Session KB: Instrumentation IV

Development of a neutron time projection chamber

Time projection chambers (TPCs) have unique capabilities for the detection of fast neutrons, particularly from special nuclear materials. This includes the ability to determine directional information from a single scattering and a higher efficiency compared to other point methods, such as the scatter camera. Also, neutron TPCs are sensitive to the entire 4pi range and automatically reject gamma ray events since the ionization profile from Compton scattering is vastly different from the scattering of heavier particles. The most recent progress in the neutron TPC hardware and software development will be discussed. Preliminary results will be presented, including a calibration analysis, the directional sensitivity, and the efficiency of the detector.   

Simulation of a Neutron Time Projection Chamber Detector

A neutron time projection chamber (nTPC) prototype constructed at Lawrence Livermore National Laboratory is a promising detector for directional detection of shielded special nuclear material, exhibiting powerful background rejection and neutron/gamma discrimination. The location of the fast neutron source is determined by detection of preferentially forward-pointed proton recoils in our hydrogen/methane-filled nTPC. A simulation of the nTPC in a real environment is conducted, characterizing the angular spread of detected proton recoils by taking into account the detector design, detector environment, and various analysis cuts. Accuracy of nTPC pointing to the neutron source is determined by simulation. Comparison of the simulation results with the experimental data undergoing the identical data analysis indicates the accuracy of the detector model and detector limitations. Among the limitations, particular attention is given to several classes of events which may reduce the pointing accuracy, including multiple scatters within the chamber and neutron scatters off of the surrounding material.   

Neutron Multiplicity Discrimination in MoNA Using Hit Pattern Analysis

The Modular Neutron Array (MoNA) at NSCL, Michigan State University, consists of 144 2-m long scintillator bars with PMT's attached at each end, designed to measure the kinematic trajectory of neutrons resulting from breakup reactions. The ability to filter data based on neutron multiplicity is critical to the study of multiple-neutron breakup reactions. The approach presented here is based on the analysis of \textquotedblleft hit patterns\textquotedblright in MoNA, consisting of singlet ($s$) and doublet ($d$) event combinations ranging from multiplicity 2 ($ss$, $d$ events) to 4 ($sds$, $dd$ events, etc.). A singlet event is defined as a hit spatially separated from all other hits by more than a \textquotedblleft separation\textquotedblright radius and a doublet event as two hits occurring within a \textquotedblleft doublet\textquotedblright radius. A doublet event can result from neutron scattering that produces a sufficiently energetic proton (through charge exchange scattering, for example) to scintillate in two adjacent bars. Since a neutron loses significant energy in doublet scattering, multiple neutron decays are predicted to produce fractionally more doublet combination events ($ds$, $dss$, $sds$, $dd$ etc.) than single-neutron decays. Neutron decay energy spectra are then gated on specific hit patterns to optimize the relative number of multiple neutron events in the dataset. Hit pattern analysis has been applied to three separate experimental data sets involving multiple neutron decay, and results will be presented.   

Simulations for DESCANT - a neutron array for TRIUMF-ISAC

A novel neutron tagging array is being developed for the study of high-spin states of neutron-rich systems. This ground- breaking design will be based upon an array of liquid deuterated scintillators for neutron detectors and is called the DEuterated SCintillator Array for Neutron Tagging or DESCANT. DESCANT will serve as an auxiliary detector for the TIGRESS spectrometer located at TRIUMF's ISAC radioactive ion beam facility. DESCANT is comprised of 70 fully close-packed neutron detectors which subtends an angle of $\theta = 65.5^{\circ}$ and covers $92.6\%$ of this solid angle or $1.08\pi$ sr. The multiple scattering of neutrons between detectors is commonly dealt with by vetoing signals collected in adjacent detectors. This results in a much-reduced detection efficiency for higher neutron multiplicity events. The measured pulse height spectrum is forward-peaked and this information can be correlated with the time-of-flight to overdetermine the neutron energy, thus rejecting multiple scattering without the need to veto nearest neighbours. Results from early feasibility tests will be presented, along with the status of our GEANT4 simulations of the array performance.   

Geant4 simulations for the Versatile Array of Neutron Detectors at Low Energies (VANDLE)

The Versatile Array of Neutron Detectors at Low Energies (VANDLE) (E$_n$ $\ circa$ 100keV - 10 MeV) has been proposed to study the structure of exotic nuclei with low-energy radioactive ion beams from the Holifield Radioactive Ion Beam Facility (HRIBF) at the Oak Ridge National Laboratory (ORNL). The VANDLE array is highly modular based on bars of scintillator allowing the configuration of the individual elements to be optimized for particular experimental requirements. Proposed experiments include (d,n) reactions and beta-delayed neutron emission studies relevant to nuclear astrophysics. Simulations performed using the GEANT4 toolkit are in progress in order to achieve the best configuration: to cover a large solid angle, to have an optimal position resolution and high efficiency. The GEANT4 simulations are presently being compared with neutron efficiency data obtained at the Edwards Accelerator Laboratory at Ohio University, as well as with cosmic-ray data acquired at Louisiana State University. This work is supported in part by the U.S. Department of Energy.   

Development of digital electronics for VANDLE

The proposed Versatile Array of Neutron Detectors at Low Energies (VANDLE) will be used in reactions and decay studies with exotic nuclei. VANDLE will consist of plastic scintillator modules for neutron energy measurement in the range between 100 keV and 10 MeV using time of flight (TOF) technique. TOF measurements require a sub-nanosecond electronic timing resolution in order to achieve good energy resolution. It is proposed to use a digital data acquisition system to instrument VANDLE. Series of tests have been performed with elements of the prototype detector and a digital data acquisition system. The data indicate that even with the fast scintillator signal sampled with relatively low (100 MHz) frequency one can achieve a low neutron detection threshold and desired timing resolution.   

Geant Simulation of a Fission Fragment Spectrometer

A dual arm, time of flight, fission fragment mass spectrometer has been simulated using Geant to determine if any improvements in mass resolution will be achieved by using a segmented silicon energy detector. The simulation was also used to determine the optimum fission fragment source size, as well as the spectrometer arm length.   

Improvements in Measuring Fission-Neutron Spectra at a White Neutron Source

The spectrum of neutrons emitted in fission induced by MeV neutrons is important for a wide range of applications and for testing models of fission physics. At the Los Alamos Neutron Science Center, we are developing a program to improve the experimental data base for neutron-emission spectra from fission induced by incident neutrons from 0.5 MeV to 200 MeV. These experiments are based on double time-of-flight techniques to determine the energies of the incident and emitted neutrons. Parallel-plate avalanche detectors with excellent timing characteristics are being developed to identify fission in actinide samples. A large neutron-detector array is being assembled to detect the fission neutrons. Design considerations for the array include neutron-gamma discrimination, neutron energy resolution, angular coverage, segmentation, detector efficiency calibration and data acquisition. The status of these developmental activities and preliminary tests of the components will be presented.   

The Fission Time Projection Chamber Project

New high-precision fission experiments have become a priority within the low-energy nuclear community. Modern sensitivity calculations have revealed unacceptable liabilities in some of the underlying fundamental nuclear data and have provided target accuracies for new measurements that are well beyond what can be delivered using current experimental technologies. A potential breakthrough in the precision barrier for these measurements is the deployment of a Time Projection Chamber (TPC). TPC detector systems were originally developed within the particle physics community and have played a central role in that field for nearly 25 years. A group of 6 universities and 3 national laboratories have undertaken the task of building the first TPC designed specifically for the purpose of measuring fission cross sections. In this talk, I will present the motivation for the fission TPC concept, a few details of the device and why we think an improvement on 50 years of fission experiments can be accomplished.   

The Fission Time Projection Chamber

New high-precision fission experiments have become a priority within the nuclear energy community due to a growing, world wide, interest in nuclear reactors. In particular, the designs of next generation reactors require reductions in the uncertainties on a number of energy dependent, neutron induced fission cross sections. The fission Time Projection Chamber (fission TPC) is the instrument that has been selected to carry out these challenging cross section measurements. This 6000 pad TPC with 2mm hex pads has a volume of only 2 liters and is filled with a hydrogen working gas. A unique set of electronics have been designed for the TPC that use all off the shelf components to reduce development costs. In this talk, I will show how the TPC will improve previous measurements, the design specifics of the fission TPC and the progress to date.   

NIFFTE software and simulations: results from the first mock data challenge

The Neutron Induced Fission Fragment Tracking Experiment will employ a novel, high granularity, pressurized time projection chamber to measure fission cross-sections of the major actinides to sub-1\% precision. The first suite of GEANT4 simulation and reconstruction software has been developed and run in a ``mock data challenge'' to validate the detector design and demonstrate the capabilities of the experiment. This talk will present the current status of results from this exercise, details for future simulation runs and plans for analysis of the first experimental data.   

Design of a Gas Delivery System for use with a Fission Time Projection Chamber

Developing advanced nuclear reactors and waste recycling techniques requires an improvement in many basic nuclear physics measurements. To address part of this need a Time Projection Chamber is being constructed to measure fission cross sections to a higher precision than traditional fission chambers. This talk will discuss how a Time Projection Chamber works and the details of a gas delivery system being constructed for use with it.   

The Data Acquisition System for the NIFFTE Fission TPC Project

The NIFFTE Time Projection Chamber (TPC) is a powerful tool that has been selected to take precision measurements of neutron-induced fission of transuranic elements. The improved data will in turn help with the development of the next generation of nuclear reactors. An innovative design has been developed to read the data from the TPC including both commercially available and custom components. For basic run control we have adopted the MIDAS system. For slow controls and monitoring we are using commercial hardware with custom written software. An overview of the system, its current status, and initial tests will be presented.