NDA technology for uranium resource evaluation. Progress report July 1-December 31, 1979. [Gamma spectra calculations; field prototype photoneutron logging probe] Page: 8 of 11
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to reduce the background produced by thermal neu-
tron captures in the small (1.4 x 10-6 ), natural
abundance of 'He in normal helium.
Three P.C. boards make up the electronics pack-
age that occupies the topmost section of the probe.
One of these provides amplification and pulse
shaping for the helium detector signals that are
transmitted uphale in analog form. The second P.C.
board contains the circuitry required to control
the direction of travel of the gamma-ray source and
to monitor the position of the source in the probe.
Power supplies and a voltage regulator required for
operating all downhole circuitry and for providing
the bias to the helium proportional counter are
located on the third P.C. board.
All power/electrical signals were transmitted
over '90 m ("300 ft) of 4 H-O logging cable via the
winch slip rings from/to the uphole electronics
control module. Tnis module serves as the control
center for powering the probe electronics, con-
trolling and monitoring the source position, and
routing the helium detector signals from the slip
rings to an Ortec 450 amplifier for further shaping
and amplification. The output signals were sent to
the NC660 computer-based multichannel analyzer
where they were digitized and stored as pulse-
height spectra. The spectra obtained were perma-
nently recorded on floppy disk for further analysis
on a nearly identical system at LASL.
D. Calibration Facility Data
The components of the photoneutron-based log-
ging system were transported to the DOE uranium
calibration facility in Grand Junction, Colorado,
by LASL personnel in November 1979. The goals of
the field trip were to determine the field-
worthiness of the probe and to assess its response
to uranium in a variety of borehole and formation
conditions. As discussed previously, the first of
these goals was clearly met. The second goal was
also achieved as described below.
Static and dynamic data were obtained in the A
and D models. The information gathered can be
classified in three general categories, 1) cali-
bration--tool response as a function of uranium ore
grade with all other parameters fixed; 2) formation
parameter effects--tool response as a function of
formation density, porosity, and neutron-absorber
content changes with ore grade fixed; and 3)borehole diameter calibration--tool response as a
function of borehole diameter and fluid with all
other parameters fixed.
1. Calibration. The calibration of the probe was
determined by static measurements in models Al, A2,
and A3, with both air and water as borehole fluids.
Model A4 was also measured but the uranium concen-
tration is not uniform with depth and the results
were not used in establishing the calibration.
Models Al through A4 are each 1.83 m (6 ft) in
diameter and 8.84 m (29 ft) deep with a vertical,
11.4-cm (4.5-in.) borehole in the center. There is
a 1.52-m (5-ft)-thick barren zone at the top of
each model, followed by a 1.83-m (6-ft) thick ore
zone, and finally a 1.22-m (4-ft)-thick barren
zone. The remaining 4.27 m (14 ft) at the bottom
of the models contains a runout tube immediately
below the borehole. The formation parameters for
the ore zones of all models studied are given in
Table I.
Careful static scans of models A3 and A4 were
made with air as the borehole fluid, whereas a more
limited number of data points were obtained in the
ore zones and barren zones in the other cases.
Table II details the calibration results both in
terms of response per unit ore grade and response
per unit U308 density. The weighted average
response per unit U308 density is determined,
at least in a relative sense, to better than 2%
for both water- and air-filled boreholes. These
results are shown in the conventional way in Fig. 3.
TE I
FORmAON PAAMETERS FOR A AM D HDELS AT DOE
GRA JJCTU CAIWAZON FACILITYA-I
A-2
A-3
A-s-T
A-s-B
4.4
*4-Ore Grade
(AP Lys)
278 36
757 42
1550 si
TO 32
824 91
686 73
797 55Dry Buil Density
2.22
2.17
2.18
2.22
2.17
2.40
1.85
2.21
2.12Porosity
(1)
is '
is '
is '
is '
17.8
17.8
28.8
16.3
22.11Paraweter
Ore-Grade
re-Grade
Ore-Grade
Ore-Gade
high L
high 4
high "
Borehole
iamter
and Fluida stimte r
bAeaavalues for rwul fauit ore ,wu5
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Evans, M.L. NDA technology for uranium resource evaluation. Progress report July 1-December 31, 1979. [Gamma spectra calculations; field prototype photoneutron logging probe], report, August 1, 1980; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1057638/m1/8/?rotate=270: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.