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369 OG: 3.2-9

369 OG: 3.2-9 LINE PRODUCTION FROM REACTIONS Silberberg,GAMMA Rein RAY LINE PRODUCTION FROM COSMIC RAY SPALLATION REACTIONS and Tsao, C.H., NRL, Washington, 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 are ray calculated. line intensities With the due most to cosmic-ray favorable spallationplausible assumptions, r'eactions inonly clouds, a fewthe lines galactic may be diskdetectable and accreting at the level binary of 10- 6 2 pulsarsper arecm -sec. calculated. The intensities With the mostare compared favorable with pla usiblethose generatedassumptions, in nuclear only a fewexcitation lines may reactions. be detectable at the level of 10-6 per cm2-sec. The intensities are compared with those 1. generatedIntroduction. in nu clearMeasurements excitation of reactions. gamma ray line energies intensities and from astrophysical sites permit the study of two types nuclear of I. Introduction.processes: (1) Meas Nuclearurements collisions of gamma by raycosmic line rays intensities and and energy other high energiesparticles. from astrophysical Possible sites sites for permit these thereactions study ofare twothe types of disk (Ramaty galactic nuclear processes:et ale (I)1979), Nuclear interstellar collisions clouds, by cosmic supernovae rays and in other high accreting clouds, energy particles.sources such Possible as beaming sites pulsars for these in reactions.close binary are systems, the galactic active galactic and disk (Ramaty et al.nuclei, 1979), with interstellar high-energy clouds, beams supernovae interacting in clouds,in the accretion disk. accreting sources(2) such Recent as beamingnucleosynthesis pulsars in(i.e. •close build-up binary of systems, nuclei) andin supernova and active galacticnova n uprecursors,clei, with as high-energy well as during beams their interacting explosive inphase the ~~layton,accretion 1973, disk. Arnett, (2) Recent 1978, Mahoney et a1. (i.e.1982, build-Clayton,up of19§4).2 nuclei) in Al line has The supernova andalready nova precursors, been observed as wellat a asflux during level their of 5x10- explosiveIcm -sec. phase rad (Mahoney et ale 1984 _layton, 1973, Arnett, 1978,and MahoneyShare et et ale al. 1985). 1982, Clayton,The latter 19_4)._ line Theis probablyA1 line due has to alreadynucleosynthesis been observed in novae at a(Clayton, flux level 1984). of 5x10--/cm_-sec. tad (Nahoney et al. 1984 and Share et al. 1985). The latter line is In probablynuclear due to collisions, nucleosynthesis there inare novae three (Clayton, processes 1984). that give gamma rise to ray lines: (1) Quasi-elastic collisions at low energies generate excited that In nuclear collisions,nuclei. thereThe arerelevant three cross processes sections that givefor risethese to reactionsgamma ray have lines: been (I)reviewed Quasi-elastic by Ramaty collisions et ale at(1979). low energies that uncertainty The main generate excitedhere is nuclei.the abundance The relevantof the low cross energy sections nuclei for(near these MeV). (2) Nuclear 10 reactions have beenspallation reviewed reactions, by Ramaty with ettheal. spallation (1979). products The main in various excited uncertainty herestates, is the abundancethat de-excite of the promptly low energy by gamma-ray nuclei (near line 10 emission. Here MeV). (2) Nucleather spallationuncertainty reactions, is due to with lack the of spallation information products of the in population of various excitedthe various states, excited that de-excite states. (3) promptly Gamma rays by gamma-rayproduced upon line theemission. decay of Here various the uncertainty radioactive is duenuclides to lack generated of information of the spallation in nuclear populationreactions. of the vario uThes excitedassociated states. gamma-ray (3) Gammaenergies rays and prod uemissionced upon probabili ties the decay offor variousthe latter radioactive case are sufficiently generatedwell known. in In nuclear this paperspallation we shall reactions. concentrate The on associatedprocesses (2) ga mma-rayand (3). energies and emission probabilities for the latter case are sufficiently well known. In this In Section paper we shall2, concentrate we calculate on processesthe spallation (2) and yields (3). and the relative J gamma t'ay line intensities. In Section 3, we apply these to calculations the.In interstellar Section 2, weclouds, calcu lathete thegalactic spallation disk, yieldsand to andpulsars the relative accreting system. in an gamma ray line intensities.In Section 4, In the Section conclusions 3, we aarepply presented, these calc andulations the detectabilityto the interstellar with the cloGROIOSSEuds, thedetector galactic is discussed disk, and • to pulsars in an • accreting system. In Section 4, the conclusions are presented, and the 2.detect The abilitySpallation with Yields the GRO and/OSSE Relative detector Gamma is discussed.Ray Intensities. at The rate which a of type j is created per unit volume interstellar in the 2. The Spallationmedium Yieldsfrom and Relativeinteractions Gamma (for Ray Intensities. in a Thegiven rate energyat which interval) a nuclide is: of type j is created per unit volume in the interstellar medium from proton interactions (for protons in a given 3 27 energy interval) is:R (nuclides/cm sec) = 10- J n F (1) 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 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 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 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 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 ° o I _ / // --14C I IL:::r:: I- //.I--_"- -._--leF ...... / _ // .0 I _',--"N :i.

_L I_ )If I%- I')°N _e i ll) 0.I 1.0 I0 0.1 1.0 10 ENERGY (GeV) Fig. 2. The energy dependence of F. for less abundant product nuclei. The energy dependence of F.J for less abundant product J nuclei.

1.'.3. The Cosmic-Ray Cosmic-Ray Induced Gamma Ray Flux from Clouds, the Galactic Disk Induced Gamma Ray Flux from Clouds, the Galactic Disk andand from from Accreting Accreting Pulsars. The flux from a large cloud is calculated, Pulsars. The flux from a large cloud is calculated, usingusing the properties properties discussed by Issa et al. (1981) i.e. we assume a discussed by Issa et al :-(198'1")T.e. we assume a cloudcloud mass mass ofof about about 1055 solar masses, or 1062 _2 hydrogen atoms. A 10 solar masses, or 10 hydrogen atoms. A distancedistance of 400 pc is assumed. If one adopts Cameron's abundances for of 400 pc is assumed. If one adopts Cameron's abundances thethe calculations, calculations, F=O.03 for the *_C 4.44 MeV llne. J, for the localfor F=0.03 for the 12C 4.44 MeV line. J, for the local inter.stellarinterstellar cosmic cosmic ray intensity is about 10/cm2-sec.2 With the most ray intensity is about 10/cm -sec. With the most cons~rvativ2conservativ_ assumptions, assumptions, the flux of the 4.4 MeV line is about the flux of the 4.4 MeV carbon line is about 2x102xi0 -9 y/cmy/cm_-sec. -sec. However, Issa et al. (1981) noted that the cosmic ray However, Issa et ale (1981) noted that the cosmic ray fluxflux is is higher higher by by a factor of 5, especially in clouds associated with a factor of 5, especially in clouds associated with O-BO-B stars, stars, where where frequent supernovae occur. Furthermore, such C-B frequent supernovae occur. Furthermore, such C-B regionsregions should should have have nucleosynthetlc enhancement of elements heavier than nucleosynthetic enhancement of elements heavier than helium.helium. Adopting Adopting a factor of 5 for this enhancement the flux is 5xi0 -8. a factor of 5 for this enhancement the flux is 5x10-a ReevesReeves (1978), based on the general abundances of of B, has• (1978), based on the general abundances of isotopes concludedconcluded that there is a very large flux of low-energy particles.of B, has A that there is a very large flux of low-energy particles. largelarge low-energy low-energy cosmic ray flux coupled to the large low-energy crossA cosmic ray flux coupled to the large low-energy cross sections would further sections would furtherincrease increase the the 4.4 4.4 MeV MeV gamma gamma ra~~lu~ ray_lu_ from from aa largelarge cloudcloud by by anan order order of of magnitude, to values near 5 x 10- /cm -sec. With a magnitude, to values near 5 x 10 /cm -sec. With a largelarge proton proton flux flux between between 5 and 30 MeV, such as considered by Ramaty et 5 and 30 MeV, such as considered by Ramaty et aleal. (1979), (1979), the the contribution contribution of nuclear excitations to the gamma ray of nuclear excitations to the gamma ray lineline flux flux becomes becomes dominant; the 4.4 MeV gamma ray line flux could then dominant; the 4.4 MeV gamma ray line flux could then bebe boosted boosted further further by by a afactor factor of of about about 10. 10. WithWith the the "optimistic" latter assumptions, the flux from the galactic "optimistic" latter assumptions, the flux from the galactic diskdisk (near (near 4 4 MeV) due to spallation is about 3 x 10-S/cm2-sec, and with MeV) due to spallation is about 3 x 10-6 /cm2-sec, and nuclearnuclear excitation excitation included, about 3x10-s/cm2-sec (Ramaty et al. 1979).with included, about 3x10-s /cin2-sec (Ramaty et a!, 1979). TheThe gamma gamma ray ray background background from the galactic disk (due largely to from the galactic disk (due largely to bremsstrahlung)bremsstrahlung) is about 10-_ photons/cm2-sec2 MeV at 4 MeV and about is about 1O-~ photons/cm -sec MeV at 4 MeV and about 10-10-22 at at 1 IMeV MeV (O'Neill et al. 1983). This background renders the lines (O'Neill et ale 1983). This background renders the fromfrom the the galactic galactic disk (near 4 MeV) difficult to observe if thelines fluxes disk (near 4 MeV) difficult to observe if the fluxes areare less less than than 1O-10-5s /cm22-sec, unless the line is narrow (i.e. if the /cm -sec, unless the line is narrow (Le. if the recoilrecoil nuclei nuclei are are produced produced in in grains grains andan dcome come to rest therein) and the instrument has an excellent resolution (aboutto 5 keV).rest therein) and the instrument has an excellent resolution (about 5 keV). ConsiderConsider a apulsar pulsar beam incident on an accretion disk that is beam incident on an accretion disk that is 372 3 7 2 OG:OG: 3.23.2-9-9 sufficientlysufficiently thickthick forfor mostmost particlesparticles toto collide.collide. AdoptingAdopting (a)(a) Cameron'sCameron's (1982)(1982) abundancesabundances forfor thethe accretionaccretion diskdisk materialmaterial,, (b)(b) powerpower 37 inputinput ofof 10 sT ergsergs/sec/sec perper decadedecade ofof energyener~y intervalinterval,, andand (c)(c) aa distancedistance ofof I1 kpc,kpc, wewe estimateestimate aa flfluxux ofof aboutabout 10-_f10- f/cm2-sec/cm2-sec forfor thethe 4.44.4 MeVMeV _2C12C spallation-inducedspallation-induced gammgammaa rays.rays. (The(The fluxflux isis aboutabout 1010 timestimes largerlarger ifif low-energylow-energy nuclearnuclear excitation reactionsreactions areare considered.)considered.) HereHere ff isis thethe gammaganma rayray suppression factor duedue toto opacity ofof thethe accretionaccretion diskdisk;; f<1.

Table I1 ssummarizesummarizes the 4.44.4 MeVMeV :_C12C fluxes from the sourcessources discusseddiscussed above.above. The 55.1-5.3.1-5.3 MeVMeV fluxes ooff IsOISO,, _SN15N,, _NI~N areare nearlynearly asas abundant.abundant.

TTableable I.1. TheThe 4.4 MeVMeV '2C12C FluxFlux (cm-_(cm-Z sec --I)*) from VariousVarious Sources

Dominant a Inner GGalacticalactic a ReReactionaction LargeLarge cloudacloud DiskDisk AccretingAccreting Pulsarpulsar a

SpSpallationallation 5 x 10-7 3 x 10-6 10-6 f b ExcitationExci tation b 5 x 10-6 3 x 10-5 10-5 f ------aTheaThe aassumedssumed proton fluxes aandnd properties of thesethese sources are given in l5he text. _he text. ExcitExcitationation dominates over spallation if low-energy cosmic rraysays dominate.

4. Conclusions. Gamma ray lines due to nuclear spspallationallation reactions should be detectable with a detector that has a threshold of should2 2be detectable with a detector that has a threshold of 10-S1O- 6 //cmcm -sec_sec from sosourcesurces like the ggalacticalactic disk (if the low-energy 20-50 MeV cosmic rrayay flux is high) aandnd from pulspulsarsars and active galgalacticactic nuclei that beam into accretion disks. The aabovebove detection threshold is aboaboutut 10 times lower than ththatat of GROGRO/OSSE./OSSE. However, if the flux between 5-30 MeV is high, as suggested by Reeves et al.a1. (1978) and RamatyRamaty et al. (1979), nuclenuclearar excitexcitationation lines will be observable from the above sites (with the GROGRO/OSSE/OSSE detector) as well as from supernova remnantsremnants in clouds (Morfill et al. 1981).

References Arnett, W.D.W.O. 1978, GammGammaa Ray Spectroscopy in , ed. T.L. Cline and R. Ramaty, Ramaty, NASA Tech. Memo. 79619, p. P. 310. Cameron, AA.G.W..G.W. 1982, Ap~p.. SpaceSpace Sci.,Sc1., 8282,, 123. & Clayton, D.O. D.D. 1973, Explosive Nucleosynthesis, ed. D. Schramm, and W.O.W.D.Arnett, Arnett, Univ. Texas Texas Press, Austin, p. 263. Clayton, 0.0.1984, D.D. 1984, Ap. J. 280,280,144. 144. C Issa, M.R. et a1. al. 1981, 17thrCRC 17th ICRC (Paris), (Paris), _,1, 150. Mahoney, W.A. et al. 1982, Ap. J., 262, 742: 742. Mahoney,Mahoney, W.A. et al. 1984, Ap. J., 286, 578. Morfill, G.E. and Meyer, P. 1981, 17th ICRC (Paris), (Paris), 2,9, 56. O'Neill, T. T. et et a1. al. 1983, 18th ICRC (Bangalore), (Bangalore), .2., 9, 45: 45. Ramaty, R. et a1. al. 1979, Ap. J. Supp1., Suppl., 40, 487. Reeves, H. et al. 1978, Gamma Ray Spectroscopy in Astrophysics, ed. ed. T.L. Cline and R. Ramaty, Ramaty, NASA Tech. Memo 79619, p. 283. Share,Share, G.H. et et a1. al. 1985, Ap. J. (Lett.), (Lett.), 292, L61.