Standard Leaky Box Model 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.

Cosmic‐Ray Sources and Source Composition

Present data on cosmic-ray elemental and isotopic relative abundances are shown to be unable to distinguish between various models of cosmic-ray sources and their composition. For example, the model of freshly nucleosynthesized material from supernova explosions as the cosmic-ray source is unable to account for some measured, key cosmic-ray elemental abundances. This and two other models are evaluated here in light of recent isotopic and elemental measurements. It is shown that model-dependent preferential injection, acceleration, and reacceleration do not allow a clear distinction of one model against the others. Future measurements of critical elements and isotopes are suggested, which should afford us the ability to do that. We base our suggestions on measurements and a quantitative comparison between the predictions of the standard leaky-box model for the Galactic propagation of cosmic rays and one in which reacceleration is taken into account.

Source composition of cosmic ray nuclei

Abstract During propagation in the Galaxy, cosmic-ray nuclei undergo spallation and as a result, their composition at the time of acceleration gets modified. Propagation models have been used to obtain the source composition from the observed abundance. We made use of the standard leaky-box model with time as the propagation variable to examine the spectra of all elements. The main ingredients in this method are the spallation cross-sections, which has considerably changed over the time. Using the latest available cross-sections, we show that the spectral index of the power-law injection spectrum in rigidity is −2.32. We also derive the escape path-length and the source abundances. The derived abundances differ from those of Webber for some of the elements.

Antiproton spectrum in the galactic wind model

Abstract The vast majority of cosmic-ray particles are protons and heavier nuclei. Antiprotons constitute only a small fraction of detected cosmic rays; and it is only recently that measurements with sufficient statistics in the range of 100 MeV to few GeV have been made and an accurate energy spectrum of antiprotons has been inferred. It is now becoming possible to compare and examine the prediction of various propagation models and search for a possible primary component of antiproton cosmic rays. In this paper we present the calculation of secondary antiproton spectrum in the Galactic Wind model. The effect of adiabatic loss in expanding Galactic wind leads to an antiproton spectrum different from the prediction of standard leaky-box model. This allows us to search for a signature of the Galactic wind in the cosmic-ray data.

Precision measurement of antiproton spectrum with BESS

The absolute fluxes of the cosmic-ray antiproton are measured at solar minimum in the energy range 0.2 to 3.2 GeV, based on 460 antiprotons unambiguously detected by BESS spectrometer during its '95 and '97 balloon flights from Lynn Lake, Canada. In the resultant antiproton spectrum we have detected a clear peak around 2 GeV and measured its flux to 10 % accuracy. The position and the absolute flux of the peak agree with the prediction of the Standard Leaky Box model for the “secondary” antiprotons. At low energies below 1 GeV, we observe an excess antiproton flux over the simple Standard Leaky Box prediction. This might indicate that the propagation mechanism needs to be modified, or might suggest a contribution of low-energy antiproton component from novel sources such as evaporating primordial black holes or the annihilating neutralino dark matter. Data from '98 and future flights are expected to help us to clarify the situation.

A New Calculation of the Interstellar Secondary Cosmic‐Ray Antiprotons

We present new results for the theoretical prediction of the interstellar secondary antiproton flux produced in cosmic ray interactions with the interstellar gas. The calculation is performed in the framework of the standard leaky box model (LBM). In comparison to earlier calculations, we believe we have reached improvements in three aspects. We use the proton and helium spectra, as recently measured by the IMAX instrument, and the Monte Carlo model DTUNUC to study the contributions to the flux from p-nucleus, nucleus-p and nucleus-nucleus collisions, and we allow for energy-changing processes caused by the nonannihilation process and by elastic scattering. We compare the results for the flux with earlier calculations and with recently published data. We illustrate that the path length distribution (PLD) remains the dominant source of uncertainty. We also point out another source of uncertainty, the attempt to find a proper fit to measured -production cross sections from p-p interactions. Published parameterizations differ and cause an uncertainty in the predicted flux of almost 40%. We show that within these uncertainties, recently published data on the flux are in agreement with the assumption that the observed antiprotons are of secondary origin.

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.

Stochastic reacceleration of cosmic rays in the interstellar medium

The effects of reacceleration on cosmic rays have been studied over a wide charge and energy range using a model of reacceleration by the interstellar turbulence. We take into account only inevitable stochastic reacceleration of cosmic rays by the random hydrodynamic waves, which supposedly exist in the interstellar medium and provide a means for cosmic-ray scattering and spatial diffusion in the Galaxy. Our calculations reproduce not only the B/C ratio but also the H and He data over the entire energy range where the measurements are available. However, the sub-Fe to Fe ratio is not fitted as well as the B/C ratio, and the reacceleration effect does not seem to remove the need for truncation of short path lengths, which is apparently required by the standard leaky box model. This work demonstrates that the cosmic-ray data can be represented at least as well by a reacceleration model with a simple rigidity power-law escape length, which agrees with the Kolmogorov-type spectrum of hydromagnetic turbulence, as they can by the standard leaky box model with its ad hoc escape lengths.

Voyager measurements of the isotopic composition of cosmic-ray aluminum and implications for the propagation of cosmic rays

view Abstract Citations (27) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Voyager Measurements of the Isotopic Composition of Cosmic-Ray Aluminum and Implications for the Propagation of Cosmic Rays Lukasiak, A. ; McDonald, F. B. ; Webber, W. R. Abstract We report a new measurement of the cosmic-ray isotopic composition of aluminum in the low-energy range form 75 to 206 MeV per nucleon.This measurement was made using the high-energy telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1993 with an average solar modulation level about 497 MV, roughly the same as at Earth near sunspot minimum. We obtain approximately 430 Al events of which approximately 35 are Al-26 and 395 are Al-27. The Al isotopes were separated with an average mass resolution sigma of 0.35 amu. Our interpretation of the isotopic composition of cosmic-ray aluminum is based on a standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the latest cross sections of the New Mexico-Saclay collaboration as well as a disk-halo diffusion model. From our observed ratio Al-26/Al-27 of 8.3 +/- 2.4 % we deduce an average interstellar density of about 0.52 (+0.26, -0.2) atoms per cu cm. This density is larger than the value of 0.28 (+0.14, -0.11) atoms per cu cm we found from an analysis of the observed abundance of the longer lived Be-10 made using data from the Voyager detectors over almost the same time interval and using essentially the same propagation program. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/187440 Bibcode: 1994ApJ...430L..69L Keywords: Abundance; Aluminum Isotopes; Beryllium Isotopes; Cosmic Rays; Interstellar Matter; Energy Distribution; Mass Distribution; Mass Ratios; Mass Spectrometers; Voyager 1 Spacecraft; Voyager 2 Spacecraft; Space Radiation; ISM: ABUNDANCES; ISM: COSMIC RAYS full text sources ADS |

The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age

We report a new measurement of the cosmic-ray isotopic composition of beryllium in the low-energy range from 35 to 113 MeV per nucleon. This measurement was made using the High Energy Telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1991. In this overall time period of 14 years the average solar modulation level was about 500 MV. The cosmic-ray beryllium isotopes were completely separated with an average mass resolution sigma of 0.185 amu. The isotope fractions of Be-7, Be-9, and Be-10 obtained are 52.4 +/- 2.9%, 43.3 +/- 3.7%, and 4.3 +/- 1.5%, respectively. The measured cosmic-ray abundances of Be-7 and Be-9 are found to be in agreement with calculations based on standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the recent cross sections of the New Mexico-Saclay collaboration. From our observed ratio Be-10/Be = 4.3 +/- 1.5% we deduce an average interstellar density of about 0.28 (+0.14, -0.11) atoms/cu cm, and a cosmic-ray lifetime for escape of 27 (+19, -9) x 10<SUP>6</SUP> years. The surviving fraction of Be-10 is found to be 0.19 +/- 0.07. Modifications to the conclusions of the Leaky-Box model when a diffusion + convection halo model for propagation is used are also considered.

The elemental and isotopic composition of Galactic cosmic-ray nuclei from scandium through nickel

Measurements of the relative elemental and isotopic abundances of iron-group Galactic cosmic rays at energies of ~ 325 Me V per nucleon have been made using data collected from 1978 to 1981 by the high-energy cosmic ray detector aboard the /SEE 3 spacecraft. Assuming a standard leaky box model of cosmic-ray propagation, it is found that the source abundance ratio of ^(60)Ni/^(58)Ni is 1.07 ± 0.39, which is a factor of 2.8 ± 1.0 larger than the solar system value. Our measurements imply the presence of ^(59)Co at the source, which can be reconciled with the predictions of conventional nucleosynthesis models if there exists a time delay of ≥10^5 yr between nucleosynthesis and acceleration. Most of the 54Mn produced by spallation during cosmic-ray propagation in the Galaxy is found to have decayed to ^(54)Fe, indicating a confinement time of greater than 2 Myr. The source ratio of ^(54)Fe/^(56)Fe corrected for the ^(54)Mn decay is 0.046 ± 0.020, which is consistent with the solar system value of 0.063. The source ratio ^(55)Mn/^(56)Fe = 0.025 ± 0.010 is a factor of 2.1 ± 0.8 greater than solar. Also, the value of the Cr/Fe elemental ratio is found to be marginally enhanced. The isotope ^(52)Cr appears to be present in the cosmic-ray source at almost the 95% confidence level. The limits obtained on the abundances of the lighter iron-group elements at the source are Sc/Fe < 0.005, Ti/Fe < 0.007, and V /Fe < 0.005.

Supernova Remnants and the ISM: Constraints from Cosmic-Ray Acceleration

AbstractSupernova remnants can reaccelerate cosmic rays and modify their distribution during the cosmic ray propagation in the galaxy. Cosmic ray observations (in particular the boron-to-carbon data) strongly limit the permitted amount of reacceleration, which is used to set an upper limit on the expansion of supernova remnants, and a lower limit on the effective density of the ISM swept up by supernova shocks. The constraint depends on the theory of cosmic ray propagation: the standard Leaky Box model requires a high effective density, &gt; 1cm−3, and is probably inconsistent with the present picture of the ISM. Modifying the Leaky Box model to include a moderate amount of weak-shock reacceleration, a self consistent solution is found, where the effective density in this solution is ≈ 0.1 cm−3, which implies efficient evaporation of the warm ISM component by young supernova remnants, during most of their supersonic expansion.

He-3 in galactic cosmic rays

Cosmic-ray ^3He/^4He observations, including a new measurement at ~65 MeV per nucleon from ISEE 3, are compared with interstellar propagation and solar modulation calculations in an effort to understand the origin of cosmic-ray He nuclei. We survey spacecraft and balloon observations of the ^3He/^4He ratio and find improved consistency among measurements in the ~50-300 MeV per nucleon energy range when a previously neglected contribution from atmospheric secondary ^3He is taken into account. These low-energy observations imply a mean escape length of 6-8 g cm ^(-2) in the standard leaky box model for cosmic-ray propagation in the galaxy, a value consistent with that derived from studies of heavier nuclei. Thus, we find no evidence for an excess of low-energy ^3He such as that reported at higher energies. Recent propagation models designed to explain the excess of cosmic-ray antiprotons observed at GeV energies also predict an excess of ^3He that is not observed at low energies.

A measurement of the cosmic-ray antiproton flux and a search for antihelium

A balloon-borne instrument has measured the cosmic-ray antiproton flux between 130 and 320 MeV and searched for antihelium between 130 and 370 MeV per nuclear. These particles were selected from the background of normal-matter cosmic rays by combining a selective trigger with a detailed spark chamber visualization of each recorded event. Antiprotons are identified by their characteristic annihilation radiation. Residue from background processes meeting the selection criteria is small. The observed 14 antiprotons yield a measured differential flux of 1.7±0.5X 10^(-4) antiprotons m^(-2) sr(-1) s^(-1)i Mev^(-1) at the top of the atmosphere. The corresponding antiproton/pro-ton ratio is 2.2±0.6X10^(-4), only slightly smaller than the ratio observed by other experiments at higher energies. Thus the antiprotons have a spectral shape similar to the protons, at least down to about 100 MeV. The expected flux of these particles can be calculated under the assumption that they were created by collisions of high-energy cosmic rays with the interstellar gas. Calculations using the standard leaky box model for propagation in the Galaxy predict a flux two orders of magnitude smaller than that observed. A small low-energy flux is predicted due to a kinematic suppression of the production of low-energy antiprotons. The discrepancy between calculations and experiment may be evidence that cosmic-ray protons have passed through substantially more than 5 g cm^(-2) of material during their lifetime. In addition, the combined results from this experiment and previous ones may be evidence for stochastic, energy-changing processes in interstellar space which act upon the secondary antiprotons after their creation. The search for cosmic-ray antihelium sets a 95% confidence level upper limit on the He /He ratio of 2.2 X 10^(-5).

Antiprotons in the cosmic radiation

Golden et al.1 have demonstrated that the measured ratio of the flux of antiprotons to protons (p/p ratio) is significantly greater than expected from the commonly adopted ‘leaky box’ model of cosmic ray propagation, a model in which the p's are secondaries generated by the interaction of cosmic rays with the interstellar medium (ISM) in the Galaxy. At the energy at which measurements were made (kinetic energy≃8 GeV), disturbing effects due to interplanetary modulation are negligible and there is now general agreement2–5 that the excess is a factor of 3 at least (an earlier calculation6 of the expected p/p which gave a result near to observation has been shown to be incorrect2–5). Bogolomov7 found a similar but statistically less compelling enhancement at somewhat lower energies. A prominent characteristic of the p/p ratio for galactic secondaries is a rapid fall with decreasing energy, below≃5 GeV, due to kinematic factors. It was therefore remarkable that Buffington et al.8 recently reported a ratio only a factor of 2.5 smaller at a very low kinetic energy (average≃0.2 GeV). This result, if correct, necessitates serious consideration of more exotic explanations. An important feature at these very low energies is the modulation of the flux by the interplanetary field and we have now examined this facet. We describe an improved calculation of the energy spectrum of p expected for the standard leaky box model and show that even the enhanced secondary p production in the ‘closed Galaxy’ model of Peters and Westergaard9 fails by a wide margin to reproduce the high observed flux at low energies. A more radical departure from conventional thinking is to regard the observed ps as primaries; a universal baryon-symmetric model and a black hole evaporation model are considered.