NUCLEAR PHYSICS Flashcards

Question

Measuring engine wear (txtbook)

Answer 1

Detecting underground pipe leaks Modelling oil reservoirs Investigating uptake of fertilisers by plants Monitoring uptake of iodine by thyroid gland

Answer 2

Light nuclei - 0

Answer 3

If the daughter nucleus is in an excited state after emitting an alpha or beta particle, it emits a gamma photon to move to its ground state

Answer 4

The work that must be done to separate a nucleus into its constituent neutrons and protons

Answer 5

The difference in mass between the nucleus and the constituent nucleons

Answer 6

* to define a precise location where the scattering takes place * so that the scattering angle can be determined accurately.

Answer 7

Some α particles are scattered through very large angles (>90°, or back towards the source). This can only occur if an α particle collides with a particle of much greater mass than its own mass.

Answer 8

α radiation is highly ionising, hence causes cancer/damages cells/kills cells/affects DNA. Outside the body it is less damaging, because it is absorbed by the skin (or is stopped by the skin, or causes a burning sensation). Inside the body it is more damaging, because it is able to produce ionisation in vital organs such as lungs. Will continue to ionise body until removed

Answer 9

γ rays are very penetrating (or α or β rays would not be detected outside the body). γ rays are less ionising, hence less hazardous to patients (or α or β rays are more ionising and more hazardous).

Answer 10

The background count rate is very much smaller than the measured count rate (background count rates are typically less than 1 counts s −1 ). Random fluctuations in the measurements are greater than the background ground count rate

Answer 11

* The activity is high (so only a small sample is needed). * The radioisotope decays quickly. * There is less risk to the patient. * The medical test is of short duration. Because T1/2 ∝1/lambda

Answer 12

* Electrons are not subject to the strong nuclear force. * With α particles the closest distance of approach is measured, rather than R. * Electrons cause far less recoil. * Electrons give greater resolution. * High energy electrons are easier to produce.

Answer 13

Knew the atom contained electrons, Rutherford discovered how the positive charge was distributed

Answer 14

α particles must have the same speed or slow α particles would be deflected more than faster particles *on the same initial path* Container must be evacuated so particles aren't absorbed by air α source must have a long half life or later readings would be lower than earlier ones due to decay of the source nuclei

Answer 15

β particles absorbed by air molecules, producing γ photons (Electron capture can produce γ photons due to excitation principles - excess e etc)

Answer 16

Time taken to regain non conducting state after receiving ion, typically of order 0.2ms - Another particle received in this time won't cause a voltage pulse, Therefore count rate should be no greater than 1/0.2s = 5000s^-1

Answer 17

Radon gas can accumulate in poorly ventilated areas of buildings in certain locations

Answer 18

2x the thickness

Answer 19

ΔN is proportional to N, the number of nuclei remaining at a time T, and proportional to the duration of time Δt Therefore ΔN = -λNΔt And A = -λN λ is decay constant, negative necessary as ΔN is a decrease

Answer 20

Fitting in a radioactive piston ring - as ring slides along piston compartment, radioactive atoms transfer from ring to engine oil, by measuring radioactivity of oil, mass of radioactive metal transferred can be measured and rate of wear calculated. Metal ring can be made radioactive by exposing it to neutron radiation in a nuclear reactor. Each nucleus that absorbs a neutron becomes unstable and emits a beta- particle

Answer 21

Detecting pipe leaks - inject tracer into flow, detector on surface above pipeline used to detect leakage Investigating uptake of fertiliser by plants - Plants watered with a solution containing fertiliser, by measuring radioactivity of leaves, amount of fertiliser reaching them can be determined Monitoring uptake of iodine by thyroid gland - Patient given solution of sodium iodide. Activity of patient's thyroid and activity of an identical sample prepared at the same time measured 24hrs later Monitoring metal foil thickness - foil made by two rollers - detector measures amount of radiation passing through foil - if reading is too low, rollers move closer together and converse

Answer 22

At said distance d, kinetic energy of particle = potential energy of system containing nucleus + particle

Answer 23

Their de broglie wavelength is about the same as the diameter of a nucleus

Answer 24

λ=h/mv, as electrons have high energy, travel close to speed of light, so λ =h/mc --- E = mc² λ =hc/E

Answer 25

of order of 10^-15 (femtometres)

Answer 26

Rsinθ = 0.61λ, where λ is the de broglie wavelength of the electrons

Answer 27

Scattering of beam electrons by nuclei occurs due to their charge - as they are attracted to nuclei, this causes the intensity to decrease as angle of incidence increases (ask why) Diffraction of electron beam causes intensity minima and maxima to be superimposed on above effect, provided de broglie wavelength isn't greater than nucleus diameter. Superimposed intensity variation similar to concentric bright and dark fringes when a beam of monochromatic light is directed at a circular gap/object. Angle from first minimum is measured and used to calculate nuclear radius

Answer 28

Charge on nucleus was Ze, however mass was greater than Zmp Used to explain why mass number of any nucleus greater than H1 is greater than its atomic number

Answer 29

Some α particles are scattered through very large angles (>90°, or back towards the source). This can only occur if an α particle collides with a particle of much greater mass than its own mass.

Answer 30

A=λN given GM detector receives all radiation from sample (which is false)

Answer 31

cosmic rays; radioactive rocks (or ground, or building materials); nuclear weapons testing (or nuclear accidents); nuclear power industry; discharge of nuclear waste; radioactive gases in the air; medical waste

Answer 32

The background count rate is very much smaller than the measured count rate (background count rates are typically less than 1 counts s −1 ). Random fluctuations in the measurements are greater than the background ground count rate.

Answer 33

* The activity is high (so only a small sample is needed). * The radioisotope decays quickly. * There is less risk to the patient. * The medical test is of short duration Because T1/2 ∝  1 , it follows that a radioisotope of short half-life will have a large value of λ, and therefore a high activity when it is introduced into the patient. The sample used is small and it soon decays to a negligible activity

Answer 34

Take two and average them

Answer 35

* Technetium 99-m emits only γ radiation... * hence radiation may be detected outside the body (or it is a weak ioniser and causes little damage). * It has a short half-life and will not remain active in the body for long after use. * Its half-life is long enough for it to remain active during diagnosis. * When needed it may be prepared on site. * It has a toxicity that can be tolerated by the body.

Answer 36

Similar to the length of the medical procedure - minimises radiation dose to patient. However if it's very close, the sample must be prepared at the place it'll be used

Answer 37

The mass of an object changes with it's speed, and no object can move at the speed of light (E=mc^2) + Moving clocks run slower than stationary clocks, fast moving objects appear shorter than when stationary

Answer 38

The parent nucleus decays to an alpha and a daughter nucleus and the difference in energy E is converted to kinetic energy of the two. However momentum is also conserved so they have equal and opposite momentum, meaning that the energy of the alpha is completely specified p^2/2Ma + p^2/2mN=E. So all alpha particles from such a decay have the same energy and the same velocity (which means the same range)

Answer 39

ΔMc² Where M is the mass of an alpha particle - energy conservation

Answer 40

Energy shared in variable proportion between β particle, nucleus ,neutrino and antineutrino. When β particle has maximum Ek, other particles have negligible in comparison. Maximum Ek of β particle is slightly less than energy released in the decay due to recoil of the nucleus

Answer 41

Nucleus emits a neutrino which carries away energy released in decay. Atom also emits an X ray photon when inner shell vacancy due to electron capture is filled.

Answer 42

Subtract mass of electrons

Answer 43

Working out magnitude of electrostatic force of repulsion between 2 protons at a separation of 1fm (approx size of nucleus)

Answer 44

High energy electron scattering experiment shows nucleons are evenly spaced at about 10^-15m away from each other - within attractive range of sf so only acts between nearest neighbour

Answer 45

Magnitude determined by equating to electrostatic force between protons. Acts over a distance of 2-3fm, so work done over this distance = fs in order of millions of ev

Answer 46

Work that must be done to separate a nucleus into constituent neutrons and protons. (When a nucleus forms from separate neutrons and protons, energy is released as the strong force does work in pulling the nucleons together - mass of nucleus is less than constituents)

Answer 47

Average work done per nucleon to remove all nucleons from the nucleus

Answer 48

Nucleus with more binding energy per nucleon is more stable

Answer 49

Nuclear fission - Large unstable nuclei splits into two smaller, more stable fragments - binding energy increases. Fusion - Small, light nuclei fusing to make a larger nucleus - has more binding energy per nucleon than smaller nuclei, so binding energy also increases in this process, provided nucleon number of new nucleus < about 50 Change in binding energy per nucleon ~ 0.5MeV in a fission reaction and can be about 10x in a fusion reaction

Answer 50

A single thermal neutron is absorbed by a nucleus - forming an unstable, heavier nucleus which undergoes fission and is split into 2 daughter nuclei and more neutrons.

Answer 51

One that is in "thermodynamic equilibrium" - moving at the same speed as its surroundings

Answer 52

Larger SA:mass ratio of fissile material, more likely for neutrons to escape, e.g. fewer neutrons would escape a sphere as opposed to a strip. In turn more neutrons go on to cause fission in a sphere

Answer 53

Mass of the fissile material must be greater than the critical mass (some neutrons escape the fissile material w/o causing fission or are absorbed by nuclei without undergoing fission). If mass is below, too many neutrons escape due to large sa:mass ratio.

Answer 54

Neutron loss depends on surface area, neutron production depends on mass - high sa:mass ratio - greater loss than there is production, more neutrons escape

Answer 55

Fossil - burns to release energy Nuclear - Decays to release energy

Answer 56

Nuclear energy in fuel Kinetic energy in fission products Internal energy of water + steam Kinetic energy of water + steam Kinetic energy of turbine

Answer 57

Neutrons are penetrating particles (bc they're uncharged), and so are likely to leave the material without interacting with any nuclei Uranium atoms only make up a small amount of the fissile material (control energy output) A slow moving neutron is more likely to cause fission than a fast moving one (think it spends longer around the pull of the nucleus)

Answer 58

Fuel rods spaced evenly in a steel vessel (reactor core) - contain enriched URANIUM. Control rods - lowered to absorb neutrons - depth is adjusted to keep the number of neutrons in the core constant so on average one neutron from each fission event goes on to cause another fission, keeps power output constant. Greater depth reduces output. Moderator - surrounds fuel rods and slows down neutrons by repeated collisions with moderator atoms. Reactor is called a thermal fission reactor as fission neutrons are reduced to the around the same Ek as moderator molecules. Coolant - Removes thermal from reactor core + neutrons(prevent overheating) should have a low specific heat capacity so that a large amount of thermal energy can be absorbed without changing its temperature (heating up), e.g. water of CO2

Answer 59

A smaller object will have a higher surface area to volume ratio compared to a larger object with the same shape. This means that for a given amount of heat energy, a smaller object will have more surface area available to lose heat than a larger object

Answer 60

Using mechanical model of moderation by elastic collision - when particles collide, there is a higher proportion of kinetic energy transfer. m(neutron =1) consider a neutron incident at velocity u on a stationary nucleus mass m, rebounds at speed v and nucleus recoils at speed V u+v = mV u²=v²+MV² solving gives v=u(1-m)/(1+m) ratio of initial to final ek = (u/v)² = [(1+m)/(1-m)]² - greater transfer as m approaches 1 - atoms with light nuclei suitable for moderation - transfer greatest proportion of Ek per collision, but it's also important that they don't absorb the neutrons. Commonly graphite(carbon) or water used as a moderator

Answer 61

Must have a high boiling point and be able to absorb neutrons well (boron + cadmium)

Answer 62

Reactor core is a thick steel vessel designed to withstand high temperature and pressure in reactor core - absorbs β radiation and some of the γ and neutron radiation from core Core is in a building with thick concrete walls - absorb neutrons and γ photons that escape from the vessel Reactors have emergency shut down system - fully insert control rods to completely stop fission Sealed fuel rods inserted and removed through remote handling devices - rods are more radioactive after than before

Answer 63

Before contain U235 and 238, which are only α emitters, and absorbed by fuel cans After use emit β and γ radiation due to many neutron rich fission products that form. Also contain Pu239 as a result of U238 absorbing neutrons - very active α emitter which can cause lung cancer if inhaled

Answer 64

Nuclear power stations, specialist users in university and industry, hospitals that use radioactive isotopes for diagnosis/therapy.

Answer 65

Disposal by diluting - diluting radioactive water from nuclear power stations' cooling systems with large quantities of water and dispersing it into the sea

Answer 66

Count rate is approximately constant

Answer 67

Electron + antineutrino - nucleus becomes net positive charge Often resolved by attracting/losing extra electron (depending on type of decay) Beta particle has a high Ek so escapes before it can be influenced by the electric field

Answer 68

e.g. spent fuel rods - removed by remote control then stored underwater in cooling ponds for up to a year as they continue to release heat due to radioactive decay. In Britain rods are transferred in large steel casks to THORP reprocessing plant - unused U and Pu removed and stored in sealed containers for further use, rest of radioactive material stored in deep trenches in Sheffield (sealed containers) -Must be stored for centuries as it contains long lived radioactive isotopes which must be prevented from contaminating food and water supplies problems - no one wants storage in their own locality, nor do people want waste to be carried through their locality to another location.

Answer 69

Radioactive isotopes with low activity and containers of radioactive materials are sealed in drums encased in concrete and stored in buildings with walls of reinforced concrete

Answer 70

e.g. Lab equipment + protective clothing are sealed in metal drums and buried in large trenches

Answer 71

Ensures that radioactive waste is stored safely in secure containers until activity in significant

Answer 72

* Both processes cause an increase in the binding energy per nucleon. * This energy is released as the kinetic energy of the products of the reaction. * The increase in binding energy per nucleon is greater in a fusion reaction than in a fission reaction. * The binding energy of a large nucleus is very much greater than that of a small nucleus, because the former contains many more nucleons. * The net increase in binding energy during the fission of a large nucleus is therefore greater than that occurring during the fusion of two small nuclei. It is useful to look at the slopes of the fusion and fission sections of the binding energy per nucleon curve. One fusion reaction may release about 5 MeV nucleon−1 , but only a few nucleons are involved, and so the total energy released may be only about 20 MeV. The fission of U 235 92 releases about 0.9 MeV nucleon−1 , but almost 240 nucleons are involved and so around 200 MeV of energy is released

Answer 73

Energy is released because * fusion of two nuclei increases their binding energy per nucleon * the fusion reaction produces an increase in the mass difference (or the nucleus formed is more stable than the two original nuclei). Fusion is difficult to achieve because * each of the two original nuclei has a positive charge * the electrostatic repulsion of these positive charges has to be overcome.

Answer 74

repulsive under 0.8fm, prevents nucleus from collapsing on itself More neutrons are needed to hold nucleus together / add to binding force/increase instability/reduce stability Fewer protons are required so as to reduce the repulsion/reduce instability/increase stability

Answer 75

(Small amounts of fossil fuel used) so little greenhouse gas emissions/less global warming/less CO2/less climate change. {not no greenhouse gas} 2. (Less fossil fuel used) so cleaner air. 3. Small amounts of fuel consumed to get the same/large amount of power/energy. 4. Nuclear power can be produced continuously{condone use of constant} (whereas renewables are dependent on sunlight/wind etc). 5. Some (but not all) nuclear power stations can adjust their output quickly. 6. Benefit of producing medical isotopes.

Answer 76

To become radioactive the nucleus has to be affected which (ionising) radiation does not do The energy of the radiation is insufficient to induce radioactivity.

Answer 77

Emission of ionizing radiation caused by changes in nuclei of unstable atoms

Answer 78

Short half life and fast decay

Answer 79

Fragments repel each other (both positive) with sufficient force to overcome strong force. Fragment nuclei and neutrons gain Ek. Two daughter nuclei are smaller and more tightly bound

NUCLEAR PHYSICS Flashcards

(109 cards)