A large area detector for thermal neutron flux measurements at the KamLAND site

Abstract

A large area (0.5 m × 0.5 m) thermal neutron detector was developed based on 0.32 mm-thick 6 LiF:ZnS(Ag) scintillator sheets. The detector was constructed for measurements of seasonal variations in low intensity thermal neutron flux at deep underground sites. The detector response to neutrons was studied using a low intensity 241 Am/ 9 Be(α,n) neutron source. The digital pulse shape discrimination technique was applied to separate neutron capture events from the background caused by traces of α-emitters from Uranium and Thorium decay chains in scintillator components. The thermal neutron detection efficiency was 0.368±0.018 (0.155±0.009) before (after) event selection based on the digital pulse shape discrimination method. The measured α-particle background event rate in the 6 LiF:ZnS(Ag) scintillator was (4.88±0.06(stat))×10 −6 α cm −2 sec −1 . As a test of detector performance we measured the thermal neutron flux at the KamLAND area of the Kamioka neutrino observatory and compared it with result of the neutron flux measurement carried out at the Super-Kamiokande site. The thermal neutron flux at KamLAND was (6.43±0.50)×10 −6 n cm −2 sec −1 that included ∼10 % contribution from neutrons with energies above 1 eV. During the detector construction we identified a source of high amplitude noise pulses generated by 5-inch R1250 photomultipliers manufactured by Hamamatsu Photonics K. K..

A backing detector for order-keV neutrons

“…The cause of these backgrounds are likely due to the presence of radioactive materials inside the neutron detector that can decay by the emission of an alpha, which mimics a neutron capture signal to some degree. The rate that has been reported earlier [25] is quite low (4.88×10 −6 cm −2 sec −1 ) as compared to our observation. The rate of Slow Pulse events observed in our backing detector is 0.5 Hz (3.4×10 −4 cm −2 sec −1 ).…”

A Passive Shield for the RED-100 Neutrino Detector

“…4 with histograms 4, 5, and 3, respectively. The obtained U/Th and K concentrations are typical of soil and concrete [22,26,27].…”

BLOSM: Boron-based large-scale observation of soil moisture: First laboratory results of a cost-efficient neutron detector

“…This property opens up a robust way to discriminate between particles using these pulse shapes. An often used method is to define a parameter calculating the fraction of the charge in the tail of the pulse with the charge of the total pulse [9] . The P -parameter is defined as, with and the integrated signal of the long part and short part of the signal, respectively.…”