Fission Multiplicity Detection With Temporal Gamma-Neutron Discrimination From Higher Order Time Correlation Statistics

Oberer, R.B.

Oak Ridge National Laboratory

关键词: Fission;    Plastics;    Multiplicity;    36 Materials Science;    Statistics;   

DOI  :  10.2172/814311
RP-ID  :  ORNL/TM-2002/9
RP-ID  :  AC05-00OR22725
RP-ID  :  814311

美国|英语

来源: UNT Digital Library

【 摘 要 】

The subject of this thesis is the nondestructive assay (NDA) of nuclear materials. NDA is made possible by the fact that fissile and fertile transuranic isotopes emit characteristic radiations. Fission Multiplicity Detection (FMD) is the name of the standard technique used in NDA of nuclear materials in the 1960s and 1970s. It was characterized by the use of fast plastic scintillating detectors. These systems were used in both active and passive mode. These FMD systems were eventually replaced by thermal well counters as the standard NDA technique. The thermal well counters use {sup 3}He detectors embedded in a moderator. Among the passive neutron assay techniques, neutron multiplicity counting (NMC) in a thermal well counter is the preferred technique for the determination of fissile mass when spontaneous fission yields are significant. it is used in conjunction with gamma-ray spectroscopy to determine the isotopic composition of a sample. The major problem with the use of fast plastic detectors as used in FMD is that both neutrons and gamma rays are detected. The pulses from the two are indistinguishable. The disadvantages of this indistinguishability between neutron and gamma rays is explained further in the explanation of NMIS multiplicity in Section 2.5.