Investigation of octupole deformation in neutronrich actinium using

Investigation of octupole deformation in neutron-rich actinium using high-resolution in-source laser spectroscopy Proposal to the ISOLDE and Neutron Time-of-Flight Committee P-556 Reinhard Heinke on behalf of the P-556 collaboration 24/6/2020 | 64 th meeting of the INTC

Octupole deformation in Ac region o Pear shaped intrinsic nuclear configurations o Resulting from opposite parity single nucleon states, differing in 3 units of orbital and total angular momentum o Breaking of reflection symmetry o Prominent around 222 Ra (Z ≈ 88, N ≈ 134) o Manifestation in near-generate parity doublets with same ang. momentum Rev. C 97, 024309 (2018) o Inverted odd-even staggering of charge radii? Lynch et al. , Phys. (Po, At, Fr, Rn, Ra) Gaffne y et al. 24/6/2020 | 64 th meeting of the INTC , Natu 2 re 497 , 199– 204 (2 0 13)

Nuclear shape investigations by laser spectroscopy Ac laser ionization scheme (used at LISOL, TRIUMF, ISOLDE, JGU, …) Ion o Isotope shift: Evolution of center frequency with changing N Atom o Hyperfine structure: Spin, magnetic dipole moment, electric quadrupole moment Fig. from Verstraelen et al. , Phys. Rev. C 100, 044321 (2019) 24/6/2020 | 64 th meeting of the INTC 3

State-of-the-art EDF calculations in comparison to laser spectroscopy data (219 Ac) Measuement range 231 Ac o Data below N = 126 described equally well 223 Ac o Neutron-rich data as benchmark cases o Incorporation of reflection-asymmetry as key parameter o Measurement of δ<r 2> to pin down behavior o Evaluation of odd-even staggering o Strong support from theory 24/6/2020 | 64 th meeting of the INTC 4 Fig. from Verstraelen et al. , Phys. Rev. C 100, 044321 (2019) Changes in mean-square charge radii

o δ<r 2> a priori potentially arising from different multipole contributions o Larger β 20 values if no octupole deformation o Disentanglement by additional observables Measuement range • Β 20 as inferred from B(E 2) in neighboring Th • Observed parity doublets in Ac • Measurements of spectroscopic quadrupole moment QS 24/6/2020 | 64 th meeting of the INTC 5 Fig. from Verstraelen et al. , Phys. Rev. C 100, 044321 (2019) Electric multipole moments

Extraction of QS prevented Ion signal (cps) 200 MHz 120 MHz Off-line measurement on 109 atoms 225 Ac using PI-LIST at JGU by in-source Doppler broadening Sub-Doppler spectroscopy technique 24/6/2020 | 64 th meeting of the INTC Frequency shift (GHz) 6 Preliminary: S. Raeder at al. , to be published High resolution in-source spectroscopy

Sub-Doppler in-source spectroscopy: PI-LIST ISOLDE’s LIST ion source vthermal Atomic beam cone Narrow band spectroscopy laser (Fiber link CRIS + RILIS, used for 2 -photon spectroscopy 2018) Ø Resolution enhancement by order of magnitude (< 200 MHz) at cost of factor 1000 in intensity compared to standard RILIS Ø Operation mode change possible at any time 24/6/2020 | 64 th meeting of the INTC 7

PI-LIST high-resolution spectroscopy at JGU 97 -99 Tc accepte d 100 – 1 by PRC 20 MH z 163, 16 5, 166 m Ph. D R. Ho He 160 MH inke z 143 -14 7 Pm Eur. Ph ys 100 – 2. J. A. 50 MH z Resolution benchmark: Ø 60 MHz @ U, Rb Overall efficiency: Ø 10 -4 … 10 -5 24/6/2020 | 64 th meeting of the INTC 8

Implementation at ISOLDE: Adapted extractor Extractor at JGU Ø Extensive simulation studies and off-line tests performed at JGU, > 1 year of routine operation without problems Ø PI-LIST unit assembled at CERN Ø Adaption of ISOLDE-type extractor approved by RBS team Ø Test planned on Off-line 2 separator Ø Test planned at on-line frontend within LS 2 optimum moment for integration! Ø Activity within EU Marie Curie Network LISA dedicated manpower and support! 24/6/2020 | 64 th meeting of the INTC 9 ign E LD O S I s de

Shift planning and detection Detection of produced ions vs. laser frequency adapted to yield and decay properties: ÷ 30 ÷ 1000 Single ion counting with Magne. To. F Lower resolution and decay detection at ISOLDE Decay Station (annular Si detector + plastic scintillators) TAC: Contamination of beam instrumentation (FC’s)? Only setup / cross checks in standard RILIS mode 24/6/2020 | 64 th meeting of the INTC 10

Summary Ø Measurement on 222 -233 Ac isotope chain Ø Extraction of δ<r 2> , I, μ, QS Ø Pin down octupole behavior in Ac region by probing state-of-the-art theoretical models Ø Achieve required resolution and selectivity with PI-LIST and IDS 24/6/2020 | 64 th meeting of the INTC 11

Collaboration 24/6/2020 | 64 th meeting of the INTC 13

Backup slides 24/6/2020 | 64 th meeting of the INTC 14

PI-LIST Spectroscopy on 166 m. Hoc Internal reflection PI-LIST mode Standard 165 Ho 166 m. Ho fit Cumulative fit in-source 24/6/2020 | 64 th meeting of the INTC fit FWHM = 160 MHz 15

Fig. from Verstraelen et al. , Phys. Rev. C 100, 044321 (2019) Inverse odd-even-staggering in actinium 228 Ac 232 Ac 24/6/2020 | 64 th meeting of the INTC 16

Fig. from Verstraelen et al. , Phys. Rev. C 100, 044321 (2019) Nuclear moments in actinium 24/6/2020 | 64 th meeting of the INTC 17

Standard LIST for IS 614 (2018) 23 Na Laser Ions Surface Ions LIST mode 24 Mg Suppression Factor: > 104 Ion Guide mode Ion. Current (A) Loss Factor: ≈ 30 Repeller Voltage (V) Radioisotopes (β counting) Before run After run (4 days) Loss Factor (22 Mg, T 1/2 = 3. 9 s) 28 26 Suppression Factor (21 Na, T 1/2 = 22. 5 s) 1. 0 · 106 1. 6 · 106 24/6/2020 | 64 th meeting of the INTC 18

The Laser Ion Source and Trap LIST 45 mm Metallic mirrors Atomize r Machined at JGU mechanical workshop Optional surface treatment by pulsed laser deposition Ø Transversal reflection by robust metallic mirror surfaces Ø Off-axis guiding of spectroscopy laser through ion beam line 24/6/2020 | 64 th meeting of the INTC 19

Efficiency considerations Loss factors RILIS LIST ~ 30 LIST PI-LIST ~4 PI-LIST opt. ~ 10 ~ 1, 000 Overall efficiency 24/6/2020 | 64 th meeting of the INTC 20 10 -4. . 10 -5