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Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a 'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5-100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.

A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-Earth orbit on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a tenfold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g., dark matter particle annihilations.

Phosphenes ("light flashes") have been reported by most astronauts on space missions and by healthy subjects whose eyes were exposed to ionizing radiation in early experiments in particle accelerators. The conditions of occurrence suggested retinal effects of heavy ions. To develop an in vivo animal model, we irradiated the eyes of anesthetized wild-type mice with repeated bursts of 12C ions delivered under controlled conditions in accelerator. 12C ions evoked electrophysiological retinal mass responses and activated the visual system as indicated by responses recorded from the visual cortex. No retinal immunohistological damage was detected. Mice proved a suitable animal model to study radiation-induced phosphenes in vivo and our findings are consistent with an origin of phosphenes in radiation activating the retina.

Most astronauts on Apollo, Skylab, and MIR reported 'flashes of light' occurring in different shapes and apparently moving across the visual field, in the absence of auditory, somatosensory, or olfactory abnormal percepts. A temporal correlation with heavy nuclei or protons has been documented in space and comparable phosphenes were observed by volunteers whose eyes were exposed to accelerated heavy ions at intensities below the threshold for Cerenkov visible radiation. An interaction between heavy ions and the retina was suggested. However, the biophysics of heavy ions or protons action remains undefined, the effects on photoreceptors and neuroretina have not been differentiated, and some direct action on the visual cortex never ruled out. Phosphenes are common in migraine and are known to occur also in response to the electrical stimulation of ganglion cells (in retinas without photoreceptors), optic pathways or visual cortex, with mechanisms that bypass the chemically gated channels. Intrinsic photosensitive ganglion cells exist in the retina of teleost fish and mammals. In the hypothesis of a peculiar sensitivity to subatomic particles of the visual system, phosphenes due to the activation of processes by-passing the photoreceptors would raise questions about human safety in space. The issue is particularly relevant with experiments of increasing duration being now operative in the International Space Station (ISS) and with plans of space travel outside the geomagnetic shield. Research is in progress both in the ISS and on animal models, in the framework of the NASA/ESA actions to improve the astronauts' health in space.

Introduction: It has long been known that many people in space experience sudden phosphenes, or light flashes. Although it is clear that they are related to high-energy particles in the space radiation environment, many details about them are still unknown. In an effort to gain more knowledge about the light flashes, a study was initiated to collect information from people who have recently flown in space., Method: A survey conducted by anonymous questionnaire was performed among astronauts regarding their experience of sudden light flashes in space. In all, 98 surveys were distributed to current NASA and ESA astronauts., Results: Among the 59 respondents, 47 noticed them sometime during spaceflight. Most often they were noted before sleep, and several people even thought the light flashes disturbed their sleep. The light flashes predominantly appear white, have elongated shapes, and most interestingly, often come with a sense of motion. The motion is described as sideways, diagonal, or in-out, but never in the vertical direction., Discussion: Comparisons with earlier studies of light flashes in space and several ground-based studies during the 1970s are made. One interesting observation from this is that it seems that a small fraction of the light flashes is caused by Cherenkov radiation, while the majority is probably caused by some kind of direct interaction with elements in the retina.

ALTEA-MICE will supplement the ALTEA project on astronauts and provide information on the functional visual impairment possibly induced by heavy ions during prolonged operations in microgravity. Goals of ALTEA-MICE are: (1) to investigate the effects of heavy ions on the visual system of normal and mutant mice with retinal defects; (2) to define reliable experimental conditions for space research; and (3) to develop animal models to study the physiological consequences of space travels on humans. Remotely controlled mouse setup, applied electrophysiological recording methods, remote particle monitoring, and experimental procedures were developed and tested. The project has proved feasible under laboratory-controlled conditions comparable in important aspects to those of astronauts' exposure to particle in space. Experiments are performed at the Brookhaven National Laboratories [BNL] (Upton, NY, USA) and the Gesellschaft für Schwerionenforschung mbH [GSI]/Biophysik (Darmstadt, FRG) to identify possible electrophysiological changes and/or activation of protective mechanisms in response to pulsed radiation. Offline data analyses are in progress and observations are still anecdotal. Electrophysiological changes after pulsed radiation are within the limits of spontaneous variability under anesthesia, with only indirect evidence of possible retinal/cortical responses. Immunostaining showed changes (e.g. increased expression of FGF2 protein in the outer nuclear layer) suggesting a retinal stress reaction to high-energy particles of potential relevance in space., (c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.)

The ALTEA project investigates the risks of functional brain damage induced by particle radiation in space. A modular facility (the ALTEA facility) is being implemented and will be operated in the International Space Station (ISS) to record electrophysiological and behavioral descriptors of brain function and to monitor their time dynamics and correlation with particles and space environment. The focus of the program will be on abnormal visual perceptions (often reported as "light flashes" by astronauts) and the impact on retinal and brain visual structures of particle in microgravity conditions. The facility will be made available to the international scientific community for human neurophysiological, electrophysiological and psychophysics experiments, studies on particle fluxes, and dosimetry. A precursor of ALTEA (the 'Alteino' project) helps set the experimental baseline for the ALTEA experiments, while providing novel information on the radiation environment onboard the ISS and on the brain electrophysiology of the astronauts during orbital flights. Alteino was flown to the ISS on the Soyuz TM34 as part of mission Marco Polo. Controlled ground experiments using mice and accelerator beams complete the experimental strategy of ALTEA. We present here the status of progress of the ALTEA project and preliminary results of the Alteino study on brain dynamics, particle fluxes and abnormal visual perceptions., (c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.)

The ALTEA project participates to the quest for increasing the safety of manned space flights. It addresses the problems related to possible functional damage to neural cells and circuits due to particle radiation in space environment. Specifically it aims at studying the functionality of the astronauts' Central Nervous Systems (CNS) during long space flights and relating it to the peculiar environments in space, with a particular focus on the particle flux impinging in the head. The project is a large international and multidisciplinary collaboration. Competences in particle physics, neurophysiology, psychophysiology, electronics, space environment, data analyses will work together to construct the fully integrated vision electrophysiology and particle analyser system which is the core device of the project: an helmet-shaped multi-sensor device that will measure concurrently the dynamics of the functional status of the visual system and passage of each particle through the brain within a pre-determined energy window. ALTEA is scheduled to fly in the International Space Station in late 2002. One part of the multi-sensor device, one of the advanced silicon telescopes, will be launched in the ISS in early 2002 and serve as test for the final device and as discriminating dosimeter for the particle fluences within the ISS., (c2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.)

In this work we present preliminary results of nuclear composition measurements on board space station MIR obtained with SILEYE-2 particle telescope. SILEYE-2 was placed on MIR in 1997 and has been working since then. It consists of an array of 6 active silicon strip detectors which allow nuclear and energetic identification of cosmic rays in the energy range between approximately 30 and 200 MeV/n. The device is attached to an helmet and connected to an eye mask which shields the cosmonaut eyes from light and allow studies of the Light Flashes (LF) phenomenon. In addition to the study of the causes of LF, the device is used to perform real time long term radiation environment monitoring inside the MIR, performing measurements in solar quiet and active days., (c2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.)

In this work we describe the instrument Sileye-3/Alteino, placed on board the International Space Station in April 2002. The instrument is constituted by an Electroencephalograph and a cosmic ray silicon detector. The scientific aims include the investigation of the Light Flash phenomenon, the measurement of the radiation environment and the nuclear abundance inside the ISS and the study of astronaut brain activity in space when subject to cosmic rays.

The phenomenon of light flashes (LF) in eyes for people in space has been investigated onboard Mir. Data on particles hitting the eye have been collected with the SilEye detectors, and correlated with human observations. It is found that a nucleus in the radiation environment of Mir has roughly a 1% probability to cause an LF, whereas the proton probability is almost three orders of magnitude less. As a function of LET, the LF probability increases above 10 keV/micrometer, reaching about 5% at around 50 keV/micrometer., (c 2002 Elsevier Science Ltd. All rights reserved.)

The ALTEA project studies the problems related to possible functional damage to the Central Nervous System (CNS) due to particle radiation in space environment. The project is a large international and multi-disciplinary collaboration. The ALTEA instrumentation is an helmet-shaped multi-sensor device that will measure concurrently the dynamics of the functional status of the visual system and the passage of each particle through the brain within a pre-determined energy window. ALTEA is scheduled to fly in the International Space Station in February 2003. One part of the multi-sensor device, one of the advanced silicon telescopes, will be launched in the ISS in early 2002 and serve as test for the final device and as discriminating dosimeter for the particle fluences within the ISS.

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.

The SilEye experiment aims to study the cause and processes related to the anomalous Light Flashes (LF) perceived by astronauts in orbit and their relation with Cosmic Rays. These observations will be also useful in the study of the long duration manned space flight environment. Two PC-driven silicon detector telescopes have been built and placed aboard Space Station MIR. SilEye-1 was launched in 1995 and provided particles track and LF information; the data gathered indicate a linear dependence of FLF(Hz) ( 4 2) 10(3) 5.3 1.7 10(4) Fpart(Hz) if South Atlantic Anomaly fluxes are not included. Even though higher statistic is required, this is an indication that heavy ion interactions with the eye are the main LF cause. To improve quality and quantity of measurements, a second apparatus, SilEye-2, was placed on MIR in 1997, and started work from August 1998. This instrument provides energetic information, which allows nuclear identification in selected energy ranges; we present preliminary measurements of the radiation field inside MIR performed with SilEye-2 detector in June 1998.