Cosmic rays and other nonsense in astronomical CCD imagers

Cosmic-ray muons make recognizable straight tracks in the new-generation CCD's with thick sensitive regions. Wandering tracks (‘worms’), which we identify with multiply-scattered low-energy electrons, are readily recognized as different from the muon tracks. These appear to be mostly recoils from Compton-scattered gamma rays, although worms are also produced directly by beta emitters in dewar windows and field lenses. The gamma rays are mostly byproducts of ⁴⁰K decay and the U and Th decay chains. Trace amounts of these elements are nearly always present in concrete and other materials. The direct betas can be eliminated and the Compton recoils can be reduced significantly by the judicious choice of materials and shielding. The cosmic-ray muon rate is irreducible. Our conclusions are supported by tests at the Lawrence Berkeley National Laboratory low-level counting facilities in Berkeley and 180 m underground at Oroville, California. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmic ray and hydrogen distributions and cosmic gamma — rays

We calculate the spectrum of the diffuse cosmic gamma ray in the single and double leaky box models for several galactic distribution laws of cosmic rays and hdydrogen. The results show that LI Ti-pei's distribution law for the cosmic rays is the best and that the number of interstellar hydrogen molecules should be less than Gordon's value divided by 1.7. The observed spectrum of gamma rays can be reproduced by a suitable choice of the galactic distributions within certain ranges.     

Changes of the cosmic-ray mass composition in the 10–10 eV energy range

Data taken with ten Cosmic Ray Tracking (CRT) detectors and the HEGRA air-shower array on La Palma, Canary Islands, have been analysed to investigate changes of the cosmic ay mass composition at the ‘knee’ of the cosmic-ray flux spectrum near 10¹⁵ eV energy. The analysis is based on the angular distributions of particles in air showers. HEGRA data provided the shower size, direction, and core position and CRT data the particle track information. It is shown that the angular distribution of muons in air showers is sensitive to the composition over a wide range of shower sizes and, thus, primary cosmic-ray energies with little systematic uncertainties. Results can be easily expressed in terms of ln A of primary cosmic rays. In the lower part of the energy range covered, we have considerable overlap with direct composition measurements by the JACEE collaboration and find compatible results in the observed rise of ln A. Above about 10¹⁵ eV energy we find no or at most a slow further rise of ln A. Simple cosmic-ray composition models are presented which are fully consistent with our results as well as the JACEE flux and composition measurements and the flux measurements of the Tibet ASγ collaboration. Minimal three-parameter composition models defined by the same power-law slope of all elements below the knee and a common change in slope at a fixed rigidity are inconsistent with these data.     

A three-dimensional code for muon propagation through the rock: MUSIC

We present a new three-dimensional Monte-Carlo code MUSIC (MUon SImulation Code) for muon propagation through the rock. All processes of muon interaction with matter with high energy loss (including the knock-on electron production) are treated as stochastic processes. The angular deviation and lateral displacement of muons due to multiple scattering, as well as bremsstrahlung, pair production and inelastic scattering are taken into account. The code has been applied to obtain the energy distribution and angular and lateral deviations of single muons at different depths underground. The muon multiplicity distributions obtained with MUSIC and CORSIKA (Extensive Air Shower simulation code) are also presented. We discuss the systematic uncertainties of the results due to different muon bremsstrahlung cross-sections.     

Cosmic rays and terrestrial life: A brief review

“The investigation into the possible effects of cosmic rays on living organisms will also offer great interest.” – Victor F. Hess, Nobel Lecture, December 12, 1936High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing it, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ∼3 billion years in presence of this background radiation, which itself has varied considerably during the period [1], [2], [3]. As demonstrated by the Miller–Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.     

双漏模式中的弥散宇宙γ射线

弥散宇宙γ射线产生于初级宇宙线的传播过程,本文利用宇宙线传播的“双漏模式”得出与实验观测谱接近的银河系弥散宇宙γ射线谱。     

Comparison of measured and simulated lateral distributions for electrons and muons with KASCADE

Lateral distributions for electrons and muons in extensive air showers measured with the array of the KASCADE experiment are compared to results of simulations based on the high-energy hadronic interaction models QGSJet and SIBYLL. It is shown, that the muon distributions are well described by both models. Deviations are found for the electromagnetic component, where both models predict a steeper lateral shape than observed in the data. For both models the observed lateral shapes of the electron component indicate a transition from a light to a more heavy composition of the cosmic ray spectrum above the knee.     

Propagation of galactic cosmic rays in the outer heliosphere

The propagation of galactic cosmic rays in heliospheric magnetic fields is studied. An approximate solution to the cosmic ray transport equation has been derived on the basis of a method that takes into account the small value of anisotropy of particle angular distribution. The spatial and energy distributions of the cosmic ray intensity and anisotropy have been investigated, and estimates of cosmic ray energy flux have been carried out.     

History of gamma-ray telescopes and astronomy

Gamma-ray astronomy is devoted to study nuclear and elementary particle astrophysics and astronomical objects under extreme conditions of gravitational and electromagnetic forces, and temperature. Because signals from gamma rays below 1 TeV cannot be recorded on ground, observations from space are required. The photoelectric effect is dominant <100 keV, Compton scattering between 100 keV and 10 MeV, and electron–positron pair production at energies above 10 MeV. The sun and some gamma ray burst sources are the strongest gamma ray sources in the sky. For other sources, directionality is obtained by shielding / masks at low energies, by using the directional properties of the Compton effect, or of pair production at high energies. The power of angular resolution is low (fractions of a degree, depending on energy), but the gamma sky is not crowded and sometimes identification of sources is possible by time variation. The gamma ray astronomy time line lists Explorer XI in 1961, and the first discovery of gamma rays from the galactic plane with its successor OSO-3 in 1968. The first solar flare gamma ray lines were seen with OSO-7 in 1972. In the 1980’s, the Solar Maximum Mission observed a multitude of solar gamma ray phenomena for 9 years. Quite unexpectedly, gamma ray bursts were detected by the Vela-satellites in 1967. It was 30 years later, that the extragalactic nature of the gamma ray burst phenomenon was finally established by the Beppo–Sax satellite. Better telescopes were becoming available, by using spark chambers to record pair production at photon energies >30 MeV, and later by Compton telescopes for the 1–10 MeV range. In 1972, SAS-2 began to observe the Milky Way in high energy gamma rays, but, unfortunately, for a very brief observation time only due to a failure of tape recorders. COS-B from 1975 until 1982 with its wire spark chamber, and energy measurement by a total absorption counter, produced the first sky map, recording galactic continuum emission, mainly from interactions of cosmic rays with interstellar matter, and point sources (pulsars and unidentified objects). An integrated attempt at observing the gamma ray sky was launched with the Compton Observatory in 1991 which stayed in orbit for 9 years. This large shuttle-launched satellite carried a wire spark chamber “Energetic Gamma Ray Experiment Telescope” EGRET for energies >30 MeV which included a large Cesium Iodide crystal spectrometer, a “Compton Telescope” COMPTEL for the energy range 1–30 MeV, the gamma ray “Burst and Transient Source Experiment” BATSE, and the “Oriented Scintillation-Spectrometer Experiment” OSSE. The results from the “Compton Observatory” were further enlarged by the SIGMA mission, launched in 1989 with the aim to closely observe the galactic center in gamma rays, and INTEGRAL, launched in 2002. From these missions and their results, the major features of gamma ray astronomy are:

Diffuse emission, i.e. interactions of cosmic rays with matter, and matter–antimatter annihilation; it is found, “...that a matter–antimatter symmetric universe is empirically excluded....”

Nuclear lines, i.e. solar gamma rays, or lines from radioactive decay (nucleosynthesis), like the 1.809 MeV line of radioactive ²⁶Al;

Localized sources, i.e. pulsars, active galactic nuclei, gamma ray burst sources (compact relativistic sources), and unidentified sources.

     

Underground water Cherenkov muon detector array with the Tibet air shower array for gamma-ray astronomy in the 100 TeV region

We propose to build a large water-Cherenkov-type muon-detector array (Tibet MD array) around the 37 000 m² Tibet air shower array (Tibet AS array) already constructed at 4300 m above sea level in Tibet, China. Each muon detector is a waterproof concrete pool, 6 m wide × 6 m long × 1.5 m deep in size, equipped with a 20 inch-in-diameter PMT. The Tibet MD array consists of 240 muon detectors set up 2.5 m underground. Its total effective area will be 8640 m² for muon detection. The Tibet MD array will significantly improve gamma-ray sensitivity of the Tibet AS array in the 100 TeV region (10–1000 TeV) by means of gamma/hadron separation based on counting the number of muons accompanying an air shower. The Tibet AS+MD array will have the sensitivity to gamma rays in the 100 TeV region by an order of magnitude better than any other previous existing detectors in the world. The Tibet ASγ Collaboration.     

宇宙线分布、氢分布和宇宙γ射线

本文利用几种典型的银河系宇宙线分布律和星际氢分布律计算单漏模式和双漏模式中的弥散宇宙γ射线谱。结果表明,几种典型的宇宙线分布中,李惕碚的分布律优于其他作者的分布律;星际氢分子数量的取值应当比Gordon值除以1.7更小;只要适当地选择宇宙线分布和氢分布就可得到与观测γ谱相近的理论谱,宇宙线分布和氢分布均可在一定范围里选取。     

Distortions of experimental muon arrival time distributions of extensive air showers by the observation conditions

Event-by-event measured arrival time distributions of extensive air shower (EAS) muons are affected and distorted by various interrelated effects which originate from the time resolution of the timing detectors, from fluctuations of the reference time and the number (multiplicity) of detected muons spanning the arrival time distribution of the individual EAS events. The origin of these effects is discussed, and different correction procedures, which involve detailed simulations, are proposed and illustrated. The discussed distortions are relevant for relatively small observation distances (R_μ<200 m) from the EAS core. Their significance decreases with increasing observation distance and increasing primary energies. Local arrival time distributions which refer to the observed arrival time of the first local muon prove to be less sensitive to the mass of the primary. This feature points to the necessity of arrival time measurements with additional information on the curvature of the EAS disk.     

Astrophysical consequences of neutron-antineutron oscillations

Grand unified theories predict baryon number violating interactions and one of the implications of this is the possible existence of neutron-antineutron oscillations. The neutron-antineutron oscillations have been considered in the neutron rich astrophysical sources such as solar flares, supernovae explosions, neutron stars and the nucleosynthetic phase of the early universe in order to partly account for the antiproton flux of the cosmic rays at low energies and the -ray emission, at GeV energies. Low magnetic fields and high neutron concentrations provide the right environment for the production of antineutrons and hence antiprotons and GeV rays.     

PeV gamma rays from interactions of ultra high energy cosmic rays in the Milky Way

The PeV gamma ray background produced in the interactions of ultra high energy cosmic rays with the ambient matter and radiations during their propagation in the Milky Way has been calculated in this paper. If the primary ultra high energy cosmic rays are produced from Galactic point sources then those point sources are also emitting PeV gamma rays. We discuss that the detection of galactocentric PeV gamma rays in the future would be a signature of the presence of EeV cosmic accelerators in the Milky Way.     

Relationship between high-energy physical phenomena on the sun and in astrophysics

High energy phenomena on the surface of the Sun are manifestations of part of the solar dynamo cycle. Convection and magnetic field give rise to unstable, twisted flux loops that become solar flares when the resistive tearing mode proceeds to the nonlinear limit. If such twisted flux loops did not dissipate rapidly due to an enhanced resistivity, then the dynamo would not work. The act of dissipation leads to intense heating and acceleration leading to X-rays and accelerated particles. The particles in turn give rise to hard X-rays, gamma rays, neutrons, and solar cosmic rays. In high-energy astrophysics such phenomena occur in accretion disks around compact objects like black holes in quasars and SS433. The resulting acceleration may explain the observed extremely high-energy cosmic rays of up to 10²⁰ eV and the high-energy gamma rays of 10¹² to 10¹⁵ eV. These high energies are more readily explained by acceleration E parallel to B as opposed to stochastic shock acceleration. The anisotropy and localization of gamma rays from solar flares potentially may indicate which mechanism is prevalent.     

Prompt muon production in cosmic rays

Results of calculations of fluxes of prompt muons reaching the sea level are given for muon energies up to 10⁷ GeV. The calculations are made in the frame of an empirical model and are based on the up-to-date data from experiments in cosmic rays, at accelerators, and on the most recent theoretical achievements on charm production in nucleon–air nucleus interactions.     

Introducing the CTA concept

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.     

Development of a new photon diffraction imaging system for diagnostic nuclear medicine

The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that uses photon diffraction and is capable of generating 1–2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100–200 keV gamma rays which are typically used in diagnostic nuclear medicine and in molecular imaging. The system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source, which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector's sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100–200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to the detection of small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system's sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment and wider treatment options, which can potentially improve the chances for cure.     

Astrophysical interpretation of small-scale neutrino angular correlation searches with IceCube

The IceCube Neutrino Observatory has discovered a diffuse all-flavor flux of high-energy astrophysical neutrinos. However, the corresponding astrophysical sources have not yet been identified. Neither significant point sources nor significant angular correlations of event directions have been observed by IceCube or other instruments to date. We present a new method to interpret the non-observation of angular correlations in terms of exclusions on the strength and number of point-like neutrino sources in generic astrophysical scenarios. Additionally, we constrain the presence of these sources taking into account the measurement of the diffuse high-energy neutrino flux by IceCube. We apply the method to two types of astrophysically motivated source count distributions: The first type is obtained by considering the cosmological evolution of the co-moving density of active galaxies, while the second type is directly derived from the gamma ray source count distribution observed by Fermi-LAT. As a result, we constrain the possible parameter space for both types of source count distributions.