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??!!...