Session HH: Instrumentation II

Evaluation of New Contact Technology for A Planar High-Purity Germanium Double-Sided Strip Detector

New technologies for making position sensitive $\gamma $-ray detectors have applications in space science, medical imaging, homeland security, and nuclear structure research. One promising approach uses high-purity germanium wafers in Low Energy Photon Spectrometer (LEPS) geometry, where segmentation of the electrodes into strips forms a Double-Sided Strip Detector (DSSD). The position-sensitivity afforded by the many strips is ideal for the study of Compton scattering and polarization. However, challenges with the manufacture and performance of the rectifying contacts continue to plague the advancement of planar DSSDs. The data gathered from the combination of multiple strips' signals suffers from cross-talk between the strips and charge loss due to wide inter-strip gaps [1]. A planar, high-purity DSSD has been developed by PHDs Co. with an alternative electrode material, amorphous germanium, that can be placed such that the gaps between the strips are half the width required by other contact material. This research seeks to quantify the performance gains of the amorphous germanium contacts and smaller inter-strip gaps while exploring the possibilities for this DSSD as an imager and polarization detector.\\[4pt] [1] S. Gross, \textit{et al.}, Nucl. Inst. Meth. A 602, 467 (2009).   

Development of a New Fast Neutron/Gamma Spectrometer Array Using CLYC

Neutron physics has long suffered from a lack of detectors that provide spectroscopic information without the need for inefficient time-of-flight techniques. Any headway made towards a spectrometer with good energy resolution and neutron/gamma pulse-shape discrimination represents an important step forward in the field. Recent investigations at the University of Massachusetts Lowell with Cs$_2$LiYCl$_6$ (CLYC) scintillators have demonstrated their potential for direct pulse-height measurements via the $^{35}$Cl(n,p) reaction. From this work, it was recognized that CLYC could be optimized for fast neutron detection by growing $^6$Li-depleted crystals to suppress the overwhelming thermal neutron response. A project is now underway to develop a versatile array of 16 1"x1" $^6$Li-depleted CLYC detectors for measurements in nuclear astrophysics, reactor data, homeland security, and nuclear structure. Initial measurements of interest include prompt fission neutrons, $\beta$-delayed neutrons, and scattering cross sections. Characterizations of the neutron and gamma-ray response for the first two detectors of the array are being carried out at various facilities with both mono-energetic and continuous fast neutron beams.   

The neutron detector array DESCANT

The DESCANT array at TRIUMF is designed to track neutrons from RIB experiments. DESCANT is comprised of 70 close-packed deuterated liquid organic scintillators coupled to digital fast read-out ADC modules. This configuration will permit online pulse-shape discrimination between neutron and $\gamma$-ray events. The anisotropy of the n-d scattering will allow to distinguish higher neutron multiplicities from scattering within the array and to determine the neutron energy spectrum directly from the pulse-height spectrum without using TOF. Comparative type-testing of candidate small deuterated scintillators to non-deuterated scintillators have been performed at the University of Kentucky. Results of these type-testing measurements will be presented together with first designs of the firmware written for the fast sampling ADC modules.   

Optimization of VANDLE for $\beta $-delayed neutron decay studies using Geant4

The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a plastic-scintillator array designed for various experimental setups including $\beta $-delayed neutron spectroscopy and (d,n) transfer reactions in inverse kinematics. The neutron energy is determined through the time-of-flight technique. The array has energy resolution of $\sim$ 120 keV @ 1 MeV and energy threshold of $\sim$ 100 keV. We have developed a Geant4 simulation of VANDLE to optimize array geometry for different types of experiments and test neutron scattering models provided by Geant4. A typical $\beta $-delayed neutron decay study involves coupling with $\gamma $ detectors to collect $\beta $-$\gamma $ coincidence information. The experimental assembly including VANDLE bars, $\beta $ plastic scintillators, HPGe detectors, along with the detector support structure was modeled to assist in the fine-tuning of the setup and give a detailed understanding of the array performance. The simulation was validated by comparing to available experimental data and could serve as an important guide for the design of future experiments.   

Development of Fast, Segmented Trigger Detector for Decay Studies

Segmented scintillation detector was developed for decay studies. The detector is build with use of position sensitive photo-multiplier (PSPMT) Hamamatsu H8500 coupled with fast (16$\times$16) pixelated plastic scintillator (Eljen EJ-204). The PSPMT anodes form a (8$\times$8) two dimensional matrix which is used for position reconstruction, position resolution with average FWHM of $\sim 1.1mm$ was achieved with $^{137}$Cs gamma-source. Signals derived from non-segmented dynode are used for timing. Digital pulse shape analysis algorithm was used for this analysis and the 500 ps timing resolution was achieved. This detector is intended to use in fragmentation type experiments which require segmented detectors in order to enable recoil-decay correlations for applications requiring good timing resolution, e.g. for the neutron time-of-flight experiments using VANDLE array.   

SPIDER: New detector for measuring fission fragments at LANSCE

Studying fission fragment yields of neutron-induced fission reactions are valuable for advancing the theoretical understanding of the fission process through validation with data and as a diagnostic tool for nuclear applications. Current yield data are limited to a small range of incident neutron energies and mass resolutions of 2-3 atomic mass units (amu). A new detector, SPIDER (SPectrometer for Ion DEtermination in fission Research), is being developed to measure fission yields with high precision as a function of incident neutron energy from thermal to 20 MeV at Los Alamos Neutron Science Center (LANSCE). The time-of-flight spectroscopy `2E-2v' method used by SPIDER measures the velocity and kinetic energy of the two main fission fragments in coincidence, to identify their masses. Bragg spectroscopy will also be employed in combination with the energy measurement to determine the charge of each fragment. Prototype work is ongoing and has indicated that 1 amu mass resolution can be achieved. Current results will be presented.\\[4pt] This work is supported by LANL Laboratory Directed Research and Development Projects 20110037DR and 20120077DR. LA-UR-13-24637.   

A continuously self regenerating high-flux neutron-generator facility

A facility based on a next-generation, high-flux D-D neutron generator (HFNG) is being constructed at UC Berkeley. The current generator, designed around two RF-driven multicusp deuterium ion sources, is capable of producing a neutron output of $>10^{11}$ n/s. A specially designed titanium-coated copper target located between the ion sources accelerates D$^{+}$ ions up to 150 keV, generating 2.45 MeV neutrons through the d(d,$^{3}$He)n fusion reaction. Deuterium in the target is self loaded and regenerating through ion implantation, enabling stable and continuous long-term operation. The proposed science program is focused on pioneering advances in the $^{40}$Ar/$^{39}$Ar dating technique for geochronology, new nuclear data measurements, basic nuclear science research including statistical model studies of radiative-strength functions and level densities, and education. An overview of the facility and its unique capabilities as well as first measurements from the HFNG commissioning will be presented.   

BECOLA commissioning tests with bunched beams

The Beam Cooling and Laser spectroscopy (BECOLA) facility has been fully realized at NSCL and performance tests were completed with a stable $^{39}$K ion beam extracted at 29.7 keV from an off-line ion source. The $^{39}$K ions were cooled, bunched and subsequently neutralized by charge exchange with Na vapor. Laser light was co-propagated with the neutral $^{39}$K beam and the laser frequency was Doppler-tuned into resonance by adjusting the velocity of the $^{39}$K ions. The fluorescence induced by the laser probing of the $^{39}$K atomic beam was collected in a photomultiplier. A newly-developed DAQ system, which integrates a FPGA-based time-resolved scaler into a real-time acquisition system, was used to record the observed fluorescence as a function of both time and ion velocity.