16O(αγ 20Ne at DRAGON

Ulrike Hager18.05.2011 ISAC Science Forum

16O(α,γ)20Ne at DRAGON

Ulrike Hager

Motivation

18.05.2011 ISAC Science Forum

He burning

T = 1 – 3 · 108 K

main end products 12C & 16O, ratio determined by 16O(α,γ)20Ne

determines abundances of products of later carbon burningmainly 20Ne, 23Na, 23,24Mg and 28Si

test case for nuclear model calculations

2 doubly magic nuclei in the entrance channel

Ulrike Hager

20Ne levels


no excited state in 20Ne at relevant ener-gies

2− cannot be populated (entrancechannel both Jπ = 0+)

higher resonances too narrow

sub-threshold resonance too low,high centrifugal barrier

reaction via non-resonant direct capture

Ulrike Hager

Current situation


Ecm Langanke Hahn Baye Knee0.3–0.45 MeV 2.34 MeVb 0.7 ± 0.3 MeVb 1.7 MeVb 3.37 MeVb1.7 MeV 3.665 MeVb 3.37 MeVb2.3 MeV 4.295 MeVb 2.8 MeVb 3.37 MeVb

Ulrike Hager

DRAGON


p/q

E/q

Inverse kinematics

precoil = pbeam

Erecoil = EbeamMbeam

Mrecoil

beam suppression108 – 1013

angular acceptance≈ ±20 mrad

Ulrike Hager

DRAGON gas target


Windowless gas target

typical pressures 4 – 8 torr

Monitor detectorsfor beam normalisation

Ulrike Hager

DRAGON gas target


30 BGOs

geometric efficiency 89-92%

possibility to locate resonance position

Ulrike Hager

DRAGON end detectors


Ion chamber

particle id, energy

Ulrike Hager

DRAGON end detectors


Ion chamber

particle id, energy

MCPs

timing

Ulrike Hager

Energies


September

beam intensity ≈ 9 × 1011 1/s≈ 10 shifts

April

beam intensity ≈ 1.8 × 1012 1/s≈ 18 shifts

Ulrike Hager

20Ne charge state distribution


0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

3 3.5 4 4.5 5 5.5 6 6.5 7

frac

tion

charge state

487 AkeV326 AkeV279 AkeV

dashed: calculated (Liu et al., NIM A 496, 2003)

Ulrike Hager

Ecm = 2263 keV (Sep. 2010)


71(4)% S2

Ulrike Hager

Ecm = 2263 keV (Sep. 2010)


Hahn (1987)

Costantini (2010)

S = 1.43 ± 0.22 MeVb

S0 = 0.42 ± 0.09 MeVb

S2 = 1.02 ± 0.17 MeVb

Ulrike Hager

Recoil Separation


IC0 (channel)200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

IC1

(cha

nnel

)

0

200

400

600

800

1000

1200

1400

1600

1800

IC_0 vs. IC_1

IC energy (channel)0 1000 2000 3000 4000 5000

MC

P T

AC

(ch

anne

l)

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

IC Sum vs. Mcp TAC

Ulrike Hager

Resonance


max gamma energy / keV0 1000 2000 3000 4000 5000 6000 7000 80000

20

40

60

80

100

120

140

SeptemberApril

Ulrike Hager

Resonance


Knee ’94: 10.8 ± 1.5 meV

DRAGON preliminary:

September 7 ± 3 meV

April 8 ± 2 meV

requires detailed GEANT simulations to determine branching ratios andefficiencies

Ulrike Hager

Ecm = 2263 keV DC


Entries 447

max gamma energy / keV0 1000 2000 3000 4000 5000 6000 70000

2

4

6

8

10

12

14

16

18

20

22Entries 447

Ulrike Hager

Outlook


resonance branching ratios

determine ratio of S0 and S2 for DC

request more beam time to measure at lower energies?

Thank you

16O(αγ 20Ne at DRAGON

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