Yacouba Diawara

Wavelength-shifting-fiber scintillation detectors for thermal neutron imaging at SNS

We have developed a wavelength-Shifting-fiber Scintillator Detector (SSD) with a 0.3 m2 area per module. Each module has 154 × 7 pixels and a 5 mm × 50 mm pixel size. Our goal is to design a large area neutron detector offering higher detection efficiency and higher count-rate capability for Time-Of-Flight (TOF) neutron diffraction in the Spallation Neutron Source (SNS). A ZnS/6LiF scintillator combined with a novel fiber encoding scheme (v.3) was used to record the neutron events. A Cross-fiber Read-Out-Card (CROC) based digital-signal processing electronics and position-determination algorithm was applied for neutron imaging. Neutron-gamma discrimination was carried out using Pulse-Shape Discrimination (PSD). A sandwiched flat scintillator detector can have a detection efficiency close to He-3 tubes (about 10 atm). A single layer and sandwiched flat scintillator detectors have count rate capabilities of about 6,000 and 35,000 cps/cm2, respectively, which can satisfy the count rate requirement of powder diffractometers at SNS. Detectors with v.3 fiber encoding have better image quality and higher spatial resolution than those with previous v.2 fiber encoding.

A neutron scintillator based on transparent nanocrystalline CaF2:Eu glass ceramic

There are no efficient Eu2+ doped glass neutron scintillators reported due to low doping concentrations of Eu2+ and the amorphous nature of the glass matrix. In this work, an efficient CaF2:Eu glass ceramic neutron scintillator was prepared by forming CaF2:Eu nanocrystals in a 6Li-containing glass matrix. Through appropriate thermal treatments, the scintillation light yield of the transparent glass ceramic was increased by a factor of at least 46 compared to the as-cast amorphous glass. This improvement was attributed to more efficient energy transfer from the CaF2 crystals to the Eu2+ emitting centers. Further light yield improvement is expected if the refractive index of the glass matrix can be matched to the CaF2 crystal.

A multi-anode photomultiplier tube based wavelength-shifting-fiber detector for neutron diffraction

Wavelength-shifting (WLS) fiber scintillator neutron detectors were developed for two time-of-flight (TOF) neutron powder diffractometers (POWGEN, VULCAN) at Spallation Neutron Source (SNS). In a recent module (v3.0), however, there are 32 l-inchdiameter photomultiplier tubes (PMTs), which are bulky and expensive. We built a new detector module (v3.1) based on four multi-anode (MA) PMTs, and tested its performance including detection efficiency, count rate capability, spatial resolution, ghosting properties, and gamma-ray sensitivity. The v3.1 module was compared with two prior v3.0 modules, and 3He tu be detectors.

A neutron sensitive microchannel plate detector with cross delay line readout

Microchannel plates containing neutron absorbing elements such as boron and gadolinium in the bulk glass are used as the sensing element in high spatial resolution, high rate neutron imaging systems. In this paper we describe one such device, using both 10B and natural Gd, which employs cross delay line signal readout, with time-of-flight capability. This detector has a measured spatial resolution under 40 μm FWHM, thermal neutron efficiency of 19%, and has recorded rates in excess of 500 kHz. A physical and functional description is presented, followed by a discussion of measurements of detector performance and a brief survey of some practical applications.

A High Count Rate Neutron Beam Monitor for Neutron Scattering Facilities

Beam monitors are an important diagnostic tool in neutron science facilities. Present beam monitors use either ionization chambers in integration mode, which are slow and have no timing information, or pulse counters which can easily be saturated by high beam intensities. At high flux neutron scattering facilities, neutron beam monitors with very low intrinsic efficiency (10-5) are presently selected to keep the counting rate within a feasible range, even when a higher efficiency would improve the counting statistics and yield a better measurement of the incident beam. In this work, we report on a high count rate neutron beam monitor. This beam monitor offers good timing with an intrinsic efficiency of 10-3 and a counting rate capability of over 1,000,000 cps without saturation.

Large area portable neutron detectors Helium-3 alternatives

PartTec, Ltd. has, for the past 3 years, pursued the development of 3He alternative neutron detectors for applications such as border security, portal monitors and handheld devices. This paper discusses PartTecs mobile, very large area, ruggedized and highly efficient neutron detector. The detectors construction and performance are outlined in the paper. The goals for development of the detector are to meet all performance standards of the ANSI N42.43 committees publication, “American National Standard Performance Criteria for Mobile and Transportable Radiation Monitors Used for Homeland Security.” The introductory model of PartTecs line of mobile neutron detectors has an active area of 3,600 cm2, consists of 1,200 wavelength shifting fibers, 12 single anode photomultiplier tubes and 60cm × 60cm 6LiF:ZnS(Ag) scintillator sheets. The purpose of the paper is to introduce to the community the successful implementation of the use of LiF scintillator-based neutron detectors in real-world applications, showing that a commercially viable helium-3 replacement can now be developed. The paper discusses issues related to this detection technology including its performance, manufacture, availability, design flexibility, and cost.