apollo-soyuz pamphlet no. 6 cosmic ray dosage

8/8/2019 Apollo-Soyuz Pamphlet No. 6 Cosmic Ray Dosage

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Apollo-SoyuzPamphlet No. 6:Cosmic RayDosage(NASA-EP-138) APOLLO-SOYDZ PAMPHLET NO. 6: N78-27152COSMIC RAY DOSAGE (National Aeronautics andSpace Administration) 46 p BF A 0 1 ; SOD HC

set of 9 volumes CSCL 22A OnclasG3/12 24994

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Apollo-SoyuzExperimentsSpace

This is one of a series of ninecurriculum-related pamphletsfor Teachers and Studentsof Space ScienceTitles in this series ofpamphlets include:EP-133 Apollo-Soyuz Pamphlet No. 1: The FlightEP-134 Apollo-Soyuz Pamphlet No. 2: X-Rays, Gamma-RaysEP-135 Apollo-Soyuz Pamphlet No. 3: Sun, Stars, In BetweenEP-136 Apollo-Soyuz Pamphlet No. 4: Gravitational FieldEP-137 Apollo-Soyuz Pamphlet No. 5: The Earth from OrbitEP-138 Apollo-Soyuz Pamphlet No. 6: Cosmic RayDosageEP-139 Apollo-Soyuz Pamphlet No. 7: Biology in Zero-GEP-140 Apollo-Soyuz Pamphlet No. 8: Zero-G TechnologyEP-141 Apollo-Soyuz Pamphlet No. 9: General Science

On The Cover The Earth's Magnetic Field andVan Allen Belt with IncomingCosmic Ray


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Apollo-SoyuzPamphlet No. 6:Cosmic Ray DosagePrepared by Lou Will iams Page and Thornton Page FromInvestigators' Reports of Exp er imental R esults and W iththe Help of Advising Teachers

NASANational Aeronautics andSpace Administrat ionWashington, D.C. 20546October1977


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For sale by the Superintendent of Documents,U.S. Government Printing Office, Washington, D.C. 20402(9-Part Set; Sold in Sets Only)Stock Number 033-800-00688-8


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Preface

The Apo llo-Soy uz Test Project (ASTP), w hic h flew in Ju ly 1975, arousedconsiderable public interest; first, because th e space r ivals of the late 1950'sand 1960's were working together in a jo in t endeavor , an d second, becausetheir mutual efforts included developing a space rescue system. The ASTPalso included significant scientif ic experiments , the results of wh ich can beused in teaching biology, ph ysics, and mathem atics in schools and colleges.

This series of pamphlets discussing the Apollo-Soyuz mission and experi-ments is a set of curriculum supplem ents designed fo r teachers, supervisors ,curriculum specialists, and textbook writers as wel l as for the general public.Neither textbooks nor courses of study, these pamphlets are intended toprovide a rich source of ideas, examples of the scientif ic method, pertinentreferences to standard textbooks, an d clear descriptions of space experiments .In a sense, they may be regarded as a pioneering form of teac hing aid. Seldomhas there been such a forthright effort to provide, directly to teachers,curr iculum-relevant repor ts of current scientif ic research. High schoolteachers who reviewed the texts suggested that advanced students who areinterested m ight be assigned to study one pam phle t and report on it to the restof the class. After class discussion, s tudents might be assigned (wi thoutaccess to the pamphlet) one or more of the "Questions fo r Discussion" fo rformal or informal answers, thus s tressing the application of what w asprev iously covered in the pa mphlets.

The authors of these pam phlets are Dr. L ou W ill iams Page, a geologist, an dDr. Thornton Page, an astronomer. Both have taught science at severaluniversities and hav e published 14 books on science for schools, colleges, andth e general reader, including a recent one on space science.

Technical assistance to the Pages w as provided by the Apollo-SoyuzProgram Scientis t , Dr. R. Thomas Giuli, and by Richard R. Baldwin,W . W ilson Lauderdale, and Susan N. M ontgo mery , members of the group atth e N A S A Lyndon B . Johnson Space Center in Houston whi c h organized th escientists ' participation in the ASTP an d published their reports of exper imen-tal results.

Selected teachers from high schools and univ ersiti es throu gho ut the Unite dStates reviewed th e pamphlets in draft form. They suggested changes inwording, the addition of a glossary of terms unfami l i a r to s tudents , andimprovemen ts in diagrams. A list of the teachers and of the scientific inves-tigators w ho reviewed th e tex ts fo r accuracy follows this Preface.This set of Apollo-Soyuz pam phlets was initiated and coordinated by Dr.Frederick B. Tu ttle, Director of Educa tional Programs, and was supported bythe NASA Apollo-Soyuz Program Office, by Leland J . Casey, AerospaceEngineer for ASTP, and by Wil l iam D. Ni xo n, Educ at ional ProgramsOfficer, all of NASA Headquar ters in Was h ing ton , D .C .


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Appreciation is expressed to the scientific investigatorsand teachers w horeviewed th e draft copies; to the NASA specialists w ho provided diagramsan d photographs; and to J. K. Holcomb, Headquarters Director of ASTPoperations, and Chester M . Lee, ASTP Program Director at Headquarters,whose interest in this educational endeavor made this publication possible.

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TeachersAnd Scientific InvestigatorsWho Reviewed the Text

Harold L. Adair, Oak Ridge National Laboratory, Oak Ridge, Tenn.Lynette Aey,Norwi ch Free Academy, Norwich, Conn.J. Vernon Bailey, NASA Lyndon B. Johnson Space Center, Houston, Tex.Stuart Bowyer , Univers i ty of California at Berkeley, Berkeley, Calif.Bill Wesley Brow n, C alifornia State Universi ty at Chico, Chico, Calif.Ronald J. Bruno, Creighton Preparatory School , Omaha, Nebr.T. F. Budinger, University of California at Berkeley, Berkeley, Calif.Robert F. Collins, Western States Chiropractic College, Portland, Oreg.B . Sue Criswell, Baylor College of Medicine, Houston, Tex.T. M. Donahu e, Un iversi ty of M ichigan, Ann Arbor, Mich.David W. Eckert, Greater Latrobe Senior High School, Latrobe, Pa.Lyle N . Edge, Blanco High School, Blanco, Tex.Victor B. Eichler, Wichita State Universi ty, Wichita, Kans.Farouk El-Baz, Sm ithsonian Inst i tut ion, W ashington, D.C.D . Jerome Fisher, Em eri tus, U niversi ty of Chicago, Phoenix, Ariz.R. T. Giuli , NASA Lyndon B. Johnson Space Center, Houston, Tex.M . D. Grossi, Smithsonian Astrophysical Observatory, Cambridge, Mass.Wendy Hindin, North Shore Hebrew Academy, Grea t Neck, N.Y.Tim C. Ingoldsby, Westside High School, Omaha, Nebr .Robert H. Johns, Academy of the New Church, Bryn A t h y n , Pa.D. J . Larson, Jr., Grumman Aerospace, Bethpage, N.Y.M. D. Lind, Rockwell Internat ional Science Center, Thousand Oaks, Calif.R. N. Litt le , Universi ty of Texas, Austin, Tex.Sarah Manly, Wade Hampton High School , Greenvil le , S.C.Katherine M a y s , B ay City In depen dent School District , B ay C i t y , Tex.Jane M. Oppenheimer , Bryn Mawr Col lege , Bryn Mawr, Pa .T. J. Pepin, Universi ty of W yom ing, Laramie, Wyo.H . W. Scheld, NA SA Lyndo n B. Johnson Space Center , Houston, Tex.Seth Shulman, Naval Research Laboratory, Washington, D.C.James W. Skehan, Boston College, Weston, Mass.B. T. Slater, Jr., Texas Educat ion Agen cy, Aust in , Tex.Robert S. Snyder, NASA George C. Marshall Space Flight Center, Huntsvil le , Ala.Jacqueline D. Spears, Port Jefferson High School, Port Jefferson Station, N.Y.Robert L. Stewart, Monticello High School, Monticel lo,N.Y.Aletha Stone, Fulmore Junior High School , Aus t i n , Tex.G. R . Taylor , N AS A Lyndon B. Johnson Space Center, H ouston, Tex.Jacob I . Trombka, NASA Robert H. Goddard Space Flight Center, Greenbelt , Md.F. O. V onb un , NA SA Robert H. Coddard Space Flight Cen ter, Greenb elt , Md .Douglas Winkler, Wade Hampton High School , Greenvil le , S.C.


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Contents

Section 1 Introduction: TheRadiation. Hazard t) Spacecraft 1A. Incoming Parficies"VerSrjt the-E^rtfi 'Magnete Field 2B.; Radiation Effects on Instruments 5C. BiologTq^l E ffects .:. . 1 . . . jv:'.-..--. 6D. Question's' fdT Discus'sioft (Gofem'iG'Bays, Magnetic Fields,Shielding) .;- 7Section 2 Light Flashes in the Eyes of Astronauts 9A. Laboratory Experiments With Flashes in the Eyes 10

B. Counts of Flashes in Spacecraft 11C. Experiment MA-106 11D. MA-106 Results: Light Flashes and Cosmic-Ray Intensity 14E. Questions for Discussion (Flashes, Cosmic Rays) 16

Section 3 Cosmic-Ray Effects on Bacterial Spores, Seeds, an d Eggs 17A. HZE Particles 17B. Mapping the HZE Hits 21C. MA-107 Results on Biological Damage From HZE Hits 22D. Qu estions for Discussion (Cosm ic Rays) 26Appendix A Discussion Topics (Answers to Questions) 27Appendix B SI Units and Powers of 10 30Appendix C Glossary 33

V I I


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Figures

Figure 1.1 Magnetic Field of the Earth and the Van Allen Belt 4Figure 2.1 Shapes an d Sizes of Light Flashes2.2 Experiment MA-106 Layout2.3 Cosmic-Ray Telescope fo r Experiment MA-1062.4 Orbit Track and Locations of Reported Light Flashes2.5 Intensity of Cosmic Rays Compared With Reported Flashes

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Figure 3.1 Biostack III Container A and Container B3.2 Cosmic-Ray Track Through Part of Container A3.3 Cosmic-Ray Energy Spectrum for Container A3.4 Disintegration-Star Tra cks3.5 Etched HZ E Track Near Seeds3.6 Micromanipulation of a Bacterial Spore and its Later G rowth3.7 Percentage of Spores Forming Colonies3.8 Malformations of Larvae Caused by HZE Hits on Eggs

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1 Introduction

The Radiation Hazard in SpacecraftAfter 4 years of preparation by the U.S. National Aeronau t ics and SpaceAdminis t ra t ion (NA SA ) and the U.S .S.R . Academy of Sciences, the Apolloan d Soyuz spacecraft were launched on July 15, 1975. Two days laterat 16:09 Greenwich mean t ime on Ju ly 17, after Apollo maneuvered intoth e same orbit as Soyuz , the two spacecraft were docked. The astronautsand cosmonauts then met for the f irst international handshake in space,an d each crew entertained the other crew (oneat a t ime ) at a meal of typic alAmerican or Russian food. These activit ies and the physics of reactionmotors, orbits around the Earth, and weigh tlessness (zero-g) are describedmore ful ly in Pamphle t I , "The Spacecraft , Their Orbits, and Docking"(EP-133).

Thi r ty - four experiments were performed while Apollo and Soyuz were inorbit: 23 by ast ronau ts , 6 by cosmonauts , and 5 j o in t ly . These exper im entsin space were selected from 16 1 proposals from scientists in n in e differentcountries. They are listed by number in Pamphlet I, and groups of two ormore ar e described in detail in Pamphle ts I I th rough IX (EP-134 throughE P - 1 4 1 , respectively) . Each experiment w as directed by a Pr inc ipa l Invest i -gator , assisted by several Co-In vestigators, and the detailed scientif ic resultshave been published by N A S A in two reports: th e Apollo-Soyuz TestProject Preliminary Science Report (NASA TM X-58173) and the Apollo-Soyuz Test Projec t Sum mary Science Re por t (N AS AS P-41 2) . The s impl i f iedaccounts given in these pam phlets have been reviewed by the Pr inc ipa lInvest igators or one of the Co-Investigators.Planners of the early NASA space missions worried about damage frommeteors and the dangers of re tu rn ing to Earth at high speed through th eatmosphere. W hen these hazards were avoided (by meteor shields and abla-t ive heat shields) , th e next concern was the effect of weigh t lessness onas t ronauts . After the Skylab 3 astronauts spent 84 weightless days in orbit ,th is anxiety passed.

Recent evidence shows that the "radiation hazard" may be of moreconcern in long spaceflights. "Radiation" is used here to mean the bom-bardment by high-en ergy particlescosm ic rays in outer space an d h ig h -speed protons and electrons in the Van Allen belt about 320 to 32 400ki lomete rs above the Ear th 's surface. T his radiation is hazardous not only toastronauts and other l iving organisms in the spacecraft but also to electronicequ ipment and i n s t r u m en t s .

Two Apollo-Soyuz Test Project experiments are described in this pam-phle t . Exper im ent MA -106 , Q uan t i ta t ive Observa t ions of Ligh t Flash S ensa-t ions (f lashes seen by "b l indfo lded" as t ronau ts) , was supervised by T. F.Bu d i n g e r of the Lawrence Berkeley Laboratory at the Univers i ty of Califor-


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nia. He was assisted by 11 Co-Inv estigators. E xperiment MA -107, BiostackIII, was a German experiment supervised by Horst Biicker of the BiophysicsSpace Research G roup at the Uni vers ity of Frankfurt. H e was assisted by 32Co-Investigators from West Germany, France, and the United States. Bio-stack III was the third in a series of experiments to measure the effects ofcosmic rays on spores, seeds, an d eggs. (Biostack I was carried on Apollo 16in April 1972 an d Biostack I I was carried on Apollo 17 in December 1972.)

A Incoming Particles Versus theEarth's Magnetic FieldCosmic rays ar e charged particles ( ions) mo ving at high velocity and co m in gin toward th e Earth from all directions. Scientists have found tha t many of thelower speed cosmic-ray particles come from the Sun. These are called solarcosmic rays. They ar e probably blown out of the Sun by vio len t exp losions .M u c h slower protons and electronsthe "solar wind"are streaming con-t inuous ly out of the Sun in large numbers. The higher energy cosmic raysc om i ng from al l other directions probably originate in our Milky W ay Galax yan d ar e called galactic cosmic rays. They pass r ight through spacecraft at arate of 2 particles/cm 2 hr. All these particles ar e deviated by the Earth 'smagnetic field: the s low, l ight ones are deflected more than th e fas t, heav y ,galactic cosmic-ray particles.

The Earth has a magnetic field1 some what like that of a large bar m agnet or"magn etic dip ole. ' ' There is a region around the Earth where a compass needlewill point along th e magnetic lines of force, represented by the dashed lines inFigure 1 . 1 . Of course, there is no bar magnet inside th e Earth. The Earth 's mag-netism is thought to arise from currents in the molten core due to the Earth's ro -tation (although th e magnetic dipole is inclined 13 to the rotation axis). Themagnetic field strength is about 500 milligauss (50 x 10~ e tesla) at the surfacean d the strength rapidly decreases outw ardly (in proportion to 1/r4, where r isth e distance from th e Earth's center). Other planets also have magnetic fields,bu t those of Mercury, Venus, an d Mars (and th e Moon) ar e muc h smal le r.Mercury 's magnetic field is about 1 percent of the Earth's and the magneticfields of Venus an d Mars ar e nearly zero. Jupiter an d Saturn have muchstronger magnetic fields (4000 milligauss, or 400 x 10~6 tesla, at the surface),probably because they ar e rotating faster than th e Earth.

'Project Physics, Sees. 14.2, 14.13; PSSC, Sees. 22-1, 22-3; and ESCP, Sees. 3 - 1 1 to 3-13.(Throughout this pamp hlet , references w i l l be given to key topics covered in these three standardtextbooks; "Project Physics," second edi t ion, Hol t , Rinehart and Winston, 1975; "PhysicalScience Study Committee" (PSSC), fou rth edit ion, D.C. Heath, 1976; and " I nv e s t i ga t i ng theEarth" (ESCP), Houghton Miff l in Com pa ny , 1973.)


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The direction of travel of a charged particle (ion) is changed by the magneticfield.2 The cosmic ray in the upper right of Figure 1. 1 thus is deflecteddownward . Such deflections of cosmic ra ys produce the "latitude effec t":cosmic rays ar e more intense at high latitudes (north an d south) than nearth e Equator .

Deflections of slower moving ionsthe protons an d electrons in the solarwind are larger, and the Earth's mag netic field has "captured" ma n y of themin the Van Allen belt3 (named after physicist James Van Allen of the Universityof Io wa , who discovered it from measurements on the Explorer 1 satellite in1958). The cutaway view of Figure 1.1 shows the doughnut-shaped regionswhere p rotons and electrons are oscilla ting north and south along the magn eticlines of force (dashed lines). These charged particles spiral around the linesof force at speeds of several kilometers per second and are reflected backwhere th e l ines of force get close together near th e magnet ic poles. Thereare no sharp boundaries to the regions where protons and electrons areoscil lat ing, but the whole Van Allen belt is between 320 and 32 400kilometers altitude and extends all around the Earth. The peak in tensi tyof protons occurs at about 3000 kilometers alt i tude, where th e protonshave energies of more than 10 megaelectronvolts and a flux of more than10 000/cm2 sec. Because of the intensity of this "radiation" in the V an Allenbelt , th is region of space is by far the most haz ardou s to l iv ing organisms (andto sensit ive instrumen ts) in spacecraft. (The N AS A Pioneer 10 mission foundthe sim ilar radiation belt of Jupiter to be several tho usand t imes m ore intense.)

2Project Physics, Sec. 14.13; PSSC, Sees. 22-4, 22-6."Project Physics, Sees. 14.2; PSSC, Sees. 22-1, 22-3.


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Figure 1.1 Schematic diagram of the magnetic field of the Earth and the Van Allen belt.The dashed lines are magnetic lines of force.

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The Ear th ' s magnetic field is not as simple as the diagram in Figure 1.1 wouldsuggest . I ts outer regions are affected by the solar w i n d , and the "magneto-sphere"the region of the upper a tmosphere that is dom inated by the Earth 'smagne t ic f ie ld has a "shock f ront" fac ing in to th e win d (more or less towardth e Sun) and a "tail" s t re tching downwind. More important fo r Earthsatellites such as Apollo-Soyuz, th e Earth 's magnetic field has a "dent"over th e At lant ic Ocean ju st east of Brazil that causes the Van Allen bel t tobulge downw ard toward th e Earth's surface in a region called th e South AtlanticAnomaly. This irregularity in the magnetic field produces a region of veryintense radiation in the lower part of the Van Allen belt there (about 1000 t imesmore intense than in nearby space). NASA scientists have learned that someins t ruments on spacecraft give erroneous readings while they are in the SouthAtlantic Anom a l y . NA S A's S ky l a b , at a 444-kilometer a l t i tude, went through itregularly. Apollo-Soyuz was below it at an al t i tude of 222 kilometers, where th eradiation dose was almost 10 time s less tha n at the Sk yla b altitude .

P Radiation Effects on InstrumentsPhotographic film in cameras, most of the e lectronic equ ipm ent in spacecraft ,and sen si t ive instrum ents designed to detect x-rays or far-ultraviolet l ight ar eaffected by Van Al len be l t rad ia t ion and cosmic rays . The de tec torsthemselves may give fa lse counts because a fast proton or cosmic ray isrecorded. (This problem is avoided by using "anticoincidence coun te r s " see Pamphlets II and III . ) Photographic film is fogged by the radiation, andelectronic parts , such as semiconduc tors or discharge tubes, m ay giveu n w a n t e d pulses of current (fa lse counts) when cosmic rays or high-speedprotons pass through them. Long exposure can permanent ly damage someelectronic parts and can also fog photographic film so that i t is unus able . Th iscan be part ly pre ven ted by shielding. On the long Skylab missions, film w askept in a cabine t that had th ick metal sides, like a bank vaul t . O n most spacei n s t ruments , the electronics are shielded by metal containers. The spacecrafthu l l also p rovides some shield ing for everyth ing inside. This shieldin g can beeffective against Van Allen bel t e lectrons and most of the medium-speed


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protons. However, most of the cosmic rays penetrate a few centimeters ofmeta l , and the few that are absorbed create "secondaries"often h ig h -energy gam ma rays. T his makes the exposure of astronau ts and other l ivingorganisms near metals in a spacecraft very complicated.

Q Biological EffectsW h en "radiation" (high-energy protons and cosmic rays as well as g am m arays or x-ra ys) is absorbed in livin g cells, it ionizes atom s or mole cules in thecell and may disorganize or kill the cell. The loss of a few cells in a largeorganism such as a hum an usu ally doesn ' t m atter . Long exposure may doharm, howe ver, and for that reason x-ray technicians and astronauts usuallyw e a r p h o to g r ap h ic b ad g es t h a t sh o w h o w m u ch ex p o su r e t h ey h aveaccumula ted . The overall biological damage is measured in "rads." One rad(radiation absorbed dose) is equ iva len t to 10~ 5 joules of energy absorbedper gram of tissue. For h u m a n s , th e lethal dose is about 400 rads. Hospitalx-ray photographs give less than 0.01 rad, and astronauts on long spacemissions have so far accumula ted only 3 or 4 rads, whic h has no s ign i f ican teffect. However , on future missions of much longer duration, cosmic-raydosage may be a serious matter .

The biological damage by a single cosmic-ray particle is measured by its"l inear-energy transfer" (LET), w hich is the cosm ic-ray energy absorbed permicrom eter of cells or l iv ing t issues penetrated. The LET is larger for high erenergy , hi ghly charged particles. In space, the im portant cosmic ray s are theheavy onesthe nucle i of carbon, nitrog en, and oxygen (atom s of atomicweight A stripped of all Z electrons) that have kine tic energies E of m a n ymil l ions of electronvolts (see Pam p h le t II). These rays have an LET of 10keV/)u,m or larger (LETis proportional to Z 2E /A) .

One unexpected biological effect of cosmic rays was the occurrence of"light flash es," first reported by Astronau t Edwin "Buzz" Aldr in on theApollo 11 mission to the Moon in July 1969. H e reported seeing th e f lasheswith his eyes closed. Other astronauts reported the flashes, and they werecounted and t imed on later Apollo and Skylab missions. A s noted in Section2, several comp licated exp lanatio ns have been proposed by biologists andphysicists. (Actua l ly , C. A. Tobiasof the Lawrence B erkeley Laboratory hadpredicted in 1954 that cosmic rays w ould produce f lash es in astronaut 's eyes,bu t few scientists remembered his prediction.)


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D Questions for Discussion(Cosmic Rays, Magnetic Fields, Shielding)1. If you wanted to describe one cosmic ra y completely, what characteris-tics would you lis t?2. Why is there no Van Allen belt around the planet Venus?3. Some rocks were magnetized by the Earth 's mag netic field as they wereformed. M easurements show that th e magnetic field has changed in strength

and direction dur ing the past 500 mill ion years. What could cause this?4. If the Earth 's atmosphere were much higher, what would happen to the

Van Allen belt?5 . Which would shield photographic film in a spacecraft better: a

1-centimeter thickness of alum inu m or a 1-centim eter thickness of lead?6. A 2000-megaelectronvolt cosmic ray has an LET of 10 keV//im. If this

ra y were to pass through your head, how much energy would remain in thecosmic ray?


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2 Light Flashes in the Eyesof Astronauts

The flashes of light, as reported by the astronauts, have various shapes (Fig.2 .1 ) . The variety of shapes complicates their explanatio n. The simplest idea isthat a cosmic ra y passes through th e eye's "detector" ( the retina) and ionizesa few atoms or molecules, which results in a signal in the optic nerve. Thesignal is interpreted by the brain as a "single star" (upper right in Fig. 2.1) , orperhaps a "comma." T he "diffuse-cloud" f lashes, howev er, would seem tobe something different.

Short streak

Long streak(thin lineof light)

Hot dog(wide lineof l ight)

Double streak

Star(single lightpoint)

Double star(doublelight points)

Supernova(very brightf lash)

Shapes andsizes of light flashes noted inspaceand incyclotron experiments. Figure 2.1

BESKK KO!E BLMEft


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O ne theory proposed by G. G. Fazio, a Harvard astronomer, is tha t th ediffuse-cloud flash is "Cerenkov radia t ion" produced in the astro nau t'seyeball. Cerenkov radiation is a "shock wave" of l ight emitted when aparticle traveling near th e speed of l ight c (3 x 10 8 m/sec) enters a substancein wh ich the speed of light \ss lower than the speed of the particle. (In glass, orplastic, or the hu ma n eyeball, light travels about 40-percent slow er than c.)For the vitreous humor in the human eye, Cerenkov radiation would beproduced whenever a 5000-megaelectronvolt cosmic ra y passed into it. Theresul t ing flash should fill th e entire eyeball. I t would be out of focus becauseth e vi t reous humo r is located between th e lens and the retina. Such out-of-focus flashes could account for the reported "diffuse clouds."A third explanation of the flashes, proposed by T. F. Budinger of theLawrence Berkeley Laboratory, involv es a nuclear reaction between high-energy protons and the nuclei of atoms in the retina (carbon, nitrogen, andoxygen). Such nuclear collisions produce high-speed alpha particles (heliumnucle i ) at the rate of one H e + + fo r each 250 000 protons entering th e eye .Budin ger 's calculations show that when S kylab passed through the SouthAtlant ic A n o m a l y , th e intensity of high-energ y protons inside th e spacecraftwould produce eight alpha particles per minu te in the two eyes of an astronaut,jus t as reported (Sec. 2B). These alpha particles have mass and energy highenough to produce stars and streaks (Fig. 2.1), whereas the Van Allen beltprotons themselves pass through th e eyes unnoticed.

In summary , there ar e probably at least three causes of light flashes inastronauts ' eyes: (1 ) ionization in the retina by high-m ass cosmic rays; (2)Cerenkov radiation in the eyeball by high-ma ss, very high energy cosm icrays; and (3) ioniza tion in the retina by alpha particles produced by nuc learcoll isions with high-energy Van Al len belt protons.

A Laboratory Experiments WithFlashes in the EyesT. F. Bud inger , the Principal Investigator for Experim ent MA -106, and C. A.Tobias, the Co-Investigator , conducted a ser ies of experiments using high-energy ions from a cyclotron at Berkeley. They k new exactly which ions werein these artificial cosmic rays and exact ly how muc h energy they had in anarrow beam. Several Berkeley physic ists volun teered as subjects. Each w asbl indfolded for 15 m in u te s or more (t o adapt his eyes to darkness) an d thengiven a few short bursts of high-energy ions through th e eyes an d head atspecific places. Budinger found that fi r ing th e ions th rough th e brain or opticnerve did not produce flashes but that firing them th rough the eye did. Thespeed (energy ) of the ions was not high enough to produce Cerenkov radia-

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t ion; therefore, Budinger and Tobias concluded that ionization in the retinawas the main cause of the light flashes in the eyes of the astronauts.

Counts of Flashes in SpacecraftThe explan ation of the l ight flashes and their different shapes is still unclear.Budinger thinks that some of the f lashes may come from light emitted byatoms near the retin a that hav e been exc ited by the passing cosmic ray , as wellas from ionization in the retina. In Earth-orbiting spacecraft such as Skylab,where Astronau t Bill Pogue saw about 8 f lashes per minute while passingthrough the South Atlant ic Anomaly , there a re obviously many differentkinds of ions (protons and heavy nu clei) passing thro ugh the eye. O n A polloflights to the Moon, far f rom Earth, there should be mostly heavy nucle i , andth e Apollo astronauts averaged 2 f lashes per minute.

Apollo-Soyuz was in a much lower orbit than Skylab and passed under-neath the South At lan t ic Anomaly . It was expected that careful countingwould show the cosm ic-ray latitu de effect as the spacecraft m oved from th eEquator to 51.8 N and then to 51.8 S lati tude.

Q Experiment MA-106The MA-106 scientists wanted t imed counts and descriptions of the flashesan d separate m easurem ents of the cosmic-ray intensity near each a stronau t 'shead. They wanted to check the astrona ut 's adaptation to darkness by measur-in g the faintest l ight that he could see jus t before the coun ting started. All thiswas accom plished wi th the equipment shown in Figure 2.2. Two astronautswere f i t ted with l ight-tight masks, each with a microphone in front of them ou t h and a sma ll , controllable l ight ("diode") in front of one eye . The twomen were placed so that their heads were beside tw o cosmic-ray detectorboxes, and they held push button s to press each t im e that they saw a f lash. Thethird astronaut operated the l ight controls and a tape recorder that recordedeach astron aut's push butto n cou nt and his verbal description of the flash andthe counts of cosmic rays from the two detector boxes. In effect , me n's eyeswere calibrated as cosmic-ray detectors!

In each de tector box, there, were two kin ds of cosmic-ray d etectors. Onewas provided by the German Co-Investigators, who had inven ted it at theNuc l e a r Physics Insti tute in Frankfur t . I t uses small wafers of silver chloride(AgC l) crystals doped w ith cadm ium (Cd). Each A gCl(C d) wafer was 1 by 2by 0.3 centimeters. Cosmic rays have been found to leave "latent tracks" inAgCl(Cd) that can be developed like photographic f i lm. Ho weve r , th e unde-veloped tracks disappear in a few minu tes un less they are "frozen in" by

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Light-tight maskDetector box

Silicon telescope-spectrometerAgCKCd) crystals

Crystal detector selectionDark adaption levelsData recorder

Figure 2.2 Experiment MA-106 layout.shining light on the crystal . Then, when th e crystal is developed, th e tracksmade while th e l ight was on (and no others) wil l show as black l ines. Theth ickness and graininess of the l ines show roug hly the ion type and speed orenergy .

The AgCl(Cd) w afers were put in four small boxes, one on each side of asmall electr ic lam p in each box. O ne lamp was turned on whi le Apol lo -Soyuzwas at 50 N la ti tude , a second one while the spacecraft was near the Eq uator ,a third one near the S outh Atlantic An om aly , and the last one over the PacificOcean , all d u r in g one orb i t whi le th e ast ronau ts were coun t ing f lashes . Afte rApol lo -Soyuz sp lashed down, th e crystals (st i l l in the i r l ight- t ight boxes)were sent to Frankfurt fo r development an d analysis.

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The second detector was a cosm ic-ray telescope developed by the PrincipalInvestigator and Co-Investigators at the U niver s i tyof California at Berkeley .This detector depends on the effect of a cosmic ra y pass ing throu gh a siliconsolid-state junction. The effect is a pulse (coun t) in the electric current f low ingthrough the junc t ion . Bud inger made a strip-shaped junc t ion ( top of Fig.2.3)tha t detected a cosmic ra y anyw here in its 17-mi l l ime te r l eng th and3-mi l l ime te r w id th . He put four of these detector strips on each of four0.3-mil l imeter - th ick silicon wafe rs. He used two of these wa fers crossed at a90 angle, as show n in Figure 2.3, to measure x andy where the cosmic rayentered the top of the telescope. That is, if he got a pulse on the x = 3 strip anda pulse on the y = 1 str ip, th e cosmic ra y entered somewhere in the squarepatch labeled 3,1.

ic leads

Y-wafer To p view ofcrossed x -y wafers Electric X-wa fe rleads

Crossed wafe r s

Energy absorber

Crossed wafers

/ E - Af

Cosmic-ray telescope for Experiment MA-106. Figure 2.3

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D

At th e bottom of the telescope, 15 mill imeters below, was another pair ofx-y wafers, and a cosmic ray is shown going through x = 1, y = 4 there.Between the two pairs of wafers was a 5-mill imeter slab of copper thatreduced th e cosmic-ray kinetic energy by an am o u n t A f that depends on thecosmic-ray chargeZ and its energy \ l 2 A v 2 , where A is the ion mass in atomicuni t s and v is the velocity . Therefore, th e pulse*sizes (larger from the topcrossed wafers and smaller from the lower crossed wafers) gave an estim ate ofthe kind of cosmic ra y that passed, as well as its direction. The smallestdetectable pulse (giv ing a cou nt) corresponded to an LET of 10 ke V//im (suchas nitrogen nuclei with 4000 megaelectronvolts of energy) .MA-106 ResultsLight Flashes and Cosmic-Ray IntensityA plot of Apollo-Soyuz orbit number 111 around the Earth from 15:00 to16:35 G M T on Ju ly 22 , 1975, is shown in Figure 2.4. Each of the 82 f lashesreported by the two blindfolded astronauts is plotted by one of the fivesymbols l isted on the left. There are 42 star flashes, 1 supernova, 26 streaks or"hotdogs," and 13 comm as. N ote that there were few flashes reported nearth e South Atlan tic An om aly (S AA) or anyw here near the Equator . Most of the

July 22. 1975Revolution 11 160 '

* Star- Streak Comma" Hotdog* Supernova

150 120 90 60 30 0 30 60 90 120 150 180 150W->-ELongitude

Figure 2.4 Orbit track and locations of reported light flashes in Experiment M A - 1 06

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flashes were seen between 30 and 50 N lat i tude an d between 30 and 50 Sla t i tude. Apollo-Soyuz at 222 kilometers altitude w as clearly below th e SouthAtlantic Anomaly, and the cosmic rays that cause f lashes are more frequentfar from the Equator, as expected from the latitude effect . Figure 2.5 show s aplot of the measu red intensity of cosm ic rays wi th LET larger than 15 ke V/jumcompared to the numbers of flashes reported by the astronauts in each3-minute segment of the 90-minute duration of the expe rime nt. The two peaksare the high lati tudes of Apollo-Soyuz at 15:06 and 15:52 GM T. The ma tch isfairly good and show s that the light flashes are caused by the hig h-en ergycosmic rays that are deflected in toward the north and south m agne tic poles ofth e Ear th .

1 .5 r

Counts offlashes ineach 3 mm

15:00 15:30 16:00 16:30G MT

Cosmic-ray intensity compared with astronaut's counts of flashes on Apollo- Figure 2.5Soyuz orbit 111.

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Questions for Discussion(Flashes, Cosmic Rays)

7. If the astronau ts had started c ou ntin g flashes with ou t wa it ing for theireyes to become adapted to the darkness , w h a t errors mig ht have been made intheir reports?

8. Wh ile Apollo-Soyuz was between 30 and 51.8latitude (north or south) ,the astronau ts reported 34 stars, 1 super nov a, 7 com ma s, and 21 streaks inabout 63 minutes . Whi le be tween 30 N and 30 S la t i tu de, they reported 8stars, 6 c om m a s , and 5 streaks in about 30 m i nu t e s . On the w ay to the Moon ,fa r from Ea rth, Apollo astronau ts counted 2 or 3 flashes per m i nu t e . W ha t canbe concluded about cosmic rays and flashes from these num bers?

9. The cosmic-ray telescope detected rays that passed through both pairs ofcrossed wafers. What cosmic rays did it miss?

10 . I f the num ber of f la shes pe r minute had been much h igher , w ha t kind oferror might have been made in the astronauts' reports?

11. The art i fic ia l cosmic rays used in the laboratory so far to produce l ightflashes are not of high enough energy and mass to produce Cerenkov radia-t i on . If higher energies and mass are used someday , wh at resul ts wo uld youexpect?

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3 Cosmic-Ray Effects onBacterial Spores, Seeds,and EggsSmal l organisms can be carried aboard spacecraft in large numbers, and theeffects of cosmic rays on them can be measured statist ically . Furthermore, itis possible to count th e actual number of cosmic-ray "hits," rather than jus tmeasure the cosm ic-ray intensity near an astronaut 's head, as w as done in theLigh t Flash Experiment. In the Biostack I I I Exper iment (MA-107) , ind iv idualcosmic rays were tracked through layers of bacterial spores, small seeds, andeggs inter leaved with layers of AgCl-crystal wafers, special plastic, andspecial photographic film that registered where each cosmic-ray particlepassed.

The objective of Experim ent MA-107 was to determine the damage causedby cosmic-ray hits on these small l iving organ ism s, especially the changes(muta t ions) in the organ isms as they grew in the laboratory after th e mission .From these studies, we hope to learn w hat damage cosmic rays may do to menan d women on long spaceflights. The Principal Investigator , Horst Bu'cker,had 32 Co-Investigators who were experts in various biological f ieldsspores, bacter ia mul t ip l ica t ion , muta t ions , development of seeds, growth ofplants, and development of eggs and insectsas well as experts on cosmicrays.

A HZE ParticlesThe most damaging cosmic-ray particles are those with high electric charge(h ig hZ , the a tomic number ) and h igh k ine t ic energy E . When such / / i gh-Z ,High-E (H ZE ) particles pass through a substance, they leave a large amo unt ofenergy along their track energy that ionizes the a to m s and d i s r u p t smolecu les . In some plastics, th e material along th e track is so changed that itca n be "etched" out by sodium hydroxide (NaOH, a strong alkali) , leaving athin tube along the track. The HZ E tracks can also be seen on "nuclear trackemulsion" (a special photographic f i lm) after it is developed. (The s i lverchloride, A gCl, is broken into si lver (Ag) and chlorine (Cl) along the track,an d th e silver particles show black on the developed f i lm . ) T he emuls ion isspread th ickly (0.6 mill imeter) on the f i lm , and physicists can see the HZEtracks in a microscope as little black lines at vario us angle s throug h thee m ul s i on . As noted in Section 2C, large crystals of AgCl(Cd) also recordH Z E tracks while they are i l luminated w i th yellow l ight .

The MA -107 scientists used all these methods to record H ZE tracks througha sealed stack of 277 wafers about 10 centimeters in diameter (Fig. 3.1). Theheight of the stack was 12.5 centimeters, and the sheets of spores, seeds, andeggs were interleaved with cellulose nitrate plastic (CN), polycarbonateplastic (Lexan), and nuclear-track photographic f i lm. Figure 3.2 shows asmall part of the stack in Con tainer A. E ach of the two layers labeled P VA has

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Figure 3.1 Biostack III Container A and Container B for Experiment MA-107.

a single layer of seeds embedded in po lyviny l alcohol (a k ind of glue) . Theetched tracks in the CN sheets showed th e path of an HZE particle through th estack. The HZE particle often passed through one or more spores, seeds, oreggs, as shown in Figure 3.2.The size of the etched tracks on CN and Lexanshowed the energy and ap proxim ate Z ( ion charge) . The photog raphic em ul-sion detected lower energy tracks, and the AgCl(Cd) crystals in Conta iner Brecorded the lowest energy cosmic rays (1 keV//Lim LET). The crystalsshowed that 1500 cosmic rays passed throug h each square ce ntim ete r of theApollo spacecraft during the 217 hours that it was in orbit.

However, of these 1500 cosmic rays/cm 2 , only 1 percent were HZEparticles (wi th Z greater than 6) that produced wide tracks in the CN etchedw i th N a O H . It is th is 1 percent that is expected to cause damage, rather thaneithe r the lower energy protons (Z = 1) or the alpha particles (Z = 2). Fromth e different n u m b er s of tracks in the crystals, photographic f i lm , an d etchedplastic, Bu'cker and his Co-Inv estigators were able to estimate the spectrum ofthe cosmic-ray en ergies plotted in Figure 3.3. They also counted "disintegra-tion stars" l ike the one shown in Figure 3.4, where an atomic nucleusexploded (upon capturing a pion) , resul t ing in many short tracks (100 to 200micrometers) going in all directions. There were about 3500 of these stars per

18 ORIGINAL PAGE B? POOR QUALIT*


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cubic centimeter of photographic em ulsion, an d presumably about th e samenumb er (undetected) pe r cubic centimeter of spores, seeds, an d eggs. Becausethese disintegration stars release n uclear energy, they are thought to damageliving organisms like HZE particles do.

Part of Biostack III Container A with cosmic-ray track. Figure 3.2

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100 200 500LE T (linear-energy t ransfer ) .

Figure 3.3 Cosmic-ray energy spectrum for MA- 107 Container A.

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' : ^ f*'Disintegration-star tracks magnified 500 times. Figure 3.4

Mapping the HZE HitsThe Frankfu rt scientists buil t a very accurate "m icrom anipulato r" withwhich they could pick up spores of 1 -micrometer size an d place droplets ofNaO H on a partly etched cosm ic-ray track wi th a precision of 0.1 microm eter .They had microscopes arranged to measure x andj coordinates on the plasticsheets and f i lms to an accuracy of 0.1 micrometer .

The p rinciple of map ping the HZE tracks through several sheets of plastican d two layers of seeds is shown in Figure 3.2. Because the NaOH used toetch the HZE tracks in the plastic would kill th e seeds, th e seed layers weresealed betwee n two plastic sheets whi le the sheets were etched in NaO H for 18hours. This etching process started a small conical hole in the plastic surfacewherever an HZE particle had passed through . W ith the mic rom anip ulator ,the scientists then put droplets of NaOH into the hole to make it deeper an ddeeper, unt i l it almost reached the seed on the other side of the plastic(Fig. 3.5). This process w as repeated fo r about 3000 tracks on 35 sheets an denabled th e scientists to identify 18 6 seeds and 409 eggs hit by HZE particles.The spores were so small that when the scientists measured the distancefrom the center of the spore to the nearest HZE track, they found morethan 40 0 spores within 10 micrometers of a track; 22 of them were with in1 micrometer .

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Figure 3.5 Etch cone of an HZE-particle track in CN, covered with Arabidopsis thalianaseeds in polyvinyl alcohol (PVA).

MA-107 Results on Biological DamageFrom HZEHitsAfter a spore, seed, or egg was identif ied as having been "hit," i t wascareful ly removed with the micromanipulato r . The spores were placed in ak n o wn place (x a n d > > measured) on a nutr ient jel l y . Some of the seeds wereplanted, and a ll the eggs were incubated to hatch . Tw o control groupsone ofspores, seeds, an d eggs from B iostack III that were not near an HZ E track andone that remained in Frankfur t dur ing th e f l ightwere handled in the samew a y .

The MA-107 scientists were aware that factors other than the HZE hitsmigh t affect th e spores, seeds, and eggs. For instance, they might havebecome disrupted by one or more of the disintegration stars (Fig. 3.4),or havebeen hit by low-energy cosmic rays, or have been affected by weightlessness(Pam phlets I and V II ) for 9 days in Apollo-Soyuz . There w as also the chancethat the HZE hit did not pass through a vital part of the spore, seed, or egg.Like many biological experiments, this experiment had to be statistical,combining the effects observed on ma ny individuals to give the probabili ty ofdamage from an HZE hit . This is why such a large n um ber of small organisms(about 5 x 109 spores, 23 000 seeds, and 30 000 eggs) were carried onApollo-Soyuz.

22 ORIGINAL PAGE ISOF POOR QUALITY


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Manipulation and growth of a single Bacillus subtilis spore. The spore to beremoved is shown at the end of the needle in (a); the spore has been removedin (b). Increasing incubation times to 250 minutes are shown in (c), (d), and (e).and the colony after 24 hours is shown in(f).

Figure 3.6

23ORIGINAL PAGE I)F POOR QUALITY"


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The spores were single-cell "eggs" of Bacillus subtilis bacteria. When"planted" in warm nutrient jel ly , they norma lly produce a colony of bacteriathat mult ip ly rapidly af ter a few hours (Fig. 3.6). The fraction of spores tha tformed colonies is plotted in Figure 3.7 against th e distance from an HZEt rack . On ly 68 percent of the 22 spores that were less than 1 micrometer froman HZE track were able to form colonies, whereas 89 to 90 percent of the 50spores in the control groups formed colonies. The fact that 50 spores carriedon Apo llo-Soyuz (but located more than 50 micrometers from any HZE track)performed just like 50 spores in the ground-control group shows that no otherfactor affected them.

Ninety seeds of the Zea mays plant were hit by HZE particles, and 17 ofthese were p lan ted immedia te ly . (The others were grown later .) Fifteen

o o

BO

60

40

20

X

I3 4 5 6

Distance from HZ E t rack.>50

Figure 3.7 Percentage of spores forming colonies.

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"^TNAL PAGE ISOf POOR QUALM

plants sprouted, but five of them had smaller leaves than the 64 control plan ts.Eighteen seeds of another plant (Arabidopsis tha l iana) were hit,but thesey o u n g plants showed no signif icant differences from th e control plants.

Most of the eggs hit by HZE particles later showed serious damage. Thenum be r that hatched was lower than in the control groups, and some of thelarvae were deformed (Fig. 3.8).By careful observation and microscopicdissection, th e MA -107 sc ien t ist s hope to learn what parts of the eggs werevu lnerab le to HZE h i ts .

M u c h more research is needed before these studies can be applied to theques t ion of how HZE particles an d other radiation in spacecraft m ay injurem en and w omen over long periods of t ime. It is worth noting that the eggs an dspores carried on Apo llo-Soyuz in Biostack I II are know n to be more resistantto x-rays than man is. The lethal dose (a dose tha t ki l l s 50 percent of theorganisms in question) is 400 rads for hum an s, about 1000 rads for the eggs,an d about 100 000 rads for the spores. A s s u m i n g that th e damage by HZEcosmic rays is similar to the damage by x-rays, men and wom en should bemore vulnerable to cosmic rays than the small organisms carried on Apollo-Soyuz .

Malformations of Anemia salina induced by HZEparticles that penetrated their Figure 3.8eggs.

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Questions for Discussion(Cosmic Rays)

12. Why should high-Z particles make larger tracks and cause morebiological damage than protons of the same kinetic energy?

13. Are HZE cosm ic rays expected to show th e same la t i tude effect as lowerenergy cosmic rays?

14. At any one mom ent, did cosmic rays come in on Apol lo-Soyuz equal lyfrom al l sides?

15. Can you tell w h i c h way the HZE particle moved along th e track inFigure 3.5?

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Appendix A

Discussion Topics (Answers to Questions)1. (Sec. ID) A cosmic ray would be completely described by its speed

(usually given as kinetic energy E), ion cha rgeZ (positive), mass/1 in atomicmass units, and direction of motion (twoangles needed). Note that becausethe ions are completely stripped of electrons, th e atomic numberZ specifies/4(because A is approximately 2Z for most elements).

2. (Sec. ID ) Venus has no magnetic field and therefore no Van Allen belt.3 . (Sec. ID ) Changes in the Ear t h ' s magnetic field detected by comparingthe magnetism of old (dated) rocks with the present field direction could bedue to two causes: (a) the currents in the Earth 's core changed, therebychanging the magnetic dipole, or (b) continental drift (see Pamphlet V)

moved the rocks from where they were formed to a different place.4. (Sec. ID) If the Earth ' s atmosphere were drawn on Figure 1.1, it would

extend only 1 millimeter or so above th e circle representing th e Earth. Theelectrons an d protons of the Van Allen belt ar e reflected back in the polarregions much higher than this. However, if the atmosphere were 10 t imesthicker, it would interfere wi th the north-south oscillations of the electronsan d protons at each end. The electrons and protons wou ld be absorbed and theVan Allen belt would be eliminated.

5 . (Sec. ID ) Lead has higher density (11.3 gm/cm 3) t han a luminum (2.7gm/cm 3); therefore, a lead shield of 1-centimeter thickness has much moremass . It is the mass per uni t area that absorbs cosmic rays an d x- rays , so 1centimeter of lead is the better shield. (The production of secondary gammarays in both shieldsm ore in leadm akes an accurate answ er more com plexthan this.) Living t issues have a density near 1 gm/cm 3 .

6. (Sec. ID) Your head is about 16 centimeters or 160 000 micrometersthick. The 2000-megaelectronvolt cosmic ra y would therefore lose 1.6 X 10 skiloelectronvolts or 1600 megaelectronvolts an d come out wi th only 400megaelectronvolts of energy.

7. (Sec. 2E) If the astronauts had counted flashes before their eyes hadadapted to darkness, they might have missed some of the smaller, fainterflashes at the begin ning of the experiment. The Principal Investigator wantedthe same eye sensi t ivi ty to f lashes throughout the experiment.

8. (Sec. 2E) At high lati tudes, th e astronauts counted 63 f lashes in 63minutes ; near th e Equator , they counted only 19 f lashes in 30 m in u te s , wh ichis equ iva len t to 40 flashes in 63 minu tes . The higher rate at high latitude

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shows that the inte nsi ty of cosmic ray s there more nea rly resembles theintensity of cosmic ray s far from the Earth w here the rate was 2 or 3 flashes perminute . (Note that th e Earth cuts th e cosmic-ray intensity in half for alow-o rbiting spacecraft because it shields one side. O n the way to the M oon,Apollo ha d no such Earth shield .) The ratio of streaks to stars and comm as w as21 to 42 for high latitud es and 5 to 14 near the Equator. These ratios may showsome differences in the kin ds of cosmic rays com ing in to polar and equatorialregions. (There is also some que stion about the relativ e sen siti vity of differentastronauts ' eyes to f lashes, but the indi vidu al reports are not availab le.)

9. (Sec. 2E ) Figure 2.3 shows that th e "field of view" (Pamphlets I I andIII) of the MA-106 cosmic-ray telescope was about 77. That is, there is acone in wh ich all the rays were counted: 12 mil l imeters wide at the top,coming to a point at the center , and 12 mill imeters wide at the bottom,15 mil l imeters be low. The angle 6 o f this cone is half th e field of v iew , and tan6 = 6/7.5 = 0.80, and 6 = 38.7. The telescope missed all the rays comingin from th e sides (and a few between th e junc t io n s t r ips).

10. (Sec. 2E) If the flash rate were m uc h high er , an astronaut migh t see twoor three f lashes almost at once an d th ink that he saw on ly one. Then he wouldreport fewer than th e ac tua l number of f lashes .

11. (Sec. 2E ) If 5000-megaelectronvolt neon ions are someday fired intoh u m a n eyes, they should produce Cerenkov radiation in the eyeball . Thesewoul d be seen as "diffuse clouds" (Fig. 2 .1) .

12. (Sec. 3D) The larger electric charge on a high-Z io n produces strongelectric forces that extend farthe r out on all sides than do those from a proton(Z = 1). The ionization along th e high-Z io n path thu s exten ds far ther out inplastic or l iv ing t issue an d affects a larger volume along it s track.

13. (Sec. 3D) The "bending" of a cosmic ray by the Earth 's ma gnetic f ieldin Figure 1.1 is caused by a force perpendicular to both th e field and thepartic le's v elo city vector v. Th is force is proportional to the ion 's charge Z andspeed v, but the acceleration is inversely proportional to its m a ss /4 , wh ich ism u c h larger for hi gh Z . Therefore, HZ E particles are deflec ted less because oflarge A and also because th e acceleration produces less bending at higherspeed. (The radius of cu r va tu r e is proportional toAv/Z.) The la t i tude effectwil l thus be smaller for HZE cosmic rays.

14. (Sec. 3D) The Earth is an effective sh ie ld , so there were never an ycosmic rays coming up from Earth toward Apollo-Soyuz.

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15 . (Sec. 3D) Unless th e track ends , there is no way to te l l which way thecosmic ray was mo vin g. (How ever, it is more likely that the ray came fro m thebottom end of Biostack III , wh ich faced th e Apollo cabin wall , unless Apollowas rolled so tha t th e wa ll faced E arth.)

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Appendix BSI UnitsPowers of 10

International System (SI) U nitsNames, symbols, an d conversion factors of SI units used in these pamphlets:Quantity Name of unit Symbol Conversion factorDistance meter m

Mass kilogram kg

Tim e second sec

km = 0.621 milem = 3.28 ftcm = 0.394 in .mm = 0.039 in .Mm = 3.9ox 10'5 in. = 10 4 Anm = 10 Atonne = 1.102 tonskg = 2.20 Ibgm = 0.0022 Ib = 0.035 ozmg = 2.20 x 10-6 Ib = 3.5 x 10'5 ozyr= 3.156 x 10 7 secday = 8.64 x 10 4 sechr = 3600 sec

Temperature kelvin K 273 K = 0 C = 32 F373 K = 100 C = 212 FArea square meter m 2 1 m 2 = 104 cm 2 = 10.8 ft2Volume cubic meter m 3 1 m 3 = 10* cm 3 = 35 ft3Frequency hertz Hz 1 Hz = 1 cycle/sec

1 kHz = 1000 cycles/sec1 MHz = 106 cycles/sec

Density kilogram per kg/m 3 1 kg/m 3 = 0.001 gm/cm 3cubic meter 1 gm/cm 3 = density of waterSpeed, velocity meter per second m/sec 1 m/sec = 3.28 ft/sec

1 km/sec = 2240 mi/hrForce newton N 1 N = 105 dynes = 0.224 Ib f

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Quantity

Pressure

EnergyPhoton energyPowerAtomic mass

Customary UnitsQuantity

Wavelength oflightAccelerationof gravity

Name of unitnewton per squaremeterjouleelectronvoltwattatomic mass unit

Used With the SI UnitsName of unit

angstrom

g

SymbolN /m 2

J

e VW

am u

SymboloA

g

Conversion factor1 N /m 2 = 1.45 x 10-" lb/in2

1 J = 0.239 calorie1 eV = 1.60 x 10-'9 J; 1 J = 10 7 er g1 W = 1 J/sec1 amu = 1.66 x 10'27 kg

Conversion factor

1 A = 0.1 nm = 10-' m

1 g = 9.8 m/sec2

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Unit PrefixesPrefix

tengigamegakilohectocentim i l l imicronanopico

Abbreviation Factor by which unitis multiplied

T IO 12G IO 9M IO 6k IO 3h IO 2c IO-2m IO-3/i IO-6n IO-9p IO -12

Powers of 10Increasing Decreasing

102 = 100103 = 1 00010" = 10 000, etc .Examples:2 x IO6 = 2 000 0002 x I O 3 0 = 2 followed by 30 zeros

i o - 2 = i / i o o = o . o ilO"3 = 1/1000 = 0.00110-" = 1/10000 = 0.000 l .e tc .Example:5.67 x JO "5= 0.0000567

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Appendix C

GlossaryReferences to sections, Appendix A (answers to questions) , and f igures areincluded in the entr ies. Those in italic type are the most helpful .AgCl(Cd) crystal silver chloride with a small amount of cadmium added ;

used to record cosmic-ray tracks. (Sees. 2C, 3, 3A; Fig. 2.2)alpha particle a helium atom (Z = 2) with two electrons removed; the heliumnucleus . (Sees. 2, 3A)Cerenkov radiation the visible l ight emitted by a particle tra velin g near thespeed of light when it enters a substance where the velocity of light is less

than th e particle's speed. (Sees. 2, 2A, 2E; App.A, no. 11)CN (cellulose nitrate) a plastic in wh ich H ZE tracks can be etched with

NaOH. (Sec. 3A; Figs. 3.2, 3.5)Co-Investigator a scientist working w i th the Principal Investigator on aNASA exper iment .control group a group of indiv idual s (spores, seeds, eggs, people) with th e

same characteristics as the experimental group an d treated th e same w ayexcept for the one factor (such as exposure to cosmic rays) that is beingtested by the exper iment . (Sec. 3C ; Fig. 3.7)

cosmic ray an ex tremely h igh speed ion;a str ipped atomic nucleus. Solarcosmic rays are blown out of the Sun; galactic cosmic rays arrive from alldirections. (Sees. 1,1 A, IB to 3E; App. A , nos. 7,5,6,8,9, 13 to 15; Figs.1.1,2.3, 2.5,3.2,3.3) See HZE, ion,radiation, track; also se e Pamphle tsII and III.

count one pulse of current or voltage from a detector , indica ting the passageof a photon or particle through th e detector. (Sees. IB, 2C) See telescope.Light f lashes were counted by astronauts for Experiment MA-106. (Sees.1C, 2B, 2C; App.A , nos. 7, 8, 10; Fig. 2.5)

cyclotron a ma chine that produces very high speed (high-energy) ions bywhir l ing them around in a magnetic f ield . (Sec. 2A ; Fig. 2.1)

disintegration star several particle tracks, from 100 to 200 micrometerslong, starting from one point, s how ing the explosion of an atomic nucleus.(Sees. 3A, 3C; Fig. 3.4)

electronvolt (eV) a un i t of energy equal to the kinetic energy of an electronaccelerated from rest by 1 volt: 1000 electronvolts = 1 kiloelectronvolt;1000 kiloelectronvolts = 1 megaelec t ronvo l t or 1.6 x 10~ 13 jou le .

emulsion th e sensit ive layer on photographic f ilm. Some emuls ions arespecially ma nuf actu red to detect tracks of ions. (Sec. 3A )

etch to dissolve a plastic where a cosmic ray has changed the composition ofthe plastic along i ts track. The etchin g of CN and Lexan plastic is done withN a O H . (Sees. 3 A , 3 B; Fig. 3.5)

gamma rays very high energy photons of w ave leng th shorter than x-rays and

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energy higher than x-rays (higher than about 100 ki loelectronvolts).Gamma rays are produced by nuclear reactions an d other processes indistant regions of space. (Sees. IB, 1C; App. A, no. 5) See Pamphlet I I .Greenwich mean time (GMT) the t ime of an event , from 0 at midnight to 12hours at noon to 24 hours at midnight, as measured at 0 longitude(Greenwich, near London, England); used on space missions to avoidconfusion with other time zones. See Pamphlet I .HZE particles cosmic rays with high atomic number Z and high kineticenergy ; atomic nuclei of atomic number Z greater than 6 and energy Egreater than 10 0 megaelectronvolts. (Sees. 3A, 3B, 3C; App. A, no. 13;Figs. 3.5, 3.7, 3.8)ion an atom with one or more electrons removed or , more rarely, added.Cosmic-ray ions have all electrons removed and ionize other atoms as theypass them at high speed. (Sees. 1A, 1C, 2 t o 2 C , 3A; App . A, nos. 1, 11 to13)junct ion the interface between two solid materials. A silicon solid-statejunction passes a pulse of current when a cosmic ray passes through. (Sec.2C ; App. A, no. 9; Fig. 2.3)

kiloelectronvolt (keV) See electronvolt.latitude effect the decrease of cosmic-ray intensity on Earth from high

latitudes to the Equator. (Sees. 1A, 2B, 2D; App. A, nos. 8, 13)LET (linear-energy transfer) th e energy lost from a cosmic ray permicrometer along its track as it passes throug h l iving tissue. It is also called"stopping power." (Sees. 1C, ID, 2C, 2D, 3A; Fig. 3.3)Lcxa n polycarbon ate plastic in whi ch HZ E tracks can be etched w ith NaOH .(Sec. 3A; Fig. 3.2)MA-106 the Light Flash E xperime nt on the Apollo-Soyuz mission. (Sees. 1,2A, 2C, 2D; App. A, no. 9; Figs. 2.2 to 2.5)MA-107 th e Biostack I I I Experiment . (Sees. 1 ,3 , 3At o3C ; F i gs . 3.1 to3.3)magnetic dipole a bar magnet with a north pole at one end and a south pole atthe other. Electric current in a coil of wire produces a similar magnetic

dipole. (Sec. 1A ; App. A, no. 3; Fig . 7 . 7 )magnet ic field the stren gth of the m agne tic force on a uni t mag netic pole in aregion of space affected by magnets or electric currents. (Sees. 1 A, ID;App. A , nos. 2, 3, 13; Fi g . / . / )magnetic l ines offeree theoretical lines givi ng the direction of the force on atest magnetic pole at any place in a magnetic field. (Sec. 1A; Fig. / . / )magnetosphere a region arou nd the Earth w hic h the solar w ind can notpenetrate because of the Earth's magnetic field. (Sec. 1 A)megaelectronvolt (MeV) See electronvolt.micrometer ( /xm) one-m i l lionth of a meter, formerly called a micron.

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Milky W ay Galaxy a disk-shaped group of more than 10 0 billion stars,including our Sun . (Sec. 1A) See Pamphlet II.mutation a change in the DNA (deoxyribonucleic acid) "code," usual ly

caused by a cosmic ray passing through the nucleus of a cell that controlsdevelopm ent. The developed organ ism, a mu tant , differs from others in itsspecies. (Sec. 3)N a O H sodium hydroxide , a strong chemical used to etch CN and Lexanplastic so tha t cosmic-ray tracks throu gh the plastic will show. (Sees. 3A ,3B )

nutrient jelly a cul ture medium made of agar, sugar, water, an d othermaterials needed as food by growing bacteria. (Sec. 3C )orbit the path fol lowed by a satellite around an astronomical body such as theEarth or Moon. The orbit num ber was used on Apollo-Soyuz to identify th etime. (Sees. 2C, 2D; Figs. 2.4, 2.5)pion an unstable nuclear particle (meson) of mass between the electron and

the proton that can cause an atomic nucleus to explode. (Sec. 3A)Principal Investigator th e indiv idua l responsible fo ra space experiment and

fo r reporting the results.proton a positive ly charged atomic particle, th e nucleus of the hydrogen

atom. Ionized hydrogen is made up of separated protons and electrons.(Sees. 1 to 1C , 2, 2B, 3A, 3D; App. A, nos. 4, 12; Fig. 1.1)PV A (polyvinyl alcohol) an inert glue used to hold small spores, seeds, an deggs to a plastic sheet in the Biostack HI Exp erim ent. (Sec. 3A ; Figs. 3.2,3.5)ra d (radiat ion absorbed dose) a uni t of radia t ion damage to l iv ingorganisms; eq ual to 10~ 5 jou le absorbed pe r gram of t issue. (Sees. 1C, 3C)

radiation a term used loosely to includ e cosm ic-ray particles an dhigh-energyprotons, as wel l as penetrat ing electromagnetic waves (x -rays and gammarays). (Sees. /, 1A, IB, 1C, 3C)

retina the region at the back of the eyeball, form ed of nerv e end s sensitive tol ight. Light is focused there by the lens at the front of the eye. (Sees. 2 to2B )

shield an absorbing m aterial that pre ven ts the passage of radiation or reducesit s intensity . (Sees. 1, IB; App. A, nos. 5, 8 , 14)Skylab a very large space workshop that NASA put into orbit on May 14,1973. It was visited by three astronaut crews who worked on scientificexperiments in space for a total of 172 days. (Sees. 1 to 1C, 2, 2B)solar wind a stream of ionized gas, mostly protons and electrons, blown outof the Sun at high speed (2 0 km/sec) on all sides. (Sec. 1 A )South Atlantic Anom aly (SAA) an irregulari ty in the Earth's magn etic fie ld,east of Brazil , where th e radiat ion in the Van Allen bel t is very intense.(Sees. 1A, 2, 2B to 2D; Fig. 2.4)

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spore a smal l seed-germ that can grow into a microbe or a plant such as a fe rn .Spores of bacteria (about 1 mic rom eter in size) were used in Ex perim entM A- 1 07 . (Sees. 1, 3 to 3B, 3C; Figs. 3.6, 3.7)

telescope an ins t rument fo r measur ing th e direction of incoming rays . (Sees.2C, 2E; App. A, no. 9; Fig. 2.3)track th e path of a cosmic ra y th rough a substance that is changed by the

passage of a high-speed ion. Photographic emu lsion must be developed an dCN and Lexan plastic etched to show th e tracks. "Latent tracks" inAgC l(Cd) crystals disappear unless the crystals are i l luminated by yellowl ight . (Secs.2C, 3A, 3B , 3D; Ap p . A, no . 15 ; F i gs . 3 .2 , 3.3, 3.4,3.5, 3.7)

ultraviolet inv is ib le l ight of waveleng ths less than 4000 angstroms (400nanometers) , shorter than those of visible l igh t. (Sec. IB)Van Allen belt a doughnut- shap ed reg ion around th e Earth from about 320 to32 400 kilometers (200 to 20 000 miles) above th e magnet ic equato r ,

where high-speed protons an d electrons oscil late north-south in the Earth 'smagnet ic f ield . (Sees. 1, 1A, IB, ID, 2 ; A p p . A , nos. 2, 4 ; Fig . / . / )

weightlessness th e condi t ion of free fall or zero-g in which ob jec ts in anorbit ing spacecraft ar e weightless. (Sees. 1, 3C)

x-rays electromagnetic radiation of very short w aveleng th (abou t 0.1 to 100angstroms, or 0.01 to 10 nanom eters) and high photon energy (about 100electronvolts to 100 kiloelectronvolts) . (Sees. IB, 1C, 3C; Ap p . A, no. 5)See Pamphle t I I .

Z atom ic numb er, or the num ber of electrons in an atom. Cosmic rays area toms w i t h all electrons remo ved; that is, ions of cha rgeZ. (Sees. 1C, 2C,3A, 3D; App. A, nos. 1 , 12, 13)