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369 Og: 3.2-9 Gamma Ray Line Production from Cosmic OG: 3.2-9 369 OG: 3.2-9 GAMMA RAY LINE PRODUCTION 369FROM COSMIC RAY SPALLATION REACTIONS Silberberg,GAMMA RAYRein LINE and PRODUCTION Tsao, FROMC.H., COSMIC NRL, RAY Washington, SPALLATION REACTIONS D.C. 20375-5000 USA Letaw, John R., Severn Communications Corp., Severna Park, MD 21146 USA Silberberg, Rein and Tsao, C.H., NRL, Washington, D.C. 20375-5000 USA Letaw, John R., Severn Communications Corp., Severna Park, MD 21146 USA The gamma ray line intensities due to cosmic-ray spallation ~e~ctions in clouds, the galactic disk and accreting binary Thepulsars gamma rayare line calculated. intensities due toWith cosmic-ray the most spallation favorable plausible r'assumptions,eactions in clouds, only the a galacticfew lines disk may and accretingbe detectable binary at the level of 6 2 p10-ulsarsper are calculated.cm -sec. WithThe the intensities most favorable plareausible compared with those generatedassumptions, in only nuclear a few lines excitation may be detectable reactions. at the level of 10-6 per cm2-sec. The intensities are compared with those 1. generatedIntroduction. in nuclear Measurements excitation reactions. of gamma ray line intensities and energies from astrophysical sites permit the study of two types of nuclearI. Introduction. processes: Meas urements(1) Nuclear of gamma collisions ray line intensities by cosmic and rays and other high energiesenergy particles. from astrophysical Possible sites permitsites thefor study these of two reactions types of are the galactic disknuclear (Ramaty processes: et (I)ale Nuclear 1979), collisions interstellar by cosmic clouds, rays and othersupernovae high in clouds, accretingenergy particles. sources Possible such sitesas beaming for these pulsars reactions in are .close the galactic binary systems, and activedisk (Ramaty galactic et al. 1979), nuclei, interstellar with high-energy clouds, supernovae beams in clouds,interacting in the accretionaccreting sodisk.urces such(2) as Recent beaming nucleosynthesis pulsars in •close binary (i.e. systems, build-up and of nuclei) in supernovaactive galactic and nnovauclei, precursors, with high-energy as beamswell interactingas during intheir the explosive phase ~~layton,accretion disk.1973, (2) Arnett, Recent nucleosynthesis 1978, Mahoney (i.e. et a1. build- 1982,up of nuclei)Clayton, in 19§4).2 The supernovaAl line andhas nova already precursors, been as observed well as during at theira flux explosive level phofase 5x10- Icm -sec. rad (Mahoney et ale 1984 and Share et ale 1985). The latter line is _layton, 1973, Arnett, 1978, Mahoney et al. 1982, Clayton, 19_4)._ The probablyA1 line hasdue already to nucleosynthesis been observed at ain flux novae level of(Clayton, 5x10--/cm_-sec. 1984). tad (Nahoney et al. 1984 and Share et al. 1985). The latter line is probablyIn nuclear due to nucleosynthesis collisions, inthere novae are (Clayton, three 1984). processes that give rise to gamma ray lines: (1) Quasi-elastic collisions at low energies that generateIn nuclear excited collisions, nuclei. there areThe three relevant processes thatcross give sections rise to for these reactionsgamma ray lines: have (I) been Quasi-elastic reviewed collisions by Ramaty at low energieset ale that(1979). The main uncertaintygenerate excited here nuclei. is the The relevantabundance cross of sections the low for theseenergy nuclei (near 10 MeV).reactions (2) have Nuclear been reviewed spallation by Ramaty reactions, et al. (1979). with The the main spallation products in variousuncertainty excited here is thestates, abundance that of the de-excite low energy nucleipromptly (near 10by gamma-ray line emission.MeV). (2) Nucle Herear spallation the uncertainty reactions, is with due the spallationto lack of products information in of the populationvarious excited of the states, various that de-excite excited promptlystates. by gamma-ray(3) Gamma line rays produced upon theemission. decay Here of the uncertaintyvarious radioactive is due to lack ofnuclides information generated of the in nuclear spallationpopulation ofreactions. the various excitedThe associated states. (3) Gammagamma-ray rays prod energiesuced upon and emission probabilithe decay ofties various for radioactivethe latter nuclides case are generated sufficiently in nuclear well known. In this paperspallation we shall reactions. concentrate The associated on processes gamma-ray (2) energies and (3). and emission probabilities for the latter case are sufficiently well known. In this paperIn weSection shall concentrate 2, we calculate on processes the (2) spallationand (3).yields and the relative J gamma t'ay line intensities. In Section 3, we apply these calculations to the.In Sectioninterstellar 2, we calc clouds,ulate the spallationthe galactic yields disk, and the and rel ativeto pulsars in an accreting system. In Section 4, the conclusions aarepply thesepresented, calculations and the gamma ray line intensities. In Section 3, we an detectabilityto the interstellar with clo theuds, GROIOSSE the galactic detector disk, and is to discussed pulsars in • are presented, and the • accreting system. In Section 4, the conclusions 2.detect The abilitySpallation with the Yields GRO/OSSE and detector Relative is discussed. Gamma Ray Intensities. The rate at which a nuclide of type j is created per unit volume in the The rate interstellar2. The Spallation medium Yields from andRelative proton Gammainteractions Ray Intensities. (for protons in a given unit volume in the energyat which interval) a nuclide ofis: type j is created per interstellar medium from proton interactions (for protons in a given R (nuclides/cm3 sec) = 10-27 J n F (1) energy interval) is: j H j Rj (nuclides/cm 3 sec)= 10-27 J nH Fj (I) 370 00OG:: 33.2-9.2-9 27 2 Here 10- 2is the conversion factor from mb to cm , J = cosmic ray I0-272is the conversion factor from mb to cm2, J = cosmic ray protonsprotons/cm/cm -sec, in a given energy interval. (We assume that the contribution of nuclei heavier than protons results in a second-order correction, though at energies of a couple of MeV/u, MeV/u, the contribution of alpha-induced reactions is 3 important.) n is the number of hydrogen alpha-induced reactions is important.) nHH is the number of hydrogen atoms in the medium, per cm cm3, , and F . := ZoLa ....f f.., , (2) J . Jl 1 FU_1 i 31 1 where o..0 .. is the cross section for protons with nuclide i, in units of 3 1 mb yiel_ingyiel~lng nuclide j, and fi is the abundance of i per H B atom in the collision medimedium.um. 50 l l = = I I I = I I I = I _I E _ mO 0o :----- Hc +- "-------14 N Clo _ 6Li I __ 7Li "1"::c _lo B '­ _ ";'Be .0 _L::t. I010 55~ __~ __~-L~LL~L- __~ __-L-L-L~~ I I i I i i 0.0.1 I 1.0 10I0 ENERGY (GeV) FigFig.. I1.. The energy dependence of F_F.,, the production rate function for J the nuclides whose secondary yields J are largest. Fig. I1 shows the values of F. as a function of cosmic ray proton energy E, using the elemental and _sotopiclsotopic abundances of Cameron (1982). AssAssuminguming that most of the prompt de-excitations pass to the ground state via the first excited state, the most prominent 1~ines induced by ~~gh energyvia the cosmic first r_r~~ excited protons state, would the be most 4_441~4 prominentMeV from I-C, _inesC, 2.12 induced MeV from by _ghB, 5.27 MeV f5'0m N1'1 5.18 MeV from O. In addition, the radioactive 5.27 MeV _r°m-JN_I, 5.18 MeV from "_0. In addition, the radioactive decay of JO0 and C yields positrons. Fig. 2 shows the F. values of other abundant products. Some of these F. values are 10w _ow at low energies, providing a test for the presence presenceJor J or absence of low-energy cosmic raysrays.. • The rate of gamma ray line emission from a volume V is R.Vk, where k is the gamma ray multiplicity from the formation of nnuclibeucl_de j. The gamma ray line flux from nuclide j at earth is: RjVk(per cm2cm2_sec),-sec), (3) 4_d2 where d is the distance from the gamma ray source to earth. 371 371 OG: 3.2-9 OG: 3.2-9 __ OBe _- ,oc V"--_ __.-- oB E ° .....o --14C o I _ / // I -._--leF IL:::r:: I- //.I--_"- ........ I / _ // _',--"N .0 :i. _L I_ )If I I _ i ll) %-')°Ne 1.0 I0 0.10.I 1.0 10 ENERGY (GeV)(GeV) Fig. 2. 2. The energyThe dependenceenergy dependence of F. for less abofu ndantF.J for prod ulessct nu clei.abundant product nuclei. J 1.'.3. TheThe Cosmic-Ray Cosmic-Ray InducedInduced GammaGamma Ray Ray Flux Flux from Clouds,from theClouds, Galactic the Disk Galactic Disk and fromfrom Accreting Accreting Pulsars. Pulsars. The flux from aThe large flux cloud isfrom calculated, a large cloud is calculated, usingusing the the properties properties discussed discussed by Issa et al. by (1981) Issa i.e. et we assalu :-(198'1")T.e.me a we assume a cloudcloud m assmass ofof aboaboutut 105 so10lar5 masses,solar or 10masses, _2 hydrogen or ato m10s.62 A hydrogen atoms. A adopts Cameron's abundances for distancedistance of 400of pc400 is pc is assumed.assumed. If oneIf one adopts Cameron's abundances for thethe calccalculations,ulations, F=O.03 F=0.03 for the *_C for 4.44 the MeV llne. 12C J,4.44 for the MeV local line. J, for the local inter.stellarinterstellar cosmic cosmic ray intensity ray intensity is about 10/ cm2-sec.is about With the10/cm most2 -sec. With the most cons~rvativ2conservativ_ ass uassumptions,mptions, the flux the of the flux 4.4 MeV of carbon the line 4.4 is aboutMeV carbon line is about 2x102xi0 - 99 y/cmy/cm_-sec.
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