Passive neutron coincidence counting with plastic scintillators for the characterization of radioactive waste drums

Conference · Wed Jul 01 00:00:00 EDT 2015

DOI:https://doi.org/10.1109/ANIMMA.2015.7465518· OSTI ID:22531170

Deyglun, C.; Simony, B.; Perot, B.; Carasco, C. ^[1]; Saurel, N.; Colas, S. ^[2]; Collot, J. ^[3]

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1. CEA, DEN, Cadarache, Nuclear Measurement Laboratory, F-13108 Saint-Paul-lez-Durance (France)
2. CEA, DAM, Valduc, F-21120 Is-sur-Tille (France)
3. Laboratoire de Physique Subatomique et de Cosmologie, Universite Grenoble Alpes, CNRS/IN2P3, Grenoble (France)

The quantification of radioactive material is essential in the fields of safeguards, criticality control of nuclear processes, dismantling of nuclear facilities and components, or radioactive waste characterization. The Nuclear Measurement Laboratory (LMN) of CEA is involved in the development of time-correlated neutron detection techniques using plastic scintillators. Usually, 3He proportional counters are used for passive neutron coincidence counting owing to their high thermal neutron capture efficiency and gamma insensitivity. However, the global {sup 3}He shortage in the past few years has made these detectors extremely expensive. In addition, contrary to {sup 3}He counters for which a few tens of microseconds are needed to thermalize fast neutrons, in view to maximize the {sup 3}He(n,p){sup 3}H capture cross section, plastic scintillators are based on elastic scattering and therefore the light signal is formed within a few nanoseconds, correlated pulses being detected within a few dozen- or hundred nanoseconds. This time span reflects fission particles time of flight, which allows reducing accordingly the duration of the coincidence gate and thus the rate of random coincidences, which may totally blind fission coincidences when using {sup 3}He counters in case of a high (α,n) reaction rate. However, plastic scintillators are very sensitive to gamma rays, requiring the use of a thick metallic shield to reduce the corresponding background. Cross talk between detectors is also a major issue, which consists on the detection of one particle by several detectors due to elastic or inelastic scattering, leading to true but undesired coincidences. Data analysis algorithms are tested to minimize cross-talk in simultaneously activated detectors. The distinction between useful fission coincidences and the correlated background due to cross-talk, (α,n) and induced (n,2n) or (n,n'γ) reactions, is achieved by measuring 3-fold coincidences. The performances of a passive neutron coincidence counting system for radioactive waste drums using plastic scintillators have been studied using the Monte Carlo radiation transport code MCNPX-PoliMi v2.0 coupled to data processing algorithms developed with ROOT data analysis software. In addition to the correlated background, accidental coincidences are taken into account in the simulation by randomly merging pulses from different calculations with fission and (α,n) sources. (authors)

• Research Organization: Institute of Electrical and Electronics Engineers (IEEE), New York, NY (United States)
• OSTI ID: 22531170
• Report Number(s): ANIMMA-2015-IO-108; TRN: US16V0513102111
• Resource Relation: Conference: ANIMMA 2015: 4. International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, Lisboa (Portugal), 20-24 Apr 2015; Other Information: Country of input: France; 7 Refs.
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ALGORITHMS
COINCIDENCE METHODS
CRITICALITY
CROSS SECTIONS
DATA ANALYSIS
ELASTIC SCATTERING
FAST NEUTRONS
FISSION
GAMMA RADIATION
HE-3 COUNTERS
INELASTIC SCATTERING
MONTE CARLO METHOD
NEUTRON DETECTION
PLASTIC SCINTILLATION DETECTORS
TIME-OF-FLIGHT METHOD
TRITIUM