Lifetime measurement of the MeV state in 15 O Naomi Galinski SFU, Department of Physics, Burnaby BC TRIUMF, Vancouver BC CAWONAPS, 10 December 2010 Recipient of a DOC-FFORTE-fellowship of the Austrian Academy of Sciences at the Institute of SFU

Globular clusters: Oldest known/visible objects in our galaxy Compact groups of 100, million stars 1980: Gyr Now: Gyr Age of the universe: WMAP  13.7±0.2 Gyr Globular clusters can’t be older than the universe L. Krauss and B. Chaboyer, Science 299, 65 (2003) 1) Primordial gas cloud 2) Globular clusters form first 3) Galactic disk forms 4) Globular clusters occupy galactic halo Motivation

Age determination of globular clusters: Correlation between luminosity at MS turnoff point & age globular cluster CNO cycle dominates energy production at end of MS lifetime 14 N(p, γ ) 15 O is the slowest reaction Reaction rate uncertainty could change globular cluster age by Gyr Main sequence (MS) branch (H->He) Red giant branch (He->C) MS turnoff point Temperature Luminosity Motivation

Need to know 14 N(p, γ ) 15 O reaction rate at low (stellar) energies E 0  30 keV (for T = 0.02 GK) Past experiments only go down to E CM = 70 keV Energy below low-energy limit of direct γ ray measurements Need to extrapolate down to low energies using R-matrix analysis of S-factor Formicola et al., Phys. Let. B 591, (2004) The 14 N(p, γ ) 15 O reaction

S-factor of 14 N(p,  ) 15 O reaction Total S-factor of the 14 N(p,  ) 15 O reaction with contributions of different transitions to states of 15 O. Angulo et al., Nucl. Phys. A 690, (2001) Largest remaining uncertainty in reaction rate is due to width, , of MeV state This will constrain the R-matrix fit Obtain width from lifetime:  = ℏ /  R-matrix fits to the 14 N(p,  ) 15 O 6.79 MeV transition. Review article: Solar fusion cross sections II, the pp chain and CNO cycles, arXiv: v3 [nucl-ex] 10 Oct 2010

Lifetime of MeV state, τ [fs] Confidence Level (%) Measurement Bertone et al. (2001) 90 DSAM, direct Yamada et al. (2004) > Coulomb excitation, indirect Schürmann et al. (2008) < DSAM, direct Results marginally disagree Only one group, Bertone et al., has claimed central value This value is not generally accepted Previous measurements

Simulated lineshapes for different lifetimes. These are fit to the data to determine the lifetime of the excited state. In DSAM an excited recoil populated by a reaction decays as it slows down in a heavy foil The Doppler shifted energy of  rays emitted from a recoil traveling with reduced velocity  (t)=v(t)/c is given by: Doppler Shift Attenuation Method (DSAM) 3 He + Au Au 16 O 15 O   E  (t)=max  E  (t)=0  (0)=max  (t)=0  ejectile

16 O 15 O 3 He  Lower  limit of DSAM ~1 fs  of MeV state ~1 fs For accuracy need to know stopping powers Electronic stopping power better known Nuclear stopping not known so well Previous measurements low recoil velocity (  ≤0.0016) Nuclear stopping region 14 N+p → γ + 15 O We had higher recoil velocity (  ≤0.055) Used inverse kinematic reaction 3 He+ 16 O → α + 15 O DSAM and MeV lifetime 3 He + Au Au 15 O   E  (t)=max  E  (t)=0  (0)=max  (t)=0

TRIUMF ISAC II: Stable beam of 16 O at 50 MeV (1st run) and 35 MeV (2nd run) 3 He was implanted in a Au and Zr target foil. We used the Doppler shift lifetime (DSL) chamber, a target chamber specifically designed for DSAM experiments. The  rays were detected using a Ge TIGRESS detector on a single mount Experiment

Collimator E Si detector (500 μm) TIGRESS detector at 0 °  E Si detector (100 μm and 25 μm) Implanted 3 He (6×10 17 atoms/cm 2 ) Au/Zr foil (25 μm) Vacuum chamber 3 He+ 16 O → α + 15 O 16 O 15 O   Experimental setup 16 O beam

Doppler Shift Lifetime chamber

 ray spectrum keV Fig. Add back spectra of  rays using the Zr foil 6791 keV 15 O Doppler shifted keV 15 O Doppler shifted keV 15 O 5183 keV 15 O Doppler shifted Full energy peak Single escape peak Double escape peak 511 keV 937 keV 18 F 3 He( 16 O,p) 1369 keV 24 Mg 12 C(16O, 4 He)

Si detector particle ID spectrum Fig. Si 2D spectrum from Zr foil. It is the energy deposited in the dE Si detector vs. the energy deposited in the E Si detector. Ejectiles can be identified this way. dE [Ch] E [Ch]  ( 15 O) 3 He (scat) p ( 18 F) Light charged particles from He + O → x + X 3 He + 16 O → x + X Heavier ejectiles

 ray spectrum gated on  Figures: Doppler shifted MeV  ray peak for the 1st and 2nd experiment using either Au or Zr target foils. Ungated spectrum Spectrum gated on  particles Au foil 1st run Au foil 2nd run Zr foil 2nd run

Lifetime fit of MeV state from the first experiment Lifetime = fs PRELIMINARY Sky Sjue

Analysis of 1st data set: Refine calibration of  ray energy to get correct addback spectra Need to know centroid with precision within 1 keV Analysis of 2nd data set: Check GEANT4 simulation of kinematics of alpha particles Get lifetime of MeV state from: lineshape analysis from Au foil data lineshape analysis from Zr foil data centroid shift analysis from Au and Zr data Work in progress

Collaborators: B. Davids 1, S. Sjue 1, T.K. Alexander, G.C. Ball 1, R. Churchman 1, D.S. Cross 1,2, H. Dare 3, M. Djongolov 1, H. Al Falou 1, P. Finlay 4, J.S. Forster 5, A. Garnsworthy 1, G. Hackman 1, U. Hager 1, D. Howell 2, M. Jones 6, R. Kanungo 7, R. Kshetri 1, K.G. Leach 4, J.R. Leslie 8, L. Martin 1, J.N. Orce 1, C. Pearson 1, A.A. Phillips 4, E. Rand 4, S. Reeve 1,2, G. Ruprecht 1, M.A. Schumaker 4, C. Svensson 4, S. Triambak 1, M. Walter 1, S. Williams 1, J. Wong 4 1 TRIUMF, Vancouver, BC, Canada 2 Dept. of Phys., Simon Fraser University, Burnaby, BC, Canada 3 Dept. of Phys., University of Surrey, Guildford, UK 4 Dept. of Phys., University of Guelph, Guelph, ON, Canada 5 Dept. of Phys., Université de Montréal, QC, Canada 6 Dept. of Phys., University of Liverpool, Liverpool, UK 7 Astr. and Phys. Dept., St. Mary’s University, Halifax, NS, Canada 8 Dept. of Phys., Queen’s University, Kingston, ON, Canada Receipient of a DOC-FFORTE-fellowship of the Austrian Academy of Sciences at the Institute of SFU

Simulation Reaction kinematics  ejectile 15 O recoil Angular detection efficiency of the  ray detector Beam and target characteristics Intrinsic lineshape of high energy  rays of the TIGRESS detector Stopping power and straggling of recoil as a function of time in the target Sky Sjue

Nuclear stopping: (  <0.005) Collisions between atoms Large energy loss Changes direction of nuclei Electronic stopping: (  ≥0.02) Long range collisions with e - Small energy transfer Small deflection of nuclei Stopping mechanisms for recoils

14 N(p, γ ) 15 O Direct kinematics 15 O has  < Nuclear stopping region 3 He ( 16 O,  ) 15 O* Higher Q-value Inverse kinematic reaction 15 O has  <0.055 Electronic stopping region Cleaner signal with coincidence detection of  We did previous measurements with 3 He implanted foils Reactions to measure lifetime

Globular cluster age uncertainties Age estimated to be between Gyrs Biggest uncertainties comes from deriving distances to globular clusters Stellar evolution input parameters that can significantly affect age estimates: Oxygen abundance [O/Fe] Treatment of convection within stars Helium abundance 14 N+p → 15 O+  reaction rate Helium diffusion Transformations from theoretical temps and luminosities to observed colors and magnitudes Biggest effect of the nuclear reactions is 14 N+p → 15 O+  Accounts for Gyrs variation in ages

S factor -> luminosity -> cluster age Degl’Innocenti et al., Phys. Let. B 590, (2004)