GeV Nucleon Research Articles

Measurement of Cosmic‐Ray Hydrogen and Helium and Their Isotopic Composition with the BESS Experiment

The cosmic-ray hydrogen and helium spectra have been measured by the Balloon Borne Experiment with a Superconducting Solenoid Spectrometer (BESS), which has been flown from Lynn Lake, Manitoba, Canada, annually since 1993. The BESS experiment provides excellent rigidity measurement and precise particle identification with a large geometric acceptance. We present here the hydrogen and helium nuclei energy spectra from 0.2 to 10 GeV nucleon-1 and their isotopic composition from 0.2 to about 1 GeV nucleon-1 for the first BESS flight. This provides the first simultaneous measurements of the cosmic-ray secondaries, deuterons, and 3He, with their primaries, protons, and 4He over this energy range in a period of solar minimum. In this paper, we have achieved significant improvements in data analysis in the following aspects. First, the latest available cross-section data and their parameterizations were utilized in the simulation code developed for this study. Second, a complete simulation was performed for both protons and heavy ions: the δ-ray effect was properly simulated and showed a large influence on the measurement of heavy ions at high energies. Third, the secondary particle correction, which dominates the systematic uncertainty at low energies for singly charged particles, protons and deuterons, was calculated iteratively with the simultaneously measured primary cosmic-ray spectra. In general, the results of this experiment are consistent with other recent measurements using balloon-borne or satellite experiments, but with better precision. The measured spectra of protons, deuterons, 3He, and 4He and their corresponding ratios are compared with different interstellar/heliospheric propagation calculations, which were derived to fit observations of heavy nuclei. The overall good agreement indicates that the propagation history for light cosmic-ray elements, protons, deuterons, and helium nuclei is similar to that of the heavy nuclei. The 2H/1H ratio is sensitive to the propagation models, and our results show a tendency of better agreement with the reacceleration model than the standard leaky-box model.

Solar minimum spectra of galactic cosmic rays and their implications for models of the near‐Earth radiation environment

The radiation dose from galactic cosmic rays during a manned mission to Mars is expected to be comparable to the allowable limit for space shuttle astronauts. Most of this dose would be due to galactic cosmic rays with energies < 1 GeV nucleon−1, with important contributions from heavy nuclei in spite of their low abundance relative to H and He. Using instruments on NASA's Advanced Composition Explorer (ACE) spacecraft, we have made the most statistically precise measurements to date of the solar minimum energy spectra of cosmic ray nuclei with charge Z = 4–28 in the energy range ∼ 40–500 MeV nucleon−1. We compare these measurements obtained during the 1997–1998 solar minimum period with measurements from previous solar minima and with models of the near‐Earth radiation environment currently used to perform shielding and dose calculations. We find that the cosmic ray heavy‐element spectra measured by ACE are as much as 20% higher than previously published solar minimum measurements. We also find significant differences between the ACE measurements and the predictions of available models of the near‐Earth radiation environment, suggesting that these models need revision. We describe a cosmic ray interstellar propagation and solar modulation model that provides an improved fit to the ACE measurements compared to radiation environment models currently in use.

The cosmic ray actinide charge spectrum derived from a [formula omitted] array of solid state nuclear track detectors in Earth orbit

The DIAS-ESTEC Ultra Heavy Cosmic Ray Experiment (UHCRE) on the Long Duration Exposure Facility, collected approximately 3000 cosmic ray nuclei with Z>65 in the energy region E>1.5 GeV nucleon −1 during a six year exposure in Earth orbit. The entire accessible collecting area of the solid state nuclear track detector (SSNTD) array has been scanned for actinides, yielding a sample of 30 from an exposure of ≈150 m 2 sr yr . The UHCRE experimental setup is described and the observed charge spectrum presented. The current best value for the cosmic ray actinide relative abundance, ( Z>88)/(74⩽ Z⩽87), is reported.

Precise Measurement of Cosmic‐Ray Proton and Helium Spectra with the BESS Spectrometer

We report cosmic-ray proton and helium spectra in energy ranges of 1-120 GeV nucleon-1 and 1-54 GeV nucleon-1, respectively, measured by a flight of the Balloon-borne Experiment with Superconducting Spectrometer (BESS) in 1998. The magnetic rigidity of the cosmic ray was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 T. Those spectra were determined within overall uncertainties of ±5% for protons and ±10% for helium nuclei including statistical and systematic errors.

The Absolute Flux of Protons and Helium at the Top of the Atmosphere Using IMAX

The cosmic-ray proton and helium spectra from 0.2 GeV nucleon^(-1) to about 200 GeV nucleon^(-1) have been measured with the balloon-borne experiment Isotope Matter-Antimatter Experiment (IMAX) launched from Lynn Lake, Manitoba, Canada, in 1992. IMAX was designed to search for antiprotons and light isotopes using a superconducting magnet spectrometer together with scintillators, a time-of-flight system, and Cherenkov detectors. Using redundant detectors, an extensive examination of the instrument efficiency was carried out. We present here the absolute spectra of protons and helium corrected to the top of the atmosphere and to interstellar space. If demodulated with a solar modulation parameter of Φ = 750 MV, the measured interstellar spectra between 20 and 200 GV can be represented by a power law in rigidity, with (1.42 ± 0.21) × 10^4R^(-2.71±0.04) (m^2 GV s sr)^(-1) for protons and (3.15 ± 1.03) × 10^3R^(-2.79±0.08) (m^2 GV s sr)^(-1) for helium.

The Cosmic‐Ray Proton and Helium Spectra between 0.4 and 200 GV

We report on the hydrogen nuclei (protons and deuterons) spectrum from 0.15 to 200 GeV and on the helium nuclei spectrum over the energy range from 0.2 to 100 GeV nucleon~1 at the top of the atmo- sphere measured by the balloon-borne experiment Cosmic Antiparticle Ring-Imaging Cerenkov Experi- ment (CAPRICE), which was —own from Lynn Lake, Manitoba, Canada, on 1994 August 8¨9. We also report on the proton spectrum over the energy range from 0.15 to 4.2 GeV. The experiment used the NMSU-WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator Ring- Imaging Cerenkov (RICH) detector and a silicon-tungsten calorimeter for particle identi—cation. This was the —rst time a RICH was used together with an imaging calorimeter in a balloon-borne experiment. These detectors allowed for clear particle identi—cation, as well as excellent control of the detector effi- ciencies. The data were collected during 18 hr at a residual mean atmospheric depth of 3.9 g cm~2. With this apparatus 516,463 hydrogen and 32,457 helium nuclei were identi—ed in the rigidity range 0.4 to 200 GV and 1.2 to 200 GV, respectively. The observed energy spectrum at the top of the atmosphere can be represented by (1.1 ^ 0.1) ) 104 E~2.73B0.06 particles (m2 GeV sr s)~1 for hydrogen (E in GeV) between 20 and 200 GeV and (4.3 ^ 0.9) ) 102 E~2.65B0.07 particles (m2 GeV nucleon~1 sr s)~1 for helium nuclei (E in GeV nucleon~1) between 10 and 100 GeV nucleon~1. These spectra are in good agreement with other recent measurements above 10 GeV. The observed spectra —atten below 10 GeV due to solar modulation and are consistent with earlier measurements when solar modulation is taken into account. Between 5 and 200 GV the hydrogen to helium ratio as a function of rigidity was found to be approx- imately constant at 6.1 ^ 0.1. Subject headings: cosmic rayselementary particles

Production Cross Sections of Fragments from Beams of 400–650 MeV per Nucleon9Be,11B,12C,14N,15N,16O,20Ne,22Ne,56Fe, and58Ni Nuclei Interacting in a Liquid Hydrogen Target. I. Charge Changing and Total Cross Sections

We have measured the charge changing cross sections from 10 individual beams of isotopes from 8 different nuclei between Be and Ni which were accelerated to energies from 400-650 MeV nucleon-1 at the SATURNE Accelerator in France in 1993 and 1994. These nuclei interacted in a 1.52 g cm-2 thick liquid hydrogen target and the fragments were observed. This is the first use of a pure hydrogen target to measure cross sections that has a thickness approximating the amount of hydrogen traversed by cosmic rays in our Galaxy. Several of the beam charges such as 9Be,11B,15N, and 22Ne have not had their fragmentation cross sections measured previously. The cross sections from the 12C,14N,16O,20Ne,56Fe, and 58Ni beams are compared with earlier measurements by our group using a CH2 - C target subtraction technique to determine the hydrogen cross sections. The overall agreement between the new measurements and the earlier measurements using CH2 - C subtraction is excellent with a systematic consistency between measurements of 3%-5%. Using these new cross sections the predictions of both the B/C and Z = (21-23)/Fe ratios at ~1 GeV nucleon-1 now agree with HEAO measurements to ~1%-2%, thus obviating the need for truncation of the exponential path length distribution path length distribution that is expected from uniform propagation models. Also, these new charge changing cross sections along with the isotopic cross sections reported in paper two of this series, define the production of cosmic-ray beryllium and boron nuclei in the galaxy and also the secondary isotopes 10Be,13C,14N,15N,18O, and all of the Fe secondary isotopes to a level of precision of 3%-5% or better. These cross sections are important for determining the abundance of these rare isotopes and others in the cosmic-ray sources as well as tracing the detailed propagation history of cosmic rays in the Galaxy. These measurements also provide high precision cross sections for the study of the nuclear physics of the interaction process.

A Study of the Surviving Fraction of the Cosmic‐Ray Radioactive Decay Isotopes10Be,26Al,36Cl and54Mn as a Function of Energy Using the Charge Ratios Be/B, Al/Mg, Cl/Ar, and Mn/Fe Measured onHEAO 3

We have used published HEAO3 data on the charge ratios Be/B, Al/Mg, Cl/Ar, and Mn/Fe to examine the decay of the radioactive cosmic-ray isotopes10Be,26Al,36Cl, and 54Mn at energies from ~600 MeV to 20 GeV nucleon-1. From these charge data we can obtain the surviving fractions of these isotopes at higher energy with a comparable accuracy to that obtained using directly measured low-energy isotopic ratios. As a result of the relativistic time dilation of the lifetimes, these higher energy surviving fractions are a probe of propagation conditions outside the disk and into the halo of the Galaxy. The data are interpreted in terms of a simple leaky-box propagation model, then a more realistic diffusion model, and finally a still more realistic Monte Carlo diffusion model for the propagation of cosmic rays. Interpreted in terms of a leaky-box model, the data for all four isotopes suggest to varying degrees that the cosmic-ray particles are propagating into regions of lower density away from the disk. The diffusion model allows one to determine that the scale size of this extended propagation region in the Z-direction is 2-4 kpc. The data are consistent only with weak Galactic winds ~20 km s-1 or less. Monte Carlo models require cosmic-ray lifetimes ~20-30 × 106 yr and a halo size 2-3 kpc. The Monte Carlo calculations suggest that it is the scale size of the diffusion coefficient in the Z-direction relative to the halo size that determines the surviving fractions of these radioactive isotopes at high energies rather than the details of the Z dependence of the matter density.

The Cosmic‐Ray3He/4He Ratio from 200 MeV per Nucleon−1to 3.7 GeV per Nucleon−1

The abundances of cosmic-ray helium isotopes between 0.2 and 3.7 GeV nucleon^(-1) were measured by the Isotope Matter Antimatter Experiment (IMAX) during a flight from Lynn Lake, Manitoba, Canada on 1992 July 16-17. The IMAX balloon-borne magnetic spectrometer realized a direct measurement of the charge, the velocity, and the rigidity of cosmic rays using plastic scintillators, a high-resolution time-of-flight system, and two silica-aerogel Cerenkov counters in conjunction with a drift chamber/multiwire proportional chamber tracking system. About 75,000 helium isotopes are identified by their mass using the velocity versus magnetic rigidity technique. The measured ^3He/^4He ratios are corrected to the top of the atmosphere, and a comparison with previous data is given. The observed isotopic composition is found to be generally consistent with the predictions of a standard leaky box model of cosmic-ray transport in the Galaxy.

Coupling of longitudinal and transverse flows in the hydrodynamics of ultrarelativistic nuclear collisions

The space—time evolution of matter produced in high energy nuclear collisions is explored using a three dimensional hydrodynamic model. A significant coupling between longitudinal and transverse hydrodynamic flows is observed. This coupling of flows may be used to infer the degree of stopping in heavy ion experiments. These results are illustrated by qualitative fits to the CERN NA35 data for S+S collisions at 200 GeV nucleon .

Space-time picture of high-energy heavy-ion collisions and scaling properties of proton spectra

A comparative analysis of predictions of three typical models of relativistic nucleus-nucleus collisions is performed. It includes the model of partial transparency, the hydrodynamical model and the intranuclear cascade model. The results of proton and pion spectra calculations are compared with the experimental data available at incident energies of 0.8, 2.1 and 3.6 GeV nucleon . The effects of deviation from thermodynamical equilibrium due to mutual transparency of projectile and target nuclei are studied. The importance of the transition layer arising on the boundary of the overlapping parts of interacting nuclei has been demonstrated. The emission from this layer gives the main contribution to inclusive proton spectra in the target fragmentation region. In this region all the three models are in good agreement with experiment and, in particular, reproduce the scaling properties of proton inclusive cross sections satisfactorily. Considerable difference in the models' predictions takes place in the central rapidity region, especially in central collisions of identical nuclei. Experiments are suggested to study the mechanisms of the transition layer formation and the nature of scaling behaviour of proton spectra.

The inclusive production of kaons in relativistic nucleus-nucleus collisions based on transport theory

We assume that in relativistic heavy-ion reactions positive kaons (K +) are produced in sequences of independent baryon-baryon collisions. The basic inputs into our calculation of the K + inclusive differential cross section thus are the baryon momentum distributions after a number n of collisions. These functions are, to a very good approximation, determined by their first and second moments which in turn are calculated by use of a transport theoretical approach. We compare our results with experimental data obtained from the reaction Ne + NaF at 2.1 GeV nucleon . This comparison is first made under the assumption that the kaons, once produced, escape from the participant region without further interactions. In this case, the observed K + total production cross section is reproduced quite well, but the corresponding differential cross sections are not. The inclusion of the K + elastic scattering on the surrounding baryons leads to a much better agreement with the experimental data. We also calculate the K + total production rate as a function of the bombarding energy per nucleon. At all energies, the number of kaons produced by multiply scattered baryons is seen to exceed by far that obtained from nucleons which scatter for the first time. The K + total production cross section remains sizeable in our approach even far below the threshold energy. For a very heavy system like Pb on Pb we estimate a cross section of 10 mb even 800 MeV below threshold.

Subthreshold K − production by coherently produced π-mesons in heavy ion collisions

We assume that the enhanced subthreshold K − production found recently in the reaction 28Si− 28Si at 2.1 GeV nucleon is due to the decay of coherently produced π-mesons. We calculate the differential K − production cross section by treating the source term of the π-meson field, which is the nucleon current, as an external c-number source. We parametrize this current by assuming a diving, a compression, and an expansion stage during the nucleus-nucleus collision where the results of the intranuclear cascade calculations serve as a reference. Assuming a reasonable time for building up three times the normal nuclear matter density we get agreement with the experimental data. We predict a differential cross section that is different from a thermal spectrum.

Total cross sections ν μ and ḡn μcharged-current interactions between 20 and 200 GeV

Exposures of the Ne/H 2 filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ∼ 3100 events with a negative, and ∼ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values σ E between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm 2 (GeV nucleon) −1, for neutrinos and antineutrinos, respectively. The scaling variable q 2 E decreases significantly with increasing energy both for neutrinos and antineutrinos.

Isobar giant resonance formation in self-conjugate nuclei

The production of isobars with concomitant giant resonance excitations due to peripheral collisions of relativistic heavy ions is investigated. The interaction is described by a modified form of the central term in the one-pion-exchange potential (OPEP) where the projectile ordinary spin operator is replaced by a transition spin operator which describes the creation of an isobar from a nucleon. The scattering is analyzed using time-dependent harmonic perturbation theory to determine the reaction total cross sections. The results obtained, which are valid for reactions involving self-conjugate nuclei, are applied to the specific collison of 2.1 GeV nucleon 16O projectiles with 12C targets at rest. Cross sections are investigated using two different models for the nuclear spin states. In the first model, the many-body nuclear spin state is reduced, in the spirit of a particle-hole state, to an equivalent two-body state called a particle-core state. In the second model, the many-body spin states are described by unsymmetrized products of individual particle spins. Properties of the spin giant resonance and isobar giant resonance states are investigated. Finally, isobar decay and isobar/pion absorption effects are discussed.

On the Observation of Two-Proton Azimuthal Angle Correlations in 2 GeV/Nucleon Heavy Ion Interactions

A weak two-proton azimuthal angle back-to-back correlation which may indicate the presence of quasi elastic first order proton-proton scattering in 16O + CNO reactions at 2 GeV nucleon has been observed. Low and medium multiplicity 16O + AgBr reactions show the same tendency, while the dominant feature of the two-proton azimuthal angle distribution for very high multiplicity events is a blockade against pairs with relative angles between 2π/3 and 7π/8.

On the interplanetary cosmic-ray scintillations

The equation for the two-particles cosmic-ray distribution function is derived by means of the Boltzmann kinetic equation averaging. This equation is valid for arbitrary ratio of regular and random parts of the magnetic field. For small energy particles the guiding-center approximation is used. On the basis of the derived equation the dependence between power spectra of cosmic-ray intensity and random magnetic field is obtained. If power spectra are degree functions for high energy particles (≈ 10 GeV nucleon−1), then the spectral exponent υ of magnetic field lies between ϱ and ϱ−2, where ϱ is the spectral exponent of cosmic-ray power spectra. The experimental data concerning moderate energy particles are in accordance with υ=ϱ, which demonstrates that the magnetic fluctuations are isotropic or cosmic-ray space gradient is small near the Earth orbit.

The cascading of cosmic-ray nuclei in various media

More than a thousand interactions of primary heavy nuclei of the cosmic radiation with charge ≥10 and energy >1 GeV nucleon−1 in nuclear emulsion have been studied with emphasis on how the primary nucleus fragments. It has been determined that the cases of multiple successive fragmentations that have been observed do not occur more frequently than expected. The fragmentation ofZ>20 nuclei does depend on the target nucleus to some extent so it is important to try to separate the interactions in emulsion by theirNh (number of evaporation prongs). The fragmentation of816O at 2.1 GeV nucleon−1 measured at the Bevalac shows a similar dependence on target nucleus. By using data from these new interactions combined with published data we have simulated on a computer nuclear cascades in both emulsion and air. Results on these cascades are given for both primary silicon and primary iron nuclei. These results are used to discuss the fluctuations expected in extensive air showers produced by heavy primary nuclei.

Mean Path Length of High Energy Galactic Cosmic Rays in the Galactic Disk

AN important measurement of the composition of cosmic ray nuclei at high energy (20<E<100 GeV nucleon−1) has been reported by Juliusson, Meyer and Muller1. They show that the ratio of galactic secondary nuclei to primary nuclei decreases very steeply when the energy of the observed nuclei is above 30 GeV nucleon−1. The ratio of predominantly secondary nuclei to predominantly primary nuclei illustration which is ∼0.31 at energies of 1.5 GeV/N is found to be 0.23 ± 0.03 at 25 and 30 GeV/N and 0.12+0.05−0.07 at 90 GeV/N. Juliusson et al.1 conclude that this effect may be explained in terms of particle propagation in the Galaxy: the leakage term which describes the probability that galactic cosmic rays leave the Galaxy must be energy dependent. Here we present a quantitative estimation of this dependence and discuss the implications of such a dependence. Open image in new window

Evidence for Differences in the Energy Spectra of Cosmic Ray Nuclei

THE existence of differences in the energy spectra of the various cosmic ray nuclei at energies ≳ 1 GeV nucleon−1 would have important implications for the method of acceleration of the cosmic rays and their propagation in interstellar space. But only recently has it been possible to isolate and compare the spectra of particular charges or charge groups with the requisite statistical accuracy over a broad enough energy range.