Flubber experiment:
17
measuring F Coulomb breakup
P. Capel, C. Sfienti, D. Baye, G. Cardella, M. De Napoli, P. Descouvemont,
F. Giacoppo, C. Mazzocchi, G. Raciti, E. Rapisarda, J.-M. Sparenberg
MSU, East Lansing; ULB, Brussels; LNS & UniCT, Catania; UniMi, Milano
– p.1/14
Outline
Introduction on Coulomb breakup
Interest of 17 F
Experimental setup
Preliminary theoretical analysis
Summary
– p.2/14
Breakup and capture
Stars powered by radiative-capture reactions
e.g. 7 Be(p,γ)8 B
Reactions take place at low energy
⇒ difficult to measure directly
Coulomb breakup ≈ inverse of radiative capture
e.g. 8 B + Pb → 7 Be + p + Pb
⇒ Idea: measure σbu to extract σcapture
This works only if:
1. Nuclear interaction negligible
2. Only dipole term plays a role
3. First-order of perturbation theory is sufficient
Does not seem fully valid for Coulomb breakup of 8 B
[G. Goldstein, P. Capel, and D. Baye, PRC 76, 024608 (2007)]
– p.3/14
17
8
F vs B
But 8 B ill-suited to test Coulomb-breakup technique:
large discrepancies in direct measurements
complex 8 B structure (7 Be not spherical,. . . )
On the contrary, 17 F is the ideal test case:
reliable direct data for 16 O(p,γ)17 F at low energy
[R. Morlock et al. PRL 79, 3837 (1997)]
17
F well described as p outside doubly-magic 16 O
[J.-M. Sparenberg et al. PRC 61, 054610 (2000)]
no resonance at low energy in 17 F spectrum
⇒ We propose to measure 17 F + Pb → 16 O + p + Pb
compare the extracted σcapture to direct measurements
– p.4/14
Flubber experiment
Measure 17 F breakup on C and Pb at LNS (Catania)
17
F produced by 20 Ne primary beam
fragmentation at 45AMeV on Be target
After separation we get 3 103 pps 17 F at 40AMeV
– p.5/14
Projectile tagging
We use a double-sided Si stripped detector (24 × 24,
300 µm) to identify the projectile event by event in
Charge and mass (Z, A) by (∆E, ToF)
Position (x, y)
– p.6/14
Detection setup
Two hodoscopes 80 cm behind secondary target
Big hodoscope
large angles (up to 21◦ )
Detects p
88 ∆E-E telescopes
3×3 cm2
Si (50+300 µm), CsI (6 cm)
Small hodoscope
forward angles (0◦ –5◦ )
Detects 16 O
81 ∆E-E telescopes
1×1 cm2
Si (300 µm), CsI (10 cm)
– p.7/14
∆E -E matrices
– p.8/14
Finally a bit of theory. . .
Meanwhile we have done 17 F breakup calculations
17
F modelled as 16 O(0+ )+p:
4.4 MeV
0d3/2
s
p
d
f
16 O+p
1s1/2
−100 keV
0d5/2
−600 keV
– p.9/14
Coulomb breakup calculation
17
F + Pb → 16 O + p + Pb 40AMeV
dσbu /dE (b/MeV)
1.5 10−3
4.4 MeV
0d3/2
DEA
1st order
1st order E1
Total
p
s
1 10−3
p
f
d
E1
E1
5×f
0.5 10−3
0
16 O+p
5×d
0
1
1s1/2
−100 keV
2
3
E (MeV)
4
5
E1
E2
E1
0d5/2
−600 keV
Dominated by E1 (populates p and f waves)
But significant E2 (d wave)
and higher orders (p and f → d)
Should be compared with data to check interpretation
– p.10/14
Summary
Coulomb breakup is proposed as a tool to infer
radiative-capture cross section at low E
However never tested
8
B study suggests hypotheses not satisfied
17
F is an ideal test case
⇒ Measure Coulomb breakup of 17 F on Pb
to test the Coulomb-breakup method
Measure has been performed at LNS (Catania)
Data are under analysis. . .
– p.11/14
Nuclear breakup calculation
dσbu /dE (mb/MeV)
1.4
Total
p
1.2
d
f
1
0.8
0.6
0.4
0.2
0
0
1
2
3
E (MeV)
4
5
6
Nuclear breakup emphasizes resonant states
⇒ can be used to test our 17 F model in continuum
In addition to Coulomb breakup, we measure
breakup on C target
d3/2 resonance should be seen experimentally
– p.12/14
17
8
F vs B
But 8 B ill-suited to test
Coulomb-breakup technique:
large discrepancy in
direct measurements
complex 8 B structure
(7 Be not spherical)
On the contrary, 17 F is the ideal test case:
reliable direct data for
16
O(p,γ)17 F at low energy
17
F well described as a p
outside doubly-magic 16 O
⇒ We propose to measure 17 F Coulomb breakup
– p.13/14
8
Analysis of B Coulomb breakup
8
B + Pb @ 44 AMeV (MSU) [Davids PRL 81, 2209 (01)]
dσbu /dpck [mb/(MeV/c)]
4.5
4
4.5
4.5
C.+N.
Coul.
4
C.+N.
E1
4
3.5
3.5
3.5
3
3
3
2.5
2.5
2.5
2
2
2
1.5
1.5
1.5
1
1
1
0.5
0.5
0.5
0
2100 1950
0
2100 1950
0
1950
2000 2050
pck (MeV/c)
2000 2050
pck (MeV/c)
C.+N.
1st
2000 2050
pck (MeV/c)
2100
Nuclear interaction Significant E1-E2 First-order:
too asymmetric
negligible
interference
⇒ higher-order
at forward angles (asymmetry)
– p.14/14