Plutonium-beryllium Neutron Research Articles

Neutron spectroscopy of plutonium using a handheld detection system

The ability to distinguish multiple forms of plutonium from one another, such as oxide and metal, is paramount in areas of nuclear nonproliferation and international safeguards. In its metal form, plutonium can be readily used in a nuclear weapon, while oxide forms are associated with nuclear reactor fuel. Oxide-based plutonium forms emit neutrons with an energy spectrum that is significantly different from the fission neutrons that are emitted from plutonium metal. Organic scintillation detectors output pulses that are proportional to the neutron energy deposited, and therefore present a means of distinguishing these plutonium forms based on their energy spectra. In this work, metal and oxide forms of plutonium were measured using a handheld detection system based on an organic glass scintillator. Monte Carlo modeling of these experiments was performed to provide insight into the origin of the features in the observed light output spectra. Through analysis of multiple regions of these spectra, in a matter of minutes we were able to unambiguously discriminate oxide and metal plutonium forms from one another and from a plutonium-beryllium neutron source, which was considered for comparison because these sources are commonly used in industrial applications. The ability to discriminate weapons-usable material from nuclear reactor fuel has applications in nuclear treaty verification and safeguards.

Systematic evaluation of fast neutron sensing with Cesium Hafnium Chloride

Cesium Hafnium Chloride (CHC) is a promising new scintillator for dual mode sensing of both neutrons and gamma-rays. The high chlorine content allows for both 35Cl(n,p)35S and 35Cl(n, α)32P reaction channels leading to reliable detection of fast neutrons. By utilizing pulse shape discrimination (PSD), these neutron interactions may be reliably separated from gamma-ray signals with a high figure-of-merit (FOM) after optimization of the PSD algorithm. In this study, the PSD algorithm settings for CHC were systematically investigated using a bare 252Cf and a lead-shielded plutonium beryllium neutron source. It was found that the PSD algorithm settings affects both the FOM and the neutron detection efficiency, but a FOM as high as 4.5 for alpha particles was observed in one data processing scenario. Further, an intrinsic 5 parts per million alpha-emitting contamination was observed in the sample, which we attribute to natural uranium.

Design and construction of a 9 MeV [formula omitted]-ray source based on capture of moderated plutonium–beryllium neutrons in nickel

We have designed and constructed a high-energy γ-ray source for detector characterisation and calibration. The source is a composite type based on a plutonium–beryllium neutron emitter embedded in a paraffin moderator, which is homogeneously mixed with nickel powder. The 9 MeV γ-ray source produces approximately 450 photons per second in 4π when 2.2×105 neutrons per second are emitted, corresponding to a surface flux of 9 MeV γ-rays of approximately 2.5×10−6 cm−2 per emitted neutron. Here we discuss the properties and design of this source, including the characterisation of homogeneity and high-energy γ-ray emission spectra.

Retrieval and Characterization of a Plutonium-beryllium Source at the University of Utah.

A shielded neutron irradiation facility has been constructed to contain a 74 GBq plutonium-beryllium neutron source at the University of Utah. Due to lack of information and recent use, the GEANT4 Monte Carlo Toolkit was used to perform dose assessments and validation of the designed shield and beam port for storage and operational geometries where the source was to be placed. Borated polyethylene was used as the primary shielding material with a lead-lined beam port to collimate neutrons and reduce gamma rays within the active beam profile. The lead lining was found to reduce the gamma-to-neutron ratio within the profile to 0.259 ± 0.001 and maintain an average neutron flux of 4,633.7 ± 10.2 n cm-2 s-1. The measured dose rate of the source at 30 cm from its constructed storage configuration was found to be 22.3 ± 1.1 μSv h-1 and in good agreement with simulated values. This was also close to the target rate of 20 μSv h-1, the public limit for whole-body dose accumulation, imposed on the design. Measurements of the source during its retrieval and placement into the shield show good agreement with the simulated results and provide a strong validation for the future use of the source in experiments at the University of Utah.

Designand commissioning of a neutron counter adapted to high-intensity laser matter interactions.

The advent of multi-PW laser facilities world-wide opens new opportunities for nuclear physics. With this perspective, we developed a neutron counter taking into account the specifics of a high-intensity laser environment. Using GEANT4 simulations and prototype testings, we report on the designof a modular neutron counter based on boron-10 enriched scintillators and a high-density polyethylene moderator. This detector has been calibrated using a plutonium-beryllium neutron source and commissioned during an actual neutron-producing laser experiment at the LULI2000 facility (France). An overall efficiency of 4.37(59)% has been demonstrated during calibration with a recovery time of a few hundred microseconds after laser-plasma interaction.

Characterization of a plutonium–beryllium neutron source

Here we present an investigation of a plutonium–beryllium neutron source available at the Horia Hulubei National Institute of Physics and Nuclear Engineering, Romania, to be used for detector characterization during the implementation of the Extreme Light Infrastructure – Nuclear Physics project. Using several different techniques and instruments, we have measured the isotopic composition for plutonium to be 75% 239Pu and 24% 240Pu, with a minor contribution from other isotopes. Furthermore, we have measured the source activity as of November 20th 2019 to be 2.220(5)×105 neutrons per second with a mean energy of 3.25(17) MeV. We have also measured both the γ-tagged and full neutron energy spectra, and discuss the origin of the observed structure in the neutron energies based on these. All these parameters are of importance both for traceability of nuclear material, radioprotection, and accurate detector characterization.

IRRADIATOR SYSTEM FOR MANGANESE SULFATE BATH EFFICIENCY MEASUREMENTS USING A PLUTONIUM-BERYLLIUM NEUTRON SOURCE.

This study describes the use of a neutron irradiator system based on a plutonium-beryllium neutron source for MnSO4 solution activation for use to determine the MSB system efficiency. Computational simulations using Monte Carlo code were performed to establish the main characteristics of the irradiator system. Among the simulated geometries and volumes, semi-cylindrical shape with 84.5 cm3 of MnSO4 solution yielded the best option to be built. Activity measurements were performed with a high-pure germanium detector to validate the new irradiation system. Results showed an average efficiency and uncertainty of the experimental standard deviation of the mean: 5.742 × 10-4 ± 0.036 × 10-4 (coverage factor k = 1), for MSB system. Efficiency value obtained shows good correlation to other published methods (i.e. a relative difference of 0.07%). This alternative metrological method demonstrated the utility of neutron sources for the irradiation of solutions in metrology laboratories providing a cost-efficient alternative to nuclear reactors or particle accelerators.

Chemical investigation of three plutonium–beryllium neutron sources

Thorough physical and chemical characterization of plutonium–beryllium (PuBe) neutron sources is an important capability with applications ranging from material accountancy to nuclear forensics. Characterization of PuBe sources is not trivial owing to range of existing source designs and the need for adequate infrastructure to deal with radiation and protect the analyst. This study demonstrates a method for characterization of three PuBe sources that includes physical inspection and imaging followed by controlled disassembly and destructive analysis.

YAP:Ce Scintillator Characteristics for Neutron Detection

YAP: Ce (YAlO3:Ce+, Yttrium Aluminum Perovskite, Ce+ doped) crystals with appropriate converters seem like prospective scintillators for neutron detection. An important aspect for neutron detection with inorganic scintillators is the ability to discriminate neutron radiation from gamma radiation by pulse height of signals. For a detailed measurement of the aspect, a YAP: Ce crystal scintillator with lithium or hydrogen converters and a photomultiplier was used. A plutonium-beryllium neutron source and horizontal neutron channel beams of the LVR-15 research reactor were used as neutron sources. The measurement confirmed the possibility to use the YAP: Ce scintillator for neutron radiation detection. The degree of discrimination between neutron and gamma radiation for different detection configurations was studied.

Neutron producing reactions in PuBe neutron sources

There are a plenty of out-of-use plutonium–beryllium neutron sources in Eastern Europe presenting both nuclear safeguards and security issues. Typically, their actual Pu content is not known. In the last couple of years different non-destructive methods were developed for their characterization. For such methods detailed knowledge of the nuclear reactions taking place within the source is necessary. In this paper we investigate the role of the neutron producing reactions, their contribution to the neutron yield and their dependence on the properties of the source.

Diamond sensor arrays for neutron detection: Preamplifier signal dependence on sensor array configuration

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. Plutonium–beryllium 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.

Elemental composition in sealed plutonium–beryllium neutron sources

Five sealed plutonium–beryllium (PuBe) neutron sources from various manufacturers were disassembled. Destructive chemical analyses for recovered PuBe materials were conducted for disposition purposes. A dissolution method for PuBe alloys was developed for quantitative plutonium (Pu) and beryllium (Be) assay. Quantitation of Be and trace elements was performed using plasma based spectroscopic instruments, namely inductively coupled plasma mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES). Pu assay was accomplished by an electrochemical method. Variations in trace elemental contents among the five PuBe sources are discussed.

Unique challenges with recent gamma spectroscopy measurements at Los Alamos National Laboratory

A variety of unique radioactive samples have been measured recently at Los Alamos National Laboratory (LANL) using an electrically-cooled high-purity germanium detector. In each case the purpose of the measurements included one or more of the following objectives: (1) an accurate determination of the isotopic weight fractions of different plutonium or uranium materials; (2) an accurate determination of the isotopic quantity in the absence of relevant calibration standards; and (3) a qualitative determination of various sample impurities for additional forensic information. This paper discusses how simple modifications to the PC-FRAM parameter sets enabled a better determination of the isotopic content of the following samples: (1) high-purity plutonium metal, (2) plutonium-beryllium (PuBe) neutron sources, (3) neutron-irradiated natural uranium, and (4) re-processed HEU fuel with elevated 236U content. The isotopic quantity in a variety of samples was determined using a combination of the Spectral Nondestructive Assay Platform (SNAP™) routine from Eberline Services and the Monte Carlo Neutral Particle (MCNP) code developed at LANL. The non-traditional sources that were quantified with these gamma ray modeling codes included dozens of neutron-irradiated targets of natural uranium, several plutonium-beryllium neutron sources, and three high-purity samples of plutonium metal.

A Handheld Neutron-Detection Sensor System Utilizing a New Class of Boron Carbide Diode

A handheld neutron-detection sensor application is described in this paper. 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-mum standard CMOS technology. With the diode and front-end microchip, a handheld neutron-detection system was realized with an embedded microcontroller for real-time processing. The handheld detector operation was then tested with a plutonium-beryllium neutron source. Test and measurement results confirm the validity of the approach and the functionality of the design

Detector asselby with a diamond detector for recording neutrons

The BDPN-1K detector assembly for neutron radiation comprises the detector and a preamplifier connected by a 10-m-long cable. The detector can be disassembled. Before the sensitive surface of the diamond there is placed a cover with a converter disk cemented to it; this disk is a U/sub 3/O/sub 8/ layer applied to an aluminum foil. Since the detector can be disassembled, the disk can be replaced and other materials can be used as the converter. In order to determine the optimal thickness of the converter, the sensitivity of recording thermal neutrons with a particular detector assembly was measured and converters with various surface densities of /sup 235/U were used in the detector. Measurements were made in a standard field of thermal neutrons from a plutonium-beryllium neutron source inserted in a paraffin moderator.

Optimized Smoothing in Neutron Spectrum Unfolding by the FERDOR Method

Smoothing is an important part of spectrum unfolding by the FERDOR method. This unfolding method is discussed, and changes to the smoothing procedure are presented. An iterative procedure for determining window widths has also been added to the method. This iterative procedure optimizes the energy resolution of unfolded spectra. A plutonium-beryllium neutron spectrum is unfolded as an example of the improvement obtained in unfolded spectra. Response matrices available for use with the FERDOR method are discussed.

Mixed radiation dosimetry of a plutoniumberyllium neutron source.

The dose rate delivered to an assumed standard tissue by the fast- neutron and gamma -radiation from a standard 1 c plutonium-beryllium neutron source was determined by measurements with ethylene-filled polyethylene and CO²-filled Teflon ionization chambers. The resulting ionization currents as measured with a calibrated vibrating-reed electrometer were used to obtain a measure of both the gamma - and fast-neutron components of the emitted radiatdon. The tissue dose rate due to the fast neutron extrapolated to 1 cm from the source was found to be 1.74 rads/hr. The gamma -component was found to contribute 0.16 rad/hr. From the neutron dosc rate and the neutron spectrum for Pu- Be, the emission rate of the source was calculated to be 1.65 x 10 neutrons/ sec-c. A discussion of the neutron and gamma spectra of the emitted radiation from this source and some aspects of ionization chamber design are also included in this report. (auth)

The preparation of a large plutonium-beryllium neutron source

A plutonium-beryllium alloy neutron source, containing 100 g of plutonium and 68 g of beryllium, was prepared by the reduction of plutonium dioxide with beryllium followed by vacuum sintering at 1450° C to form a mechanically strong, non-friable compact. The compact was sealed in a double aluminum container. Neutron output from the source is 1.01 ± 0.03 × 10 7 neutrons/second. In preparation of the source, tongs with 25 cm handles were used in all operations after mixing of the original ingredients, to prevent serious overexposure of personnel. The source is now in use for the calibration of neutron-counting instruments and for the irradiation of small experimental samples.

P/700. Plutonium-Beryllium neutron sources, their fabrication and neutron yields: A.S. Coffinberry and R. E. Tate (U.S.A.)

P/700. Plutonium-Beryllium neutron sources, their fabrication and neutron yields: A.S. Coffinberry and R. E. Tate (U.S.A.)