| how can radiation be detected using film badges? | when exposed to ionising radiation, photographic film will turn from being transparent to dark and non transparent
on each
the open window allows all types of radiation through, therefore showing exposure to beta and gamma radiation
one set of windows are plastic of different thicknesses allowing the person examining the film to tell what kinds of beta radiation they have been exposed to
another set of windows are different types of metals (including lead and tin) allowing the detection of gamma rays and other ionising radiation
the final exposure of the film will show how much and what kind of radiation someone has been exposed to |
| what three subatomic particles make up an atom | protons
neutrons
electrons |
| what is meant by ionisation | the addition or removal of electrons from an atom to form an ion, this can be carried out by nuclear radiation |
| why can ionisation take place? | because ionising radiation may come close to or collide with the atom and forces the electron away from the atom |
| what is alpha radiation | helium nucleus with 2 protons and 2 neutrons.
It has a large mass compared to other ionising radiation and a strong positive charge |
| what is beta radiation | a beta particle is a fast moving electron
it has a very small mass and a negative charge |
| what is a gamma ray | a high energy electromagnetic wave
caused by changes within the nucleus
they are part of the electromagnetic spectrum and so travel at the speed of light
they have no mass or charge |
| what is meant by penetrating power | ability to penetrate materials
the material is said to have absorbed the radiation |
| describe the penetrating power of alpha radiation | alpha radiation has a low penetrating power and the range of the alpha radiation in an absorbing material is less than that of beta or gamma.
alpha radiation transfers more energy to an absorber than beta or gamma radiation.
alpha radiation is absorbed by the thickness of the skin or by a few centimetres of air |
| describe the penetrating power of beta radiation | beta radiation is more penetrating than alpha radiation. it can pass through the skin but is absorbed a few centimetres of body tissue or a few millimetres of aluminium |
| describe the penetrating power of gamma radiation | the most penetrating of the three radiations. it can easily penetrate body tissue. it requires several centimetres of lead or about 1m of concrete to absorb it |
| describe the range, ionising power and detection in an electric field of alpha radiation | 3-5cm range
highly ionising
deflected towards the negative plate in an electric field |
| describe the range, ionising power and detection in an electric field of beta radiation | around 15cm range
regular ionising power
deflected towards the positive plate in an electric field |
| describe the range, ionising power and detection in an electric field of gamma rays | very long range (much longer than beta and alpha)
weak ionising power
no detection in an electrical field |
| what is meant by a radioactive atom | the nuclei of the atom is unstable and will naturally undergo radioactive decay, causing the release of ionising radiation which allows the nucleus to become more stable |
| what is each type of radiation caused by | a decay, either spontaneous (natural) or induced (a reaction has caused the decay) |
| name some sources of natural background radiation | cosmic rays - radiation that reaches the earth from outer space
animals
rocks - some rocks contain radioactive substances that produce a radioactive gas called radon
soil and plants |
| name some sources of artifical background radiation | x-rays - a form of radiation we use when going through air security or have an x ray in hospital
nuclear missiles - bombs have been exploded by man, releasing radiation into the environment
nuclear power - nuclear power stations have released radiation into the atmosphere |
| what percentage of background radiation does artificial radiation account for? | around 15 percent
nearly all of it comes from medical procedures |
| describe how radiation can be detected | using a Geiger muller tube
the gm tube is a hollow cylinder filled with gas at low pressure. the tube has a thin window made of Mica at one end. There is a central electrode inside the GM tube. A high-voltage supply is connected across the casing of the tube and the central electrode.
When the alpha, beta or gamma radiation enters the tube it produces ions in the gas, the ions created enable the tube to conduct. A current is produced in the tube for a short time, producing a voltage pulse. Each voltage pulse corresponds to one ionising radiation entering the GM Tube. The voltage pulse is amplified and counted |
| how can radiation be detected using film badges? | when exposed to ionising radiation, photographic film will turn from being transparent to dark and non transparent
on each side of the film badge are various 'windows'
the open window allows all types of radiation through, therefore showing exposure to beta and gamma radiation
one set of windows are plastic of different thicknesses allowing the person examining the film to tell what kinds of beta radiation they have been exposed to
another set of windows are different types of metals (including lead and tin) allowing the detection of gamma rays and other ionising radiation
the final exposure of the film will show how much and what kind of radiation someone has been exposed to |
| what is the formula for (radio)activity | A=N/t
where time is in seconds
Activity in Becquerels (Bq)
Number of disintegrations has no unit |
| what is meant by activity | the number of radioactive atoms which disintegrate and emit radioactivity per second
number of disintegration per unit time |
| what is background radiation | Radiation that is present in the atmosphere; can be caused by
natural materials (granite rocks) or man-made materials (hospital
waste) |
| what must be done to ensure activity of a radioactive source is calculated correctly | background activity must first be measured and taken into account |
| how can background radiation level be found | with no radioactive sources in the room, start a stopwatch and GM Tube with a counter at the same time
After 60 seconds, stop the GM tube and counter and record the number of counts in 60 seconds
Calculate the background activity in the room
repeat this process a number of times and find the average background activity |
| what is meant by half life | the time taken for the activity of a radioactive source to reduce by half |
| describe how half life of a source can be measured | before the source is used, the background count rate is measured using a GM tue connected to a counter, the count rate from the source is measured at fixed intervals over a period of time
the background count is then subtracted from each measurement of the count rate and the actual count rate from the source is calculated (this is known as corrected count rate)
a table and a graph can then be plotted of corrected count rate against time and this can be used to calculate the half life of the source |
| what is dosimetry | the way in which we can quantify the biological effect of radiation on humans |
| what is meant by absorbed dose | the energy absorbed per unit mass of the absorbing material
it is given the symbol 'D'
ionising radiation carries energy, and this energy can be absorbed by tissue and possibly cause damage to the tissue |
| what is the formula for absorbed dose? | D=E/m
Where D is absorbed dose in Grays (Gy)
E is energy in Joules
m is mass in kg |
| what is meant by equivalent dose? | a measure of the biological effect of radiation due to several factors
It is given the symbol 'H' |
| what factors do equivalent dose depend on? | type of radiation
the absorbed dose
the body organs/tissues that have been exposed to said radiation |
| what is meant by radiation weighting factor? | a measure of the harmful effect of nuclear radiation on human tissue
It is given the symbol Wr |
| What is the formula for equivalent dose? | H=DWr
Where H is measured in Sieverts (Sv)
Absorbed dose in Grays (Gy)
Radiation Weighting factor has no unit |
| what is meant by equivalent dose rate | the equivalent dose absorbed per second |
| what is the formula for equivalent dose rate | Ḣ=H/t
Where Ḣ is equivalent dose rate in sieverts per second (Sv s-1)
H is equivalent dose in sieverts
t is time in seconds |
| what is meant by effective dose? | measure of the risk of long-term effects of ionising radiation on the human body, organs and tissues |
| what is the average annual background radiation in the UK/ average equivalent dose for a member of the public due to background radiation | 2.2mSv |
| what is the annual effective dose limit for a member of the public? | 1mSv |
| what is the annual effective dose limit for a radiation worker? | 20mSv |
| describe ways in which we can minimise the dangers of ionising radiation? | keeping radioactive sources away from the body and never bringing them close to the eyes
limiting time of exposure to ionising radiation
shielding radioactive sources fro the body and handling them using tongs
storing radioactive sources in lead lined containers to ensure they have no exposure to the environment while in storage
wearing goggles and washing hands after using radioactive sources
monitoring radiation a person receives using film badges
all areas containing ionising radiation will show the hazard symbol |
| what are the biological effects of radiation? | cells can be altered and their functions changed because of ionising radiation
cells can be destroyed
exposure to ionising radiation can lead to the creation of cancer cells |
| name practical uses of ionising radiation | destroying cancer cells
radioactive tracers
sterilising medical instruments
irradiating foods |
| describe how ionising radiation can be used to kill cancer cells | gamma rays can be directed through the body to target tumours that cannot be treated with conventional surgery
the positioning and the intensity of the gamma ray sources are carefully calculated to ensure that the cancer cells receive enough radiation to kill them while the surrounding tissue remains in healthy condition |
| describe how radiation is used in radioactive tracers | ionising radiation can also be used to trace blood flow around the body. If a liquid containing a gamma source with a short half life is injected into your blood, it will be traced around your body
where there is a blockage the activity of the radiation will be highest due to collection of blood. Using a gamma camera , a special gamma ray detector - these areas can be located |
| how can ionising radiation be used to sterilise medical equipment | medical instruments are too expensive to be thrown away so are washed several times in hot water and then resealed in plastic wrapping. Then the whole package is irradiated with a dose of gamma rays.
Any bacteria in the container are now destroyed and the instrument remain sterile until the package is opened. |
| how can ionising radiation be used to irradiate food | foods with a high sugar and water content are often irradiated with gamma radiation to destroy any bacteria which may cause them to spoil quickly
the food does not remain radioactive after exposure to gamma rays so is safe to eat |
| what is a nuclear reaction | when the nucleus of an atom changes, new nuclei are formed and energy is released |
| describe nuclear fission | the process by which energy is released when a large atom is hit by a neutron, becomes unstable and splits into two or more smaller pieces plus two or three neutrons
when this happens some of the mass of the atom is lost and is converted directly to heat energy. This heat energy can be used to generate electricity in a nuclear power station |
| what is a chain reaction | Process that normally happens in a nuclear reactor; the splitting of an
uranium nucleus by a neutron which releases neutrons and causes
further nuclei to split; release large values of energy |
| what is nuclear fusion | the process by which energy can be released when two smaller nuclei fuse together to form a larger nucleus
this is the same process that occurs within stars such as our sun that produces heat energy and light |
| describe how nuclear reactions are used in nuclear power stations to generate electrical energy | in nuclear power stations, nuclear fuels like uranium and plutonium undergo controlled chain reactions in the reactor to produce heat energy. The chain reaction is controlled by Boron control rods. As boron is a non-fissile material it will not undergo a fission reaction when bombarded with neutrons. When the boron absorbs the neutrons, the chain reaction will slow down due to the lack of neutrons producing reactions. In times of high energy demand, control rods are raised, allowing more reactions to take place, and control rods are lowered in times of low demand to absorb neutrons and lower the number of reactions and the heat energy produced. The heat from the nuclear reaction is used to change water into steam in the boiler, this steam drives the turbine as heat energy is converted to kinetic energy. This then causes the production of electrical energy from kinetic energy. |
| describe the advantages of nuclear fuels | unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulphur dioxide
1kg of nuclear fuel is the same as 2.9 million kg of coal
nuclear fuels can easily be transported by road or rail since smaller volumes of nuclear fuels are used compared to the likes of coal
Waste products are produced in small volumes |
| describe the disadvantages of nuclear fuels | nuclear fuels are non-renewable sources of energy
if there is an accident, large amounts of radioactive material could be released into the environment (although, modern reactor designs are extremely safe so this rarely happens)
nuclear waste remains radioactive and hazardous to health for thousands of years, so it must be stored safely |
| what is a fusion reactor | a proposed form of power generation which would be an ideal way of generating electrical energy from nuclear fusion reactions
it would work by combining isotopes of hydrogen |
| what would be the difficulties of using a fusion reactor to generate electrical energy | there would have to be huge amounts of energy in order for the fusion reaction to take place
once the reaction has begun, it can be sustained but the atoms that fuse form a plasma, which would be at a temperature of millions of degrees, so would have to be contained using a very strong magnetic field |
