Portable Neutron Generator Research Articles

Method of the known cross sections for calibration of the fast neutron spectrometer with a single-crystal stilbene based detector

The present work is devoted to implementation of the stilbene-based neutron spectrometer energy calibration method. The results of experiments with portable neutron generators and 238PuBe source and scattering materials with known cross sections are used for this method. It is shown that the submitted method makes it possible to carry out fast neutron spectrometry in the energy range from 1 to 15 MeV with the uncertainty of the unfolded neutron energy no more than 200 keV. Neutron spectra unfolding was carried out based on the measured spectra and a Geant4 simulated response matrix. Unfolded spectra were compared with the literature data and reference spectra.

Reconstruction of neutron spectrum emitted by portable 14 MeV neutron generator by a combination of different methods

The presented paper is a continuation of the Tikhonov Regularisation, Minimum Fisher Information, Maximum Entropy, and Maximum Likelihood methods application to unfolding the neutron spectra emitted by the fusion devices from activation measurement. The aim of the analysis is the evaluation of the possible uncertainty improvement. The developed algorithms and methodology were validated with 14 MeV portable neutron generators before application to the analysis of the neutron spectrum emitted from tokamak. The analysis concerns plasma-target generator did not provide satisfactory uncertainty of the results. The modification of the irradiation foils’ set and the improvement in the activity measurement precision progress the results. The sealed tube portable neutron generator irradiated the Al, Fe, Ni, Zr, Au, Mg, and Nb foils. The HPGe spectrometer measured the induced activity with an uncertainty of about 10 %. The synthetic data analysis was made to establish the ratio between the error of the spectrum reconstruction and the discrepancy between the input data and activities reconstructed for this spectrum by the FISPACT-II inventory code. Two bin structures were considered. One was compatible with the FISPACT-II code, but the energy resolution was not regular. The second was characterised by constant bin spacing connected with the modification requirement before simulation and additional uncertainty of about 5 %. The best results were obtained by calculation of the mean value from all methods. The corresponding reconstruction uncertainty is equal to 11 %. The reconstructed spectrum has a dominant deuterium tritium peak slightly shifted to the higher energies due to the beam-target reaction kinematics. The evaluation of the impact of the deuterium-deuterium reaction due to the long-term operation was not reachable due to the measured high intensity from scattered neutrons.

Development of a portable pulsed fast ⩾106 neutron generator based on a flexible miniature plasma focus tube

A plasma focus device is a laboratory fusion device that is used to produce pulsed neutrons for a few tens of ns duration. A compact plasma focus tube (volume ≈ 130 cm3) has been developed, and this was connected to a newly developed capacitor bank using 24 coaxial cables, each 10 m long. The capacitor bank was of compact size and consisted of four energy storage capacitors (each 6 µF, 20 kV, size: 20 cm × 20 cm × 30 cm). The peak discharge current of the capacitor bank was estimated to be 176 kA with a rise time of around 3.6 µs at maximum 4.8 kJ operation energy. The average neutron yield was observed to be maximum (3.1 ± 1.0) × 106 neutrons/pulse with a pulse duration of 15–25 ns at an operating energy of 2.7 kJ (15 kV) and deuterium gas filling pressure of 4 mbar. Long coaxial cables allow only the plasma focus head (neutron source) to be moved as per need, making this a portable pulsed neutron source that is useful in many applications, including in extreme conditions, such as in borehole logging applications for oil and mineral mapping. This report describes the various components of this portable neutron generator together with its neutron emission characteristics.

Портативный нейтронный генератор на лазерно-плазменном ионном диоде с магнитной изоляцией

The article presents a new experimental portable pulsed neutron generator based on a laser-plasma ion diode with magnetic insulation and the results of the first experiments. The laser-plasma diode makes it possible to obtain large ion current pulses that generate high-intensity neutron radiation. The source of optical radiation was a pulsed neodymium-doped yttrium aluminum garnet laser with a wavelength of 1064 nm, a pulse energy of up to 0.7 J, and a duration of ~10 ns. The ion beam is accelerated by an Arkadiev-Marx pulsed voltage generator with a voltage amplitude of up to 250 kV, a duration of up to 1.5 µs, and an energy of up to 160 J. Neutrons were generated using the reaction d(d,n)3He. A neutron yield of 2·107 neutron/pulse was obtained.

Physical Processes in a Portable Neutron Generator with a Laser Plasma Source

Physical Processes in a Portable Neutron Generator with a Laser Plasma Source

Delayed neutron counting of uranium pins using moderated neutrons from portable DD neutron generator in high frequency mode

Delayed neutron counting is often used to verify the characteristics of nuclear material. Use of portable neutron generators in high frequency pulsing mode enables effective analysis with higher counting efficiency and lower radiation protection demands. The paper deals with delayed neutron counting of uranium pins with P385 portable DD neutron generator in polyethylene-based setup. Counting is performed in high frequency mode of neutron generator. The viability of such measurement in the frequency range from 100 Hz to 250 Hz was demonstrated and optimal pulsing parameters for P385 neutron generator were found. Delayed neutron counting was then performed for two types of uranium rods. Delayed neutrons were counted both inbetween neutron pulses during neutron generation and once the emission of neutrons stopped. The results were further validated by Monte Carlo (MCNP) simulations. For the geometry of studied rods, the MCNP calculation were done to calculate the dependence of the response to delayed neutrons on rod enrichment, to show the viability to use the method for rod enrichment verification. An option of using cadmium inset in irradiation channel to overcome the effect of self-shielding for samples with higher enrichment was proposed, experimentally tested, and evaluated through MCNP calculations.

Developing a basis for heavy metal in-situ detection using CZT

Heavy metal contamination is a global concern–this type of contamination in the environment has been on the rise since the industrial age. Current guidelines from the United States Environmental Protection Agency and the World Health Organization limit arsenic concentration in water sources to 10 μg/kg. Typically, detection of heavy metals in industrial processes include spectrophotometry and colorimetry. A viable alternative for heavy metal detection can be implemented using a room temperature gamma spectrometer paired with a portable neutron generator for in-situ neutron activation analysis. In this paper, we explore detection of an arsenic salt diluted in a water sample to specific concentrations; the arsenic sample is utilized to determine the capability of a 5 mm × 5 mm × 5 mm CZT detector for heavy metal detection by neutron activation analysis. Several arsenic dilutions were irradiated in the University of Utah TRIGA reactor (UUTR), and the samples were measured on both HPGe and CZT detectors. The direct comparator method was used to determine the sample mass in a sample attributed by each detector, and the results were compared to the known dilution arsenic mass. We determined that a CZT gamma spectrometer can reliably detect 10 mg/kg arsenic with high confidence, and as low as 1 mg/kg arsenic with low confidence. For comparison, an HPGe gamma spectrometer can reliably detect 1 mg/kg arsenic with high confidence, and as low as 0.1 mg/kg with low confidence. Based upon our MDA, the CZT spectrometer can detect samples with a total activity of 1.8×10-5 mCi and higher, and the HPGe detector can detect an activity of 1.8×10-6 mCi. These results suggest the method has potential in portable gamma spectrometry solutions for wastewater effluents from industrial processes such as paint manufacturing, pharmaceutical, and smelting operations.

Simplified Approach for Preliminary Evaluation of Effective Dose Rates for Field Applications of D-T Neutron Generators

Portable neutron generators are one of the most widespread sources of fast neutrons for different applications, from activation analysis to quantitative estimation of fissile and fertile materials in radioactive waste packages. New techniques based on these devices have been developed for homeland security, e.g. neutron interrogations of packages suspected of containing substances such as explosives. When using portable generators determination of radiation protection quantities is affected by a series of boundary conditions that could differ from an experimental set-up to another, and Radiation Protection Experts cannot assess operator exposure without the aid of time-expensive Monte Carlo simulations. As it is impossible to foresee all kind of scenarios involving such applications, and time is often a critical variable, safety assessment requires faster, even if less accurate, tools for exposure evaluation. In this article experimental measurements of dose rates in a real scenario involving a D-T neutron generator are considered, to validate the Monte Carlo model developed. Consequently, it was possible to demonstrate that the calibration factor at 14 MeV for a neutron dosimeter provides conservative dose estimates and to propose a stand-alone, fast, and easy-to-use calculation tool which is usable on field by the Radiation Protection Expert without full Monte Carlo calculations.

Comparison between NIS and TNC for the Detection of Nickel in Soil Samples Using a Portable Neutron Generator

Comparison between NIS and TNC for the Detection of Nickel in Soil Samples Using a Portable Neutron Generator

TANGRA multidetector systems for investigation of neutron-nuclear reactions at the JINR Frank Laboratory of Neutron Physics

In the framework of TANGRA-project at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear research in Dubna (Russia), two experimental setups (Fig. 1) have been designed and tested for investigation of 14-MeV neutron-induced nuclear reactions on a number of important for nuclear science and engineering isotopes. As a source of 14-MeV “tagged” neutrons we are using the VNIIA ING-27 steady-state portable neutron generator with embedded in its vacuum tube 64-pixel charge-particle detector. The “Romashka” system is an array of up-to 24 hexagonal NaI(Tl)-crystal scintillation probes, while the “Romasha” array consists of 18 cylindrical BGO-crystal detectors of neutrons and gamma-rays. In addition to these detectors there is a HPGe gamma-ray spectrometer and a number of Stilbene detectors that can be added for high-resolution gamma-ray spectrometry and neutron-gamma detection. The main characteristics of the neutron-induced nuclear reaction products can be investigated by commissioning the detectors in suitable for these experiments’ geometries. Both setups can be used for doing basic and applied scientific research, because they permit simultaneously to measure the energy, angle and multiplicity distributions of gamma-rays and neutrons, produced in the competitive neutron-induced nuclear reactions (n, n’γ), (n,2n), (n, xnγ) and (n, f) in pure or complex substances.

A Fast Neutron Radiography System Using a High Yield Portable DT Neutron Source.

Resolution measurements were made using 14.1 MeV neutrons from a high-yield, portable DT neutron generator and a neutron camera based on a scintillation screen viewed by a digital camera. Resolution measurements were made using a custom-built, plastic, USAF-1951 resolution chart, of dimensions 125 × 98 × 25.4 mm3, and by calculating the modulation transfer function from the edge-spread function from edges of plastic and steel objects. A portable neutron generator with a yield of 3 × 109 n/s (DT) and a spot size of 1.5 mm was used to irradiate the object with neutrons for 10 min. The neutron camera, based on a 6LiF/ZnS:Cu-doped polypropylene scintillation screen and digital camera was placed at a distance of 140 cm, and produced an image with a spatial resolution of 0.35 cycles per millimeter.

Development and performance characterization of a compact plasma focus based portable fast neutron generator

The design details and performance characterization results of a newly developed plasma focus based compact and portable system (0.5 m × 0.5 m × 1.2 m, weighing ≈100 kg) that produces an average neutron yield of ∼2 × 108 neutrons/shot (of fast D-D neutrons with typical energy ∼2.45 MeV) at ∼1.8 kJ energy discharge are reported. From the detailed analysis of the experimental characterization and simulation results of this system, it has been conclusively revealed that specifically in plasma focus devices with larger static inductance: (i) pinch current is a reliable and more valid neutron yield scaling parameter than peak current, (ii) the ratio of pinch/peak current improves as static inductance of the system reduces, (iii) the benign role of the higher static/pinch inductance ratio enables the supply of inductively stored energy in densely pinched plasma with a larger time constant and it is well depicted by the extended dip observed in the discharge current trace, (iv) there is the need to redefine existing index values of the pinch (Ipinch4.7) and peak (Ipeak3.9) currents in neutron yield scaling equations to higher values.

Sulfur analysis in bulk samples using a DD portable neutron generator based PGNAA setup

Prompt gamma ray analysis of sulfur-contaminated soil samples was carried out using a Genie 16 DD portable neutron generator and a 12.7 cm × 12.7 cm (diameter × height) BGO detector. The minimum detectable concentration MDC ± $$\sigma_{\text{MDC}}$$ was measured from soil samples containing 4.4, 7.1, 9.6, and 13.47 wt% sulfur using the 5.42 MeV sulfur capture gamma rays. The measured value of MDC ± $$\sigma_{\text{MDC}}$$ for sulfur, which was 1.30 ± 0.40 wt%, is in good agreement with the corresponding values reported earlier with intense 252Cf source-based PGNAA setups.

High rate neutron and gamma ray spectroscopy of magnetic confinement fusion plasmas

An important instrumental development work has been done in the last two decades in the field of neutron and gamma ray spectroscopic measurements of magnetic confinement plasmas. Starting from the present state of the art instrumentation installed at JET, this paper reviews the recent development that has been carried out within the EUROFUSION programme for the forthcoming high power JET D and DT campaign. This development was dedicated to the realization of new compact neutron and gamma-ray spectrometers which combine very high energy resolution (typically better than 5%) and MHz counting rate capabilities allowing for time resolution in the 10 ms time scale. One of the advantages offered by the compact dimensions of these spectrometers is to make possible their use in multiple sight-line camera configurations, such as for future burning plasma reactors (ITER and DEMO). New compact neutron spectrometers based on single crystal diamond detectors have been developed and installed at JET for measurements of the 14 MeV neutron spectrum. Measurements on a portable DT neutron generator have shown that neutron spectroscopy of the accelerated beam ions at unprecedented energy resolution (∼1% at 14 MeV) is possible, which opens up new opportunities for diagnosing DT plasmas. For what concerns gamma ray measurements, the JET gamma ray camera has been recently upgraded with new compact spectrometers based on a LaBr3 scintillator coupled to Silicon Photomultiplier with the dual aim to improve the spectroscopic and rate capabilities of the detectors. The upgrade camera system will reconstruct the spatial gamma ray emissivity from the plasma in the MeV energy range at MHz counting rates and energy resolution in the 2–4% range. This will allow physics studies of gamma rays produced by the interaction of fast ions with impurities in the plasma and bremsstrahlung emission from runaway electrons.

Portable neutron generator with microwave ion source for wide applications

The paper presents the issues related to the development of a portable neutron generator with a microwave source of heavy hydrogen ions for a wide range of applications. The paper analyzes the effect of electromagnetic microwave field strength and the magnetic induction value of a constant external magnetic field on the ionization rate of molecular deuterium and determines their optimal ratios. It also describes the configuration of the magnetic system of permanent magnets made of NdFeB material, which provide a homogeneous magnetic field with an induction of 850 Gs necessary for the effective operation of the device using the electron cyclotron resonance (ECR). The dynamics of the primary deuteron flux, as well as secondary particles in the ion-optical system are analyzed. Elements of a conceptual design of a portable neutron generator are described.

Analysis of the Ion-Optical Systems of Portable Neutron Generators

The results of numerical modeling of the ion-beam dynamics and the dynamics of secondary ions and electrons formed in the ion-optical system of a portable neutron generator are presented. The calculation was performed with the aid of the KARAT code in a two-dimensional flat geometry and axisymmetric geometry. To suppress back electrons, the magnetic field of permanent magnets was used in the flat geometry and a blocking electric field of an additional electrode was used in the axisymmetric geometry. The working configurations of both systems are shown.

Analysis of the Operation of the Microwave Ion Source in the Electron–Cyclotron Resonance Mode for a Portable Neutron Generator

The authors present the results of numerical simulation of the kinetic processes in deuterium microwave-resonator plasmas with electron–cyclotron resonance at a nonuniform distribution of the magnetic and electric fields. For the actual configuration of the resonator module, the authors show the optimal magnetic field distribution in terms of energy efficiency. The solution of the kinetic scheme of the microwave discharge in deuterium plasmas makes it possible to relate the gas-discharge plasma properties with the parameters of the deuterium-ion source: the residual gas pressure, the gas flow into the microwave resonator, the charged particle flows on the wall and into the ion-optical system, the electrical and magnetic field strength and distribution in the resonator, and the power input into it. The results make it possible to reveal and implement generator operation modes with the highest characteristics ever recorded.

An optimization study for shielding design of D-D and D-T neutron generators

Neutron generators (NG) are being increasingly used in various industrial and research areas such as neutron activation analysis, neutron radiography, and neutron capture therapy. In such applications of neutron generators, compactness is one of the most important issues. Since a neutron source is generated by deuterium-deuterium (D-D) or deuterium-tritium (D-T) fusion reaction, a relatively thick shield for both fast neutrons and related photons is usually required. In this study, optimization of shielding designs for D-D and D-T neutron generators were investigated by adopting appropriate moderator and shielding materials. Based on the optimized moderator and shield thicknesses, the final dimensions of neutron generators were derived for various source strengths of D-D and D-T neutron conditions. Considering conventional condition of a container, we concluded that a 1010 n/sec D-D source and a 108 n/sec D-T source could be a portable NG.

Measurement of Angular Distributions of Gamma Rays from the Inelastic Scattering of 14.1-MeV Neutrons by Carbon and Oxygen Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays originating from the inelastic scattering of 14.1-MeV neutrons by carbon and oxygen nuclei are presented. The measurements in question were performed by the tagged-neutron method in a beam of an ING-27 standard portable neutron generator. The angular distributions of gamma rays emitted by the 2+ state of 12С at 4.43 MeVand the 3− state of 16O at 6.13 MeV were obtained.

Yield measurement and Monte Carlo correction of CPDG neutron generator

Abstract It is useful to obtain the exact neutron yield and distribution of a portable neutron generator. In this paper, the neutron yield of a K400 accelerator D-D neutron source under conditions of 160 kV and 25 uA is 1.69 × 106 ± 4.1 × 104 n/s, which is calibrated using the associated proton method. A long counter consisting of a 3He counter surrounded by a paraffin cylinder was used as secondary standard after efficiency calibration using a K400 accelerator. The Monte Carlo method is then used to evaluate the distribution change of emitted neutrons from each surface of the CPDG caused by its structural materials. Energy spectrum distortion and angle distribution distortion of emitted neutrons are studied. Simulation results show that the proportion of the forward neutron is reduced and the proportion of the lateral neutron is increased. The number of neutron transporting into the counter has been reduced by 28.1%, 28.4%, 29.8%, 29.0%, 28.7%, and 28.0% for acceleration voltages of 90 kV, 100 kV, 110 kV, 120 kV, 130 kV, and 160 kV, respectively. In addition, the respective yield correction factors caused by structural materials are 1.36, 1.38, 1.38, 1.34, 1.37, and 1.39. The neutron yield of the CPDG is 1.28 × 106 and 1.75 × 106 before and after Monte Carlo correction when working at conditions of 130 kV and 600 μA. The total uncertainty of this result is approximately 6%.