Energetic neutron and gamma-ray spectra under the earth radiation belts according to “SALUTE-7”-“KOSMOS-1686” orbital complex and “CORONAS-i” satellite data

The spectra of neutrons >10 MeV and gamma-rays 1.5–100 MeV under the Earth Radiation Belts, restored from the data, obtained onboard orbital complex “SALUTE-7”-“KOSMOS-1686”, are presented. The spectra shapes are similar to those for albedo neutrons and gamma-rays, but absolute values of their fluxes (0.2 cm⁻² s⁻¹ for neutrons, 0.8 cm⁻² s⁻¹ for gamma-rays at the equator and 1.2 cm⁻² s⁻¹, 1.9 cm⁻² s⁻¹, accordingly, at L=1.9) are several times as large. It is possibly explained by the fact that most of the detected particles were produced by the cosmic ray interactions with the orbital complex matter. Neutron and gamma-ray fluxes obtained from “CORONAS-I” data are near those for albedo particles.     

Statistical properties of SEP event flux declines

The interplanetary space is not a passive medium, which merely constitutes a scene for the propagation of previously accelerated energetic particles, but influences the distribution of particles by changing their energies as well due to interactions with magnetic field inhomogeneities. Such processes manifest themselves in the energy spectra of solar energetic particle (SEP) events. In this paper the fluxes of protons with energies of 4–60 MeV are investigated on the basis of two data sets. Both sets are homogeneous, obtained by the CPME instrument aboard the IMP 8 satellite between 1974 and 2001. The first includes all SEP events where the integral fluxes of >4 MeV protons exceeded 2 particle/cm² s sr. The other set consists of fluxes recorded in differential energy windows between 0.5 and 48 MeV. Important characteristics of SEP events include the rates of decrease of particle flux, which, as well as peak flux time, is an integral feature of the interplanetary medium within a considerable region, surrounding the observation point. The time intervals selected cover the decay phases of SEP events following flares, CMEs and interplanetary shocks of different origin. Only those parts of declines were selected, that could reasonably be described by exponential dependence, irrespective of the gradual/impulsive character of the events. It is shown that the average values of characteristic decay time, τ, and energy spectral index, γ, are all changing with the solar activity phase. Distributions of τ and γ values are obtained in SEPs with and without shocks and during different phases of events: just after peak flux and late after maximum.     

Geminga pulsar observations with gamma-telescope Gamma-1

The Geminga light curve obtained with the “Gamma-1” telescope features two peaks separated by 0.5 ± 0.03 period. The light curve is pronounced for γ-quanta energies higher than 400 MeV. The pulsed flux upper limit (1σ) in the energy interval 50 – 300 MeV is 6·10⁻⁷ cm⁻²sec⁻¹. For energies >300 MeV the pulsed component power law spectrum has an exponent 1.1 _−0.3^+1.1 and an integral flux (1.1±0.3)·10⁻⁶ cm⁻²sec⁻¹.     

Distribution of energetic particles and secondary radiation according to orbital station “MIR” data obtained in 1991

A set of instruments for measuring energetic particle fluxes, containing two neutron detectors under different plexiglas shielding thicknesses, a scintillation detector, measuring energy release >0. I MeV and 0.5 MeV and a Geiger counter were launched onboard OS ‘MIR’. The latitude dependencies of the cosmic ray measurements were obtained and studied. The distributions of primary particle fluxes (protons and electrons) as well as secondary particle fluxes (bremsstrahlung gamma-rays and neutrons) produced in interactions of radiation belt particles with the station materials were obtained. The electron belt, generated during the storm of March 24 1991, is studied.     

A first step towards proton flux forecasting

We present a preliminary version of a potential tool for real time proton flux prediction which provides proton flux profiles and cumulative fluence profiles at 0.5 and 2 MeV of solar energetic particle events, from their onset up to the arrival of the interplanetary shock at the spacecraft position (located at 1 or 0.4 AU). Based on the proton transportation model by Lario et al. [Lario, D., Sanahuja, B., Heras, A.M. Energetic particle events: efficiency of interplanetary shocks as 50 keV E < 100 MeV proton accelerators. Astrophys. J. 509, 415–434, 1998] and the magnetohydrodynamic shock propagation model of Wu et al. [Wu, S.T., Dryer, M., Han, S.M. Non-planar MHD model for solar flare-generated disturbances in the Heliospheric equatorial plane. Sol. Phys. 84, 395–418, 1983], we have generated a database containing “synthetic” profiles of the proton fluxes and cumulative fluences of 384 solar energetic particle events. We are currently validating the applicability of this code for space weather forecasting by comparing the resulting “synthetic” flux profiles with those of several real events.     

Dynamics of the low altitude secondary proton radiation belt

At the interface between the upper atmosphere and the radiation belt region, there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and the main radiation belt and then re-ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64 – 35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the three year period from 21 February 1984 to 26 March 1987 using data obtained with the HEP experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of −1.2 cm⁻² s⁻¹ sr⁻¹ was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically two orders of magnitude). These flux decreases were also long in duration (lasting up to three months). We also registered abrupt flux increases where the magnitude of the proton flux enhancements could reach three orders of magnitude with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.     

Controllable passive detectors for study of the radiation environment in space and the atmosphere

We propose to study the radiation environment on board different flight vehicles: cosmos-type satellites, orbital stations, Space Shuttles and civil (sonic and supersonic) aircraft. These investigations will be carried out with single type of passive detector, namely, nuclear photoemulsions (NPE) with adjustable threshold of particle detection within broad range of linear energy transfer (LET) that is done by means of the technique of selective development of NPE exposed in space.

These investigations will allow one to determine:

• integral spectra of LET of charged particles of cosmic ray (CR) over a wide range from 2.0 to 5×10⁴ MeV/cm in biological tissue;

• differential energy spectra of fast neutrons (1–20 MeV);

• estimation of absorbed and equivalent doses from charged and neutral component CR;

• charge and energy spectra of low energy nuclei (E≤100 MeV) with Z≥2 having in view the extreme hazard radiation to biological objects and microelectronic schemes taken on board inside and outside of these different flight vehicles with exposures from several days to several months.

The investigation of radiation environment on board the airplanes depending on the flight parameters will be conducted using emulsions of different sensitivity without any controlling of threshold sensitivity (Akopova et al., 1996). The proposed detector can be used in the joint experiments on the new International Cosmic Station “Alpha”.     

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.     

Modeling of “gradual” solar energeticparticle events using a stochastic differential equation method

We have modeled “gradual” solar energetic particle events through numerical simulations using a StochasticDifferential Equation (SDE) method. We consider that energetic particle events are roughly divided into two groups: (1) where the shock was driven by coronal mass ejections (CMEs) associated with large solar flares, and (2) where they have no related solar events apart from the CMEs. (The detailed classification of energetic particle events was discussed in our previous paper.) What we call “gradual” solar energetic particle events belong to the former group. Particles with energies greater than 10 MeV are observed within several hours after the occurrence of flares and CMEs in many gradual events. By applying the SDE method coupled with particle splitting to diffusive acceleration, we found that an injection of high energy particles is necessary for early enhancement of such a high-energy proton flux and that it should not be presumed that the solar wind particles act as the seed population.     

Experimental investigations of quasistable radiation belts formed after solar proton events in September–October 1989 and March 1991 based on measurements made by “Liulin” dosimeter-radiometer on board the “MIR” space station

Since 1988 high sensitivity dosimeter-radiometer “Liulin” has been installed on board the MIR space station. Device measured absorbed dose rate and flux of penetrating particles. Results of measurements showed that after powerful solar proton events (SPE) September–October, 1989 and March, 1991 additional quasistable radiation belts were formed in the near earth space within the interval L=1.8−3.0. These “new” belts were observed as an additional maximums in flux (and sometimes dose) channels when crossing the SAA region. “New” belts were quasi stable and existed at least several months, decaying slightly after SPE. Dose to flux ratio analysis showed that major components of these belts were energetic electrons and protons arising in connection with preceding SPEs.     

Energy content of accelerated electrons and ions in intense solar flares

The energy content of nonthermal particles in solar flares is shared between accelerated electrons and ions. It isimportant for understanding the particle acceleration mechanism in solar flares. Yohkoh observed a few intense flares which produced both strong gamma-ray lines and electron bremsstrahlung continuum. We analyze energy spectra of X-class solar flares on October 27, 1991(X6.1), November 6, 1997 (X9.4), July 14, 2000 (X5.7) and November 24, 2000 (X2.3). The accelerated electron and proton spectra are derived from a spectral analysis of their high-energy photon emission and the energy contents in >1 MeV electrons and >10 MeV protons are estimated to be 6×l0²⁸ – 4×10³⁰ and 2×10²⁸ – 5×10²⁹ erg, respectively. We study the flare to flare variation in the energy content of >1 MeV electrons and >10 MeV protons for the four Yohkoh gamma-ray flares. Ratios of >1 MeV electron energy content to >10 MeV proton energy content are roughly within an order of magnitude.     

Space radiation quality factor investigations with “NAUSICAA”-device on board the “MIR” space station

The estimation of radiation quality factor in space flights is a serious problem of space dosimetry. The solution of this problem is based on LET-spectra measurements. The “NAUSICAA”-device installed on the “MIR” station has a detector with a large geometric factor, that gives the possibility of measuring LET-spectra with sufficient statistic in relatively short time interval and hence the corresponding Q. LET-spectra are accumulated through 24 hour periods and equivalent dose (H), absorbed dose (D), quality factor and flux (F) are measured every 10 minutes. The obtained data permit the estimate of the diurnal Q and Q in South Atlantic Anomaly. These values vary in the range of 1.4 – 2.2. The analysis of these values including their comparison with the calculated results is given in this paper.     

Energetic particle fluxes data base of “CORONAS-I” satellite observations

The data base DB SCR uses data obtained by the SCR instrument package on the CORONAS-I satellite. DB SCR contains information about fluxes of relativistic electrons (0.5–124 MeV), protons (1–300 MeV), nuclei (1–19 MeV/nucl) and γ-radiation (0.1–7 MeV) in the low altitude region (500 km). The time resolution of the data is 2.5 s. Magnetic field parameters (B, magnetic latitude and longitude), L-shell and local times (LT and MLT) are included in DB SCR. Since all parameters are equivalents it is possible to perform the multidimensional analysis for any set of DB SCR parameters. The additional DB SCR software packages may be used to develop different semi-empirical models.     

Modeling of artificial plasma “bubble” in ionosphere

Results of a combination of radio-crossing and in situ measurements of plasma density in an artificial plasma “bubble” in the ionosphere are presented. Shaped — charge barium injection was made at short distance (≤50 m) to plasma diagnostics on the rocket. After injection the rocket passed through expanding plasma shell. Plasma density depletion inside was more than one order and plasma enhancements on the boundary about 3–5 times that of background. When the rocket passed the shell and went away by 2.1 km an abrupt drop of telemetry signal level (≤ 65 dB) was registered though plasma density was not more than 3×10³sm⁻³. An estimation of high frequency signal refraction on the plasma shell is in good accordance with refraction data of geostationary satellite signals on equatorial bubbles.     

Investigation of magnetospheric processes with the use of a source of strong magnetic field in the ionosphere

More than 20 years ago V.P. Shabansky suggested that the magnetic system installed aboard the satellite, could be used as a physical instrument for studying the processes which occur in the near Earth space. The corresponding space scales of an artificial “magnetosphere”—“magnisphere”—are 10 m in the experiment with relatively small magnets in the ionosphere and 100 m in the solar wind. The corresponding similarity criteria are estimated. The possible scheme of the experiment with a superconducting magnet (magnetic moment 10⁵ A · m²) installed aboard the satellite is considered. The experimental complex includes a number of systems for measuring the fluxes of charged particles in a wide energy range, DC electric and magnetic fields, the electromagnetic fields in different frequency bands (from X-rays to radio). The scientific objectives are discussed in detail.     

Comptel measurements of the omnidirectional high-energy neutron flux in near-earth orbit

On four occasions, twice in 1991 (near solar maximum) and twice in 1994 (near solar minimum), one COMPTEL D1 detector module was used as an omnidirectional detector to measure the high-energy (>12.8 MeV) neutron flux near an altitude of 450 km. The Dl modules are cylindrical, with radius 13.8 cm and depth 8 cm, and are filled with liquid scintillator (NE213A). The combined flux measurements can be fit reasonably well by a product of the Mt. Washington neutron monitor rate, a linear function in the spacecraft geocenter zenith angle, and an exponential function of the vertical geomagnetic cutoff rigidity in which the coefficient of the rigidity is a linear function of the neutron monitor rate. When pointed at the nadir, the flux is consistent with that expected from the atmospheric neutron albedo alone. When pointed at the zenith the flux is reduced by a factor of about 0.54. Thus the production of secondary neutrons in the massive (16000 kg) Compton Gamma-Ray Observatory spacecraft is negligible. Rather, the mass of the spacecraft provides shielding from the earth albedo.     

Diurnal variations of ion flux intensity on a synchronous orbit

The data from the synchronous-orbit satellites of the Gorizont series are used to study the dependences of the ion flux variation amplitudes in the synchronous altitude region (the diurnal behaviour) on particle energies and on the form and rigidity of the particle energy spectrum. The proton fluxes were measured in the energy range E 60–120 keV, and the [N,0]²⁺ and [C,N,0]⁴⁺ ion fluxes in the energy range E 60–70 keV/e.

The ratio of the diurnal variation amplitudes of the studied ions is shown to correspond to the similarity of their energy spectra in the E/Q representation. The magnetically-quiet time gradient of the distribution function F(μ,J,L) in the synchronous-orbit region is shown to be (∂F/∂L)=0 for the H⁺ and [N,0]²⁺ ions and (∂F/∂L) > 0 for the [C,N,0]⁴⁺ ions (at the values of μ corresponding to the examined energy ranges). During magnetically-disturbed periods the inner boundary of the (∂F/∂L)=0 region shifts to lower L and (∂ F/∂L) = O in the synchronous altitude region must be also for the [C,N,O]⁴⁺ ions.     

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 Earth's 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.     

Different space weather effects in anomalies of the high and low orbital satellites

Preliminary results of the EU INTAS Project 00810, which aims to improve the methods of safeguarding satellites in the Earth’s magnetosphere from the negative effects of the space environment, are presented. Anomaly data from the “Kosmos” series satellites in the period 1971–1999 are combined in one database, together with similar information on other spacecraft. This database contains, beyond the anomaly information, various characteristics of the space weather: geomagnetic activity indices (Ap, AE and Dst), fluxes and fluences of electrons and protons at different energies, high energy cosmic ray variations and other solar, interplanetary and solar wind data. A comparative analysis of the distribution of each of these parameters relative to satellite anomalies was carried out for the total number of anomalies (about 6000 events), and separately for high (5000 events) and low (about 800 events) altitude orbit satellites. No relation was found between low and high altitude satellite anomalies. Daily numbers of satellite anomalies, averaged by a superposed epoch method around sudden storm commencements and proton event onsets for high (>1500 km) and low (<1500 km) altitude orbits revealed a big difference in a behavior. Satellites were divided on several groups according to the orbital characteristics (altitude and inclination). The relation of satellite anomalies to the environmental parameters was found to be different for various orbits that should be taken into account under developing of the anomaly frequency models.     

Results of cosmic radiation dose field measurements aboard the “Salyut-6” orbital station

During the 3rd main expedition on board the “Salyut-6” orbital station in 1979 the integral characteristics of cosmic radiation were measured in various positions inside the manned modules (experiment “Integral”). Measurements were performed with thermoluminescent dosimeters, photographic films and solid state plastic detectors supplied for the experiment by specialists of the USSR, Bulgaria, Hungary, GDR and Romania. The dose gradient inside the manned modules of the station amounted to 70 % for long intervals of time. During the experimental period the dose rate inside the station was 15 to 30 mrad per day. The mean flux of particles with z 6 and LET 200 keV/μm was found to be 0.22 cm⁻² day⁻¹.