Fichas
Unit 5: Nuclear and Thermal Physics
Fichas del conjunto (48)
- 1Define binding energyThe energy released when a nucleus is formed
or
The energy required to separate the nucleons from a particular nucleus - 2Describe the nature and properties of alpha radiation2 protons and 2 neutrons, +2 relative charge, highly ionising, relatively slow (10^7 m/s), low penetrating ability (stopped by paper / skin)
- 3Describe the nature and properties of beta radiationelectron emitted from the nucleus, -1 relative charge, medium ionising ability , fast speed but variable (~10^8 m/s), medium penetrating ability (stopped by 5 mm of aluminium)
- 4Describe the nature and properties of gamma radiationhigh energy EM radiation, 0 relative charge, low ionising ability, speed of light (3x10^8 m/s), highly penetrating (absorbed by 10cm of lead / metres of concrete)
- 5Describe the principles of Rutherford scatteringAlpha particles fired at gold foil, most particles pass straight through undeflected or with very small deflections.
1 in 8000 suffer a large deflection (greater than 90 degrees). Atom is mostly empty space with a tiny, dense positive nucleus. - 6Compare the dangers of different radiation inside and outside the bodyGamma - least dangerous, most passes through body without absorption, least ionising also.
Beta - dangerous inside and outside, as beta penetrates the skin, damages DNA
Alpha - only dangerous inside the body, highly ionising and damages DNA - 7Describe how background radiation should be measured and taken account of in experimentsUse G-M tube to record counts over 5 minutes without source present. Calculate count rate for background. Subtract background count rate from all readings taken during experiment.
- 8Describe the tracks of alpha, beta and gamma radiation in cloud and bubble chambersAlpha - bold and straight
Beta - fainter tracks, may be tortuous if travelling slowly
Gamma - no tracks, but may cause secondary radiations
(Alpha and beta will be curved if magnetic field is applied) - 9Describe the inverse square law for gamma radiationIntensity is proportional to the inverse of the distance to a source squared.
If the distance is doubled, the intensity decreases by a factor of 4. - 10Define the BecquerelAn activity of 1 Becquerel means 1 nucleus decays each second
- 11Define radioactive decay constantThe probability of a nucleus decaying in a certain time period (usually per second)
- 12Define half lifeThe time for half the radioactive nuclei in a sample to reach half the original level
or
The time for the intensity of radiation from a source to reach half the original level - 13Carbon-14 has a half life of 5700 years Why is radiocarbon dating only useful if an artefact is older than a few hundred years old, but not older than 60 000 years?200 years - little change in the activity of the carbon-14 in an artefact
60 000 years - too few carbon-14 nuclei remain in sample to differentiate between sample and background radiation - 14Describe the features of the N against Z graph for nuclear stabilityN = Z up to approx. 20
Line curves upwards and passes through points Z=80, N=120
Alpha emitters - heavy nuclei
Beta minus (and neutron) emitters - above line
Beta positive emitters - below line - 15How do atomic number and mass number change in alpha particle emission?Atomic number decreases by 2, mass number decreases by 4
- 16How do atomic number and mass number change in beta minus particle emission?Atomic number increases by 1
Mass number doesn't change - 17How do atomic number and mass number change in beta plus particle emission?Atomic number decreases by 1
Mass number doesn't change - 18How do atomic number and mass number change in gamma ray emission?No change to either number
Gamma rays are emitted by a nucleus in an excited state as it returns to ground level - 19Carbon-14 decays by beta minus decay What are the products of the decay?A neutron changes to a proton
An electron (beta minus particle)
An anti-electron neutrino - 20Oxygen-15 decays by beta plus decay What are the products of the decay?A proton changes to a neutron
A positron (beta plus particle)
An electron neutrino - 21Describe electron captureAn atomic electron from an inner orbital is absorbed by a proton in the nucleus.
The proton decays to a neutron, emitting a neutrino. - 22Technetium-99m is used in radiotherapy Describe whyTechnetium 99-m is a gamma emitter (gamma rays can be detected outside the body) and has a half life of 6 hours
6 hours is long enough for the procedure to take place but not too long that the patient remains radioactive for extended time periods - 23Describe two methods to determine nuclear radius and the basic principles involvedElectron diffraction - electrons fired at thin slice of material, electrons behave like waves forming a diffraction pattern
Rutherford scattering - alpha particles are scattered by gold nuclei and the angle measured to determine closest approach - 24Describe how nuclear radius depends on mass numberAs mass number increases so does nuclear radius, the density of the nucleus remains constant
- 25Define the moleThe number of atoms in 12g of carbon-12
- 26How is the mass defect used to calculate the energy released in fission and fusion reactions?The mass defect in amu is multiplied by
931.5 MeV/c^2
or the mass defect is converted to kg and
E = mc^2
is used - 27Explain how the binding energy curve shows that energy is released in both fission and fusionEnergy is released when binding energy (per nucleon) increases
Movement towards the peak of the curve involves fusion (joining) of lighter nuclei and fission (breaking up) of heavier nuclei
The peak is at a mass number of 56 (iron) - 28In a nuclear power station, what is meant by chain reaction?Each fission releases one neutron (on average) which goes on to cause another successful fission reaction
- 29State one material that is used as a moderator in a nuclear power stationgraphite
or
water - 30State one material that is used as a coolant in a nuclear power stationwater
- 31State one material that is used to make control rods in a nuclear power stationboron
- 32How is the chain reaction controlled in nuclear power stationsControl rods are lowered to decrease the number of neutrons released for further fission reactions (and decrease energy output)
The opposite happens to increase energy output - 33Uranium used in nuclear reactors needs to be enriched. What does this mean?Uranium ore dug out of the ground contains 1% U-235. Uranium fuel needs to contain 2-3% U-235. The uranium is therefore enriched to increase the proportion of U-235.
- 34U-235 is fissile, U-238 is not. What happens to U-238 in a nuclear reactor?U-238 absorbs neutrons and (after two beta decays) becomes Pu-239
- 35What is the function of the moderator in a nuclear reactor?To reduce the speed of neutrons to thermal speeds. Only slow moving neutrons are absorbed by U-235 and cause fission. Fast moving neutrons are scattered elastically.
- 36What is the function of the coolant in a nuclear reactor?Transfer energy from the reactor vessel to the heat exchanger which uses the energy to boil water, steam turns a turbine which turns a generator
- 37How is different levels of radioactive waste dealt with?Low Level - Buried in sealed containers
Intermediate Level - Solidified in concrete and buried in sealed containers
High Level - Placed in cooling ponds until activity decreased (a few months), then vitrified and buried in sealed containers - 38Describe the shielding around a nuclear reactorThick walled steel cylinder to absorb gamma radiation
Several metres of concrete to absorb neutron radiation (and further reduce gamma) - 39Define specific heat capacityThe energy required to raise the temperature of 1 kg of a substance by 1 degree Celsius (or Kelvin) with no change of state
- 40Define specific latent heat of fusion / vaporisationThe energy required to change the state of 1 kg of a substance from solid to liquid (fusion) or from liquid to gas (vaporisation) with no temperature change
- 41Define the Avogadro constantThe no. of atoms in 1 mole of a substance
(specifically 12g of carbon-12) - 42State Boyle's LawFor a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume
- 43State Charles' LawFor a fixed mass of gas at constant pressure the volume is directly proportional to temperature in Kelvin.
- 44State the pressure lawFor a fixed mass of gas at constant volume, the pressure is directly proportional to the temperature in Kelvin.
- 45What is the equation of state for an ideal gaspV = nRT
- 46What are the properties of an ideal gas?High temperature
Identical molecules
Low pressure - 47What assumptions are made in the derivation of: pV = 1/3Nmc^2The molecules are identical. Collisions between molecules and with the container are perfectly elastic. The motion is random. There are a very large no. of molecules so that statistics can be applied. Molecules are small compared to the distances between them.
- 48How does increasing the temperature of a gas affect the movement of the molecules (at constant volume)?The rms speed increases, so mean kinetic energy increases, which means the frequency of collisions increases, which raises the pressure within the container
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- Flashcards for AQA A Level Physics Unit 5: Nuclear and Thermal Physics
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- Michael Priest
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