Optimization of the lead probe neutron detector.

Technical Report · Mon Mar 01 04:00:00 EST 2004

DOI:https://doi.org/10.2172/918771· OSTI ID:918771

Ziegler, Lee ^[1]; Ruiz, Carlos L; Franklin, James Kenneth ^[2]; Cooper, Gary Wayne; Nelson, Alan J

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1. Bechtel/Nevada, Las Vegas, NV
2. Ktech Corporation, Albuquerque, NM

The lead probe neutron detector was originally designed by Spencer and Jacobs in 1965. The detector is based on lead activation due to the following neutron scattering reactions: {sup 207}Pb(n, n'){sup 207m}Pb and {sup 208}Pb(n, 2n){sup 207m}Pb. Delayed gammas from the metastable state of {sup 207m}Pb are counted using a plastic scintillator. The half-life of {sup 207m}Pb is 0.8 seconds. In the work reported here, MCNP was used to optimize the efficiency of the lead probe by suitably modifying the original geometry. A prototype detector was then built and tested. A 'layer cake' design was investigated in which thin (< 5 mm) layers of lead were sandwiched between thicker ({approx} 1 - 2 cm) layers of scintillator. An optimized 'layer cake' design had Figures of Merit (derived from the code) which were a factor of 3 greater than the original lead probe for DD neutrons, and a factor of 4 greater for DT neutrons, while containing 30% less lead. A smaller scale, 'proof of principle' prototype was built by Bechtel/Nevada to verify the code results. Its response to DD neutrons was measured using the DD dense plasma focus at Texas A&M and it conformed to the predicted performance. A voltage and discriminator sweep was performed to determine optimum sensitivity settings. It was determined that a calibration operating point could be obtained using a {sup 133}Ba 'bolt' as is the case with the original lead probe.

• Research Organization: Sandia National Laboratories
• Sponsoring Organization: USDOE
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 918771
• Report Number(s): SAND2004-1163
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CALIBRATION
DISCRIMINATORS
EFFICIENCY
GEOMETRY
HALF-LIFE
METASTABLE STATES
NEUTRON DETECTORS
NEUTRONS
Neutrons-Monitoring-Instruments-Design and construction.
Neutrons-Scattering.
OPTIMIZATION
PERFORMANCE
PLASMA FOCUS
PLASTIC SCINTILLATORS
PROBES
Probes (Electronic instruments)
SCATTERING
SENSITIVITY