Beta-delayed neutron measurements with the BELEN detector

Transcription

1 Beta-delayed neutron measurements with the BELEN detector Iris Dillmann Helmholtz Young Investigators Group LISA Universität Giessen and GSI Helmholtzzentrum Darmstadt/ Germany 1

2 Overview Who? What? Why? Where and how? Which? What else and when? 2

3 Who? (The collaboration) S323/S410 Collaboration 3

4 What? Extremely neutron-rich, short-lived isotopes b-delayed n-emitters: t 1/2 and P n "rapid neutron capture process": 50% of heavy elements 4

5 b-delayed neutron emission Q b S n Discovered in 1939 Delayed : emission with b- decay half-life of the precursor A Z t 1/2 few ms s ( 87 Br) 8 He- 150 La: 200 datasets available, 75 in nonfission region (A<70) S n < Q b Important nuclear structure information: Time-dependence of n-emission t 1/2 ( A Z) P n : b-strength above S n Only 1 measurement for A>150: P n = ( ) % Validation missing G. Stetter, Nucl. Sci. Abstr. 16, 1409, Abstr (1962) 5

6 Why? Nuclear physics input for network calculations: Theory + few experimental information t 1/2 (b) (s- ms): Shape Masses (S n 2-3 MeV): Path b-delayed neutron emission (P n ): Extra-neutrons, detour of path (n,g)/ (g,n) cross sections Z>80: fission barriers, b-delayed fission, (n,f)-cross sections t 1/2 (a) for A>210 6

7 Astrophysical influence During Freeze-out : detour of b-decay chains r-abundance changes FRDM(GT+ff) predictions: b-decay: 6.9% P(1n): 6.5 % P(2n): 86.7% P. Möller et al., Phys. Rev. C 67, (2003) In ms bn, b2n 7

8 Late-time influence Production of additional neutrons, influence on n/seed ratio at later times A. Arcones and G. Martinez-Pinedo, PRC83, (2011) 8

9 N=82 Data! Existing data contrains models (strong even-odd staggering?) Next N=82 isotope in reach: 128 Pd P n value of 129 Ag? Data! Q. Zhi et al., arxiv:

10 N=126 Factor 5-10 difference No data! No data! Q. Zhi et al., arxiv:

11 Recent progress on the n-rich side Recent GSI-FRS: ~130 new isotopes identified Z=59-87 (Pr-Fr) T. Kurtukian-Nieto, PhD thesis (2007) H. Alvarez-Pol et al., Phys. Rev. C 82 (2010) (R) L. Chen et al., Phys. Lett. B 691 (2010) 234 J. Kurcewicz et al., Phys. Lett. B717 (2012) 371 Recent RIKEN-BigRIPS: 45 new isotopes identified: 71 Mn- 152 Ba T. Ohnishi et al., Journal of the Physical Society of Japan 79, (2010) 11

12 Where and how? Experimental GSI Darmstadt

13 GSI Helmholtzzentrum für Schwerionenforschung Darmstadt/Germany Ion Sources Linear Accelerator up to 0.2c SchwerIonen Synchrotron (up to 0.9c) FRagment Separator Experimental Area 1 GeV/u 238 U ions/spill on 1-3 g/cm² Be 13

14 Setup 70 m Target FRS 1 m S4 focal area n n Implantation detector SIMBA Neutron-rich 238 U fragments n n Neutron detector BELEN-30 Shielding (PE + borated rubber) 14

15 BEta delayed Neutron detector (BELEN-30) Universidad Politecnica de Cataluna, Barcelona IFIC Valencia CIEMAT Madrid 30 high pressure 3 He long counters PE matrix, size 1m 3 MC Simulation (M.B. Gomez, UPC) M.B. Gómez Hornillos et al., Proc. Int. Conf. on Nucl. Data for Science and Techn. (2010) 15

16 Silicon IMplantation detector and Beta Absorber SIMBA Constructed and developed at 60x segm. X and Y-detector 7x segm. b-absorber (front and back) Implantation area: DSSD, 60x40 segm. Fragment beam Tracking: (X,Y) Implants Front b- absorber DSSD: b-energy and position Rear b- absorber PhD thesis C. Hinke, TUM (2010) Diploma thesis K. Steiger, TUM (2009) 16

17 Which (isotopes)? t 1/2 and P n -values "South-west" of 132 Sn: n-rich Ag, Pd, Rh "South-east" of 208 Pb: n-rich Tl, Hg, Au 17

18 Preliminary status Showing prelim. data from K. Smith (Notre Dame/ GSI) R. Caballero-Folch (UPC Barcelona) 18

19 "South-west" of 132 Sn 4 days beamtime: Aim: new t /2 Pd, x Rh New P n values Improved t 1/2 and P n values Identification of fragments Sn In Cd Ag Pd Rh Ru N=82 132Sn 131In 130Cd 129Ag 128Pd Courtesy of K. Smith and F. Montes 19

20 "South-east" of 208 Pb Ra Fr Rn At Po Bi Pb Tl Hg Au Pt Identification of fragments ( 211 Hg setting) 210Tl 205Au 209Hg 219Bi 215Pb 204Pt 224At 213Tl 222Po 229Rn A/Z Last isotope with measured t 1/2 R. Caballero, NIC-XII proceedings (2012), NIC XII_109 20

21 43 s 13.5 s 4.4 s 410 ms 12 s 2 s 16 s 8.5 s 5 s 97 s 40 s 21 s 12 s 161 s 98 s 49 s 25.5 s 5718 s 777 s 197 s 41 h 2.8 h 1621 s 352 s "South-east" of 208 Pb Implanted fragments ( 211 Hg setting) t 1/2 (GT+ff) DDME-1* (T. Marketin et al., TU Darmstadt) R. Caballero, NIC-XII proceedings (2012), NIC XII_109 Heaviest bdn-emitters measured so far! 21

22 Production Detection of bn FRS SIMBA BELEN We have detected you! TOF ca. 300 ns b - half-life moderation time Analysis in progress: identification of implants, b-n correlations t 1/2, P n 22

23 What else and when? (Outlook) 23

24 r-process around N=126 Gap to N=126 progenitors: 194 Er (-16n: 178 Er) 195 Tm (-14n: 181 Tm) Need: better detection setup and higher beam intensities Maximum at N=126: 194 Er, 195 Tm 24

25 BELEN is growing up! BELEN , 8 & 10 FAIR/ DESPEC ~65% 8 (AIDA) /15... >2018 R. Caballero, BRIKEN Workshop ( ) 25

26 Future RIB facilities Facility for Antiproton and Ion Research (>2018) Super-FRS facility Similar RIB projects: RIBF (Japan, since 2007) Spiral 2 (France) FRIB (USA) RAON (Korea) More bxn-emitters in reach, priorities shifted 26

27 What else: Measure P 2n S 2n < Q b First experimental identification of P 2n : Experiment in JYFL (2013): measure P 2n of 136 Sb 11 Li (t 1/2 = 8.6 Azuma et al., PRL 43, 1652 (1979) Na (t 1/2 = Detraz et al., Phys. Lett. 94B, 307 (1980) 98 Rb (t 1/2 = 114 Reeder et al., PRL 47, 483 (1981) 18 b2n and 4 b3n emitter ( 11 Li, 14 Be, 17 B, 31 Na) known AME2011: 247 b2n cases energetically possible 27

28 Summary BELEN (+AIDA) is a powerful setup for bdn and t 1/2 BELEN: GSI JYFL RIKEN... FAIR TETRA: DESIR@Spiral2 3Hen: ORNL TRIUMF CARIBU FRIB 28

29 The big improvement: Digital electronics R. Caballero, BRIKEN Workshop ( ) 29

30 Upgrade for Inclusion of additional counters from JINR Dubna upgrade to 96 counters New implantation detector AIDA Efficiency: BELEN-30: 40% BELEN-96: 65% Advanced Implantation Detector Array (AIDA) Pictures: M.B. Gomez Hornillos and T. Davinson 30

31 FRS: fragment production, in-flight separation, and identification 70m Be 1-3 g/cm U ions / spill at E = 1 GeV A Separation Br DE Br In-flight particle identification: 2x Plastic Scintillators ToF b 4x Time Projection Chambers x,y position r Br m q cb b m/q 2x MUSIC (MUltiple Sampling Ionisation Chamber) E loss Z m/q and Z identify the fragment (validation with Isomer TAGging) H. Geissel et al., NIM B 70, 286 (1992) 31

32 What else: Measure P 2n Highly efficient setup needed: upgrade to BELEN-48 Proposal for IGISOL@Jyväskylä/ Finland: e(bn) 11 % e(bnn) 5 % 136 Sb P 2n % events/ 5d 32

33 136 Sb 33

34 First next-generation RIB facility online (since 2007) Same production mechanism as GSI/ FAIR (fragmentation and in-flight separation), with lower primary beam energy (345 MeV/u instead of 1 GeV/u) and higher intensity ( 10 pna for 238 U) Advantage: Possibility to test FAIR-like setup (BELEN+AIDA) under realistic conditions 34