Neutron Burst Research Articles

Cosmic ray modulation studies with Lead-Free Gulmarg Neutron Monitor

A lead-free neutron monitor operating at High Altitude Research Laboratory (HARL), Gulmarg optimized for detecting 2.45MeV neutron bursts produced during the atmospheric lightning discharges is also concurrently used for studying background neutron component present in the atmosphere. These background neutrons are produced due to the interaction of primary cosmic rays with the atmospheric constituents. In order to study and extract the information about the yield of the neutron production during transient atmospheric lightning discharges, the system is continuously operated to monitor and record the cosmic ray produced background secondary neutrons in the atmosphere. The data analysis of the background neutrons recorded by Lead-Free Gulmarg Neutron Monitor (LFGNM) has convincingly established that the modulation effects due to solar activity phenomena compare very well with those monitored by the worldwide IGY or NM64 type neutron monitors which have optimum energy response relatively towards the higher energy regime of the cosmic rays. The data has revealed various types of modulation phenomena like diurnal variation, Forbush decrease etc. during its entire operational period. However, a new kind of a periodic/seasonal variation pattern is also revealed in the data from September 2007 to September 2012, which is seen to be significantly consistent with the data recorded by Emilio Segre observatory, Israel (ESOI) Neutron Monitor. Interestingly, both these neutron monitors have comparable latitude and altitude. However, the same type of consistency is not observed in the data recorded by the other conventional neutron monitors operating across the globe.

Neutron Bursts in Lab Lightning

Neutron Bursts in Lab Lightning

Observation of Neutron Bursts Produced by Laboratory High-Voltage Atmospheric Discharge

For the first time the emission of neutron bursts in the process of high-voltage discharge in air was observed. Experiments were carried out at an average electric field strength of ∼1 MV·m(-1) and discharge current of ∼10 kA. Two independent methods (CR-39 track detectors and plastic scintillation detectors) registered neutrons within the range from thermal energies up to energies above 10 MeV and with an average flux density of ≳10(6) cm(-2) per shot inside the discharge zone. Neutron generation occurs at the initial phase of the discharge and correlates with x-ray generation. The data obtained allow us to assume that during the discharge fast neutrons are mainly produced.

Neutron bursts during cloud-to-ground discharges of lightning

Neutron bursts of up to 30% per minute resolution are recorded by the Yakutsk cosmic ray spectrograph during jumps of an electric field undergoing changes in the vicinity of the neutron monitor upon cloud-to-ground discharges of lightning. The electric field variations are recorded with an electrostatic fluxmeter (±50 keV m−1).

Total fluence influence on the detected magnitude of neutron burst using proportional detectors

The measurement of very short neutron bursts, when individual neutrons cannot be counted in the usual manner, is possible with proportional detectors (such as 3 He) taking the integration of the total electric charge due to many overlapped interactions, as the measure of the amount of the neutron signal. This method requires a correction related to the total amount of neutrons that interacted with the detector. This correction originates in the well-known build-up of positive electric charge too slow to be dislodged from the detection volume during the neutron burst. This causes self-shielding of the applied electric field with the ensuing reduction of the charge multiplication process in the gas, described in the literature. Short neutron bursts from a plasma focus device and a conventional isotopic neutron source were employed in the experimental phase and the known theory was applied in the analysis, which justifies assigning the observed effects to the space-charge shielding of the externally applied electric field. This work introduces a correction to the neutron yield derived from the registered electric charge, through a model of collected charge reduction as a function of total neutrons measured.

Bursts of gamma-rays, electrons and low-energy neutrons during thunderstorms at the Tien-Shan

New data of the last measurement season held at the Tien-Shan complex for investigation gamma-radiation, accelerated electrons and low-energy neutrons during thunderstorms are presented. The flux of gamma-radiation in the energy range of 40 – 1200 keV shows a strict correlation with instantaneous intensity of atmospheric discharge. Its energy spectra measured for the first time with riches statistics and improved resolution typically have an absolute intensity about 50 – 100 quanta·cm−2·s−1, and demonstrate considerable evolution in the course of discharge. The signals from an avalanche of accelerated electrons have been directly observed inside thunderclouds. A lower energy estimation for these electrons is about 10 MeV. For the first time, during electric discharge moments in thunderstorms, there were found considerable intensity enhancements of the neutron intensity in the range of thermal energies: up to 100 – 200 standard deviations, or 3 – 8 times above the background, so the observed neutron flux reaches the values of (20 – 40) · 103 m−2 · min−1.

Neutron bursts associated with lightning cloud-to-ground discharges

We consider bursts in the neutrons registered by the Yakut spectrograph of cosmic rays and the electrostatic fluxmeter (± 50 kV/m). Bursts were observed during a significant change in the field, which changes abruptly from − 16 kV/m to 18 kV/m during negative lightning. It was found that during the positive lightning have not been observed bursts of neutrons, despite that the electric field changes abruptly from 10 kV/m up to −30 kV/m during the lightning discharge.

Experimental observations of strengthening the neutron flux during negative lightning discharges of thunderclouds with tripolar configuration

We consider neutron bursts (Yakutsk cosmic ray spectrograph,105m above sea level) and the electric field during lightning discharges. It was found that the neutron bursts are observed in the negative lightning discharg only. We discuss the possibility of generation of neutrons in the lower part (the point of impact into the ground) lightning discharge.

Gamma-Rays in Association with the Rocket-Triggered Lightning Caused by Neutron Bursts

In this work, it shows that nuclear reactions in lightning channel, which are produced by the deuterium-deuterium (D-D) and deuterium-tritium (D-T) nuclear reactions, represent a plausible mechanism for gamma-ray bursts observed at ground. Gamma-ray emissions from lightning can be explained by neutron inelastic scattering in the air. Neutrons (produced in lightning channel) will delay a definitive time (~33 ms) to cover the atmosphere before hitting a molecule and producing gamma rays, which is somewhat longer than the gamma-ray time delay (~20 ms) observed at ground.

Ultraintense Lasers as a Promising Research Tool for Fusion Material Testing: Production of Ions, X-Rays and Neutrons

Laser fusion environments are characterized by prompt bursts of high energy neutrons, ions and X-rays which are absorbed by different components of the fusion reaction chamber. In particular, plasma facing components are subjected to extreme conditions and prior to their use in the reactors they must be validated under stringent irradiation tests. However, the particular characteristics of the fusion products, i.e. very short pulses, very high fluences and broad particle energy spectra are difficult to reproduce in test laboratories, making those validations hard to be carried out. In the present work, the ability of ultraintense lasers to create the appropriate characteristics of laser fusion bursts is addressed. A description of a possible experimental set-up to generate the appropriate ion pulses with lasers is presented. At the same time, the possibility of generating X-ray or neutron beams which reproduce those of laser fusion environments is also pointed out and assessed under current laser intensities. It is concluded that ultraintense lasers should play a relevant role in the validation of materials for laser fusion facilities and immediate action for this systematic study is called for. c

Ion Fokker-Planck simulation of D-3He gas target implosions

Recently performed inertial confinement fusion implosion experiments involving D-3He gas-filled microballoons have shown discrepancies between expected and measured nuclear fusion yields as the relative abundances of D and 3He are varied. The latter have been tentatively attributed to a sedimentation, or stratification phenomenon occurring in the target core. This work investigates the possibility of ion species sedimentation in a detailed way through multi-species ion-kinetic Vlasov-Fokker-Planck simulations of the implosion process. A noticeable amount of sedimentation is found to build up during the main shock propagation to the target center, but then disappears as the implosion proceeds. As a result, only the yield of the first burst of neutrons, associated with shock convergence, is appreciably modified, leaving the main neutron production phase during fuel compression and stagnation unaffected. The sedimentation of fuel ion species found, thus, cannot explain the experimental discrepancies.

Anomalous Neutron Burst Emissions in Deuterium-Loaded Metals: Nuclear Reaction at Normal Temperature

Conventional nuclear fusion occurs in plasma at temperatures greater than 107°C or when energy higher than 10 keV is applied. We report a new result of anomalous neutron emission, also called cascade neutron burst emission, from deuterium-loaded titanium and uranium deuteride samples at room temperature. The number of neutrons in the large bursts is measured as up to 2800 in less than a 64-μs interval. We suggest that the anomalous cascade neutron bursts are correlated with deuterium-loaded metals and probably the result of nuclear reactions occurring in the samples.

First experimental observations of neutron bursts under thunderstorm clouds near sea level

The connection of short-term neutron bursts near sea level with the electric and geomagnetic atmospheric fields during thunderstorms in 2009–2011 has been experimentally studied. The data from the cosmic-ray spectrograph named after Kuzmin, an electrostatic fluxmeter, and a three-component fluxgate magnetometer in Yakutsk have been analyzed. It has been shown that short-term (no longer than 4 min) neutron bursts are due to negative lightning discharges. The bursts are detected at the ground level 1–3 km below thunderstorm clouds. In this case, the neutron flux is about 4 × 10−3 cm−2 s−1. The minimum energy of the neutrons that are efficiently detected by the monitor is about 10 MeV. It has been found that short-term neutron bursts are detected when the electric field strength reaches a threshold value of −16 kV/m.

Revisiting the form of dead time corrections for neutron coincidence counting

Abstract A standard nondestructive assay technique for determining the mass of plutonium in an item is passive neutron coincidence counting. In passive neutron coincidence counting, the dead time or rate loss corrections for the singles and doubles neutron counting rates are routinely made using empirical relationships that are based on the design and performance of the individual counter used to make the measurements. The empirical methods were developed ahead of any supporting theory for dead time losses and have worked well to date for the majority of safeguards measurement scenarios. Modern applications using highly efficient systems with short neutron lifetimes together with the challenges posed by highly multiplying items mean dead time corrections of higher fidelity are needed. While many attempts have been made to develop dead time corrections that are based on the physical principles of the measurements being performed, these corrections have often been found to be difficult to implement in a real system. For instance, Matthes and Haas developed an approach in 1985 which did not gain favor largely because the form of the doubles correction apparently required numerical integration which was difficult to implement with the computer technology of that time. A recent review into the approach that was developed by Matthes and Haas has determined that a straightforward analytical expression can be derived for the doubles correction that is similar to the singles rate correction that was developed in their original work. An analysis of the expressions is presented here to show how they relate to the traditional empirical methods. Further, we illustrate their implications and limitations. For instance the empirical methods do not address within burst losses i.e. rate related losses due to the correlated neutron bursts from fission, whereas the Matthes and Hass expression for singles counting does exhibit such an effect.

Neutron bursts associated with thunderstorms

The basis of our analysis is the observation of the simultaneous enhancements of the gamma ray and neutron fluxes detected in 2009--2010 during thunderstorm ground enhancements at the mountain altitude of 3200 m. We investigate the correlated time series of the gamma rays and neutrons measured by the surface particle detectors of Aragats Space Environmental Center. The photonuclear reactions of the gamma rays born in the runaway breakdown (RB, now referred to as relativistic runaway electron avalanche, RREA) process with air were considered as the main process responsible for the copious neutron production. We consider also the mesoatom nuclei decay as a possible source of the additional neutrons registered by the neutron monitor due to enhanced population of the negative muons accelerated in the thunderclouds.

Electromagnetic and neutron emissions from brittle rocks failure: Experimental evidence and geological implications

It has been observed energy emission in the form of electromagnetic radiation, clearly indicating charge redistribution, and neutron bursts, necessarily involving nuclear reactions, during the failure process of quasi-brittle materials such as rocks, when subjected to compression tests. The material used is Luserna stone, which presents a very brittle behaviour during compression failure. The observed phenomenon of high-energy particle emission, i.e., electrons and neutrons, can be explained in the framework of the superradiance applied to the solid state, where individual atoms lose their identity and become part of different plasmas, electronic and nuclear. Since the analysed material contains iron, it can be conjectured that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. These complex phenomenologies are confirmed by Energy Dispersive X-ray Spectroscopy (EDS) tests conducted on Luserna stone specimens, and found additional evidences at the Earth’s Crust scale, where electromagnetic and neutron emissions are observed just in correspondence with major earthquakes. In this context, the effects of piezonuclear reactions can be also considered from a geophysical and geological point of view.

Cavitation inception and damage effects in liquid mercury exposed to a high-energy pulsed proton beam.

The Oak Ridge National Laboratory Spallation Neutron Source (SNS) employs a high-energy proton beam incident on a liquid mercury target to generate short bursts of neutrons. Concomitant with neutron production is the rapid heating of the mercury, resulting in the formation of acoustic shock waves and the nucleation of cavitation bubbles. The subsequent collapse of these bubbles may result in the premature erosion of the target’s steel walls. We report on a multi-pronged effort to both understand and address the problem by (1) inhibiting cavitation inception using bubble injection, (2) analyze cavitation and cavitation cloud dynamics using passive noise diagnostics, and (3) mitigating vessel wall damage using surface modification techniques. [Work supported by the ORNL Spallation Neutron Source, which is managed by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy.]

Detection of SNM by delayed gamma rays from induced fission

The Pulsed Neutron Interrogation Test Assembly (PUNITA) is an experimental device for research in NDA methods and field applicable instrumentation for nuclear safeguards and security applications. PUNITA incorporates a standard 14-MeV (D-T) pulsed neutron generator inside a large graphite mantle. The generator target is surrounded by a thick tungsten filter with the purpose to increase the neutron output and to tailor the neutron energy spectrum . In this configuration a sample may be exposed to a relatively high average thermal neutron flux of about (2.2±0.1)×10 3 s −1 cm −2 at only 10% of the maximum target neutron emission . The sample cavity is large enough to allow variation of the experimental setup including the fissile sample, neutron and gamma detectors , and shielding materials. The response from SNM samples of different fissile material content was investigated with various field-applicable scintillation gamma detectors such as the 3×2 in. LaBr 3 detector. Shielding in the form of tungsten and cadmium was applied to the detector to improve the signal to background ratio. Gamma and neutron shields surrounding the samples were also tested for the purpose of simulating clandestine conduct. The energy spectra of delayed gamma rays were recorded in the range 100 keV–9 MeV. In addition time spectra of delayed gamma rays in the range 3.3–8 MeV were recorded in the time period of 10 ms–120 s after the 14-MeV neutron burst. The goal of the experiment was to optimize the sample/detector configuration including the energy range and time period for SNM detection. The results show, for example, that a 170 g sample of depleted uranium can be detected with the given setup in less than 3 min of investigation. Samples of higher enrichment or higher mass are detected in much shorter time.

Experiment based on spacesuit “Orlan‐M”: Neutron fluxes from thunderstorms

We present a new experiment on the detection of thunderstorm neutrons at orbital altitudes. The aims of the experiment called “Scafandr” are to establish the nature of the neutrons and to explore their properties. Also, the dosimetric measurement program is included in the experiment mission. For the neutron program, measurement of the thermal neutron fluxes from an altitude of 350 km down to 200 km is planned. We plan to obtain substantial statistics and resolution of neutron bursts. This will allow for mapping of the neutrons' distribution on the considered altitudes for their comparison with the thunderstorm activity maps and for comparison with the results of neutron burst numerical modeling. Previous experiments carried out are discussed, and their comparative analysis with the presented one is given.

Localization of the source of terrestrial neutron bursts detected in thunderstorm atmosphere

To localize an altitude of the neutron source responsible for the neutron flux enhancements observed on the ground, numerical simulations of photonuclear production and transport to on‐ground detector locations were carried out. The neutron fluence calculated for the volumetric source located at the altitudes 8–12 km is consistent with that estimated from neutron numbers measured on the ground. This altitude range is consistent with the idea that the burst of hard γ rays detected recently by Tsuchiya et al. (2007, 2009) originate from a volumetric intracloud γ ray source. Most likely, the photonuclear reactions caused by bremsstruhlung of descending relativistic runaway electron avalanches account for the neutron flux increases observed in the thunderstorm atmosphere.