We have developed, fabricated and tested a prototype imaging neutron spectrometer designed for real-time neutron
source location and identification. Real-time detection and identification is important for locating materials. These
materials, specifically uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other forms
of radiation (e.g. gamma rays), penetrating neutron emission is very uncommon. The instrument detects these neutrons,
constructs images of the emission pattern, and reports the neutron spectrum. The device will be useful for security and
proliferation deterrence, as well as for nuclear waste characterization and monitoring. The instrument is optimized for
imaging and spectroscopy in the 1-20 MeV range. The detection principle is based upon multiple elastic neutron-proton
scatters in organic scintillator. Two detector panel layers are utilized. By measuring the recoil proton and scattered
neutron locations and energies, the direction and energy spectrum of the incident neutrons can be determined and
discrete and extended sources identified. Event reconstruction yields an image of the source and its location. The
hardware is low power, low mass, and rugged. Its modular design allows the user to combine multiple units for increased
sensitivity. We will report the results of laboratory testing of the instrument, including exposure to a calibrated Cf-252
source. Instrument parameters include energy and angular resolution, gamma rejection, minimum source identification
distances and times, and projected effective area for a fully populated instrument.
SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus, is designed to measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV. SONNE is a double scatter instrument that employs imaging to maximize its signal-to-noise ratio by rejecting neutral particles from non-solar directions. Under the assumption of quiescent or episodic small-flare activity, one can constrain the energy content and power dissipation by fast ions in the low corona.
Although the spectrum of protons and ions produced by nanoflaring activity is unknown, we estimate the signal in neutrons and γ−rays that would be present within thirty solar radii, constrained by earlier measurements at 1 AU. Laboratory results and simulations will be presented illustrating the instrument sensitivity and resolving power.
FNIT (the Fast Neutron Imaging Telescope), a detector with both imaging and energy measurement capabilities,
sensitive to neutrons in the range 0.8-20 MeV, was initially conceived to study solar neutrons as a candidate design for
the Inner Heliosphere Sentinel (IHS) spacecraft of NASA's Solar Sentinels program and successively reconfigured to
locate fission neutron sources. By accurately identifying the position of the source with imaging techniques and
reconstructing the Watt spectrum of fission neutrons, FNIT can detect samples of special nuclear material (SNM),
including heavily shielded and masked ones. The detection principle is based on multiple elastic neutron-proton
scatterings in organic scintillators. By reconstructing n-p event locations and sequence and measuring the recoil proton
energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources
identified. We describe the design of the FNIT prototype and present its energy reconstruction and imaging
performance, assessed by exposing FNIT to a neutron beam and to a Pu fission neutron source.
Illicit nuclear materials represent a threat for the safety of the American citizens, and the detection and interdiction of a
nuclear weapon is a national problem that has not been yet solved. Alleviating this threat represents an enormous
challenge to current detection methods that have to be substantially improved to identify and discriminate threatening
from benign incidents. Rugged, low-power and less-expensive radiation detectors and imagers are needed for large-scale
Detecting the gamma rays emitted by nuclear and fissionable materials, particularly special nuclear materials (SNM), is
the most convenient way to identify and locate them. While there are detectors that have the necessary sensitivity, none
are suitable to meet the present need, primarily because of the high occurrence of false alarms.
The exploitation of neutron signatures represents a promising solution to detecting illicit nuclear materials. This work
presents the development of several detector configurations such as a mobile active interrogation system based on a
compact RF-Plasma neutron generator developed at LBNL and a fast neutron telescope that uses plastic scintillating-fibers
developed at the University of New Hampshire. A human-portable improved Solid-State Neutron Detector
(SSND) intended to replace pressurized 3He-tubes will be also presented. The SSND uses an ultra-compact CMOS-SSPM
(Solid-State Photomultiplier) detector, developed at Radiation Monitoring devices Inc., coupled to a neutron
sensitive scintillator. The detector is very fast and can provide time and spectroscopy information over a wide energy
range including fast neutrons.
We report on recent progress in the development of the Fast Neutron Imaging Telescope (FNIT), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV range. FNIT was initially conceived to study solar neutrons as a candidate design for the Solar Sentinels program under formulation at NASA. This instrument is now being configured to locate fission neutron sources for homeland security purposes. By accurately identifying the position of the neutron source with imaging techniques and reconstructing the energy spectrum of fission neutrons, FNIT can locate problematic amounts of Special Nuclear Material (SNM), including heavily shielded and masked samples. The detection principle is based on multiple elastic neutron-proton (n-p) scatterings in organic scintillators. By reconstructing the n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron point sources identified. The performance of FNIT is being evaluated through a series of Monte Carlo simulations and lab tests of detector prototypes. The Science Model One (SM1) of this instrument was recently assembled and is presently undergoing performance testing.
The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4 - 50 MeV) and bridge the huge sensitivity gap between the COMPTEL and
OSSE experiments on the Compton Gamma Ray Observatory, the SPI and IBIS instruments on INTEGRAL, and the visionary Advanced Compton Telescope (ACT) mission. The scientific goals include, among other things, compiling a much larger catalog of sources in this energy
range, performing far deeper searches for supernovae, better measuring the galactic continuum and line emissions, and identifying the components of the cosmic diffuse gamma-ray emission. MEGA will accomplish these goals using a tracker made of Si strip detector (SSD) planes surrounded by a dense high-Z calorimeter. At lower photon energies (below ~ 30 MeV), the design is sensitive to Compton interactions, with the SSD system serving as a scattering medium that also detects and measures the Compton recoil energy deposit. If the energy of the recoil electron is sufficiently high (> 2 MeV) its momentum vector can also be measured. At higher photon energies (above ~ 10 MeV), the design is sensitive to pair production
events, with the SSD system measuring the tracks of the electron and positron. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results from the prototype and describe the proposed satellite mission.
Inner heliosphere measurements of the Sun can be conducted with the proposed Solar Sentinel spacecraft and mission. One of the key measurements that can be made inside the orbit of the Earth is that of lower energy neutrons that arise in flares from nuclear reactions. Solar flare neutrons below 10 MeV suffer heavy weak-decay losses before reaching 1 AU. For heliocentric radii as close as 0.3 AU, the number of surviving neutrons from a solar event is dramatically greater. Neutrons from 1-10 MeV provide a new measure of heavy ion interactions at low energies, where the vast majority of energetic ions reside. Such measurements are difficult because of locally generated background neutrons. An instrument to make these measurements must be compact, lightweight and efficient. We describe our progress in developing a low-energy neutron telescope that can operate and measure neutrons in the inner heliosphere and take a brief look at other possible applications for this detector.
Features of the hadronic interactions of cosmic ray particles that make it difficult to measure their energies and identities precisely also provide tools by which these limitations can be partially overcome, if the detector in question is properly instrumented. I review a growing body of experimental and theoretical work to demonstrate methods by which calorimetry of cosmic rays using thin calorimeters may be optimized, and performance improved, by the use of multiple methods to read out the energy deposited by the developing shower. Examples are given using scintillating fiber, Cherenkov readout of quartz optical fiber, and silicon dE/dx information.