# Low Radioactivity Techniques Workshop - LRT2013

10-12 April 2013
INFN - Laboratori Nazionali del Gran Sasso
Europe/Rome timezone

## A Fast Neutron Spectrometer for Underground Science

10 Apr 2013, 10:40
20m
E. Fermi auditorium (INFN - Laboratori Nazionali del Gran Sasso)

### E. Fermi auditorium

#### INFN - Laboratori Nazionali del Gran Sasso

oral presentation Screening facilities and low background detectors

### Speaker

Thomas Langford (University of Maryland)

### Description

The University of Maryland and National Institute of Technology developed the Fast Neutron Spectrometers (FaNS) as high efficiency, full-energy reconstructing, neutron detectors. The first generation, FaNS-1, consisted of 18 liters of plastic scintillator, separated in six optically decoupled segments, and six $^3$He proportional counters. The detector operated under the principle of capture-gated spectroscopy, a technique that demands a delayed coincidence between a neutron thermalizing in the scintillator and then capturing in a helium counter. FaNS-1 was calibrated at NIST using $^{252}$Cf for efficiency and mono-energetic neutron generators, based on deuterium-deuterium and deuterium-tritium fusion, to test energy reconstruction. After measuring the surface fast neutron spectrum from 1 MeV to 150 MeV at NIST Gaithersburg, the detector was installed at the Kimballton Underground Research Facility in Ripplemead, VA, where it operated for two years. During this time FaNS-1 measured the fast neutron backgrounds from the surrounding rock, and placed a limit on the cosmic-ray spallation induced neutron flux. The fast neutron spectrum measured at KURF is presented along with the calibration and surface data. An upgraded detector was designed to measure neutron energies from 250 keV to 2 GeV. FaNS-2 consists of sixteen segments of plastic scintillator, with total active volume of 73 liters, interspersed with 21 $^3$He proportional counters for thermal neutron detection. FaNS-2 was calibrated at NIST using a variety of sources; $^{252}$Cf spontaneous fission neutron sources, an AmBe $(\alpha,n)$ source, and two mono-energetic neutron generators. The absolute efficiency was also measured using the $^{252}$Cf source at multiple distances from the detector. All calibration data types are compared to detailed Monte Carlo simulations using MCNP. We present the fast neutron fluence and spectrum measured at 100 m above sea level for neutrons from 250 keV to 2 GeV. We discuss installation of FaNS-2 in a shallow underground lab at 100 meter water equivalent overburden.

### Primary author

Thomas Langford (University of Maryland)

### Presentation Materials

 Slides
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