: , oe 4p a ON wt = PO @ els oi wtys Seog ne ence nmemeno wey A Mase cena TY ore ate hae . watt le abtah Se te OE TOS ee ae Fig. 307 Gounting Equipment in Laboratory Trailer Every sample was counted for a total of 10,000 counts or for a total counting time of 30 min, whichever occured first. The former provided for a 0 95 error of 2 per cent (i.e., a 95 per cent probability of being within 2 per cent of the true counting rate), but a time restriction was necessary hecause of the wrk lead, The background was continuously monitored with a General Radio count rate meter to . indicate any severe variations in the background which would invalidate the counting done at that time, Counting rates in excess of 5000 ¢/m were correctcd for coincidence lots. Oe Standards. ef each fission product of interest were separated from a sample of U°3> irradiated with thernal neutrons in the Brookhaven reactor, ‘Thésée standards were used for three purposes: . . 1, Crosse-calibration of counters for each shelf position, New counters pleced in service later in the operation were crosscomiene by means of fission products separated from the fallout 2, Ratios forthe standardization of Revalues, (R-valuas are obtained by dividing the observed ratio of tvo nuclides in a shot sample, corrected to zero time. by the activity ratio of the sane two nuclides for thermal neutron fission of u235 counted under the same conditions.) 25 SECRET ~ RESTRICTED DATA