Se rp-process waiting point and the 69

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1 68 Se rp-process waiting point and the Kr -delayed proton emission experiment Marcelo Del Santo Joint Institute for Nuclear Astrophysics National Superconducting Cyclotron Laboratory Frontiers 2010 Workshop on Nuclear Astrophysics October 21-23,2010 Abbey Resort, Lake Geneva WI 1

2 The Joint Institute for Nuclear Astrophysics Outline X-ray bursts and rp-process Waiting point nuclei in the rp-process Proton separation energy of Br Kr -delayed proton emission experiment 2

3 X-ray bursts and rp-process scenario Neutron stars: 1.4 M o, 10 km radius average density: ~ g/cm 3 strong gravitational field Binary System Donor Star ( normal star, white dwarf) H, He rich material Accretion Disk X ray emission: persistent flux Thermonuclear explosion Temperature sensitive fusion reactions X-ray Burst rp-process Typical systems: accretion rate 10-8 /10-10 M o /yr ( kg/s/cm 2 ) orbital periods days orbital separations AU s Neutron Star 3

4 X-Ray Burst characteristics and classification Type I: Nuclear energy (rp-process) Energy proportional to preceding inactivity period Fast rise: 1-2s Exponential decay profile Burst energy thermonuclear s Persistent flux gravitational energy Typical X-ray bursts: duration: 10s 100s recurrence: hours-days regular or irregular energy: erg/s (stars erg/s) To interpret quantitatively: Need precise nuclear data to make full use of high quality observational data - masses (proton separation energies) - -decay rates - reaction rates (p-capture,,p) 4

5 p-process 14 O+ 17 F+p 17 F+p 18 Ne The Joint Institute for Nuclear Astrophysics rp-process 18 Ne+ 40 Ca end p-process 3 reaction C rp-process 41 Sc+p 42 Ti 42 Ti+p 43 V 43 V+p 44 Cr 44 Cr 44 V + e + + n e 44 V+p... Wallace & Woosley (1981) Schatz et al. (1998) F (9) O (8) N (7) C (6) B (5) Be (4) Li (3) He (2) H (1) Cu (29) Ni (28) Co (27) Fe (26) Mn (25) Cr (24) V (23) Ti (22) Sc (21) Ca (20) K (19) 2324 Ar (18) Cl (17) 2122 S (16) P (15) Si (14) Al (13) 1516 Mg (12) Na (11) 14 Ne (10) SnSbTe cycle Set the end point Schatz et al. (2001) As (33) Ge (32) Ga (31) Zn (30) Tc (43) Mo (42) Nb (41) Zr (40) Y (39) Sr (38) Rb (37) Kr (36) Br (35) Se (34) Sb (51) Sn (50) In (49) Cd (48) Ag (47) Pd (46) Rh (45) Ru (44) CNO cycle Breakout X-ray Burst starts 15 O(, ) 0.68GK 18 Ne(,p) 0.77GK Xe (54) I (53) Te (52) Waiting points (N=Z) 64 Ge, 68 Se, 72 Kr,... Long lived -decay rp-process slow down extend burst duration 5

6 68 Se Waiting point Kr 52ms 70 Kr 100ms 71 Kr 72 Kr 67 Br 68 Br <24ns Br 70 Br 71 Br 65 Se 33ms 136ms 35s 66 Se 67 Se 68 Se Se 70 Se 64 As 65 As 66 As 67 As 68 As As 6

7 Effective life time of the 68 Se waiting point Saha equation: decay rate: Se + p Br Q 1 = S p Proton unbound CPT [Clark et al. 2004] Penning trap, AW extrap. Br mass [Wöhr et al. 2004] -decay end point, AW extrap. Br mass [Rogers et al. 2010] Measurement of 68 Se+p decay products [Savory et al. 2009] LEBIT 68 Se mass - Penning trap Br mass - Coulomb displacement Sp (kev) Error (kev) T 1/2 eff (s) Error (s) T = 1.5x10 9 K = 10 6 g/cm 3 [A. Wöhr et al.2004] non-observation of Br in projectile fragmentation experiments [Pfaff1996] Br T 1/2 < 24 ns Sp < -500 kev 7

8 Sensitivity studies of rp-process calculations Influence of the proton capture Q-values on Type I X-ray burst models [Brown et al. PRC (2002)] -Coulomb displacement energy -exp. masses from the neutron rich side Wainting point SkX SkX min -SkX max 64 Ge 30 % % 68 Se 0.5 % % 72 Kr 0.0 % 0.0-8% Branching for proton captures - Large errors in 64Ge and 68Se masses provide the dominant uncertainty in the rp-process calculations. - Improve underlying nuclear physics 8

9 Experiment carried out at NSCL (May 2010) How unbound is Br? What s the proton separation energy? delayed proton emission of Kr Kr e + + e + Br decay (ms) 68 Se + p 9

10 Kr -delayed proton emission (90 kev)(3/2-) (5/2-) Kr T 1/2 = 32 (10) ms [Xu et al. PRC (1997)] (129 kev)(3/2-) (40 kev)(5/2-) (1/2-) IAS Br Ep = 4070 kev Only know p transition [Xu et al. PRC (1997)] Energy is too high to play a direct role in the rp-process. (2+) 854 kev [Fischer et al. PRC (2003)] 68 Se 10

11 Kr -delayed proton emission (90 kev)(3/2-) (5/2-) Kr T 1/2 = 32 (10) ms [Xu et al. PRC (1997)] (129 kev)(3/2-) (40 kev)(5/2-) (1/2-) IAS Br Ep = 4070 kev Only know p transition [Xu et al. PRC (1997)] Energy is too high to play a direct role in the rp-process. (2+) 854 kev [Fischer et al. PRC (2003)] Our Goal 68 Se Identify branches of -delayed proton emission, particularly from the lower states in Br to better constrain the proton separation energy 11

12 Beam production at NSCL K500 Cyclotron Secondary beam: Kr + contaminants Purity of % Radio Frequency Fragment Separator Primary beam: MeV/u A1900 Fragment Separator Superconducting magnets B = mv/q selection K1200 Cyclotron Be target 142 mg/cm 2 Superconducting magnets B = mv/q selection Wedge-shaped Al degrader 173 mg/cm 2 de/dx ~ Z 2 12

13 Y position (mm) The Joint Institute for Nuclear Astrophysics The Radio Frequency Fragment Separator at NSCL ( Kr, 67 Se, 66 As, 62 Cu, 60 Ni, 59 Co, ) RFFS Vertical slits (mm) Time of flight (ns) Time of flight (ns) RF electric field: Frequency range: 17MHz to 27 MHz Maximum peak voltage of 100 kv Electrodes parallel deflecting plates: 1.5m long, 5cm gap Kr (pps) Contaminants (pps) Purity (%) Without RFFS With RFFS ~ factor 60 13

14 Beta Counting System - BCS Identify each fragment and correlate with their subsequent or p decay p PIN Heavy Fragment (secondary beam) Plastic Scintillator Detector PINs 4x4cm Silicon Detectors DSSD Double-sided Silicon Strip Detector 4cm x 4cm x 500 m 40x40 strips 1600 virtual pixels 14

15 BCS and SeGA SeGA: 16 high purity segmented Ge detectors surrounding BCS for for gamma detection BCS: PIN detectors + 3 DSSDs Resolution of 100 kev at 8 MeV Total efficiency 7% at 1MeV 15

16 Particle Identification (PID) Implants on DSSD 66 As 67 Se Kr 66 As and 67 Se: Kr: 100% p Next step: Look for correlated decays in the same pixel of the implant in the DSSD 16

17 Correlations How correlation works: Implant or decay event Heavy Fragment Kr Implant (GeV) p decay (MeV) p Find a decay: - only a signal in DSSD look back for implants: - a signal in PIN1,2,3 and in DSSD - in the same pixel (or in a small box) - within 1 second - particle ID: gate on Kr - decay time (dt) dt dt 1 s 1 s 1 s Event Time Line (ms) 17

18 Kr decay curve and half life T 1/2 (ms) Kr Previous [Xu et al. (1997)] 32 ± 10 This work 28 ± 1 18

19 delayed proton energy spectra Preliminary Results Br IAS 68 Se*??? p Br IAS 68 Se g.s.??? Summing Effect E T = E p + E [see Zach Meisel s talk] Corrections ~100 kev GEANT 4 simulation minimize summing effect select mult. 1 events 19

20 Summary Waiting point nuclei slow down the energy generation and can explain some observed bursts with long duration Effective life time of the 68 Se depends on the S p Determines the shape and duration of X-ray Bursts light curves Experiment to constrain the S p of Br -decay branches to low energy levels Collaboration: Hendrik Schatz, Paul Mantica, Marcelo Del Santo, Heather Crawford, Geoff Grinyer, Jorge Pereira, Fernando Montes, Giuseppe Lorusso, Ana Becerril, Zach Meisel, Alfredo Estrade, Karl Smith, Richard Cyburt 20

21 -ray spectra 511 (1) kev 511 kev line Electron-positron annihilation energy Good test for calibration 853 (1) kev 853 (1) kev decay from 68 Se * 68 Se g.s.

22 Beta Decay NSCL MAR-APR 2010 B-delayed proton decay of the proton rich 39Ti: - improve constraints on the energy window for 2p emission - prediction of direct 2p candidates below 45Fe Charged particle decay of proton rich 22,23 Si isotopes: - ground state two proton (2p) emitter candidate - characterize the -decay and subsequent charged particle emission ( 2p, 3p,, p ) Beta delayed proton emission of Kr and the rp-process in X- ray bursts: - identify branches of beta delay proton-emission - better constrain the proton separation energy of Br 22

23 Bursts characteristics Typical X-ray bursts: duration: 10s 100s recurrence: hours-days regular or irregular energy: erg/s (stars erg/s) Very bright and frequent phenomenon! Today: ~230 X-ray binaries known ~160 LMXB s (low mass x-ray binary) ~70 burst sources 4U [Haberl (1987)] [Sztajno (1985)] 23

24 X-Ray Burst profile and classification Type I: Nuclear energy (rp-process) Energy proportional to preceding inactivity period Burst energy thermonuclear s Fast rise: 1-2s Exponential decay profile Type II: Gravitational energy Energy proportional to following inactivity period Persistent flux gravitational energy To interpret type I X-ray bursts: - masses (proton separation energies) - -decay rates - reaction rates (p-capture,,p) 24

25 Proton Separation Energy (kev) Wöhr et al. The Joint Institute for Nuclear Astrophysics 68 Se(p, ) Br Q-value non-observation of Br in projectile fragmentation experiments [Pfaff1996] Br lifetime T 1/2 < 24 ns Sp < -500 kev Sp (kev) Error (kev) CPT [Clark et al. 2004] Penning trap, AW extrap. Br mass [Wöhr et al. 2004] decay end point, AW extrap. Br mass 25