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Point Kernel Calculator

A fast engineering tool for neutron and photon shielding calculations.

What it does

Point Kernel Calculator estimates radiation dose and flux behind shielding using the point-kernel method. It handles:

  • Photon sources - monoenergetic (e.g. Cs-137) or multi-line spectra (e.g. Co-60)
  • Neutron sources - monoenergetic (DT) or mixed spectra (DT + DD)
  • Secondary photons - gammas produced by neutron interactions in the shield (coupled neutron-photon transport)
  • Multi-layer shields - any combination of materials and voids
  • Build-up factor correction - Monte Carlo computed (OpenMC), with Gaussian Process extrapolation and uncertainty
  • ICRP-116 dose coefficients - 6 irradiation directions (AP, PA, RLAT, LLAT, ROT, ISO)

When to use it

The point-kernel method is a fast approximation for shielding design. Use it when:

  • You need quick dose estimates for shield thickness scans
  • You're doing preliminary design before committing to full Monte Carlo
  • You want to screen many material/geometry combinations rapidly
  • You need an analytical baseline to compare against transport codes

It is not a replacement for Monte Carlo transport codes for final design, but it gets you closer to an answer in seconds instead of hours.

How it works

  1. Point kernel (Rust, instant): Computes uncollided flux through concentric spherical layers using removal cross sections and secondary photon production cross sections generated from ENDF/B-VIII.0
  2. Build-up correction (OpenMC): Runs Monte Carlo on a few thin shields to determine how much scattered radiation adds to the uncollided estimate
  3. GP extrapolation (inference-tools, instant): Fits a Gaussian Process to the Monte Carlo build-up factors and predicts B at any thickness with uncertainty bounds

Quick start

import rad_point_kernel as rpk

# Define a material and source
concrete = rpk.Material(
    composition={"H": 0.01, "O": 0.53, "Si": 0.34, "Ca": 0.04, "Al": 0.03, "Fe": 0.01},
    density=2.3,
    fraction="mass",
)
source = rpk.Source(particle="neutron", energy=14.1e6)  # D-T fusion

# Define the shield geometry
layers = [
    rpk.Layer(thickness=1000),                    # 10 m void
    rpk.Layer(thickness=100, material=concrete),  # 1 m concrete
]

# Calculate neutron dose rate
result = rpk.calculate_dose(
    source_strength=1e12,
    layers=layers,
    source=source,
    geometry="AP",
)
print(f"Dose rate: {result.dose_rate} Sv/hr")

Dose rate: 0.0001497583248122068 Sv/hr

See the installation guide for setup, including OpenMC and cross-section data.