Cosmic Rays Editorial

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 lights 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 particles that reach SPATIUM see shadows on the walls of their us from the depth of the universe. 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 light of the Sun 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 supernova 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 Neutron Monitor, see parable – an unexpected second Figure 6. SPATIUM 11 2 Cosmic Rays The Early Years 1 that the radiation came from the the radiation actually increased. Earth,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 electroscopes to study the conduc- tivity of gases discovered that no matter 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 atmosphere, possibly radiation like Roentgen 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 mysterious radiation by 30%. An additional 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 electroscope.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 Geiger counter 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- electrons, and hence protons were ry of cosmic ray acceleration and scopes. On 12 August 1912, using most plausibly the dominant con- transport. The close link between the hydrogen-filled Böhmen, Hess stituent. radio astronomy 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 ion chambers, he found that the University of Minnesota 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- astrophysics. 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 latitude with a lower intensity was synchrotron radiation – 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 Galaxy including some discrete primary cosmic rays were charged sources as well as extragalactic particles. In 1930 Bruno Rossi 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 University of Chicago, 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 Nature Low- Anom- Galactic U-High T Energy alous of Cosmic Rays Turnup Oxygen T–2.6 sec st MeV)] 2 All Particles 0 Oxygen Cosmic rays consist of electrons, neutrons 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 isotopes 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.

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