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Home , Cosmic ray, Radiometric calibration

INTERNATIONAL SPACE SCIENCE INSTITUTE No 11, November 2003

Published by the Association Pro ISSI

Cosmic Rays Editorial

In a deep cave some people have fire up in the background Impressum been caught since their early child- casting additional shadows from hood. They are chained down in the unknown objects onto the wall a way that they even cannot turn of our cave. This second fire are their heads around. They can only the cosmic ray that reach SPATIUM see shadows on the walls of their us from the depth of the . Published bythe inconvenient shelter, which are Apart from the electromagnetic Association Pro ISSI cast by a fire blazing in the back- spectrum,where astronomical ob- twice a year ground. The shadows stem from servations have taken place since objects of unknown form and ma- mankind started looking at the terial carried by some servants. stars, the cosmic rays are inde- INTERNATIONAL SPACE During the years they have given pendent and complementary mes- SCIENCE the shadows names and they inter- sengers from violent processes in INSTITUTE pret them as the real it y. the universe. That is why cosmic Association Pro ISSI rays are such a fascinating topic, Hallerstrasse 6,CH-3012 Bern One of these cave dwellers is able which is still in our days rich of Phone +41 (0)31 631 48 96 to shake-off his chains and leave mysteries. Fax +41 (0)31 631 48 97 the cave. His eyes get dazzled by the of the at first, but This issue of Spatium is a short President after a while he becomes able to summary of articles edited by the Prof.Heinrich Leutwyler, see all the wonderful objects that International Space Science Insti- University of Bern cast the shadows. tute in several of its fascinating Publisher publications as outlined on the Dr.Hansjörg Schlaepfer, And again he names them all and back-cover. We are convinced that legenda schläpfer wort & bild, calls them the reality.But,upon his our readers will enjoy these in- CH-8185 Winkel return to his pitiable colleagues, sights into the mysteries of cosmic Layout he is far from being welcome: his rays. Marcel Künzi,marketing · kom- view of reality has been revolu- munikation, CH-8483 Kollbrunn tionised by his stunning experi- Printing ence outside and has nothing more Druckerei Peter + Co dpc to do with the prisoners’ view of Hansjörg Schlaepfer CH-8037 Zurich reality. Zürich,October 2003

So far Plato’s cave parable. It tells us about the relation between our ideas and the objects behind them. We are in a similar situation like the cave dwellers when it comes to exploring the universe. What we Front Cover: The remnants of can see with the best of our sophis- the N49 in the Large ticated technical means are noth- Magellanic Cloud, a source of cos- ing more than shadows of the real- mic ray particles (credit: Hubble ity out there and,like the prisoners Heritage Team [STScI/AURA], in the cave, we have to content Y. Chu [UIUC] et al., NASA).The ourselves with the images on the lower part shows data from the wall. But – in contrast to Plato’s Climax Monitor, see parable – an unexpected second Figure 6.

SPATIUM 11 2 Cosmic Rays

The Early Years 1 that the came from the the radiation actually increased. ,theyexpected to find a rapid Intrigued by the conf licting re- decrease in the radiation as they sults obtained by Wulf and his col- moved away from the surface. leagues a young Austrian nuclear They did not find the decrease physicist, Viktor Hess, obtained Cosmic ray studies now span an they expected and in some cases support from the Austrian Imperi- epoch of almost exactly 100 years. there seemed to be evidence that al Academy of Sciences and the At the close of the nineteenth century, scientists using gold-leaf to study the conduc- tivity of gases discovered that no how carefully they isolated their electroscopes from possible sources of radiation they still dis- charged at a slow rate. In 1901 two groups investigated this phenome- non, J. Elster and H.Geitel in Ger- many, and C.T.R.Wilson in Eng- land. Both groups concluded that some unknown source of ionising radiation existed.Wilson even sug- gested that the ionisation might be “due to radiation from sources outside our , possibly radiation like rays or like cathode rays, but of enormously greater penetrating power.” A year later two groups in Canada, Ernst Rutherford and H. Lester Cooke at McGill University, and J. C. McLennan and E.F.Burton, at the University of Toronto showed that 5 cm of lead reduced this mysteri- ous radiation by 30%. An addi- tional 5 tonnes of pig lead failed to reduce the radiation further.

In 1907 Father Theodore Wulf of the Institute of Physics of Ignatus College in Valkenburg, Holland, invented a new .Wulf’s electroscope enabled scientists to carry the search for the origin of the mysterious radiation out of the laboratory, into the mountains, atop the Eiffel Tower and, ulti- Figure 1 mately,aloft in balloons.Assuming Viktor Hess after a balloon landing in 1912

1 ) See reference list at the end of this article SPATIUM 11 3 Royal Austrian Aero Club to con- In a series of balloon f lights in the mation and cosmic ray generation. duct a series of balloon f lights to late 1930s, M. Schein and his co- Fermi in 1949 regarded cosmic study the radiation. Hess obtained workers used tele- rays as a gas of relativistic charged a license to pilot balloons in order scopes interspersed with lead ab- particles moving in interstellar to reduce the size of the crew and sorbers to determine that most of magnetic fields. His paper laid the thereby increase the altitude to the primary particles were not groundwork for the modern theo- which he could carry his electro- , and hence were ry of cosmic ray acceleration and scopes. On 12 , using most plausibly the dominant con- transport. The close link between the -filled Böhmen, Hess stituent. radio and cosmic rays reached an altitude of 5,350 m. was conclusively established at the Carrying two hermetically sealed In 1948 research groups from the time of the Paris Symposium on chambers, he found that the and the Radioastronomy in 1958. This ionisation rate initially decreased, University of Rochester flew nu- marked the birth of cosmic ray but that at about 1500 m it began clear emulsions and cloud cham- . The basic model of to rise, until at 5,000 m it was over bers on the same high-altitude the origin of galactic cosmic rays twice the surface rate. Hess con- Skyhook balloon f light and dis- was developed by Ginzburg and cluded that the results of these ob- covered the presence of heavy nu- Syrovatskii in 1964. servations can best be explained clei in the primary cosmic radia- by the assumption that radiation of tion. Further studies by many a veryhigh penetrating power other groups soon established that from above enters into the atmos- essentially all of the elements be- phere and partially causes, even at tween H and Fe were present in the lower atmospheric layers, ioni- the cosmic radiation near the top sation in the enclosed instruments. of the atmosphere – including an overabundance of the light ele- On a voyage from Amsterdam to ments Li, Be, and B. Then in 1950 Java, Clay observed in 1927 a vari- it was found that a significant frac- ation in cosmic ray intensity with tion of the cosmic radio emission with a lower intensity was – indi- near the equator, thus establishing cating the presence of highly rela- that before entering the Earth’s tivistic electrons throughout our magnetic field, the bulk of the including some discrete primary cosmic rays were charged sources as well as extragalactic particles. In 1930 sources. However, because of their showed that if the cosmic rays small abundance (1% of the inten- were predominantly of one charge sity of cosmic ray nuclei) electrons or the other there should be an were not directly detected in the east–west effect. In the spring primary cosmic radiation until of 1933 two American groups, 1962. These discoveries made it Thomas H. Johnson of the Bartol possible to begin constructing re- Research Foundation and Luis alistic models of the origin and Alvarez and Arthur H. Compton interstellar transport of galactic of the , cosmic rays. simultaneously and independently measured the east–west effect. It As early as 1934, Baade and showed the cosmic radiation to be Zwicky linked the appearance of predominantly positively charged. supernovae with neutron star for-

SPATIUM 11 4 The Low- Anom- Galactic U-High T Energy alous of Cosmic Rays Turnup T–2.6 sec st MeV)] 2

All Particles

0 Oxygen Cosmic rays consist of electrons, and atomic nuclei, which have been accelerated to very high Log [dj /dT (flux/m speed. Their elemental composi- tion provides information on chemical fractionation in the source region as well as some in- sight into the nature of this region and of the propagation of cosmic –10 rays in interstellar space. Cosmic ray probe more deeply the nature of the source region and Knee the timescales of the injection and initial acceleration. Radioac- tive isotopes such as 10 Be, 26Al,and 36Cl reveal the temporal history of cosmic rays in the disk and halo re- –20 gions. The variation of the charge and mass composition with energy –their energyspectra –can be re- lated to the acceleration process and to transport in the Galaxy.When improved measure- ments are available at ultrahigh energies it should be possible to determine whether these particles –30 are of galactic or extragalactic ori- 5101520 Log[T(eV)] gin. At the highest energies the Figure 2 cosmic ray arrival direction may Energy spectrum of cosmic rays measured at the Earth. also indicate the approximate di- rection of the most powerful At energies below a few GeV the are partially ionised interstellar sources. inf luence of solar modulation be- accelerated at the comes important with significant termination shock. Near 10 MeV The most remarkable feature of temporal variations at 1AU related there is a highly variable turn-up cosmic rays is their energy spec- to the 11- and 22-year solar and in the ion spectrum produced by trum (Figure 2).From 109 eV to heliomagnetic cycles. At energies particles of solar/interplanetary 1020 eV these spectra, over some of less than 40 MeV the oxygen origin although the acceleration 10 orders of magnitude variation spectra in Figure 2 show the pres- up to energies more than tens of in intensity show a relatively fea- ence of so-called anomalous cos- GeV was registered in some solar tureless power-law distribution. mic rays as discussed later. Those flareevents.

SPATIUM 11 5 The experimental limitation im- tensity at energies greater than 3 x pernova shocks becomes difficult. posed by the size of current detec- 10 20 eV.Above 1012 eV the compo- It is generally assumed that the tor systems does not allow meas- sition is not well known; this is the cosmic ray “knee” at 1015 eV may urements of the cosmic-ray in- region where acceleration by su- ref lect a gradual transition in the composition to particles of in- 106 creasingly higher charge. At ener- gies 1019 eV questions of galactic He magnetic confinement lead to the 105 assumption that these particles are of extragalactic origin.At energies 19

Relative Abundance above 4 x 10 eV even protons should experience significant de- 4 10 celeration by the 3 K blackbody radiation (the Greisen–Zatsepin– O Kuzmjn effect). At energies of C 12 14 103 Cosmic Rays 10 –10 eV there are small of 0.1%, which are Ne thought to be due to local effects. Mg Si At this time there are no meaning- 102 N Fe S ful anisotropies observed at higher energies except the ultra-high en- A Ca ergies 1018 eV. Ti Cr 10 Ni Al Cosmic ray particles are mostly Na hydrogen (87%), and some

01 (12%) with diminishing amounts Mn of ,oxygen,etc and of heav- P Cl ier elements (Figure 3). All are fully K Co ionised. Electrons account for ap- 10–1 prox. 1% of the cosmic rays. With F a few exceptions, their chemical composition corresponds to the el- V 10–2 emental abundances in our solar system. The exceptions (H, He are

Sc under-abundant, Li, Be, B are over- Li B abundant) yield important infor- 10–3 mation about the matter traversed by cosmic rays. Isotopic abun- dances of galactic cosmic rays are 10–4 Be very similar to the isotopic compo- sition of the interstellar gas. An important exception is the larger 22 20 10–5 ratio of Ne/ Ne. The isotopic 246810121416 18 20 22 24 26 28 composition provides key infor- Neutrons mation about the origin, acceler- Figure 3 The relative abundance of He to Ni in cosmic rays (red line),and in the Solar System ation and transport mechanisms (blue line). of cosmic rays in our galaxy.

SPATIUM 11 6 The Origins galactic magnetic field; they have Anomalous Cosmic Rays been accelerated to nearly the of Cosmic Rays , probably by super- The discovery of a totally new novae explosions. A supernova is a component of nuclear radiation in star of several times the mass of the – now called an- our Sun, that has run out of the omalous cosmic rays (ACR) –has “nuclear fuel” of light elements, greatly expanded our understand- Cosmic ray particles arrive evenly especially hydrogen, needed to ing of pickup ,particle acceler- from all directions of the sky, but keep it shining.Its nuclear burning ation and our knowledge of neu- this does not necessarily mean that gradually converts the light ele- tral atomic abundances in the local their sources are evenly spread ments into heavier ones, and the . The story be- around us. More likely, they are heat it produces keeps it from col- gins with measurements constantly def lected and scattered lapsing under its own immense at 1 AU of the and helium by magnetic fields in the galaxy, weight. When the star can no spectra as the heliospheric modu- until any trace of their original longer produce nuclear heat, it lation of galactic cosmic rays de- motion is lost. suddenly collapses to a small vol- clined towards solar minimum ume, releasing enormous amounts condition in 1971–1972. A spec- There are three categories of cos- of gravitational energy. Much of trum of helium nuclei with ener- mic ray particles according to their that energy is spent in a grand gies below 100 MeV per nucle- energy content: explosion as shown in Figure 4, on appeared which could not be accounted for by either the solar modulation of helium of galactic Energy level [eV] Cosmic ray type; origin and acceleration origin or its isotopic composition. mechanism It soon became clear that this an- omalous helium component was Below the knee Galactic cosmic rays I (GCR I); E 3 10 15 eV also accompanied by anomalous galactic origin, diffuse shock and oxygen. More recent- acceleration in the shock waves of ly, there has appeared evidence for supernova remnants (SNR) C, Ne, Ar and H. Garcia-Munoz and collaborators showed that the Above the“knee” Galactic cosmic rays II (GCR II); anomalous component of He is 15 18 3 10 E 10 eV 4 galactic origin, second stage modulated He with no acceleration of GCR I by shocks 3He and, therefore, must have a “local” origin. Fisk, Koslovsky Above Extragalactic cosmic rays; and Ramaty proposed the most E 10 18 eV successful model to account for acceleration in extragalactic the anomalous components. As shocks? sketched in Figure 5, interstellar neutral atoms with high ionisation Galactic cosmic rays come from out- blowing the star’s outer layers potentials enter the heliosphere, side the solar system but generally out to space and creating thereby undergo single ionisation by solar from within our . They a huge expanding shock front. It ultra-violet radiation in the inner have probably been accelerated is this shock front which is be- solar system and–by charged parti- within the past few million years, lieved to accelerate the cosmic cle pickup in the solar wind – are and have travelled many times ray particles to nearly the speed carried outward to the solar wind across the galaxy, trapped by the of light. termination shock, where they are

SPATIUM 11 7 and hard X-rays, gamma rays and neutrons. On a long-term aver- age, cosmic ray ground level in- tensity enhancements due to rela- tivistic solar particles occur about once per year, while events with lower-energy particles are much more frequent. There is a distinct dependence on solar sunspot ac- tivity, with particle events being more frequent and having a larger f luence from around two years be- fore to about four years after a solar maximum. However, there is evidence that the most energetic events do not occur right in the maximum phase of solar activity.

Figure 4 In the current paradigm, solar en- This artist’s illustration shows a supernova explosion (at left) and a conical sec- ergetic particle events are general- tion of the expanding cloud of ejected material. Atoms are torn from the brownish ly classified as “impulsive events" bands of “dust" material by shock waves (represented by orange rings). The shocks in or “gradual events". Impulsive the expanding blast wave then accelerate the atoms to near light speeds firing them into interstellar space like cosmic bullets. (Credit: M.DeBord, R. Ramaty and B.Ko- events are characterized by the zlovsky [GSFC],R.Lingenfelter [UCSD],NASA) presence of type III radio bursts, that are radio emissions generated by streams of energetic electrons accelerated. Some of these acceler- vided bydirect observations of the injected from the Sun into inter- ated nuclei – now possessing high energetic particles in interplane- planetary space. Furthermore high magnetic rigidities since they are tary space or at Earth, and by the energy protons, ions, and electrons singly charged – propagate inward detection of various neutral radia- are emitted by the Sun and acceler- to undergo solar modulation, along tions produced in interactions of ated in the deep corona in regions with the galactic low energy cos- the accelerated particles with the with temperatures 107 K. In mic ray nuclei. solar atmosphere and the solar gradual events, the solar cosmic magnetic field. Solar protons, ions rays are produced by shock acceler- and electrons of energies extend- ation in the high corona and in in- ing into the 100 MeV region are terplanetary space near the Sun. Solar Cosmic Rays directly measured by space borne An expanded classification of instruments. Solar protons with solar cosmic ray events includes Most of the time the cosmic rays energies above 500 MeV/nucle- also the high-energy solar parti- arriving at Earth are of galactic or on become increasingly rare and cles, which cause nuclear reactions even extragalactic origin. Howev- therefore must be detected by con- in the solar atmosphere leading to er, from time to time, the Sun is tinuously operating ground-based the emission of gamma rays and also a source of cosmic rays. Evi- cosmic ray detectors. The neutral neutrons. dence for the acceleration of ener- with an unambiguous getic protons, ions and electrons in link to interactions of accelerated The Sun is the most powerful par- close association with solar f lares particles in the solar atmosphere ticle accelerator in our neighbour- and coronal mass ejections is pro- are radio- and , soft hood and, therefore of fundamen-

SPATIUM 11 8 tal physical and astrophysical in- Detecting terest. Ongoing research concen- trates on the nature and the prop- Cosmic Rays erties of the acceleration processes. One of the key instru- ments supporting these efforts is the Reuven Ramaty High Energy The earliest cosmic radiation data Solar Spectroscopic Imager acquired on a worldwide basis (RHESSI),a NASA Small Ex- were obtained from Wilson cham- plorer mission launched on Feb- bers on ships. Routine monitoring ruary 5, 2002 with contributions of the cosmic radiation was initiat- from the ETH Zürich and the Paul ed in January 1932 with the op- Scherrer Institute, Würenlingen. eration of ionising chamber at Its primary mission is to explore Hafelekar, Austria. Wilson cham- the basic physics of particle accel- bers respond to generated eration and explosive energy re- by incident high-energy protons; lease in solar f lares. however only nucleons greater than about 4 GeV have sufficient energy to generate a cascade capable of penetrating the atmos- phere and reaching the Earth’s Solar System surface. Thus it was desirable to Motion develop a detector that would re- spond to lower energy nucleons as Neutrals well as being relatively easy to He, O, Ne from LIS maintain. In the 1950s John A. Simpson, at the University of Single Chicago, invented and developed the and found that the Earth’s magnetic field Interplanetary could be used as a spectrometer to Sun Acceleration allow measurements of the cosmic Earth Orbit ray spectrum down to low pri- mary energies. The magnetic lat- itude of a particular neutron monitor determines the lowest magnetic rigidity of a primary that can reach the monitor, the so- Solar Modulation called “cut-off rigidity". The sta- tion’s altitude determines the amount of absorbing atmosphere above the station and hence the amount of absorption of the sec- ondary cosmic rays (the higher the

Figure 5 station, the higher the counting Sketch of the concept for the production and acceleration of the anomalous cosmic rate). By using a combination of rays. lead (to produce local interac-

SPATIUM 11 9 tions),paraffin or polyethylene (to Climax Corrected Neutron Monitor Values moderate or slow down the neu- Smoothed Sunspot Numbers 1950–2002 tron component) and multiple 450 225 slow-neutron counters, Simpson greatly increased the counting rate in his monitor design.After the in- vention of the standard neutron monitor this type of detector be- 400 150 Sunspot Number came widely used for cosmic ray monitoring all over the world. One of the longest uninterrupted

observations is made by the Cli- Monthly Mean Counts/Hour/1000 max Neutron Monitor of the Uni- 350 75 versity of Chicago, see Figure 6.

As the counting rate of high ener- gy particle counters increases with 300 0 increasing altitude high elevation 1950 1960 1970 1980 1990 2000 research stations became attrac- Monitor Data Smoothed SSN tive locations for neutron moni- Figure 6 tors. In 1958 the first neutron This plot shows data from the Climax Neutron Monitor operated by the University of Chicago. The cosmic rays show an inverse relationship to the sunspot cycle because monitor was installed on the Jung- Sun’s magnetic field is stronger during sunspot maximum and shields the Earth from fraujoch where it is operated by the cosmic rays.

International Foundation High Altitude Research Stations Jung- fraujoch and Gornergrat (HFSJG) with headquarters in Bern, Figure 7.

A second detector was installed in 1986. The effective vertical cut- off rigidity at Jungfraujoch is 4.5 GeV. Hermann Debrunner, the former President of the Pro ISSI association, has started his career there as a student and served later as the foundation’s director.

Figure 7 Two neutron monitors are installed at the Sphinx laboratory of the Jungfraujoch at an altitude of 3570 m. The 18-IGY-Detector is in continuous operation since 1958, while the Standard 3-NM64-neutron monitor operates since 1986.

SPATIUM 11 10 Propagation N, P = High Energy Nucleons of Cosmic Rays n, p = Disintegration Incident Primary Product Particle in the Earth’s Nucleons = Nuclear 0 Environment Disintegration ± – N P n The magnetic f ield and the atmos- p ± Low Energy phere form two powerful protec- N n P n Nucleonic tive layers against the cosmic radi- Component – n p (Disintegration ation on the Earth’s surface. The e+ N p n P Product n Neutrons magnetic field acts both as a shield – e± N n e n p Degenerate and as a giant natural spectrometer p n n to “Slow” for cosmic ray particles. If the par- n p n P Neutrons) n n ticles possess energy, which is N p greater than the magnetic cut-off n p Electromagnetic energy, they will cross through the or “Soft” or “Hard” and reach the Component Component Nucleonic Component upper layers of the atmosphere. But if their energy is insufficient, Energy Feeds across from Nuclear Small Energy Feedback from to Electromagnetic Interactions Meson to Nucleonic Component theywill have a tendency to follow the magnetic lines of force, with Figure 9 which they move “easily", due to Schematic Diagram of a Cosmic Ray Shower.An incident cosmic ray particle inter- acts with the atoms at the top of the atmosphere. Due to its high energy it disintegrates their lack of energy,and succeed in the atoms producing a cascade of electromagnetic radiation, of muons and nucleons, reaching the poles. It is the reason of which the neutrons are detected by the neutron monitors.

1.9 why the areas located near the 1.8 poles receive radiation in higher Solar Minimum quantities than near the equator, 1.7 which is better protected by the 1.6 Earth’s magnetic field,see Figure 8. 1.5 The second protective layer is the Earth’s atmosphere. Upon arriving 1.4 Solar Maximum in the upper parts of the atmos- 1.3 phere, the cosmic ray particles in- 1.2 teract with the atoms, which they Figure 9 1.1 encounter. As shown in

Cosmic Ray Particle Flux in Relative Units these collisions create new cas- 1.0 cades of particles that produce 0 1020304050607080further successively lower energy Magnetic Latitude Figure 8 nuclear disintegrations. This nu- Illustration of the cosmic ray latitude curve. The minimum value occur at the cleonic cascade process caused by equator and the maximum values at polar . The values are relative since the primary cosmic particles can be numbers vary with altitude and solar activity.At high latitudes the cosmic ray f lux lev- els off, since the shielding effect of the Earth’s atmosphere becomes larger than the detected at the surface of the cosmic ray cut-off by the magnetic field. Earth by means of fast neutrons

SPATIUM 11 11 Figure 10 Sources of radioactivity as a percent- age of the dose received by an average individual. (UNSCEAR,United Na- tions Scientific Committee on the Ef- fects of Atomic Radiations) Inhaled () or Ingested Radioactive Elements produced in the atmosphere,which are counted by neutron monitors. As shown in Figure 10 cosmic radia- 1.5 mSv tion represents at ground level only a small part (11%) of the ion- ising radiation to which an indi-

0.1 mS v Industrial Activities vidual is commonly exposed. Nat- 1.3 mSv 0.4 mSv ural land-based sources Mean Exposure each of us to an average total dose of Medical Origin of 2.4 mSv per year (see box), 0.5 mSv Cosmic Radiation though with significant variations according to regions. The larger part of the sources is a gaseous de- scendant of natural uranium, i.e. radon, which concentrates in en- Telluric Radiation closed areas such as houses. There is also soil-based radiation, coming from surface rocks, granite in par- ticular, which contain radioactive elements such as uranium, dating from the formation of the planet. The The and foods,which we in- Assessing the biological risk of ionising radiation gest also contain radioactive ele- ments. Finally, there is also the in- When it comes into contact with matter, ionising radiation collides with ternal radiation, i.e. coming from the atoms comprising it. During these interactions, it releases a part within our own bodies,namely or all of its energy. The absorbed dose (expressed in ) is defined by from the potassium 40 which is the ratio of this released energy over the mass of the matter. A Gray naturally present in our tissues. corresponds to one of energy released in one kilogram of matter.

In order to have a single unit which expresses the risk of the occurrence of the stochastic effects associated with all possible exposure situations, physicists developed an indicator known as the “effective dose”, a measurement using the Sievert (Sv), named after the Swedish physicist who was one of the pioneers in protection against ionising radiation.

The effective dose is calculated from the dose (expressed in Gy) ab- sorbed by the various exposed tissues and organs, by applying weighting factors which take into account the radiation types (alpha, beta, gamma, X, neutrons), the means of exposure (external or internal) and the specific sensitivity of the organs or tissues.

SPATIUM 11 12 Cosmic Rays Cosmic Rays basic model for understanding ra- diation damage.When ionising ra- and and diation interacts with cells, it may or may not strike a critical part of the cell. We consider the chromo- somes to be the most critical part of the cell since they contain the Changes in the Earth’s climate are Since the cosmic radiation increas- genetic information and instruc- generally attributed to internal es with increasing altitude, it could tions required for the cell to per- causes, e.g. volcanic dust in the at- be expected that people living at form its function and to make mosphere, atmospheric/ocean os- high altitudes suffer more from copies of itself for reproduction cillations like the El Niño South- cosmic rays than those at . purposes. Obviously, cosmic radia- ern Oscillation, and to external For example at Denver, Colorado tion has been an intrinsic bound- causes like variations in the Earth’s at an altitude of 1’600 m the expo- ary condition for the evolution of orbital parameters and in the Sun’s sure to cosmic radiation is twice life on Earth since its very begin- luminosity. Recently, it was sug- than for people living near sea nings and nature, therefore, had to gested that the Earth’s cloud cover level. Medical records for these develop efficient repair mecha- is correlated with the intensity of populations exist for a significant nisms,which are able to repair cel- galactic cosmic rays. The idea is number of years thus making it lular damage – including chromo- that droplet formation is inf lu- possible to search for health prob- some damage. enced by ionisation of atmospher- lems that might be correlated ic by cosmic rays. The to differences in the exposure to Public concern and legal regula- ionisation could potentially inf lu- background cosmic radiation. tions that became effective in Eu- ence optical transparency of the When these studies are done, a rope in May 2000 address the radi- atmosphere, by either a change in surprising paradox is found: the ation risk and the individual dose aerosol formation or an inf luence population living at mountain alti- assessment of airline crewmem- on the transition between differ- tudes is generally healthier and has bers. On the average, at f light alti- ent phases of water. As these longer life span than the popula- tude radiation dosage is of the hypotheses are still controversial tions living at sea level. The con- order of 10 microsievert / hour. Of and highly speculative they are clusion is that other factors must course, this value varies with alti- currently the objects of intense be dominant and exposure to cos- tude, latitude, and solar activity, world-wide research activities. mic radiation at altitudes where and it must be interpreted in com- people live does not appear to parison with the average natural present a health hazard. dosage. Thus, approx. 400 hours per year at f light altitude would Biological effects of ionising radi- lead to the equivalent of the natu- ation in living cells begin with the ral yearly radiation load of around ionisation of atoms. Ionising radia- 4 mSv. Interested f light passengers tion absorbed by living cells has can evaluate the expected dosage enough energy to remove elec- using publicly available programs trons from the atoms that make up as e.g.SIEVERT (http:// molecules of the cell. When the www.sievert-system.org/). that was shared by the two atoms to form a molecular Above the Earth’s first protective bond is dislodged by ionising radi- layer,the atmosphere,the radiation ation, the bond is broken and thus, exposure increases strongly. The the falls apart. This is a assessment of the radiation risk of

SPATIUM 11 13 for example during the Cosmic Rays ment or even to the complete loss ongoing construction of the Inter- of the spacecraft. The most widely national Space Station is essential and Matter known disturbances and failures to safeguard their health. The as- are those of the Canadian ANIK tronauts’ suits provide some pro- satellite on January 20/21, 1994 tection against cosmic rays espe- and of the Telstar satellite on Janu- cially against low energy particles ary 11, 1997, which both have been and in areas, where human organs The disintegrating effect of cos- attributed to cosmic ray effects. more susceptible to radiation haz- mic rays on molecular bonds not The commercial losses amounted ards are, like for example the head only effects living cells but of to more than 135 m il l ions US $. or the heart. In any case, however, course also anorganic materials. the layout of such a suit remains a Due to their large areas and their compromise between its protec- long exposure time the solar pan- tive efficiency and the residual els of spacecraft are especially en- mobility required by the . dangered by cosmic rays.A contin- The US orbit the uous degradation of their power Earth with an inclination of production efficiency or even their 28° and receive between 42 to complete breakdown may be the 62 Gy per day, while in the 51° result of cosmic rays. In addition, inclination orbit of the Inter- electronic micro-components are national Space Station the radia- prone to radiation damages lead- tion dose is higher due to the ing to malfunctioning of equip- coverage of higher geomagnetic latitudes and amounts to 90 to 150 Gy per day. Reference List Outside the Earth’s second protec- 1 tive layer, the magnetosphere, the ) Excerpt from Frank B.Mc.Donald and Vladimir S.Ptuskin,Galactic Cosmic Rays,The Century of Space Science,Kluwer Academic Publish- radiation loads become still more ers 2001; p.677–697 important.When it comes to plan- ning a mission to the other planets 2) Excerpt from John A.Simpson,The Cosmic Radiation,The Century of like for example to the radia- Space Science,Kluwer Academic Publishers 2001; p.117–151 tion protection of the astronauts on their long-duration f lights is a 3) Extracts from M.A.Shea and D.F.Smart; Fifty Years of Cosmic Radiation key issue. In order to systematical- Data; Cosmic Rays and Earth; Space Science Series of ISSI; Kluwer ly broaden the available radiation Academic Publishers 2000; p.229–262 database the European Space 4) NOAA Satellite and Information Services, Agency regularly equips its space- http://www.ngdc.noaa.gov/stp/SOLAR/COSMIC_RAYS/cosmic.html craft with the Standard Radiation Environment Monitor (SREM). 5) The International Foundation High Altitude Research Stations Jungfrau- The SREM,a high-energyparticle joch and Gornergrat (HFSJG); http://www.ifjungo.ch counter for electrons with up to 6 6 MeV and protons up to 300 MeV ) Extracts from M.A.Shea and D.F.Smart; Cosmic Ray Implications for has been jointly developed by Human Health; Cosmic Rays and Earth; Space Science Series of ISSI; Kluwer Academic Publishers 2000; p.187–205 Contraves Space AG,ofZürich and the Paul Scherrer Institute of 7) The Sievert System; http://www.sievert-system.org Würen l ingen.

SPATIUM 11 14 Conclusions

Cosmic rays are the messengers from distant regions in our galaxy and beyond. Solar cosmic rays re- leased occasionally in association with energetic processes at the Sun, provide first-hand informa- tion on astrophysical processes re- sponsible for particle acceleration. Anomalous cosmic rays reveal new insight in the dynamic processes in the heliosphere and its interaction with the local interstellar medium. Apart from the , where the classical as- tronomical observations take place, cosmic rays open a second window to the universe providing an attrac- tive complementarydiagnostic tool for our understanding of the pro- cesses in the universe.Although the research of cosmic rays began near- ly 100 years ago much is still un- known especially with regard to their origins and the mechanisms Figure 11 providing the particles nearly the 15,000 years ago a star in the constellation of exploded – the shockwave speed of light.That is why the cos- from this supernova explosion is still expanding into interstellar space! Credit: J. Hester (ASU), NASA mic ray research continues to be one of the most fascinating adven- tures of modern space science.This article is based on publications of the International Space Science Institute on cosmic rays,which are strongly recommended for further reading. In addition I am very thankful to Erwin Flückiger, In- stitute for Physics, University of Bern and Rudolf von Steiger, In- ternational Space Science Institute for their his most valuable contri- butions.

Hansjörg Schlaepfer

SPATIUM 11 15 The Publications of ISSI as of October 2003

All books are published by Kluwer Academic Publishers, Dordrecht, Boston, London

Reports from Workshops

ISSI Scientific Reports

Volume 1 Analysis Methods for Multi-Spacecraft Data,1998 Volume 2 The Radiometric Calibration of SOHO, 2002

Space Science Series of ISSI

Volume 1 The Heliosphere in the Local Interstellar Medium,1996 Volume 2 Transport Across the Boundaries of the Magnetosphere, 1997 Volume 3 Cosmic Rays in the Heliosphere,1998 Volume 4 Primordial Nuclei and Their Galactic Evolution,1998 Volume 5 Solar Composition and its Evolution–from Core to Corona,1998 Volume 6 Magnetospheric Plasma Sources and Losses,1999 Volume 7 Corotating Interaction Regions, 2000 Volume 8 Composition and Origin of Cometary Materials,1999 Volume 9 From Dust to Terrestrial Planets, 2000 Volume 10 Cosmic Rays and Earth, 2000 Volume 11 Solar Variability and Climate, 2000 Volume 12 Chronology and Evolution of Mars, 2001 Volume 13 The Astrophysics of Galactic Cosmic Rays, 2002 Volume 14 Matter in the Universe, 2002 Volume 15 Auroral Plasma Physics, 2003 Volume 16 Solar System History from Isotopic Signatures of Volatile Elements, 2003

Review of the Space Science Achievements in the 20 th Century

The Century of Space Science

Two volumes,1846 pages, 2002