1. Called E. P. Blizard of ORNL, who is probably the best authority on shielding. The relaxation lengths quoted in ORNL which I have noted are for fast neutrons, and represent the reduction in intensity as measured by thermal neutron counters. Barytes is probably the best bet for our use, with a λ of 8. A report by Lansing, Thornton and Lane on MTR shielding will be out soon, and is most appropriate for our study, according to Blizard. There is to be a meeting with some Canadian people on the week of Feb. 26, in which ORNL will describe the whole picture of shielding, particularly of the inexpensive variety for permanent reactors. He highly recommends that we attend this, and will call or telegraph the exact date(s) of the meeting.

2. Discussed several items with A. D. Callihan. (a) Reactor building design. He objected to the cut-up center rooms, suggesting one large room with partitions if desired. Provisions for women's dressing rooms are needed. Also, the dressing rooms should be off the traffic line, because of the visitors that are sure to come around to see the labs. He liked the sizes of the rooms. (b) Water window. Callihan thinks it should be made in panels of reasonable size, and of stainless steal to avoid rust. Urges solid live rubber gaskets rather than caulking, addition of a salt in the water to inhibit organic growths. Their windows are truncated pyramids 5' 6" square on the front (near reactor), 3 1/2' x 2 1/2' on bask. Glass thickness 1 1/4" front, 5/8" back of "Herculite" a tempered glass put out by Pittsburgh Plate Glass Co. (c) Cd vs. B shielding at the end of the thermal column. He agreed B would be preferable.