Neutron & Activation neutron_moderation_calc
Fast Neutron Elastic Scattering & Moderation
Models two-body s-wave elastic scattering kinematics in nuclear reactors and laboratory moderators to determine average logarithmic energy decrement ξ and collisions to thermalize.
ξ = 1 + [α ln α / (1 − α)]; N_coll = ln(E₀ / E_th) / ξ
RADCALC HEALTH PHYSICS & NUCLEAR ENGINEERING WORKSHEET
Fast Neutron Elastic Scattering & Moderation (Neutron Moderation)
Domain: Neutron Shielding & Activation · Tool ID:
neutron_moderation_calc · Engine: 100% Local Browser WASM ξ = 1 + [α ln α / (1 − α)]; N_coll = ln(E₀ / E_th) / ξ
Operational Notes:
Guided Stepper Workflow All Input Parameters & Solver
1
What do you want to calculate?
Select your target output variable. The stepper will guide you through only the required inputs.
2
Start from a Field Scenario Preset (Optional)
Pre-fill realistic health physics values, then refine individual parameters or jump straight to the result.
All Parameters Entered
Review Inputs & Calculated Result
Solved Output Live WASM Readout
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Entered Input Parameters (Tap any row to edit)
Calculated Result & Visual Analysis
Nominal Solved Value Updated automatically
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Enter parameters on the left to calculate.
CLIENT-SIDE 3D SIMULATION Fast Neutron Elastic Scattering & Moderation 3D Transport Field
Interactive 3D Geometry & Particle Transport
WebGPU / WebGL2 Ready
3D Hardware Acceleration & Browser Compatibility Status Inspect Requirements ↓
Checking Browser 3D Capabilities… Probing WebGPU adapter, WebGL 2.0, and WebGL 1.0 contexts locally.
Geometry & Field Diagram
Interactive Model
Sensitivity Curve
Normalized Base-Unit & WebMCP Tool Payload neutron_moderation_calc
1. Input & Solved Parameter Ledger
| Role | Symbol | Parameter Name | Entered / Display Value | Normalized Base Unit | Definition |
|---|
2. Neutron Physics & Activation Schedule
Governing Equation & Parameters
Mean Energy Decrement (ξ) ≈ 2 / (A + 2/3); Required Collisions = ln(Initial Energy / Thermal Energy) / ξ
| Symbol | Parameter | Default Unit | Definition |
|---|---|---|---|
| A | Moderator Atomic Weight | amu | Atomic mass number of the moderating target nucleus in amu. |
| E₀ | Initial Neutron Energy | mev | Initial kinetic energy of the fast neutron in Mega-electronvolts. |
| E_th | Target Thermal Energy | ev | Target thermalized neutron energy in electronvolts (standard 0.0253 eV). |
| ξ | Mean Logarithmic Decrement | dimensionless | Average fractional decrease in the logarithm of energy per collision. |
| N_coll | Thermalizing Collisions | collisions | Average number of elastic scattering collisions required to reach thermal energy. |
Health Physics Notes & Related Calculators
Operational Guidance & Physics Assumptions
- Hydrogen (A=1) is the most efficient moderator with ξ = 1.0, allowing a neutron to lose up to 100% of its kinetic energy in a single head-on collision.
- Slowing down a 2.0 MeV fission neutron to thermal room temperature (0.0253 eV) corresponds to a total lethargy gain of Δu = ln(2×10⁶ / 0.0253) ≈ 18.2.
- Collisions required: Hydrogen (H₂O) ~18 collisions; Heavy water (D₂O) ~25 collisions; Beryllium ~87 collisions; Graphite (Carbon-12) ~115 collisions; Uranium-238 ~2170 collisions.
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