Two xenon extraction runs were made this month. It appears that a small design change in Trap #2 will be necessary so that a dry ice-trichloroethylene slurry can be used for coolant rather than liquid freon. For each of the runs this month the enriched generator was exposed for four hours in the est pile operating at 100 watts. A period of eight hours for cooling and xenon builidup was allowed before the collection and separation runs were started.

In obtaining the results reported here a double focusing magnetic type spectrometer was used. Momentum spread was about 1%, and in most cases 2560 counts per point were taken. An end window Geiger tube was used as a detector. The window was of mica with areal density of 1.6 mg/cm2.

Various organizations in the Biophysics Section of the Radiological Sciences Department participated in evaluating local radioactive particle fallout as influenced by the nuclear explosions at the Nevada Proving Grounds during the early part of 1953. Data collected from approximately 50 air monitoring stations operated by the Regional Survey forces were used to determine the trend of radioactive particle concentrations in the atmosphere between March and June. These measurements were supplemented with the findings of associated organizations in the Biophysics Section during and immediately after the peak influx on May 26.

The investigation to be described in this paper was one of several undertaken to resolve a curious discrepancy that had arisen in measurements of the diffusion length of graphite. Those diffusion lengths measured with the graphite layups of 100 Area piles were three to six centimeters higher than the value obtained with the Hanford Standard Pile. The fact that the 100 Area structures of the order of 40 ft. X 40 ft. X 30 ft, not including reflector, approximated an infinite medium, whereas sigma piles are of the order of 8 ft. X 8ft. X 10 ft., suggested the possibility that the diffusion length obtained by mensuration of relative fluxes and application of the conventional equations depended in some way on the size of the medium. Therefore, in order to determine if such a dependency actually exists, it was proposed to erect a series of graphite stacks of different dimensions and to make diffusion length measurements in each.

The purpose of this manual is to present available data which can be used to determine disintegration rates of radioactive samples from counting rates measured under given circumstances with routinely used laboratory instruments. There is also brief discussion on the methods by which the various factors have been determined with reference to the accuracy with which they are known and to what extent the finally quoted disintegration rate is affected by these errors. Emphasis has been placed on those isotopes of particular interest to Radiological Sciences programs and the manual is intended as a standard through the use of which comparable values can be reported from all units in the Department.