8th International Conference on Nuclear Physics at Storage Rings Stori11, October 9-14, 2011 Laboratori Nazionale di Frascati, Italy. 

Storage rings offer the possibility of measuring proton- and alpha-induced reactions in inverse kinematics. The combination of this approachwith a radioactive beamfacility allows, in principle, the determination of the respective cross sections for radioactive isotopes. Such data are highly desired for a better understanding of astrophysical nucleosynthesis processes like the p-process. A pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSI using a stable 96Ru beam at 9-11 AMeV and a hydrogen target. Monte-Carlo simulations of the experiment were made using the Geant4 code. In these simulations, the experimental setup is described in detail and all reaction channels can be investigated. Based on the Geant4 simulations, a prediction of the shape of different spectral components can be performed. A comparison of simulated predictions with the experimental results shows a good agreement and allows the extraction of the cross section

Aumann, Thomas

Bishop, Shawn

Blaum, Klaus

Boretzky, Konstanze

Bosch, Fritz

Brandau, Carsten

Bräuning, Harald

Davinson, Tom

Dillmann, Iris

Dimopoulou, Christina

Ershova, Olga

Fülöp, Zsolt

Geissel, Hans

Gyürky, György

Heil, Michael

Kelic-Heil, Aleksandra

Kozhuharov, Christophor

Käppeler, Franz

Langer, Christoph

Le Bleis, Tudi

Litvinov, Yury A.

Lotay, Gavin

Marganiec, Justyna

Münzenberg, Gottfried

Nolden, Fritz

Petridis, Nikos

Plag, Ralf

Popp, Ulrich

Rastrepina, Ganna

Reifarth, René

Riese, Björn

Rigollet, Catherine

Scheidenberger, Christoph

Scücs, Tamas

Simon, Haik

Sonnabend, Kerstin

Steck, Markus

Stöhlker, Thomas

Sümmerer, Klaus

Weber, Günter

Weick, Helmut

Winters, Danyal F. A.

Winters, Natalya

Woods, Philip J.

Zhong, Qi-Ping

English

Davinson, Thomas

Litvinov, Yuri A.

Winters, Danyal Ferdinant Alexander

Woods, Philip John

Hochschulschriftenserver - Universität Frankfurt am Main

PoS(STORI11)005Measurements of proton-induced reactions onruthenium-96 in the ESR at GSIG. Rastrepina∗a,b T. Aumanna, S. Bishopc, K. Blaumd, K. Boretzkya, F. Boscha,H. Bräuninga, C. Brandaua,c, T. Davinsone, I. Dillmannc, C. Dimopouloua,O. Ershovaa,b, Z. Fülöp f, H. Geissela, G. Gyürkyf, M. Heila, F. Käppelerh,A. Keli´ c-Heila, C. Kozhuharova, C. Langera,b, T. Le Bleisc, Y.A. Litvinova,d, G. Lotaye,J. Marganieca, G. Münzenberga, F. Noldena, N. Petridisb, R. Plagb, U. Poppa,R. Reifarthb, B. Riesea, C. Rigolleti, C. Scheidenbergera, H. Simona, K. Sonnabendb,M. Stecka, T. Stöhlkera, K. Sümmerera, T. Scücsf, G. Webera, H. Weicka,D.F.A. Wintersa, N. Wintersa, P.J. Woodse, Q. ZhongjE-mail:g.rastrepina@gsi.dea Gesellschaft für SchwerionenforschungmbH, Darmstadt, D-64291, Germanyb J.W. Goethe-Universität, Frankfurt am Main, D-60438, Germanyc Technische Universität München, 85748 Garching, Germanyd Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germanye University of Edinburgh, Edinburgh, UKf Institute of Nuclear Research, Debrecen, H-4026, Hungaryh Karlsruhe Institut für Technologie, Institut für Kernphysik, 76021 Karlsruhe, Germanyi Kernfysisch Versneller Instituut, NL-9747 AA Groningen, Netherlandsj China Institute of Atomic Energy, 102413 Beijing, ChinaStorage rings offer the possibility of measuring proton- and alpha-induced reactions in inversekinematics. Thecombinationofthisapproachwitharadioactivebeamfacilityallows,inprinciple,the determination of the respective cross sections for radioactive isotopes. Such data are highlydesired for a better understanding of astrophysical nucleosynthesis processes like the p-process.A pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSIusing a stable 96Ru beam at 9-11 AMeV and a hydrogen target. Monte-Carlo simulations ofthe experiment were made using the Geant4 code. In these simulations, the experimental setup isdescribedin detailandall reactionchannelscanbeinvestigated. Based ontheGeant4simulations,a prediction of the shape of different spectral components can be performed. A comparisonof simulated predictions with the experimental results shows a good agreement and allows theextraction of the cross section.8th International Conference on Nuclear Physics at Storage Rings-Stori11,October 9-14, 2011Laboratori Nazionale di Frascati, Italy∗Speaker.c ￿ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. Rastrepina1. IntroductionMost of the elements heavier than iron are built up in stars via neutron capture in the s- or r-processes. s-(slow)-process is the process of neutron capture with the emission of gamma radiation(n,g) which takes place on a long time-scale with neutron densities in the order of 106 to 1011cm−3.The neutron captures occur at slow rates compared to the intervening b-decays. The s-processproduces the abundance peaks at A=90, 138 and 208. The r-(rapid)-process is the process ofneutron capture on a very short time-scale with neutron densities greater than 1020 cm−3. Theneutron captures occur then much faster than the competing beta-decays. The r-process producesthe abundance peaks at A=80, 130 and 194 [1].There are, however, 35 nuclei on the proton-rich side of the valley of stability, which cannotbe produced by neutron capture, because the path of these processes are blocked by stable isotopes.These are the so-called p-nuclei, which typically have much lower natural abundances compared totheir more neutron-rich stable isotopes. The proton-rich nuclei are produced by a combination ofthe (p,g), (g,n), (g,p) and (g,a) reactions on existing s- or r-nuclei at stellar temperatures around afew GK, characteristic of explosive environments. To adequately describe the p-process nucleosyn-thesis, one needs reliable information on the thousands of reaction rates involved. Unfortunately,there is a considerable lack of experimental data on the relevant cross sections in the p-processenergy range, because a direct measurement is very difﬁcult for most g-induced reactions [2]. Toovercome this difﬁculty, the charged particle induced reaction cross sections are measured and theirinverse photodisintegration reaction cross sections are calculated using the detailed balance theo-rem [3]. The p-process occurs in supernovae, where (p,g) and (g,n) reactions occur on the seedof s- and r-nuclei at high temperatures. The p-nucleus 96Ru was chosen for testing a new experi-mental approach to determine the proton capture cross section at astrophysical energies in inversekinematics (Figure 1).Figure 1: Synthesis of the elements in the mass regionbelow A=100. 96Ru is shielded from s- and r-processpaths by unstable resp. stable isotopes and can only be produced via p-process.2PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. RastrepinaMost of the few existing data in the Gamov window of the p-process have been obtainedapplying the activation technique. But this method is limited because it is only applicable if thereaction product is radioactive and the sample material is not too short-lived to produce a sample.No such limits exist for the proposed new experiments in storage rings with circulating heavy-ionbeams, since the reaction products are identiﬁed by their mass-over-charge ratios and isotopes withhalf-lives down to a few minutes could be investigated. The purpose of this experiment was tobenchmark the new approach by comparing our results with the activation method and to explorethe possibilities of a new method for measuring the same reactions with short-lived isotopes andstable reaction products.2. Experimental techniqueA pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSIusing a stable 96Ru beam and a hydrogen gas target. The primary beam was sent from the UNILACaccelerator to the synchrotron SIS (Figure 2) where it was accelerated to 100 AMeV and thenstripped using a carbon foil (11mg/cm2). Afterwards the fully stripped ions were injected into theESR (Figure 3) and slowed down to energies of 9, 10 and 11 AMeV. After slowing down, theruthenium ions were stored in the ESR for several minutes. The thickness of the newly developedhydrogen target was 1013/cm2 [4].Figure 2: The accelerator complex at GSI.The most important interactions of fully strip ruthenium ions with hydrogen molecules areelectron pick-up and proton-induced nuclear reactions like (p,g), (p,n) and (p,a).Because of their different A/Z ratio, the products of proton-induced reactions (97Rh) are spa-tially separated from the unreacted 96Ru ions after the ﬁrst dipole and could be detected by twoDouble Sided Silicon Strip Detectors (DSSSD) mounted in a pocket on the inside of the ESR. Eachdetector had 16 strips in X- and Y- direction. The strip pitch was 3 mm and the strip length was49.5 mm. The detectors were arranged side by side to increase the covered area. However, due3PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. Rastrepinato connecters etc., a gap of 25 mm remained between both active areas. In order to measure acontinous spectrum, data were taken with different detector positions, e.g. at nominal position andshifted by 25 mm. The efﬁciency for (p,g) events was close to 100%.Figure 3: The Experimental Storage Ring (ESR) at GSI.As the experiment was performed at energies of 9-11 AMeV, competing (p,n) and (p,a) reac-tions occured too and they could not be neglected. These events have to be discriminated from thedesired proton capture reactions based on the position on the DSSSD. An additional backgroundcomponent is the elastic scattering of ruthenium ions on protons.Multi-Wire Counters were installed on the outer side of the ﬁrst dipole after the hydrogentarget to detect products from electron pick-up. Germanium X-ray detectors were mounted closeto the target at angles 35 and 90 degree to detect the emitted X-rays.The particle position in the DSSSD for both detector positions is shown in Figure 4. The com-bined spectrum for both detector positions is represented in Figure 5. Events from 96Ru(p,g)97Rhwere normalised by events from the electron capture reaction in our target.3. Monte-Carlo simulations with Geant4 codeIn order to understand and subtract background from competing reactions, the most intensebackground sources were simulated using Geant4 [5]. The simulation comprises all beam pipes,quadrupole magnets and the dipole between the hydrogen target and the detector location as wellas the DSSSD itself (Figure 6).Based on Geant4 simulations, a prediction of the distribution of the reaction products in thedetector for different reactions was performed. Figure 7 shows the results for the 96Ru(p,g) reactionitself as well as for background from (p,n), (p,a) and elastic scattering (p,p).4. Cross section determinationThe reaction cross section was measured relative to the well known 96Ru44+(e−)96Ru43+ crosssection, thereby eliminating uncertainties from target thickness and number of primary 96Ru ions.4PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. RastrepinaFigure 4: Position distribution of secondary particles on the DSSSDs with the detector at the nominalposition (top) and shifted by 25 mm to the right (bottom). The region above x=125mm was shielded by thebeam pipe.Figure 5: Combined spectrum of DSSSD for detector positions at 0 and 25 mm. The peak of 96Ru(p,g) isclearly visible at x=85 mm.If Zp,g is the number of nuclei produced by proton captures (peak area), sp,g the proton capturecross section, Zec the number of nuclei produced via electron pick-up and s ec the electron pick-upcross section then5PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. RastrepinaFigure 6: Geant4 simulations of secondary particles from 96Ru(p,g)97Rh reaction.Figure 7: Simulated position distribution of reaction products from different reactions on the DSSSD.sp,g = sec·Zp,gZec(4.1)Since the atomic electron pick-up cross section is well known, the desired proton capture crosssection can be determined solely based on the ratio of detected counts in the silicon detectors and inthe multi-wire chamber. Based on Geant4 simulations the background for the 96Ru(p,g)97Rh reac-tion can be estimated. The important background components are 96Ru(p,n)96Rh, 96Ru(p,a)93Tc,96Ru(p,p)96Ru reactions. A rough estimate of the proton capture cross section of 96Ru at 11 AMeV6PoS(STORI11)005Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI G. Rastrepinagives 1.5-3.5 mb, which is comparable to the predictions from the NON-SMOKER code [6].5. Summary and outlookA pioneering experiment was performed at the Experimental Storage Ring (ESR)at GSI. Fullystripped ions of 96Ru were injected into the storage ring and slowed down to 9-11 MeV per nucleon.The 97Rh ions following the 96Ru(p,g) reaction at a cryogenically cooled liquid microjet hydrogentarget were detected with Double Sided Silicon Strip Detectors (DSSSD) mounted inside a pocket.We could prove the feasibility of this approach and clearly detected events originating from protoncaptures on 96Ru. The analysis is still in progress and we could therefore only report an upper limiton the cross section at 11 MeV, which is slightly above the prediction from the NON-SMOKERcode. The detailed analysis will be extended down to 10 and 9 MeV. In the future, such experimentshave to be performed with particle detectors inside the ultra-high vacuum of the ESR in order tomeasure in the Gamov window. Additionally a demonstration experiment for (a,g) reactions isplanned.AcknowledgmentsThis work is supported by the HGF Young Investigators Projects VH-NG-327 and VH-NG-331, the ERC grant no. 203175, HIC for FAIR and F&E Frankfurt/GSI.References[1] E. Burbidge, G. Burbidge, W. Fowler, F. Hoyle. Rev. Mod. Phys. 29 (1957) 547.[2] H. Utsunomiya, P. Mohr, A. Zilges, M. Rayet. Nucl. Phys. A 777 (2006) 459.[3] C. Angulo, M. Arnould, M. Rayet, P. Descouvemont, D. Baye, C. Leclercq-Willain, A. Coc,S. Barhoumi, P. Aguer, C. Rolfs, et al. Nucl. Phys. A 656 (1999) 3.[4] Q. Zhong, T. Aumann, S. Bishop, K. Blaum, K. Boretzky, et al. 96Ru(p,g)97Rh measurement at the GSIstorage ring. Journal of Physics: Conference Series 202 (2010) 012011.[5] S. Agostinelli, J. Allison, K. Amako, J. Apostolakis, H. Araujo, et al. Nucl. Phys. A 506 (2003) 250.[6] T. Rauscher, F.-K. Thielemann. Astrophysical Reaction Rates From Statistical Model Calculations.Atomic Data Nucl. Data Tables 75 (2000) 1.7

96Ru(p,g)97Rh measurement at the GSI storage ring.

Astrophysical Reaction Rates From Statistical Model Calculations. Atomic Data Nucl.

Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI

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