X-ray Measurements of a Thermo Scientific P385 DD Neutron Generator Page: 3 of 5
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FIGURE 1. Comparison of two 100-second spectra measured with an HPGe detector
using the P385 generator as the neutron source.In order to more accurately identify the
source of the x rays within the neutron generator tube,
the lead shield was removed and the neutron generator
was scanned by collimated scintillation detectors.
X-RAY SCANNING METHODS
During the scans, the neutron generator was
mounted on a sliding track that was equipped with an
optical linear encoder and digital readout, and the
encoder precision is 0.5 microns. The generator was
viewed through a 1.27-mm by 25.4-mm (0.05-inch by
1.0-inch) slit in a set of tungsten shielding blocks. The
long axis of the slit was transverse to the long axis of
the generator tube2. The generator was scanned with
both a plastic scintillation detector and a sodium
iodide detector, and both detector crystals were 25.4-
mm diameter by 25.4-mm long (1.0-inch diameter by
1.0-inch long). Prior to scanning, the neutron
generator target plane, marked on the outside of the
generator tube with a painted line, was aligned with
the viewing slit by replacing a detector with a laser
pointer, and the linear encoder position was zeroed at
this location.
During the scans, the neutron generator was
operated at 100% duty cycle with a target current of 60
pA and an accelerating voltage of 90 kV.SCANNING RESULTS
The scan results are presented in Figure 2, and they
are discussed below.
Plastic Scintillator Measurements
An initial scan of the P385 neutron generator
tube was performed using the plastic scintillation
detector. The signal was passed through an amplifier,
constant fraction discriminator, and scaler to determine
the number of counts recorded in the detector in the
energy range of the x rays. Eight ten-second counting
measurements were taken at various distances along a
190 millimeter length of the generator, from the end of
the generator housing without cable connectors to a
point approximately 60 millimeters beyond the target
plane. The number of counts at each distance was
recorded and averaged. For much of the scan, the
distance between measurement points was 2.5
millimeters, but in areas where a large increase in
counts was seen the distance between measurement
points was decreased to 0.5 millimeters. The results of
the scan show the primary source of x-ray emission
from the P385 neutron generator is an area 60 mm to
the left of the neutron production target in the vicinity
of the ion source.
In addition to the linear scan of the neutron
generator, six measurements were performed with the
detector stationary with its strongest x-ray emission-
bare P385 neutron generator
P385 with lead shielding
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Seabury, E. H.; Chichester, D. L.; Caffrey, A. J.; Simpson, J.; Lemchak, M. & Wharton, C. J. X-ray Measurements of a Thermo Scientific P385 DD Neutron Generator, article, August 1, 2001; Idaho Falls, Idaho. (https://digital.library.unt.edu/ark:/67531/metadc837623/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.