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A Measurement of from 0.5-2.9 GeV/ G.A Nolfoe d . 1, L.M. Barbier2, E.R. Christian2, A.J. Davis1, R.L. Golden . Hof5,M 4, K.E. Krombel2, A.W. Labrador6, W. Menn4, R.A. Mewaldt1, J.W. Mitchell2, J.F. Ormes2,1.L. Rasmussen Reimer. 7,O 3, S.M. Schindler . Simon1,M 4, S J. Stochaj5, R.E. Streitmatter2, W.R. Webber5

1 California Institute of Technology, Pasadena, California 91125 2NASA/Goddard Space Flight Center, Greenbelt, 20771MD 3Max-Planck-lnstitut fuer extraterrestrische Physik, Garching, Germany Universitat4 Siegen, Siegen, Germany 5New Mexico State University, Cruces,Las 88003NM 6 , Chicago, IL 60637 7Danish Space Research Institute, Copenhagen, Denmark

Abstract. The rare 2H and 3He in cosmic rays are believed to originate mainly from the interaction of high heliud an s m wit galactie hth c unique Th . e propagation histor f thesyo e rare isotopes provides important constraint galactin so c cosmi sourcy cra e spectrmodeln o d their aan sfo r propagation within the . and isotopes were measured with the balloon-borne experiment, MAX, which flew from Lynn Lake, Manitob n 1992 ai e energ Th . y spectru f deuteriumo GeV/nucleo2 m3. betweed an 5 n0. n measurey db experimenX theMA wels a tpreviousl s a l y published resultfroe same H 3 m th f seo instrument wil comparee b l d with prediction f cosmiso galactiy cra c propagation models observee Th . d compositio lighe th tf no founs se i b o dt generally consistent wit predictione hth standare th f so d Leak Modex yBo l derive observationt fi o dt heavief so r nuclei.

INTRODUCTION affecte fewey b d r nuclear destruction processes during propagation. These isotope alsy oma s provid tesea f o t Extensive observation cosmif so abundancey cra s over whether cosmic rays undergo continuous acceleratior no a wide range in energy help to form a comprehensive "reacceleration" during their passage through the Galaxy pictur f cosmio e y origi ra cpropagationd nan e th n I . (8). Hydroge heliud nan m isotopes have been measured simplest picture such as the standard Leaky Box Model, by the Isotope - Experiment (MAX) in- cosmic rays propagate withi Galaxe nth y influencey db strument over a wide range in extending to 2.9 the competing processes of nuclear interactions and es- GeV/nucleon (6) thin I . s paper presen e meaX w , -MA t cape fro e Galaxymth e lighTh .t isotopes, sucLi s ha surements of 2H as well as the previously published re- Be, B are significantly enhanced over abun- sults of 3He (6) and compare these observations with pre- dances indicating that these elements are produced as sec- dictions from current propagation models. ondary or products of primary C, N, and O ele- ments. Thus, the determination of the secondary/primary INSTRUMENT AND FLIGHT ratio provides a measure of the amount of material tra- versed by primary cosmic rays during propagation. At 1 MAX was designed to measure and the GeV/nucleon, the mean free pathlength for escape from isotopes ove widra e energy range. IMAX employed Galaxe th g/cm0 1 founs yXi e ~ 2 b . o dt a combinatio f detectorno s includin gsuperconductina g The isotopes 2H and 3He are of particular interest as magnetic (2) time-of-fligha , t (TOP) sys- these isotopes are considered to be interaction products of tem, scintillation counters (S1,S2), and large-area aero- more th e abundant hydroge heliud nan m nuclei addin I . - gel Cherenkov detectors. identification is accom- tion, the abundance of 2H and 3He can, in principle, pro- plishe measuriny db particle gth e velocity (3, charg, eZ vide a more sensitive determination of the escape path- and rigidity R (momentum/charge). For further details on length than heavier cosmic ray nuclei, since H and He are the performance of the IMAX instrument see (1).

CP528, Acceleration and Transport of Energetic Observed in the : ACE 2000 Symposium, edited by Richard A. Mewaldt, et al. © 2000 American Institute of Physics l-56396-951-3/00/$17.00 425

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FIGURE 1. IMAX mass separation for Z=l, (3=1 particles along with the corresponding mass histograms in two separate energy intervals mase Th determines .si d between 2.5-2.860 GeV/nucleon usin velocite gth y obtained fro Cherenkoe mth v counterse Th . thick solid lines represen instrumenn a t t simulation, whil thie eth n solid lines refe measureo t r d distributions.

IMAX fle Julyn wi , 1992 from Lynn Lake, Manitoba, from the interaction of and helium in the 5 g/cm2 Canada. The flight lasted 16 hours at float including a residual abov instrumente eth attenuae Th . - long ascent of ^7 hours. IMAX reached a maximum float tion of 2H within the instrument and atmosphere is de- g/cm5 ( residuaf m altitud2o k 6 3 f elo atmosphere)e Th . termined using a universal parametrization for the total geomagnetic cutoff varied betwee nLynt a 0.3 V n5 G Lak e reaction given by Tripathi et al. (10). This an dPeact a 0.6 V 3eG River, Alberta. model is in good agreement with current measurements inelastie foth r c cross section 2f H+ so 3 d He+pan p reac- DATA ANALYSIS tions (10), (11). IMA meaa s Xnha grammag- in e th n ei strument of 13.8 g/cm2. The different materials encoun- IMAX event acceptee sar d base four-fola n do d coin- tered durin particle'e gth s traversal throug IMAe hth - Xin cidence betwee photomultipliee nth r signal- s froop e mth strumen accountee tar thin i sr dcalculationfo . bottod positscintillatorsan P p mTO to e e sideth e f so Th . selection criteria employe obtaio dt ncleaa n samplef o charge one particles are discussed in (1). °'08 : Atmospheric Model (Papini 1993) --- 0.06 r Figure 1 shows the isotopic separation for charge particlee on s usin (3-rigidite gth y technique corree Th . - 0.04 sponding mass histogram representativo tw n si e energy 0.02 200-80: V 0Me intervals are shown in Figure 1, where the velocity in 0.00 0 10 20 30 highee th r energy interva s obtainei l d fro aerogee mth l Residual Atmosphere (g/cm2) Cherenkov counter. Due to the non-gaussian behavior 0.060 Atmospheric Model (Papini 1993) ___ distributionse oth f simulatioa , s developenwa - ac o dt 0.045 curately model the instrument response (6),(7). The sim- 0.030 ulation takes into account evenn a eveny n b to , t basis, 0.015 the actual spectral incomine shapth f eo g particlese th , 0.000 800-1200 MeV timinP TO g resolution photoelectroe th , n statistical fluc- 0 10 20 30 tuation 8-rad an s y contribution Cherenkoe th o st v light Residual Atmosphere (g/cm2) yield t alsI . o takes into accoun spatiae tth l resolutiod nan

rigidity resolution of the tracking system, and the effects FIGURE 2. IMAXH/H as a function of atmospheric depth 1

of multiple coulomb . The simulation results separato intw e energy intervals mode2 e Th .f Papin o l nors i i - showe ar thice Figurn th i ks a soli1 e d lines; . malize IMAe th o dt X dat discusses aa text.e th n di

2 RESULTS contributioe Th n from atmospheric secondars i H y determined from calculation Papiny . b s(4),(5)al t e i . In orde determino rt fluf e deuteriuo f e th x o p to e th mt a Several other calculations have been performed includ- atmospheree th necessars i t i , accouno yt nuclear tfo - rin ing those of Webber (12) and Lijowski et al. (3). Current teraction losses withiinstrumene th n ni atmospherd an t e calculations differ by as much as a factor of 2-3 where as well as for the secondary population of 2H produced the differences are most likely due to the assumed pri-

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Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp mary proton and helium spectra and the assumed interac- growth curve consistene ar s t with Papini's atmospheric tion cross sections orden I . betteo rt r constrai estir nou - secondary calculation at solar minimum conditions. On contributioe matth f eo f secondarno obtaie w e , nth H y 2 the other hand, the BESS secondary calculations result 2H/1H ratio as a function of depth in the atmosphere dur- in fluxe factoa s f ~o r2 lower, close Papini'o t r s solar ing IMAX's long ~7 hour ascen floao t t altitudes. Fig- maximum calculation (11). Table 1 lists the IMAX mea- ure 2 shows the 2H/1H ratio at seven separate depth instrumene th f so p d to tan e surementfluth H 2 t xa e th r sfo atmospheree inth dashee Th . d curvcalculatioe th s ei n atmosphere. by Papini (4) for the production of secondary deuterium in 5 g/cm2 residual atmosphere during solar minimum Table 1. 2H Flux at the top of the instrument (TOI) and conditions Papine Th . i IMAe calculationth o t X t fi e sar atmosphere(TOA). 2H/1H ratio as a function of depth resulting in a top of the atmosphere ratio of 0.036 ±.004 at 600 MeV/nucleon Energy Mean Energy 2Hro/ 2Hro4 and 0.022 ±.003 at 1 GeV/nucleon, as shown in Figure (GeV/n) (GeV/n) contributioe Th . 2 secondarf no y deuterium predictey db 0.4-0.6 0.5 2 35.2. 8± 30.0 ± 3.5 Papini's mode s consisteni l t wit rate f growthth eo f ho 0.6-0.8 0.7 25.5 ± 1.5 24.3 ± 1.9 2H/1H as a function of depth in the atmosphere measured 0.8-1.0 0.9 18.3 ±1.2 18.0 ±1.5 by IMAX. Secondary deuterium produced within the in- 1.0-1.2 1.0 15.5 ±1.0 15.8 ±1.1 strument is vetoed by the instrument trigger and event se- 1.2-1.4 1.2 12.8 ± 0.8 13.1 ±0.9 lection criteria. 1.4-1.6 1.5 7 10.0. 4± 7 10.0. 7± 1.6-1.8 1.7 9.7 ± 0.7 10.1 ±0.7 DISCUSSION AND CONCLUSION 2.5-2.9 2.7 2.6 ± 0.3 2.6 ± 0.3

atmoe Figurth f -o showspectrue3 p H 2 to e e sth th mt a The ratio 2f H/so 2d H/1Han 3 Hshowe ear Figuren i s sphere along with recent measurements from the BESS 4 [a] and 4[b] along with the predictions of propagation experiment during three separate flights from 1993 to models base standara n do d Leak calculatiox yBo o Se y nb 1995 (11). The solar modulation during the IMA Xreacceleratioa d 199an ) 2 (9 . al Ptuski t n& e modeo Se n y (8)lb . fligh s consisteni t t wit hmodulatioa n parametee th n i r The 2H/1H ratio is in excess of the model predictions at spherically symmetric force-fielV dM mode0 75 $f = o l low energies where the atmospheric secondary contribu- energiesw lo (1)t A . , wher effecte eth f atmospherio s c tio s largestni IMAe Th . X 2e resultH/th 3r Hsfo e ratio ar betten ei r agreemen highet a t r energies unexpectt no , - edly, sinc 2e H/eth 3He rati essentialls oi y independenf to pathlength in the interstellar medium. 2 4 100 IMAX (92) * _ A measure H/th f Heo e ratio ove wida r e energy I ; n BESS (93) BESS 94 A range may help to distinguish between existing propa- ' o o ( ) - 2 4 D ^ « 3 - o BESS (95) gation models, especially as we expect the H/ He ra- Dl a ? o D 2 tio to exhibit a strong energy dependence resulting from HO * X 2 ¥ the H production cross sections. Reacceleration, on the 10 ~ ° ^^ I other hand, would smea thit rsou energy dependencee Th . 2H/ 43d HHe/ean 4He ratio showe ar s Figuren ni s 4[c] and 4[d] and are compared with predictions from Seo & * Ptuskin (8), Webber (14) and Reimer et al. (6). Web- 1 ber's calculation is a standard Leaky Box Model with 6 0 1. 10.0 1 0. a pathlength X=31.6pR-°- for R>4.7 GV and X=12.5p Energy (GeV/nucleon) below 4.7 GV that is based on B/C measurements (15). The solid curve in Figure 4[c] is a calculation by Seo & FIGURE 3. IMAX top of the atmosphereH flux compared Ptuskin that includes the affects of reacceleration (8). Fi-

with measurements from the BESS experimen 2 t (11). nally, the solid curve in Figure 4[d] is a standard Leaky calculatiox Bo tha) Reimey (6 nt b . assumeal t re s similar secondarie significante sar , IMAX observe highesa r deu- input parameter Webbee th o st r calculations (14), though terium flux than BESS observations during 1993, con- with slightly different cross sections. trary to what one might expect from solar modulation ef- IMAe Th X generallobservatione ar H 2 e y th con f so - fects alone. The discrepancy appears to be in the choice sistent with prediction standare th f so d Leak Modex yBo l of the absolute value for the calculated contribution of in which proton heliud san m hav same eth e propagation atmospheric secondary deuterium. We find the IMAX history as the heavier component of cosmic rays. How-

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Seo & Ptuskin (1994) Seo & Ptuskin (1994) ———— . (1994al Se t e o ) : . (1994al t e )o Se : : 0.08 o o 3 ; cd ; (I °-06 PH OJ 2 r

^ 0.04 CO ; ffi ^ h ,,4 ; w ffi 1 L V—_li4i|L^ 0.02 ; ^ i 0.00 [a] 0 0.1 1.0 10.0 0.1 1.0 10.0 Energy (GeV/nucleon) Energy (GeV/nucleon)

0.8 0.3 o & Se Ptuskin (1994) Webber (1997) .2 0.6 ctf "S 0.2

FIGUR . E[a]-[b]4 : IMAX 2H/ 2d H/1Han 3 He ratios compared wit propagatioe hth n model with reacceleratio Ptuski& o ) Se n(8 f no (solid standar e curveth d (dashe) an )d (9 Leak. calculatioal x dt e ycurve)Bo o Se f n,o [c]-[d]: 2H/4 He3d He/an , 4He ratios compared with propagation models of Webber (14) (dot-dashed curve), and Reimer et al. (6) (solid curve). The dashed curves in [d] represent the uncertaintie Reimee th . calculation al n s i t re .

ever, there is a tendency for the 2H/4He and 2H/1H ob- 3. Lijowski, M., (1994), Ph.D. Dissertation, Louisiana State servation somewhae li o st t abov modee eth l predictions. University. Understanding this possible excess will requir thorea - . Papini4 t al,e , Proc.P. , 23rd Int. Cosmic Conf.y Ra (Cal- ough investigation of the dependence of these ratios on gary), (1993), 503. 2 relevanthe t productionthe croson s sectionand H sfor 5. Papini al,t e , IP. ,I Nuovo Cimento, , (1996)19 , 367. assumed pathlength distribution. 6. Reimer al.,ApJ,t e , O. , 496, (1998) 490. 7. Reimer, O., et al, Proc. 24th Int. Cosmic Ray Conf. ACKNOWLEDGMENTS (Rome) , (1995)2 , , 614. The IMAX project was supported in the United 8. Seo, E.S., and Ptuskin, VS., ApJ, 431, (1994), 705. States by NASA under NAG5-5227 (Caltech) and un- 9. Seo, E.S., et al,ApJ, 432, (1994), 656. der RTOP 353-87-02 (GSFC) and grants NAGW-1418 10. Tripathi, R.K., etal, MASA/TP-1999-209726, NASA Lan- (NMSU/BBMF n Germani e Deutsch th d an y ) b y e gley Research Center, (1999). Forschungsgemeinschaf te Bundesminth (DFG d an ) - 11. Wang, J.Z., et al, Proc. 26th Int. Cosmic Ray Conf. (Salt isterium fiir Bildung, Wissenschaft, Forschung und Lake City , (1999))3 . 37 , Techologie(BMBF). 12. Webber, W.R. al,ApJ,t e , 380, (1991), 230. 13. Webber, W.R. al,ApJ,t e , 392, (1992), L91. REFERENCES 14. Webber, W.R., Adv. Space , (1997)5 . Res.,No ,, 75519 . 1 , .accepte al Mennt e , publicatior dW. ,fo ApJ,n i 533. ,No 15. Webber, W.R., et al,ApJ, 457, (1996), 435. 1, (2000). 2 .al,t e Hof , NuclM , Inst. Meth.,& A345, (1994), 561.

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