Vitaly Mogulian

Monte Carlo Variance Reduction Research & Code Developing & Nuclear Engineering

Ueki 3-layer shielding experiment (Type 3)

A californium-252 neutron source of intensity $5.33 \cdot 10^8$ n/s is placed into a conic paraffin collimator. The goal is computation of neutron and secondary (capture) gamma dose rates behind 3-layered shield of steel (25 cm) - polyethylene (15 cm) - steel (10 cm) slabs.


Figure 1: Cross-section of the model

In this calculation, the following techniques are used:

Expected value estimators;
Exponential transform (actually demanded for secondary gamma only);
Simplified adaptive splitting.

The primary computational gain is achieved here thanks to the simplified adaptive splitting and exponential transform (for secondary gamma) techniques.

Computed flux functional - rates of equivalent dose ANSI 77 [2].

Thicknesses of volumetric detectors are equal to 2 cm. Results of a 2 h 52 min long computation are presented in Figures 2 and 3 (see details in [3]).


Figure 2: Neutron dose rates plot, μSv/h


Figure 3: Secondary gamma dose rates plot, μSv/h

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References

K. Ueki, A. Ohashi, Nobuteru Nariyama, S. Nagayama, T. Fujita, K. Hattori, and Y. Anayama. Systematic evaluation of neutron shielding effects for materials. Nuclear Science and Engineering, 124:455-464, 10 1996.
American National Standard: neutron and gamma-ray ux-to-dose rate factors. American Nuclear Society, United States, 1977.
V.G. Mogulian. An approach to radiation shielding evaluations using estimators by expected scoring. 2025. doi:10.5281/zenodo.16781416.