CORRECTION FACTORS FOR DETECTORSN 496 DOE/ERSP TECH NOTE NO.5.2 DATED: 19 August 1978 AUTHOR: R. Jaffe, EG&G The subject detector is an intrinsic germanium detector produced by Princeton Gamma Tech, Model IG 1916, with preamplifier Model RG-11, as are all the detectors used in the IMP radiation measurement vans. Detector SN 496 was shipped to EG&G, Las Vegas, 17 July 1977. It arrived at Enewetak and was calibrated at the ERSP counting laboratory starting 31 January 1978. It was brought to Ursula 2 February and installed in IMP L The IMP I ~ detector 496 combination was in use until 12 July 1978. This memo discusses 2414m measurements using detector 496. A correction factor is required for data obtained with detector 496 to correctly relate that data to the data from the other detectors in use. This is due to the smaller effective area of the detector, as noted by the manufacturer, and by previous use at the Nevada Test Site. The factor was stated as 1.06. Direct comparison of readings taken with detector 496 and detector 393 at eleven locations gave a ratio of 1.10 + 0.07 as the factor by which detector 496 readings are multiplied to make them comparable to detector 393 readings. Table B-5-1 gives the comparison data. This factor of 1.10 has been applied to all data taken with detector 496.* Time Period - 3 February to 25 February The detector was mistakenly operated at a bias voltage of -2000 rather than -3000 from 3 February to 25 February 1978. This was discovered on 25 February and steps were taken to determine the correction factor needed for the data accumulated during the period of misoperation. The islands which had been measured were: Lucy, 3 and 4 February; Alice, 7 to 9 February; Belle, 13 to 15 February and Sally, 21 to 25 February. (Table B-5-2 lists islands, dates and comments.) Remeasurements at nine grid locations and data analysis (Tech Note 5, Correction Factor for Detector (SN: 496) Operating at Low Voltage) gave a factor of 1.6 + 0.24. A similar comparison of 13 other grid locations plus two at the grid locations included in the nine just mentioned (a total of 15 grid locations) gave a correction factor of 1.6 + 0.11 (EG&G ERSP Office File, Sally IMP I - I Cross Check). Additional corroboration is provided by the experiments conducted at that time using a field calibration source. The ratio of response at -3000/-2000 volts bias was 1.69 for a single measurement pair. Since 25 February the islands of Sally, Lucy, and Alice have been remeasured. For Lucy, the 1.6 factor was verified. For Alice, the remeasurements did not verify the 1.6 factor, and an additional factor of 1.72 was applied, as discussed in Tech Note 5.1 (Correction Factor for Detector (SN: 496) Operating at Low Voltage on Island Alice, by M. Barnes.) Time Period 21 March to 12 July Field calibration of detectors is performed three times daily when on-site. A sourceis installed in a sample pan at a reproduced distance below the detector entrance window. The source consists of 24lAm, 137Cs, 60Co (and a minor amount of 155gu), sealed in glass beads and plastic in a 3-1/2 inch plastic dish. The source is counted for five minutes and the detector preamplifier gain and zero settings are adjusted to locate the 59.5, 661.6, 1173.2, and 1332.5 keV peaks inthe correct channels of the pulse height analyzer. Typically, about 20,000 counts are accumulated for 241Am. Data seatter is attributed to the effect of environmental conditions on the detector and electronics. The detector "barrel" is exposed to temperatures ranging above 94°F, a mean relative humidity of 77%, and intense rain squalls. First stages of the preamp are built into the detector Dewar. The other electronics are located in the air conditioned pod. The standard *See Appendix D for correction factors used later in the project. B-5-3