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