Nuclear Physics Flashcards
(121 cards)
1
Q
Atom
A
Particle made of protons, (neutrons) and electrons.
2
Q
Element
A
Type of atom with a specific number of protons.
3
Q
Nucleus
A
Core of an atom, consisting of protons and neutrons held together by the strong force.
4
Q
Nucleon
A
Particle in the nucleus i.e. protons and neutrons.
5
Q
Proton
A
Particle with 1 mass and 1 charge.
6
Q
Neutron
A
Particle with 1 mass and 0 charge.
7
Q
Electron
A
Particle with approximately 0 mass and -1 charge.
8
Q
Atomic Number
A
Z, number of protons in the nucleus of a specific atom.
9
Q
Atomic Mass
A
A, number of nucleons in the nucleus of a specific atom.
10
Q
Isotope
A
Type of atom, with specific numbers of protons and neutrons. Isotopes of an element have the same chemical properties due to having the same number of protons but have different physical properties due to differing numbers of neutrons.
11
Q
Nuclide
A
Specific nucleus, with certain numbers of protons and neutrons.
12
Q
Nuclear reaction
A
Any process causing changes to a nucleus. Mass number and charge must be conserved.
13
Q
Stable Nuclide
A
Specific nucleus that will remain the same indefinitely. Strong force is enough to overcome electrostatic repulsion between protons. For light elements (Z<21), require 1:1 ratio of protons to neutrons. For medium elements, require slightly more neutrons than protons. Heavy elements (Z>82) cannot be stable – size of nucleus is too great for the very short ranged strong force to hold it together.
14
Q
Stable isotope
A
Specific atom with a nucleus that will remain the same indefinitely.
15
Q
Unstable nuclide
A
Specific nucleus that will spontaneously change to become more stable.
16
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Radioisotope/unstable isotope
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Specific atom with a nucleus that will spontaneously change to become more stable.
17
Q
Radioactive
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Material containing unstable nuclei.
18
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Nuclear decay
A
Emission of particles (or energy) from a nucleus to become more stable.
19
Q
Activity
A
Number of decay events per second for a radioactive substance
20
Q
Half life
A
Measure of exponential decay rate for a nuclide. Time for half of the remaining particles to decay.
21
Q
Transmutation
A
Changing of one nuclide into another through nuclear decay.
22
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Daughter nuclide/isotope
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Product nucleus of nuclear decay.
23
Q
Decay series
A
A sequence of nuclear decays through multiple unstable nuclides to an eventual stable nuclide.
24
Q
Nuclear radiation
A
Particle or energy emitted from a nucleus.
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Alpha decay
Emission of an alpha particle from a nucleus that is too large to be stable.
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Beta minus decay
Emission of a beta (minus) particle from a nucleus that has too many neutrons as a neutron becomes a proton.
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Beta plus decay
Emission of a beta plus particle from a nucleus that has too few neutrons as a proton becomes a neutron.
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Gamma decay
Emission of a gamma ray from a nucleus that has too much energy to be stable. Commonly occurs after an alpha or beta decay.
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Ionising radiation
Radiation capable of adding electron to or removing electrons from atoms, turning them into ions. Alpha, beta and gamma radiation.
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Alpha particle/radiation
He-4 nucleus (2 protons, 2 neutrons). 2+ charge, travels at 0.1c, highly ionising, weakly penetrating.
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Beta minus particle radiation
Electron. -1 charge, travels at 0.9c, moderately ionizing, moderately penetrating.
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Beta plus particle radiation
Antielectron/positron. +1 charge, travels at 0.9c, moderately ionising, moderately penetrating. If it collides with an electron they will mutually annihilate emitting gamma radiation.
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Gamma ray/radiation
High energy photon of light. 0 charge, travels at c, weakly ionising, highly penetrating.
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Neutron radiation
Neutron. Not ionizing but can be absorbed by a nucleus, potentially transforming it into an unstable nuclide.
35
Mass defect
The difference in mass between a number of free nucleons and that many nucleons as a nucleus. Mass of the binding energy.
36
Binding energy
The energy lost by free nucleons in order to bond together as a nucleus. The energy required to separate all the nucleons in a nucleus into free particles.
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Binding energy per nucleon
The average energy lost by each nucleon in a nucleus. Measure of stability of the nucleus. Higher binding energy per nucleon – more stable nuclide. Peaks at Fe-56.
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Nuclear fusion
Joining of light nuclei to form heavier nuclei. Releases energy if the binding energy per nucleon increases, i.e. if moving towards Fe-56.
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Fusion reactor
Machine maintain stable fusion reaction to generate heat to generate electricity. Requires enormous temperatures and pressures to cause collisions between nuclei, overcoming the electrostatic repulsion. Currently consumes more energy than is produced – developing technology.
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Nuclear fission
Splitting of heavy nuclei into multiple lighter nuclei (and free neutrons). Releases energy if the binding energy per nucleon increases, i.e. if moving towards Fe-56. Can be spontaneous or triggered by absorption of free neutron.
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Fissile
Nuclides that will readily undergo fission reactions.
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Fission reactor
Machine maintaining stable fission reaction, typically to generate heat to generate electricity. Relies on stable chain reaction, fission can be triggered by neutrons and it emits neutrons.
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Fuel rods
Fuel must be enriched to contain a higher proportion of fissile material.
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Control rods
Material that absorbs free neutrons to control reaction rate in reactor. Control rods inserted if reaction rate too high.
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Moderator
Slows neutrons so that they can be more easily absorbed by nuclei to trigger further fission reactions.
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Shielding
Fission reaction and radioactive fission products emit radiation dangerous to workers. Reaction chamber must be shielded by metres of lead and concrete to absorb radiation, protecting plant workers.
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Nuclear waste
Fuel lasts a long time but produces waste that remains radioactive for extremely long timespans – must be stored safely.
48
Critical mass
The minimum mass of fuel required to sustain a fission chain reaction. Shape dependent, sphere is most efficient.
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Absorbed dose
Measure of amount of radiation exposure, based on energy of radiation and mass of target. d=e/m
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Dose equivalent
Measure of amount of radiation exposure, based on absorbed dose and type of radiation.
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Electrostatic Force
The long-range force of attraction between unlike charges and repulsion between like charges
The electrostatic and strong nuclear forces are responsible for holding atoms together
The electrostatic attraction between protons and electrons prevents electrons from leaving
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Strong Nuclear Force
Short range attractive force between nucleons in a nucleus
The strong nuclear force between nucleons balances the electrostatic repulsion between protons and holds the nucleus together
Keeps an atom from falling apart
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Neutron bombardment
Where neutrons are fired at nuclei until a neutron is absorbed by the nucleus
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Charge
A property of matter causing electric effects
Charged particles can be deflected by electric and magnetic fields and can be repelled by like charges, reducing their penetrating ability
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Ionising Ability
The ability of particles or radiation to ionise matter, generally by removing electrons in collisions
Ionising ability increases with increasing charge and decreasing speed
56
Penetrating Ability
A measure of how easily radiation passes through matter
Penetrating ability is greatest for radiation with a low ionising ability, e.g. faster moving, uncharged radiation that does not readily interact with matter
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Natural transmutation
Alpha and beta decay are examples of spontaneous transmutation, where one element is transformed into another in a natural process
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Artificial transmutation
Transmutations can also occur when a nucleus is deliberately struck by another nucleus or a subatomic particle, such as an α particle
This is known as artificial transmutation
Artificial transmutations include the nuclear reactions that occur in nuclear reactors and nuclear weapons
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Nuclear fission and fusion
In these reactions, larger nuclei can split into smaller nuclei (fission) or smaller nuclei can join together into larger nuclei (fusion), releasing huge amounts of energy
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Fission
In fission reactions, a target nucleus absorbs a neutron before splitting into two or more pieces, often releasing additional neutrons
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Fission Absorption
A nuclide that can undergo fission is said to be fissile
All fissile nuclides have high atomic numbers (e.g. 235U, 239Pu) and most do not occur naturally
Nuclides that need to absorb a very high energy neutron to undergo fission are said to be fissionable, but non-fissile
Most fission products radioactive
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Energy release in nuclear reactions
The mass of a nucleus is always less than the mass of its individual nucleons
He showed that mass can be converted into energy (and vice versa) under some circumstances
E = mc^2
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Binding energy
The energy required to split a nucleus into its individual nucleons (e.g. to split a helium nucleus into two protons and two neutrons)
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Chain Reaction
For a chain reaction to be sustained, enough of these neutrons must be absorbed by other fissile nuclei
If each fission can induce the fission of two other nuclei, the amount of fission reactions occurring and the energy released will grow exponentially
Whether this occurs depends on the proportion of fissile atoms present in the nuclear fuel
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Nuclear Fuel
A sufficient percentage of neutrons released must be absorbed by fissile nuclei
Naturally occurring uranium, consists of about 99.7 % non-fissile 238U and 0.7% fissile 235U (too low to sustain chain reaction)
To be used as nuclear fuel, the uranium ore must be enriched to ~4% 235U for nuclear reactors or ~90% for nuclear weapons
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Enrichment
Enrichment generally occurs by ultracentrifuge or electromagnetic separation or gaseous diffusion separation
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Critical Mass
The minimum spherical mass of enriched material required for sustained fission
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Nuclear Reactors
Fuel rods: long thin rods of fissile material
Moderator: material that slows the neutrons so they can be more readily captured
Control rods: material that absorbs neutrons to slow the chain reaction
Coolant: absorbs heat energy released in fission and transfers it to water to produce steam
69
Fuel Rods
Fuel rods typically consist of ~96% 238U and 4% 235U. The 235U undergoes fission, releasing energy and neutrons
While 238¬U is not fissile, it can absorb a neutron and form the fissile isotope 239Pu which can undergo fission, releasing more energy and neutrons
“Fast breeder reactors” take advantage of this reaction to produce more fissionable fuel (in the form of 239Pu)
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Moderator
The fast moving neutrons released in fission of 235U can be more readily captured by fissile nuclei if they are slowed down
A moderator is a material with small nuclei that is able to slow (moderate) these neutrons when they collide
Heavy water, graphite, H2, CO2
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Control Rods
If the nuclear chain reaction is able to continue in an uncontrolled manner, it will grow exponentially releasing more and more energy any neutrons
Control rods act to control the rate of fission by absorbing neutrons into their nuclei, preventing those neutrons from causing addition fission reactions
Boron
72
How a Nuclear Reactor works
A nuclear reactor core consists of the fuel and control rods inserted into the moderator
The control rods are raised or lowered into the core to control the rate of fission
The heat produced by fission heats the coolant which is piped to a heat exchanger/boiler
Heat from the coolant is used to boil water to produce steam which drives the turbines that power the generator
73
Nuclear Waste
While nuclear power is one of the safest power sources in terms of deaths per GW of electricity generated, it does produce waste that remains radioactive for thousands of years
This waste mostly consists of fission fragments produced in the decay of uranium and plutonium
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Nuclear Fusion
2 small nuclei fuse to make bigger one
Fusion releases more energy per nucleon than fission and does not produce radioactive waste (e.g. fission fragments)
Very difficult to achieve, electrostatic force of repulsion must be overcome to force nuclei close enough so strong nuclear force can take over
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Nuclear Fusion must overcome repulsion
To overcome this repulsion, the reactants must have extremely high kinetic energies (e.g. hundreds of millions of degrees, as found in stars)
In our sun, huge temperatures and gravitational pressure forces hydrogen and helium isotopes to fuse in the following reactions
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Higher binding energy
Nuclei with a higher binding energy are more stable as they take more energy to break apart
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Iron 56
Iron-56 has the highest binding energy per nucleon (e.g. is the most stable nucleus) with binding energy decreasing as mass number decreases or increases
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Very stable nuclei, what mass number?
Nuclei with a mass number between 40 and 80 are very stable due to their high binding energy
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Nuclei larger than iron
Nuclei larger than iron can undergo fission, releasing the extra binding energy as a lighter, more stable nuclei are formed resulting in a mass defect
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Nuclei smaller than iron
Nuclei smaller than iron can undergo fusion, releasing the extra binding energy as a larger more stable nucleus (that has a lower mass than the combined mass of the reactants) is formed
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Applications of fusion
Hydrogen bombs
The extreme temperatures required for fusion make it very difficult to design these reactors and commercial fusion reactors have not yet been developed
Fusion reactors have been a target of research, due to their potential to generate electricity without producing large amounts of harmful nuclear waste or greenhouse gases
82
Pest control
Small pests (e.g. aphids, as seen in the diagram to the right) can be sprayed with radioactive materials. Sometime later, a range of predators in the area are captured. The main predator of the pest can easily be identified as it will be the one that has the largest quantity of the radioactive isotope inside it. This knowledge is then used when releasing natural predators to provide biological control of pests.
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Sterile Insect Technique
Male insects can be sterilised using gamma radiation and then released into the wild. They mate with females which then lay eggs that are infertile. Over time, this reduces the population of that insect.
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Tracers in Plants
Phosphorus 32 injected into root of plant. Geiger counter used to detect movement and concentration of element through plant, helping biologist find how plant grows and reproduces.
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Thickness Gauges
Beta radiation used because it can be stopped by thicker metal but passes through thinner metal. If material is too thick, reading decreases and rollers adjusted to make material thinner. Opposite if reading too high.
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Leaks in Underground Pipes
Leaks detected by adding small amount of gamma emitting radioisotope to fluid. Area above ground where high concentration of radiation is detected corresponds to leak in pipe.
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Gaps in welds
Penetrating radiation passed through weld on radiographic film resulting in image of objects internal structure being formed on film. Energy absorbed by object is proportional to its thickness and energy. Energy not absorbed = exposure of the radiographic film. These areas will be dark on film. Areas of film exposed to less energy remain lighter. Areas of object where thickness has been changed by porosity and cracks appear darker.
88
Why are fission fragments radioactive?
Heavy isotopes require more neutrons to keep them stable. When fission occurs, there’s an excessive ratio of neutrons to protons. Therefore, the fragments undergo beta decay to try and become stable.
89
Explain whether an alpha emitter would be a more suitable radiation source to be used in the thickness detector.
No, Alpha particles have low penetrating ability and will be stopped by the plastic sheet
90
Would it be reasonable to use tritium as a radioisotope in medical treatment or diagnosis? Explain your reasoning.
No, it would be hard for the body to absorb a form of hydrogen gas for diagnostic purposes. The half life of the tritium is also too long for a radioactive isotope to be in the body emitting Beta negative particles.
91
Describe how the neutrons released in this reaction differ from those that took part in the initial fission reaction.
Uranium-235 can only absorb slow neutrons but the neutrons produced will have much greater speed when the nucleus splits
92
State and explain two precautions that workers at customs would employ to prevent any unwanted personal health issues.
Shielding from device: gamma rays require ~2m of concrete or many cm of lead to absorb the ionising radiation and prevent the workers from receiving an absorbed dose
Distance: workers would distance themselves from the device when in operation as the intensity is
inversely proportional to distance squared
93
Why is iodine-123 selected for different procedures?
Gamma has a lower ability to ionise hence less destructive to other cells. Gamma has greater penetrating ability than alpha or beta. Short half-life to reduce exposure time. Ability to concentrate at thyroid (if for thyroid cancer)
94
State the major obstacle needed to overcome in order to create a fusion reactor.
To create a fusion reaction, a large amount of energy is needed. The hydrogen particles must have sufficient kinetic energy to collide and fuse.
95
State and explain two benefits of a fusion reactor compared to a fission reactor.
No dangerous nuclear waste. Fusion is typically creating elements with low mass numbers that are stable.
Greater energy released per fusion number of nucleons/mass. About 10 times greater energy released
96
State and explain two ways the medical team can reduce or eliminate the effects of radiation on their own body:
Shielding from radiation. Staff can wear lead aprons or stand behind dense walls (concrete). These
materials stop the radiation.
Increase distance from source. Radiation can only travel a set distance in air.
97
Are fast neutrons or slow neutrons more damaging to humans? Explain why.
The effect of radiation on humans is measured in terms of the quality factor. The quality factor for fast neutrons is 10 compared to 3 for slow neutrons. This is because of the higher energy of the fast neutrons and they will therefore be more harmful.
98
Explain in detail how you could determine the type of radiation emitted.
Use the Geiger counter to measure the background radiation and then the activity of the sample at a certain distance. Measure activity at the same distance with some paper in the way. Measure activity at the same distance with aluminium foil in the way. Subtract background radiation from all measurements. If the activity didn’t change, it’s gamma radiation, if the activity decreased a lot with paper, it’s alpha radiation, and otherwise beta radiation.
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Gamma knife
Many sources of gamma rays are placed around the head, all aimed at cancer in the brain.
Each individual beam of gamma rays is too weak to cause significant damage.
* The individual beams intersect at the cancer, so it receives a much higher dose of radiation.
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Why are fission fragments radioactive?
Heavy isotopes need more neutrons to keep stable so when fission occurs, the fragments have an excessive ratio of neutrons to protons, so they undergo beta decay in an attempt to be stable.
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SPECT
Single photon emission computerised tomography. Detected by gamma camera.
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PET
Positron Emission Tomography
Position emitting radionuclide injected and accumulates in target tissue. As it decays it emits a positron which combines with a nearby electron resulting in 2 gamma rays in different directions. Detected by PET camera. Most used in oncology. Fluorine 18 tracer.
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PET-CT
PET with computed X ray tomography (CT)
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PET-MRI
Good for brain imaging, enables diffusion weighted imaging in soft tissue with dynamic contrast and magnetic resonance imaging
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Nuclear imaging and other techniques (X rays)
Difference is the positioning of radiation source. Inside (nuclear), outside (xray).
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Gamma imaging
Provides a view of the position and concentration of the radioisotope within body.
Organ malfunction indicated if isotope is partially taken up in organ (cold spot) or excess (hot spot).
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Advantage of Nuclear Imaging over X ray
Both bone and soft tissue can be imaged successfully
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Diagnostic Pharmaceuticals
Some chemical are absorbed by specific organs. You can attach various radioisotopes to biologically active substances. Once a radioactive form of these substances enters body, its incorporated into normal biological processes and excreted in usual ways.
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What do diagnostic pharmaceuticals do?
Theyre used to examine blood flow to brain, funcitoning of liver, lungs, heart, to asses bone growth. It can predict the effects of surgery and assess changes since treatment
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Radiation dose
Amount of pharmaceutical given is just sufficient to obtain required info before decay. Its medically insignificant. Paitent experiences no discomfort. Radioisotope must emit gamma rays of sufficient energy to escape from body and short enough half life to decay as soon as imaging finished
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Technetium 99 - in 80% of nuclear medicine procedures, isotope of artificially produced technetium
Half life 6 hours long enough to examine metabolic processes, short enough to minimise radiation dose
Decays by isomeric process (emitting gamma, low energy electrons so no high energy beta emission, radiation dose to patient low)
Low energy gamma escape body easily, accurately detected
It can form tracers by being in biologically active substances
112
Technetium Generators
Lead pot in glass tube containing radioisotope
Contain Molybdenum 99, half life 66hrs, decays to Tc99
Tc 99 washed out of pot when required
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Flurodeoxyglucose (FDG) F-18
Main radiopharmaceutical
Half life under 2 hours as a tracer
Readily incorporated into cell without being broken down, good indicator of cell metabolism
114
Radiosurgery
Cancerous growths are sensitive to damage by radiation. Some cancerous growths are controlled or eliminated by radiation by irradiating area containing growth, this is radio surgery.
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Tele-therapy (external irradiation)
Using gamma bean from radioactive Co-60 source. External radiation procedure known as gamma knife radiosurgery involves focusing gamma radiation from 201 sources of Co-60 on precise area of brain with cancerous tumour.
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Internal radionuclide therapy (brachytherapy)
Planting small radiation source, gamma or beta emitter in target area. Short rage radiotherapy known as brachytherapy. Iodine 131 mainly used for thyroid cancer. Gives less overall radiation to body and more localised to target tumour, cost effective.
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TAT Targeted Alpha Therapy
Short range of every energetic alpha emissions in tissue means alot of radioactive energy goes to cancer cells.
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NCEPT Neutron Capture Enhanced Particle Therapy
Inject the paitent with neutron capture agent before irradiation with protons or heavy ions
This boosts target dose without increasing dose to healthy tissue and delivers significant dose
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Therapeutic Radiopharmaceutical
For some medical conditions its useful to destroy or weaken malfunctioning cells using radiation. Beta radiation causes destruction of damaged cells. This is radionuclide therapy (RNT) or radiotherapy. Short range radiotherapy is brachytherapy.
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Ideal therapeutic radioisotope is a strong beta emitter with just enough gamma to enable imaging
Lutetium-177 and Yttrium-90
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