On the acceleration of ultra-high-energy cosmic rays

Ultra-high-energy cosmic rays (UHECRs) hit the Earth's atmosphere with energies exceeding 10(18)eV. This is the same energy as carried by a tennis ball moving at 100 km h-1, but concentrated on a subatomic particle. UHECRs are so rare (the flux of particles with E>10(20)eV is 0.5 km -2 per century) that only a few such particles have been detected over the past 50 years. Recently, the HiRes and Auger experiments have reported the discovery of a high-energy cut-off in the UHECR spectrum, and Auger has found an apparent clustering of the highest energy events towards nearby active galactic nuclei. Consensus is building that the highest energy particles are accelerated within the radio-bright lobes of these objects, but it remains unclear how this actually happens, and whether the cut-off is due to propagation effects or reflects an intrinsically physical limitation of the acceleration process. The low event statistics presently allows for many different plausible models; nevertheless observations are beginning to impose strong constraints on them. These observations have also motivated suggestions that new physics may be implicated. We present a review of the key theoretical and observational issues related to the processes of propagation and acceleration of UHECRs and proposed solutions.     

Modelling of aircrew radiation exposure from galactic cosmic rays and solar particle events

Correlations have been developed for implementation into the semi-empirical Predictive Code for Aircrew Radiation Exposure (PCAIRE) to account for effects of extremum conditions of solar modulation and low altitude based on transport code calculations. An improved solar modulation model, as proposed by NASA, has been further adopted to interpolate between the bounding correlations for solar modulation. The conversion ratio of effective dose to ambient dose equivalent, as applied to the PCAIRE calculation (based on measurements) for the legal regulation of aircrew exposure, was re-evaluated in this work to take into consideration new ICRP-92 radiation-weighting factors and different possible irradiation geometries of the source cosmic-radiation field. A computational analysis with Monte Carlo N-Particle eXtended Code was further used to estimate additional aircrew exposure that may result from sporadic solar energetic particle events considering real-time monitoring by the Geosynchronous Operational Environmental Satellite. These predictions were compared with the ambient dose equivalent rates measured on-board an aircraft and to count rate data observed at various ground-level neutron monitors.     

Detectors/Dosemeters of galactic and solar cosmic rays

Different passive multidetector stacks have been developed at the Italian National Agency for Environmental Protection (ANPA-stack), which makes it possible to measure directly ionising radiations, low-energy and high-energy neutrons, and high-energy charged (HZE) particles. The stack consists of several types of passive devices, namely recoil-track and fission-track detectors, bubble detectors, thermoluminescence dosemeters and an electronic personal dosemeter. Most of these detectors have been used on earth for the assessment of the occupational exposure, or in outer space for cosmic ray physics and/or for the assessment of the dose received by astronauts. A great deal of efforts and new developments have been required to make these detectors useful for in-flight measurements. As outcome of these extensive efforts, different new detectors have been developed, which exploit some of the most successful principles of radiation detection, such as the use of avalanche processes to facilitate the registration of nuclear tracks and the use of coincidence-counting to increase the signal-to-noise ratio. On the basis of these new detectors, different systems (generally referred to as ANPA-stack) have been obtained, which have been successfully applied for a variety of different measurements of cosmic ray radiation fields and doses.     

Measurements of covariance for cascading gamma rays

An apparatus has been developed to measure covariance and delayed covariance of the counting rates of detectors of the separate members of gamma ray cascades. This method offers advantages over conventional time coincidence measurements, particularly for long lived intermediate nuclear states. The method has been used to measure the half-life of the 304 keV level (16.9±0.6 ms) and anisotropy (0.543±0.002) of the 121–280 keV gamma cascade in ⁷⁵As produced by the radioactive decay of ⁷⁵Se. Other applications are discussed.     

Predicting the response of a submillimeter bolometer to cosmic rays

Bolometers designed to detect submillimeter radiation also respond to cosmic, gamma, and x rays. Because detectors cannot be fully shielded from such energy sources, it is necessary to understand the effect of a photon or cosmic-ray particle being absorbed. The resulting signal (known as a glitch) can then be removed from raw data. We present measurements using an Americium-241 gamma radiation source to irradiate a prototype bolometer for the High Frequency Instrument in the Planck Surveyor satellite. Our measurements showed no variation in response depending on where the radiation was absorbed, demonstrating that the bolometer absorber and thermistor thermalize quickly. The bolometer has previously been fully characterized both electrically and optically. We find that using optically measured time constants underestimates the time taken for the detector to recover from a radiation absorption event. However, a full thermal model for the bolometer, with parameters taken from electrical and optical measurements, provides accurate time constants. Slight deviations from the model were seen at high energies; these can be accounted for by use of an extended model.     

Recording of high-energy cosmic rays by observation of the radio signal reflected from the ionosphere

Feasibility is shown for a method of detecting superhigh-energy (>10²² eV) cosmic rays on the surface of Antarctica with an event rate acceptable for observation purposes. This situation can be attributed to various favorable circumstances such as 1) the large area of the continent (10⁶–10⁷ km²); 2) the location of the vast majority of the ice cap at an altitude of 3–4 km; 3) the low level of atmospheric noise because this area is as far as possible from the equatorial thunderstorm belt; and 4) the effective band of the radio pulse frequency spectrum (0–7 MHz) not exceeding the highest frequencies used. Estimates of the electromagnetic pulse intensity were made using previously published studies. Pis’ma Zh. Tekh. Fiz. 24, 65–68 (December 26, 1998)     

French population exposure to radon, terrestrial gamma and cosmic rays

In France, natural sources account for most of the population exposure to ionising radiation. This exposure varies widely with area. Radon and gamma-ray exposure data come from national measurement campaigns; cosmic doses were calculated from city altitude. These data were corrected for season of measurement, housing characteristics and population density to study their relationship with health indicators. The crude average of indoor radon concentrations was 89 Bq m(-3), and the average corrected for season and housing characteristics was 83 Bq m(-3) (range over districts: 19-297). Weighting by district population density yielded a national average of 63 Bq m(-3). Gamma-ray dose rates averaged 55 nSv h(-1) (23-96) indoors and 46 nSv h(-1) (25-85) outdoors; corrections did not change the means. Corrected cosmic annual doses averaged 0.28 mSv (0.27-0.38). These corrections estimated the radiation exposure of the French population more accurately and represented its distribution well, thereby allowing its study as a cofactor in ecological studies.     

Contribution of cosmic ray heavy ions to the radiation hazard in manned space flights

Primary cosmic radiation arriving near the Earth may be classified into two general categories: the gamma component and the hadronic component. The hadronic component contains mainly protons, a small amount of alpha particles and a smaller amount of heavier charged nuclei (ions). Although the fluxes of these heavier ions are very small in comparison to those of protons, they are able to originate a huge linear energy transfer (LET). This work studies the contribution of heavy ions from cosmic rays to the radiation hazard to which the crew of a manned long duration space flight might be exposed. The geometry of the energy deposition by a heavy ion is studied, and it is found that energies of the order of up to 10(23) J kg-1 are deposited.     

Investigation of the properties of galactic cosmic rays with the KASCADE-Grande experiment

The properties of galactic cosmic rays are investigated with the KASCADE-Grande experiment in the energy range between 10¹⁴ and 10¹⁸ eV. Recent results are discussed. They concern mainly the all-particle energy spectrum and the elemental composition of cosmic rays.     

The relative transit time of high-rigidity and low-rigidity cosmic rays through the solar system

A study of neutron monitor count rates with vertical cut-off rigidities from 0.6 to 13 GV indicates that high-energy and low-energy galactic cosmic rays arrive at earth orbit with small time differences compared to a month. This is in contradiction to the theory of the deceleration potential which states that cosmic-ray particles with rigidities greater than 36 V arrive at earth orbit about three months before cosmic-ray particles with lesses rigidines.     

Bibliometric analysis of publications in experimental particle physics on cosmic rays and with accelerators

In the first part, the present paper presents a quantitative analysis of physics publications in the domain of experimental particle physics, before the Second World War in the field of cosmic rays physics and for the modern times in the field of accelerator and collision rings experiments. In the second part, a more general study is made on publications in the various fields of physics separating contributions from experiment, theory and techniques. Three aspects of physics are enlightened: physics of exploration, physics of applications, and forefront physics.     

Prospects for detection of ultrahigh-energy cosmic rays on the surface of the moon

A theoretical foundation is laid for the development of a radio detector for cosmic rays with energies E≥10²¹ eV. The detection system envisages a radio detector on the Earth or a system of radio antennas on artificial lunar satellites, which would record the radio emission pulse produced by a shower in the lunar soil. Pis’ma Zh. Tekh. Fiz. 23, 57–62 (May 26, 1997)     

Monte Carlo calculation of the angular distribution of cosmic rays at flight altitudes

The angular distribution of the secondary radiation produced by the galactic component of cosmic rays has been determined by simulating the penetration of the primary spectra in the Earth's atmosphere. The simulations have been carried out with the latest version of the FLUKA code. Particles have been scored at various altitudes according to their angle of incidence for some significant values of vertical cut-off rigidity and solar modulation parameter. The calculated results at typical cruise altitudes for a civil aircraft are presented. The data at 10.7 km have been fitted with simple mathematical equations. It has been demonstrated that the major contribution to the doses at aviation altitudes arises from downward-directed particles. The isotropic irradiation usually assumed for the evaluation of aircrew exposure could be a very poor approximation.     

Identification of the light nuclei component of cosmic rays with the PAMELA experiment

The PAMELA (Payload for Antimatter Matter Exploration and Light nuclei Astrophysics) experiment is a satellite-borne apparatus that will make long duration measurements of the cosmic radiation with a particular focus on antiparticles and light nuclei. The main scientific objective of the PAMELA mission is to investigate the nature of the dark matter that pervades the universe, the apparent absence of cosmological antimatter, the origin and evolution of matter in the Galaxy. Specifically PAMELA will measure the cosmic-ray antiproton and positron spectra over the largest energy range ever achieved and will search for antinuclei with unprecedented sensitivity. Furthermore, it will measure the light nuclear component of cosmic rays from Hydrogen up to Oxygen in the interval 200 MeV/n–150 GeV/n. Accurate measurements of the elemental composition are required in order to understand the origin, propagation and lifetime of the cosmic radiation. The primary cosmic rays (e.g. C, N and O), produced at the sources, propagate through the interstellar medium giving information about the composition at the source. Secondary elements (e.g. Li, Be, and B) are tracers of amount of matter traversed by the cosmic rays. The relative abundances of the constituents of galactic cosmic rays provide information about cosmic-ray transport within the Galaxy. PAMELA consists of a magnetic spectrometer, a Time-of-Flight and trigger system, an electromagnetic calorimeter, an anticoincidence system, a shower tail catcher scintillator and a neutron detector. The combination of these devices allows antiparticles to be reliably identified from a large background of other charged particles. This paper reviews the capability of the PAMELA subdetectors to identify light nuclei. Analysis techniques to discriminate light-charged particles will be presented.     

JACEE emulsion chambers for studying the energy spectra of high energy cosmic ray protons and helium

Emulsion chambers are being used in a series of stratospheric balloon flights to study nuclear interactions, charge composition, and energy spectra of cosmic ray nuclei over the energy range 10¹²–10¹⁵ eV. Charge identification involves grain, gap, and/or delta-ray counting in emulsion plates having different sensitivities on two sides of an acrylic base. Electromagnetic cascade energies are measured with resolutions of about 25% by the three-dimensional track counting method. This report describes the apparatus, the measurement techniques, and the analysis methods used to determine the primary proton and helium spectra.     

Up-and-down journeys: The making of Latin America's uniqueness for the study of cosmic rays

In 1942, American Nobel Prize-winning physicist Arthur Compton pointed out that, “Because in this field of cosmic ray studies certain unique advantages are given by their geographical position, this field of physics has been especially emphasized in South America.” This paper seeks to interrogate the making of Latin America's uniqueness with respect to cosmic-ray research through an analysis that considers Compton's geographical argument, but also goes beyond it, referring to the interactions of nature, knowledge, practices, scientific communities, and diplomacy. To begin with, it highlights the place-based strategies and practices associated with cosmic-ray research. Once research in the field at different altitudes demonstrated that cosmic rays traveled from outer space to the Earth surface, their nature was scrutinized by expeditions that covered broad vertical and horizontal expanses. The study of cosmic rays in Latin America displayed the mobilization of that strategy, which reinforced the reliability of certain sites located at high altitudes and close to the geomagnetic equator in projected investigations. Moreover, such analysis of cosmic rays involved research practices in the field, the emergence of (local, regional, or international) research traditions, and the creation of spaces of knowledge at different scales. By centering on the interaction of knowledge and place, this paper shows that an exploration of the “up-and-down journeys” of cosmic-ray research in Latin America expands our understanding of the geographies and practices of 20th-century physics.     

Calculation of the radiation environment caused by galactic cosmic rays for determining air crew exposure

The spectra of secondary particles resulting from interactions of primary galactic cosmic rays with the nuclei in the atmosphere have been calculated using the Monte Carlo transport code FLUKA. The simulations have been carried out at solar minimum and solar maximum activity, for several values of the vertical geomagnetic cut-off. The effective dose rate and the ambient dose equivalent rate as a function of geomagnetic cut-off and altitude have been obtained using appropriate sets of conversion coefficients. The calculated results are discussed and compared with experimental data and other calculations. A simple method is proposed to calculate the radiation exposure at aircraft altitudes.     

Telomere alterations and genomic instability in long-term cultures of normal human fibroblasts irradiated with X rays and protons

Telomeres are the end of linear chromosomes, responsible for chromosome stability and cell viability. It is well known that radiations are able to induce chromosome instability but it has not yet been investigated whether telomere structure is affected by the radiation exposure and if radiations with different quality act in a different way on telomeres. The effect of radiations with different quality on telomere structure and chromosome instability was analysed in human primary fibroblasts exposed to X rays or low-energy protons (28.5 keV μm(-1)). Telomere length was evaluated at different harvesting times from 24 h up to 360 h (15 days), whereas chromosome instability was evaluated in terms of sister chromatid exchanges (SCEs) (48 h from irradiation) and chromosome painting (360 h from irradiation). Results indicated a delayed telomere lengthening 360 h after X-ray treatment, whereas protons were able to induce such a lengthening shortly from irradiation as well as at longer harvesting times. Data obtained from chromosome instability analysis indicated an increase of SCE frequency only after proton irradiation, but, on the contrary, at the longer harvesting time chromosome painting analysis displayed a higher frequency of aberrations after X-ray treatment, suggesting a role of selective process against highly damaged cells.