Theoretical and experimental study of the reduction in sensitivity of a multisphere system having an epithermal detector used for fast neutron radioprotection

Technical Report · Mon Dec 31 04:00:00 EST 1973

OSTI ID:4938940

Kobeissi, M

Thesis. In an attempt to improve the multisphere technique, the problem of measuring the sensitivity losses of a /sup 6/LiI crystal used at the center of the sphere and subsequently enclosed in Cd (which detects only epithermal neutrons) is considered. A theoretical analysis is presented on the interaction between a fast neutron beam (14 MeV in polyethylene spheres containing a /sup 6/ LiI crystal at their centers. The different phenomena occurring from the time of the initial shock up to thermalization were studied in order to determine the effect of the variations in the diameter of the sphere and in the size of the / sup 6/LiI crystal. A mixed method of simulation was employed, this method simultaneously involving a transport code adapted to the problem and a Monte- Carlo method. In the case of a 15 inch sphere, the Monte-Carlo method yielded the source term, a sufficient number of results being obtained. Multigroup analytical calculations permitted the slowing-down flux in the sphere to be determined in a particular energy range and a classical geometry, together with the reaction rate of /sup 6/Li(n, alpha ) reactions for all energies, account being taken of the self absorption correction for the case of thermal neutrons. In this way a drop in sensitivity of 91.6% was deduced, this value lies well within the observed experimental uncertainties. (FR)

• Research Organization: Grenoble-1 Univ., 38 (France)
• Sponsoring Organization: Sponsor not identified
• NSA Number: NSA-29-026902
• OSTI ID: 4938940
• Report Number(s): FRNC-TH--414
• Country of Publication: France
• Language: French

Related Subjects

BONNER SPHERE DETECTORS
COMPUTER CODES
CORRECTIONS
FAST NEUTRONS
LITHIUM 6
LITHIUM IODIDES
MATHEMATICAL MODELS
MONTE CARLO METHOD
N46120* --Instrumentation--Radiation Detection Instruments-- Radiation Dosimeters
NEUTRON BEAMS
NEUTRON DOSIMETRY
NEUTRON FLUX
NEUTRON TRANSPORT THEORY
POLYETHYLENES
SELF-ABSORPTION
SENSITIVITY
SIZE
SOLID SCINTILLATION DETECTORS