6LiF:ZnS(Ag) Neutron Detector and Data 

Acquisition/Processing System Development

Nathaniel Kaneshige - University of Hawaii at Mānoa

Dr. Nick Maliszewskyj and Kevin Pritchard

Abstract:

The Chromatic Analysis Neutron Diffractometer or Reflectometer (CANDOR) is a new instrument under 

development at the NIST Center for Neutron Research (NCNR) that will use scattering by a broad 

energy spectrum of neutrons to investigate the structures of materials. The triggering, discrimination, 

and acquisition of neutrons from a broad energy spectrum over a range of scattering and reflecting 

angles brings unprecedented design challenges. As well-established 3He neutron detectors would not 

meet the form factor requirements of CANDOR, it was necessary to develop an ultrathin neutron 

detector using 6LiF:ZnS(Ag) plastic scintillator coupled to wavelength shifting fibers leading to a Silicon 

Photomultiplier (SiPM) for readout. The signal from the SiPMs must then be processed using fast 

electronics to discriminate neutron capture events from other event types. At this stage, we have a 

highly efficient, extremely thin, neutron detector whose performance is on par with traditional 3He gasfilled tubes at a fraction of the price.

The CANDOR data acquisition (DAQ) system includes waveform digitizers, which use digital signal 

processing (DSP) techniques to accurately identify neutron events. For this project the neutron 

detection and data acquisition/processing systems were characterized and evaluated for use in the 

CANDOR instrument as well as for other applications. 
CANDOR – Chromatic Analysis Neutron 

Diffractometer Or Reflectometer

• Neutron Diffractometry and Reflectometry is useful for analyzing the 

structures and dynamics of materials.

• CANDOR will use a broad range of wavelengths to allow for faster 

measurements. 

• CANDOR required the development of a novel ultrathin detector.
Why not He-3?

• He-3 tubes are the most widely 

used detector for their 

simplicity and gamma rejection 

ratio.

• He-3 is a gaseous and is 

optimally used under pressure

• Cylindrical form factor 

• Volume requirements increases 

proportional to the effective 

area squared

• Very costly due to supply issues

• As a solid, LiF has a higher 

molar density than He3
Neutron Detection Schematic

• Neutrons are generally detected 

indirectly through the products of a 

neutron capture.

• Left: Detection schematic for 

CANDOR’s LiF:ZnS(Ag) detector. 
n

• To the right is a Lithium-Fluoride salt

• Li-6 has a large neutron absorption 

cross section.

• An alpha and a triton are ejected after 

the absorption

Absorbing the Neutron
• This is the tough part! 

• Harvesting the energy from the high 

energy Alpha and Triton is a 

complicated process.

• We use a second material to create 

visible light from Alpha and Triton: 

Silver Activated Zinc-Sulfide

Harvesting the Energy
Detector Optimization

• GEANT4 was used to 

computationally optimize grain 

size and proportions for 6LiF:ZnS 

proportions

• Scintillator thickness was also 

evaluated using GEANT4

• These were then verified with a 

high purity neutron beam.

• Left Bottom: Scanning Electron 

Microscope (SEM) image of the 

scintillator mixture without binder. 

Courtesy of CNST
SiPM and Digitizer
Pulse Shape Discrimination

• To distinguish neutron captures from gammas and thermal noise, 

pulse shape discrimination is used.

• Two window integral discrimination can be done using digital or 

analog electronics. 

- Neutron

- Noise
Characterizing the Detector

• Python scripts were developed to 

analyze the digitizer’s output.

• Goal of transitioning from a full test 

rack of analog and digital electronics 

to a compact digitizer and computer 

for detector characterization.

Old Equipment New Equipment
Optical Figure of Merit

• FOM =

PPPPPPPPPPPPPPPPP CC CCCC CC

VV VV CC CCCC CC

PPPPPPPPPPPPPPPPP CC CCCC CC

VV VV CC CCCC CC

• Designed to be independent of gain.

• Characterizes individual detectors.

• Pulse height spectrum generated 

using a pure neutron data set.
Detector Optimization

• Over 6 batches of detectors we have substantially optimized our detector.

• Optical Figure of Merit (FOM) is a figure derived from the pulse height 

distribution that helps describe the noise-neutron discrimination.
Detector

• Going from a neutron detection 

efficiency of 40% to 91%

• The other ~9% of neutrons will 

either

• Pass through the detector

• Scatter off the detector

• Produce an unrecognizable signal

• Keeping the total cost under 

$500/3-channel detector

• Detector were developed in 

partnership with Eljen 

Technologies.
Thank You

And a Special Thanks to: • Kevin Pritchard

• Nick Maliszewskyj

• Peter Tsai

• Alon Osovizky

• Ed Binkley

• Jeff Ziegler

• Nancy Hadad

• Chuck Majkrzak

• Christoph Brocker

• Kobi Zada

• Julie Borchers

• Joseph Dura

• Brandi Toliver

CANDOR Team Members

SURF Directors

Certain commercial equipment, instruments, or materials are identified in this presentation to foster understanding. Such identification 

does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the 

materials or equipment identified are necessarily the best available for the purpose.
Appendix

• Why Neutrons?

• Neutron Use Example: Determining Cell Membrane Thickness

• Wavelength Discrimination: Pyrolytic Graphite (PG)

• Optical Figure of Merit (FOM)
Why Neutrons?

• Useful for determining the positions and 

motions of atoms in materials.

• Accessible wavelengths comparable to 

interatomic spacing.

• Magnetic moment allows for probing of 

magnetic structure.

mm=1.675× 10

−27kkkk

Charge = 0, Spin = 1⁄2

Magnetic dipole moment: μμ = −1.913 μμNN
Neutron Use Example: Determining Cell 

Membrane Thickness

• Cell membrane is comprised of a lipid-bilayer 

that we now know is ~2 nm thick.

• Neutrons will scatter differently off of the 

hydrophilic head and the hydrophobic tail.

• Alternative techniques would not have been 

usable.
Wavelength Discrimination: Pyrolytic 

Graphite (PG)

• PG has a consistent plane spacing

• Bragg diffraction “selects” the required neutron 

wavelength. 

• Allows access to 4-6 Å neutrons

• nnnn = 2dd ssss ss