Ultimate ground level enhancements of solar cosmic ray intensity

Possible values of ground level enhancements (GLEs) of the intensity of solar cosmic rays (SCRs) that can be recorded by neutron monitors (NMs) are estimated in two different ways for the ultimate spectra of solar protons. The first approach uses the statistical dependence between the maximum values of the integral proton flux >100 МeV and the GLE recorded by an NM. The second is to calculate the expected effect for the ultimate spectrum at a particular NM with known couple coefficients, atmospheric depth, and the threshold of the geomagnetic cutoff. Estimates using the first method vary from 9600 to 160000% for high-latitude NMs; estimates using the second method, from 1200 to 750000%. The obtained lower limits approximately correspond to GLE values observed earlier, and the upper limits are two orders of magnitude higher. Studies of the possible impact of solar proton events with spectra close to ultimate on the Earth’s atmosphere and biosphere should be continued.     

Identification of Primary Y-Rays by the Characteristics of Time-Space Structure of the Cosmic-Ray Air Showers

The time-space structure of particles for individual air showers induced by primary γ-rays and protons at the observation level is analysed by Monte Carlo simulation. It is shown that air showers induced by the primary γ-rays can be effectively separated from the air showers induced by protons (background) using the combination cuts on the arrival time fluctuation and the lateral distribution width of secondary particles in air showers. This method can be used for reducing the background of hadrons in searching for γ-ray point sources for ARGO experiment coorperated by China and Italy at Yangbajing. The effect of this method on the significance of γ-ray signals is also estimated.     

羊八井ARGO实验中原初γ和质子的区分

利用Ｍｏｎｔｅ Ｃａｒｌｏ模拟数据研究由γ和质子引起的空气簇射中的粒子在羊八井ＡＲＧＯ实验中的空间分布和时间分布的不同,提出了利用人工神经网络区分原初γ和质子的方法,结果表明在１００ＧｅＶ～１０ＴｅＶ能区可以较好地区分γ和质子。     

Study of dynamics of global disturbances of the Earth’s magnetosphere using muon detectors

Amethod is developed, whichmakes it possible to predict in advance disturbances in the Earth’s magnetosphere, caused by solar flares or changes in the heliospheric magnetic field, since the cosmic particle flux reaches the Earth much earlier than coronal plasma bursts. To scan the celestial hemisphere, wide-aperture muon detectors are used. A unique system of muon hodoscopes was developed at the NEVOD Science and Education Center (MEPhI, Moscow). The data of the URAGAN muon hodoscope on two-dimensional dynamics of the muon flux during the Forbush effect of November 14, 2006 are analyzed. Changes in the muon flux intensity, measured at various directions with an interval of 30 min are shown. The results obtained demonstrate the muon flux sensitivity to solar plasma cloud motion, which offers prospects to use muon detectors to probe interplanetary space at long distances from the Earth and to predict geomagnetic disturbances.     

Evaluation of the energy spectrum of solar protons according to the balloon measurement data and Monte Carlo simulation

The method for evaluating the energy spectra of solar protons at the boundary of the Earth’s atmosphere according to the data of balloon measurements carried out at the Lebedev Institute of Physics, Russian Academy of Sciences, and the results of Monte Carlo simulation of the processes of proton interaction in the Earth’s atmosphere has been developed. The balloon measurements during solar proton events make it possible to determine the absorption spectra of solar cosmic rays in the atmosphere. Comparison of the experimental data with the results of the simulation of propagation of solar protons (E _p = 10 MeV-10 GeV) in the atmosphere, based on GEANT-4, allows determination of the energy spectra of solar protons at the atmospheric boundary. The results of the determination of the energy spectra of solar protons in a number of solar proton events in the current (23th) solar activity cycle are reported.     

Properties of the lighest known caesium isotopes 114–118Cs

Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.7}\text{sec}$) in ¹¹⁶Cs has been observed and the new delayed-particle precursors ¹¹⁶Cs (protons and α-particles), ¹¹⁵Cs (protons), and ¹¹⁴Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for ¹¹⁸Cs (pγ and αγ) and ¹¹⁶Cs (pγ). A search for the possible proton-radioactive isotope ¹¹³Cs has been performed and an upper limit for its production yield is given.     

Measurements of neutron fluxes with energies from thermal to several MeV in near-Earth space: SINP results

Neutron measurement results obtained at SINP MSU since 1970 are presented. These measurements were made using techniques based on neutron moderation and subsequent detection in a Li6I(Eu) crystal or a He3 coronal counter. The measurements were mainly carried out in orbits with inclination of 52 degrees and altitudes of 200-450 km. The spatial and angular distributions of the measured neutron fluxes were studied. The albedo neutron flux was estimated according to the count rate difference for opposite detector orientations towards Earth and away from it. This flux is comparable to the local neutron flux outside the Brazil anomaly region, where local neutrons dominate. Neutron fluxes, generated by solar protons, were detected during a solar flare on June 6, 1991 for the first time. Their spectrum was estimated as a power law with alpha>2.     

Development and applications of “Mössbauer cameras”

Two different types of “Mössbauer camera” are presented in this review article. The first one uses an imaging technique for γ-rays which are converted to visual light by a Photon-counting Image Acquisition System (PIAS) combined with a Fiber Optic plate with CsI (Tl) Scintillator (FOS), while the second one is a mapping technique for γ-rays which are first focused by a Multi Capillary X-ray lens (MCX), and subsequently electrons and γ-rays are detected as function of the sample position by a micro-channel plate (MCP) and a Si-PIN detector, respectively. A mapping image of a silicon solar cell is shown as an example obtained by the latter system. We also report on the present status in developing a new combined lens for the mapping using a MCX and a Fresnel Zone Plate (FZP) in order to realize a submicron-meter spatial resolution in a laboratory.     

Propagation of solar cosmic rays in loop-like interplanetary magnetic field structures

Features of propagation of relativistic solar cosmic rays in magnetic clouds have been considered on the basis of model calculations. Magnetic clouds have a structure of magnetic flux ropes and are extended from the Sun to the Earth via coronal mass ejections. Features of propagation of particles of different energies in a magnetic cloud are discussed. The propagation of high-energy solar protons in the loop-like structure of the interplanetary magnetic field in the event of October 28, 2003 is analyzed.     

Study on the separation of 100 TeV γ-rays from cosmic rays for the Tibet ASγ experiment

A γ/hadron separation analysis is described for the observed air shower events with primary energy above 100 TeV based on the Tibet AST detector configuration. The shower age and size parameters are fitted from the measured lateral density distribution and used as discrimination variables. According to the MC simulation while taking into account the systematic uncertainty estimated from data and MC comparison,it is found that 70% of the cosmic ray (CR) background can be rejected while more than 78% of the γ-rays can be retained. Sensitivity for 100 TeV γ-rays observation can thus be improved by at least 40%.     

Study on Multifractal Structure of the Distribution Fluctuation of Secondary Perticles in the Core Region of EAS

The differences of space distributions and time profiles between the γ-ray and proton induced shower particles are studied using Monte Carlo simulation data. The multifractal analysis is performed with the G-moment method for the distribution fluctuation of secondary particles near the core of showers induced by γ-rays and protons. From the spectrum functions of γ and proton events, it is seen that this method can be adopted as a basis for the γ/proton separation. It is shown that the separation of γ and proton can be achieved with a good efficiency in the energy region of 1—10TeV.     

Etude du noyau 63Cu par la reaction 60Ni(α, pγ)63Cu

The level structure and the decay properties of low-lying levels in ⁶³Cu have been investigated via the ⁶⁰Ni(α, pγ)⁶³Cu reaction at E_α = 11.7MeV. Using a Ge(Li) detector, the correlations of twenty-five primary γ-rays in coincidence with protons, stopped in an annular detector at approximatively 180° with respect to the beam direction, were measured. From these measurements, branching ratios, γ-ray mixing ratios and spin assignments have been obtained for most of the levels up to 2.4 MeV excitation.     

A study of low-lying states of 72As using the 72Ge(p,nγ)72As reaction

Several low-lying states of ⁷²As have been studied via the γ-rays following the bombardment of ⁷²Ge by protons in the energy range 5.1–6.2 MeV. Gamma-ray spectra were obtained using a Ge(Li) detector, and gamma-gamma coincidences between this detector and a NaI crystal were also investigated. Besides the single previously known excited state at 46 keV, 12 additional excited states were determined in ⁷²As at energies of 213, 242, 308, 317, 333, 343, 413, 438, 454, 512, 523 and (561) keV. The angular distributions of the γ-rays from the 213 and 242 keV levels have also been measured, and the results have been analyzed using the compound nucleus statistical model. The excited states at 213 and 242 keV were found to have spins of (2) and 3 respectively.     

Observation of heliospheric disturbances in the muon component of cosmic rays

The possibilities of using ground-based muon hodoscopes to study heliospheric disturbances are discussed. Mapping of the matrices of muon flux angular distributions recorded at the ground level in geocentric solar ecliptic coordinates with allowance for the asymptotic directions of primary protons of galactic cosmic rays makes it possible to observe the dynamics of heliospheric disturbances in the near-Earth space. Variations in some other characteristics of muon flux angular distributions are also analyzed.     

Superluminal cascade spectra of TeV γ-ray sources

Astrophysical radiation sources are scrutinized in search of superluminal γ-rays. The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. The superluminal spectral maps of the unidentified TeV γ-ray sources HESS J1303−631, TeV J2032+4130 and HESS J1825−137 are inferred from EGRET, HEGRA and HESS data. Tachyonic cascade spectra are quite capable of generating the spectral curvature seen in double-logarithmic plots, as well as the extended spectral plateaus defined by EGRET flux points in the GeV band. The curvature of the TeV spectra is intrinsic, caused by the Boltzmann factor in the source densities. The spectral averaging with thermal and exponentially cut power-law electron densities can be done in closed form, and systematic high- and low-temperature expansions of the superluminal spectral densities are derived. Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits, such as power-law indices, temperature and source counts. The cutoff temperatures of the source densities suggest ultra-high-energy protons in MSH 15-52, HESS J1825−137 and TeV J2032+4130.     

Cosmogenic neutrinos and gamma rays

We describe the photoproduction interactions of ultrahigh energy protons on the universal photon backgrounds and the production of very high-energy neutrinos and γ-rays in such interactions. We compare the production in propagation in the microwave background to that in the extragalactic background light. The propagation of heavy nuclei is discussed only briefly. We show the extreme models for cosmogenic neutrino production and the limits set on them by different experiments.     

The beta decay of 48Mn: Gamow-Teller quenching in fp-shell nuclei

A new nuclide, ⁴⁸Mn, has been identified and its decay has been studied, using on-line mass separation of ¹²C(⁴⁰Ca, p3n) reaction products. The half-life of this nuclide was determined to be 150 (10) ms, and spectra of β-delayed protons and γ-rays have been obtained. A branching ratio of 2.7 (12) × 10⁻³ was deduced for the emission of β-delayed protons, while an upper limit of 6 × 10⁻⁶ was determined for β-delayed α particle emission. A partial level scheme is proposed for ⁴⁸Cr on the basis of γ-singles and γγ-coincidence data. The deduced Gamow-Teller strength function is compared with predictions from shell model calculations suggesting a quenching factor of 0.53 (17) for the lowest lying states. This result is discussed in comparison with other quenching factors from β-decay studies, in particular those obtained for mirror β-decays in the fp-shell.     

Angular distribution of 4.43-MeV γ-rays produced in inelastic scattering of 14.1-MeV neutrons by <Superscript>12</Superscript>C nuclei

The work is devoted to measuring the angular distribution of 4.43-MeV γ-rays produced in inelastic scattering of 14.1-MeV neutrons by ¹²C nuclei. A portable ING-27 neutron generator (designed and fabricated at VNIIA, Moscow) with a built-in 64-pixel silicon α-detector was used as a source of tagged neutrons. The γ-rays of characteristic nuclear radiation from ¹²C were detected with a spectrometric system that consisted of 22 γ-detectors based on NaI(Tl) crystals arranged around the carbon target. The measured angular distribution of 4.43-MeV γ-rays is analyzed and compared with the results of other published experimental works.     

中子在大气中产生氮俘获γ的蒙特卡罗模拟研究

为了精确计算早期核辐射,建立了中子及次级γ在大气中输运的蒙特卡罗计算模型,并利用几何分裂算法与时间分裂算法等减方差技巧提高计算效率,计算得到了距源点不同距离球面上中子与中子次级γ的信息,给出了不同位置不同时间的氮俘获γ能量释放率。开展了氮俘获γ能量释放率的规律性研究,并分析了中子能量对氮俘获γ的影响。结果表明,氮俘获γ能量释放率先随源点的距离增加而增大,在距源点约500 m达到峰值,而后随距离增加指数衰减。氮俘获γ能量释放率在时间上服从指数衰减规律,衰减时间在0.1 s左右。引入表征氮俘获γ辐射强度参数a和特征衰减时间参数τ,拟合得到了不同距离不同时间氮俘获γ能量释放率的快速计算公式。研究表明,氮俘获γ辐射强度、衰减时间及其空间分布均与中子能量密切相关。     

LET spectra measurements on LDEF: variations with shielding and location

LET spectra measurements made with passive plastic nuclear track detectors (PNTDs) were found to depend on detector orientation, shielding and experiment location. LET spectra were measured at several locations on LDEF as part of the P0006 LETSME experiment (Benton and Parnell, 1984), the P0004 Seeds in Space experiment (Parks and Alston, 1984), the A0015 Free Flyer Biostacks and the M0004 Fiber Optics Data Link experiment (Taylor, 1984). Locations included the east, west and Earth sides of the LDEF satellite. The LET spectra measured with PNTDs deviated significantly from calculations, especially for high LET particles (LET_∞·H₂O ≥ 100 keV/μm). At high LETs, short-range inelastic secondary particles produced by trapped proton interactions with the nuclei of the detector were found to be the principal contributor to LET spectra. At lower LETs, the spectra appeared to be due to short-range, inelastic and stopping primary protons, with primary GCR particles making a smaller contribution.

The dependence of LET spectra on detector orientation and shielding was studied using the four orthogonal stacks in the P0006 experiment. Both measurements of total track density and LET spectra showed a greater number of particles arriving from the direction of space than from Earth. Measurements of LET spectra in CR-39 PNTD on the east (leading) and west (trailing) sides of LDEF showed a higher rate of production at the west side. This was caused by a larger flux of trapped protons on the west side as predicted by the east/west trapped proton anisotropy in the South Atlantic Anomaly (SAA).

Track density measured in CR-39 PNTDs increased as a function of shielding depth in the detector stack. A similar measurement made in a thick stack of CR-39 interspersed with layers of Al and exposed to 154 MeV protons at a ground-based accelerator showed a similar result, indicating that a significant fraction of the particle events counted were from secondaries and that the total cross-section for production of proton-induced secondaries increased as the energy of primary protons attenuated. Little change was seen in either total differential or integral LET spectra as a function of shielding depth, indicating that the increase in cross section with decreasing proton energy affected mostly the shorter range secondary components. Similarity in the slopes of LET spectra from ground-based proton exposures and the A0015 LET spectra showed that modeling of a monoenergetic proton beam transported through a 1-D geometry was a useful first step in modeling the production of secondary particles by trapped protons in the SAA.