Letters Received to C.B. Lee, May 9, 1936

MASSACHUSETTS INSTITUTE OF TECHNOLOGY DEPARTMENT OF PHYSICS CAMBRIDGE, MASS. May 13, 1936 Mr. H. H. Barker Vice President United States Radium Corporation 535 Pearl Street New York Dear Mr. Barker: Thank you for your letter of April 27th which was waiting for me wh en I returned from the Washington Meeting. I am very sorry that we missed each other there. The sensitive gamma ray detector which I described, is based on the quantum counter principle. It is mounted in a portable carrying case slightly smaller than an ordinary Glad- stone bag and is completely self contained, operating on 110 volts a. C. Although it has not been yet pushed to its limit of sensitivity, I believe it will probably detect 1 millimicro- gram of radium. Of course, our radon apparatus will go much further than this, having an observational limit of about 2 X 10-14 curies, but its operation is, of course, much more laborious. I hope to have the pleasure of meeting you personally in the future. Most cordially yours, Robley Do Evans RDE : R