Nuclear astrophysics with radioactive ions at FAIR

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Journal of Physics: Conference Series 665 (2016) 012044 doi:10.1088/1742-6596/665/1/012044

N u clea r a str o p h y sic s w ith ra d io a ctiv e ion s at F A IR

R R e ifa r th 1, S A lt s t a d t 1,2, K G o b e l1, T H e ftr ich 1,2, M H e il2, A K o lo c z e k 1,2, C L an ger1,2,60, R P la g 1,2, M P o h l1, K S o n n a b en d 1, M W eig a n d 1, T A d a c h i47, F A k so u h 5, J A l-K h a lili18, M A lG a ra w i5, S A lG h a m d i5, G A lk h a zo v 3, N A lk h o m a sh i4, H A lv a rez -P o l6,

R A lv a rez-R o d rig u ez7, V A n d r e e v 3, B A n d rei8, L A ta r2, T A u m a n n 9, V A v d e ich ik o v 10, C B a c r i11, S B a g ch i47, C B a rb ie ri18, S B ece iro 6, C B e c k 12, C B ein ru c k er1, G B e lie r 13, D B em m e r e r 14, M B e n d e l15, J B en lliu re 6, G B e n z o n i16, R B e r jillo s17, D B ertin i 2, C B e r tu la n i19, S B is h o p 15, N B la si85, T B lo c h 9, Y B lu m en feld 21, A B o n a cco rso 22, K B o r e tz k y 2, A B o tv in a 23, A B o u d a rd 24, P B o u ta ch k o v 9,

I B o z to s u n 25, A B ra cco 85, S B ra m b illa 85, J B riz M o n a g o 26,

M C aa m an o 6, C C aesar2, F C am era85, E C asarejos27, W C a tfo rd 18, J C ed erk all10, B C ed erw a ll28, M C h a rtier31, A C h a tillo n 13,

M C h erciu 32, L C hu lkov33, P C o lem a n -S m ith 34, D C o rtin a -G il6, F C resp i16, R C resp o 35, J C ressw ell31, M C sa tlo s36, F D ec h e r y 24, B D a v id s37, T D a v in so n 38, V D ery a 39, P D e tis to v 40, P D iaz F ern an d ez6, D D iJ u lio 10, S D m itr y 33, D D o r e 24, J D u e n a s 17, E D u p o n t24, P E g elh o f2, I E gorova8, Z E le k e s14, J E n d ers9, J E n d res39, S E rsh ov8, O E rsh ova1, B F ern a n d ez-D o m in g u ez6,

A F etiso v 3, E F iori41, A F o m ich ev8, M F o n seca 1, L Fraile7, M Freer42, J F riese15, M G. B o rg e26, D G alaviz R ed o n d o 44, S G a n n o n 31,

U G arg41,84, I G asp aric9,86, L G asq u es45, B G a stin ea u 24, H G e isse l2, R G ern h a u ser15, T G h o sh 20, M G ilb e r t1, J G lo riu s1, P G o lu b e v 10, A G orsh k ov8, A G o u rish etty 46, L G rigoren k o8, J G u ly a s36,

M H a id u c32, F H a m m a ch e11, M H arakeh47, M H a ss48, M H e in e9, A H e n n ig 39, A H en riq u es44, R H erzb erg 31, M H o ll9, A Ig n a to v 9, A Ig n a ty u k 50, S Ilieva9, M Ivan ov40, N Iw asa51, B J a k o b sso n 10, H J o h a n sso n 49, B J o n so n 49, P J o sh i52, A J u n g h a n s14, B J u ra d o 53, G K orn er54, N K a la n ta r47, R K a n u n g o 55, A K e lic -H e il2, K K ezza r5, E K h a n 11, A K h a n z a d eev 3, O K ise le v 2, M K o g im tzis34, D K o rp er2, S K rack m an n 1, T K ro ll9, R K ru ck en 15, A K raszn ah ork ay36, J K r a tz56, D K resa n 9, T K rin g s57, A K ru m b h olz9, S K rup k o8, R K u le ssa 58, S K u m ar59, N K u rz2, E K u zm in 33, M L ab ich e34, K L anganke2, I L azarus34, T Le B le is 15, C L ed erer1, A L em a sson 60, R L em m o n 34, V L ib era ti30, Y L itv in o v 2, B L oher41, J L opez H erraiz7,

G M u n zen b erg 2, J M a ch ad o44, E M a ev 3, K M a h a ta 61, D M a n cu si24, J M argan iec41, M M a rtin ez P e r e z 7, V M a ru so v 39, D M en g o n i63, B M illio n 85, V M o rcelle64, O M o ren o 7, A M o v sesy a n 9, E N a ch er26, M N a ja fi47, T N akam u ra65, F N a q v i66, E N ik o lsk i33, T N ilsso n 49, C N o cifo ro 2, P N o la n 31, B N o v a tsk y 33, G N y m a n 49, A O rnelas44,

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Nuclear Physics in Astrophysics VI (NPA6)

Journal of Physics: Conference Series 665 (2016) 012044

IOP Publishing doi:10.1088/1742-6596/665/1/012044

R P a lit67, S P a n d it61, V P a n in 9, C P a ra d ela 6, V P ark ar17,

S P a sch a lis9, P P a w ło w sk i62, A P er ea 26, J P er eira 60, C P etr a c h e 68, M P e tr i9, S P ic k sto n e 39, N P ie tr a lla 9, S P ie tr i2, Y P iv o v a ro v 69, P P o tlo g 32, A P rok o fiev70, G R a str e p in a 1,2, T R a u sch er72,

G R ib eir o 26, M R iccia rd i2, A R ich ter9, C R ig o lle t47, K R iisa g er43, A R io s 18, C R it te r 1, T R od rig u ez F ru to s2, J R o d rig u ez V ig n o te 26, M R o d e r 14,71, C R o m ig 9, D R o ssi2,60, P R o u ssel-C h o m a z24, P R o u t61, S R o y 67, P S o d erstro m 73, M Saha Sarkar29, S S a k u ta 33, M S alsac24, J S am p so n 31, J Sanchez d el R io S a ez26, J Sanchez R o sa d o 26,

S S an jari1, P S arriguren 26, A S a u erw ein 1, D Savran 41, C S ch eid en b erg er2, H S ch e it9, S S ch m id t1, C S c h m itt74,

L S ch n orren b erger9, P Schrock9, R S ch w en gn er14, D S ed d o n 31, B S h errill60, A S h rivastava61, S Sidorchuk8, J Silva41, H S im o n 2, E S im p so n 18, P S in g h 2, D S lo b o d a n 75, D S o h ler36, M S p iek er39, D S ta ch 14, E S ta n 32, M S ta n o iu 76, S S tep a n tso v 8, P S te v e n so n 18, F S tried er77, L S tu h l36, T S u d a51, K S u m m erer2, B S treich er2, J T a ieb 13, M T akechi2, I T an ih a ta78, J T aylor31, O T en gb lad 26, G T er-A k op ian 8, S T erash im a79, P T eu b ig44, R T h ies49,

M T h o e n n e sse n 60, T T h o m a s1, J T h o rn h ill31, G T h u n g stro m 80, J T im a r36, Y T ogan o41, U T om oh iro73, T T orn yi36, J T o s te v in 18, C T o w n sley 18, W T ra u tm an n 2, T T rived i67, S T y p e l2, E U b e rsed er84, J U d ia s7, T U esak a73, L U v a ro v 3, Z V a jta 36, P V elh o 44, V V ik h ro v 3, M V o lk n a n d t1, V V olk ov33, P von N e u m a n n -C o se l9, M v on S ch m id 9, A W a g n er14, F W am ers9, H W eick 2, D W ells31, L W esterb erg 81, 0 W ie la n d 16, M W iesch er84, C W im m e r 1, K W im m er60,

J S W in fie ld 2, M W in k e l15, P W o o d s38, R W y s s 28, D Y ak o rev 14, M Y avor82, J Z am ora C ard on a9, I Z artova83, T Z ergu erras11, 1 Z gura32, A Z h d anov3, M Zhukov49, M Z ieb lin sk i62, A Z ilges39, K Z u b er71

1 U niversity of F ran k fu rt, G erm any 2 GSI D arm sta d t, G erm any 3 P N P I G atchina, R ussia

4 A tom ic E nergy R esearch In stitu te , Saudi A rabia 5 K ing Saudi University, Saudi A rabia

6 U niversity of S antiago de C om postela, Spain 7 U niversidad C om plutense de M adrid, Spain 8 JIN R D ubna, R ussia

9 T U D arm sta d t, G erm any 10 L und University, Sweden 11 IP N Orsay, France

12 IP H C - C N R S /U dS S trasbourg, France 13 CEA B ruyeres le C hatel, France

14 H elm holtz-Z entrum D resden-Rossendorf, G erm any 15 Technische U niversitat M unchen, G erm any 16 IN FN M ilano, Italy

17 U niversity of Huelva, Spain

18 U niversity of Surrey, U nited K ingdom 19 Texas A&M U niversity-C om m erce, USA 20 V E C C K olkata, India

21 C ER N , Switzerland 22 IN FN P isa, Italy

23 IN R RAS Moscow, R ussia 24 CEA Saclay, France 25 Akdeniz University, Turkey

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26 CSIC M adrid, Spain 27 U niversidad de Vigo, Spain

28 Royal In stitu te of Technology K T H Stockholm , Sweden 29 SIN P K olkata, India

30 U niversity of th e W est of Scotland, U nited K ingdom 31 U niversity of Liverpool, U nited K ingdom

32 I n s titu te of Space Sciences, R om ania 33 N RC K urchatov In stitu te Moscow, R ussia 34 S T F C D aresbury L aboratory, U nited K ingdom 35 In s titu to S uperior Tecnico, P o rtu g a l

36 A TO M K I D ebrecen, H ungary 37 T R IU M F , C an ad a

38 U niversity of E dinburgh, U nited K ingdom 39 U niversity of Cologne, G erm any

40 IN R N E BAS Sofia, B ulgaria

41 E x trem e M a tte r In s titu te /G S I D a rm sta d t, G erm any 42 U niversity of B irm ingham , U nited K ingdom

43 U niversity of A arhus, D enm ark 44 U niversity of Lisboa, P o rtu g a l 45 U niversity of Sao Paulo, B razil

46 In d ian In stitu te of Technology Roorkee, India 47 K V I/U n iv ersity of G roningen, T h e N etherlands 48 T h e W eizm ann In stitu te of Science Rehovot, Israel 49 C halm ers U niversity of Technology, Sweden 50 I P P E O bninsk, R ussia

51 U niversity of Tohoku, J a p a n 52 U niversity of York, U nited K ingdom 53 C EN B G , France

54 N uP E C C , E urope

55 S aint M ary University, C an ad a 56 U niversity of M ainz, G erm any 57 SEM IK O N D etector Gm bH , G erm any 58 Jagiellonian U niversity of K rakow, P oland 59 U niversity of Delhi, India

60 N SC L /M SU , USA 61 B A R C M um bai, In d ia 62 I F J PAN Krakow, Poland 63 U niversity of Padova, Italy

64 F ederal Flum inense University, Brazil 65 Tokyo In stitu te of Technology, J a p a n 66 U niversity of Yale, USA

67 T IF R M um bai, In d ia 68 CSNSM Orsay, France

69 Polytechnic U niversity of Tom sk, R ussia 70 T h e Svedberg L aboratory, Sweden 71 T U D resden, G erm any

72 U niversity of Basel, Sw itzerland 73 R IK E N , J a p a n

74 GANIL, France 75 ESS Bilbao, Spain

76 IFIN -H H B ucharest, R om ania 77 R u h r U niversity Bochum , G erm any 78 R C N P O saka, J a p a n

79 B eihang University, C hina 80 M id Sweden University, Sweden 81 U ppsala University, Sweden 82 IAI RAS S t. P etersburg, R ussia 83 U niversity of Stockholm , Sweden 84U niversity of N otre D am e, USA

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85 IN FN Rom e, Italy

86RB I, Zagreb, C ro atia

E-m ail: r e i f a r t h @ p h y s i k .u n i - f r a n k u r t .d e

A b s t r a c t . T he nucleosynthesis of elem ents beyond iron is d o m inated by n eu tro n captures in th e s and r processes. However, 32 stable, proton-rich isotopes cannot be form ed during those processes, because they are shielded from th e s-process flow and r -process ,8-decay chains.

T hese nuclei are a ttrib u te d to th e p and rp process.

For all those processes, cu rrent research in nuclear astrophysics addresses th e need for more precise reaction d a ta involving radioactive isotopes. D epending on th e p articu la r reaction, direct or inverse kinem atics, forw ard or tim e-reversed direction are investigated to determ ine or a t least to co n strain th e desired reactio n cross sections.

T he Facility for A n tip ro to n and Ion R esearch (FAIR) will offer unique, unprecedented o p p o rtu n ities to investigate m any of th e im p o rta n t reactions. T he high yield of radioactive isotopes, even far away from th e valley of stability, allows th e investigation of isotopes involved in processes as exotic as th e r or rp processes.

1. In tro d u ctio n

Radioactive beams offer the opportunity to extend the experimentally based knowledge about nuclear structure far beyond the valley of stability. Especially within the planned international Facility for A ntiproton and Ion Research (FAIR) at GSI [1], radioactive ions will be produced with highest intensities. It is very often not feasible to collect the respective radioactive ions in order to produce a sample for irradiation with e.g. neutrons, protons or gammas. Experiments in inverse kinematics - irradiating a stable target with the desired radioactive ions - are the solution to th a t problem. In this article, we will mostly report about performed and upcoming in-beam experiments and not about the wide field of possible ring experiments.

The proposed R 3B setup [2], a universal setup for kinematically complete measurements of Reactions with Relativistic Radioactive Beams will cover experimental reaction studies with exotic nuclei far off stability, with emphasis on nuclear structure and dynamics. Astrophysical aspects and technical applications are also concerned. R 3B is a versatile reaction setup with high efficiency, acceptance, and resolution for reactions with high-energy radioactive beams.

The setup will be located at the High Energy Cave which follows the high-energy branch of the new fragment separator (Super-FRS). The experimental configuration is based on a concept similar to the existing LAND setup at GSI introducing substantial improvement with respect to resolution and an extended detection scheme, which comprises the additional detection efficiency of light (target-like) recoil particles and a high-resolution fragment spectrom eter. The setup is adapted to the highest beam energies (corresponding to 20 Tm magnetic rigidity) provided by the Super-FRS capitalizing on the highest possible transm ission of secondary beams. The experimental setup is suitable for a wide variety of scattering experiments, such as heavy-ion induced electromagnetic excitation, knockout and breakup reactions, or light-ion (in)elastic and quasi-free scattering in inverse kinematics, thus enabling a broad physics program with rare- isotope beams to be performed [2].

Applying the Coulomb dissociation method [3, 4] R 3B contributes already now to almost every astrophysical scenario. W ith the expected increase in the production of radioactive species at FAIR, even more exotic reactions can be investigated. Both, the current situation and the prospects at FAIR are shown in section 2 for the s process, in section 4 for the r process and in section 5 for the rp process. Recent experiments and future prospects investigating charge exchange reactions are discussed in section 3 for the s process and section 6 for the vp process.

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F igu re 1. The s-process path between Fe and Co. The neutron densities during the s process have to be sufficiently high to overcome the rather short-lived isotope 59Fe ( t1/ 2 = 45 d).

2. 60Fe - a p ro d u ct o f th e s p rocess

A significant contribution to the interstellar abundance of the radiogenic 60Fe is provided by the slow neutron capture (s) process in massive stars, the weak component of the s process.

The s process in massive stars operates in two m ajor evolutionary stages, first during convective core He-burning and, subsequently, during convective shell C-burning. Neutrons are mainly produced by the 22N e(a,n) reaction in both cases, but at rather different tem peratures and neutron densities [5, 6].

As illustrated in Figure 1, the s-process path to 60Fe, which starts from the most abundant seed nucleus 56Fe, is determined by the branching at 59Fe ( t1/ 2 = 44.5 d). At the low neutron densities during convective core He burning, 60Fe is shielded from the s-process chain, because the P - -decay rate of 59Fe dominates over the (n,y) rate by orders of magnitude. On the other hand, the production of 60Fe becomes efficient during the shell C-burning phase, where higher tem peratures of T = (1.0 — 1.4) ■ 109 K give rise to the neutron densities in excess of 1011 cm -3 necessary for bridging the instability gap at 59Fe. The interpretation of all the above observations depends critically on the reliability of the stellar models as well as on the reaction rates for neutron capture relevant to the production and depletion of 60Fe [7]. These rates can only be determined reliably in laboratory experiments, because theoretical calculations are too uncertain.

Since the neutron capture cross section of 60Fe(n,y) has been measured in the astrophysically interesting energy region [8] and a reliable value for the half life of the P - -decay has been provided [9], the most im portant missing piece to understand the stellar production of 60Fe is the 59Fe(n,y) cross section under stellar conditions, see Figure 1.

Because the half-life of 59Fe is only 45 d, indirect methods have to be applied to determine the neutron capture cross section. Since 60Fe is unstable too, the method of choice is the determ ination of the desired A (n,y)B via the inverse reaction B (y,n)A applying the Coulomb dissociation (CD) method at the L A N D /R 3B setup (Figure 2).

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N uclear Physics in Astrophysics VI (NPA6)

F igu re 2. The R 3B setup at GSI optimized for detecting neutrons in the exit channel. The beam enters Cave C after passing the FRS (bottom , left), passes several detectors used for incoming identification and hits the target in the center of th crystal ball (half of the ball is drawn). Afterwards charged fragment and neutrons are separated by the ALADIN magnet. The fragments are bent to the right analysed with a suite of scintillator detectors while the neutrons rem ain unchanged and are detected w ith LAND.

60Fe ions have been produced by fragm entation of 64Ni. After passing the fragment separator (FRS, [10]) most of the unwanted species are removed and a beam consisting of almost only 60Fe arrives in at the LA N D /R 3B setup, where each ion is identified in charge and mass, Figure 3.

All reaction products are detected and characterised in term s of charge, mass and momentum.

This allows the investigation of the neutron removal of 60Fe for different experim etal settings, Figure 4 (left). A lead target was used to determine the Coulomb breakup cross section, while runs with carbon and no sample at all have been performed to determine different background components. After scaling and subtracting the contribution from nuclear interaction (measured with the carbon target) as well as interaction with other components in the beam line (empty), the pure Coulomb breakup can be extracted, Figure 4 (right).

Under certain conditions, stars may experience convective-reactive nucleosynthesis episodes.

It has been shown with hydrodynamic simulations th a t neutron densities in excess of 1015 cm3 can be reached [11, 12], if unprocessed, H-rich m aterial is convectively mixed w ith an He-burning zone. Under such conditions, which are between the s and r process, the reaction flow occurs a few mass units away from the valley of stability. These conditions are sometimes referred to as the i process (interm ediate process). One of the most im portant rates, but extremely difficult to determine, is the neutron capture on 1351, Figure 5. The half-life tim e of 1351 is about 6 h. Therefore the 135I(n,y) cross section cannot be measured directly. The much improved

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F ig u re 3. Incoming particle identification at the R3B setup.

F ig u re 4. Left: Mass identification of different ion isotopes after requiring an incoming 60Fe ions a a neutron detected by LAND. Right: Spectra shown on the left subtracted such th a t only the mass distribution of Coulomb breakup events are left.

production rates of radioactive isotopes at FAIR, however, offer the possibility to investigate the Coulomb dissociation of 136I. This reaction can then in tu rn be used to constrain the 135I(n ,y ) rate.

3. 152E u - branch p o in t in th e s p rocess

The laboratory based measurements of beta-decay and electron capture rates can not directly be used in stellar simulations. Electron capture can occur on excited states which are energetically not allowed on earth [13]. Also beta-decays which occur from therm ally excited states cannot be

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Journal o f Physics: Conference Series 665 (2016) 012044

F igure 5. Im pact of th e 1351(n,Y) rate on the final abundances of th e i process. This reaction rate affects most of the abundances beyond 135I and is therefore of global im portance.

measured in the laboratory. These effects can sometimes alter the decay rates by a few orders of m agnitude [14, 15]. For the theoretical calculations of stellar rates, Gamow-Teller strength distributions B(G T) for low lying states are needed [16, 17, 18]. Charge-exchange reactions, like the (p,n) reaction, allow access to these transitions and can serve as input for rate calculations.

In particular, there exists a proportionality between (p,n) cross sections at low momentum transfer (close to 0°) and B(GT) values,

- ^ ( Q = 0) = d GT (q = 0 ) B ( G T ), daCE (1)

where <tg t (q = 0) is the unit cross section for GT transitions at q=0. [19]. In order to access GT distributions for unstable nuclei experiments have to be carried out in inverse kinematics w ith radioactive ion beams. This requires the detection of low-energy neutrons at large angles relative to the incoming beam.

An astrophysically interesting test case, 152Sm(p,n), has been investigated at GSI in inverse kinematics. In the case of inverse kinematics, all inform ation about the scattering angle in the center of mass and th e excitation of the product nucleus can be determined from the energy and emission angle of the neutron in th e laboratory reference system. Therefore a new detector for low-energy neutrons (LENA) has been developed [20] and was used at th e LAND/R3B setup, Figure 6. The analysis of this experiment is currently ongoing and first results are very promising.

4. Light e le m e n ts in th e r p rocess

The rapid neutron capture process (r process) produces half of the elements heavier th an iron.

However, the nuclear physics properties of the involved nuclei are not well known and its astrophysical site is not yet identified. The neutrino-driven wind model w ithin core-collapse supernovae are currently one of th e most promising candidates for a succesful r process. These neutrino winds are thought to dissociate all previously formed elements into protons, neutrons

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F igu re 6. The R 3B setup at GSI optimized for charge-exchange reactions with low-energy neutrons in the exit channel. The LENA detector, optimized for the detection of low-energy neutrons em itted at high angles can be seen surrounding the target area. In forward direction, LaB r3 detectors have been used to detect the decay of excited states.

and a particles before the seed nuclei for the r process are produced. Hence, the neutrino- driven wind model could explain the observational fact th a t the abundances of r nuclei of old halo-stars are similar to our solar r-process abundances [21]. This also indicates th a t the r process is a prim ary process and, thus, independent of the chemical composition of the progenitor star. Therefore, the investigation of the nuclear reactions among light elements forming seed nuclei prior to the r process leads to a better understanding of this process.

Model calculations within a neutrino-driven wind scenario find a crucial change in the final r-process abundances by extending the nuclear reaction network towards very light neutron- rich nuclei [22]. Subsequent sensitivity studies point out the most im portant reactions, which include succesive (n,y) reactions running through the isotopic chain of the neutron-rich boron isotopes 11 B (n ,y)12B (n,y )13B (n ,y )14B (n ,y )15B (^ - ) 15C [23]. Almost all reaction rates used in these model calculations are only known theoretically, and their uncertainties were estim ated to be at least a factor of two [23]. Since the reaction rates of unstable isotopes are very difficult to determine experimentally, neutron breakup reactions of the neutron-rich beryllium isotopes were investigated in inverse kinematics via Coulomb dissociation. Figure 7 shows the incoming identification as well as the example of Coulomb breakup of 11 Be, which served as a benchmark of the measurement. The setup used for this experiment was the same as shown in Figure 2.

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F igu re 7. Left: Incoming identification plot. Right: Coulomb breakup cross section of 11 Be at almost 500 AMeV.

F igu re 8. Left: The rp-process p ath at light elements. Right: The R 3B setup at GSI optimized for detecting protons in the exit channel. In particular the proton drift chambers are of importance.

5. B reak ou t rea ctio n s in th e rp p rocess

The most likely astrophysical site of X-ray bursts are a very dense neutron stars, which accrete H /H e-rich m atter from a close companion [24, 25]. While falling towards the neutron star, the m atter is heated up and a therm onuclear runaway is ignited. The exact description of this process is dom inated by the properties of a few proton-rich radioactive isotopes, which have a low interaction probability, hence a high abundance (Figure 8, left).

Therefore the short-lived, proton-rich isotopes 31 Cl and 32Ar have been investigated applying the Coulomb dissociation m ethod at the GSI. An Ar beam was accelerated to an energy of 825 AMeV and fragmented in a beryllium target. The fragment separator was used to select the desired isotopes w ith a remaining energy of 650 AMeV. They were subsequently directed onto a 208P b target. The measurement was performed in inverse kinematics. All reaction products were detected and inclusive and exclusive measurements of the respective Coulomb dissociation

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F igu re 9. (Prelim inary data) Left: The reaction rate for the im portant 30S(p,y)31Cl bottleneck reaction in the rp process. Maximum peak tem peratures in the rp process are typically around 2 GK. Three contributions can be seen, from (a) the low-lying resonance, (b) the direct capture, and (c) the second excited state in 31 Cl. Right: Comparison of different previous estimations with the reaction rate derived in this work (left). a) Iliadis et al. (red) [26], b) Wallace and Woosley (blue) [27] and c) Wrede et al (black) [28]. Especially in the low-tem perature region, a deviation of up to 4 orders of magnitudes is observed.

cross sections were possible, Figure 8, right. Prelim inary results for the im portant 30S(p,y)31 Cl reaction and a comparison with previously known estim ates are shown in Figure 9.

6. 64G e - a w a itin g p o in t in th e vp p rocess

Heavy a-nuclei are typically waiting points in the rp-process because of their small ( p ,y ) cross sections and the long P+-half lives. Under certain conditions following a core collapse supernova, these waiting points can be overcome via (n,p) reactions in presence of small amount of neutrons.

These neutrons stem from reactions like v + p ^ n + P+. This process is therefore called the vp-process, [29]. One im portant waiting point is 64Ge, which implies the im portance of the 64G e(n,p)64Ga reaction rate [30]. This reaction is very difficult to constrain experimentally. In combination with the planned storage rings, it would be possible to produce 64Ga beam at FAIR and store in one of the rings. In combination with a hydrogen je t target, the inverse reaction 64G a(p,n)64Ge could be investigated at astrophyscally interesting energies in inverse kinematics.

The principle of this approach could be successfully proven with the reaction 96R u(p,y), [31]

7. S u m m ary

Nuclear d ata on radioactive isotopes are extremely im portant for modern astrophysics.

FAIR offers contributions to almost every astrophysical nucleosynthesis process. Im portant developments are currently ongoing while FAIR is under construction.

A ck n o w led g m en ts

This project was supported by the H GF Young Investigators Project VH-NG-327, EMMI, H4F, HGS-HIRe, JINA, NAVI, DFG and ATHENA.

R eferen ces

[1] H H G u tb ro d and I A ugustin and H Eickhoff and K-D Grofi and W F H enning and D K ram er and G W alter 2006 Facility for a n tip ro to n and ion research fair baseline technical rep o rt, isbn-3-9811298-0-6 Tech. rep.

GSI

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