Shielding Wall

We have made modifications in the shielding wall design.

It is now 32 inches thick and made of ordinary concrete blocks, mortared together. This thickness ensures better shielding and is convenient for standard 16” wide blocks. We’ve determined that boron-doping of the concrete is not needed. However, since neutrons could escape by bouncing their way through the plywood roof, we are replacing that roof over the walls with 2’ wide strips of Borotron plastic, which is a 5% boron-enriched polyethylene. This absorbs neutrons better than the concrete but is water-proof.

We’ve carefully checked our analysis with worse-case calculations of how many neutrons can leak out, using experimental results on the shielding of neutrons by concrete and Borotron. It turns out the worst problems are with the 14.5 Mev DT neutrons which are produced during our experiments with deuterium. Half of the DD reactions produce tritium, which then reacts with the deuterium to produce the DT neutron. These neutrons are valuable for diagnostic purposes, as the ratio of DT to DD neutrons is proportional to plasma density in the plasmoid. However, they are very penetrating. Our shielding is mainly designed to block them. The lower-energy neutrons produced by the DD reactions and the secondary He-B11 reaction, when we are running pB11, are much less penetrating and will be blocked to insignificant levels.

Even with worst case assumptions for the DT neutrons, we still expect at least a factor of 2 safety margin below background radiation for LPP personnel and for personnel in neighboring buildings.

We have accepted the lower of two construction bids for the shielding wall and for the installing of air-conditioning. An architect is now completing drawings and, after getting permits form Middlesex Borough, we expect wall construction to begin about June 17 and to be completed by the end of June at the latest, when construction of the device will begin.