A Measurement of Cosmic Ray Deuterium from 0.5-2.9 GeV/nucleon 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 University of Chicago, Chicago, IL 60637 7Danish Space Research Institute, Copenhagen, Denmark
Abstract. The rare isotopes 2H and 3He in cosmic rays are believed to originate mainly from the interaction of high energy proton heliud an s m wit galactie hth c interstellar medium 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 Galaxy. Hydrogen and helium 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 isotope 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 Matter-Antimatter Experiment (MAX) in- cosmic rays propagate withi Galaxe nth y influencey db strument over a wide range in energies 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 solar system 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 spallation 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 antiprotons and the GeV/nucleon, the mean free pathlength for escape from light 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 spectrometer (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. Particle 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 Particles Observed in the Heliosphere: ACE 2000 Symposium, edited by Richard A. Mewaldt, et al. © 2000 American Institute of Physics l-56396-951-3/00/$17.00 425
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp 2 4 0 2. 5 1. 0 Rigidity (GV) Mass (amu)
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 protons and helium in the 5 g/cm2 Canada. The flight lasted 16 hours at float including a residual atmosphere 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 cross section 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 scattering. 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. 428 Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp