MeV Neutron Generator Research Articles

Neutron emission characterization of IPR 14 MeV neutron generator

Accelerator-based neutron sources are being developed worldwide due to their wide applications. Institute for Plasma Research in India has developed an accelerator-based high-yield 14 MeV neutron generator based on deuterium-tritium (D-T) reaction to perform fusion-related benchmark experiments. This neutron generator is designed to produce 1012 neutrons per second in both mode continuous and pulse. The emission of neutrons from an accelerator-based neutron generator is not isotropic due to target geometry and angular dependency of reaction cross-section. A detailed and accurate description of neutron source emission and distribution is required to use such a neutron generator for various experiments. The neutron generator is characterized using experiments and simulations to accomplish the request. Energy and angular distributions of emitted neutrons are measured using a calibrated single crystal diamond (SCD) detector. Experimental data of neutron distributions are used to validate source neutron definition for Monte Carlo N Particle (MCNP) simulation. An accurate model of the Titanium Tritide (TiT) target and its holder geometry is prepared for the simulation. Finally, to validate the simulation model, simulated neutron fluxes are compared with measured ones by the SCD detector. This paper discusses the methodology adopted to characterize emitted neutrons and its results.

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.

A CFD analysis of the rotating target holder of the 14-MeV neutron generator

An accelerator based 14-MeV neutron generator is installed at Institute for Plasma Research, Gandhinagar to generate high energy neutrons by using a water-cooled rotating tritium target. In this device, neutrons would be generated from the nuclear reaction 3H(D, n)4He by bombarding accelerated deuterium ions on a solid tritium target. The rotating target holder mainly consists of a rotating copper disc water-cooled case mounted on the rotating shaft. The high-energy deuterium ion beam impacted on solid TiT target fitted on the copper case imparting its energy to the case. This energy is taken away from the system through the water passing through the annulus cavity of the shaft. This paper presents details of the engineering CFD (computed fluid dynamics) analysis carried out for optimizing two important parameters of the rotating target. Firstly optimization of the location of flow parameters of the water as mass flow rate and Secondly optimization of speed of the rotating target and the design of fins inside the copper case.

Physics design of 14 MeV neutron generator facility at the Institute for Plasma Research

A high energy and high yield neutron source is a prime requirement for technological studies related to fusion reactor development. It provides a high-energy neutron environment for small-scale fusion reactor components research and testing such as tritium breeding, shielding, plasma-facing materials, reaction cross-section data study for fusion materials, etc. Along with ITER participation, the Institute of Plasma Research, India is developing an accelerator-based 14 MeV neutron source with a yield of 1012 n s−1. The design of the source is based on the deuterium–tritium fusion reaction. The deuterium beam is accelerated and delivered to the tritium target to generate 14 MeV neutrons. The deuterium beam energy and tritium availability in the tritium target are the base parameters of the accelerator-based neutron source design. The paper gives the physics design of the neutron generator facility of the Institute for Plasma Research. It covers the requirements, design basis, and physics parameters of the neutron generator. As per the analytical results generator can produce more than 1 × 1012 n s−1 with a 110 keV D+ ion beam of 10 mA and a minimum 5 Ci tritium target. However, the detailed simulation with the more realistic conditions of deuteron ion interaction with the tritium titanium target shows that the desired results cannot be achieved with 110 keV. The safe limit of the ion energy should be 300 keV as per the simulation. At 300 keV ion energy and 20 mA current, it reaches 1.6 × 1012 n s−1. Moreover, it was found that to ensure sufficiently long operation time a tritium target of more than 20 Ci should be used. The scope of the neutron source is not limited to the fusion reactor research studies, it is extended to other areas such as medical radioisotopes research, semiconductor devices irradiations, and many more.

Neutronic simulation of medical radioisotope 99Mo and 177Lu production in IPR 14 MeV neutron generator facility

An accelerator based 14 MeV neutron generator is commissioned at Institute for Plasma Research India. The generator is based on the linear accelerator concept where the deuterium ion beam impinged to the tritium target to produce neutrons. The generator is designed to produce 5 × 1012 n/s (max.). The 14 MeV neutron source facilities are an emerging tool for the lab scale experiments and research. In order to utilize the generator for the welfare of humanity, the assessment is made for the production of medical radioisotopes using the neutron facility.The usage of radioisotopes in the treatment and diagnosis of a disease is an important factor in the healthcare sector. A series of calculations are conducted to generate radioisotopes, especially 99Mo and 177Lu those are having huge applications in the medical and pharmaceutical industries. 99Mo can be also generated through neutron reactions 98Mo(n, g)99Mo and 100Mo(n, 2n)99Mo apart from fission reaction. The cross section of 98Mo(n, g)99Mo is high in the thermal energy range whereas 100Mo(n,2n)99Mo occurs at a high energy range. 177Lu can be produced using the reactions 176Lu (n, g)177Lu and 176Yb (n, g)177Yb. The cross section of both 177Lu production routes is higher at thermal energy range. The neutron flux level near the target is around 1010 cm−2s−1. In order to enhance production capabilities, the neutron energy spectrum moderators are used to thermalize the neutrons. The materials used as a moderator are beryllium, HDPE, graphite, etc. Moderators enhance the capabilities of medical isotope production in neutron generators.

Development of distributed and automated system for 14MeV neutron generator laboratory

Neutron generators are becoming an attractive alternative to reactors and radioactive neutron sources in a variety of applications in science and technology. Fast neutron activation analysis was firstly supposed to be a complementary method for the purpose of determining the absolute value of the neutron yield then become an elemental analytical technique. The arrangements necessary for using neutron generator for elemental analysis have been discussed including design, construction and characterization of the neutron generator. Source of errors has to be discussed that are assessed in the validation process and its expression in a standardized form. The contribution of these errors to the expanded uncertainty in the concentrations of Na, Mg, Al, Si, Cl, K, Ca and Fe in some domestic cement samples using 14 MeV neutron beam was assessed. and sample and assuming that all these errors were independent. the total estimated error was 5–7%.

Fast neutron interrogation of special nuclear material using differential die-away technique

The paper reports the development of a RF ion source-based transportable compact neutron generator and its application in detecting special nuclear material using the differential die away approach. We present experimental results for the detection of nuclear material in a low-density metallic matrix using an in-house developed 14 MeV (D-T) neutron generator. We have used multi-linear regression for accurately determining the quantity of fissile material even with a small data set.

Radioactivation analysis of 14 MeV neutron generator facility

Institute for Plasma Research (IPR) is establishing an intense neutron generator facility. It is an accelerator-based 14 MeV neutron generator that produces 1012 neutrons per second. The neutron generator facility has various components that are made of different kinds of materials. It gets radio-activated due to the direct interaction of neutrons and secondary radiations. The radio activation of components has short term and long term effects in neutron generator operation and maintenance. The facility is built with concrete shielding. It will be operated at atmospheric pressure. The concrete walls and air in the hall also face neutron irradiation, which needs to be estimated for precautionary safety measures during maintenance. Long term operation of neutron generator can also affect the ground soil. The production of tritium in the soil can also become an issue for the general public health and can create a safety concern. Therefore, the simulation has been carried out to estimate the radio-activation of the neutron generator facility, which may impact neutron generator operation and maintenance. The estimation will also provide the level of radioactive waste generated due to the long term operation of the neutron generator. The operational licensing of the neutron generator is also required the estimation of radionuclide and dose rates after irradiation. The present work contains the neutron activation of neutron generators components that are present in the hall. The analysis is conducted for air activation, soil activation, concrete wall activation, and doors activation. The generation of ozone due to radiation interaction with air is also estimated to avoid ozone hazards during the maintenance. The simulation has been carried out using the Monte Carlo radiation transport tool and radionuclide inventory estimation tool FISPACT. Estimated results are compared with the regulatory limits. The analyses conclude that the facility is safe for long term operation.

Search for tritium in air in a room equipped with 14 MeV neutron generator with tritiated targets

Eight documented tritiated targets were stored, as well as some very old targets with unknown activity, in a room equipped with an ING-114 14 MeV fast neutron generator. When the neutron generator was running, the tritiated targets were irradiated with a deuterium beam. The aim of this work is to determine the tritium content in the room's atmosphere, as well as the radiation exposure of workers in the room. In this study, isotopic exchange was assumed. This means that tritium from the targets diffused into the air, where it reacted immediately with oxygen particles to form vapour. These vapour molecules diffused into open vessels containing deionized water (50 ml in 120 ml plastic containers). Fifty vessels were arranged along the length (every 0.50 m) and width (every 1 m) of the room. Additionally, there were three vessels placed in the room for shorter periods (5, 7, and 12 days) together with a vessel that was exposed to the tritium for the full duration of the experiment (18 days) to determine the saturation curve. Based on the measured tritium contents, a map of the spatial distribution of tritium in the room was created. The results were used to calculate the radiation dose for a person working in the room and showed no significant contribution to the approved average annual dose for workers.

Development and performance of a 14-MeV neutron generator

An accelerator-based 14-MeV neutron generator for fusion neutronics studies has been developed in Fusion Neutronics Laboratory (FNL) at Institute for Plasma Research (IPR). The generator is initially designed to produce a neutron yield of 1010 n/s and operated for 1.1×109 n/s. It will be further upgraded to the neutron yield of 1012 n/s. The neutron generator consists of various components such as 2.45 GHz ECR ion source, 300 kV linear accelerator, beam diagnostic system, TMP based vacuum system, solid tritium target, and control system. Various direct and indirect neutron detection techniques are deployed to evaluate the performance of the neutron generator in terms of neutron emission. These techniques include foil activation, alpha particle diagnostic, and He-3 proportional counter. The reaction rates for the foil activation are estimated using the Monte Carlo technique. Results of all independent diagnostics are obtained and compared. The paper describes the experimental setup and neutron diagnostics. It also describes the performance of the 14-MeV neutron generator highlighting its stability under continuous operation.

Occupational radiation exposure control analyses of 14 MeV neutron generator facility: A neutronic assessment for the biological and local shield design

The 14 MeV neutron generator facility is being developed by the Institute for Plasma Research India to conduct the lab scale experiments related to Indian breeding blanket system for ITER and DEMO. It will also be utilized for material testing, shielding experiments and development of fusion diagnostics. Occupational radiation exposure control is necessary for the all kind of nuclear facilities to get the operational licensing from governing authorities and nuclear regulatory bodies. In the same way, the radiation exposure for the 14 MeV neutron generator facility at the occupational worker area and accessible zones for general workers should be under the permissible limit of AERB India. The generator is designed for the yield of 1012 n/s. The shielding assessment has been made to estimate the radiation dose during the operational time of the neutron generator. The facility has many utilities and constraints like ventilation ducts, accessible doors, accessibility of neutron generator components and to conduct the experiments which make the shielding assessment challenging to provide proper safety for occupational workers and the general public. The neutron and gamma dose rates have been estimated using the MCNP radiation transport code and ENDF –VII nuclear data libraries. The ICRP-74 fluence to dose conversion coefficients has been used for the assessment. The annual radiation exposure has been assessed by considering 500 h per year operational time. The provision of local shield near to neutron generator has been also evaluated to reduce the annual radiation doses. The comprehensive results of radiation shielding capability of neutron generator building and local shield design have been presented in the paper along with detailed maps of radiation field.

MCNP modelling of a neutron generator and its shielding for PGNAA in mineral exploration

This paper present results of Monte Carlo simulations of shielding design against neutron and gamma-rays from a D-D 2.5MeV neutron generator. The generator will be located in a restricted access la...

Assessment of a Hardware-Implemented Machine Learning Technique Under Neutron Irradiation

Hardware-implemented intelligent systems running autonomous functions and decisions are today becoming more and more ubiquitous in many fields of applications, demanding reliable operation even under harsh conditions as in nuclear power plants and avionics altitudes. Support vector machine (SVM) is a prominent machine learning solution to optimize hardware-implemented autonomous systems. This paper is the first to assess the operation of a field-programmable gate array (FPGA)-designed SVM architecture under radiation effects. A fault emulation campaign along with radiation test experiments with a 14-MeV neutron generator has been performed, and the results show that 27% of the neutron radiation-induced errors in the target SVM architecture provoked critical failures.

Specific Features of Fiber Optics Application in ITER

Silica-based optical fibers have high transmission in the visible range and are widely used for transmitting light from plasma to detectors in modern fusion devices. Pure silica-core/F-doped silica-clad fibers are mainly applied for plasma diagnostics. The possible problems that can be encountered with fiber optics in ITER diagnostics are discussed. The neutron fluence to be accumulated in the bundles during the ITER lifetime is estimated. The results of the irradiation tests of the optical fibers at the fission reactor and the 14 MeV neutron generator are used for analysis of radiation resistance of the optical fibers. The results of radiation tests and neutron calculations prove the requirement to apply silica fibers with high radiation resistance in ITER. It is recommended to place the fiber bundles in the port cell behind the biological shielding, where the neutron flux from the plasma is attenuated to a value of ~107 n/(cm2 s). The conclusion is made that it is possible to use the modern optical fibers in the plasma optical diagnostics (in a spectral range of 450–700 nm), the optical fibers being capable of surviving the radiation load during the whole ITER lifetime.

Application of track detectors to measure neutrons emitted from a 14 MeV neutron generator

This paper reports on applicability of a polyallyl-diglycol-carbonate (PADC) detectors of the CR-39 TASTRAK type as integrated neutron fluence sensors for monitoring of neutrons emitted from 14 MeV neutron generator. Neutron generators such as SODERN Model: GENIE 16 D are powerful emitters of fusion neutrons from DT reactions with yields up to 2 × 108 n·s−1. The presented generator is now available worldwide as a source of neutrons with a rather wide range of applications in medicine, industry and in the detection of hazardous materials. Before using in those measurements, the CR-39 TASTRAK type detector was precisely calibrated. Rectangular track detector samples prepared for neutron flux measurements are in the form of “sandwiches” consisting of a detector plate covered by a thick polythene (PE) radiator and in some part by a Cu-filter. In order to estimate how many neutrons could be converted into recoil-protons we have performed computer calculations by means of MC methods.

Practical aspects of using beta-delayed gamma emission for copper ore analysis on a running belt conveyor

In this study, we investigated the feasibility of copper ore analysis on a running belt conveyor by measuring the delayed positron annihilation quanta based on the beta-decay of 62Cu, which was previously activated by a D-T, 14 MeV neutron generator. We constructed a model of a belt conveyor that measured 10 m in length to test this method. Our measurements demonstrated the feasibility of the method but practical constraints imposed by user demands and the industrial environment would make the design impractical and cost inefficient.

Experimental Assessment of a Flat Sandwich-Like Self-Powered Detector for Nuclear Measurements in ITER Test Blanket Modules

Neutron and gamma flux measurements in designated positions in the test blanket modules (TBMs) of ITER will be important tasks during its campaigns. Investigations on self-powered detectors (SPDs), a class of reactor flux monitors are undertaken in the framework of an ongoing project on development of nuclear instrumentation for European ITER TBMs. This paper reports the findings of experiments performed with an SPD in flat sandwich-like geometry. A detector with vanadium emitter is chosen for preliminary studies. Its irradiation in a thermal neutron field gives a proof of the principle of flat SPDs. It is further irradiated in the mixed neutron–gamma field of a 14-MeV neutron generator and a bremsstrahlung photon field. The test SPD signals are proportional to the incident fluxes, deeming it suitable for flux monitoring. Whereas both neutrons and gammas can be detected with appropriate optimization of geometries, materials, and sizes of the components, the present design is more sensitive to gammas than fast neutrons. Based on the measured sensitivities of the SPD, its response under TBM conditions is predicted.

Investigation of the Energy Spectra of 14-MeV Neutron Generators

The energy spectra of 14 MeV neutron generators of different types were measured using spectrometers with organic scintillators. Additional neutron peaks with energy less than 14 MeV, which are due to the neutrons produced in the ancillary reaction 2H + 2H = 3H + p, and neutrons generated in the material of the target blocks and the scintillation crystals of the spectrometers were identified in the neutron spectra of the generators. Specifically, a peak at 3.6 MeV was found in the resulting neutrons spectra; this peak is produced when carbon nuclei present in the scintillators of the spectrometers decay under the action of 14 MeV neutrons.

14 MeV calibration of JET neutron detectors—phase 2: in-vessel calibration

A new DT campaign (DTE2) is planned at JET in 2020 to minimize the risks of ITER operations. In view of DT operations, a calibration of the JET neutron monitors at 14 MeV neutron energy has been performed using a well calibrated 14 MeV neutron generator (NG) deployed, together with its power supply and control unit, inside the vacuum vessel by the JET remote handling system. The NG was equipped with two calibrated diamond detectors, which continuously monitored its neutron emission rate during the calibration, and activation foils which provided the time integrated yield. Cables embedded in the remote handling boom were used to power the neutron generator, the active detectors and pre-amplifier, and to transport the detectors’ signal. The monitoring activation foils were retrieved at the end of each day for decay γ-ray counting, and replaced by fresh ones. About 76 hours of irradiation, in 9 days, were needed with the neutron generator in 73 different poloidal and toroidal positions in order to calibrate the two neutron yield measuring systems available at JET, the 235U fission chambers (KN1) and the inner activation system (KN2). The NG neutron emission rates provided by the monitoring detectors were in agreement within 3%.Neutronics calculations have been performed using MCNP code and a detailed model of JET to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the NG neutrons, and taking into account the anisotropy of the neutron generator and all the calibration circumstances. These calculations have made use of a very detailed and validated geometrical description of the neutron generator and of the modified MNCP neutron source subroutine producing neutron energy-angle distribution for the neutrons emitted by the NG.The KN1 calibration factor for a DT plasma has been determined with ±4.2% experimental uncertainty. Corrections due to NG and remote handling effects and the plasma volume effect have been calculated by simulation modelling. The related additional uncertainties are difficult to estimate, however the results of the previous calibration in 2013 have demonstrated that such uncertainties due to modelling are globally ⩽ ±3%.It has been found that the difference between KN1 response to DD neutrons and that to DT neutrons is within the uncertainties in the derived responses. KN2 has been calibrated using the 93Nb(n,2n)92mNb and 27Al(n,a)24Na activation reactions (energy thresholds 10 MeV and 5 MeV, respectively). The total uncertainty on the calibration factors is ±6% for 93Nb(n,2n)92mNb and ±8% 27Al(n,a)24Na (1σ). The calibration factors of the two independent systems KN1 and KN2 will be validated during DT operations.The experience gained and the lessons learnt are presented and discussed in particular with regard to the 14 MeV neutron calibrations in ITER.

System of Standard Neutron Sources on Neutronic Setups for Monitoring, Certification, and Calibration of Apparatus and Equipment

A methodological provision system for neutron measurements performed using neutronic setups is described. The metrological characteristics of standard sources of neutrons of five different groups, created based on nuclear reactors and 14 MeV neutron generators, are presented. The neutron spectra are calculated by a standard method and presented in a unified analytical form as a superposition of physically validated spectra.