Slides - Indico

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Slides - Indico
Coulomb dissociation experiments on
proton-rich nuclei for nuclear
astrophysics
Yasuhiro Togano
Ken’ichiro Yoneda
RIKEN Nishina Center
Rapid proton capture (rp) process
• Accreting neutron stars
• Synthesize A~100 nuclei
– Synthesis of light p nuclei?
– Proton capture and b decay
Z=50
Mass known
Half-life known
nothing known
Waiting points
Timescale of the process
Abundance of elements
protons
neutrons
Waiting point in rp process
• Waiting point
– Reaction flow waits the b decay of this nucleus
• Candidate: even-even nuclei
– T=-1 nuclei (20 < A < 40)
• 22Mg, 26Si, 30S, 34Ar, …
– N=Z nuclei (50 < A < 90)
• 56Ni, 60Zn, 64Ge, 68Se, …
Proton capture on waiting point
+ bypass reactions around it
Wallace & Woosley 1981
Measurement of (p,g) reaction
g ray
Reaction products: Z+1
Unstable beams (<1 MeV/u)
g
Hydrogen
(gas) target
• Direct measurement is difficult
A+1Z+1
– Small cross section (~nb order)
 Intense low energy beam: ~109 pps, <1 MeV/u
Not available for present facilities
AZ
proton
Coulomb dissociation
• (g,p) reaction by virtual photons
– Virtual photons: EM interaction between beam and target
– Detailed balance: (g,p)  (p,g)
– Cross section (mb order: ~106 times larger)
p

• Lower intensity beams (~1000 pps)
Pp
– Excitation energy  invariant mass

 2
2
Z
• M  ( EZ  Ep )  ( PZ  Pp )
Virtual photon absorption
Z+1

PZ
Z+1
g
AZ
Pb
A+1Z+1
+p
Studies related to waiting points
• Coulomb dissociation of 23Al, 27P, 31Cl
– Beam energies: ~50 MeV/u
– 22Mg(p,g)23Al, 26Si(p,g)27P, 30S(p,g)31Cl reactions
PPACc
t
0.1 mm plastic
208Pb
target
31Cl
30S
proton
PPACa PPACb
0.1 mmt Si
Position sensitive
Si telescope
DALI2
NaI(Tl) x 160
Hodoscope
CD of 27P for 26Si(p,g)27P reaction
• Coulomb dissociation of 27P
– Extract the reaction rate through the resonance
Improvement needed
• Better resolution, more beams
Relative energy resolution: 0.15
0.25 [email protected] Erel = 1 MeV
(dp/p)proton = 0.4%,
2.5%, (dp/p)HI=0.2%,
=0.7%, dqopen412mrad
mrad
Proton
Heavy Ion
Setup with SAMURAI
• Large Acceptance mode
• weaker magnetic field
– ~Half of max. field
• Momentum resolution
– 1/600 for A/Z=2 particle
– 1/350 for proton
• Relative energy resolution
– 0.15 MeV @ Erel=1MeV
( )
Beam
DALI2
Candidates for the first experiment
• Coulomb dissociation of 57Cu, 65As
– 56Ni(p,g)57Cu, 64Ge(p,g)65As: Breakout from the waiting point
– Beam intensity > 104 pps using 78Kr primary beam (30 pnA)
Candidate for the first experiment
• Coulomb dissociation of 28S and 24Si
–
26Si(p,g)27P(p,g)28S, 22Mg(p,g)23Al(p,g)24Si:
Breakout from the
waiting point/ reaction cycle
– Beam intensity > 104 pps using 36Ar primary beam (50 pnA)
Beam time estimation
•
57Cu, 65As:
resonance captures are dominant
– Assume 5 mb for a resonance
•
24Si, 28S:
no resonances around the astrophysically
important energy (Erel<1 MeV)
– Direct capture  Assume 6 mb/MeV (same as 27P case)
• Beam intensity: both 104 pps
• Target: 200 mg/cm2 Pb
•
•
& 65As  1000 events/day: ~2 days
24Si & 28S  1200 events/MeV/day: ~4 days
57Cu
Summary and future prospect
• Proton capture reactions around the waiting point in rp
process will be studied with SAMURAI.
• Coulomb dissociation method will be employed.
– Efficient to measure the radiative capture cross sections.
• First experiment (2013~)
–
56Ni(p,g)57Cu, 64Ge(p,g)65As, 27P(p,g)28S, 23Al(p,g)24Si
• Future
– (g,p) reaction relevant to the p-nuclei
– Two proton capture reaction (17Ne , 70Kr…)

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