1990 yearly calibration of Pacific Northwest Laboratory's gross-gamma borehole geophysical logging system

Abstract

OISTFIIIBLIJION OF "l'i fiGDOOUM_' ;I ' ',_q observed count rate in before-and after-logging field calibrations to equivalent uranium concentrations. The temperature drift of the gamma-ray probe was documented and amounts to less than 0.1%/°C within the temperature range O°C to 42°C. The low'energy cutoff for the gross gamma-ray probe was determined to be between 46.5 and 59.5 keV.

1991 Yearly calibration of Pacific Northwest Laboratory's gross gamma-ray borehole geophysical logging system

“…Values computed by measurements on other scales and at different count rates suffer from either difficulty in precisely reading the count rate from the chart recorder output (at high count rates on high scales), sometimes coupied with the effects of hysteresis in the chart recorder, or insufficientstatisticsas a result of low count rates (low count rates on lower scales). Measurementstaken on the IOK scale without switchingto other scales will probably always give the most accurate dead-time correctionvalue• For example, using data from the previous report (Arthur 1990) on the IOK scale, one obtains a dead-time correction value of 12.2 _s as shown by the data in Table 6.…”

“…A digitally based collection/recordingsystem was recently acquired, so that many of the procedureswere performed with the old analog system and the The initial base calibration of the system is described in a previous report (Brodeur and Koizumi • 1989), from which one can obtain a more thorough understanding of the basic function of the system. The base calibration report (Brodeur and Koizumi 1989) and the subsequent yearly calibration report (Arthur 1990 Tables I and 2, it was previously concluded (Arthur 1990) that the chart recorder had a nonlinear response in the middle region.…”

“…A discrepancy does exist_ however, in that the dead time alone does not explain the saturation of the system at the maximum count rate oF 14500 counts/s originally observed in the course of the base calibrationstudy (Brodeur and Koizumi 1989) when counting high gamma-ray fields• A maximum, well in excess of 70000 coL, nts/s, is predictedwhen the dead time of 12 _s is the sole source of the system saturation. (Arthur 1990). The source of the contamination was later shown to be radon adhering to the cool surface of the probe, lt is suggested that the probe be encased in a polyethylene bag for future calibration runs.…”

1993 yearly calibration of Pacific Northwest Laboratory`s gross gamma-ray borehole geophysical logging system

“…round by 2. The base calibrationreport (Brodeurand Koizumi 1989) and subsequent % yearly calibrationreports (Arthur 1990(Arthur , 1991(Arthur , 1992 Table 3. Measured linearityrefers to a least-squaresfit of output voltage versus percentageof full-scaleinput.…”

“…for half of full scale. Because of the strict linearityobserved for the rate meters, as indicatedin Tables ] and 2, Arthur (1990) previouslyconcluded that the chart recorder had a nonlinearresponse in the mid-region,which continuesto be manifest. The nonlinearbehavior of the chart recorder is evident in the data resulting from the calibratedvoltagecheck (Table 4).…”