Cosmic Neutron Research Articles

Possible application of scintillation detectors with semiconductor PMT for cosmic-neutron and gamma-ray detection

Solar system planets exploration and cosmic neutrons and gamma-ray flux research have been dynamically evolving for several decades. Different scintillation crystals are used for this purpose along with photo signal receivers, such as vacuum photomultiplier tubes (PMT). Many studies are being performed in order to provide alternative devices for photon signal capture: PIN-diodes,avalanche photodiodes, semiconductor silicon photomultipliers. We study the applicability of a silicon PMT in employing highresolution crystals in space applications.

Neutron guide shielding for the BIFROST spectrometer at ESS

We report on the study of fast-neutron background for the BIFROST spectrometer at ESS. We investigate the effect of background radiation induced by the interaction of fast neutrons from the source with the material of the neutron guide and devise a reasonable fast, thermal/cold neutron shielding solution for the current guide geometry using McStas and MCNPX. We investigate the effectiveness of the steel shielding around the guide by running simulations with three different steel thicknesses. The same approach is used to study the efficiencies of the steel wall a flat cylinder pierced by the guide in the middle and the polyethylene layer. The final model presented here has a 3 cm thick steel shielding around the guide, 30 cm of polyethylene around the shielding, two 5 mm thick B4C layers and a steel wall at position Z = 38 m, being 1 m thick and 10 m in radius. The final model finally proves that it is sufficient to bring the background level below the cosmic neutron rate, which defines an order of magnitude of the lowest obtainable background in the instruments.

Disputed dark-matter result gets put to the test

Despite nearly two decades of scrutiny, nobody has yet explained away—or confirmed—DAMA’s claim of detecting the elusive matter.

CHARACTERIZATION OF A THIN SILICON SENSOR FOR ACTIVE NEUTRON PERSONAL DOSEMETERS.

A thin silicon sensor has been developed for active neutron personal dosemeters for use by aircrews and first responders. This thin silicon sensor is not affected by the funneling effect, which causes detection of cosmic protons and over-response to cosmic neutrons. There are several advantages to the thin silicon sensor: a decrease in sensitivity to gamma rays, an improvement of the energy detection limit for neutrons down to 0.8 MeV and an increase in the sensitivity to fast neutrons. Neutron response functions were experimentally obtained using 2.5 and 5 MeV monoenergy neutron beams and a (252)Cf neutron source. Simulation results using the Monte Carlo N-Particle transport code agree quite well with the experimental ones when an energy deposition region shaped like a circular truncated cone is used in place of a cylindrical region.

Debendra Mohan Bose (1885-1975)-An Eminent Physicist of India

Debendra Mohan Bose was one of the leading experimental physicists of India in the 20th century. He did notable work with Wilson cloud chambers, successfully photographing the recoil tracks of radioactive nuclei during the process of alpha-emission. He earned international eminence for his contributions in the field of simple and complex compounds containing paramagnetic and rare-earth ions and for the determination of the mass of μ-mesons using the photographic emulsion method. He was also responsible for initiation of research in India in the areas of cosmic rays, artificial radioactivity and neutron physics. He was a member of the committee which recommended the formation of the Atomic Energy Commission in India. He was also a member of the CSIR committee which planned the setting up of the National Physical Laboratory and the National Chemical Laboratory.

Cosmogenic radionuclide production in NaI(Tl) crystals

The production of long-lived radioactive isotopes in materials due to the exposure to cosmic rays on Earth surface can be an hazard for experiments demanding ultra-low background conditions, typically performed deep underground. Production rates of cosmogenic isotopes in all the materials present in the experimental set-up, as well as the corresponding cosmic rays exposure history, must be both well known in order to assess the relevance of this effect in the achievable sensitivity of a given experiment. Although NaI(Tl) scintillators are being used in experiments aiming at the direct detection of dark matter since the first nineties of the last century, very few data about cosmogenic isotopes production rates have been published up to date. In this work we present data from two 12.5 kg NaI(Tl) detectors, developed in the frame of the ANAIS project, which were installed inside a convenient shielding at the Canfranc Underground Laboratory just after finishing surface exposure to cosmic rays. The very fast start of data taking allowed to identify and quantify isotopes with half-lives of the order of tens of days. Initial activities underground have been measured and then production rates at sea level have been estimated following the history of detectors; values of about a few tens of nuclei per kg and day for Te isotopes and 22Na and of a few hundreds for I isotopes have been found. These are the first direct estimates of production rates of cosmogenic nuclides in NaI crystals. A comparison of the so deduced rates with calculations using typical cosmic neutron flux at sea level and a carefully selected description of excitation functions will be also presented together with an estimate of the corresponding contribution to the background at low and high energies, which can be relevant for experiments aiming at rare events searches.

Examination of radioargon production by cosmic neutron interactions

Radioargon isotopes, particularly 37Ar, are currently being considered for use as an On-Site Inspection (OSI) relevant radionuclide within the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In order to understand any soil air measurements taken during an OSI, the radioargon background due to cosmic ray induced activation along with other sources must be understood. An MCNP6 model was developed using the cosmic ray source feature within the code to examine the neutron flux at ground level as a function of various conditions: date during the solar magnetic activity cycle, latitude of sampling location, geology of the sampling location, and sampling depth. Once the cosmic neutron flux was obtained, calculations were performed to determine the rate of radioargon production for the main interactions. Radioargon production was shown to be highly dependent on the soil composition, and a range of 37Ar production values at 1 m depth was found with a maximum production rate of 4.012 atoms/sec/m3 in carbonate geologies and a minimum production rate of 0.070 atoms/sec/m3 in low calcium granite. The sampling location latitude was also shown to have a measurable effect on the radioargon production rate, where the production of 37Ar in an average continental crust is shown to vary by a factor of two between the equator and the poles. The sampling date's position within the solar magnetic activity cycle was also shown to cause a smaller change, less than a factor of 1.2, in activation between solar maxima and solar minima.

Fast-neutron activation of long-lived nuclides in natural Pb

We measured the production of the long-lived nuclides 207Bi, 202Pb, and 194Hg in a sample of natural Pb due to high-energy neutron interactions using a neutron beam at the Los Alamos Neutron Science Center. The activated sample was counted by a HPGe detector tomeasure the amount of radioactive nuclides present. These nuclides are critical in understanding potential backgrounds in low background experiments utilizing large amounts of Pb shielding due to cosmogenic neutron interactions in the Pb while residing on the Earth’s surface. By scaling the LANSCE neutron flux to a cosmic neutron flux, we measure the sea level cosmic ray production rates of 8.0±1.3atoms/kg/day of 194Hg, 120±25atoms/kg/day 202Pb, and <0.17±0.04atoms/kg/day 207Bi.

Space weather driven changes in lower atmosphere phenomena

During a period of heliospheric disturbance in 2007–9 associated with a co-rotating interaction region (CIR), a characteristic periodic variation becomes apparent in neutron monitor data. This variation is phase-locked to periodic heliospheric current sheet crossings. Phase-locked electrical variations are also seen in the terrestrial lower atmosphere in the southern UK, including an increase in the vertical conduction current density of fair weather atmospheric electricity during increases in galactic cosmic ray-induced neutron monitor count rate at the surface and energetic proton count rates measured by geosynchronous spacecraft. At the same time as the conduction current increases, changes in the cloud microphysical properties lead to an increase in the detected height of the cloud base at Lerwick Observatory, Shetland, with associated changes in surface meteorological quantities. As electrification is expected at the base of layer clouds, which can influence droplet properties, these observations of phase-locked thermodynamic, cloud, atmospheric electricity and solar sector changes are not inconsistent with a heliospheric disturbance driving lower troposphere changes.

Space Weather and the Ground-Level Solar Proton Events of the 23rd Solar Cycle

Solar proton events can adversely affect space and ground-based systems. Ground-level events are a subset of solar proton events that have a harder spectrum than average solar proton events and are detectable on Earth’s surface by cosmic radiation ionization chambers, muon detectors, and neutron monitors. This paper summarizes the space weather effects associated with ground-level solar proton events during the 23rd solar cycle. These effects include communication and navigation systems, spacecraft electronics and operations, space power systems, manned space missions, and commercial aircraft operations. The major effect of ground-level events that affect manned spacecraft operations is increased radiation exposure. The primary effect on commercial aircraft operations is the loss of high frequency communication and, at extreme polar latitudes, an increase in the radiation exposure above that experienced from the background galactic cosmic radiation. Calculations of the maximum potential aircraft polar route exposure for each ground-level event of the 23rd solar cycle are presented. The space weather effects in October and November 2003 are highlighted together with on-going efforts to utilize cosmic ray neutron monitors to predict high energy solar proton events, thus providing an alert so that system operators can possibly make adjustments to vulnerable spacecraft operations and polar aircraft routes.

Measurement depth of the cosmic ray soil moisture probe affected by hydrogen from various sources

We present here a simple and robust framework for quantifying the effective sensor depth of cosmic ray soil moisture neutron probes such that reliable water fluxes may be computed from a time series of cosmic ray soil moisture. In particular, we describe how the neutron signal depends on three near‐surface hydrogen sources: surface water, soil moisture, and lattice water (water in minerals present in soil solids) and also their vertical variations. Through a combined modeling study of one‐dimensional water flow in soil and neutron transport in the atmosphere and subsurface, we compare average water content between the simulated soil moisture profiles and the universal calibration equation which is used to estimate water content from neutron counts. By using a linear sensitivity weighting function, we find that during evaporation and drainage periods the RMSE of the two average water contents is 0.0070 m3 m−3 with a maximum deviation of 0.010 m3 m−3 for a range of soil types. During infiltration, the RMSE is 0.011 m3 m−3 with a maximum deviation of 0.020 m3 m−3, where piston like flow conditions exists for the homogeneous isotropic media. Because piston flow is unlikely during natural conditions at the horizontal scale of hundreds of meters that is measured by the cosmic ray probe, this modeled deviation of 0.020 m3 m−3 represents the worst case scenario for cosmic ray sensing of soil moisture. Comparison of cosmic ray soil moisture data and a distributed sensor soil moisture network in Southern Arizona indicates an RMSE of 0.011 m3 m−3 over a 6 month study period.

Dosimetry of cosmic radiation in the troposphere based on the measurements at the summit of Mt. Fuji

Abstract Dose rate of cosmic-ray origin neutrons (abbreviated to “cosmic neutrons”) at aviation altitude was estimated based on the measurements at Mt. Fuji. Cosmic neutrons were measured in a facility of the Mt. Fuji Weather Station located at the summit of Mt. Fuji, the highest mountain in Japan (3776 m in altitude), in the summer of 2008 and 2009. The average of 1 cm ambient dose equivalent H*(10) for two measurements was verified by numerical model simulation and then used to empirically estimate the solar force field potential (FFP). The H*(10) rates at aviation altitude estimated from the measurements at Mt. Fuji were compared to those obtained in in-flight measurements onboard a civilian aircraft flying near Mt. Fuji at the time between the two measurements at the mountain. According to the results obtained, we expect that the empirical estimation based on the measurements at Mt. Fuji will work effectively for dosimetry of cosmic radiation in troposphere.

Analysis of seasonal variations of the cosmic ray muon flux and neutrons produced by muons in the LVD detector

The Russian-Italian Large Volume Detector (LVD) is located at the Gran Sasso underground laboratory at a depth of 3300 m w.e. To study the seasonal variations of the penetrating component of cosmic rays, the data on cosmic ray muons detected in 2001–2008 was analyzed, along with those associated with neutrons produced by muons since April 2003. One-year periodic variations of muons and neutrons produced by them were found. The maximum intensity is observed in July, in accord with theoretical concepts.

Radiocarbon in Vegetation of coastal Zone of Finnish Bay (Russia)

Radiocarbon is a radioactive isotope of carbon, which is forming in the nature constantly by interaction of cosmic fast neutrons and nitrogen nuclei at the low atmospheric layers. Another source of radiocarbon in the environment is pollution in processes of Nuclear Power Plant exploitation. The expanding construction of nuclear industrial plants and nuclear power stations on the shores of the Baltic Sea is creating a real possibility for the introduction of radioactive wastes into environment of Finnish Bay basin. The activity of radiocarbon in the plant of coastal zone was determined by a system of Sample Oxidizer 307 and low-level liquid scintillation system Quantulus 1220 (Wallace, Turku, Finland) The Radiocarbon analysis is a sensitive tool for the registration of pollution. The variations of radiocarbon concentration in the one-years grasses can be used as an indicator of carbon dioxide pollution of the urban environment. The variation of radiocarbon in tree-rings reflects the local and global radioactive contaminations.

Cosmic ray background effects on the neutron intercepting silicon chip (NISC)

Abstract Cosmic rays are mainly composed of galactic and solar particles. Galactic particles have enormous energies and interact in the atmosphere causing cascades of secondary particles, which can travel through the atmosphere and reach sea level. The origin of the cosmic terrestrial neutrons is galactic particles and these neutrons contribute almost 97% of the cosmic rays at sea level. Solar particles originate from the sun and have less energy compared to galactic particles. Almost all the solar particles are absorbed in the atmosphere before reaching sea level. The solar particle flux depends on the 11-year solar cycle and varies by multiple orders of magnitude between these cycles. In this study, cosmic ray induced soft errors in the neutron intercepting silicon chip (NISC) are investigated via the NISC Soft Error Analysis Tool (NISCSAT), which uses Geant4 as the transport and tracking engine. The NISC is a new unconventional neutron monitoring/detection system, designed to enhance the soft error occurrences in the semiconductor memories by introducing 10B-enriched regions in the memory node structure. The main driving force comes from the reaction products of 10B (n,α) 7Li reaction because both α and 7Li particles can induce soft errors in the memory. Since the 10B (n,α) 7Li reaction strictly depends on the incoming neutron energy and has a high cross-section at the thermal neutron energies, effects of the background cosmic thermal neutrons on the NISC are investigated in this study.

A dual-detector extended range rem-counter

The design and characterization of a dual-detector spherical rem counter is discussed in this paper. The rem counter is based on a polythene sphere with lead and cadmium insets, designed to host at its centre either an active ( 3 He SP9 proportional counter) or a passive (CR39 + 10 B radiator) thermal neutron detector. Its sensitivity ranges from thermal energies up to 1 GeV. A Monte Carlo characterization of this dual-detector rem counter has shown no significant change in the shape of the response curve obtained with the two detectors. The rem counter has been calibrated with a Pu–Be source. An intercomparison in a high-energy neutron field has been carried out at the CERF facility at CERN among the rem counter in the two configurations, two commercial units and the original version of the active LINUS in use at CERN. Both the active and passive versions of the rem counter agree, within the statistical uncertainties, with the CERN LINUS and with the facility reference values. Both versions of the instrument have proved to be capable of measuring the cosmic neutron background, thus providing a nonzero background measurement in environmental monitoring application.

Modelling neutron transport in planetary media via analytical multigroup diffusion theory

A novel analytical solution to the 1D, steady-state, multi-slab, multi-group diffusion equation is proposed as a mean to compute the energy-dependent galactic cosmic ray-induced neutron fluxes established in planetary media. More specifically, the proposed algorithm is implemented to allow fast and highly accurate determination of low-energy cosmic ray neutrons inside the Earth's surface and atmosphere. Two sets of experimental measurements have been considered to validate our model. In both cases, a good agreement between the calculated and observed neutron fluxes is achieved. Subsequently, neutron diffusion calculations have been performed for various Earth-based scenarios comprising (a) two-slab (air–soil) configuration and (b) three-slab (air–soil–ice) configuration to investigate the functional relationship between soil composition and neutron spatial distribution.

Results With the Neutron Scatter Camera

We describe the design, calibration, and measurements made with the neutron scatter camera. Neutron scatter camera design allows for the determination of the direction and energy of incident neutrons by measuring the position, recoil energy, and time-of-flight (TOF) between elastic scatters in two liquid scintillator cells. The detector response and sensitive energy range (0.5-10 MeV) has been determined by detailed calibrations using a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf neutron source over its field of view (FOV). We present results from several recent deployments. In a laboratory study we detected a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf neutron source at a stand off distance of 30 m. A hidden neutron source was detected inside a large ocean tanker. We measured the integral flux density, differential energy distribution and angular distribution of cosmic neutron background in the fission energy range 0.5-10 MeV at Alameda, CA (sea level), Livermore, CA (174 m), Albuquerque, NM (1615 m) and Fenton Hill, NM (2630 m). The neutron backgrounds are relatively low, and non-isotropic. The camera has been ruggedized, deployed to various locations and has performed various measurements successfully. Our results show fast neutron imaging could be a useful tool for the detection of special nuclear material (SNM).

RESPONSES OF SELECTED NEUTRON MONITORS TO COSMIC RADIATION AT AVIATION ALTITUDES

Cosmic radiation exposure of aircraft crew, which is generally evaluated by numerical simulations, should be verified by measurements. From the perspective of radiological protection, the most contributing radiation component at aviation altitude is neutrons. Measurements of cosmic neutrons, however, are difficult in a civilian aircraft because of the limitations of space and electricity; a small, battery-operated dosimeter is required whereas larger-size instruments are generally used to detect neutrons with a broad range of energy. We thus examined the applicability of relatively new transportable neutron monitors for use in an aircraft. They are (1) a conventional rem meter with a polyethylene moderator (NCN1), (2) an extended energy-range rem meter with a tungsten-powder mixed moderator (WENDI-II), and (3) a recoil-proton scintillation rem meter (PRESCILA). These monitors were installed onto the racks of a business jet aircraft that flew two times near Japan. Observed data were compared to model calculations using a PHITS-based Analytical Radiation Model in the Atmosphere (PARMA). Excellent agreement between measured and calculated values was found for the WENDI-II. The NCN1 showed approximately half of predicted values, which were lower than those expected from its response function. The observations made with PRESCILA showed much higher than expected values; which is attributable to the presence of cosmic-ray protons and muons. These results indicate that careful attention must be paid to the dosimetric properties of a detector employed for verification of cosmic neutron dose.

Temporal variation of 7Be concentrations in atmosphere for 8 y from 2000 at Yamagata, Japan: solar influence on the 7Be time series

We have been continuously observing the daily 7Be concentrations in surface air at Yamagata, Japan (38.25° N, 140.35° E) since 2000. The yearly profile of the 7Be concentration indicates the variation in galactic cosmic rays owing to solar modulation. Over 8 y, the 7Be concentration, cosmic neutrons, and number of sunspots varied by 37.4%, 12.2%, and 92.8%, respectively. The influence of precipitation on the 7Be variability was approximately 5%. Hence, the yearly 7Be concentration was mainly varied by the solar modulation of the 7Be production rates. Based on the production rates found in an EXPACS simulation, the observed variability indicates 7Be transport from high latitudes. The daily 7Be concentrations have two significant periodic components of 19 d and 36 d. The 36-d component implies a relationship between the sun's rotation and the vertical transport of air masses under quiet solar activity.