Ionizing Radiation and Risk Flashcards
What is an alpha particle in terms of mass, constituents and charge?
42He2+= α
What is beta-minus, or beta radiation?
A high speed electron (charge -1) - β-
What is beta-plus radiation?
High speed positrons, β+
What is gamma radiation?
High frequency (high energy) electromagnetic waves of zero mass and charge - γ
What are the defining characteristics of alpha radiation?
Alpha radiation is slow, strongly ionising, **easily absorbed by a few cm of paper or air **and is affected by magnetic fields.
What are the defining characteristics of beta-minus radiation?
Beta-minus radiation is fast-moving, weakly ionising, **absorbed by ~3cm of aluminium **and is affected by magnetic fields.
What are the defining characteristics of gamma radiation?
**Gamma **radiation is very weakly ionizing, travels at the speed of light, **absorbed by many cm of lead **or a few m of concrete and is not affected by magnetic fields.
Why is beta-plus radiation not worthy of concern in most situations?
Because it is annihilated almost instantly by an electron.
What happens to the intensity of gamma radiation as it passes through concrete?
It decreases exponentially.
What is the Gray (Gy) a unit of measurement for?
Absorbed dose of radiation.
What is the absorbed dose of radiation?
The energy absorbed per kilo - E/m = Dose [Gy]
E = energy in joules
m = mass in kg
What factors is radioactive tissue damage dependent upon?
The type of ionizing radiation and the type of body tissue.
Why is a measurement of effective radiation does helpful?
Because it allows comparisons between body tissues.
The Sievert [Sv] is a measurement of what?
Effective radiation dose.
Effective dose = ?
Absorbed dose x Radiation quality factor
Why are alpha particles strongly ionizing and quickly?
Alpha particles are highly positively charged and can easily release an electron from its atom - they transfer energy from themselves to the atom, doing this approximately 10 000 times before losing its energy.
Why is β- radiation weakly ionizing?
β-’s high speed means it is still able to remove electrons from their atoms, in spite of its low mass and relative charge. It also interacts with fewer atoms than α radiation does before losing all of its energy.
What determines a radiation’s quality factor?
How many atoms it ionizes before losing all of its energy - how many ‘interactions’ it has.
What is risk equivalent to?
Risk = Probability x Consequence
Probability = how likely it is to happen
Consequence = how severe the effects would be were it to happen
What are the uses of radiation?
Power generation by nuclear reactors.
Medicine - treatment and diagnosis.
Food preservation and treatment - radiation can be used to delay ripening and kill harmful microorganisms.
What is a risk with great consequence but low likelihood?
A nuclear reactor meltdown.
When is it acceptable to take the risk of using radiation to treat cancerous cells?
When the treatment would improve or prolong the patient’s life.
Describe binding energy.
Binding energy is the energy which would be required to seperate all the nucleons in a nucleus and it is equivalent to the mass defect. It is also measured in MeV.
Why is it that when nucleons join together, they release energy?
Because their total mass decreases - this mass (the ‘mass defect’) is converted into energy and released.
How much energy is released when nucleons join together?
The mass defect, converted according to the mass-energy equivalence equation (E=mc2).
Binding energy per nucleon = ?
Binding energy
Nucleon number
Why is it that all unstable nuclei tend towards the formation of Iron (nucleon number 56)?
Because Iron has the largest binding energy, and is thereby the most stable nucleus.
What type of nuclear reaction do nuclei with a nucleon number less than 56 favour?
Fusion
What is nuclear fusion?
The combining of nuclei to form larger, more stable nuclei of a higher binding energy per nucleon. Lots of energy is released by nuclear fusion, and that energy is equivalent to the mass defect between the reactants and the product.
Describe nuclear fission.
The splitting of nuclei to form small nuclei and emit neutrons and gamma ray photons; these smaller nuclei have a higher binding energy per nucleon and are therefore more stable.
What is the change in binding energy for the nuclei of a fusion or fission reaction equal to?
The energy released by that fusion or fission reaction.
What nuclei size, by proton number, is classed as the smallest that will fission?
Nuclei with at least 83 protons are prone to fission because they are unstable.
What does the likelihood of spontaneous fission increase with?
Nuclear size.
Why is there a limit to the number of possible elements?
Because as the mass of a nucleus increases, so too does its likelihood of spontaneous fission. Spontaneous fission limits nucleon number, thereby limiting the number of possible elements.
Why does fission release energy?
Because smaller nuclei have a larger binding energy per nucleon.
How is fission induced?
By firing a neutron at a massive nucleus, such as 235U, causing it to become more unstable and fission.
What is fuel is used in nuclear fission reactors?
235U
Describe nuclear fission in a nuclear reactor.
A neutron is fired at a 235U nucleus, causing it to become unstable and fission. This further produces more neutrons which collide with other 235U nuclei and cause further fissioning. A moderator (such as water) must be used to slow the emitted neutrons (thermal neutrons) down to allow them to induce fission in other nuclei.
What is critical-mass?
The amount of fuel in a nuclear reactor at which there is a steady rate of fission and thereby energy production; 1 fission induces 1 more, and so on.
What is super-critical mass for a reactor?
When more than one fission is induced by one fission - i.e. there is enough fuel that, if left unmoderated, the energy production of the reactor would increase exponentially.
What mass amount do nuclear reactors use? How do they control this?
Nuclear reactors use a super-critical amount of mass, and moderate their reactions using boron control rods, which absorb neutrons, preventing them from causing further nuclei to fission.
How does a nuclear reactor produce energy?
Coolant is passed through the reactor chamber to absorb the energy released from nuclear fission of 235U; this reactant then heats a tank of water, which turns to steam and runs a turbine.
What is the best type of moderator to have for a nuclear reactor?
A moderator which absorbs more neutrons as the reactor heeats up - this type of moderator reduces the likelihood of meltdown.
What should be done, then what can be done with the waste products of nuclear fission for power production?
The waste should first be cooled by placing it in cooling ponds, then it can be used as either a tracer in medicine or buried underground in sealed containers.
What force must be overcome in order for two nuclei to fuse?
The electrostatic repulsion force between the nuclei - once the two nuclei are close enough, they interact via the strong force and fuse.
How much energy is required to fuse two nuclei?
Approximately 1MeV.
Describe hydrogen fusion.
Hydrogen fusion is the combining of two hydrogen nuclei (deuterium and tritium) to produce a 4He nuclueus and lots of energy.
Where does fusion occur naturally? Why is it able to occur there?
In stars - it is able to occur in them because they are hot and strip all their atoms of their electrons, forming a hot plasma (ionic gas). These nuclei then fuse to produce a larger nuclei of a higher binding energy, producing more energy within the star.
