O. B. Shchegolev

The array for EAS neutron component detection

The idea of a novel type detector array is the following: delayed thermal neutrons generated by hadronic component of Extensive Air Showers (EAS) can be detected over the whole array area using special electron-neutron detectors (en-detectors). The array PRISMA-32 consists of 32 en-detectors, deployed over the area of 450 m2. En-detectors are able to detect two main EAS components: electromagnetic one in a case of a synchronous passage of several charged particles, and hadronic component through thermal neutron captures. Detectors are based on a specialized inorganic scintillator, being a granulated alloy of ZnS(Ag) with LiF, enriched up to 90% with 6Li isotope. The array is triggered by the electromagnetic component of EAS, and provides information about the energy deposit (mostly electrons) and delayed neutrons accompanying the EAS within 20 ms after the trigger. During 2 years of operation more than 105 events were recorded. Examples of EAS detection are presented.

Novel method for detecting the hadronic component of extensive air showers

A novel method for studying the hadronic component of extensive air showers (EAS) is proposed. The method is based on recording thermal neutrons accompanying EAS with en-detectors that are sensitive to two EAS components: an electromagnetic (e) component and a hadron component in the form of neutrons (n). In contrast to hadron calorimeters used in some arrays, the proposed method makes it possible to record the hadronic component over the whole area of the array. The efficiency of a prototype array that consists of 32 en-detectors was tested for a long time, and some parameters of the neutron EAS component were determined.

Spatial distribution function of electrons and thermal neutrons in extensive air showers at sea level

The spatial distributions of electrons and hadrons in extensive air showers, obtained during the PRISMA-32 experiment simulation, are considered. The experiment was simulated for primary protons and iron nuclei using the CORSIKA6.9 and GEANT4.10 software packages. The simulated spatial distribution functions of electrons and neutrons in the extensive air showers (EAS) at the Moscow altitude are compared to the published experimental data of the PRISMA-32 setup.

Electron and thermal neutron lateral distribution functions in EAS at high altitude

EAS array of novel type have been constructed on the base of ARGO-YBJ experiment (Tibet, China). It consists of the four specially designed scintillator en-detectors capable to measure two main EAS components: hadrons through thermal neutrons (n) and electrons (e). The results of simulation for these arrays using CORSIKA and GEANT4 codes are presented. Simulated thermal neutron and electron lateral distributions are compared with experimental data. Obtained distributions are compared with those obtained by other arrays.

Variations in the neutron flux during thunderstorms

The results from the registration and analysis of sporadic variations of atmospheric thermal neutron flux during thunderstorms are reported. Measurements were performed in Moscow and at the Baksan Neutrino Observatory of the Institute for Nuclear Research of the Russian Academy of Sciences. The neutron flux was detected by unscreened scintillation en-detectors based on 6LiF + ZnS (Ag) compound targets with signals selected according to pulse shape. Reductions of 5–10% in the neutron flux due to shower precipitates during thunderstorms are detected. No incidents of increased neutron flux during thunderstorms were detected over four summer seasons. The upper limits for the integrated and pulsed flux of neutrons from thunderbolts are estimated.

Low-background EN-detector for the investigation of the neutron component of EASs

Thermal neutrons are detected using a scintillator compound based on ZnS(Ag) with B2O3 added to it. The pulse height generated by single charged particles in a scintillator of small thickness (50 mg/cm2) is not larger than that of a noise signal due to a low sensitivity to single charged particles. As a result, the detector satisfies the requirements of a low-background one in the context of cosmic-ray experiments. The detector is to be used for neutron detection in extensive air showers.

Temporal and lateral distributions of EAS neutron component measured with PRISMA-32

Some results on the EAS neutron component measurements by means of the PRISMA-32 array are presented. The array consists of 32 electron-neutron detectors (en-detectors) capable to detect two main EAS components: electromagnetic one consisting of charged particles, and hadronic one by measuring delayed thermal neutrons accompanying the showers. For thermal neutrons detection, a compound of a well-known inorganic scintillator ZnS(Ag) and LiF, enriched to 90 % with 6Li isotope is used. The setup allows us to record neutron component over the whole array area.

Underground physics and the barometric pumping effect observed for thermal neutron flux underground

It is known that neutron background is a major problem for low-background experiments carrying out underground, such as dark matter search, double-beta decay searches and other experiments known as Underground Physics. We present here some results obtained with the en-detector of 0.75 m2, which is running for more than 4 years underground at a depth of 25 m water equivalent in Skobeltsyn Institute of Nuclear Physics, Moscow State University. Some spontaneous increases in thermal neutron flux up to a factor of 3 were observed in delayed anti-correlation with barometric pressure. The phenomenon can be explained by the radon barometric pumping effect resulting in similar effect in neutron flux being produced in (α, n)-reactions by alpha-decays of radon and its daughters in surrounding rock. This is the first demonstration of the barometric pumping effect observed in thermal neutron flux underground.

Cosmic ray spectrum measured by the PRISMA-32 setup

The results of measurements of the spectrum of extensive air showers (EASs) by the number of neutrons detected by the PRISMA-32 setup are presented. The neutron component is formed during the interaction of high-energy shower hadrons with nuclei of atmospheric and Earth’s surface atoms. The PRISMA-32 setup consists of 32 en-detectors and operates in the continuous mode for about 5 years.

Long-term variations in the natural thermal neutron flux at 4300 m above sea level

Long-term variations in the natural thermal neutron flux in Tibet at an altitude of 4300 m above sea level are studied using scintillation en-detectors developed at the Institute for Nuclear Research, Russian Academy of Sciences. Substantial growth (on the level of several per cent each year over the last three years) in both the thermal neutron flux and the background recorded by the detectors is observed. This growth is associated with the intensity of cosmic rays. The effect is explained by an increase in the low-energy cosmic ray flux, due to reduced solar activity in the current solar cycle.