R-Process Experiments at ISOL Facilities

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1 R-Process Experiments at ISOL Facilities Karl Ludwig Kratz Institut für Kernchemie, Universität Mainz VISTARS University of Notre Dame January, Notre Dame, IN

2 As the Director of JINA reminded us beforehand, - the purpose of this workshop should mainly be to discuss open questions rather than results, - to stimulate discussion and to trigger new ideas, exchange and collaborations on r process related topics. With respect to r-process experiments using ISOL techniques one has to recognize that most of the experiments feasible with standard isotope production, separation and detection methods have already been done. What has become essential during the past few years, are the continuous technical improvements of the above techniques, in order to obtain background-free, isotopically pure beams of the rare isotopes of astrophysical interest. Clearly, the catchword request in this context is SELECTIVITY

3 History and progress in analyzing r-process nuclei In years ago a new era in experimental nuclear astrophysics started: - at the ISOL facilities OSIRIS and TRISTAN the N=50 r-process waiting-point nucleus 80 30Zn 50 was measured, with a T ½ 550 ms. - at the ISOL facility ISOLDE the N=82 r-process waiting-point isotope 130 Cd was measured, with a T ½ 200 ms. Today in early 2005 altogether 35 isotopes have been measured (at least) via its T ½, which lie in the r-process boulevard for moderate neutron densities of < n n < cm -3. These r-process isotopes range from double-magic 78 Ni 50 to 147 Xe 93. Out of the 35 r-process nuclei, only 78 Ni and 139 Te have been measured at fragmentation facilities (MSU, GSI); the large majority was identified at ISOL facilities, in particular at ISOLDE / CERN.

4 What we knew already in Shell-model (QRPA; Nilsson/BCS) prediction T 1/2 = (195 ± 35) ms T 1/2 = 230 ms Q β = 8.0 MeV IKMz 155R(1986) K.-L. Kratz et al (Z. Physik A325; 1986) Exp. at old SC-ISOLDE with plasma ion-source and βdn counting νg 7/2, πg 9/2 4.1 Problems: high background from -surface ionized 130 In, 130 Cs -molecular ions [ 40 Ca 90 Br] + Request: SELECTIVITY! T 1/2 (GT) = 0.3 s

5 Mass units away from Isotope β-stability r-process path As shown in this table, the regions at N=50 and beyond (up to Kr), and at N=82 and beyond (up to Sn) are resonably well studied by now. The majority of these r-process isotopes were identified by, or in close collaboration with the Kernchemie Mainz group. Experimental information is still missing in the A 120 region and for A 140 (and here in particular for the 3rd N r, peak and beyond). 70 Fe Ni in 79 Cu in 81 Zn in (+1) 84 Ga in (+1) 85 Ge Br Kr in (+3) 102 Rb Zr Pd Ag in (+1) 133 Cd in (+3) 135 In in (+4) 138 Sn in (+2) 139 Te 87 9 in (+1) 147 Xe in (+1) 162 Eu Tm Pb

6 Usually, study of individual (short-lived) isotopes requires separation from bulk radioactivity chemical separation acc. to Z isotopic chain mass separation acc. to A isobaric chain In particular, for rare isotopes often not sufficient; additional selectivity required isotopically clean beam S E L E C T I V I T Y production specific reaction A(x,y)B, thermal fission, fast fission/spallation target temp. τ release = f(t target ) T target T desorpt. =f( H adsorpt. ) = f(z) duty-cycle ionisation separation detection optimize acc. to beam structure, t release, T ½, T ½ (isobars) positive/negative surface ionization; laser ionization TOF-DE/E isobaric mass separation (HRS) chemistry before or after mass separation; isomers (HF-splitting) shielding against background; specific decay modes, e.g. β n-γ t multi-fold coincidences

7 CERN-ISOLDE Th-foil target; hot plasma source Thermal desorption from Th-target will not be released will be released Desorption-Temp. For 50% volatilisation as fct. of Adsorption-Enthalphy with 1800 K, Th-target too slow!

Heft 1 /2005 Kernphysik Von Schalen, Clustern und Halos moderne Aspekte der Kernstruktur Hans Feldmeier und Thomas Neff Epilog: Auf dem Weg der Erkenntnis was unsere Welt im Innersten zusammenhält,

starke Wechselwirkung der Quantenchromodynamik die größte Rolle spielt. Trotzdem verbrachte die Kernstrukturphysik die letzten Jahrzehnte in einem Dornröschenschlaf.

8 Heft 1 /2005 Kernphysik Von Schalen, Clustern und Halos moderne Aspekte der Kernstruktur Hans Feldmeier und Thomas Neff Epilog: Auf dem Weg der Erkenntnis was unsere Welt im Innersten zusammenhält, wie es Goethe formulierte, sind die Atomkerne eine reichhaltige Informationsquelle, denn in ihnen sind drei der vier fundamentalen Kräfte (starke, schwache und elektro-magnetische) aktiv, wobei die starke Wechselwirkung der Quantenchromodynamik die größte Rolle spielt. Trotzdem verbrachte die Kernstrukturphysik die letzten Jahrzehnte in einem Dornröschenschlaf. Durch neue theoretische ab-initio-methoden und neue experimentelle Möglichkeiten, insbesondere aber auch durch die großen Fortschritte in der astrophysikalischen Erkundung unseres Universums, konnten die Wissenschaftler die Geldgeber überzeugen, sie wieder aufzuwecken. Davon zeugen z. B. die zur Zeit neu ausgeschriebenen Lehrstühle für nukleare Astrophysik oder auch der SFB Kernstruktur, nukleare Astrophysik und fundamentale Experimente bei kleinen Impulsüberträgen am supraleitenden S-DALINAC an der TU Darmstadt, der in engem Zusammenhang mit den jetzigen und zukünftigen Forschungen der GSI zu sehen ist. Die Erforschung der Kernstruktur wird heute zu einem großen Teil von der Astrophysik angetrieben. Will man verstehen, was in der Weite des Weltalls die Evolution antreibt, muss man auf der Erde das experimentelle und theoretische Studium der exotischen Kerne erweitern. Noch ist man zum Beispiel nicht zu den Isotopen vorgedrungen, die an der Synthese schwerer Elemente durch schnellen Neutroneneinfang (r-prozess) in explodierenden Sternen beteiligt sind.... as an example for long diffusion time from Mainz GSI (Darmstadt) from experimentalist theoretician

9 Selectivity at ISOLDE the Ag needle in the Cs haystack today, at PSB-ISOLDE Fast UC x target Neutron converter Laser ion-source (RILIS) Hyperfine splitting (πg 9/2 ) Isobar separation (HRS) Multi-coincidence setup for A=130 Cd >10 5 Ag Cd In Sn Sb Te I Xe Cs

10 Cd 4 + Comparison of - laser-off (surface-ionized In and Cs) and - laser-on (in addition laser-ionized Ag) γ spectra Total beam-time at ISOLDE ca. 11 hours!!!

11 Accessibility of Elements by RILIS Status 01/2005 Elements studied with dye laser RIS 45 Dye - laser RIS possible 33 U. Köster, LAP 2002 & Spec Acta 58B, 2003 B. Federov, LASER 2004 Poznan & Hyp Int to be publ. 1 H 2 He Ti:Sa laser RIS demonstrated 10 3 Li 4 Be Ti:Sa laser RIS with doubl. & tripl B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg Quadrupling needed 5 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac Rf Ha Ce 95 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Fc 99 Es 100 Fm 101 Md 102 No 103 Lr from K. Wendt

12 Isobar separation HRS design Μ/Μ 1/10 4 in reality, on a good day M/M 1/4000 M/M=7.5*10-5 Mass scan at HRS (ISOLDE) in 2002; efficiency corrected

13 Comparison of spatial beam profiles 28 VOLT repeller: Selection between - laser ions (laser & repeller on) and - surface ions (laser & repeller off) from K. Wendt

15 Differences in βdn energy spectra of 129 Cd 129g Cd 129m Cd νh 11/2 Q β GT (9/2,11/2,13/2) - γ high l n 1 + γ 128 In S n (3 + ) νd 3/2 νh 11/2 GT (Q β +x) (1/2,3/2,5/2) + γ low l n 1 + S n γ 128 In (3 + ) 129 In 129 In hard βdn-spectrum mainly outer 3 He ring soft βdn-spectrum mainly inner 3 He ring of longcounter 2 T 1/2 components T ½ ( 129g Cd) = 242(8) ms T ½ ( 129m Cd) = 104(6) ms O. Arndt (Diploma Thesis; 2003)

16 The r-process waiting-point nucleus 130 Cd...obtain a physically consistent picture! T 1/2, Q β, E(1 + ), I β (1 + ), log ft S n Q β J π =1 + {νg 7/2, πg 9/2 } 2QP 4QP free choice of combinations: low E(1 + ) with low Q β high E(1 + ) with low Q β low E(1 + ) with high Q β high E(1 + ) with high Q β

17 Example: Cd 82 just one proton-pair below double magic 132 Sn. -RPA model prediction in 1986 quite good: - E(1 + ) 2.1 MeV - log(ft) 4.1 T ½ (GT) 300ms -Q β 8.0 MeV Most recent shell modell calculations are inconsistent: (i) Martinez-Pinedo & Langanke (ANTOINE) (ii) Brown et al. (OXBASH) - E(1 + ) 1.55 MeV - E(1 + ) 1.38 MeV - log(ft) 3.8! T ½ (GT) 146ms - log(ft) 4.2 -Q β 7.56 MeV -Q β 8.75 MeV T ½ (GT) 180ms (iii) Vretenar & Ring (RMF+QRPA) - no information about E(1 + ), log(ft), Q β, but correct T ½ however, 132 Sn predicted to be stable!

18 130 Cd decay spectroscopy spectroscopy ISOLDE experiment Q β from measurement of β-spectrum endpoint energy: Q β =8.34 MeV Large Q β value best reproduced by mass models with N=82 shell quenching Mass model predictions Hilf et al. (GTNM, 1976) Möller et al. (FRDM, 1995): Aboussir et al. (ETFSI, 1995): Duflo & Zuker (1995) Dobaczewski et al. (HFB/SkP, 1996): Pearson et al. (ETFSI-Q, 1996): Audi & Wapstra (Mass Eval., 1997): Goriely et al. (HFBCS, 2001) Samyn et al. (HFB-2, 2002) Brown et al. (local OXBASH, 2003): Q β 7.57 MeV 7.43 MeV 7.87 MeV 7.56 MeV 8.93 MeV 8.30 MeV 8.50 MeV 7.00 MeV 7.64 MeV 8.75 MeV

19 The N=82 shell gap FRDM ETFSI-1 HFB-2 ETFSI-Q NONE of the mass models predicts the trend correctly! Request mass measurements south of 132 Sn

20 ...mainly resulting from new nuclear-structure information: better understanding of formation and shape of as well as r-process matter flow through no justification to question waiting-point concept (Martinez-Pinedo et al., PRL 83, 1999) no need to request sizeable effects from ν-induced reactions (Qian et al., PRC 55, 1997) Astrophysical consequences the A 130 N r, peak r-process abundances in the Solar System and in UMP Halo stars......are governed by nuclear structure! solar r abundances old T 1/2 Nuclear masses from AMDC, 2003 & ETFSI-Q new T 1/2 Normalized to N r, ( 130 Te)

21 What do we calculate? 3rd N r, peak and Pb abundances as reliability criterion for Th,U region! excellent agreement above Ba Th, U cosmochronometry

22 old <σ> HF =35 µb <σ> HF = 20 µb RIB experiment: (d,p) in inverse kinematics E L, ln(j π ), C²S

23 Near-future perspectives As shown by selected examples, the study of r-process isotopes requires the combination of several optimizations in isotope production, separation and detection. However, we nearly have reached the top of the flagpole of present ISOL facilities. What can still be done? 1. Detailed decay-spectroscopy of N=50 79 Cu and N= Ag (similar to 80 Zn and 130 Cd) Cd βγ, 132 Cd βnγ π-hole states in 131 In Ag βγ E(2 + ), E(4 + )/E(2 + ) in N= Cd Cd (d,p) simulate n-capture on classical waiting point 5. Clever target-ionsource chemistry doubly semi-magic Zr 70 as new waiting point? 49

Nuclear Spectroscopy of Very Neutron-rich rich Ag and Cd Isotopes

132 Nuclear Spectroscopy of Very Neutron-rich rich Ag and Cd Isotopes Iris Dillmann*,# for the Mainz- Maryland- Oslo- CERN/ ISOLDE- Collaboration * Institut für Kernchemie, Universität Mainz (Germany)