用于宇宙射线μ子成像的MLS-EM重建算法加速研究

宇宙射线μ子检测技术具有穿透力强、对高Z材料敏感等特点,特别适合检测特殊核材料,是监控核材料走私的有效方式.图像重建问题是实现该技术的一个关键难点,MLS-EM算法是目前成像质量较好的算法,但其过长的运算时间制约了该算法在实际μ子检测系统中的应用.根据μ子检测系统的特点,本文提出了一种加速方法,在使用POCA重建图像作为迭代初值基础上进一步采用OS方法进行EM加速.模拟实验结果表明该方法能够有效地对MLS-EM重建算法进行加速,这对于宇宙射线μ子成像技术早日投入实际应用具有积极的意义.     

Calculation of the solar activity effect on the production rate of cosmogenic radiocarbon in polar ice

The propagation of cosmic rays in the Earth??s atmosphere is simulated. Calculations of the omnidirectional differential flux of neutrons for different solar activity levels are illustrated. The solar activity effect on the production rate of cosmogenic radiocarbon by the nuclear-interacting and muon components of secondary cosmic radiation in polar ice is studied. It has been obtained that the ¹⁴C production rates in ice by the cosmic ray nuclear-interacting component are lower or higher than the average value by 30% during periods of solar activity maxima or minima, respectively. Calculations of the altitudinal dependence of the radiocarbon production rate in ice by the cosmic radiation components are illustrated.     

1997年1月7日至11日广州站宇宙线强度变化特征的小波分析

1997年1月6日爆发的日冕物质抛射（CME）到达地球时引起了强烈的地球物理效应,CME在行 星际空间传播时,广州的多方向μ介子望远镜观测到银河宇宙线强度的变化. 本文采用 小波分析方法分析了磁暴前后广州台宇宙线强度的频谱变化特征,结果表明,在磁暴前 宇宙线周期为16～32h的信号发生了较明显的变化,其中周期为24～32h的周期特征过去没有 被报道过. 广州台垂直方向宇宙线强度的谱在磁暴发生前48h就出现明显的变化,比各向异 性分析方法得到的时间提前量更大. 同时还分析了几个方向宇宙线强度的最强信号以及达到 最大值的时间,并进行了简要的分析与讨论.     

Calculation of shielding factors for production of cosmogenic nuclides in fault scarps

The distribution of concentration of cosmogenic nuclides in fault scarps is used to determine slip histories. The complicated part is the calculation of cosmic radiation shielding by the escarpment body and the overlying wedge of the colluvial sediment. To improve reconstruction of earthquake ages and slip histories, we developed a mathematical model and corresponding MATLAB^® code for computation of shielding factor profiles in fault scarp geometry. In the model, cosmic radiation received by a point of footwall is represented as unit rays attenuated exponentially in scarp geometry. This approach allows producing very precise results both for the fault scarp and the sloped surface. The code is presented as a m-function and as a stand-alone program with a user-friendly interface. Shielding factors are calculated by the code for fast neutrons or for muons and include all general shieldings: topographical, sloped surface, fault scarp surface, colluvium cover, snow cover and self-shielding. A variety of input parameters enables one to adjust the model and the code to almost all possible shielding cases. The code and stand-alone version are provided as supplementary materials and equipped with help and explanatory notes.     

Zenith angular distributions of atmospheric high-energy neutrinos

In this paper, we present a new calculation of the atmospheric neutrino flux in the energy range 10–10⁷ GeV, which reveals sizable differences in muon neutrino flux predictions obtained with known hadronic models. The calculation is based on the method of solving nuclear cascade equations in the atmosphere, which takes into account the nonscaling behavior of inclusive cross sections for particle production, the increase in the total inelastic hadron-nucleus cross sections, and the non-power-law character of the primary cosmic ray spectrum. The efficiency of the method was recently tested in atmospheric muon flux calculations. The results of neutrino spectrum calculations have been compared with Frejus, AMANDA-II, and IceCube measurement data.     

The energy spectrum of Forbush decreases during the growth phase of solar cycle 24

The Forbush decrease energy spectrum, observed during the growth phase of cycle 24 in 2010–2012, was studied based on the measurements performed with the Kuzmin cosmic ray spectrograph. The data of the 24-NM-64 neutron monitor and muon telescopes, installed at water equivalent levels of 0, 7, 20, and 40 m, was used. The performed analysis indicated that a softer energy spectrum was observed during the growth phase of cycle 24 than during the previous cycle (cycle 23). The conclusion was been drawn that a more turbulent magnetic field with the predominant diffusion mechanism in the formation of the Forbush decreases in the cosmic ray intensity exists in the current cycle (cycle 24).     

Production of selected cosmogenic radionuclides by muons 1. Fast muons

To investigate muon-induced nuclear reactions leading to the production of radionuclides, targets made of C₉H₁₂, SiO₂, Al₂O₃, Al, S, CaCO₃, Fe, Ni, Cu, Gd, Yb and Tl were irradiated with 100 and 190 GeV muons in the NA54 experimental setup at CERN. The radionuclide concentrations were measured with accelerator mass spectrometry and γ-spectroscopy. Results are presented for the corresponding partial formation cross-sections. Several of the long-lived and short-lived radionuclides studied are also produced by fast cosmic ray muons in the atmosphere and at depths underground. Because of their importance to earth sciences investigations, calculations of the depth dependence of production rates by fast cosmic ray muons have been made.     

宇宙线μ子能谱及其应用

完成由两块大面积塑料闪烁体组成的粒子望远镜的研制,并测得合肥地区地面宇宙线μ子能谱.简要报道这台粒子望远镜的实际应用.     

Production rate calculations for cosmic-ray-muon-produced 10Be and 26Al benchmarked against geological calibration data

First, I benchmark existing methods of calculating subsurface ²⁶Al, ¹⁰Be, and ¹⁴C production rates due to cosmic-ray muons against published calibration data from bedrock cores and mine excavations. This shows that methods based on downward propagation of the surface muon energy spectrum fit calibration data adequately. Of these methods, one that uses a simpler geographic scaling method based on energy-dependent attenuation of muons in the atmosphere appears to fit calibration data better than a more complicated one that uses the results of a global particle transport model to estimate geographic variation in the surface muon energy spectrum. Second, I show that although highly simplified and computationally much cheaper exponential function approximations for subsurface production rates are not globally adequate for accurate production rate estimates at arbitrary location and depth, they can be used with acceptable accuracy for many exposure-dating and erosion-rate-estimation applications.     

Radiocarbon in the Antarctic ice: The formation of the cosmic ray muon component at large depths

This study is devoted to the production of ¹⁴C by the secondary cosmic radiation in polar ice. The radiocarbon production in the reactions caused by the nuclear-active and muon components is considered. The data on ¹⁴C from the Vostok and Taylor Dome Antarctic boreholes are analyzed. The ¹⁴C concentration values at depths larger than the firn—ice boundary by a factor of 2—3 can be explained by a deep production of radiocarbon in the reactions caused by the cosmic radiation muon component.     

Cosmic ray flux variations, modulated by the solar and earth’s magnetic fields, and climate changes. 1. Time interval from the present to 10–12 ka ago (the Holocene Epoch)

Direct and indirect data on variations in cosmic rays, solar activity, geomagnetic dipole moment, and climate from the present to 10–12ka ago (the Holocene Epoch), registered in different natural archives (tree rings, ice layers, etc.), have been analyzed. The concentration of cosmogenic isotopes, generated in the Earth’s atmosphere under the action of cosmic ray fluxes and coming into the Earth archives, makes it possible to obtain valuable information about variations in a number of natural processes. The cosmogenic isotopes ¹⁴C in tree rings and ¹⁰Be in ice layers, as well as cosmic rays, are modulated by solar activity and geomagnetic field variations, and time variations in these concentrations gives information about past solar and geomagnetic activities. Since the characteristics of natural reservoirs with cosmogenic ¹⁴C and ¹⁰Be vary with climate changes, the concentrations of these isotopes also inform about climate changes in the past. A performed analysis indicates that cosmic ray flux variations are apparently the most effective natural factor of climate changes on a large time scale.     

Long-term variations in the muon flux angular distribution

The intensity of the atmospheric muon flux depends on many factors: the energy spectrum of primary cosmic rays and the state of the Earth’s heliosphere, magnetosphere, and atmosphere. The wide-aperture URAGAN muon hodoscope (Moscow, Russia, 55.7° N, 37.7° E, 173 m a.s.l.) makes it possible to investigate not only variations in the muon flux intensity but also temporal changes in the parameters of its angular distribution. These changes are analyzed using the vector of local anisotropy and its projections, which have different sensitivities to the parameters of modulation of both primary cosmic rays in the heliosphere and the Earth’s magnetosphere and secondary cosmic rays as they pass through the Earth’s atmosphere. The vector of local anisotropy is the sum of unit vectors (directions of the reconstructed muon tracks) normalized to the number of tracks. The results of an analysis of long-term variations in mean hourly projections of the vector of local anisotropy obtained from the 2007–2011 URAGAN hodoscope data are presented.     

Behavior of the cosmic ray density during the initial phase of the Forbush effect

Variations in the cosmic ray density during the initial phase of the Forbush effect during the first hours after the arrival of the interplanetary shock wave have been studied with the use of data on variations in the cosmic ray density with a rigidity of 10 GV obtained by the global survey method by the world network of neutron monitors in 1957?2012. It is found that behavior of this parameter after the arrival of the shock wave demonstrates high variability. A small (~1/5 of total number), though distinct, group of Forbush effects, in which the density of the cosmic ray increases (not decreases) after the arrival of the shock wave, is defined. As a whole, the initial variation in cosmic ray density is correlated with the Forbush effect magnitude and the strength of the associated geomagnetic disturbance.     

SUBSURFACE GRAVITY MEASUREMENTS AND DENSITY MAPPING IN THE MAILARAM COPPER MINES,ANDHRA PRADESH,INDIA*

Gravity measurements were made in the Mailaram copper mines, Andhra Pradesh. The observations were distributed between the two shafts situated about 220 m apart and in the three levels up to a maximum depth of 100 m. Assuming a normal free-air gradient, average densities for the three layers were determined as 2.631, 2.604, and 2.823 g cm^-3, respectively. Upon incorporating the weighted mean density values from measurements on samples, the free-air gradients were found to be 0.315 mGal m^-1 for the second layer (i.e. between the first and second levels) and 0.2978 mGal m^-1 for the third layer (i.e. between the second and third levels). The density variation map obtained from the gravity data, the deduced anomalies, the weighted mean density values from measurements on rock samples, and the varying free-air coefficients all suggest correspondence with the concentration of ore lodes.     

Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons

We have determined the production yields for radionuclides in Al₂O₃, SiO₂, S, Ar, K₂SO₄, CaCO₃, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides ¹⁰Be, ¹⁴C and ²⁶Al produced in quartz targets, ²⁶Al in Al₂O₃ and S targets, ³⁶Cl in K₂SO₄ and CaCO₃ targets, and ⁵³Mn in Fe₂O₃ targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ⁻ capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ⁻ capture, by fast muons and by neutron capture.     

Solar modulation in surface atmospheric electricity

The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of air's electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes, varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential gradient measurements made independently at Lerwick Observatory, Shetland, from 1978 to 1985 are compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum (solar minimum), with a proportional change greater than that of the cosmic ray change.     

A study of atmospheric processes based on neutron monitor data and Cherenkov counter measurements at high mountain altitude

The cause of the correlation between cloud cover and cosmic ray intensity is still a subject of discussion. The atmospheric transparency is the primary signature of the atmospheric state. The ability to use neutron monitor and Cherenkov telescope data in order to study atmospheric processes is demonstrated. The recently designed lead free neutron monitor at the Basic Environmental Observatory Moussala (42.11N, 23.35E, 2925 m a.s.l.) is described. The possibility to use Cherenkov telescope measurements for estimation of atmospheric transparency is demonstrated on the basis of Monte Carlo simulations and experimental data. The Monte Carlo simulations are carried out with CORSIKA code assuming FLUKA and QGSJET II hadron interaction models. Experimental data from Cherenkov telescope are presented. Several physical mechanisms related to the influence of cosmic rays on the cloud cover, respectively, the atmospheric transparency are widely discussed.     

根据VLF的相位变化确定D层宇宙线强度变化的可能性

银河宇宙线是电离层D层的重要电离源之一,它的急剧变化会使D层电子密度发生改变,从而影响VLF波的夜间传播。本文根据在西安接收英国GBR台的VLF波（16kc/s）的相位变化,讨论了在有宇宙线暴（Forbush下降）和强磁暴时,中纬D层电子浓度的变化和相应的VLF波的相位漂移;并根据VLF的相位变化,估计了相应的宇宙线强度变化。由于D层中的宇宙线强度变化通常难于观测,通过VLF波的相位漂移来估计它,这是很有意义的。所以,VLF波的传播效应可能成为间接探测宇宙线强度变化的有用工具。     

Depth-dependence of the production rate of in situ 14C in quartz from the Leymon High core,Spain

To constrain the depth-dependence of in situ ¹⁴C production we measured the cosmogenic ¹⁴C concentration of quartz separates along a quartzite core from the Leymon High site in northwest Spain. A total of 16 quartz samples were measured over a depth range of 1–1545 cm (3–4017 g cm⁻²). The obtained ¹⁴C profile was modeled using a neutron production rate, exponentially decreasing with depth, and a fast and negative muon production parameterized as a function of the local muon flux as derived by (Heisinger et al., 2002a, 2002b). This model yields a total negative muon capture probability of 1.72 (+0.22/−0.56) × 10⁻² and a fast muon reaction cross section of 0 (+11.8/−0.00) μb. Rescaled to sea level high latitude using a Lal/Stone scaling scheme, these estimates yield a surface muon production rate of 3.31 (+0.43/−1.07) and 0 (+0.42/−0.00) at·g⁻¹ yr⁻¹ for negative muon capture and fast muons, respectively. This is the first muon production estimate for in situ ¹⁴C from a natural setting and is within uncertainty of the previous experimental estimates. The present contribution also provides new long-term blank and standard (PP-4, CRONUS-A & CRONUS-N) in situ ¹⁴C data from the ETH Zürich ¹⁴C extraction line.     

Calculation of Electromagnetic Radiation Criterion for Rockburst Hazard Forecast in Coal Mines

— Intensive micro-fracturing of rock close to mining operations accompanies an increase in the likelihood of rockbursting. This fracturing causes an increase of the electromagnetic radiation (EMR) level by up two orders of magnitude, depending on the mining environment. Several examples of this enhanced EMR are presented in this paper. We first treat the EMR theoretical criterion of rockburst hazard in coal mines and compare it with the empirical criterion of EMR activity that was revealed on the basis of more than 400 different hazardous and non-hazardous situations in underground coal mines. Only the following parameters are needed to estimate the EMR criterion of rockburst hazard: limiting value of gum volume, mine working width, coal seam thickness, and coal elastic properties.