thickness.
Care should be taken to ensure workers cannot come within range of the radiation from the source. The source must be stored in a secure container that is lined with lead to ensure no ionising radiation can escape. The storage area and the part of the paper-making works in which
the radiation source is being used should be clearly identified with standard signs. The source must be selected and screened to ensure that it emits only beta radiation.
How is C-14 made?
Cosmic radiation causes C-14 to form from nitrogen in the atmosphere.
Why does all living matter contain C-14?
Carbon-14 has the same chemical behaviour as the abundant stable isotope C-12. Carbon reacts
with oxygen to form carbon dioxide. Through photosynthesis, carbon-14 enters the food chain
and therefore all living material.
What happens to the proportion of C-14 in an organism when it dies?
Once an organism is dead, no new C-14 is taken in via photosynthesis (plants) or food
(animals). The proportion of C-14 in organic material decreases as the C-14 decays.
What assumptions are made in radiocarbon dating?
The principal assumption is that the rate of production of C-14 through cosmic rays has remained constant over time. In practice this is not so, but it is possible to make adjustments for the variation in C-14 by taking samples from objects of known age.
Why is carbon dating not suitable when measuring material older than 50,000 years?
The half-life of C-14 is roughly 5600 years. After 10 half-lives have elapsed, the activity remaining C-14 is too small for accurate measurement.
An isotope that decays by alpha emission is relatively safe when outside the body by dangerous if absorbed.
Why?
Alpha radiation has a very limited range. After alpha particles have travelled only a few centimetres in air, they have lost most of their kinetic energy and thus lose their ionising power. Alpha particles are stopped completely by quite thin layers of material that are not very dense.
Thus alpha radiation is not particularly dangerous to living cells, as in the human body, unless the source is very close to living tissue. If a source is very close to the skin it may, if the exposure is prolonged, cause burns and other tissue damage.
The greatest danger is when alpha emitting material is absorbed into the body. Inside the body, cells do not even have the protection of a layer of skin and fat, so are readily affected by the highly ionising alpha particles. This will result in cell destruction or mutation.
Why is radon-220 a v.dangerous isotope?
Radon-220 is an alpha-emitter. It is a dense gas and therefore accumulates in the lower parts of buildings, etc. As it is a gas, it is readily inhaled and thus comes into close contact with internal cells.
As described above, this is the most hazardous condition for alpha sources.
Give one difference between Thomson’s and R’s model?
In Thomson’s model, the mass of the atom is uniformly distributed through the whole of the atom.The atom was thought to be a positively charged sphere with negative charges distributed evenly throughout the sphere.
In Rutherford’s model, nearly all the mass of the atom and all its positive charge is concentrated in the small central core or nucleus.
What did the results of G and M’s experiment reveal about the atom?
That most of the volume of a gold atom is empty space, and most of the mass and positive charge is concentrated in a very small volume at the centre of the atom.
How would deflection change if particles had only half the electric charge?
The particles would have travelled closer to the nucleus before suffering a rebound and be deflected through smaller angles at any specific distance from the nucleus than the more highly charged particles.
What is a fissile material?
The nuclei of its atoms can be split apart by a nucleus.
What is a chain reaction?
A reaction that produces further reactions – in this case, neutrons produced when a uranium nucleus splits can cause further nuclei to split.
Why does a chain reaction depend on the amount of fissile material in one piece?
If there is only a small amount, neutrons can escape the material without hitting any more nuclei.
Advantages and Disadvantages of nuclear fission as an energy resource?
Advantages:
virtually inexhaustible supply of energy
does not produce ‘greenhouse’ gases.
Disadvantages:
produces waste that remains extremely dangerous for thousands of years
very highset-up and decommissioning costs.
What are alpha particles?
Alpha particles are helium nuclei (1) ejected at high speed from the decaying nucleus (1).
Describe the results of G and M’s expand what R drew from the results?
Most alpha particles passed straight through, undeflected (1). Some were deflected (1) and a
very small proportion actually rebounded (1).
Rutherford deduced that the mass and charge of
an atom was concentrated in a very small central core or nucleus (1)
Describe the plum model?
In the plum pudding model, the mass is uniformly distributed throughout the volume of the atom
(1). The atom was considered to be a positively charged sphere with electrons studded in it like
plums in a pudding or raisins in a cake (1).
Will an experiment with more or less particle representers be better?
The 200-dice experiment is more likely to produce the best model (1). In radioactive decay, millions of atoms are involved. The larger the number of dice, the more statistically valid the
experiment will be (1).
What is an isotope?
Isotopes of an element have the same atomic number (1) and the same chemical properties (1).
Isotopes differ in their atomic mass (having different numbers of neutrons) (1) and have different physical properties (1).
How does radiocarbon dating work?
Living organisms take in carbon-14, and so have a relatively fixed proportion of carbon-14 to carbon-12 in their body (1). When they die, the carbon-14 decays and is not replenished (1) so the proportion of carbon-14 decreases (1).
By measuring the relative amounts of the two isotopes of carbon, we can work out how long ago the organism died (1).
How to measure the half-life of a radioactive isotope?
Using a GM tube and counter (1), measure the background radiation over a period of time to find the average count rate (1). Place the radioactive sample a fixed distance from the detector, taking care to handle the source with handling tongs at arm’s length (1). Measure the activity of the sample at regular intervals (of a minute or two) (1).
Plot a graph of activity against time (activity corrected for background count) (1). Measure how long it takes for the activity to halve from the graph (1).
What isotope is best for cancer treatment?
An alpha-emitter (1) that can be attached to a material that is readily absorbed by the target tissue (1). Alpha radiation is heavily ionising (so short range) and will destroy the tissue in the
immediate vicinity of the emitter (1).
What isotope is best for diagnosis?
A beta-emitter (1) with a relatively short half-life (1). The radiation can be detected outside the body (1) and will fall to a safe level of activity in a short period (1)
Why is iodine isotope used in preference for thyroid cancer treatment?
Iodine is taken up by the thyroid (1). An overactive thyroid concentrates more iodine than a healthy one (1). Using a radioisotope of iodine means that cancerous cells within the thyroid can be destroyed without damage to other surrounding tissue (1).
What is the effect of an emission of a beta particle on a nucleus?
Less neutron and one more proton. Mass number overall still the same.
Sources of background radiation?
Radiation from rocks/buildings
Cosmic radiation from stars/Sun
Radiation from medical sources
Nuclear waste/accidents
How would you measure for cosmic background radiation and adjust count rate accordingly?
Remove radioactive source going to be tested
Measure background count rate
Repeat the measurement/repeat for a long time
Subtract this value from each reading
Explain why radioactive sources can be dangerous?
ionizing radiation
cells mutate
cancer
What can be used to detect beta particles?
GM counter
zinc sulfide
photographic film
gold leaf electroscope
Granite is a rock. It contains a radioactive isotope of uranium that decays very slowly. Explain how scientists can use this radioactivity to find the age of a piece of granite.
There is a known proportion of activity when rocks form. Measure activity now and COMPARE.
Hence determine the number of half lives elapsed and then calculate the age from that.
Suggest why the age of a piece of granite could not be found using a uranium isotope with a half-life of 15 hours.
The half life is too short; it decays too rapidly.
The isotope would have decayed long ago and its current activity would be too small to measure or distinguish from background radiation.
Explain what is meant by the term unstable.
Will decay/emit radioactive particles
Explain what is meant by the term half-life.
Time taken for half of the radioactive nuclei /atoms to decay
Describe how a teacher should measure the activity of a radioactive source using
a Geiger-Muller detector.
Use a rate meter
Measure background radiation
Safety precaution with use of tongs, shielding
Control time/distance by keeping the source near/by the detector for a minute
Repeat; average; reset scaler
Mention becquerel
Iodine-131 is used to treat thyroid cancer. This radioactive isotope is allowed to enter the tumour. Explain why iodine-131 is suitable for this treatment.
Beta is moderately ionizing and has a short range and short half life
Easily absorbed by thyroid
Reduces damage to healthy cells and doesn’t penetrate out of body
Kills mainly tumour cells
What form of energy is produced by nuclear fission?
Kinetic energy
What is the job of a moderator?
slow down neutrons
increase rate of fission
increase absorption of neutrons by uranium/fuel
Suggest why Uranium 238 is the most common isotope of Uranium?
Other isotopes have decayed more quickly and it has the longest half-life
What is produced from nuclear fission?
gamma radiation (thermal energy)
more neutrons
krypton/barium/xenon
What happens in the reactor when the control rod is removed?
The rate of reaction increases
Fewer electrons are absorbed by control rod
MORE COLLIDE WITH URANIUM
Temperature increases
Explain why it is difficult to make the surrounding area safe again after a nuclear accident?
harmful nature of radiation/danger to life
high levels
long half/life
difficulties for workers to access the area
need special handling equipment
radioactive material can mix with local environment and spread material further (air, water, fire, soil, plants)
Describe nuclear fission and how it is controlled?
nucleus absorbs neutron
splits into daughter nuclei
extra electrons are released
kinetic energy released
released neutrons collide with other uranium nuclei
CONTROLLED BY MODERATOR than slows down neutrons
control rods absorb extra electrons
Control rods prevent a runaway chain reaction
What form of energy is released during fission?
KINETIC
How does shielding improve safety?
Absorbs radiation and some particles’ energy
Explain how nuclear fission can lead to a chain reaction
neutrons released
slowed by moderator
absorbed by other nuclei
causes further fissions
Why is shielding needed on reactor?
Reactor material is radioactive and so is waste
Radiation ionizes cells/tissues/organs
Causes cancer
Radiation is very PENETRATING
How should scientists deal with anomalous results?
check and repeat measurement/experiment
work out why this result ocurred
Why is it important to carry out experiments in physics?
to make new discoveries
validate existing theories
disprove hypotheses
gather evidence
confirm other scientists’ findings
What is the Geiger counter?
Device to measure, detect and quantify the amount of radiation passing through
COUNTS NUMBER OF DECAYS/SECOND
What does a ratemeter do?
indicates the number of pulses/counts per second.
Number of protons and neutrons in uranium 238?
p = 92
n = 146
Why are gamma and alpha radiation not used in paper industry?
Gamma would penetrate the paper either way
Alpha would be absorbed by the paper
Why is a long half like needed in paper industry?
If you have a long half life then fluctuations in radiation detected must be due to paper thickness and not just a half life! If you get a drop you know that its because of a change in thickness of the paper and not because its decaying…
What half life is needed in checking for pipe cracks?
medium half life - otherwise radiation will stay in and contaminate water!
What radiation is used in finding leaks?
Gamma b/c alpha and beta wouldn’t penetrate earth and pipe material
What radiation is used in tracers?
Gamma so it can be detected outside of the body - Alpha would just be absorbed by cells and this is VERY DANGEROUS AS IT IS IONIZING
Risk of alpha inside and outside body?
OUTSIDE: minimal risk cannot penetrate past skin cells to reach living ones
INSIDE: high risk; every particles will interact with a body cell and cause damage
Risks of beta inside and outside body?
OUTSIDE: medium risk; can penetrate and interact with cells
INSIDE: medium risk - many will pass out of body and many will interact with cells
Risks of gamma inside and outside body?
OUTSIDE: high risk; many penetrate body but some interact other pass straight through
INSIDE: low risk - every gamma ray will pass through the body
What decay does C-14 undertake?
beta
What two isotopes undergo nuclear fission?
uranium 235
plutonium 239
What is alpha stopped by?
Few mm of paper
What is beta stopped by?
Few mm of aluminium
What is gamma ‘stopped’ by?
reduce with metres of concrete / lead
When is high intensity and long term exposure to radiation good and why?
It causes so much cell damage - good when sterilisation is to occur to kill microbes on surgical equipment for example.
What does low intensity radiation do to a cell?
Causes mutations - some beneficial, some harmful
How can a harmful mutation pose a threat?
If it increase by the cells affected dividing uncontrollably CANCER
Safety precautions when handling radioactive material?
handle with tongs/forceps
at arms length, pointing way from body
far away from eyes
Why don’t rocks contain carbon-14 atoms?
In rocks that are generally quite old. the amount of 14C is too small to measure accurately. Rocks make poor C14 samples because they do not include much-if any- free atmospheric gases which is the source of C14, the gases they include come from underground sources. All organic samples, plants and animals, do include C14,, as a part of their normal respiration.
What is the half life?
The average time for half of the unstable nucleus to decay.
What is the activity?
A measure of the number of decays per second.
What is background radiation
Small arounds of radiation present in our surroundings due to the natural decay of unstable nuclei.
What are 5 sources of background radiation?
food and drink, buildings, artificial, cosmic rays, radon gas from ground
How do tracers work?
Gamma is attached to a molecule that is absorbed in the body by tumors and growths. radiation is then emitted and detected. SAFETY: short half life and low activity.
What is the nature of alpha?
two protons and two neutrons
What is the nature of beta?
an electron from the nucleus
What is the charge of beta?
-1
What is the mass number and atomic number of beta?
mass: 0 atomic: -1
Define nuclear fusion:
When two small nuclei join together to form one large nucleus.
What is the function of control rods?
to absorb neutrons to control the rate
What is the function of the moderators?
to slow down neutrons
Which is the most penetrating form of radiation?
γ-radiation
How can you detect ionising radiation?
Using a Geiger-Muller detector (counter)
Name three sources of background radiation
rocks, the Sun, cosmic microwave background radiation
What is activity measured in?
Bequerels (Bq = 1/s)
What is a “half-life”?
The time taken for half of the atoms of a radioactive substance to decay
What are the dangers of ionising radiation
Mutations; cancer; disposal issues
What are α and β radiation, and how much can they penetrate respectively?
α: Helium nucleus with a 2+ charge and a RAM of 4. Stopped by thin card. Cannot travel very fast because it is easily stopped by air particles.
β is an electron with a 1- charge and a RAM of 0. Stopped by 1-2mm of aluminium foil. Can travel relatively fast.
