Enhanced low-energy γ-decay probability implications for r-process (n,γ) reaction rates

Transcription

1 Enhanced low-energy γ-decay probability implications for r-process (n,γ) reaction rates Ann-Cecilie Larsen, Dep. of Physics, University of Oslo ERC StG 8 - gresonant 14th International Conference on Nuclear Reaction Mechanisms, Varenna, June 1-19, 01

2 Thanks to all collaborators! The Oslo group: F. L. Bello Garrotte, L. Crespo Campo, A. Görgen, M. Guttormsen, K. Hadynska-Klek, T. W. Hagen, M. Klintefjord, T. Renstrøm, S. J. Rose, E. Sahin, S. Siem, and G. M. Tveten Stephane Goriely, Université Libre de Bruxelles Artemis Spyrou, Sean N. Liddick, Farheen Naqvi, Alex Brown, NSCL/MSU George Perdikakis, CMU & NSCL/MSU Ronald Schwengner, HZDR Dresden Alexander Voinov, Ohio University Lee A. Bernstein, Darren L. Bleuel, Lawrence Livermore National Lab Bethany L. Goldblum, UC Berkeley Mathis Wiedeking, B. Vincent Kheswa, ithemba LABS Angela Bracco, Franco Camera, Silvia Leoni, INFN Milano Hiroaki Utsunomiya, Konan University Andrew Rogers, UMass Lowell Sotirios Harissopulos, NCSR Demokritos Stefan Frauendorf and Anna Simon, University of Notre Dame

3 Heavy-element nucleosynthesis and the nuclear chart Figure: courtesy of Prof. M. Hjort-Jensen # protons # neutrons

4 Heavy-element abundances reaction rates Opticalmodel potential Level density Gammadecay strength M. Arnould, S. Goriely, and K.Takahashi, Phys. Rep. 40, 9 (00) # 8 & N A σ v (T ) = % ( $ πm ' 1/ N A (kt ) / G(T ) 0 G(T ) = (I µ +1) / (I 0 +1)exp( E x µ / kt ) µ µ (I µ +1) (I 0 +1) σ * µ (E)E exp (E + E x, + kt µ ) - / de. 4

5 Nuclear-data needs for the rapid neutron capture process S n +*E n * γ9strength*func'on*(log*scale)* upbend* Excita'on*energy*E x * γ* γ*energy*eγ" scissors* pygmy* Ground*state** of*compound*nucleus**

6 Stable-beam & target OCL

7 Stable-beam & target OCL CACTUS: collimated NaI(Tl) crystals, x NaI(Tl) He α 40 4 o Si ΔE- E telescope SiRi: 8x8 Si ΔE-E particle detectors ( 9% of 4π) [Guttormsen et al., NIM A 48, 18 (011) Target nucleus

8 Stable-beam & target OCL CACTUS: collimated NaI(Tl) crystals, x NaI(Tl) He α 40 4 o Si ΔE- E telescope SiRi: 8x8 Si ΔE-E particle detectors ( 9% of 4π) [Guttormsen et al., NIM A 48, 18 (011) Ex (kev) Target nucleus Fe(p,p ) Eγ (kev) 8

9 The Oslo method a crash course E x Yrast line Ex (kev) Fe(p,p ) 0 - I Eγ (kev) 0. Get a hold of an (Eγ,Ex) matrix 1. Correct for the NaI response [Guttormsen et al., NIM A 4, 1 (199)]. Extract distribution of primary γ s for each Ex [Guttormsen et al., NIM A, 18 (198)]. Get level density and γ-strength from primary γ s [Schiller et al., NIM A 44, 498 (000)] 4. Normalize & check systematic errors [Schiller et al., NIM A 44, 498 (000), Larsen et al., PRC 8, 041 (011)] 9

10 Nuclear level densities constant temperature [L.G. Moretto et al., arxiv:140.4 and references therein] ρ (E) (MeV -1 )! ,149 (a) Sm OCL data, even-even OCL data, even-odd Fit, CT model 1,14 (e) Dy (i) Th 4, ,11 (b) Dy 1,1 (f) Er, (j) Pa ,1 (c) Dy 10,11 (g) Yb,8 (k) U excitation energy E (MeV)! 1,1 (d) Dy 11,1 (h) Yb 8,9 (l) U 0 1 4

11 ρ (E) (MeV -1 )! Nuclear level densities constant temperature 148,149 (a) Sm OCL data, even-even OCL data, even-odd Fit, CT model 1,14 (e) Dy (i) Th 4, 10,11 (b) Dy 1,1 (f) Er, (j) Pa [L.G. Moretto et al., arxiv:140.4 and references therein] 11,1 (c) Dy 10,11 (g) Yb,8 (k) U For downloading all published data and references: excitation energy E (MeV)! 1,1 (d) Dy 11,1 (h) Yb 8,9 (l) U

12 The low-energy enhancement upbend 1

13 The 9 Mo case: confirmation of the upbend 94 Mo(d,pγγ) 9 Mo LBL experiment, STARS-LIBERACE Model-independent technique, Ge detectors, [M. Wiedeking et al., Phys. Rev. Lett 111, 40 (01)] 1

14 Iron revisited multipolarity of the upbend CACTUS: LaBr (Ce),. x 8 From the Milano HECTOR + array NaI(Tl), x 14

15 Iron revisited multipolarity of the upbend ) - γ-ray strength function (MeV - - CACTUS: LaBr (Ce),. x 8 From the Milano HECTOR + -8 array NaI(Tl), x 9 Fe( He,αγ), Voinov et al. Fe(p,p γ), NaI:Tl Fe(p,p γ), LaBr :Ce Co(γ,n), Alvarez et al γ-ray energy E (MeV) γ Dominated by dipole transitions ( 8-90%) [A.C. Larsen et al., PRL 111, 404 (01)] 1

16 Theoretical approaches electromagnetic nature of the upbend x" %9 " γ"strength"func1on"(mev % )" Electric dipole? [E. Litvinova and N. Belov, PRC 88, 010(R) (01)] γ"energy"e γ "(MeV)" Magnetic dipole? [R. Schwengner, S. Frauendorf, and A. C. Larsen, PRL 111, 04 (01)] 1

17 ) -1 i (MeV ρ ) -1 i Recent shell-model calculations,, Fe (MeV ρ (a) Fe (p,p'γ) (b) Fe Fe, Larsen et al. (01) ( He,α'γ) Fe, Schiller et al. (00) SM calc. (π = +), J = 0- (p,p'γ) Fe, Larsen et al. (014) ( He, He'γ) Fe, Schiller et al. (00) SM calc. (π = -), J = 1/-1/ (MeV) E i E i (MeV) (MeV) E i (a) Fe ) (µ B(M1) N (MeV) (b) Fe ) (µ B(M1) (MeV) [B. Alex Brown and A.C. Larsen, Phys. Rev. Lett. 11, 0 (014)] N E (MeV) E E

18 ) -1 i i Recent shell-model calculations,, Fe (MeV ρ ) -1 (MeV ρ (a) Fe (p,p'γ) (b) Fe Fe, Larsen et al. (01) ( He,α'γ) Fe, Schiller et al. (00) SM calc. (π = +), J = 0- (p,p'γ) Fe, Larsen et al. (014) ( He, He'γ) Fe, Schiller et al. (00) SM calc. (π = -), J = 1/-1/ (MeV) E i ) - f M1 (MeV E i (MeV) ) - f M1 (MeV) (MeV E i (a) Fe (b) Fe (a) Fe ( He, ) Fe, Voinov et al. (004) (p,p ) Fe, Larsen et al. (01) SM calc ) (µ B(M1) N (MeV) E (MeV) E (MeV) (MeV) E ( (b) He, He ) Fe Fe, Voinov et al. (004) (p,p ) Fe, Larsen et al. (01/014) SM calc [B. Alex Brown and A.C. Larsen, Phys. Rev. Lett. 11, 0 (014)] ) (µ B(M1) N E

19 Upbend and (n,γ) reaction rates TALYS: Koning et al., r-process reaction rates for T = 1 GK Rate <σv> (upbend)/rate (GLO-up)/<σv> (no upbend) (GLO) 1 0 Mo Fe Cd N but is the upbend really there for n-rich nuclei? [A.C. Larsen and S. Goriely, Phys. Rev. C 8, (0)] 19

20 The brand new β-oslo method NSCL/MSU 1) Implant a neutron-rich nucleus in a total-absorption spectrometer (preferably with Q β S n ) ) Measure β-particle in coincidence with γ s from the daughter nucleus Ge primary beam, 10 MeV/nucleon on Be target Ga: T 1/ =.s; Q β =.91 MeV Beta-decay of Ga => Ge Segmented, total absorption spectrometer SuN [A. Simon, S.J. Quinn, A. Spyrou et al, NIM A 0, 1 (01)] [A. Spyrou, S.N. Liddick, A.C. Larsen, M. Guttormsen et al., Phys. Rev. Lett. 11, 0 (014)] 0

21 The brand new β-oslo method NSCL/MSU ) - ) (MeV f(e (b) Ge (norm-1) Ge (norm-) 4 Ge, Renstroem et al. Upper limit Lower limit (MeV) E - Ge(,n) ) -1 s -1 mol (cm Reaction N A rate v 9 8 (n,γ) rate -1 lower/upper, previous lower/upper, this work 1 9 T ( K) [A. Spyrou, S.N. Liddick, A.C. Larsen, M. Guttormsen et al., Phys. Rev. Lett. 11, 0 (014)] 1

22 Summary & future plans Nuclear properties for E x = 0 S n are very important for understanding the nucleus and the heavy-element nucleosynthesis Upbend: finally we know more, but el.mag. character remains to be measured The β-oslo method is promising when Q beta S n, n-rich Ge proposal in preparation Inverse-kinematics experiments: n-rich HIE- ISOLDE in 01 (S. Siem, M. Wiedeking et al.), proposal preparations for n-rich NSCL/MSU (HiRA+S800+CAESAR)