Yasuhiro Togano Kenichiro Yoneda RIKEN Nishina Center Rapid proton capture rp process neutrons protons rp process Mass known Halflife known nothing known Accreting neutron stars ID: 1045424
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1. Coulomb dissociation experiments on proton-rich nuclei for nuclear astrophysicsYasuhiro ToganoKen’ichiro YonedaRIKEN Nishina Center
2. Rapid proton capture (rp) processneutronsprotonsrp processMass knownHalf-life knownnothing knownAccreting neutron starsSynthesize A~100 nucleiSynthesis of light p nuclei?Proton capture and b decayZ=50Waiting points Timescale of the process Abundance of elements
3. Waiting point in rp processWallace & Woosley 1981Waiting pointReaction flow waits the b decay of this nucleusCandidate: even-even nucleiT=-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
4. Measurement of (p,g) reaction Direct measurement is difficultSmall cross section (~nb order) Intense low energy beam: ~109 pps, <1 MeV/uReaction products: Z+1Hydrogen (gas) targetUnstable beams (<1 MeV/u)g rayAZA+1Z+1protongNot available for present facilities
5. Coulomb dissociation(g,p) reaction by virtual photonsVirtual photons: EM interaction between beam and targetDetailed balance: (g,p) (p,g)Cross section (mb order: ~106 times larger)Lower intensity beams (~1000 pps)Excitation energy invariant mass Z+1Z+1ZpPbVirtual photon absorptionAZ + pA+1Z+1g
6. Studies related to waiting pointsCoulomb dissociation of 23Al, 27P, 31ClBeam energies: ~50 MeV/u22Mg(p,g)23Al, 26Si(p,g)27P, 30S(p,g)31Cl reactions31ClPPACa PPACb0.1 mmt plasticPPACc208Pb targetDALI2NaI(Tl) x 160Position sensitiveSi telescopeHodoscope30Sproton0.1 mmt Si
7. CD of 27P for 26Si(p,g)27P reactionCoulomb dissociation of 27PExtract the reaction rate through the resonance
8. Improvement neededBetter resolution, more beamsRelative energy resolution: 0.25 MeV@ Erel = 1 MeV(dp/p)proton = 2.5%, (dp/p)HI=0.7%, dqopen = 12 mradRelative energy resolution: 0.15 MeV@ Erel = 1 MeV(dp/p)proton = 0.4%, (dp/p)HI=0.2%, dqopen= 4 mradProtonHeavy Ion
9. Setup with SAMURAILarge Acceptance modeweaker magnetic field~Half of max. fieldMomentum resolution1/600 for A/Z=2 particle1/350 for protonRelative energy resolution0.15 MeV @ Erel=1MeV( )DALI2Beam
10. Candidates for the first experimentCoulomb dissociation of 57Cu, 65As56Ni(p,g)57Cu, 64Ge(p,g)65As: Breakout from the waiting pointBeam intensity > 104 pps using 78Kr primary beam (30 pnA)
11. Candidate for the first experimentCoulomb dissociation of 28S and 24Si26Si(p,g)27P(p,g)28S, 22Mg(p,g)23Al(p,g)24Si: Breakout from the waiting point/ reaction cycleBeam intensity > 104 pps using 36Ar primary beam (50 pnA)
12. Beam time estimation57Cu, 65As: resonance captures are dominant Assume 5 mb for a resonance24Si, 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 Pb57Cu & 65As 1000 events/day: ~2 days24Si & 28S 1200 events/MeV/day: ~4 days
13. Summary and future prospectProton 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)24SiFuture(g,p) reaction relevant to the p-nucleiTwo proton capture reaction (17Ne , 70Kr…)