Lifetime measurement of the 6 791 mev state in 15 o
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Lifetime measurement of the 6.791 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:

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Lifetime measurement of the 6 791 mev state in 15 o

Lifetime measurement of the 6.791 MeV state in 15O

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 100,000 - 1 million stars

1980: 16-20 Gyr

Now: 10-15 Gyr

Age of the universe:

WMAP  13.7±0.2 Gyr

Globular clusters can’t be older than the universe


1) Primordial gas cloud

2) Globular clusters form first

L. Krauss and B. Chaboyer, Science 299, 65 (2003)

3) Galactic disk forms

4) Globular clusters occupy galactic halo


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

14N(p, γ)15Ois the slowest reaction

Reaction rate uncertainty could change globular cluster age by 0.5-1 Gyr


Red giant branch


MS turnoff point

Main sequence

(MS) branch




The 14 n p 15 o reaction

Need to know 14N(p, γ)15Oreaction rate at low (stellar) energies

E0 30 keV (for T = 0.02 GK)

Past experiments only go down to ECM = 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

The 14N(p, γ)15Oreaction

Formicola et al., Phys. Let. B 591, 61-68 (2004)

S factor of 14 n p 15 o reaction
S-factor of 14N(p,)15O reaction

R-matrix fits to the 14N(p,)15O 6.79 MeV transition.

Review article: Solar fusion cross sections II, the pp chain and CNO cycles, arXiv:1004.2318v3 [nucl-ex] 10 Oct 2010

Total S-factor of the 14N(p,)15Oreaction with contributions of different transitions to states of 15O.

Angulo et al., Nucl. Phys. A 690, 755-768 (2001)

  • Largest remaining uncertainty in reaction rate is due to width, , of 6.791 MeV state

  • This will constrain the R-matrix fit

  • Obtain width from lifetime:  = ℏ / 

Previous measurements
Previous measurements

  • Results marginally disagree

  • Only one group, Bertone et al., has claimed central value

    • This value is not generally accepted

Doppler shift attenuation method dsam
Doppler Shift Attenuation Method (DSAM)

3He + Au

 ejectile








  • 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:

Simulated lineshapes for different lifetimes. These are fit to the data to determine the lifetime of the excited state.

Dsam and 6 791 mev lifetime
DSAM and 6.791 MeV lifetime

3He + Au










  • Lower  limit of DSAM ~1 fs

  •  of 6.791 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

    • 14N+p →γ+15O

  • We had higher recoil velocity (≤0.055)

    • Used inverse kinematic reaction

    • 3He+16O→α+15O



  • Stable beam of 16O at 50 MeV (1st run) and 35 MeV (2nd run)

  • 3He 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 GeTIGRESS detector on a single mount

Experimental setup
Experimental setup


  • 3He+16O→α+15O

E Si detector

(100 μm and 25 μm)

Vacuum chamber

E Si detector

(500 μm)

16O beam


Au/Zr foil (25 μm)

Implanted 3He

(6×1017 atoms/cm2)


detector at 0°


Ray spectrum
 ray spectrum

Full energy peak

Single escape peak

Double escape peak

5239.9 keV 15O

5183 keV 15O Doppler shifted

6176.3 keV 15O Doppler shifted

511 keV

6791 keV 15O Doppler shifted

937 keV 18F 3He(16O,p)

1369 keV 24Mg 12C(16O,4He)


Fig. Add back spectra of  rays using the Zr foil

Si detector particle id spectrum
Si detector particle ID spectrum

Light charged particles from

3He + 16O → x + X

Heavier ejectiles

dE [Ch]

 (15O)

3He (scat)

p (18F)

E [Ch]

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.

Ray spectrum gated on
 ray spectrum gated on 

Ungated spectrum

Spectrum gated on  particles

Au foil

2nd run

Zr foil 2nd run

Au foil

1st run

Figures: Doppler shifted 6.791 MeV  ray peak for the 1st and 2nd experiment using either Au or Zr target foils.

Work in progress
Work in progress

  • 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 6.791 MeV state from:

      • lineshape analysis from Au foil data

      • lineshape analysis from Zr foil data

      • centroid shift analysis from Au and Zr data

Lifetime measurement of the 6 791 mev state in 15 o


B. Davids1, S. Sjue1, T.K. Alexander, G.C. Ball1, R. Churchman1, D.S. Cross1,2, H. Dare3, M. Djongolov1, H. Al Falou1, P. Finlay4, J.S. Forster5, A. Garnsworthy1, G. Hackman1, U. Hager1, D. Howell2, M. Jones6,R. Kanungo7, R. Kshetri1, K.G. Leach4, J.R. Leslie8, L. Martin1, J.N. Orce1, C. Pearson1, A.A. Phillips4, E. Rand4, S. Reeve1,2, G. Ruprecht1, M.A. Schumaker4, C. Svensson4, S. Triambak1, M. Walter1, S. Williams1, J. Wong4

1TRIUMF, Vancouver, BC, Canada

2Dept. of Phys., Simon Fraser University, Burnaby, BC, Canada

3Dept. of Phys., University of Surrey, Guildford, UK

4Dept. of Phys., University of Guelph, Guelph, ON, Canada

5Dept. of Phys., Université de Montréal, QC, Canada

6Dept. of Phys., University of Liverpool, Liverpool, UK

7Astr. and Phys. Dept., St. Mary’s University, Halifax, NS, Canada

8Dept. 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


 ejectile

15O recoil

Reaction kinematics

Intrinsic lineshape of high energy  rays of the TIGRESS detector

Beam and target characteristics

Angular detection efficiency of the  ray detector

  • Stopping power and straggling of recoil as a function of time in the target

Sky Sjue

Stopping mechanisms for recoils
Stopping mechanisms for recoils

  • 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

Reactions to measure lifetime
Reactions to measure lifetime

  • 14N(p,γ)15O

    • Direct kinematics

    • 15O has <0.0016

    • Nuclear stopping region

  • 3He (16O,)15O*

    • Higher Q-value

    • Inverse kinematic reaction

    • 15O has <0.055

    • Electronic stopping region

    • Cleaner signal with coincidence detection of 

    • We did previous measurements with 3He implanted foils

Globular cluster age uncertainties
Globular cluster age uncertainties

  • Age estimated to be between 10 - 15 Gyrs

  • Biggest uncertainties comes fromderiving 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

    • 14N+p→15O+ reaction rate

    • Helium diffusion

    • Transformations from theoretical temps and luminosities to observed colors and magnitudes

  • Biggest effect of the nuclear reactions is 14N+p→15O+

    • Accounts for 0.5 - 1 Gyrs variation in ages

S factor luminosity cluster age
S factor -> luminosity -> cluster age

Degl’Innocenti et al., Phys. Let. B 590, 13-20 (2004)