Binding energies of neutron-rich isotopes as measured with the CPT at CARIBU Jason Clark CIPANP 2015 May 19-24, 2015

Binding energies of neutron-rich isotopes as measured with the CPT at CARIBoU Jason Clark CIPANP 2015 May 19-24, 2015

Outline What can the precise mass measurements of nuclides tell us? How do we get access to the nuclides of interest? How are precise mass measurements made? Summary and outlook

General Physics fundam. constants test of CPT  m/m  1· Atomic Physics binding energy  m/m  1·10 -9 Weak Interactions symmetry tests, CVC hypothesis  m/m < 3·10 -8 Astro- physics nuclear synthesis, r-, rp-process  m/m < 1·10 -7 Nuclear Physics mass formula, models, halo  m/m  1·10 -7 Physics & Chemistry basic information required  m/m  1·10 -6 Weighing atomic masses K. Blaum Mass precision requirements

What we can learn from masses of neutron-rich isotopes Neutron-rich isotopes are interesting for studies of nuclear structure and astrophysics: Nuclear structure Single-particle strength near closed shells Pair correlations Collective aspects Astrophysics Studies of the s, r, and rp-processes Understand explosive stellar phenomena Learn how all the elements in the universe were created R.B. Cakirli et al., Phys. Rev. Lett. 102, (2009).

What we can learn from masses of neutron-rich isotopes What new magic numbers appear? Do we continue to observe a quenching of other magic numbers? Open questions: Mass known Half-life known nothing known neutrons protons How does the structure and shape of nuclei change with neutron excess? What is the source and path (along the chart of nuclides) of the astrophysical r process?

Creation of the elements – the astrophysical r process CARIBU yields r process thought to be responsible for production of >50% of the elements heavier than iron Exact site of r process unknown Understanding requires knowledge of astrophysical conditions AND nuclear properties (S n, σ c, t 1/2, P n ) S n determines path while gross β-decay properties determines final abundances Difficult to study nuclear properties far from stability Abundances of the elements as produced by various processes r-process model

Effect of mass uncertainty in r-process models Uncertainties in the nuclear physics: masses β-decay lifetimes β-delayed neutron emission (n, γ) rates fissionability from Matt Mumpower’s talk at the ATLAS Users’ Workshop R. Surman, M. Mumpower et al., arXiv: v1. Hot r-process Supernova neutrino- driven wind cold r-process Neutron-star merger cold r- process Abundances of the elements compared with modelsStudies of sensitivity of r-process yields to masses

CARIBU (Californium Rare Isotope Breeder Upgrade) Have delivered both stopped and reaccelerated beams using 1.7 Ci 252 Cf source CARIBU beams can be accelerated through ATLAS to ~ 15 MeV/A Basic properties of fission fragments can be measured with instruments in ‘stopped’ beam area 252 Cf Spontaneous Fission: 1.7 Ci source 3% fission branch 2.6 year halflife CARIBU: uses 252 Cf spontaneous fission source to provide neutron-rich isotopes

ATLAS ‘Stopped’ beam experimental area Buncher, Elevator CPT BPT X-ARRAY TAPE STATION Overview of CARIBU 1.7 Ci 252 Cf source Gas catcher (collect fission fragments) Isobar separator (select specific fragment) R ~ 20,000 Switchyard Delivery of beam to ‘stopped’ area through low-energy beamline reaccelerated through ATLAS after charge breeding

CPT apparatus 2 kV beam Cryogenically cooled linear Paul trap to capture, cool, and accumulate ions. Precision Penning trap situated in the bore of a 5.9 T superconducting magnet

Mass measurements of neutron-rich nuclides Canadian Penning Trap (CPT) has measured more than 150 neutron- rich nuclides, including more than 80 from CARIBU (including >6 isomers) Currently reaching isotopes produced at the fission branch level For some nuclei, no prior information on the nuclide existed! Mass precision ~ to ( keV/c 2 ) for masses approaching the r process Masses determined via a measurement of the ions’ cyclotron frequency (TOF-ICR) 132 Sb J. A. Clark and G. Savard, Int. J. Mass Spectrom , 81 (2013).

Comparison with the 2003 atomic mass evaluation In Sn Sb Te I Xe Cs Pr Nd Pm Sm EuGd Higher N Trends indicate nuclei are less bound with neutron excess (affects the location of the r- process path) Good agreement with other Penning trap results and reaction Q value measurements Large disagreement with results obtained with β- decay measurements J. Van Schelt et al., Phys. Rev. C 85, (2012) J. Van Schelt et al., Phys. Rev. Lett., submitted (2013) Less binding J. Van Schelt et al., Phys. Rev. C 85, (2012). J. Van Schelt et al., Phys. Rev. Lett. 111, (2013).

Effect on the r process: comparisons with the FRDM mass model r-process path Ran simulations to compare our new measurements with mass models for the r process Result: FRDM (and other mass models) have insufficient mass precision for r process models Effect of masses on r-process simulations (with T = 1.5 GK) J. Van Schelt et al., Phys. Rev. Lett. 111, (2013). J. Van Schelt et al., Phys. Rev. C 85, (2012).

Measurements of light 252 Cf fission products Z = 50 RECENT N = 50N = 82 First measurements of light 252 Cf fission fragments started just a few months ago First measurements show great agreement with JYFLTRAP where overlap exists Deviations from 2012 atomic mass evaluation are for those isotopes that were not previously measured with ion traps Initially starting with isotopes to help evaluate performance/yield of light beams from CARIBU

Upgrade to CARIBU: MR-TOF ‘Fast’ isobar separator: Based on ISOLTRAP/ISOLDE design: ~ 1.3 m long MR-TOF Resolving power > 50,000 R.N. Wolf et al., Nucl. Instrum. Methods Phys. Res., Sect. A 686, 82 (2012). Transmission > 80% Takes 10s of ms Installed December 2014 Commissioning underway!

Upgrade to CPT: position sensitive MCP detector Replacing channeltron with position-sensitive MCP detector Phase imaging – ion cyclotron resonance Online testing with 133 Cs at CPT S. Eliseev et al., Phys. Rev. Lett. 110, (2013). The orbital frequency of the ion’s motion is calculated from the phase change over time.

What we expect to reach with upgrades MR-TOF and PI-ICR technique will extend reach of CPT to nuclides with 1-2 neutrons more than those within reach today

Summary Precise binding energies (mass differences) of nuclei are important. The r process is thought to create half the elements heavier than iron Sensitive to uncertainties ~ 100 keV/c 2 Penning traps allow the most precise determination of a nuclide’s mass Can easily obtain better than 100 keV/c 2 precision Access to previously elusive neutron-rich nuclides is becoming available with new facilities and new techniques CARIBU now provides rare, short-lived neutron-rich nuclides Upgrades (MR-TOF, PI-ICR) promise to extend reach of measurements to even more exotic neutron-rich isotopes

Collaboration T. Hirsh, G. E. Morgan, K.S. Sharma F. Buchinger, J.E. Crawford, R. Orford M. Burkey, J.A. Clark, J.P. Greene, A.F. Levand, A. Perez Galvan, G. Savard, B.J. Zabransky A. Czeszumska, E.B. Norman, S. Padgett, N.D. Scielzo, B. Wang A. Aprahamian, M. Brodeur, S. T. Marley, M. Mumpower, A. Nystrom, N. Paul, K. Siegl, S. Y. Strauss