The increased use of tritium monitoring devices has made it necessary to devise a scheme for the calibration of such instruments. Several methods for setting up known concentrations of tritium were considered. A dynamic system containing tritium as HTO vapor or gaseous HT was selected because of the ease of control of variables. The variables that have been considered are: ,1. The effect of rate of air flow through the instruments. 2. The effect of humidity on instrument response. 3. The effect of ion collection ahead of the ion chamber. 4. The variation of “hold time” from the generation of tritium to its passage through the ion chamber. 5. The instrument response to several concentrations of tritium as HTO vapor and gaseous HT. The following three types of monitoring devices have been calibrated:1. Model 101 Sniffer of Group P-1. 2. Cl-1 Vibrating Reed Electrometer of Group CMR-7. 3. Modified TIB of Group H-6.

This report brings together an extensive accumulation of material replacement (danger coefficient) data for the various oralloy critical assemblies at Pajarito. Corresponding values of effective absorption and transport cross sections are derived. In certain favorable cases, inelastic scattering contributions to the effective absorption cross sections are estimated. Special applications of material replacement data include computation of the relationship between oralloy critical mass and concentration of a diluent and hydrogen isotopic analysis of heavy water and heavy polythene.

The development of sampling methods and some field results of the off- site air sampling stations at the Nevada Proving Ground are reviewed. A technique of radioautography is presented which yields information about the activities of individual fall-out particles. This technique gives a comparison of particle activities from air drops and tower shots and a reason for the greater contamination associated with the latter. It also indicates that air samplers do not capture the most active fall-out particles, presumably because of their large size.