The CLAS12 Backward Angle Neutron Detector (BAND)

E. P. Segarra, F. Hauenstein*, A. Schmidt, K. Price, I. Vega, J. Barlow, E. Barriga, A. Beck, W. Brooks, E. Cohen, R. Cruz-Torres, A. Denniston, M. Duer, P. Eugenio, C. Fogler, H. Hakobyan, T. Hartlove, A. Hrnjic, I. Korover, T. KutzS. May-Tal Beck, A. Nambrath, A. Ostrovidov, E. Piasetzky, J. R. Pybus, M. Ungerer, L. B. Weinstein, O. Hen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted at backward angles of 155∘ to 175∘, with momenta between 200 and 600 MeV/c0. It is positioned 3-m upstream of the target, consists of 18 rows and 5 layers of 7.2-cm by 7.2-cm scintillator bars, and read out on both ends by PMTs to measure time and energy deposition in the scintillator layers. Between the target and BAND there is a 2-cm thick lead wall followed by a 2-cm veto layer to suppress gammas and reject charged particles. This paper discusses the component-selection tests and the detector assembly. Timing calibrations (including offsets and time-walk) were performed using a novel pulsed-laser calibration system, resulting in time resolutions better than 250 ps (150 ps) for energy depositions above 2 MeV (5 MeV). Cosmic rays and a variety of radioactive sources were used to calibration the energy response of the detector. Scintillator bar attenuation lengths were measured. The time resolution results in a neutron momentum reconstruction resolution, δp∕p<1.5% for neutron momentum 200≤p≤600 MeV/c. Final performance of the BAND with CLAS12 is shown, including electron–neutral particle timing spectra and a discussion of the off-time neutral contamination as a function of energy deposition threshold.

Keywords

  • CLAS12
  • Plastic scintillator
  • Time of flight
  • Ultrafast neutrons

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