Ruhr-Universität BochumLehrstuhl für Physik mit Ionenstrahlen (EP III)

Nukleare AstrophysikProf. Dr. C. Rolfs

Inverse kinematic studies of12C(α,γ)16O with ERNA

Daniel SchürmannERNA Collaboration

The Status of 12C(α,γ)16O, the ‘Holy Grail’ of Nuclear Astrophysics, Caltech 2006/12/15

Recoil Separator ERNA:an alternative approach to measure the reaction 12C(α,γ)16O

ion sourcedynamitron

tandem accelerator

ion beam purification

Gastarget & Post-Stripper

singlet

60° magnet

∆E-Etelescope

recoilseparation

doubletanalysingmagnet

recoilfocussing

Wien filter

Wien filter Wien filter

Wien filter

magneticquadrupolemultiplets

triplet

side FC

Nrecoils detected = Nprojectiles ⋅ ntarget ⋅ σ ⋅ TERNA ⋅ pq

Requirements• angular / energy acceptance• knowledge of charge state distribution• high purity of incoming 12C beam• suppression of 12C beam

Advantages•high efficiency ~pq•measure σtot•independent of γ‘s•(mostly) background free•γ-ray coincidences possible

FromFrom CaltechCaltech to Bochumto Bochum

Recoil Separator ERNA:an alternative approach to measure the reaction 12C(α,γ)16O

ion sourcedynamitron

tandem accelerator

ion beam purification

Gastarget & Post-Stripper

singlet

60° magnet

∆E-Etelescope

recoilseparation

doubletanalysingmagnet

recoilfocussing

Wien filter

Wien filter Wien filter

Wien filter

magneticquadrupolemultiplets

triplet

side FC

Nrecoils detected = Nprojectiles ⋅ ntarget ⋅ σ ⋅ TERNA ⋅ pq

Requirements• angular / energy acceptance• knowledge of charge state distribution• high purity of incoming 12C beam• suppression of 12C beam

Advantages•high efficiency ~pq•measure σtot•independent of γ‘s•(mostly) background free•γ-ray coincidences possible

GastargetGastarget

Density Determination• Energy Loss (Stopping Power)• 7Li(α,γ)11B• 7Li(α,α´)7Li*

Position [mm]-150 -100 -50 0 50 100 150

Aus

beut

e [a

.U.]

-510

-410

-310

-210

-110Messung upstream (d=2 mm)

Messung downstream (d=2 mm)

Messung ausserhalb (d=4 mm)

Integrand

Recoil Separator ERNA:an alternative approach to measure the reaction 12C(α,γ)16O

ion sourcedynamitron

tandem accelerator

ion beam purification

Gastarget & Post-Stripper

singlet

60° magnet

∆E-Etelescope

recoilseparation

doubletanalysingmagnet

recoilfocussing

Wien filter

Wien filter Wien filter

Wien filter

magneticquadrupolemultiplets

triplet

side FC

Nrecoils detected = Nprojectiles ⋅ ntarget ⋅ σ ⋅ TERNA ⋅ pq

Requirements• angular / energy acceptance• knowledge of charge state distribution• high purity of incoming 12C beam• suppression of 12C beam

Advantages•high efficiency ~pq•measure σtot•independent of γ‘s•(mostly) background free•γ-ray coincidences possible

Charge State DistributionCharge State Distribution

Charge State DistributionCharge State Distributionelectron losselectron loss

pressure p[mbar]0 1 2 3 4 5

prob

abili

ty

0

0.2

0.4

0.6

0.8

1

pressure p[mbar]0 1 2 3 4 5

prob

abili

ty

0

0.2

0.4

0.6

0.8

1

calculatedqrecoil = qcarbon

measured

qrecoil = qcarbon +2

12C3+ → 16O6+

Ecm=3.2 MeV

pressure [mbar]0 1 2 3 4 5

prob

abili

ty [%

]

0

10

20

30

40

50

60

70

80

90

100q=3+q=4+q=5+q=6+q=7+

16 3+ 4O 9.60 MeV in He

inte

grat

e

Solution:post-target stripper

Recoil Separator ERNA:an alternative approach to measure the reaction 12C(α,γ)16O

ion sourcedynamitron

tandem accelerator

ion beam purification

Gastarget & Post-Stripper

singlet

60° magnet

∆E-Etelescope

recoilseparation

doubletanalysingmagnet

recoilfocussing

Wien filter

Wien filter Wien filter

Wien filter

magneticquadrupolemultiplets

triplet

side FC

Nrecoils detected = Nprojectiles ⋅ ntarget ⋅ σ ⋅ TERNA ⋅ pq

Requirements• angular / energy acceptance• knowledge of charge state distribution• high purity of incoming 12C beam• suppression of 12C beam

Advantages•high efficiency ~pq•measure σtot•independent of γ‘s•(mostly) background free•γ-ray coincidences possible

AcceptanceAcceptanceMatrix calculations:COSY INFINITY

These just give STARTING values:

Tune Separator with 16O pilot beam!

Good tuning

Bad tuning

Angular acceptanceAngular acceptance

Ecm = 2.4 MeV qrec = 6+

AngularAngular AcceptanceAcceptance

[mrad]ϑ-40 -30 -20 -10 0 10 20 30 40

Tran

smis

sion

0

0.2

0.4

0.6

0.8

1

Bext. Triplet changed by 0.7% !

Energy AcceptanceEnergy Acceptance

-20 -15 -10 -5 0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

trans

mis

sion

∆E / E0 [ % ]experimental

calculated

by variation of beam energy

Recoil Separator ERNA:an alternative approach to measure the reaction 12C(α,γ)16O

ion sourcedynamitron

tandem accelerator

ion beam purification

Gastarget & Post-Stripper

singlet

60° magnet

∆E-Etelescope

recoilseparation

doubletanalysingmagnet

recoilfocussing

Wien filter

Wien filter Wien filter

Wien filter

magneticquadrupolemultiplets

triplet

side FC

Nrecoils detected = Nprojectiles ⋅ ntarget ⋅ σ ⋅ TERNA ⋅ pq

Requirements• angular / energy acceptance• knowledge of charge state distribution• high purity of incoming 12C beam• suppression of 12C beam

Advantages•high efficiency ~pq•measure σtot•independent of γ‘s•(mostly) background free•γ-ray coincidences possible

Typical ∆E-E Spectra

Ecm = 4.4 MeVsuppression ~ 3·109

Ecm = 2.2 MeVsuppression ~ 1·1011

SuppressionSuppression

E [MeV]1.5 2 2.5 3 3.5 4 4.5 5

Rat

e R

910

1010

1110

R = # beam particles# leaky beam in ∆E-E

1212C(C(α,γα,γ))1616O total cross O total cross sectionsection

[MeV]cmE2 2.5 3 3.5 4 4.5 5

[nb]

σ

-110

1

10

210

310

410

-1

+2+4 +4

+2

+0

Background ?Background ?

Sources:• 16O impurities in 12C beam• scattering of 16O restgas• 12C + 12C

Beam purification systemWien-Filters

Purification WF: OFF On [channel]restE

500 1000 1500 2000 2500 3000 3500 4000 [channel]restE

0 500 1000 1500 2000 2500 3000 3500 4000

E [c

hann

el]

∆

0

500

1000

1500

2000

2500

3000

3500

4000

C12

O16

RT*50

PO ~ 10-12

PWF < 10-9

Background: Background: 1212C + C + 1212CC

[channel]restE0 20 40 60 80 100 120 140

E [c

hann

el]

∆

0

20

40

60

80

100

120

140

[channel]restE0 20 40 60 80 100 120 140

restE0 50 100 150 200 250

E∆

0

20

40

60

80

100

120

140

160

180

200

C (leaky beam)12

O16

restE0 50 100 150 200 250

20

40

60

80

100

120

140

160

180

200

Ne20

O16

restE0 50 100 150 200 250

1

10

210

310

pre target aperture-> Rate x50

carbonfoil

Background ?Background ?

Sources:• 16O impurities in 12C beam 105 to small

• scattering of 16O restgas 102 to small• 12C + 12C most probably !

(but: background almost constant)

Comparison ERNA <-> Calculation Kunz. et al.(Kunz R. et al., ApJ 567, 643-650 2002)

Basic resonance properties well reproducedClear need for improved (new) R-Matrix calculation

ERNA CollaborationERNA CollaborationBochumBochumA. A. DiDi LevaLevaR. KunzR. KunzD. D. RogallaRogallaC. RolfsC. RolfsF. F. SchümannSchümannD. SchürmannD. SchürmannF. F. StriederStriederH.H.--P. P. TrautvetterTrautvetter

Naples & CasertaN. De CesareL. GialanellaA. D’OnofrioG. ImbrianiC. LubrittoA. OrdineV. RocaM. RomanoF. Terrasi

Thank you!

Leaky BeamLeaky Beam

qrecoil = 3+qcarbon, initial = 6+

Triplet Wien Filter

[MeV]cmE2 2.5 3 3.5 4 4.5 5

S(E

) [k

eV-b

arn

]

10

210

310

1-

2+

4+

4+

2+

0+

12C(α,γ)16O total cross section

[MeV]cmE0.5 1 1.5 2 2.5 3

[keV

-bar

n]E1S

1

10

210

E1 calcFey (Turntable)Fey (Eurogam)Kunzouellet

[MeV]αE0.5 1 1.5 2 2.5

N

1

10

210

310

410

510

16N decay

[MeV]αE0.5 1 1.5 2 2.5

N

1

10

210

310

410

510

16N decay

[MeV]cmE0.5 1 1.5 2 2.5 3

[keV

-bar

n]E1S

1

10

210

E1 calcFey (Turntable)Fey (Eurogam)Kunzouellet

Fit to E1 groundstate data Assuncao et al.

E1 groundstate transition:5-6 MeV states

Charge State DistributionCharge State Distribution

γγ--Recoil CoincidencesRecoil CoincidencesEcm = 2.4 MeV (1-)8x BaF2

channel0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

cou

nts

1

10

102

103

104

105

E = 2.4 MeVSINGLE

coinc.γO-16

cascade

ground state transition

γ-Recoil Coincidences

Ecm = 2.4 MeV (1-)2“x2“ BGO

GastargetGastarget: pressure profile: pressure profile

7Li(α,γ)11B, Γcm=4keV

7Li(α,α’)Γcm=130keV

Independent of stopping powers!

p0/p > 20!

12C(α,γ)16O - 16O level scheme

0-

0+

0+

3-

1-

1-

2+

2+

4+

2-

6049

6130

0

6917

7117

8872

9580

9847

10367

10957

Jπ

400

Ex(keV) Γcm(keV)

27

0.6

Gamow window

2418

2685

3195

Ecm(keV)

Experiments E1 E212C+4He

Q = 7162 keV - 45- 245

16O g.s. casc.