Nuclear Reactions and Nuclear Astrophysics
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Transcript of Nuclear Reactions and Nuclear Astrophysics
Nuclear Reactions and Nuclear Astrophysics
Focus on Physics
Speakers• Phillipe Collon – Possibilities for AMS
experiments at ATLAS• Livius Trache – Single-nucleon transfer between
p-shell nuclei around 10 MeV/u• William Peters – (d,p) as a surrogate for (n,)• Lee Sobotka – Decay spectroscopy – next up
14C• Catherine Deibel – Studying the (,p) process at
ATLAS• Xiaodong Tang – The 12C+12C fusion reaction
Themes
• Nucleon transfer reactions for structure, astrophysics, and applications
• Other reactions for structure• (In)elastic scattering for optical-model
potentials, structure• Other means – AMS, production/counting
for astrophysics
Transfer reactions for structure and astrophysics
• Heavy-ion single-particle transfer for nuclear astrophysics
• ANC studies linked to determination of (p,) reaction rates
• Need for accurate optical-model potentials• Need high-quality beams, intensity for
production of high-quality secondary beams (energy resolution, low emittance)
Details and problemsEnergy resolution (bad!)Beam res. 1-2% 2-4 MeV
angular resolution (limited!)Beam res. 0.8 – 2 deg!
Ang distr → ANC → astrophys S-factor → react rate
12N on melamineTAMU exps @ 12 MeV/u
A. Banu ea,PRC 79, 025805 (2009)
Optical Model Potentials for Nucleus-Nucleus collisions
for RNBs ~ 10 MeV/u
Essential to make credible DWBA calc needed in transfer r.
Have established semi-microscopic double folding using JLM effective interaction:
• Established from exps with stable loosely bound p-shell nuclei: 6,7Li, 10B, 13C, 14N … @ 10 MeV/u
• Parameters: renormalization coeff. • Predicts well elastic scatt for RNBs:
•7Be, 8B, 11C, 12N, 13N, 17F• 7-10% uncertainty in DWBA calc
L. Trache ea, PRC 61 (2000)F Carstoiu ea PRC 70 (2004)OMP: need extension to sd-shell:
•Work on stable projectiles at TAMU
•RNB of good quality – ATLAS ?!
•Energy and angular resolution
Trojan-horse with RNB ?!
Transfer reactions as surrogates – Inverse (d,p) as a tool to probe (n,), (n,2n)
• Applications:– Astrophysics– Nuclear reactors and device modeling– Stockpile stewardship and waste storage
• Needs:– Reasonable intensity for RNBs – at least 105 to 106
pps– Coulomb-barrier energy beams– Gammasphere for efficiency– Particle detector with reasonable spatial resolution
• See also instrumentation & Steve Pain’s talk
• 73As/74As = 1/2 σ74(n,2n) Фn (D.Vieira)
–Isotope ratios measured after event• (n,2n) reactions most important• (n,γ) reactions can effect results
August 8, 2009ANL 8
Gamma Spectrum (keV)
Spectrum not Doppler corrected
165 511
Partial level scheme (from ENDSF) of 76As used to identify successful (d,pγ) events. Quoted branching are from (n,γ) experiments.
August 8, 2009ANL 9
Doppler corrected6 keV FWHM
My two cents• Nucleon transfer for “Classical” nuclear physics
with RNB– Spectroscopic factors to test wave functions from
(d,p), (d,3He), (d,t), (,t) ...– In light nuclei – tests of ab-initio calculations– Single-particle states around, say, 132Sn...
• Needs: More intense RNB further than 1 nucleon from stability at Coulomb-barrier + energies– Intense primary beams– High energies (20 MeV/u) for very negative Q-value
reactions– Robust production targets– New separator– RF sweeper at HELIOS– CARIBU!
(,p) reactions and HELIOS
• Information about p process and X-ray bursts
• Requires “intense” secondary in-flight beams, Coulomb-barrier- energies
• Tool – HELIOS instrumented with cryogenic 4He target, A~30 recoil detector
p-process in X-Ray Bursts
The early rp-process a series of (p,), () and (,p) reactions
Stalls where (p,) and (,p) reactions come into equilibrium and must wait for + decay
(,p) reactions can break out if they are faster than the + decay
May be responsible for double-peaked luminosity profiles
Sensitivity studies have shown many of these reactions have significant effects on final abundances and energy output
p-process studies with HELIOS
Si Array
Gas target
PPAC and IC
Original design– Solid targets– Detection of backward light recoils– Detection of heavy recoils at 0°
Additions:– Gas target: allows 3,4He targets– Full Si array allows almost 4
acceptance– PPAC and IC allows for more
robust particle identification of heavier recoils, beam, and beam contaminants
Beam
Other reactions for structure: Breakup and resonant particle spectroscopy
• Study multi-particle correlations following inelastic excitation
• Physics of exotic cluster states at high excitation energy
• Needs high energy, “intense” (at least few X 105) pps
Decay Continuum spectroscopy – Using MARS-HiRA
6Be 10CPL B 677, 30 (2009); PRC in press (2009) PRC 78 031602 (2008); 75 051304 (2007); in press (2009)
1. Decay paths, branching ratios determined for all known levels.
2. A branch of the 6.57 MeV state has the best “diproton” correlation observed to date!
3. Did NOT confirm previous “identified” state at 4.2 MeV thought to be the 0+ (Curtis et al., PRC77, 021301 (2008).
4. Found new state at 8.4 MeV
Momentum Achromat Recoil Separator (MARS)
Scale (meters)
0 5
15 MeV/amu
B10H GasTargetP = 1.7 atmT = 77 K
2
Velocity
Filter
10.7 MeV/amu > 99.5%
10C Emittance
Slits
DP SlitsFaraday Cup
Q5Q4
D3
V1
D2S1 Q3
D1 Q2Q1
TSW2 QY QX
SW1
Perhaps we should do 10C + p (inelastic) to really find this 0+. (But will it be excited? Just above threshold.)
9Be(7Li,10Be+a)Soic’, PRC 68, 014321 (03)
2+
2+,1-,0+,2-
But most channels not Observed, i.e.12C + 2n12C* + 2n8Be + 6He8Be* + 6He
i.e. 6He (and intermediates)
Calls for a 3 cp + neutron correlation Experiment.
HiRA + WU neutron detectors
After that – perhaps 14C
Gd.st
1st excited state
2 nd grp
26He
(In)elastic scattering • Necessary, especially for RNBS, to determine
optical potentials– Needed to interpret ANC measurements– And Spectroscopic factor measurements
• 15-20 MeV/u measurements of (p,p) on RNBs as a benchmark for higher energy studies, probe asymmetry dependence in dispersive optical potential
• Use (p,p’) as a spectroscopic tool – search for the excited 0+ cluster state in 10C? Moments and transition matrix elements? – Needs high-energy beams, HELIOS is the tool
Other means
• AMS as a tool for astrophysics
Present status of AMS experiments at ATLAS
• A number of AMS experiments have been performed at ATLAS– Environmental science (39Ar, 81Kr, …)– Stellar nucleosynthesis (59Ni, 62Ni(n,)63Ni, 146Sm, 182Hf,
…)– WIMP dark matter detector development (39Ar)
• AMS relies on a number of factors– Good isobaric separation (high energies help!)– Stability of the entire system– High overall transmission
Other means
• AMS as a tool for astrophysics• Production studies for p-process nuclei
– Use intense ATLAS beam to do, e.g., 144Sm(,), 142Nd(,), 154Gd(,) followed by AMS counting – needs very intense, high-energy beams
Discussions – my interpretation so blame me
• (d,n) reactions as a spectroscopic tool – neutron detection capabilities?
• Resolution and sensitivity are key for uncovering the physics. (No kidding, really?)
• High beam energies are most welcome• High intensities useful for extending the
reach of the secondary in-flight program• Where can we get a tritium target??!!...