Radioactivity and Particles Flashcards
What is meant by the term half-life?
Time take for radioactivity to halve
What is the purpose of the moderator in reactors in nuclear power stations?
1) slow down neutrons
2) increase rate of fission
3) increase absorption of neutrons by fuel
What happens in a nuclear reactor when the control rods are removed?
1) rate of reaction increases
2) more neutrons collide with uranium as fewer neutrons are absorbed by the control rods
3) temperature increases
What is the formula of alpha radiation?
a a-4 4
X —> Y + A
z z-2 2
What is an alpha particle?
A helium nucleus (2 protons and 2 neutrons)
What happens in Beta decay?
A neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves.
What is the formula for beta radiation?
a a 0
X —> Y + B
z z-1 -1
What piece of equipment can be used to detect radiation?
Geiger-Muller counter or photographic film
How can scientists use radioactivity to find the age of a piece of rock?
1) there is a known activity of rocks when formed
2) measure the activity now
3) compared activity now to original activity
4) determine the number of half lives that have elapsed
5) calculate the age from reference to half life
What are Gamma rays?
Very high frequency electromagnetic waves
Order the ionising power of different types of radiation from most ionising to least
1) alpha
2) beta
3) gamma
Order the penetrating power of different types of radiation from most penetrating to least
1) gamma
2) beta
3 alpha
What is the range of alpha radiation in air?
A few cm
What is the range of beta radiation in air?
Several 10s of cm
What is the range of gamma radiation in air?
Virtually infinite
What stops alpha radiation?
Paper
What stops beta radiation?
A few mm of aluminium
What stops gamma radiation?
A few cm of lead
What is meant by the term fission?
Splitting of a nucleus
What are sources of background radiation?
1) radiation from rocks/buildings/radon gas
2) cosmic radiation/radiation from the sun
3) radiation from medical sources
4) nuclear waste/accidents
5) some foods (bananas)
What is the activity of a sample of radioactive decay measured in?
Bq (becquerel) - 1 count per second - 1 Bq
How is radioactivity used in medical tracers?
1) a source which emits gamma radiation is injected into the skin
2) radiation is penetrating so is able to escape from the body and is detected by gamma cameras
3) the computer converts the reading to an on-screen displays showing where the radiation is being emitted from so the doctor can monitor the performance of various organs
4) radioactive material has to have a short half life so it decays before doing significant damage to the patient
Why is a source of alpha radiation not used in medical tracers?
1) would have insufficient range as not very penetrating
2) would be absorbed by patient
3) more ionising than gamma rays
How is radiation used in radiotherapy?
1) barrow beam of gamma rays is directed at an area of tissue (e.g. a tumour) that needs to be destroyed
2) done from a variety of different angles so as not to destroy the healthy surrounding tissue
Describe carbon dating
1) carbon dating can only be used on marrer that was once living
2) the same proportion of C-14 is found in the atmosphere and in living things
3) when organisms dies the C-14 becomes trapped inside of them and begins to decay so it’s radioactivity decreases over time
4) compared proportion of C-14 in dead tissue to living tissue and you can tell how many half lives have passed and hence estimate the age
How do smoke detectors work?
1) radiation from an alpha source ionises the air inside the detector
2) a voltage applied to a pair of electrodes causes a small ionisation current to flow between them
3) when smoke enters the detector the alpha particles are blocked by the larger smoke particles and the ionisation current fails triggering an alarm to go off
How can nuclear fission lead to a chain reaction?
1) neutrons released
2) neutrons slowed by moderator
3) can be absorbed by other uranium nuclei
4) causing further fissions
Why is shielding needed in nuclear reactors?
1) reactor material is radioactive
2) radiation ionises cells
3) radiation is very penetrating
What effect does the emission of a beta particle have on a nucleus?
Neutron changes into a proton
Why can radioactive sources be dangerous?
1) can not be seen
2) can damage cells
3) can cause cancer
How can the risks of working with radioactive sources be reduced?
1) reduce exposure time
2) handle with tongs
3) use shielding
4) wear film badge to monitor exposure
How can ionising radiation cause harm?
1) can damage cells
2) can cause mutation
3) can cause cancer
Why is it dangerous to live near rocks that release radon?
1) radon is heavier than air
2) collects in building
3) breathe into lungs
4) radioactive
What is fusion?
The joining of two atomic nuclei to form a different nucleus
Where does nuclear fusion happen naturally?
The sun
Why is fusion better than fission?
Doesn’t create waste
What are the differences between nuclear fission and nuclear fusion?
1) in nuclear fission the nucleus is split into two nuclei
2) in fusion two nuclei are joined together to form one nucleus
How do control rods control nucleus reactions?
They absorb some of the neutrons
What is meant by the term unstable?
Substance is radioactive so will emit radioactive particles or gamma rays
What does shielding do in a nuclear reactor?
Absorbed dangerous radiation
What does the coolant do in a nuclear reactor?
Removes energy from the reactor
What is the role of a fuel rod in a nuclear reactor?
Contains uranium for fission
What type of energy is released in a fission reaction?
Kinetic energy
Explain the role of the moderator in a fission reaction
1) slows neutrons
2) so neutrons can be absorbed by uranium
Explain in terms of neutrons what is meant by the term controlled nuclear fission
1) each fission of a nucleus is caused by a single neutron
2) each fission releases more than one neutron
3) excess neutrons can speed up the reaction
4) more fissions releases excess energy
5) control rods absorb neutrons
6) control rods regulate the rate of fission
Describe nuclear fission and how the chain reaction is controlled
1) nucleus absorbs neutron
2) splits into two daughter nuclei
3) extra neutrons releases
4) kinetic energy released
5) releases neutrons hit further nuclei
6) moderator slows down the neutrons
7) control rods absorb neutrons
8) control rods help prevent ‘runaway’ chain reaction
What is meant by the term fission products?
1) particles formed after fission
2) neutron and daughter nuclei
Why is it important to contain fission products for such a long time?
1) they are still radioactive
2) they have a long half life
Why is it dangerous to remove most of the control rods from a reactor?
1) fewer neutrons would be absorbed
2) fission rate would increase
3) too much energy produces
4) meltdown of core/reactor
why are beta particles used to detect the thickness of an aluminium sheet?
1) alpha particles would be stopped before they reached the detector as they do not penetrate enough
2) gamma rays would be too penetrative so would not be affected by changes in thickness
3) some beta particles will pass through the foil
4) thinner aluminium absorbs fewer beta particles
what happens to the nucleus of an atom when it undergoes beta decay?
1) proton number increases by 1
2) neutron number decreases by 1
