Tutorial stuff Flashcards
What is the absolute efficiency of a detector setup.
Fraction of radiation from the source that is detected.
Why are scintillation detectors used for beta counting carbon-14 rather than semiconductor detector?
Scintillation detectors have a higher effiency but lower resolution compares to semiconductor detectors. Carbon-14 has a long half life so you need high effiency. We only need decay rate to determine age.
Explain AMS
Negative ion source produces ions which are deflected based on m/z. Tandum accelerator towards positive terminal of CDG generator next to stripper. Positive ions are repelled from VDG, moves through second magnet separating out C14.
List three effects that have casued a variation in the amount of atmospheric 14C.
Variation in cosmic ray flux, emission of old carbon from fossile fuels (suess effect), atmospheric nuclear weapons testing.
How does Uranium-lead dating work
Uranium-235 and 238 both decay to Pb207 and Pb206 respectively. The ratio of the parent and daughter nuclear from two different points in the rock is used to determine the age
Energy of head on collision
4Em/M «_space;E
Avogadros law
Atom density = (rho*N_A) / A. Multiply by Z for electron density.
relationship between stopping power, charge and speed
S \propto z^2/v^2
neutron collision parameter
min energy = E_0*alpa
Photon attenuation
I = I_0exp(-mu x)
Neutron attenuation
I = I_0exp(-Sigma x), Sigma = rhoN_Asigma/A
Proportional counter electric field
E = rho/(2piE_0r)
Absorbed dose
D = E/m
Equivelant dose
H = wD
Effective dose
Sum of all equivelant doses
Dose rate approx
dD/dt approx= (A(Mbq)*E(MeV)/6r^2
Neutron flux
phi = nv
reactuin rate
r = Sigma nv
4 factor formula
k (8) = eta E p f (infinite reactor)
6 factor formula
k = eta E p f P_(fast nuetron leak) P_( (infinite reactor)
reactor period
T_p = l / (k-1)
Fusion reaction rate
n1n2 <sigma></sigma>
Fusion gain factor
Q = Pfus/Pheat
Breakeven
Q = 1
Transient equilibrium
N2 = y1/(y2-y1)N1(0)(exp(-y1t)-exp(-y2t))
Activity from measured gamma spectrum
alpha = n / (eps(abs)*Egamma T I)
Secular equilibrium
A1 = A2, y2»y1
Distance for infinite thickness
d> 7/mu
Difference between electron mass stopping power in Aluminium and lead.
Lead has a higher atomic number, so greater deflection and greater braking radiation.
Give the definition of the absorbed dose
Energy deposited per unit mass (JKg-1) Gy
How does the energy of the photon change the way it interacts with a detector
Higher energy is less likely to interact with the detector so it will have a lower efficiency. Higher energy are more likely to do compton scattering, not giving all of their energy compared to photoelectric effect
List the radiation weighting factors
Photon: 1, electrons and muons: 1, Protons and charged pions: 2, alpha particles or fission fragments: 20
What are the sum of weighting factors for different tissues, Bladder thyroid liver osophagus
Bone marrow + loads of shit: 0.72, Gonads 0.08, bladder + thyroid +liver +osopagus: 0.16, bone , saliver,brain skin: 0.04
Name the acute radiation syndromes and the doses at which they occur
Haematopoeitic: 2Gy, Gasto-intestinal: 6 Gy, Nuerovascular: 12
What is the UK dose limit for whole body
1 m Sv yr-1
Why is zircon useful
zircon is a mineral that holds uranium but expels lead, any lead in zircon is produced by radioactive decay
Name all parameters in k_infinite
eta - thermal reproduction factor = fast neutrons produced from thermal fission / thermal neutrons absorbed in fuel. epsilon - Fast fission factor = number of neutrons from all fission / number of fast neutrons from thermal fissions. p - resonance escape probability = neutrons that reach thermal energy / neutrons that slow down. f - thermal utilisation factor = number of thermal neutrons absorbed/number of thermal neutrons absorbed in fuel
Name where energy of fission is deposited and the percent of energy.
PROMPT: FIssion fragments (80%) - Fuel rods. Fission neutrons (2.5%) - moderator/ sheilfing. gamma rays (3%) - sheilding / reactor core. DELAYED: B- electron (4%) fuel rod. B- antu neutrino (6%) - lost. gamma ray from B- (3%) reactor core/ sheilding. Radiative Capture (2.5%) reactor core/ sheild
What is the purpose of the frisch grid
Same radiaiton causes the same signal in the detector independant of where the radiation interacts.
How can a gas filled detector be adaptes to detect thermal neutrons.
If the gas is He-3, Bf-10 or has Uranium -235 lining.
Describe how you could find the level of enrichment of a 10mm plate of uranium.
Gamma ray spectroscopy with HPGe detector. Calibrate for absolute efficiency against E (done with152 Eu) and background spectrum. Activity then determined and then N
Intrinsic calibration method
Using a samples own emission as calibration. good for irregular shapes
