Neutron Detection

Two, 111 GBq (3 Curie) radium-beryllium (RaBe) sources were in underground storage at the Brookhaven National Laboratory (BNL) since 1988. These sources originated from Princeton Plasma Physics Laboratory (PPPL) where they were used to calibrate neutron detection diagnostics. In 1999, PPPL and BNL began a collaborative effort to expand the use of an innovative pilot-scale technology and bring it to full-scale deployment to shield these sources for eventual transport and burial at the Hanford Burial site. The transport/disposal container was constructed of depleted uranium oxide encapsulated in polyethylene to provide suitable shielding for both gamma and neutron radiation. This new material can be produced from recycled waste products (DU and polyethylene), is inexpensive, and can be disposed with the waste, unlike conventional lead containers, thus reducing exposure time for workers. This paper will provide calculations and information that led to the initial design of the shielding. We will also describe the production-scale processing of the container, cost, schedule, logistics, and many unforeseen challenges that eventually resulted in the successful fabrication and deployment of this shield. We will conclude with a description of the final configuration of the shielding container and shipping package along with recommendations for future shielding designs.

JRC has developed the Scrap Neutron Multiplicity Counter (SNMC): an advanced neutron multiplicity counter for the verification of inhomogeneous Pu samples, such as scrap material in MOX fuel fabrication plants. The innovative features of this counter with respect to existing ones rely on two aspects: (i) an optimised design based on Monte Carlo calculations in order to select the most appropriate materials, geometry and detector disposition for maximum efficiency and (ii) novel electronics based on digital signal processing (DSP) reducing the system dead time. The paper recalls the design process, the electronics, the construction and assembly of the counter. Then the results of the first experimental tests will be reported. We will show the characterization of the main physical parameters of the counter, the calibration and the verification of a wide variety of plutonium bearing samples available in the PERLA laboratory at JRC Ispra. This will include pure homogeneous samples (Pu dioxide powders, metal Pu, MOX powders and pellets) and some tests on heterogeneous samples representative of scrap material.

Research investigating the application of pressure-cycled bubble chambers to fast neutron detection is described. Experiments with a Halon-filled chamber showed clear sensitivity to an AmBe neutron source and insensitivity to a 137 Cs gamma source. Bubble formation was documented using high-speed photography, and a ceramic piezo-electric transducer element registered the acoustic signature of bubble formation. In a second set of experiments, the bubble nucleation response of a Freon-134a chamber to an AmBe neutron source was documented with high-speed photography. r

The method of cosmic ray neutron sensing - measuring soil moisture non-invasively at the hectometer scale has turned out to be feasible by detecting the environmental albedo neutron density. The key feature of the method is that neutrons generated by cosmic rays show an exceptionally different behavior interacting with hydrogen. It slows down fast neutrons whereas any other heavier element, independent of the chemical composition, rather reflects them. In the recent years the understanding of neutron transport by Monte Carlo simulations led to major advancements in precision, which have been successfully targeted meanwhile by a manifold of experiments.
We are now developing boron-lined neutron detectors using spin-off technologies from the upcoming European Spallation Source and instrument design experience from past experiments. These detectors shall also offer an alternative platform to current Helium-3 based systems. In order to reduce costs we recently have developed readout electronics and data acquistion systems based on Arduino microcontrollers.

We present new results on the measurement of correlated, outgoing neutrons from spontaneous fission events in a Cf-252 source. 16 EJ-309 liquid scintillation detectors are used to measure neutron-neutron correlations for various detector angles. Anisotropy in neutron emission is observed. The results are compared to MCNPX-PoliMi simulations and good agreement is observed.

In this paper, we propose a technique for the detection of neutrons that relies on the sensitivity of SRAM cells to particle radiation. In particular, we introduce a system based on a memory test bench that records the neutron reactions in the memory array. This system allows a good flexibility from different points of view. It is conceived to be modular, programmable, low power consuming and portable. Consequently, it can operate in various experimental conditions such as under artificial sources of particles as well as in natural ambience, from the earth surface to spatial environment. The system is also independent of the type of memory, allowing the use and the study of the interaction between particles and electronic devices built with different technologies.

An effect, which has been considered for more than 50 years as a detector background, turns out to be one of the promising spin-off technologies to access our most important resource: water. The method, called cosmic-ray neutron sensing (CRNS), is able to uniquely measure at typical correlation scales of soil water of several ten to hundred meters, which other techniques barely reach. This information is most valuable to support climate modeling and hydrology to direct applications in precision farming, draught monitoring and also snow height measurements.
Although it was known that neutrons created in cosmic-ray induced air showers form a gas above the ground, which can be related to the presence of hydrogen, the lack of computational resources prevented a precise description for the relation of neutron intensity to environmental water. Now, in a recent interdisciplinary cooperation of Particle Physics and Earth Sciences the quest to understand the particle propagation in the soil-atmosphere
interface has been solved. With the COSMOS collaboration having meanwhile deployed
more than one hundred sensors, the focus is now set to design and build large-scale neutron detectors in order to improve the measurement precision. This talk provides an overview of the detection technologies, Monte Carlo simulation methods and data challenges of CRNS
as well as it shall exemplarily show how Nuclear and Particle Physics can give birth to a new and unexpected field of applications.

The globally increased demand of Helium-3 along with the limited availability for this gas asks for the development of alternative technologies as the nowadays standard technology is still based on the Helium counter tube. In this article as a short summary insights will be given which lead to the Helium-3 crisis.

Cerium-doped LiCaAlF 6 (Ce:LiCAF) crystals have been studied as scintillators in application to thermal neutron detection. Three crystals: high-doping Ce:LiCAF, low-doping Ce:LiCAF with 50% enrichment of 6 Li (both 10 mm  10 mm  2 mm, rectangular) and high-doping Ce:LiCAF with 95% enrichment of 6 Li (Ø50.8 mm  2 mm, discus) coupled to Photonis XP5300B PMT, were tested. The response of these crystals to neutrons emitted from a paraffin moderated 238 PuBe source has been investigated. Thermal neutron peaks have been found at a Gamma Equivalent Energy (GEE) of $ 2.5 MeV for high-doping Ce:LiCAF (50% 6 Li), $ 2 MeV for low-doping Ce:LiCAF (50% 6 Li) and $ 1.9 MeV for high-doping Ce:LiCAF (95% 6 Li). The light output of Ce:LiCAF was also measured (175-250 phe/MeV from sample to sample). Lithium-6 glass GS20 from Saint Gobain was used as a reference scintillator (Ø50 mm  2 mm, circle). Relative neutron efficiency, normalized to that of GS20 lithium glass, as well as gamma-neutron intrinsic efficiency for all tested samples was calculated. Intrinsic efficiency on thermal neutron detection for small Ce:LiCAF samples was estimated at about 32-35% of that of GS20 and for large Ce:LiCAF sample as about 82% of that of GS20.

A recent shortage in 3 He for neutron detection has caused an increase in research efforts for a viable replacement. Three materials, borosilicate aerogel, 6 LiF saturated foam, and natural lithium foil, have been investigated as neutron detection materials. The materials of focus are designed in such a way that allow both reaction products from the 6 Li(n,a) 3 H and lO B(n,afLi interactions to escape the absorber and enter a detector volume simultaneously. This attribute dramatically increases the neutron detection efficiency of the detector. The neutron response pulse-height spectra of borosilicate aerogel, 4.5 percent saturated 6 LiF foam, and 10 layers of 30, 50, and 75 11m thick Li foil are presented. The theoretical neutron detection efficiencies of saturated foam and Li foils of different thicknesses are presented and compared to experimentally obtained values.

Neutrons can be indirectly detected by high-energy photons. The performance of a 4 00 Â 4 00 Â 16 00 NaI portal monitor was compared to a 3 He-based portal monitor with a comparable cross-section of the active volume. Measurements were performed with bare and shielded 252 Cf and AmBe sources. With an optimum converter and moderator structure for the NaI detector, the detection efficiencies and minimum detectable activities of the portal monitors were similar. The NaI portal monitor preserved its detection efficiency much better with shielded sources, making the method very interesting for security applications. For heavily shielded sources, the NaI detector was 2-3 times more sensitive than the 3 He-based detector.

The world of detectors used in thermal neutron scattering instrumentation has changed. By alerts on the future Helium-3 supply, critical to perspectives of the large-scale research infrastructures, the run on substitutional technologies started. Most of the solutions could be adapted from developments of particle physics and are comprised of one or more layers of Boron-10. The Time Projection Method achieves a very high resolution by projecting ionization tracks onto a readout with dense spatial and time information. The university of Bonn is developing a novel system employing the TimePix technology - CMOS based chips with 55 micrometer sized pixels operated at clock speeds up to 80 MHz. In a first prototype with 8 TimePix chips, which are arranged in parallel to a boron layer, the track topology with this unrivaled high resolution has been studied. By reconstructing the origin of the conversion ions a time resolution of <50 ns and a spatial resolution of 100 micrometer has been achieved.

The research work presented here includes our efforts to develop a useful neutron detection device using He-3 detectors, a standard neutron detection methodology widely used in homeland security applications. The design of a He-3 neutron spectroscopy system, simulated entirely via computational methods, is proposed to resolve the spectra from Special Nuclear Materials (SNM) neutron sources of high interest. We incorporate a unique ability to effectively perform robust large-scale radiation transport simulations for SNM detection, using parallel computing methods. To demonstrate our methodology, we present the optimally detected spectral differences between SNM materials (Plutonium and Uranium), metal and oxide, using ideal filter materials. Specific focus was made to establish the limits of He-3 spectroscopy using ideal filter materials. The proposed design was then determined by replacing ideal filters with real materials, and comparing reaction rates with similar data from the ide...

1-Radiation portal monitor systems have been deployed to screen for illicit trafficking of radioactive materials at international border crossings. This report reviews some of the neutron detection requirements and capabilities of passive detection systems used for such applications. Simulations show the effects of cargo materials on neutron spectra, different detector geometries, using a large-array of neutron detectors, and the effects of backgrounds including "ship effect" neutrons.

The Department of Energy Office of Nuclear Safeguards (NA-241) is supporting the project "Coincidence Counting With Boron-Based Alternative Neutron Detection Technology" at Pacific Northwest National Laboratory (PNNL) for the development of an alternative neutron coincidence counter. The goal of this project is to design, build and demonstrate a boron-lined proportional tube-based alternative system in the configuration of a coincidence counter. This report discusses the validation studies performed to establish the degree of accuracy of the computer modeling methods currently used to simulate the response of boron-lined tubes. This is the precursor to developing models for the uranium neutron coincidence collar under Task 2 of this project. The strategy for this project going forward is to use the model parameters that provide adequate comparison to experiment, which may or may not be related to the actual material or thickness of the lining. No information from the vendor on the actual boron coating was used in this study. A boron metal thickness of 0.75 µm appears to be an adequate value to use for models of boronlined tube systems based upon the current tubes supplied by General Electric Reuter-Stokes for testing. Good agreement between measurement and model was obtained for close geometries, though agreement was not as good at larger distances, where the models over predict response. This may indicate that the model of the room environment needs to be improved. This work will be extended over the next several months to more comparisons of models to experiments to improve the agreement that can be obtained. The results from this work will be applied to the development of the coincidence collar models using boron-lined tubes.

In this paper, a hand-held neutron radiation sensor application is described. The sensor system utilizes a new class of boron-carbide diode that interacts with incoming neutrons. To interface with the boron-carbide diode an integrated front-end is designed in a 1.5/spl mu/m standard CMOS technology. With the diode and front-end microchip, a hand-held neutron detection system was realized with an embedded microcontroller for realtime processing. The hand-held detector operation was then tested with a plutonium-beryllium neutron source. Testing results confirm the validity of the approach and the functionality of the design.

The world of detectors used in thermal neutron scattering instrumentation has changed. By alerts on the future Helium-3 supply, critical to perspectives of the large-scale research infrastructures, the run on substitutional technologies started. Most of the solutions could be adapted from developments of particle physics and are comprised of one or more layers of Boron-10. The Time Projection Method achieves a very high resolution by projecting ionization tracks onto a readout with dense spatial and time information. The university of Bonn is developing a novel system employing the TimePix technology - CMOS based chips with 55 micrometer sized pixels operated at clock speeds up to 80 MHz. In a first prototype with 8 TimePix chips, which are arranged in parallel to a boron layer, the track topology with this unrivaled high resolution has been studied. By reconstructing the origin of the conversion ions a time resolution of <50 ns and a spatial resolution of 100 micrometer has been achieved.

Description and testing of novel Dynamic Path Generation Monte Carlo technique. Characterization of the physical structure of RVC foams with various porosities. Preliminary validation of Dynamic Path Generation by comparison to MCNP6. Optimization study of simulated B 4 C-coated RVC foam materials. a b s t r a c t Porous media incorporating highly neutron-sensitive materials are of interest for use in the development of neutron detectors. Previous studies have shown experimentally the feasibility of 6 LiF-saturated, multi-layered detectors; however, the random geometry of porous materials has limited the effectiveness of simulation efforts. The results of scatterless neutron transport and subsequent charged reaction product ion energy deposition are reported here using a novel Monte Carlo method and compared to results obtained by MCNP6. This new Dynamic Path Generation (DPG) Monte Carlo method was developed in order to overcome the complexities of modeling a random porous geometry in MCNP6. The DPG method is then applied to determine the optimal coating thickness for 10 B 4 C-coated reticulated vitreous-carbon (RVC) foams. The optimal coating thickness for 4.1275 cm-thick 10 B 4 C-coated reticulated vitreous carbon foams with porosities of 5, 10, 20, 30, 45, and 80 pores per inch (PPI) were determined for ionizing gas pressures of 1.0 and 2.8 atm. A simulated, maximum, intrinsic thermal-neutron detection efficiency of 62.8 70.25% was predicted for an 80 PPI RVC foam with a 0.2 mm thick coating of 10 B 4 C, for a lower level discriminator setting of 75 keV and an argon pressure of 2.8 atm.

Perforated silicon diodes with two different etched patterns were tested for neutron counting efficiency and angular response. The etched patterns consisted of circular holes on a square lattice or continuous sinusoidal waves. Normal incident neutron counting efficiencies were determined to be 21% and 35% for circular hole and sinusoidal devices, respectively. A nonuniform angular response was identified for the circular

The globally increased demand of Helium-3 along with the limited availability for this gas asks for the development of alternative technologies as the nowadays standard technology is still based on the Helium counter tube.
We report on the CASCADE Project - a novel detection system, which has been developed for the purposes of neutron spin echo spectroscopy. It features 2D spatially resolved detection of thermal neutrons at high rates. The CASCADE detector is comprised of a stack of solid 10B coated Gas Electron Multiplier (GEM) foils, which serve both as a neutron converter and as an amplifier for the primary ionization deposited in the standard Argon-CO2 counting gas environment.
For the application in MIEZE spin echo techniques it has furthermore been managed to extract the signal of the charge traversing the stack to identify the very thin conversion layer of about 1μm. This allows to precisely determine the time-of-flight [2].
The detector concept and measurement results will be presented.

[1] M. Klein, C.J. Schmidt, Nucl. Instr. and Meth. A 628 (2011) 9-18
[2] W. Häussler et al., J. Phys.: Conf. Ser. 251 012067 (2010)

Talk Presented at the International Workshop on Position Sensitive Neutron Detectors, 2014

Optical and scintillation properties of Pr-doped Li-glass, 20Al(PO 3) 3-80LiF:Pr 3%, have been studied for applications in neutron detection systems. Based on optical transmission and reflectivity, the absorption coefficient and refractive index were calculated from the Beer Lambert law. The absorption edge was apparently shifted to the longer wavelength from 160 nm to 240 nm due to 4f → 5d transitions of Pr ions. The strong absorption peaks of praseodymium 4f → 4f transitions were observed from 420 nm to 500 nm and around 590 nm. The radio-luminescence spectrum excited by 241 Am 5.5 MeV α source was measured. Strong emission peaks were observed around 250 nm. The α-ray excited pulse height spectrum and decay kinetics were also examined. Light yield was estimated to be 400 ± 40 photons/5.5 MeV α and the main component of the decay time was evaluated to be about 12 ns. Furthermore, the pulse height spectrum of the glass excited by 252 Cf neutrons was also measured, and the light yield was estimated to be 140 ± 10 photons/neutron.

This work describes an innovative solid state device structure that leverages advanced semiconductor fabrication technology to produce an efficient device for thermal neutron detection which we have coined the ¿Pillar Detector¿. State-of-the-art thermal neutron detectors have shortcomings in simultaneously achieving high efficiency, low operating voltage while maintaining adequate fieldability performance. By using a three dimensional silicon PIN diode pillar array

ABSTRACT Experimental verification of simulated results of series and parallel diamond detector arrays is reported. Eight commercially available electronic grade single crystal CVD diamond plates were used in series and parallel array configurations and were characterized through alpha particle and neutron exposures. It was found that a series array of diamond detectors is inherently limited due to the impedances of the diamond plates. Plutoniumeberyllium neutron exposures were conducted with each of these diamond plates and on a parallel array of all eight diamond plates. It was found that the detection efficiency scaled linearly with the number of plates and that the pulse height from the preamplifier was not affected by the parallel array configuration. However, the additional capacitance introduced to the charge sensitive preamplifier indicates that there is a limitation to the total size that can be realized with a parallel diamond sensor array before significant signal degradation occurs.

A novel and evolutionary multiplexing technique is introduced in this work where electronic grade single crystal chemical vapor deposition (CVD) diamond plates are multiplexed together in both a series and parallel configuration, sending electronic signals from each diamond plate to a single electronic acquisition system. Modeling of this novel multiplexing technique consisted of MCNPX simulations and significant post processing. The model developed allowed for the characterization of charge collection efficiency corrections to the location of charge creation to determine the effect of increasing detection medium size with respect to charge collection direction on the measured pulse height spectrum. This work was conducted to show that this technique is theoretically capable of replacing a single crystal diamond plate of similar size for use in neutron detection without the immediate need of advancing CVD diamond growth technologies. Further, this work indicates the expected pulse height evolution from a singular large single crystal diamond if such a crystal is produced in the future. The results of this work indicate that a 14.1 MeV neutron induced energy pulse of 8.4 MeV (due to the 12 C(n,a o) 9 Be reaction) in the pulse height spectrum has its energy resolution broadened by a factor of two to a total value of 0.225 percent for a multiplexed array with a thickness from 0.05 to 1 cm and an intrinsic detection efficiency of 25.4 percent for a 1 cm thick diamond crystal. It is also qualitatively discussed that the number of secondary neutron interactions with the diamond detector array may be about 5 percent. The results of this work indicate the capability of multiplexing diamond plates together for spectroscopic neutron detection with a combined intrinsic detection efficiency and energy resolution greater than any other diamond-based neutron detection system reported to date.

Two, 111 GBq (3 Curie) radium-beryllium (RaBe) sources were in underground storage at the Brookhaven National Laboratory (BNL) since 1988. These sources originated from Princeton Plasma Physics Laboratory (PPPL) where they were used to calibrate neutron detection diagnostics. In 1999, PPPL and BNL began a collaborative effort to expand the use of an innovative pilot-scale technology and bring it to full-scale deployment to shield these sources for eventual transport and burial at the Hanford Burial site. The transport/disposal container was constructed of depleted uranium oxide encapsulated in polyethylene to provide suitable shielding for both gamma and neutron radiation. This new material can be produced from recycled waste products (DU and polyethylene), is inexpensive, and can be disposed with the waste, unlike conventional lead containers, thus reducing exposure time for workers. This paper will provide calculations and information that led to the initial design of the shielding. We will also describe the production-scale processing of the container, cost, schedule, logistics, and many unforeseen challenges that eventually resulted in the successful fabrication and deployment of this shield. We will conclude with a description of the final configuration of the shielding container and shipping package along with recommendations for future shielding designs.

One of the main uses for 3 He is in gas proportional counters for neutron detection. Radiation portal monitors deployed for homeland security and non-proliferation use such detectors. Other uses of 3 He are for research detectors, commercial instruments, well logging detectors, dilution refrigerators, for targets or cooling in nuclear research, and for basic research in condensed matter physics. The US supply of 3 He comes almost entirely from the decay of tritium used in nuclear weapons in the US and Russia. A few other countries contribute a small amount to the world's 3 He supply. Due to the large increase in use of 3 He for homeland security, the supply has dwindled, and can no longer meet the demand. This white paper reviews the problems of supply, utilization, and alternatives.

The shortage of 3He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is

Radiation portal monitor systems based upon polyvinyl toluene scintillator gamma-ray detectors and pressurized 3 He-based neutron detector tubes have been deployed to detect illicit trafficking in radioactive materials at international border crossings. This paper reviews the neutron detection requirements and capabilities of passive, as opposed to active interrogation, detection systems used for screening of high-volume commerce for illicit sources of radiation at international border crossings. Computational results are given for the impact of cargo materials on neutron spectra, for the response of various detector geometries, the effects of backgrounds including ''ship effect'' neutrons, and for simulation of a large neutron detection array.

Inorganic scintillators play an important role in the detection and spectroscopy of gamma and X-rays, as well as in neutrons and charged particles. For a variety of applications, new inorganic scintillation materials are being studied. New scintillation detector applications arise continuously and, consequently, the interest in the introduction of new fast scintillators becomes relevant. Scintillation crystals based on cesium iodide (CsI) have relatively low hygroscope, easy handling and low cost, features that favor their use as radiation detectors. In this work, lithium and bromine doped CsI crystals were grown using the vertical Bridgman technique. In this technique, the charge is maintained at high temperature for 10 h for the material melting and complete reaction. The temperature gradient 21° C/cm and 1 mm/h descending velocity are chosen as technique parameters. After growth is finished, the furnace is cooled at a rate of 20° C/h to room temperature. The concentration of the lithium doping element (Li) studied was 10-3 M and the concentration of the bromine was 10-2 M. Analyses were carried out to evaluate the scintillators developed concerning the neutron from the AmBe source, with energy range of 1MeV to 12 MeV. Lithium can capture neutrons without gamma-ray emission, thus, reducing the background. The neutron detection reaction is 6 Li(n,α) 3 H with a thermal neutron cross section of 940 barns. In this paper, it was investigated the feasibility of the CsI:Li and CsI:Br crystals as neutron detectors for monitoring, due to the fact that in our work environment there are two nuclear research reactors and calibration systems.

ABSTRACT Reticulated vitreous carbon (RVC) foams coated with 3-11 μm thick layers of boron carbide (B4C) are experimentally characterized for use as an active material for neutron detection. The potential advantage of this material over thin films is that it can be fabricated in any shape and its porous structure may enhance the emission surface area for ionizing charged particles following thermal neutron capture. A coated foam is also advantageous because the neutron-absorbing material is only on the surface, which is more efficient for α particle emission on a per captured neutron basis. Measurements of the B4C layer thickness of an RVC coated foam, and determination of its elemental composition, are performed using scanning electron microscopy. Neutron transmission measurements using neutron radiography are presented and α particle emission from the coated foam in response to a moderated 252Cf thermal neutron source is demonstrated.

Techniques have been developed to exploit abundant prompt emissions from photonuclear reactions for the identification of special nuclear material (SNM). These enhancements are designed to reduce inspections times and delivered dose in systems which have, historically, relied solely on delayed emissions. Experimental evidence is presented for prompt neutron time-of-flight measurements, neutron/photon correlations in multiple detectors, and novel detector development, specifically