The radiation risk radiometer-dosimeter (R3D)-R2 instrument was situated outside the Russian segment of the International Space Station (ISS) and inside the ESA EXPOSE-R2 facility in the period November 2014 - January 2016. We detected a penetration of the relativistic electrons below L=2.5 in the recovery phase of the magnetic storm after 18 March 2015. In the period March 18-28 2015, the lower boundary of L=1.8 was reached. The relativistic electrons at low L disappeared on March 28, 2015. The magnetic storm on 25th of June 2015 again generated relativistic electrons' fluxes from the Outer Radiation Belt (ORB) at the L values below 2.5. The ORB enhancement on July 4 2015 emphasized them again. In this specific case, the minimal L values reached L=1.6. Almost all disturbances in the Disturbance Storm Time (Dst) index from July 11th, 2015 until January 1st, 2016 generated new portions of relativistic electrons in the L-values below 2.5. They existed for few days and disappeared until the next Dst disturbance.

The paper presents the space radiation extreme events observed with Liulin type instruments. The following events, characterized by fast increase of the dose rate were classified as extreme: solar energetic particles (SEP) events, relativistic electron enhancements (REE) and burst type REE in the outer radiation belt (ORB). We compare the dose rates data from 4 SEP events in 1989, 2012, 2015 and 2022, 2 REE events in 2010 and 2015 and 1 burst type REE in 2015. All data were selected to cover periods of 6 hours and 30 minutes that are the average continuation of the extra vehicle activities (EVA) on the ISS. The time intervals were chosen to coincide with the maximum of the observed dose rates during different events. Only the REE1 event data was chosen simultaneously with real EVA-1 of STS-131 astronauts on April 9 2010. The dose rates data in the inner and the outer radiation belt maxima measured by RADOM instrument in 2008 at about 3,000 and at about 20,000 km altitude, respectively, are compared with the extreme events data.

Ionizing radiation is recognized to be one of the main health concerns for humans in the space radiation environment. Estimation of space radiation effects on health requires the accurate knowledge of the accumulated absorbed dose, which depends on the global space radiation distribution, solar cycle and local shielding generated by the 3D mass distribution of the space vehicle. This paper presents an overview of the spectrometer-dosimeters of the Liulin type, which were developed in the late 1980s and have been in use since then. Two major measurement systems have been developed by our team. The first one is based on one silicon detector and is known as a Liulin-type deposited energy spectrometer (DES) (Dachev et al., 2002, 2003), while the second one is a dosimetric telescope (DT) with two or three silicon detectors. The Liulin-type instruments were calibrated using a number of radioactive sources and particle accelerators. The main results of the calibrations are presented in the paper. In the last section of the paper some of the most significant scientific results obtained in space and on aircraft, balloon and rocket flights since 1989 are presented.

Based on Polar satellite data, the authors have studied the auroral disturbances that arose during the passage by the Earth of compressed plasma regions formed in front of high-speed solar wind streams (the CIR region) and in front of magnetic clouds (the Sheath region). The aurorae observed by the Polar satellite possessed basic signatures of a substorm: a localized onset and expansion toward the pole and westward and eastward. However, in these cases they had a very large size in longitude and latitude and occupied a very large area. All disturbances observed by the Polar satellite during the Sheath and CIR regions of the solar wind in December of 1996, in 1997–1998, and in 2000 were analyzed. Eight events during disturbance development in the ionosphere, when the Geotail satellite was located in the plasma sheet of the magnetospheric tail, were selected. It is shown that in all selected cases some typical signatures of substorm development in the magnetospheric tail were observed, namely: (1) fast plasma flows (flow reversal, i.e., from tailwards to Earthwards) and (2) a sharp decrease of the total pressure, which followed an interval of total pressure increase. One can draw the conclusion that in the CIR and Sheath regions with a high solar wind density, substorm disturbances of a specific type are observed, with large latitudinal and longitudinal size (sometimes occupying the entire polar cap).

We present and discuss observations of a region in the high-latitude near-Earth outer magnetosphere when over a distance of 9RE – from GSM [0.83RE, 1.6RE, 8.5RE] to [−0.957RE, 10.175RE, 12.738RE] – Interball-1 observed multiple alternative changes in plasma characteristics: hot plasma sheet population is replaced by a region of mixed magnetosheath – plasma sheet population with the presence of ionospheric ions and vice versa. In the ‘mixed’ region, both ion populations were nearly stagnant, their velocity rarely exceeded 50km/s and plasma-sheet electrons were absent. Most of the time interplanetary magnetic field (IMF) clock angle was less than 90°, rotating to more than 270° at the end of the interval, IMF Bx being positive and dominating. A flux transfer event was registered near the magnetopause. Plasma characteristics suggest that observations took place at the high-latitude boundary of the near-Earth plasma sheet on closed field lines. We suggest that the mixed regions are formed on filed lines first reconnected to the magnetosheath magnetic field, then draped and convected duskward and tailward and secondary reconnected and closed.

Measurements on board the MIR space station by the Bulgarian-Russian dosimeter LIULIN have been used to study the solar cycle variations of the radiation environment. The fixed locations of the instrument in the MIR manned compartment behind 6-15 g/cm(2) of shielding have given homogeneous series of particle fluxes and doses measurements to be collected during the declining phase of 22nd solar cycle between September 1989 and April 1994. During the declining phase of 22nd solar cycle the GCR (Galactic Cosmic Rays) flux observed at L>4 (where L is the McIlwain parameter) has enhanced from 0.6-0.7 cm(-2) s(-1) up to 1.4-1.6 cm-2 s(-1). The long-term observations of the trapped radiation can be summarized as follows: the main maximum of the flux and dose rate is located at the southeast side of the geomagnetic field minimum of South Atlantic Anomaly (SAA) at L = 1.3-1.4. Protons depositing few (nGy cm(2))/particle in the detector predominantly populate this region. At practically the same spatial location and for similar conditions the dose rate rises up from 480 to 1470 mu Gy/h dose in silicon in the 1990-1994 time interval, during the declining phase of the solar cycle. On the other hand the flux rises from 35 up to 115 cm(-2) s(-1) for the same period of time. A power law dependence was extracted which predicts that when the total neutral density at the altitude of the station decreases from 8 x 10(-15) to 6 x 10(-16) g/cm(3) the dose increase from about 200 mu Gy/h up to 1200 mu Gy/h. At the same time the flux increase from about 30 cm(-2) s(-1) up to 120 cm(-2) s(-1). The AP8 model predictions give only 5.8% increase of the flux for the same conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.

Measurements on board the Mir space station have been used to study the dose rate and the particle flux distribution in the inner magnetosphere. The measurements have been performed with the Bulgarian-Russian dosimeter-radiometer Liulin. The paper concentrates on the dynamics of the observed "new" and "second" maxima which were created after Solar Proton Events (SPE) in the 1989-1994 time. The "second" belt was first observed after the SPE on October 20, 1989, and the last observation was after the SPE on February 20, 1994. The creation of the "new" belt is a unique phenomena seen in the Liulin data set after the SPE on March 23, 1991 and relates to the magnetic storm on March 24. The new belt fully disappears in the middle of 1993.

Tissue equivalent and Solid State Detector (SSD) measurements of the radiation environment inside the Mir space station were performed during the Antares mission in 1992 and long period after it. Interesting results about radiation measurements show (a) the South Atlantic Anomaly (SAA) crossing, (b) the increase of radiation near the poles and (c) the effects of solar eruptions (the most important one occurring in early November 1992). These data give also information about the dose and the quality factor of the radiation received by the cosmonauts during different missions.

Since 1988 high sensitivity semiconductor dosimeter-radiometer "Liulin" worked on board of MIR space station. Device measured the absorbed dose rate and the flux of penetrating particles. The analysis of the data shows the following new results: In October 1989 and after March 24, 1991, two additional stable maximums in flux channel were observed in the southern-eastern part of South Atlantic Anomaly (SAA). These two maximums existed at least several months and seem to be due to trapped high energy electron and proton fluxes. In April 1991 additional maximums were localized in the following geographical coordinates regions: latitude = (-35 degrees)-(-50 degrees) longitude = 332 degrees-l6 degrees and lat.(-46 degrees)-(-52 degrees) long. 360 degrees-60 degrees. Additional maximums diffusion occurs inside radiation belt. Appearance of these maximums seems to be closely connected with preceding powerful solar proton events and associated geomagnetic dynamics of new belt disturbances. Alter the series of solar proton events in June 1991 we observed significant enhancement of this new radiation belt formation. To achieve sufficient accuracy of dose rate predictions in low Earth orbits the structure and dynamics of new belt should be carefully analyzed to be included in a new environment model. From the inter comparison of the data from "Liulin" and French developed tissue equivalent LET spectrometer NAUSICAA in the time period August-November 1992 we come to the following conclusions: Mainly there is good agreement between both data sets for absorbed dose in the region of SAA; Different situation of the instruments on the station can explain the cases when differences up to 2 times are observed; At high latitudes usually the tissue equivalent absorbed dose observations are 2 times larger than "Liulin" doses.

Radiation risk on a future long-duration manned space mission appears to be one of the basic factors in planning and designing the mission. Since 1988 different active dosimetric investigations has been performed on board the MIR space station by the Bulgarian-Russian dosimeter-radiometer LIULIN and French tissue-equivalent proportional counters CIRCE and NAUSICAA. A joint French-Bulgarian-Russian dosimetry experiment and the dosimetry-radiometry system RADIUS-MD have been developed for the future MARS-96 mission. On the base of the results and experience of these investigations a conception for a new radiation dose control system for the future orbital stations,lunar bases and interplanetary space ships is proposed. The proposed system which consists of different instruments will allow personal radiation control for crew members, radiation monitoring inside and outside each habitat, analysis and forecasting of the situation and will suggest procedures to minimize the radiation risk.

Using data from dosimetry-radiometry system "Liulin" on board of "Mir"-space station the particle flux and doserate during September-October, 1989 has been studied. The orbit of the station was 379 km perigee, 410 km apogee and 51.6 degrees inclination. Special attention has been paid to the flux and doserate changes inside the station after intensive solar proton events (SPE) on 29 of September, 1989. The comparison between the doses before and after the solar flares shows increase of the calculated mean dose per day by factor of 10 to 200. During the SPE on the 29 of September the additional dose was 310 mrad. The results of the experiment are compared with the data for the solar proton fluxes obtained on the GOES-7 satellite.

An experiment involving active detection of space radiation was carried out in the Space Research Institute (SRI) of Bulgarian Academy of Sciences, in preparation of the flight of the second Bulgarian cosmonaut. The radiations that would be encountered on the flight were modelled including solar and galactic cosmic rays and the particle radiation in the Earth's radiation belts. The dose rate was calculated for these different radiations behind the shielding of the space station. The variations in dose rates over the period of the flight were calculated and compared with measurements made during the orbit of the Mir Space Station. The calculated and measured dose rates agreed within 15-35%.

A dosimetry-radiometry system has been developed at the Space Research Institute of the Bulgarian Academy of Science to measure the fluxes and dose rates on the flight of the second Bulgarian cosmonaut. The dosimetry system is designed for monitoring the different space radiations, such as solar cosmic rays, galactic cosmic rays and trapped particles in the earth radiation belts. The system consists of a battery operated small size detector unit and a "read-write" and telemetry microcomputer unit. The sensitivity of the instrument (3.67 x 10(-8) rad/pulse) permits high resolution measurements of the flux and dose rate along the track of the Mir space station. We report our initial results for the period of the flight between the 7th and 17th June 1988.