Physics 7 - Radioactivity and Particles Flashcards
7.1 List the units and unit symbols of: activity of a radioactive sample
Becquerel (Bq)
7.2 what is the relative mass of an electron
1/2000
7.4 Where are alpha (α) particles, beta (β−) particles, and gamma (γ) rays emitted from and which ones are ionising
All are ionising and are emitted from an unstable nucleus
7.5 Describe the nature of alpha (α) particles, beta (β−) particles, and gamma (γ) rays **and give their nuclear symbol
Alpha ((_2^4)α) - slow moving helium nuclei (2p + 2n).
Beta ((_−1^0)e) - fast moving electrons.
Gamma ((_0^0)γ) - high energy electromagnetic radiation. Emitted after either alpha or beta
A + B have charge so are deflected by magnetic and electric fields. Gamma doesn’t.
7.5 Describe the penetrating power of alpha (α) particles, beta (β−) particles, and gamma (γ) rays
Alpha - poor penetration in materials because they have a large charge and mass. Stopped by paper and a few cm of air
Beta - moderately penetrating - few mm of aluminium
Gamma - very penetrating - stopped by a few cm of lead or a few metres of concrete
7.5 Describe and explain the ionising ability of alpha (α) particles, beta (β−) particles, and gamma (γ) rays
Alpha - strongly ionising - large charge and mass so easily knock off electrons
Beta - moderately ionising - have charge but small mass
Gamma - weakly ionising - no charge or mass and tend to pass through atoms. When they do collide they can cause damage.
7.6 practical: Design an experiment to investigate the penetration powers of different types of radiation
Set up a Geiger-Muller counter, and measure the background count for 30s (stopwatch). Divide the count by 30 and repeat and take an average.
Place the source in front of the detector and measure the count over 30s and determine the rate per second - then subtract background count. Repeat and take an average
Insert different materials between the source and the detector (paper, a few mm of aluminium, lead) and repeat the procedure.
If the count remains unchanged then it can penetrate the material; if it drops considerably then it can’t.
7.7 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the four main types of nuclear radiation (alpha, beta, gamma and neutron radiation)
Alpha - mass number drops 4, atomic number drops 2
Beta - mass number is unchanged, atomic number adds 1
Gamma - no change
Neutron - mass number decreases by 1, atomic number is unchanged
7.8 Explain how to balance nuclear equations in terms of mass and charge and give examples of the four main types of nuclear radiation
Mass and charge must remain equal before and after the decay.
The charge of a nucleus = atomic number. Mass of a nucleus = mass number
7.9 Give examples of how to detect ionising radiation
Photographic film or Geiger-Muller detectors
7.10 List the sources of background (ionising) radiation
Substances on Earth: air, food, building materials, soil, rocks
Cosmic rays: from the sun and outside our solar system (possibly supernovae or possibly other galaxies)
Living things: isotopes in plants and animals can be radioactive
Human activity: fallout from nuclear explosions, nuclear waste (tiny proportion)
7.11 Define the activity of a radioactive sample
The rate of decay of an unstable nucleus
N.B. detectors only pick up a fraction of activity - small aperture size
7.11 Describe how the activity of a radioactive source changes over time
Activity decreases exponentially over time (decreases by half every half-life)
7.11 Give the unit for activity and describe what it means
Becquerels - number of detections per second
7.12 Define half-life
Time taken for half of the nucleus to decay OR time taken for the activity to drop by half
7.12 How can a radioactive isotope be determined from a sample
Every radioactive sample has a different half life so you can use this to determine the isotope
7.12 Give the range of half-lives and state what determines the half-life of an isotope
The more unstable the nucleus, the shorter the half life.
Half lives vary from billions of years to thousandths of a second
7.13 Describe how to determine the half-life of an isotope given the initial activity, the final activity and the time taken
Remove the background radiation count from the initial and final activity.
Determine how many times it takes to divide the initial by two to get to the final (# of half lives)
Divide time taken by # of half lives
7.13 Describe how to determine the half-life of an isotope given an activity-time graph
Draw a line from half of the activity to the curve. Draw down.
To check, do the same for the next half and the time taken should be the same.
7.14 Give three uses of radioactivity in medicine and describe how the radioactive isotopes are used, including the properties of the radioactive isotope.
Medical tracers
• Use beta or gamma sources so they can penetrate the body and disappear quickly (short half life)
• Source is injected or swallowed and can be detected externally. Used to check whether organs use the elements they expect
Treat Cancer
• Use a gamma source to penetrate the patient, with a long half life so activity remains constant.
• Gamma kills cancer cells - and is carefully directed at the tumour to not harm the rest of the body.
Food and equipment sterilised
• Use strong gamma sources with a long half life
• Irradiate food or medical equipment to kill microbes
• Doesn’t damage equipment or food like high temperatures or chemicals
7.14 Give two uses of radioactivity in industry and describe how the radioactive isotopes are used, including the properties of the radioactive isotope.
Industrial tracers
• Short half life so its isn’t a long term hazard and gamma so it can be detected through pipes
• Detect leaks in pipes by placing the source in it, and where there is increased count above ground, the source is leaking.
Smoke detector
• Alpha, because it is stopped by air
• Ionize air so complete circuit is made, long half life so lasts a long time
• If smoke gets between detector and source, the alpha particles are absorbed and the circuit is broken so the alarm goes off.
7.15 Describe the difference between contamination and irradiation
Contamination - radioactive atoms get onto or into an object - then decay releasing radiation and causing harm
Irradiation - objects near a radioactive source are irradiated by it but do not become radioactive
7.16 describe the dangers of ionising radiations
Can cause mutations in living organisms, causing them to rapidly multiply - cancer
Can kill cells or tissues in higher doses.
7.16 Describe how you can reduce risks from contamination and irradiation
Irradiation
• Keep sources in clearly labelled lead boxes
• School - Use tongs to increase distance to source
• Industry - Stand behind barriers, be in a different room, use a remote-controlled arm
• Limit exposure time
Contamination
• School - wear gloves and use tongs
• Industry - wear protective suits and masks to stop breathing it in
7.16 Give examples of low-level radioactive waste
Clothing and syringes from hospitals and nuclear power stations
7.16 Give examples of high-level radioactive waste
Spent fuel rods, material from the processing of radioactive material
7.16 Describe the disposal of different levels of radioactive waste and the problems arising
Low-level waste - bury in a secure landfill site
High level waste - seal into glass blocks, then into metal canisters, then bury deep underground - can stay highly radioactive for thousands of years so is very dangerous
Issues - difficult to find a place to bury: must be geologically stable so it doesn’t leak (which could contaminate soil, plants or even drinking water)
