Low-energy Galactic Cosmic Rays Research Articles

Observations of enhanced sub-iron (Sc-Cr) to iron abundance ratios in the low energy galactic cosmic rays in Spacelab-3 and their implications

The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57° for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30–300 MeV/N were determined from the measurements made in four different depths of the CR-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30–300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth’s magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications.

Ionization states of low-energy cosmic rays - Results from Spacelab 3 cosmic-ray experiment

view Abstract Citations (10) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ionization States of Low-Energy Cosmic Rays: Results from Spacelab 3 Cosmic-Ray Experiment Dutta, A. ; Goswami, J. N. ; Biswas, S. ; Durgaprasad, N. ; Mitra, B. ; Singh, R. K. Abstract The Indian cosmic ray experiment Anuradha, conducted onboard Spacelab 3 during April 29-May 6, 1985 was designed to obtain information on the ionization states of low-energy cosmic rays, using the geomagnetic field as a rigidity filter to place an upper limit on the ionization state of individual cosmic ray particles. This paper presents data confirming the presence of three distinct groups of energetic particles in the near-earth space: (1) low-energy (15-25 MeV/nucleon) anomalous cosmic rays that are either singly ionized or consistent with their being in singly ionized state, (2) fully ionized galactic cosmic ray ions, and (3) partially ionized iron and sub-iron group ions (which account for about 20 percent of all the iron and sub-iron group ions detected at the Spacelab 3 orbit within the magnetosphere in the energy interval 25-125 MeV/nucleon). It is argued that these partially ionized heavy ions are indeed a part of the low-energy galactic cosmic rays present in the interplanetary space. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172844 Bibcode: 1993ApJ...411..418D Keywords: Energetic Particles; Galactic Cosmic Rays; Heavy Ions; Magnetospheric Ion Density; Spacelab; Weak Energy Interactions; Geomagnetism; Interplanetary Space; Ionization Cross Sections; Metal Ions; Space Radiation; ISM: COSMIC RAYS full text sources ADS |

Superconducting cosmic strings near the electroweak scale and cosmic-ray propagation.

A method to search experimentally for superconducting cosmic strings with a symmetry-breaking mass scale near the electroweak scale is described. Strings in the Galaxy act as scattering centers because of their coherent and bounded magnetic field, and thus contribute to the diffusion of galactic cosmic rays. The rigidity dependence of the string-induced diffusion coefficient is very specific. This allows us to search for superconducting strings in a fairly model-independent way by studying the diffusion properties of low-energy galactic cosmic rays. Particle emission by galactic strings near the electroweak scale is also discussed. Although the very model-dependent γ-ray emission from galactic strings near the electroweak scale would not have been detected up to now even under favorable conditions, it might be within the reach of forthcoming experiments

Observation of enhanced sub-iron (ScCr) to iron ration in low energy cosmic rays of 50–100 MeV/N in spacelab-3

Relative abundances of sub-iron (Sc-Cr) to iron nuclei in low energy (50–100 MeV/N) galactic cosmic rays have been determined from an analysis of about 100 events of heavy ions (Z = 10−28) recorded in a detector assembly flown in the Anuradha cosmic ray experiment in the Spacelab-3 on a six day mission in April–May 1985. The measured abundance ratio of (Sc-Cr)/Fe nuclei in 50–100 MeV/N energy range is 1.1 ± 0.3, and the present result of enhanced ratio of sub-iron to iron nuclei is in agreement with other experimental results in 200–800 MeV/N range. The over-abundance of iron secondaries at these low energies cannot be explained in the conventional models for propagation of cosmic rays. Available experimental data indicate a very different time history for the low energy iron-group, as compared to those of lighter nuclei in galactic cosmic rays.

New Triggering Mechanism for Red Dwarf Flares

The flare phenomenon associated with dMe stars has received much attention in recent years (Gershberg 1975). Most of the flares have been detected in both optical and radio band (Lovell 1969; Kunkel 197U; Karpen et al, 1977). But as expected (Tandon 1976) only a few display weak soft X-ray emission (Karpen et al, 1977; Haisch and Linsky 1978)- Simultaneous X-ray, optical and radio observations of YZ CMi by Karpen et al (1977) shows no X-ray emission above 3σ level accompanying minor flares. Even coincident X-ray coverage with seven radio bursts shows no enhanced X-ray emission. Recently Haisch et al (1981) detected one well resolved X-ray flare on dM5e flare star Proxima Centauri and one coincident optical and radio flare out of five optical and twelve radio flare events. However, the X-ray flare on Proxima Centauri is not accompanied by any ultraviolet, optical or radio emission. Observations on flare stars show that they are more energetic, 102 - 103 times, than the corresponding solar flares. Considering the flare activity in dwarf M-stars to be similar but more energetic to that of a large solar flare, Tandon (1961) proposed red dwarf flares to be the source of low energy galactic cosmic rays. This hypothesis has been reexplored recently by Lovell (1974).

The heliospheric intensity gradients of the anomalous He4 and the galactic cosmic-ray components

Measurements made with Pioneers 10 and 11 over the radial range of 1 to about 25 AU from 1972 to 1981 are presented to show that at solar minimum (1972-1977), the radial gradient for the anomalous helium component from 11 to 20 MeV/n is about 14%/AU. This result is significantly smaller than that predicted for either charge state of the component based on the observed spectrum and assumptions of conventional solar modulation for particles propagating inward from the heliospheric boundary. It is confirmed that the solar modulation mechanism that determines the level and distribution of low-energy galactic cosmic rays in the heliosphere, also modulates the He(A) spectrum. With increasing modulation between solar minimum and maximum, the 10-20 MeV/n He(A) flux decreases below the flux of modulated galactic He first at 1 AU and then progressively outward to 22-25 AU over an approximately two year period.

The low-energy galactic cosmic ray carbon, nitrogen, and oxygen isotopic composition

It is found that C, N, and O elemental and isotopic ratios in the galactic cosmic rays measured near the earth with the IMP 7 telescope of the University of Chicago have had the values N/O = 0.25 + or 0.02; C/O = 1.06 + or - 0.03; C-13/C = 0.04-0.10; N-15/N = 0.47 + or - 0.06; and O-18/O less than or equal to 0.03. It is noted that these results are confirmed by IMP 8 measurements. The measurements are extrapolated back to the cosmic ray source using exponential and truncated exponential path length distributions whose parameters have been determined by fitting cosmic ray B/C and sub-Fe/Fe ratios measured previously.

On the charge state of the anomalous oxygen component

We report our observations of a phase lag between the intensity variations of high energy galactic cosmic rays and the quiet time oxygen flux in the energy region 7.6‐24 MeV/nucleon during the time period 1974‐1975. Phase lag or hysteresis effects have been observed during the 11‐year solar cycle for low energy galactic cosmic rays and several authors have shown that this hysteresis effect is a function of the velocity and rigidity (and therefore of the ionic charge) of the particles. Assuming a similar rigidity dependence of the phase lag during the transient intensity decrease of both galactic cosmic rays and the anomalous oxygen component in the time period 1974‐1975, and comparing the phase lag as observed for protons and helium during the same period with our oxygen measurements, we derive an upper limit of ∼4 for the ionic charge of the anomalous oxygen component.

Nucleosynthesis in white dwarf atmospheres.

Consideration of events by which both s- and r-process nucleosynthesis may occur on the surfaces of white-dwarf stars. The main requirement is that the accreted hydrogen be mixed with comparable numbers of C-12 (or other alpha nuclei) before a runaway capture of protons takes place. Subsequent events offer many possibilities for nucleosynthesis and stars of peculiar composition. A new mechanism for a surface s-process due to few-MeV protons is also described. Concluding comments concern cosmic gamma-ray bursts and the origin of anomalous low-energy galactic cosmic rays.

The Distribution of Cosmic Rays in the Galaxy and Their Dynamics as Deduced from Recent V-Ray Observations

Recent data from SAS-2 on the galactic gamma ray line flux as a function of longitude reveal a broad maximum in the gamma ray intensity in the region absolute value of l approximately smaller than 30 deg. These data imply that the low energy galactic cosmic ray flux varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. This enhancement can be plausibly accounted for by first order Fermi acceleration, compression and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4 to 5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the galaxy.

Cosmic rays in the outer solar system

A space mission to Jupiter and Saturn, and beyond, provides an opportunity to explore the low energy galactic cosmic rays, which are largely excluded from the inner solar system by the outward sweep of the magnetic fields in the solar wind. The low energy cosmic rays are believed to be responsible for much of the heating of the gaseous disk of the galaxy, so a measurement of their intensity will have far reaching effects on theories of the interstellar gas and the evolution of the galaxy. The nuclear abundances, and in particular the presence or absence of high Z nuclei, will give critical information on the proximity of cosmic ray sources.

Modulation of low-energy galactic cosmic rays over solar maximum (Cycle 20)

A preliminary report is presented on detailed observations of low energy approximately (60 MeV/nucleon) galactic cosmic rays made during the recent period of solar maximum. For this particular cycle a significant time lag between intensity changes in the low energy and high energy components was observed. There are a number of possible explanations of this hysteresis effect. In the simplest form these include either changes in the form of the magnetic field power spectrum or changes in the size of the effective modulating region, or both.

Energy losses and modulation of galactic cosmic rays

Numerical solutions of the cosmic-ray transport equation for the interplanetary region and including the effects of diffusion, convection, and energy loss, have been obtained for a galactic differential number-density spectrum of gaussian form, central kinetic energyT0, and a width at half height maximum of 0.1T0. These solutions have been used to show the redistribution in energy, and the reduction in number density, within the solar cavity. The mean energy loss is shown to be usefully approximated by the force-field potential Φ when Φ/T0≲1/2. The principal finding is that galactic cosmic-ray protons and helium nuclei, with kinetic energies less than about 80 MeV/nucleon, virtually, are completely excluded from near Earth by convective effects. As a result of this exclusion, it is found that it is not possible to demodulate the proton and helium-nuclei spectra, observed in 1964–65, to obtain information about low-energy galactic cosmic rays.

The role of stochastic fields in admitting low-energy galactic cosmic rays to the solar system

Free access of low energy galactic particles to solar wind lines of force due to stochastic nature of lines

The composition of galactic cosmic rays

Recent measurements of low-energy galactic cosmic rays obtained on sounding rockets and satellites exhibit a composition different from that obtained for intermediate and high-energy radiation obtained at balloon altitudes. In particular the ratio of light to medium nuclei is observed to be 0.2–0.3 in the 50–100 MeV/nucleon interval as compared with values near 0.5 in the 200–500 MeV/nucleon region. Lower values of the ratios C/O, N/O, F/O, and odd-Z/even-Z are also found. In the light of these new measurements and of new measurements on the fragmentation cross sections for cosmic-ray nuclei in interstellar space, an attempt has been made to calculate the composition expected if similar source spectra are assumed. It is found that neither passage through a fixed amount of material nor an equilibrium condition (exponential path-length distribution) is adequate to explain the observed features. The effects of including other mechanisms such as rigidity-dependent escape from the galaxy and Fermi acceleration in interstellar space are evaluated.

A study of low-energy galactic cosmic rays from 1961 to 1965

The results from a series of balloon flights beginning in 1961 and ending in 1965 are presented. Measurements of the cosmic-ray intensity were made using a dE/dx and E detector sensitive to energies from 15 to 80 Mev/nucleon. Proton and helium intensities at 85 Mev/nucleon are presented for the five-year period covered by the balloon flight series. The behavior of the proton to helium ratio as a function of time is discussed within the framework of Parker's model for the solar modulation of cosmic rays. In 1965 a modified version of the dE/dx and E detector with an extended energy range was flown for the first time. A cosmic-ray helium spectrum from 60 to 500 Mev/nucleon measured by this detector is presented. The change in proton and helium intensities as a function of particle velocity in this energy region from 1963 to 1965 is examined and compared with the results predicted by the various special cases of Parker's model.

Nuclear effects of “solar” and “galactic” cosmic-ray particles in near-surface regions of meteorites

Changes in isotopic composition in the near-surface regions of stone and iron meteorites due to nuclear processes associated with the low-energy “solar” and “galactic” cosmic ray particles are evaluated theoretically. The processes considered are, nuclear-stopping due to ionization losses and nuclear-interactions. It is shown that these effects which are confined to the top few centimetres depth in meteorites are distinguishable from the more permeating isotopic changes induced by energetic galactic cosmic-rays. Their studies would allow one to estimate precisely the parameters characterizing the continuous flux of low-energy galactic cosmic-rays and the average flux of charged particles accelerated sporadically by the sun during the last tens to hundreds of million years. Combining such information with measurements of the prehistoric rates of accretion of certain nuclides, e.g. Al 26, (based on analysis of deep sea sediments), it should become possible to deduce the terrestrial accretion rate of cosmic dust during the past few million years.

Measurement of hydrogen nuclei in primary cosmic rays

The isotopic composition and the energy spectrum of singly charged particles of low energy were analysed using the emulsion stack which was launched on September 4, 1959 from Sioux Falls, S.D. (geomagnetic latitude ~ 53.5 °N) and floated for 8.8 hours under 2.0 g cm°-2 of residual atmosphere and materials. The grain densityvs. range method and the multiple scattering method were used for identification of particles. Fluxes of primary protons and deuterons at the top of the atmosphere are (0.22±0.02) protons m2 s1 sr1 MeV-1 for the kinetic energy range of 82 to 305 MeV for protons, and (0.020±0.008) deuterons m-2 s-1sr-1 (MeV/nucleon)-1 for 56 to 200 MeV/nucleon for deuterons, respectively. The differential energy spectrum of primary protons is given by E-(1.2±0.2). On the basis of the experimental results the possibility of the following origins is discussed: 1) galactic cosmic rays, 2) re-entrant albedo particles, 3) solar particles, and 4) particles from the inner Van Allen radiation belt. It seems to be probable that the particles observed are partly due to those leaked from the inner radiation belt by the distortion of the earth’s magnetic field, although low energy galactic cosmic rays and solar particles may be a part of them.