Study of the 40 Ca( ) 44 Ti reaction at stellar temperatures with DRAGON Christof Vockenhuber for the DRAGON collaboration Vancouver, B.C., Canada.

Study of the 40Ca()44Ti reaction at stellar temperatures with DRAGON

Christof Vockenhuber for the DRAGON collaboration

Vancouver, B.C., Canada

Christof Vockenhuber 40Ca()44Ti at DRAGON NIC-IX June 27 2006

Collaboration

L. Buchmann, J. Caggiano, J.M. D’Auria, B. Davids, A. Hussein, D.A. Hutcheon, D. Ottewell, M.M. Pavan, C. Ruiz, G. Ruprecht, M. Trinczek, C. VockenhuberDRAGON collaboration at TRIUMF, Vancouver, BC, Canada

A. Chen, C. Ouellet, J. PearsonMcMaster University, Hamilton, ON, Canada

M. PaulHebrew University / Weizmann Institute, Israel

W. Kutschera, A. WallnerUniversity of Vienna, Austria

D. FrekersUniversity of Münster, Germany

A.M. Laird, R. LewisUniversity of York, England

H. Crawford, L. Fogarty, E. Ó’Conner, B. Wales, Summer students from Canada and Ireland

poster – No Number

B. Laxdal, M. Marchetto, K. Jayamana, ISAC operatorsTRIUMF staff, Vancouver, BC, Canada


Role of 44Ti in Astrophysics

laboratory half-life of 60.0 +/- 1.0 years decay through electron capture, if ionized half-life becomes longer

detected in space by -ray satellites and in pre-solar grains

produced in supernova detection of relatively recent supernovae alpha-rich freeze-out just above the collapsing core observed quantity of 44Ti depends critically on ‘mass-cut’

understanding of production requires reliable reaction rates dominated by 4 reactions:

3 process 44Ti(,p)47V45V(p)46Cr 40Ca()44Ti


Previous measurements of 40Ca()44Ti

prompt ray measurements in the 1970sE. L. Cooperman et al., Nucl. Phys. A 284 (1977) 163

W. R. Dixon et al., Phys. Rev. C 15 (1977) 1896; Can. J. Phys. 58 (1980) 1360

resonance strength of a few isolated resonances

recent AMS measurementH. Nassar et al., PRL 96 (2006) 041102

integral measurement of a large energy range

discrepancy by a factor of ~5


Level scheme

H. Nassar et al., Nucl. Phys. A 758 (2005) 411c


Astrophysical Reaction Rate

Reaction rate:

Resonance strength:

Measured Yield ( 44Ti / 40Ca ): Y( = 1 eV ) ~ 10 –11



Experiment at DRAGON

alpha-rich freeze-out takes place at a large temperature regime

cover a large energy range ( Ecm ~ 2.0 – 4.2 MeV )

several narrow resonances contribute to the yield

‘thin’ target for sufficient resolution

’thick’ target to apply thick target yield

energy loss in the gas target Ecm ~ 10 keV / Torr

1 Torr: 220 energy steps

8 Torr: 30 energy steps



Advantage:

direct detection of recoils (44Ti) and rays measurement of single resonances high efficiency

windowless He gas target + BGO detector array acceptance: < 20 mrad (44Ti recoils ~ 6 mrad) high suppression of beam

recoil separator ~107

detector ~104

coincidence ~103

measurements of < meV possible



Challenges:

40Ca beam from Off-line Ion Source

2+ required for acceptance at RFQ accelerator (A/q < 30) 40Ar contamination (can be measured with ion chamber)

suppression of 40Ca depends on selected charge state ( ~106 – 1011 ) A/q ambiguities 44Ti11+ ↔ 40Ca10+

charge state distribution after the gas target acceptance of recoil spectrometer

identification of 44Ti ion chamber, TOF


What we measure

40Ca beam on target elastically scattered He atoms with collimated SB detectors beam contamination with ion chamber

produced 44Ti recoils 44Ti detected at the ion chamber charge state fraction after the target detection efficiencies

rays in coincidence with 44Ti energies and multiplicity z-position along the gas target


DRAGON windowless Gas Target

Target thickness

1 – 10 Torr H2 or He gas

~1018 atoms / cm2

Elastic monitor detectors:

detect scattered gas particles

Charge State Booster (CSB):

100 nm SiN foil (30 g/cm2)

increase mean charge state by ~2

charge state distribution independent of position along the path in the target

CSB

gas foil


30 BGO Gamma detectors surrounding gas target

geometrical efficiency of ~ 90 % effective efficiency depends on energy and

multiplicity determined from GEANT simulations and point source studies

DRAGON detector Array


Recoil Mass Separator

Inverse Kinematics:

Energy spread a few percent achromatic system

Cone angle a few 10 mrad large gaps, large detectors

Energy of recoils < beam energy problem of energy loss tails


Particle Identification

entrance window 130 µg/cm² Mylar, 50 µg/cm² PP, 15-30 µg/cm² SiNdiameter 5 cmenergy resolution: ~ 1 % for 1 MeV/u 40Ca

Cathode

Frisch Grid

Anode 1 Anode 2 Anode 3

Ionization chamber


Beam Contamination

Hybrid-surface ion source

14

IC Anode 2

IC A

no

de

1

+


44Ti identification Ionization chamber

singles


44Ti identificationIonization chamber – ray coincidence

coincidences Y ~ 1 x 10-10


44Ti identificationTime-of-Flight through Spectrometer


Beam Suppression


Charge State Distribution of 44Ti

12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr

Ch

arg

e S

tate

Fra

ctio

n F

q



12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr Sayer Solid

Ch

arg

e S

tate

Fra

ctio

n F

q



12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr Sayer Solid beam CSB

Ch

arg

e S

tate

Fra

ctio

n F

q



12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr Sayer Solid beam CSB beam 2 Torr

Ch

arg

e S

tate

Fra

ctio

n F

q



12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr Sayer Solid beam CSB beam 2 Torr beam 4 Torr

Ch

arg

e S

tate

Fra

ctio

n F

q



12 13 14 15 16 170.0

5.0x10-12

1.0x10-11

1.5x10-11

2.0x10-11

Ra

w Y

ield

N44

Ti /

N40

Ca

Charge State q

0%

10%

20%

30%Ti, 0.93 MeV/u

recoils 8 Torr Sayer Solid beam CSB beam 2 Torr beam 4 Torr beam 8 Torr

Ch

arg

e S

tate

Fra

ctio

n F

q


Excitation function 40Ca()44Ti

1.0 T9 temperature regime 2.8 T9

preliminary !


BGO ray spectrum

1.130 MeV 40Ca


coincidence

measured ray data will be used to estimate BGO efficiency


Summary

We measured the 40Ca()44Ti reaction at the recoil mass spectrometer DRAGON in the energy regime of supernova nucleosynthesis (T9 ~ 1 – 2.8)

A first preliminary analysis gives a total 44Ti yield between prompt ray and AMS data, a detailed analysis including ray data and GEANT simulation for BGO efficiency will follow

Additionally, we learned a lot:

could demonstrate to measure resonance strength for astrophysics in mass 40 region

measure an excitation function over a large energy range

important for reactions with radioactive beams


R. Diehl et al. (2005)


IC spectra 44Ti10+

singles

44Ti 10+

40Ca7+ 850 keV/u 8 Torr He

Y ~ 4 x 10-12


IC spectra 44Ti10+

44Ti 10+

coincidences


Y ~ 4 x 10-12


IC spectra 44Ti9+

44Ti 9+

singles


Y ~ 2 x 10-13


IC spectra 44Ti9+

44Ti 9+

coincidences


Y ~ 2 x 10-13



without charge state booster foil

Study of the 40 Ca( ) 44 Ti reaction at stellar temperatures with DRAGON Christof Vockenhuber for the DRAGON collaboration Vancouver, B.C., Canada.

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