Neutron dose

Three levels of calculation, each building on the previous:

Function	What it computes	Considers geometry?
calculate_transmission	Material attenuation only (exp(-Sigma*t))	No
calculate_flux	1 / (4piR^2) * exp(-Sigma*t) * B per source particle	Yes (inverse square law)
calculate_dose	Flux * ICRP-116 dose coefficient (per source particle)	Yes (inverse square law)

The same calculate_dose interface applies to neutrons; just create a neutron Source. The irradiation geometries are the same as for photons. As with photons, the dose result is per source particle - apply an absolute strength via result.scale(strength=...). For pulsed neutron devices (e.g. an inertial-confinement burn) supply neutrons per shot to get Sv/shot.

Example

import rad_point_kernel as rpk

iron = rpk.Material(composition={"Fe": 1.0}, density=7.874)
layers = [
    rpk.Layer(thickness=1000),               # 10 m void
    rpk.Layer(thickness=10, material=iron),  # 10 cm iron
]

source = rpk.Source(particle="neutron", energy=14.1e6)
# Pulsed DT shot: 1e16 neutrons per shot, result in Sv/shot
result = rpk.calculate_dose(layers=layers, source=source, geometry="AP").scale(
    strength=1e16,
)
print(f"Neutron dose: {result.dose} Sv/shot")

Neutron dose: 0.11028531005505514 Sv/shot

With a manual build-up factor

import rad_point_kernel as rpk

iron = rpk.Material(composition={"Fe": 1.0}, density=7.874)
layers = [
    rpk.Layer(thickness=1000),
    rpk.Layer(thickness=10, material=iron),
]

source = rpk.Source(particle="neutron", energy=14.1e6)

B_dose = 2.5
result = rpk.calculate_dose(
    layers=layers,
    source=source,
    geometry="AP",
    buildup=rpk.BuildupModel.constant(B_dose),
).scale(strength=1e16)
print(f"Neutron dose (B={B_dose}): {result.dose} Sv/shot")
print(f"Applied build-up:        {result.buildup_factor}")

Neutron dose (B=2.5): 0.2757132751376378 Sv/shot
Applied build-up:        2.5

See Calculate build-up with MC for how to compute B from first principles.

Secondary photons

Fast neutrons generate secondary photons through inelastic scatter and capture. Those photons can contribute significantly to the dose, especially for high-Z shields. See Dose (coupled) for how to include them via Monte Carlo.