2- Chapter 18 - Radiation Flashcards
What is absorbed dose?
The energy deposited per Kg of tissue.
measured in grays.
Effective dose(absorbed dose) =
absorbed dose (in grays) x quality factor
measured in Sieverts/Sv
what is quality factor?
used to calculate effective dose, and its based off the type of radiation and type of tissue effected.
What stops beta radiation?
small thickness of metal
what stops alpha radiation
skin, few cm of air
Fraction absorbed equation
I/I0 = e-μX
(I=intensity, μ = absorbtion coefficent, X = thickness)
Half thickness absorbed (X1/2)=
ln2/μ
What is conserved in neuclear decay?
- Energy/mass (through E=mc2)
- Momentum
- Proton number
- Charge
- Neucleon Number
What is mass defect?
The difference in mass between bound and unbound neucleons.
Mass in neucleus - Mass of individual protons
What is binding energy?
The energy needed to bind neuclons into the neucleus.
Mass defect (in kg) used in E=Δmc2
(is negative)
Binding energy per neucleon
Binding energy divided by number of neuclons
whats the neuclear valley
plot mass number against binding energy per neucleon, forms a valley around iron.
What causes mass defect?
the mass is less as its been converted to potential energy in the nucleus.
Relationship between binding energy per neuclon and stability?
more negative BEPN means its more stable as more energy is needed to seperate neuclus.
What happenes to proton and neuton number as you go down the periodic table and why
there starts to be more neclouns per proton the further you go down. As the neutral neutons will dilute the protons and reduce the repulsion so PE and BE is lower. They also provide futher nuclear attration.
Binding energy per unit mass=
Binding energy/Mass defect =931MeV
What can cause a neucleous to becoms unstable, and the decay it causes. (4 things)
- Too many neutrons - β- decay
- Too Few neutrons - β+ decay
- Too many nucleons - Alpha Decay
- Too much energy - Gamma Decay
Example Equation for β- decay and what happens.
Neutron converts to a proton and electron - Anti neutrino is also created to conserver momentum.
Example Equation for β+ decay and what happens.
proton converts to a neuton and positron - neutrino is also created to conserver momentum.
risk=
probability x consequence
how does fission split a nucleus?
Neutron can set the nucleus ocilating, into a dumbbell like shape which can split into two smaller nuclei.
The two smaller ones have less energy so are more stable.
rough order of energy per particl in fission
1 MeV per particle
Chain reaction principle?
One neutron is fired at a nucleus, which splits into two spaller nucli and 2-3 more neutrons which can split more neucli.
What is critical mass?
Reaction is at a steady rate, one new fission follows each fision.
super critical and sub critical mas?
Super - more then one new fissions per fission
Sub - more neutrons esape, the reaction eventually stops.
Design of a steam presurised water reactor
What does the moderator do?
Slows the neutrons down which greatly increases the chance of their capture by a U-235 nucleus
What are the control rods for?
making sure the reactor doesnt go super critical by absorbing varying amounts of neutrons
What does the coolant do?
carry away energy
Fusion in the sun
Fusion on earth
What happens to the neutrons that dont cause a fission?
absorbed in moderator/U-238 or escape.
