Decay spectroscopy for nuclear astrophysics:  - and  -delayed p-decay Livius Trache Texas A&M University College Station, TX, USA Nuclear Physics for Astrophysics V, Eilat, Israel, April 3-8, 2011

Nuclear Physics for Astrophysics Indirect methods with RIB Indirect methods in NPA with or w/o RIB –A. Coulomb dissociation –B. Transfer reactions (ANC method) –C. Breakup of loosely bound nuclei –D. Spectroscopy of resonances:  -decay, transfer reactions, resonant elastic scatt., etc Decay spectroscopy –E. Trojan Horse Method –… 2

= studied at TAMU 12 C 13 C 13 N 15 N 15 O 14 N 17 O 17 F 16 O 18 F 18 O 14 O 19 Ne 18 Ne 13 O 11 C 12 N 8B8B 7 Be 9C9C 10 C 10 B 11 N 11 B 9B9B 8 Be 22 Ne 21 Ne 9 Be 23 Na 17 Ne 16 F 15 F 22 Na 20 Na 24 Al 23 Al 25 Al 24 Mg 23 Mg 22 Mg 21 Mg 20 Mg 19 Na 19 F 20 Ne 25 Si 24 Si 26 Si 15 C 14 C 27 Al 26 Al 28 Si 27 Si 29 Si 26 Mg 25 Mg 27 P 26 P 28 P 30 P 29 P 31 P 28 S 27 S 29 S 31 S 30 S 32 S 32 Ar 31 Ar 33 Ar 35 Ar 34 Ar 36 Ar 31 Cl 30 Cl 32 Cl 34 Cl 33 Cl 35 Cl 34 S 33 S = planned 12 O 16 Ne 22 Al 23 Si 25 P 21 Al 30 Si (p,n) possible stable used at TAMU (p,2n) possible 21 Na also 38 Ca, 46 V, 57 Cu, 62 Ga, … 14 F p-shell : direct component dominant or important sd-shell : resonant components dominant

Decay spectroscopy Beta- and beta-delayed proton-decay & IAS in T z =-3/2 nuclei Isospin mixing GT strength distribution Explosive H-burning in novae 22 Na depletion in novae 23 Al→ 23 Mg*  22 Na(p,  ) 23 Mg* & 22 Mg(p,  ) 23 Al bottleneck r. in novae 31 Cl→ 31 S*  30 P(p,  ) 31 S* See Jordi’s list!

Radius Energy p Coulomb Barrier Nuclear Potential Resonant Capture a two-step process Same compound system: 23 Mg pp  Decay spectroscopy Resonant contributions to the reaction rate: Need energy, J r and resonance strength SpSp  + 23 Mg  23 Mg *  22 Na+p 23 Mg 23 Al 5/2 +, 7/2 +  / /2 + Conditions: Q EC >S p +2m e c 2 J=3/2+, 5/2+, 7/2+ Selection rules  =(2J+1)/(2j+1)(2I+1)b  b p * 

NeNa cycle Explosive H-burning in novae: “ 22 Na puzzle” - what are the stellar reaction rates for the 22 Mg(p,  ) 23 Al and 22 Na(p,  ) 23 Mg? - novae: explosive H-burning of accreting material in binaries star-WD. ~ 30/yr. -  rays from the decay of long-lived isotopes like 26 Al have been detected - E=1.275 MeV  ray following the decay of 22 Na predicted (Clayton, Hoyle), but not observed by space gamma-ray telescopes 22 Na depletion in novae: how does it happen? Q: why?! Novae model(s) inappropriate?! Nuclear data incorrect?! Not enough 22 Na produced or depleted?! T 1/2 =2.6 yr 24 Si NPA V poster by A Banu

MARS Primary beam 24 48A MeV – K500 Cycl Primary target LN 2 cooled H 2 gas p=1.6-2 atm Secondary beam A MeV 24 Mg 48A MeV Purity: 90%, or >99% after en degrader Intensity: ~ 4000 pps First time - very pure & intense 23 Al 23 Al 40A MeV In-flight RB production (p,2n) reaction 23 Al

Isotope selection with MARS Final cut with focal plane slits E Pos ~ q/m 24 Al used for en and eff calibration of Ge detector to E  =8 MeV N=Z-3 N=Z-1 N=Z-2

 decay study of pure RB samples

23 Al  -  coincidence spectrum IAS BGO

23 Al  -decay results First clean and intense 23 Al source Found decay scheme established g.s. J  =5/2 + (not 1/2 + ) [VE Iacob ea, PRC 74, Oct 2006; also A. Ozawa ea, PRC 74, Aug 2006 from magn mom meas]  22 Mg(p,  ) 23 Al not important for depletion of 22 Na in novae absolute branching ratios (not easy or common!) measured T 1/2 =446(4) ms (<1% accuracy) - w.  -ray multiscaling and absolute log ft identified IAS E*=7802.9(5) keV by logft=3.31(2) – meas! used IMME to get new 23 Al mass  S p ( 23 Al)=143(3) keV –Note: after mass meas in Jyvaskyla, became best IMME check! and S p =141.11(43) keV Located IAS & state at E*=7787 keV – important resonance in 22 Na(p,  ) 23 Mg

23 Al  -decay results First clean and intense 23 Al source Found decay scheme established g.s. J  =5/2 + (not 1/2 + ) [VE Iacob ea, PRC 74, Oct 2006; also A. Ozawa ea, PRC 74, Aug 2006 from magn mom meas]  22 Mg(p,  ) 23 Al not important for depletion of 22 Na in novae absolute branching ratios (not easy or common!) measured T 1/2 =446(4) ms (<1% accuracy) - w.  -ray multiscaling and absolute log ft identified IAS E*=7802.9(5) keV by logft=3.31(2) – meas! used IMME to get new 23 Al mass  S p ( 23 Al)=143(3) keV –Note: after mass meas in Jyvaskyla, became best IMME check! and S p =141.11(43) keV (A. Saastamoinen ea, PRC 80, 2009) Located IAS & state at E*=7787 keV – important resonance in 22 Na(p,  ) 23 Mg

23 Al  -decay results First clean and intense 23 Al source Found decay scheme established g.s. J  =5/2 + (not 1/2 + ) [VE Iacob ea, PRC 74, Oct 2006; also A. Ozawa ea, PRC 74, Aug 2006 from magn mom meas]  22 Mg(p,  ) 23 Al not important for depletion of 22 Na in novae absolute branching ratios (not easy or common!) measured T 1/2 =446(4) ms (<1% accuracy) - w.  -ray multiscaling and absolute log ft identified IAS E*=7802.9(5) keV by logft=3.31(2) – meas! used IMME to get new 23 Al mass  S p ( 23 Al)=143(3) keV –Note: after mass meas in Jyvaskyla, became best IMME check! and S p =141.11(43) keV Located IAS & state at E*=7787 keV – most important resonance in 22 Na(p,g) 23 Mg

23 Al  no-BGO vs BGO shield 23 Mg ?!% p 451 gs IAS, T=3/

23 Mg 7803 IAS 5/ (7/2) / / (3,5/2) /2+ NO! / /2+ 0 3/2+ 22 Na Sp=7580 keV β+β+ β+β+ IAS: ft=2140 s +/-5% 22 Na(p,  ) 23 Mg resonances Most important:  7787 =__._?! meV 23 Al 0.446(4)s Q ec =12240keV 5/2+ 22 Mg(p,  ) 23 Al p ?!% Proton br. total=?!% Tighe ea, LBL 1995 Perajarvi ea, JYFL 2000 E=207 keV =>  E=16 keV VE Iacob, et al., PRC 74, Oct & Y Zhai thesis Unusually strong isospin mixing! (?!)

thermocooler  =80 mm OD  150 mm >110 mm connectors Energy degrader 18” dia chamber 64 mm 275 mm  -detector – thick Si det 1 mm p-detector – v. thin DS Si strip 65 or 45  m W1-65 BB2-45  -detector – HPGe 70% effic Pulsed beam E=E p +kE recoil + MARS implantation station Method: implantation in very thin Si detectors!

proton  HI Signal=E p +  E  Signal=  E  Si 1000  m Si strip 61  m Gamma-ray measure simultaneously:  -proton and  coinc. Si stops protons: ½ 65  m E p <1.5 MeV “  -proton mode” “HI telescope mode” – control implantation Signal=  E HI Signal=E  17  m  p/p=+/-0.25%  E (p) E (  ) 36 ° 30 ° 0°0°

E=223 keV IAS 23 Al  -delayed p-decay sp – after bkg subtraction Gamow window Antti Saastamoinen et al., PRC accepted “world record” Resonances for 22 Na(p,  ) 23 Mg

Eres (keV) Eexc (keV)br-p (of 100 beta) (3)% IAS ?! (4)% (1)% (2)% (2)% (3)% (1)% total1.22(5)% /2 +, T=1/2 23 Mg 22 Na + p 7787 (7/2) + IAS, 5/2 + T=3/2 3.7% 78.2% 18.0% p (5/2, 7/2) + 5/ Al Most important resonance: E res =207 keV  =1.4 meV (+.5,-.4)  from  =10(3) fs Jenkins ea, PRL /2 + 5/2 +  allowed GT Superallowed F Rare cases of  & p-branching measured simultaneously ! ?!  =(2J+1)/(2j+1)(2I+1)b  b p * 

Results 22 Na(p,  ) 23 Mg Most important resonance: E res =207 keV, J  =(7/2) +, T=1/2  =1.4 meV (+.5/-.4) - using our branchings and t 1/2 =10(3) fs from Jenkins et al. (PRL 2004) -direct meas, p on radioactive 22 Na target:  =1.4(3) meV – Stegmueller et al. NPA1996 New resonances found: 267, 337 keV No resonance at E p =198 keV - as suggested in Jenkins ea, PRL 92 (2004)  =5.7(16) meV – Salaska et al. PRL 2010

Background subtracted using decay of 22 Mg (not a proton emitter) Full disclosure!

23 Al  p meas with Si det Low energy beta background hurts!

Future: ASTROBOX E Pollacco (CEA Saclay) proposed: Gas detector w MICROMEGAS Low proton energies (~1-200 keV), good resolution (5-10%) Reduced  background Two weeks ago emitted proton electrons beam

Run0311B: 23 Al  p-decay with ASTROBOX Implantation control Outer-far Center detector Outer + center 223 IAS 206 keV betas Off-beam spectrum 337

23 Al  p meas with Si det Low energy beta background hurts!

A few images are worth a thousand words! W1-65 det 16 x 16 strips 3.1 mm BB2-45 det 24 x 24 strips, 1 mm

Radius Energy p Coulomb Barrier Nuclear Potential Resonant Capture a two-step process Same compound system: 31 S pp  Decay spectroscopy Resonant contributions to the reaction rate: Need energy, J r and resonance strength SpSp  + 31 S  31 S *  30 P+p 31 S 31 Cl 1/2 +, 3/2 +  /2 + 3/2 + Conditions: Q EC >S p +2m e c 2 J=1/2+, 3/2+, 5/2+

MARS Primary beam 32 40A MeV – K500 Cycl Primary target LN 2 cooled H 2 gas p=2 atm Secondary beam A MeV 32 S 40A MeV Purity: > 85 % (at target det) Intensity: ~ pps difficult - pure & intense 31 Cl 31 Cl 34A MeV In-flight RB production (p,2n) reaction 31 Cl

31 Cl production and separation 31 Cl 32 Cl 29 S Energy (a.u.) Position (0.1 mm) = q/m

31 Cl  -decay - status 2006 Old:    =150(25) ms

31 Cl  decay IAS

31 Cl  -decay - status 2006/present exp Old:    =150(25) ms New: T 1/2 = 190(1) ms S p =6.133 MeV

Proton Detectors The W1 Detector: –Thickness: 65 μm –Number of Strips: 16 –Width of Strips: 3.1mm –Detection Volume: ~0.625 mm 3 Used in our 23 Al 2007 and 31 Cl 2007 Experiments The BB2 Detector: –Thickness: 45 μm –Number of Strips: 24 –Width of the Strips: 1mm –Detection Volume: ~0.045 mm 3 Used in our 31 Cl 2008 and 23 Al 2009 Experiments Both made by Micron Semiconductor LTD. W1 BB2

Lowering  background: W1-65 –Large amount of background in the regions of 500 keV or lower BB2-45 –Only part of the statistics are shown, but Resolution is visibly better And the minimum energy threshold goes below 300 keV Lose efficiency at E p > 1.5 MeV Conclusions: –Thinner detector with thinner strips was better at measuring the proton energies as low as keV W1 BB2 Un-luckily: no new states here!

31 Cl  -decay results First clean and intense 31 Cl source established  -decay scheme determined relative branching ratios measured T 1/2 =190(1) ms (<1% accuracy) identified IAS E*=6279.5±0.3±1.5 (syst) keV and its decay used IMME to get new, more precise 31 Cl mass ME( 31 Cl)=-7064(8) keV  Q EC =11,980(8) keV and S p ( 31 Cl)=289(8) keV (imp for 30 S(p,  ) 31 Cl !) found precise energy of E * =6256(1) keV  E res =123(2) keV – important reson in 30 P(p,  ) 31 S did not find IAS proton branching (at E p =146 keV – very difficult !!)

Results  -delayed p-decay Technique works well – can go to E p ~100 keV and, maybe, lower Can work with lifetimes ~100 ms or less Very selective: can separate well beam cocktails (by implantation depths) Very sensitive: could obtain results for 21 Mg, 29 S at rates ~ 1-10 pps in 8 hrs Could study very weak branches in 20 Mg … Strengths: –Good isotope separation (MARS) –In-flight production: need MeV/u (can be implanted) –ASTROBOX opens new possibilities

Collaborators A Banu, JC Hardy, VE Iacob, M McCleskey, E. Simmons, BT Roeder, A Spiridon, G Tabacaru, RE Tribble – Cyclotron Institute, Texas A&M University PJ Woods, T Davinson, G. Lotay – Univ of Edinburgh J Aysto, A Saastamoinen, A Jokinen – Univ of Jyvaskyla MA Bentley – Univ of York L Achouri – LPC Caen E Pollacco, A Obertelli et al. –CEA Saclay