Astrophysics experiments at CARIBU

1. Astrophysics experiments at CARIBU Jason Clark Nuclear Astrophysics Town Meeting 2012 October 10, 2012

2. CARIBU (Californium Rare Isotope Breeder Upgrade) status • Have delivered both stopped and reaccelerated beams using 400 mCi 252Cf source • accelerated 141Cs27+ to 4.5 MeV/A and delivered 10,000 / s to Gammasphere • observed ~ 1500 141Cs / s at the CPT (50 mCi) • Outstanding issues: • Stable-ion contaminants delivered with CARIBU beam • x10 less intensity than proposed • Solutions: • see next slide

3. CARIBU intensity and purity Fall 2012: • RFQ to replace PII Expect X2 gain Summer 2013: • New cryomodule 2013 ???: • New stronger, thinner source: Expect X5-10 gain 2014 – 2015: • EBIS to replace ECR: Expect X2 gain • In-Flight Mass Separator • takes advantage of high-intensity beams -> more than X50 gain from current in-flight radioactive beam yields • gain of a factor of 10-100 with targets designed to withstand increased beam intensities

4. 95Mo 94Zr Pn? 95Rb Astrophysics with CARIBU – the r process CARIBU yields • r process thought to create > 50% of the elements heavier than iron • Essential to understanding elemental abundances • Exact site unknown • Path critically depends on nuclear properties of neutron-rich nuclei: • mass • lifetime • β-delayed neutron emission • (n, γ) rates • fissionability

5. CARIBU stopped beam area Gas catcher (collect fission fragments) Isobar separator (select specific fragment) 400 mCi 252Cf source ‘Stopped’ beam experimental area ATLAS X-ARRAY BPT Buncher,Elevator CPT TAPE STATION • Delivery of beam • to ‘stopped’ area through low-energy beamline Switchyard

6. Stopped beam area • Delivers 1.5 kV to 10 kV beam to experimental stations • Pulsed beams with rates from ~ 100 ms to seconds • Low emittance • Experimental stations: CPT (installed) TAPE STATION (installed) X-ARRAY (available) BPT (late 2013) LASER SPECTROSCOPY: After CPT move (2013/2014) • Limited amount of space … removal of Tandem will provide new experimental area

7. Precise mass measurements • Masses determined via a measurement of the ions’ cyclotron frequency • Can measure the mass with a production rate of ~ 1 ion / s • Mass precision ~ 10-7 to 10-8 (10 keV) for masses approaching the r process • Canadian Penning Trap (CPT) has measured ~ 70 neutron-rich nuclides at CARIBU (including 6 isomers) • ~ 20 had never been previously measured by any technique • currently reaching isotopes produced at the 10-4 fission branch level • for some nuclei, no prior information on the nuclide existed!

8. In Sn Sb Te I Xe Cs Pr Nd Pm Sm Eu Gd Precise mass measurements CARIBU yields Higher N J. Van Schelt et al., Phys. Rev. C 85, 045805 (2012). • Trends showing nuclei less bound with neutron excess (affects location of r-process path) • Goal: Measure > 100 neutron-rich masses with CARIBU which have never been previously measured • With any luck, will measure 130Cd, an r-process waiting point

9. Beta-delayed neutron measurements • Let ion decay from rest at center of ion trap (Paul trap) • Surround ion trap (Paul trap) with plastic scintillators (to detect β’s) and MCPs (to detect decay recoils) • Beta-delayed neutron decay produces recoil detected by TOF with MCP 136Xe ions following b-delayed neutron emission Counts/6.5 ns 137Xe ions following b decay (+ g emission) Trap chamber and instrumented trap Time of flight (ms)

10. Z 50 50 82 N Beta-delayed neutron measurements • Data obtained using 1 mCi 252Cf source: • branching ratios obtained with different methods give similar results • Designing new trap for dedicated program of beta-delayed neutron measurements at CARIBU (more detectors, stronger source) • Ωβ = 12% • Ωr = 26% • Ωγ = 28% • sensitive to 0.1 ions/s production rate (to obtain a 10% precision in branching ratio) • En resolution: 5% • En threshold: 50 keV • β threshold: 25 keV BPT results World Average neutron recoils vs. β particles neutron recoils vs. 137Xe g rays neutron recoils vs. slow b/g recoils Yield of >1 ion/s delivered to low-energy experiments at CARIBU β-delayed neutron emission energetically allowed Nuclides where Pn measurement precision < 10%

11. HELIOS GAMMASPHERE FMA Reaccelerated beams • CARIBU beams up to 12 MeV/u • 82.5 ns time structure of beam

12. HELIOS (Helical orbit spectrometer) B.P. Kay et al., Phys. Rev. C 84, 024325 (2011). A. H. Wuosmaa et al., NIMA 580, 1290 (2007) J. C. Lighthall et al., NIMA 622, 97 (2010) • Sample of spectra in CARIBU mass region • Resolution of ~ 70-100 keV • With CARIBU beams, study surrogate reactions for (n,γ) r-process inputs such as: • 132Sn(d,p) • 134Te(d,p) • … • Beam axis along magnetic field axis • Beam travels through hollow detector array to target • Light particles from reaction follow helical path back to axis and are detected in array • Measure flight time, position, and energy to identify particle and determine center-of-mass energy, angle

13. Summary • CARIBU is NOW: • has delivered over 70 beams to ‘low-energy’ experimental area • starting reaccelerated beam program • call for proposals to go out soon (~ within a week) • estimate of yields can be obtained from proposal (for now, assume x10 less): • http://www.phy.anl.gov/atlas/caribu/Cf252_upgrade_proposal_final_Rev4.pdf • Experimental equipment available (now or soon) to take advantage of CARIBU beams: • CPT (masses until late 2013) • BPT (beta-delayed neutron branching ratios from 2013 onward) • HELIOS (surrogate reactions from 2013 onward)