Week 6 Nuclear Fission Part 1 Flashcards
for what atomic masses does fission occur
A >~ 120
what is the general concept of nuclear fission
a neutron collides with a large unstable nuclei to produce multiple smaller daughter nuclei releasing energy
define Q factor
difference in mass energy between parent nuclei and daughter nuclei
what is the Mass Excess equation
Δe = Atomic Mass - 1u * A
what is the mass defect equation
Z * H + N * m - (A + Δe)
what is true of the signs of mass defect and mass excess
mass defect is always positive
mass excess can be positive or negative
what is the process of radioactive decay
unstable nuclei transforms to a more stable nuclide
what are the two radioactivity equations
A(t) = -dN/dt = Nλexp[-λt]
A(t) = Bexp[-λt]
λ is just a decay constant
what is the half life equation
t1/2 = ln2/λ
what are the three types of radioactive decay
α, β, γ
how can you determine if fission will be spontaneous or not
considering Coulomb potential
requires binding energy to be greater than the coulomb potential
why does fission require activation energy
although can sometimes be spontaneous this is very rare so needs to be triggered requiring the activation energy input
define a prompt neutron and the 4 energies it can be released with
neutrons that are released 10^-14s after reaction
can have thermal, epithermal, slow or fast energy
what is a delayed neutron
neutron that is released by later emissions by unstable fission
what is the reaction rate equation
R = σNφ
φ is flux
σ is the cross sectional area
what is the mean free path equation
λ = 1/nσ
how does cross section compare for fast and slow neutrons
fast neutrons have a far smaller cross section that slow ones
what three reactions resultant of fast-neutron-nuclei collisions compete with fission
elastic scattering
inelastic scattering
radiation capture
what is true of cross section for a good fission reaction rate
want the cross section of fission to be the dominant cross section out of the 4 possible reactions
what is the number of neutrons available to induce fission equation
ηa = n σf/(σf+σc)
where σf is the cross section of fission and σc is that of radiation capture
define neutron time constant
τ is the mean time before absorption
what is the neutron absorption equation
N = N0exp[(k-1)t/τ]
k is the neutron multiplication factor
what is the fission power equation
P = QN/τ = QN0exp[(k-1)t/τ] / τ
briefly describe the three neutron multiplication factor situations
k<1 is sub-critical so energy production slows
k~1 is critical so energy produced linearly
k>1 is super-critical so energy increases exponentially
