[Paper Review] Neutron shielding for particle astrophysics experiments

J. E. McMillan|ArXiv.org|Oct 20, 2005

Nuclear Physics and Applications6 references3 citations

TL;DR

This paper evaluates low-cost hydrogenous materials for neutron shielding in particle astrophysics experiments, focusing on raw polymer pellets and Water Extended Polyester (WEP). It demonstrates that WEP mixed with polypropylene pellets forms a cost-effective, load-bearing composite with shielding properties comparable to PMMA, offering a practical, scalable solution for large-volume neutron shielding at reduced cost.

ABSTRACT

Particle astrophysics experiments often require large volume neutron shields which are formed from hydrogenous material. This note reviews some of the available materials in an attempt to find the most cost effective solution. Raw polymer pellets and Water Extended Polyester (WEP) ae discussed in detail. Suppliers for some materials are given.

Motivation & Objective

• To identify cost-effective, large-volume neutron shielding materials for particle astrophysics experiments.
• To evaluate the feasibility of raw polymer pellets and Water Extended Polyester (WEP) as alternatives to expensive extruded slabs.
• To develop a low-cost, load-bearing shielding composite using WEP and polypropylene pellets.
• To assess the compatibility of WEP with neutron-capturing inorganics like boron and lithium compounds for enhanced shielding.
• To provide practical guidance on material selection, sourcing, and fabrication for experimental shielding systems.

Proposed method

• Compares raw material costs of hydrogenous shielding materials, including polyethylene, polypropylene, paraffin, and WEP, from UK suppliers as of 2002/03.
• Proposes using raw, virgin polymer pellets (e.g., from Albis) as a low-cost alternative to extruded slabs, noting a price as low as £0.48/kg.
• Describes a method for fabricating WEP by blending Crystic 1381PA resin with water and curing with methylethyl ketone peroxide catalyst.
• Introduces a composite material by mixing WEP with polypropylene pellets to improve packing density and create a load-bearing shield.
• Outlines procedures for blending inorganic neutron absorbers (e.g., borax, lithium carbonate) into the WEP matrix without disrupting curing.
• Recommends outdoor or well-ventilated mixing due to styrene monomer fumes during preparation, with curing occurring in ~15 minutes at specified ratios.

Experimental results

Research questions

• RQ1 What are the most cost-effective hydrogenous materials for large-volume neutron shielding in particle astrophysics experiments?
• RQ2 Can raw polymer pellets be used effectively as a low-cost alternative to extruded polymer slabs in neutron shielding?
• RQ3 How does the shielding performance of WEP compare to standard materials like PMMA or polyethylene?
• RQ4 Can WEP be effectively loaded with neutron-capturing inorganics such as boron or lithium compounds without compromising curing or structural integrity?
• RQ5 What are the practical fabrication challenges and cost implications of using WEP and pellet composites in real experimental setups?

Key findings

• Raw polypropylene pellets from Albis cost £0.48/kg, approximately 3–4 times less than extruded polyethylene slabs, making them a highly cost-effective shielding option.
• WEP mixed with polypropylene pellets forms a solid, concrete-like composite that is load-bearing and significantly cheaper than pure WEP or slab materials.
• The composite material demonstrated minimal air entrapment during production, even with minimal process control, indicating good workability.
• WEP can be successfully blended with inorganic neutron absorbers such as borax (£1.63/kg) and lithium carbonate (£9.08/kg), with no adverse effects on curing or stability.
• Curing of WEP occurs in about 15 minutes when proper ratios of catalyst and resin are used, and the material becomes odorless and stable after full polymerization.
• The use of WEP with inorganics has been validated in DOE studies for encapsulating radioactive waste, indicating long-term durability and suitability for shielding applications.