U.B. Jayanthi

Nuclear reactions in the uppermost Earth atmosphere as a source of the magnetospheric positron radiation belt

A physical mechanism for the formation of a natural positron belt in the Earths magnetosphere is considered. It is assumed that a natural source of energetic positrons as well as electrons can be created owing to the decay of charged pions π± → μ± → e±, which have their origin in nuclear collisions between energetic trapped inner zone protons and heavier atoms (He and O) in the upper atmosphere of the Earth. Simulations of these processes demonstrate that there is a predominant production of positive pions over negative pions, and consequently the decays result in a substantial excess of positrons over electrons at energies greater than tens of MeV. This positron excess is found to be energy-dependent and to decrease with increasing incident proton energy; this excess is essentially absent at proton energies corresponding to cosmic ray primaries of ≥8 GeV. Our numerical computations for the resulting e+/e− fluxes provide ratio values of ∼4 at multi-MeV energies and at L = 1.2 ± 0.1. The simulation results presented herein are compared to the existing and recent experimental evidence.

Electron precipitation associated with geomagnetic activity: Balloon observation of X ray flux in South Atlantic anomaly

A stratospheric balloon experiment was conducted on December 20, 1994, with an X ray detector to measure fluxes of precipitation electrons in the South Atlantic anomaly (SAA) region of Brazil. For the first time in the SAA, this detector system of high sensitivity monitored three events of increases in X ray fluxes which axe associated with simultaneous decreases in geomagnetic H field component. The most prominent event with an X ray emission equivalent to ≈1/4 of the diffuse cosmic X ray flux permitted the determination of the spectrum in the energy range of 18.6 to 120 keV. The inferred electron spectrum showed a steep low-energy component below 150 keV (E0=16 keV). The electron flux estimates are lower compared to earlier balloon results obtained at the time of a severe magnetic storm. The inferred fluxes from our balloon experiment are consistent with the electron fluxes observed by the S3–2 satellite and are lower than the OGO 5 satellite measurements, both obtained in the SAA at L= 1.3. Further, the estimates are compatible with the P78-1 satellite fluxes present in the drift loss cone at L = 1.25. The presence of sufficient electron fluxes at L = 1.3 region in the SAA, and the similarity between the electron spectrum observed by the satellite experiments and that inferred in our balloon experiment, prompted us to investigate the possibility of the access of these electrons present at satellite altitudes into L = 1.13 regions during a mild storm. Interestingly, this prominent X ray flux event is associated with two succesive southward turnings of Bz component of the interplanetary magnetic field (IMF). Precipitation of essentially low-energy electrons below 150 keV occurred at the first northward reversal of IMF Bz and after the latter northward reversal higher energy electrons (> 150 keV) also precipitated. We suggest the diffusion of particles from higher L regions into flux tubes connected to the SAA region, due to electric field fluctuations associated with succession of substorms, in a process similar to the “enhanced radial diffusion” proposed by Lyons and Schulz [1989]. To compare or to relate the inferred fluxes from the balloon experiment with the satellite measurements and for a better understanding of the precipitation of electrons during magnetic disturbances, it is necessary to have additional experimental investigations in the SAA.

Antiprotons confined in the earth’s inner magnetosphere

Abstract The possible existence of noticeable fluxes of antiparticles in the Earth magnetosphere is considered theoretically in this article. These antiparticles (antiprotons in this paper) that are confined by geomagnetic field at the altitudes of several hundred kilometers are predominantly not of immediate extraterrestrial origin, but rather are the products of nuclear reactions of the high energy primary cosmic rays (CR) with constituents of the terrestrial atmosphere. Direct extraterrestrial antiprotons impinging upon the Earth’s magnetosphere are themselves also secondary in origin, i.e. they are born in nuclear reactions of the same CR passing through 5–7 g/cm 2 of interstellar matter. These exhibit lower fluxes compared to the magnetospheric antiprotons that are born at a pass length of hundreds g/cm 2 in the residual Earth atmosphere. Such locally generated antiprotons can be confined by the magnetic field of the Earth (or equivalently by another planet) and so accumulated in the magnetosphere. We here present the results of numerical simulation of antiproton fluxes in the energy range from 10 MeV to several GeV produced by CR in the Earth’s atmosphere at altitudes of about 1000 km, and we compare this to antiprotons born in interstellar matter. The estimates presented herein show a significant (up to two orders of magnitude) excess of magnetospheric antiproton fluxes over those formed in the interstellar media at energies

Trapped positron flux formation in the innermost magnetosphere of the Earth

The possible existence of a positron radiation belt in the inner magnetosphere of the Earth, its space location, flux, energy distribution and the ratio of e+/e− fluxes is considered. The source of the positrons/electrons is assumed to be the decay of charged pions (π - μ - e decay chain) produced, in the nuclear interactions between protons and the neutral constituents of the atmosphere. The production of excess positron fluxes over electron ones through this process is examined for two different proton populations and their atmospheric interactions in the altitude range of 80 to 1000 km. Monte Carlo simulations of intranuclear cascade process through SHIELD code was utilized to simulate these interactions. Considering the trapped proton fluxes in the inner magnetosphere as a source, the simulations for interactions in rarified atmosphere shows excess of positrons over electrons with ratios above 2 for proton energies below 2.5 GeV. Although, protons above this energy do not produce excess of positrons compared to electrons in atmospheric interactions, we assumed the primary cosmic rays with the energy greater than 8–10 GeV also as a source for these interactions, and utilizing the east-west asymmetry in the arrival directions of these primary cosmic rays combined with the exponential nature of the atmosphere density we also obtained an excess of positrons over electrons escaping from the atmosphere to the altitudes of satellite orbits. A comparison is attempted with the recent data of AMS experiment on board the space shuttle.

A mura-based coded mask telescope

Abstract A high-energy telescope that employs a Modified Uniformly Redundant Array (MURA) coded mask is described. The imaging device is a 19×19 element square MURA-based extended mask mounted in a single mask-antimask configuration. This is the first experiment to use such a mask pattern and configuration for astrophysical purposes. The detector system consists of a 41 cm diameter, 5 cm thick NaI(Tl) crystal coupled to 19 photomultipliers. The anticoincidence system is composed of plastic scintillators on the sides and a NaI(Tl) crystal at the bottom. The angular resolution is approximately 14′ over a 13° field of view. The expected 3 σ sensitivity for an on-axis source observed for 104 s at a residual atmosphere of 3.5 g.cm−2 is 1.4 × 10−5 photons cm−2 s−1 keV−1 at 100 keV and 1.0 × 10−6 photons cm−2 s−1 keV−1 at 1 MeV.

Ring current ion motion in the disturbed magnetosphere with non-equipotential magnetic field lines

Transport of ring current ions during the main phase of the geomagnetic storm is modeled. Particle trajectories are simulated by the Lorentz equation for dipole and Tsyganenko magnetic field models. The convection electric field is described by variations on the Kp dependent Volland–Stern model structure in the equatorial plane. Out of that plane the electric field is assumed to be the same as in the equatorial plane at least at the low latitudes. This consideration implies the possibility of non-equipotentiality of geomagnetic field lines at least for L⩾6 during strong magnetic storms. In our modeling energetic protons, typically of several tens of keV, start on the night side at L=4 or at L=7, and move initially under gradient magnetospheric drift largely confined to the equatorial plane. However, soon after crossing the noon–night meridian, the protons rather abruptly depart from the equatorial plane and deviate towards high latitude regions. This latter motion is essentially confined to a plane perpendicular to the equator, and it is characterized by finite periodic motion. The calculations indicate a slow violation of the first adiabatic invariant at the point of ion departure from the equatorial region, with slower non-adiabatic variation later along the orbit. The greater the convection electric field, the higher is the energy of the protons participating in this off equatorial divergent flow. The more energetic ions, of hundreds of keV and higher, however, rather continue their magnetic drift around the Earth uninterruptedly and these ions form the symmetric ring current ion population. The numerical calculations described herein explicitly indicate that the perpendicular divergent ion flow can contribute to the morning–evening component of the magnetic field perturbation during magnetic storm conditions, and can result in populating the high latitude and tail regions by the energetic protons.

Antiparticles and light element isotope ions in the earth's magnetosphere

Abstract The ratio of positron/electron fluxes originating in nuclear reactions in the Earths Magnetosphere is considered. It is supposed that positrons as well as electrons are mainly produced in the decay of charged pions π ± → μ ± → e ± born in nuclear collisions of trapped relativistic inner zone protons and of cosmic rays with the residual atmosphere. These positrons and electrons are captured in the magnetosphere and create a positron and electron radiation belt of nuclear origin. The positron/electron trapped magnetospheric fluxes formed with this mechanism from radiation belt proton source are simulated and the resulting computed e + / e − flux ratio ≈4 appears to be in agreement with the recent observations made by the Alpha Magnetic Spectrometer (AMS) ( The AMS collaboration, 1999 ). A >200 MeV positron flux with an intensity about 4 times higher than the electron flux of the same energy was registered in the equatorial region at the altitude of ≈400 km . This ratio is significantly different from the computed ratio ≈1 obtained from the primary cosmic ray source through the same mechanism. As our modeling of nuclear spallation reaction shows, in the same reaction nuclei of isotopes of hydrogen and helium are also produced, which are the source of light element isotope radiation belts of D, T, 3 He and 4 He with a significant excess of 3 He over 4 He fluxes. The AMS instrument, as we have known, also looked at the distribution of helium nuclei and only 3 He was observed, which is one more evidence in favor of the above hypothesis.

X-ray observations in the SAA—Pulsations in electron precipitation accompanied by Pc4 events

Abstract A balloon experiment conducted on December 20, 1994, in the South Atlantic Anomaly (SAA) region, detected events with increases in x-ray flux due to electron precipitation coincident with a mild substorm activity. For the first time in the SAA, the analysis of the x-ray flux associated with the electron precipitation and the geomagnetic H-field component showed simultaneous Pc4 pulsations at periods in the range 95 to 100s. Analysis of a prominent precipitation event of this flight showed direct correlation between the pulsation strength in the x-ray and in the magnetic data and are related to the intensity of the precipitation. While the substorm associated electric fields and currents in the ionosphere can induce amplification of Pc4 pulsations, the x-ray pulsations due to electron precipitation may be related to wave modulated pitch angle scatterings.

FEM code simulation of the magnetospheric proton fluxes

We report a study of the numeric solution to the diffusive transport equation for energetic protons magnetically trapped in the Earths equatorial magnetosphere. The analysis takes into account the pertinent physical processes in this region, including deceleration of protons by Coulomb collisional interactions with free and bound electrons, the charge exchange process, cosmic ray albedo neutron decay source, and electric and magnetic radial diffusion. These results were obtained using the Finite Element Method with magnetic moment and geomagnetic L-shell as free variables. Steady state boundary conditions were imposed at L=1 as zero distribution function and at L=7 with proton distribution function extracted from ATS 6 satellite observations. The FEM-code yields unidirectional proton flux in the energy range of 0.1–1000 MeV at the equatorial top of the geomagnetic lines, and the results are found to be in satisfactorily agreement with the empirical NASA AP-8 model proton flux within the energy range of 0.5–100 MeV. Below 500 keV, the empirical AP-8 model proton fluxes are several orders of magnitude greater than those computed with the FEM-code at L<3. This discrepancy is difficult to explain by uncertainties of boundary spectrum parameters or transport coefficients.

Global scale Earth's upper atmosphere monitoring by SACI-1 micro-satellite

Abstract The first Brazilian scientific micro-satellite, SACI-1, is scheduled to be launched in the 2nd semester of 1999. It will be placed in a sun-synchronous polar orbit at a height of 750 km. Four scientific payloads, airglow photometer, high energy particle telescopes, plasma probes and high sensitive magnetometer, are on board to monitor the Earths upper atmosphere environment. The main scientific goal is focused on upper atmospheric dynamics, ionospheric plasma irregularities, anomalous cosmic ray and field-aligned electric current system in the magnetosphere. International collaboration will be necessary, and this will be a key point in order to maximize the utilization of the data.