Session L07: Instrumentation: Low-Energy Particle Detectors

Measurements of Neutron Scattering from Carbon Using a Diamond Detector

Organic scintillators are commonly used for neutron detection at rare isotope facilities for nuclear structure studies. The majority of the total cross-section for neutrons in this energy range is due to interactions with carbon, which often result in a low scintillation light yield. The light produced is often below threshold (i.e. "dark" scattering), which introduces uncertainty into the neutron position reconstruction in measurements for which the detectors are used. To address this uncertainty, an experiment will be conducted at Los Alamos Neutron Science Center (LANSCE) in which a spectroscopic diamond detector will be used as both a target and a detector. These diamond detectors have a much lower threshold than most neutron detectors and thus can detect neutron-carbon interactions. A wall of Modular Neutron Array (MoNA) bars downstream of the diamond will be used to determine the angular distributions of the scattered neutrons. The neutron flux will be measured with fission chambers, enabling absolute cross-section measurements. This experiment will extend the empirically derived cross-section libraries to higher energies (20-200 MeV), which are relevant to the fast beam experiments performed at rare isotope facilities. These cross-sections will be used to improve simulation and in turn improve interpretation of experimental data.   

Developing a Next-Generation Neutron Detector

The MoNA Collaboration has been utilizing the MoNA-LISA neutron detector array for over 20 years for the investigation of neutron-unbound states in invariant mass measurements. One of the main limiting factors in the resolution of the extracted decay energy spectra is due to the position resolution of the neutron detector. The Collaboration has set out to develop a next generation neutron detector in an attempt to overcome this limitation. The new dector will use SiPM sensors to read out the scintillation light of the plastic scintillator. A test kit for the evaluation of SiPM sensors and for benchmarking of detector simulations has been developed. The test kit uses a simple custom PCB design and off-the-shelf components to construct a small scintillation detector. The detector is being read out by a desktop waveform digitizer. With this test kit, undergraduate students learn basic principles of scintillation detector assembly and perform tests using cosmic ray muons and radioactive sources. The results of the measurements are used to benchmark our detector simulation and to optimize the new detector design.   

Development and Fielding of a Spectrometer for High Flux CW/Pulsed Neutron Beam Characterization

Fast, high-flux neutrons are an attractive source for imaging due to their ability to penetrate high-Z materials. Intense neutron sources also provide a powerful tool to measure neutron scattering cross sections needed to advance basic and applied nuclear science and engineering. However, intense continuous neutron sources are difficult to characterize due to the inapplicability of traditional time-of-flight techniques and detection challenges associated with high count rates. A novel neutron diagnostic system for use at an advanced fast neutron imaging facility is being developed at Lawrence Livermore National Laboratory (LLNL). This scatter time-of-flight (sTOF) neutron spectrometer will: (1) have high energy resolution for fast neutrons; (2) be compatible with both low current, pulsed neutron sources and high current, continuous neutron beams; and (3) function in a high radiation background environment. A successful test of the sTOF spectrometer was conducted at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory using neutrons produced from a 14 MeV deuteron beam incident on a 3.7-mm-thick carbon target.   

Neutron Leakage Spectra of the EUCLID Experiment

Integral experiments with sub-critical and critical configurations of special nuclear material are performed in support of nuclear data validation and adjustment.  Different nuclear data evaluations may have different values for individual cross sections due to uncertainties in (or lack of) differential experiments, but compensating errors in these data sets can lead to the same k_eff results for one application while vastly different for another application.  One example of this is ²³⁹Pu, where both ENDF/B-VIII.0 and JEFF-3.3 correctly compute k_eff of the Jezebel critical assembly, but the individual contributions from each reaction are vastly different.  To help resolve this specific case, the Experiments Underpinned by Computational Learning for Improvements in Nuclear Data (EUCLID) project used machine learning to design a set of experiments to help resolve the compensating errors in ²³⁹Pu.  A total of six responses were measured during the experimental campaign, which constrain the data in ways that k_eff alone cannot and will be used for adjustment of the nuclear data.  One of these responses is the neutron leakage spectrum, which recent work has shown to be useful for constraining the prompt fission neutron spectrum and inelastic scattering.  The neutron leakage spectra were measured utilizing a 3 in. right cylinder EJ-301D detector.  The measured signal in the detector was deconvoluted using spectrum unfolding techniques, which are presented and compared to simulations.   

Testing the DESCANT prototype with monoenergetic neutrons

The DESCANT array at TRIUMF is designed to detect neutrons from RIB experiments. DESCANT is composed of 70 close-packed deuterated organic liquid scintillators coupled to digital fast read-out ADC modules. This configuration permits online pulse-shape discrimination between neutron and $gamma$-ray events. A prototype detector was tested with monoenergetic neutrons at the University of Kentucky Accelerator Laboratory. The data from these tests was compared to Geant4 simulations. The results of the tests will be presented.   

Development work for the Detector Array for Energy Measurements of Neutrons (DAEMON)

As one moves away from the stable isotopes and deeper into the neutron-rich region, the likelihood of β-delayed neutron (βn) emission increases. The ability to understand the the neutron emission probabilities and the neutron energy spectrum can reveal highly sensitive details of the nuclear structure that a conventional β-decay study using only γ-ray detection cannot. We propose to build the Detector Array for Energy Mesaurements of Neutrons (DAEMON) that will employ the time-of-flight technique to enable high-resolution energy measurements of the neutrons following βn emission. DAEMON will be used in conjunction with the GRIFFIN and DESCANT spectrometers at the TRIUMF-ISAC radioactive beam facility. The initial trials, performed at the University of Guelph, involving testing the rudimentary geometries of EJ200 plastic scintillators and various electronic parameters of silicon photomultiplier (SiPM) arrays, will be presented. Comparisons of data collected using γ-ray sources with GEANT4 simulations are made.    

Optimization of a timing scintillator for the MoNA-Sweeper setup at FRIB

The MoNA Collaboration performs experiments to measure neutron-unbound states using invariant mass spectroscopy. This method requires the coincident measurement of one or more decay neutrons, the resulting charged fragment, and sometimes gamma-rays. A central aspect of this analysis is to identify the charged fragments resulting from the decay of the populated unbound states. With the Facility for Rare Isotope Beams (FRIB) currently in operation, higher energy and intensity beams allow for the study of neutron-unbound states in higher mass systems (A > 30). Sufficient isotopic separation of charged fragments in this mass region using the typical MoNA-Sweeper setup requires a Time-of-Flight (ToF) resolution of better than 100 ps. A high-resolution SiPM-based plastic scintillation detector design is being investigated as an alternative to the well-established PMT-based plastic scintillation detector for ToF measurements. A prototype is under development following Geant4 simulations that were performed to optimize the timing resolution of the SiPM-based detector design, and to compare it to the timing resolution obtained using a PMT-based design. Preliminary results from this study will be presented and discussed.   

Characterization of CZT detectors for particle detection studies

Cadmium Zinc Telluride (CZT) is a room temperature solid-state semiconductor material predominantly used in X-ray detection. Due to trapping effects, CZT is difficult to use as a particle detector. This research aims to characterize individual CZT detectors to be used in at a beam facility to study the effects of charge trapping on particle detection. The trapping characteristics are analyzed against beam line performance. Methods of characterization will be presented with how they relate to preliminary proton beam results. Specifically, this presentation will focus on the investigation of alpha source tests used to produce Hecht curves and the analysis to extract the mobility lifetime product (µt), and how it informs proton beam results.   

First results from LACES-X-Array-SATURN: Isomeric State Half-Life in 156Pm

A new conversion electron detector has been commissioned at the ATLAS/CARIBU facility at

Argonne National Laboratory. The LSU-Argonne Conversion Electron Spectrometer (LACES) is

a LN₂-cooled Si(Li) detector system designed to be coupled to the X-Array/Scintillator and Tape

Using Radioactive Nuclei (SATURN) decay station. The beta-decay of ¹⁵⁶Nd has been employed

to populate states in the deformed, odd-odd nucleus ¹⁵⁶Pm. Within the experiment, the half-

life of the low-spin K^π = 1⁺ isomeric state at 150.3 keV has been determined. The initial results,

including internal conversion coefficients and transition multipolary assignments, will be presented.   

Results from the first fast beam test of the Energy Loss Optical Scintillation System

The Energy Loss Optical Scintillation System (ELOSS) is a proposed high luminescence-yield gaseous detector used for atomic number identification of rare, short-lived atomic nuclei [1]. ELOSS will function as part of the focal-plane detector system of the S800 spectrograph [2] for particle identification (PID) in nuclear physics experiments at the Facility for Rare Isotope Beams (FRIB). FRIB is among the world’s premier rare-isotope beam facilities producing a majority of the isotopes that are created in the cosmos, which then decay into the elements found on Earth. State-of-the-art experimental equipment like ELOSS will tap into FRIB’s unprecedented discovery potential by studying isotopes at high beam rate and with high performance, having a broad, global impact on radiation-detection physics and technology. ELOSS also represents a prototype for the development of PID detector systems of other planned and future spectrometers, such as the High Rigidity Spectrometer at FRIB [3].

     This work will focus on the operational mechanism and performance of ELOSS, demonstrated in a fast beam (150 MeV/u) experiment with ³⁶Ar at FRIB. The initial detector response and DAQ configuration to CF4 scintillation, effective area scanning for finishing the calibration of the optical readout, comparison between primary and proportional scintillation modes and the performance as a function of beam rate are discussed.   

Innovative Microwave Resonators for Very High Mass Axion Dark Matter Searches

The most sensitive searches for axion halo dark matter are based on the resonant conversion of axions to photons within a microwave cavity permeated by a strong magnetic field.  Current and future experiments such as HAYSTAC and ALPHA seeking to reach recent predictions of the post-inflation axion of masses of 40-180 μeV (~10-45 GHz) are challenged both by the rapidly diminishing volume of conventional microwave cavities with frequency (thus loss of signal power) and by the proliferation of other modes which hybridize with the mode of interest (thus loss of frequency coverage).  We will present results on metamaterial-inspired resonators which can simultaneously have the requisite high frequency and large volume, and on photonic band gap structures which can trap the mode of interest (TM₀₁₀) while radiating away most of the interfering modes (TE_lmn).  Finally we will present the design and first experimental results from a resonator incorporating both of these features, opening the path to the post-inflation axion.