Recent Progress in Nuclear Recent Progress in Nuclear Astrophysics at TRIUMF Astrophysics at TRIUMF Using Indirect TechniquesUsing Indirect Techniques

Barry Davids, TRIUMFBarry Davids, TRIUMF

5 Mar 20095 Mar 2009

Radiative Capture Reactions in Radiative Capture Reactions in the Sunthe Sun

Rates of radiative capture Rates of radiative capture reactions needed for predictions reactions needed for predictions of solar neutrino flux of solar neutrino flux

88B solar B solar flux now measured flux now measured to ± 8.6% by SNO, to ± 8.6% by SNO, 77Be flux Be flux measured to ± 10% by Borexinomeasured to ± 10% by Borexino

SSmnmn(0) is the astrophysical S (0) is the astrophysical S

factor for the radiative capture factor for the radiative capture m + n m + n (m+n) + (m+n) + at zero at zero energy: Senergy: S1717 is for is for 77Be(pBe(p))88B and B and

SS3434 for for 33He(He())77BeBe

88B flux B flux S S1717(0), S(0), S3434(0)(0)0.810.81

77Be flux Be flux S S3434(0)(0)0.860.86

Radiative Captures in Big Bang Radiative Captures in Big Bang NucleosynthesisNucleosynthesis

BBN a robust prediction of hot big BBN a robust prediction of hot big bang cosmology for > 40 yrbang cosmology for > 40 yr

Explains origin of large universal He Explains origin of large universal He abundance, trace quantities of D, abundance, trace quantities of D, 33He, He, & & 77LiLi

Given general relativity, cosmological Given general relativity, cosmological principle, abundance predictions principle, abundance predictions depend only on mean lifetime of depend only on mean lifetime of neutron, number of active, light neutron, number of active, light neutrino flavours, universal baryon neutrino flavours, universal baryon density, and nuclear reaction ratesdensity, and nuclear reaction rates

77Li produced via Li produced via 33He(He())77BeBe Primordial Primordial 77Li abundance proportional Li abundance proportional

to Sto S3434(300 keV)(300 keV)0.960.96

Theoretical STheoretical S34 34 ModelsModels

Potential model and cluster model of Potential model and cluster model of Kajino [NPA 460, 559 (1986)] shapes Kajino [NPA 460, 559 (1986)] shapes agree below 500 keV, but is it agree below 500 keV, but is it fortuitous? Absolute values of fortuitous? Absolute values of calculations significantly calculations significantly underestimate dataunderestimate data

Uncertainty in cluster model SUncertainty in cluster model S3434(E) (E) derived from theoretical estimates of derived from theoretical estimates of uncertainty in Suncertainty in S3434(0) and its (0) and its logarithmic derivative, shown by logarithmic derivative, shown by dotted linesdotted lines

Can we use data and well-known Can we use data and well-known physics to determine Sphysics to determine S3434(E) (E) independent of structure model?independent of structure model?

We (Cyburt, BD) use a formalism We (Cyburt, BD) use a formalism capable of handling discrepant modern capable of handling discrepant modern measurements dominated by measurements dominated by systematic uncertaintiessystematic uncertainties

Modern SModern S3434 Data Data

Shape of cross section near threshold described by Mukhamedzhanov Shape of cross section near threshold described by Mukhamedzhanov and Nunes, NPA 708, 437 (2002)and Nunes, NPA 708, 437 (2002)

We take account of fact that only We take account of fact that only ll = 0 and = 0 and ll = 2 incoming partial = 2 incoming partial waves can contribute to the waves can contribute to the EE1 capture, finding1 capture, finding

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S(E) =Q

E + Qs0 1+ aE + ...( )

2+ s2 1+

4π 2E

EG

⎛

⎝ ⎜

⎞

⎠ ⎟ 1+

16π 2E

EG

⎛

⎝ ⎜

⎞

⎠ ⎟1+ cE + ...( )

2 ⎡

⎣ ⎢

⎤

⎦ ⎥

Modern Branching Ratio DataModern Branching Ratio Data

Precise data for the branching ratio between the ground and first excited state Precise data for the branching ratio between the ground and first excited state transitions permit simultaneous fit of both transitions using same form but different transitions permit simultaneous fit of both transitions using same form but different parametersparameters

Modern data allow simultaneous determination of 3 parameters, Modern data allow simultaneous determination of 3 parameters, ss00, s, s22, , & & aa for each for each transition; 4 parameter fit was not higher quality, hence transition; 4 parameter fit was not higher quality, hence c c 00

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S(E) =Q

E + Qs0 1+ aE + ...( )

2+ s2 1+

4π 2E

EG

⎛

⎝ ⎜

⎞

⎠ ⎟ 1+

16π 2E

EG

⎛

⎝ ⎜

⎞

⎠ ⎟1+ cE + ...( )

2 ⎡

⎣ ⎢

⎤

⎦ ⎥

Partial Wave ContributionsPartial Wave Contributions

Comparison with Cluster ModelComparison with Cluster Model Significant differences with most Significant differences with most

commonly used cluster model foundcommonly used cluster model found Data are able to determine shape Data are able to determine shape

without dependence on structure without dependence on structure modelmodel

SS3434(0) = 0.580 ± 0.043 keV b at the (0) = 0.580 ± 0.043 keV b at the

68.3% CL (± 7.4%)68.3% CL (± 7.4%) SS3434(0) = 0.580 ± 0.054 keV b at the (0) = 0.580 ± 0.054 keV b at the

95.4% CL (± 9.3%)95.4% CL (± 9.3%) Size of latter smaller than 68.3% CL Size of latter smaller than 68.3% CL

interval from 1998 RMP evaluation of interval from 1998 RMP evaluation of solar nuclear fusion cross sectionssolar nuclear fusion cross sections

Cyburt and Davids, Phys. Rev. C 78, Cyburt and Davids, Phys. Rev. C 78, 064614 (2008)064614 (2008)

Comparison of Observations Comparison of Observations with BBN Predictionswith BBN Predictions

Using this SUsing this S3434(E), the BBN (E), the BBN prediction based on the WMAP5 prediction based on the WMAP5 universal mean baryon density (± universal mean baryon density (± 2.7%) differs from the primordial 2.7%) differs from the primordial 77Li Li abundances inferred from globular abundances inferred from globular cluster stars and halo field stars by cluster stars and halo field stars by 4.24.2and 5.3and 5.3respectively [Cyburt, respectively [Cyburt, Fields, & Olive, JCAP 11, 012 Fields, & Olive, JCAP 11, 012 (2008)](2008)]

Unresolved, this discrepancy shakes Unresolved, this discrepancy shakes the foundations of “precision” the foundations of “precision” cosmology (one of the pillars!)cosmology (one of the pillars!)

Assumptions of Assumptions of CDM cosmology CDM cosmology must be questioned (effects of must be questioned (effects of inhomogeneities, Copernican inhomogeneities, Copernican principle, alternative gravitational principle, alternative gravitational theories?)theories?)

77Be(p,Be(p,))88B DataB Data

Results of AnalysisResults of Analysis Model-dependent analysis of high precision Seattle data Model-dependent analysis of high precision Seattle data

finds slight preference for finds slight preference for 77Li + Li + n n potential model over potential model over cluster model, but difference not significantcluster model, but difference not significant

Using a minimally structure-dependent pole model taking Using a minimally structure-dependent pole model taking account of rise at low energy, fit radiative capture data account of rise at low energy, fit radiative capture data below 425 keV, allowing data to determine shape, below 425 keV, allowing data to determine shape, consistent with cluster and potential models; 2 parameter fit, consistent with cluster and potential models; 2 parameter fit, with with aa fixed at 45 keV fixed at 45 keV

Junghans Junghans et al.et al. result: 21.4 ± 0.7 eV b result: 21.4 ± 0.7 eV b All other radiative capture: 16.3 ± 2.4 eV bAll other radiative capture: 16.3 ± 2.4 eV b€

S17(E) = S17(0) 1− aE

Q(E + Q)

⎡

⎣ ⎢ ⎤

⎦ ⎥+ βE

TRIUMF ExperimentTRIUMF Experiment Asymptotic normalization coefficients (ANC’s) derived from transfer Asymptotic normalization coefficients (ANC’s) derived from transfer

reactions allow inference of S(0) directlyreactions allow inference of S(0) directly Measure ANC of the valence neutron in Measure ANC of the valence neutron in 88Li via the elastic scattering/transfer Li via the elastic scattering/transfer

reaction reaction 77Li(Li(88Li,Li,77Li)Li)88Li at 11 and 13 MeVLi at 11 and 13 MeV Interference between elastic scattering and neutron transfer produces Interference between elastic scattering and neutron transfer produces

characteristic oscillations in differential cross sectioncharacteristic oscillations in differential cross section Amplitudes of maxima and minima yield ANCAmplitudes of maxima and minima yield ANC Identical initial and final states => single vertex is involvedIdentical initial and final states => single vertex is involved Statistical precision greater (compared with distinct initial and final states)Statistical precision greater (compared with distinct initial and final states) Single optical model potential neededSingle optical model potential needed Elastic scattering measured simultaneouslyElastic scattering measured simultaneously More than one beam energy allows evaluation of remnant term in DWBA More than one beam energy allows evaluation of remnant term in DWBA

amplitude (in principle)amplitude (in principle) Absolute normalization of cross section enters only as a higher-order effect in Absolute normalization of cross section enters only as a higher-order effect in

ANC determinationANC determination

FRESCO DWBA Calculations by FRESCO DWBA Calculations by Sam WrightSam Wright

Experimental SetupExperimental Setup

Two annular, segmented Si Two annular, segmented Si detectorsdetectors

25 µg 25 µg cm-2 7-2 7LiF target on LiF target on 10 µg cm10 µg cm-2-2 C backing C backing

LEDA detector covers lab LEDA detector covers lab angles from 35-61°angles from 35-61°

S2 detector covers 5-15° in S2 detector covers 5-15° in the labthe lab

77Li cm angular coverage Li cm angular coverage from 10-30° and 70-122°from 10-30° and 70-122°

88Li beam intensities of Li beam intensities of 2-4 2-4 10 1077 s s-1-1

11 MeV Data11 MeV Data

Coincidences: Energy-Angle Coincidences: Energy-Angle CorrelationCorrelation

11 MeV Data Revisited11 MeV Data Revisited

All S2 data, Elastics in LEDA

1414N + p N + p 1515O + O + Ages of the Oldest StarsAges of the Oldest Stars

Old stars and massive stars fuse Old stars and massive stars fuse H into He via the CNO cyclesH into He via the CNO cycles

C, N, O are catalystsC, N, O are catalysts At low temperatures found in At low temperatures found in

oldest globular cluster stars, oldest globular cluster stars, energy release controlled by energy release controlled by slowest reaction, slowest reaction, 1414N(p,N(p,))1515OO

Reaction rate predominant Reaction rate predominant nuclear uncertainty in age nuclear uncertainty in age determinationdetermination

Stars can’t be older than Stars can’t be older than universe!universe!

1414N + p N + p 1515O + O + Solar Solar Neutrinos and Core CompositionNeutrinos and Core Composition

Temperature of solar core implies Temperature of solar core implies 99% of energy released through 99% of energy released through pp chains, ~ 1% via CN cyclepp chains, ~ 1% via CN cycle

Predicted solar neutrino fluxes due Predicted solar neutrino fluxes due to to 1313N, N, 1515O exceed 10O exceed 1088 cm cm-2-2 s s-1-1 on on EarthEarth

Measurements reveal primordial Measurements reveal primordial composition of solar corecomposition of solar core

Flux predictions depend on Flux predictions depend on 1414N(p,N(p,))1515O rate at very low O rate at very low energy, require ± 3.5% errorenergy, require ± 3.5% error

Reaction rate depends on lifetime Reaction rate depends on lifetime of subthreshold 6.79 MeV state in of subthreshold 6.79 MeV state in 1515OO

Lifetime MeasurementsLifetime Measurements Lifetimes measured via Doppler Lifetimes measured via Doppler

shift of emitted shift of emitted rays as nucleus rays as nucleus slows down in foil slows down in foil

Short lifetime Short lifetime large Doppler shift, large Doppler shift, long lifetime long lifetime small Doppler shift small Doppler shift

Shapes of detected Shapes of detected ray lines yield ray lines yield lifetime; sensitive to fs lifetimeslifetime; sensitive to fs lifetimes

Previous measurements of 6.79 Previous measurements of 6.79 MeV state lifetime marginally MeV state lifetime marginally inconsistent, not generally accepted; inconsistent, not generally accepted; TUNL reported TUNL reported = 1.60 (+ 0.75, - = 1.60 (+ 0.75, -0.72) fs, Bochum finds 0.72) fs, Bochum finds < 0.77 fs, < 0.77 fs, both @ 90% CLboth @ 90% CL

Doppler Shift Lifetimes (DSL) Doppler Shift Lifetimes (DSL) ChamberChamber

Collimator

16O beam

E Si detector(500 μm)

TIGRESSdetector at 0°

E Si detector(100 μm)

Implanted 3He(6 × 1017 cm-2)

Au foil

Vacuum chamber

16O

15O

Experimental SetupExperimental Setup

DSL chamberDSL chamber TIGRESS DetectorTIGRESS Detector

Si Telescope Particle IdentificationSi Telescope Particle IdentificationE

(M

eV)

E (MeV)

( 15 15OOGSGS)

(15OEx)

Elastic 3He

p (18F)

d (17F)

Gamma Ray Energy SpectrumGamma Ray Energy Spectrum

Future WorkFuture Work

33He(He())77Be measurement Be measurement at large relative energy at large relative energy using DRAGONusing DRAGON

Measurement of Measurement of 1212C(C(88Li,Li,77Li)Li)1313C for valence C for valence neutron ANC in neutron ANC in 88LiLi

Collect additional Collect additional 1515O O lifetime data using lifetime data using 33He-He-implanted Zr target foilimplanted Zr target foil

Figure credit: F. Strieder

SummarySummary Improvements in precision of solar neutrino flux measurements and observations of Improvements in precision of solar neutrino flux measurements and observations of

cosmic microwave background radiation require continued attention to nuclear reaction cosmic microwave background radiation require continued attention to nuclear reaction rate uncertainties, namely radiative capture ratesrate uncertainties, namely radiative capture rates

77Be(pBe(p))88B has been measured very precisely once, and this measurement dominates B has been measured very precisely once, and this measurement dominates other radiative capture measurements and ANC determinations which are 1-2other radiative capture measurements and ANC determinations which are 1-2lower; lower; TRIUMF ANC determination via TRIUMF ANC determination via 77Li(Li(88Li,Li,77Li)Li)88Li and Li and 1212C(C(88Li,Li,77Li)Li)1313C still under analysisC still under analysis

33He(He())77Be measured precisely several times since turn of century; quality of data Be measured precisely several times since turn of century; quality of data permit determination of reliable, structure model-independent best value and confidence permit determination of reliable, structure model-independent best value and confidence intervals using MCMC methodintervals using MCMC method

55 disagreement of primordial Li abundances inferred from observations of field halo disagreement of primordial Li abundances inferred from observations of field halo stars with precise BBN predictions made possible by new stars with precise BBN predictions made possible by new 33He(He())77Be and CMB Be and CMB measurements raises serious doubts about the assumptions of the standard cosmological measurements raises serious doubts about the assumptions of the standard cosmological modelmodel

Precision of Precision of 1414N(p,N(p,))1515O reaction rate determination at low energy limited by knowledge O reaction rate determination at low energy limited by knowledge of lifetime of 6.79 MeV subthreshold state in of lifetime of 6.79 MeV subthreshold state in 1515O; Ongoing TRIUMF measurement O; Ongoing TRIUMF measurement promises to be best yetpromises to be best yet

Derek Howell & Naomi Galinski, Simon Fraser University

Sky Sjue, TRIUMF

Richard Cyburt, Joint Institute for Nuclear Astrophysics & National

Superconducting Cyclotron Laboratory, Michigan State University

CANADA’S NATIONAL LABORATORY FOR PARTICLE AND NUCLEAR PHYSICS

Owned and operated as a joint venture by a consortium of Canadian universities

via a contribution through the National Research Council Canada

LABORATOIRE NATIONAL CANADIEN POUR LA RECHERCHE EN PHYSIQUE NUCLÉAIRE ET EN PHYSIQUE DES PARTICULES

 

Propriété d’un consortium d’universités canadiennes, géré en co-entreprise à partir d’une contribution administrée par le Conseil national de recherches Canada