Mass measurements on very neutronrich isotopes with a new Penning trap phase detection technique Guy Savard Argonne National Laboratory amp University of Chicago Nuclear Structure 2016 Knoxville Tennessee July 2529 2016 ID: 769800
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Mass measurements on very neutron-rich isotopes with a new Penning trap phase detection technique Guy Savard Argonne National Laboratory & University of Chicago Nuclear Structure 2016 Knoxville, Tennessee, July 25-29, 2016
Main original motivation for mass measurements in this region: R-process sensitivity to nuclear physics input Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 2 From R. Surman et al, EPJ Web of Conferences 66, 07024, 2014 Hot r-process Supernova neutrino-driven wind cold r-process Neutron-star merger cold r-process binding energy neutron-capture rate lifetime Clear regions of interest for most scenarii … need to make them accessible experimentally
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 ATLAS/CARIBU facility Stable beams at high intensity and energy up to 10-20 MeV/u Light in-flight radioactive beams light beams, no chemical limitations, close to stability, acceptable beam properties CARIBU beams heavy n-rich from Cf fission, no chemical limitations, low intensity, ATLAS beam quality, energies up to 15 MeV/u State-of-the-art instrumentation for Coulomb barrier and low-energy experimentsOperating 5000-6000 hrs/yr (+ 2000 hrs/yr CARIBU stand alone) at about 95% efficiencyCommon PAC for ATLAS and CARIBUAbout 400 users per year performing experiments at ATLAS 3 Access to n-rich region via fission of the most neutron-rich “available” very heavy nuclei (i.e. 252Cf)
4 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Neutron-rich beam source: CARIBU “front end” layout Main components of CARIBU PRODUCTION : “ion source” is 252Cf source inside gas catcher Thermalizes fission fragmentsExtracts all species quicklyForms low emittance beamSELECTION: Isobar separator Purifies beamDELIVERY: beamlines and preparationSwitchyardLow-energy buncher and beamlinesCharge breeder to Increase charge state for post-accelerationPost-accelerator ATLAS and weak-beam diagnostics tape station X-array
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 “Thin” 1 Ci 252 Cf source about 20% of total activity extracted as ions works for all species complementary to uranium fission Expected isotope yield distribution at low energy (50 keV) > than 500 neutron-rich species extracted at > 1/s 5
6 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Precision mass measurements in a Penning trap Can use:Recall: w c depends only on:the massthe magnetic field not on the electric fields or the energy as long as g is smallCan use wc to make accurate and precise mass measurements
7 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Sample time-of-flight (TOF) spectrum Unknown: Well-known calibrant mass is a requirement for accurate measurements, use 133 Cs (known to ~ 0.01 keV) in this region. f c =663,104.706(3) Hz (560 eV/c 2 ) Time of Flight (arb units)
Mass measurements of neutron-rich nuclides Canadian Penning Trap (CPT) has measured more than 120 neutron-rich nuclides with this technique so farCurrently reaching isotopes produced at the 10-7 fission branch level For some nuclei, no prior information on the nuclide existed! Mass precision ~ 10-7 to 10-8 (1 -100 keV/c2) for masses approaching the r process Masses determined via a measurement of the ions’ cyclotron frequency Original Area II 2012 CARIBU 2013J. Van Schelt et al., Phys. Rev. C 85, 045805 (2012)J. Van Schelt et al., Phys. Rev. Lett. 111 , 061102 (2013)Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 20168
9 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 1 s (Hz) ± 3.7 keV± 132 keVTypical precision 10-15 keV 0.1 s 132 Sb – 132mSb
10 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 What we really collect? 1000s of scans, each with ~40 frequency points, each with a few ions 105-106 ions for a better than 1 keV/c2 measurementabout 1/3 are collected on resonance, others are determining the baselineFor a pure sample, can do an “acceptable” measurement with ~ 1000 ions total
11 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Main limitations: purity, lifetime and yield pure sample … not so pure sample incomplete cleaning decay in trap random noise
12 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Sample purity effect
13 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 For Penning trap mass measurements, impurities and short-lived isotopes are a bad mix Impurity hurts “squared” since we measure TOF, not ion numberImpurity hurts once moreLimit number of ions in trap to minimize interaction … if rate too high, must cut backGood guys are short-lived, impurities are long-lived … the longer you take, the worst it getsNeed to speed things up, and/or find better way to discriminate against impurities, for the shortest-lived isotopes
Purity upgrade to CARIBU: MR-TOF system ‘Fast’ isobar separation: ~ 1.3 m long MR-TOF Based on ISOLTRAP/ISOLDE design Goals: resolving power > 40,000 transmission > 50%Status: Installed December 2014 Current performance: R ~ 50,000 - 150,000 with ≥ 50% transmission in 10 - 30 ms R.N. Wolf et al. , NIM A 686, 82 (2012). Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 14 V d E + D E E E - DE
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 15 New mass measurement technique: PI-ICR Phase imaging – ion cyclotron resonance 133 Cs (offline source) S. Eliseev et al. , Phys. Rev. Lett. 110, 082501 (2013). The orbital frequency of the ion’s motion is calculated from the phase change over time. (PI-ICR) 657844.90(8) Hz Advantages over TOF-ICR: Spend all of the time at resonance (make better use of beamtime) Presence of contaminants is no longer a dominant issue (and also don’t lose ions of interest due to decay) Excitation scheme is faster (therefore don’t lose as many ions to decay) Result: factor of roughly 100 gain in sensitivity, with no loss in precision! A=146 from CARIBU
Evolution of PI-ICR signal 16 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016
17 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
18 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
19 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
20 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
21 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
22 PI-ICR Resolution Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Evolution of PI-ICR signal
p-hole – n-hole interaction around 132Sn 23 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 132 Sn131Sn130In131In
Isomer separation75 ms wc excitation 130Intacc = 75msCan almost completely resolve the two states.Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201624
tacc = 97.075ms Excitation energy ~50 keV. Resolution of ~1.8million in 100ms. Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201625 Isomer separation97.075 ms wc excitation 130InResolution with standard excitation ~70000 25 times worst
130 In n 130Inm130Ingg,m on same turn, n is not.In-g decayed a bit compared to 100ms files. Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201626 Isomer separation347.965 ms wc excitation 130 In
W. Nazarewicz, et. al, NPA429, 269, 1984 Coulomb excitation of 144,146 Ba: Direct measurements of B(E1) , B(E2) and B(E3)(C. Y. Wu et al., exp 1448) Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 27
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 650-MeV 144 Ba + 208 Pb (1mg/cm 2) GRETINA + CHICO2 + CARIBU/ATLAS expt. Rochester – LLNL – LBL- ORNL – Liverpool – Scotland – Ohio U – Tennessee – Georgia IT – Richmond - ANU –Washington – Toronto - Saclay – IHL Warsaw – GANIL – TU Darmstadt – Oslo – Notre Dame - ANL collab. Coulomb excitation of CARIBU beams with GRETINA/CHICO2GRETINA + CHICO2 provide excellent Doppler reconstructioncharge breeder + upgraded ATLAS provide post-acceleration with ~10% total efficiency and exquisite beam properties 28 144 Ba, 146 Ba, 142 Cs, 110Ru, 100Zr, 98Zr, 98mY, 106Mo
148Ba measurements Accumulation time Frequency (Hz) Mass Excess (keV)78ms1181998.60(0.05)-575**.*(8.5)95.11ms1181998.64(0.04)-575**.*(7.7)97.129ms 1181998.82(0.05)-575**.*(7.7)84.965ms1181999.05(0.06)-575**.*(13.4)97.075ms1181998.99(0.05)-575**.*(11.9) Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201629
149Ba measurements Accumulation time Frequency (Hz) Mass Excess (keV)75.017ms1174022.68(0.1)-528**.*(32.1)97.125ms1174022.76(0.07)-528**.*(25.4) 98.219ms1174022.8(0.05)-528**.*(7.0)Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201630
150Ba measurements Accumulation time Frequency (Hz) Mass Excess (keV)60.005ms1166165.27(0.09)-495**.*(21.3)80.131ms1166165.21(0.05)-495**.*(7.8)80.131ms 1166165.22(0.04)-495**.*(5.5)85.174ms1166165.4(0.04)-495**.*(7.3)84.402ms1166165.29(0.03)-495**.*(32.6)95.2ms 1166165.45(0.05)-495**.*(7.1) 80.135ms1166165.31(0.06)-495**.*(32.3) 95.134ms1166165.4(0.04)-495**.*(7.1) 80.135ms1166165.28(0.06)- 495**.*(32.8)Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 201631
Weighted Averages Nuclide Mas s Excess Weighted Average (keV)*148Ba-575**.*(5.1)149Ba-528**.*(5.4)150Ba-495**.*(4.4)*Uncertainty does not account for systematic uncertainties – only statistical uncertainties are represented here.Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 32
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 33
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 34
150Ba – ion rate dependence on time in trap (t1/2 = 0.3s) 2 shots - 0.097ips 8 shots - 0.011ips95.194mswcGuy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 35
150Ba – ion rate dependence on time in trap (t1/2 = 0.3s) 2 shots - 0.037ips 8 shots - 0.019ips80.135mswcGuy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 36
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 37
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 38
Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 39
40 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 Status CPT mass spectrometer now operating at CARIBU with phase sensitive cyclotron motion detection new technique allows us to beat the Fourier limit: a factor of ~25 gain in resolution for short-lived isotopes compared to standard techniqueMR-TOF in operation at CARIBU to improve beam purity when combined with phase sensitive cyclotron motion, gain of > 100 in sensitivityPenning trap mass measurement program has measured over 140 neutron-rich isotopes so far, mostly aimed at nuclei with r-process sensitivity … but also to nuclear structure studies and applicationsRecent improvements to CPT detection system will allow us to continue measurements one to two neutrons outside the predicted range for the CARIBU facility
CPT collaboration41 Guy Savard Penning Trap Phase Imaging Nuclear Structure 2016 July 25-29, 2016 T. Hirsh, G. E. Morgan, K.S. SharmaF. 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