Исследование запаздывающего деления и сосуществования форм в ядрах таллия, астата и золота (ISOLDE, CERN) A. E. Барзах, П. Л. Молканов, М. Д. Селиверстов, Д. В. Федоров

IS 466: Identification and systematical studies of the electron-capture delayed fission (ECDF) in the lead region ECDF of 178,180 Tl (Z=81) IS 534: Beta-delayed fission, laser spectroscopy and shape-coexistence studies with radioactive 85 At beams ISOLDE IS 534 (addendum): Laser spectroscopy and shape-coexistence studies with radioactive 79 Au beams

Scanning the laser frequency of the first/second step of the selective ionisation scheme for a particular isotope (or an isomer) Isotope shift (IS), hyperfine structure (HFS) measurements Measuring FC current, or ToF spectra while scanning the frequency Isotope/isomer shift 1 ppm A,Z A-1,Z Laser beams Experiments Mass separation Target Hot Cavity Extractor Ion Source Reaction products (neutral) Ions Protons Target material 60 kV Laser Ion Source at ISOLDE

Windmill System at ISOLDE Annular Si Si pure 30 keV beam from RILIS+ISOLDE Setup: Si detectors from both sides of the C-foil Large geometrical efficiency (up to 80%) 2 fold fission fragment coincidences ff- γ, γ-α, γ-γ, etc coincidences C-foils 20 mg/cm 2 Si detectors 30 keV beam from ISOLDE Si Annular Si ff C-foil MINIBALL Ge cluster A. Andreyev et al., PRL 105, (2010)

Beta-Delayed Fission Q EC (A, Z) > B f (A, Z-1) ~

192,194,196 At β DF 192,194,196 Po 186,188 Bi β DF Beta-Delayed Fission N/Z ~ 1.55–1.59 N/Z ~ 1.22–1.31

Five Essential Fission Shape CoordinatesQ 2 ~ Elongation (fission direction) α g ~ Mass asymmetry (M1-M2)/(M1+M2) ε f1 ~ Left fragment deformation ε f2 ~ Right fragment deformation d ~ Neck ε f1 εf2εf2 d Q2Q2 P. Möllers calculations (2D projection of the total 5D picture) : symmetric valley, 90 Zr+ 90 Zr asymmetric valley, 80 Kr+ 100 Ru

178 Tl: 0.1 ions/μC/s, 8 fission events 180 Tl: 1111 fission events P βDF ( 178 Tl)=0.15(6)% P βDF ( 180 Tl)=3.2(2)×10 -3 % corresponds to A=80(1)A=100(1) Fragment mass distribution in DF of Tl isotopes experiment FWHM 9 amu

Model: BSM(M) Brownian shape motion on five- dimensional (5D) potential energy surfaces in Metropolis random-walk approximation Calculated yields for four Hg isotopes at three excitation energies. For the lighter isotopes the yields become more symmetric with decreasing energy, an unusual behavior. P. Möller, J. Randrup, A. Sierk, Phys. Rev. C 85, (2012) Fragment mass distribution in DF of Tl isotopes calculations

M. Veselsky et al. Phys. Rev. C 86, (2012) B f, exp (model), MeV B f, theor MeV 180 Hg7.5(1.5) Hg~ 79.3 P βDF ( 180 Tl) theor = 2×10 -6 % to be compared with the experimental value 3.2(2)×10 -3 % Fission barriers for Hg isotopes

Nuclear spectroscopic information for 178 Tl

Development and use of laser-ionized At beams at ISOLDE Determination of optical lines and efficient photoionization scheme. First measurement of the ionization potential of the element At Beta delayed fission of 194,196 At Charge radii measurement for At isotopes

(a) Verification of the two transitions from the ground state at λ 1 = 216 nm and 224 nm. (b) Ionization threshold: Scan of the ionizing laser wavelength λ 2. (c) Development of a three-color scheme: Scan of λ 2 in the infra-red region for second excited states starting with λ 1 = 216 nm first step. (d) Verification of the levels found by exciting via the λ 1 = 224 nm first step. (e) Rydberg series: A wavelength scan of the ionizing laser (λ 3 ) in the visible range using the {216, 795, λ 3 } excitation path. At Photoionization scheme for the radioactive element At Optimal photoionization scheme. Narrow band lasers for 1 st and 2 nd transitions 216 nm 795 nm 532 nm IP

IP (At)= (84) eV Precise determination of the Ionization Potential for the radioactive element At

IS534, 9-14 May 2012: Mass Distributions Measurements for DF of 194,196 At Two isomers (~40 and 250 ms) were reported in 194 At. Therefore, to obtain true mass distribution and P DF isomer selectivity is needed 180 Tl Energy in Si1 (MeV) Energy in Si2 (MeV) Energy in Si1 (MeV) 194 At 196 At Clear difference in energy (thus, mass) distribution between fission of 180 Hg and 194,196 Po

Shape Coexistence in the Pb region Pb (Z=82) g.s.: 0p-0h) – spherical Pb (Z=82) g.s j j Protons Neutrons s 1/2 h 9/2 d 3/2 Z=82 Proton pair excitations across Z=82 shell gap (neutrons are spectators): 1 pair excitation: 2p-2h) -oblate 2 pair excitation: 4p-4h) -prolate Pb (Z=82) 0 + prolate A.Andreyev et al. Nature, 405, 430 (2000) 186 Pb 0p-0h 2p-2h 4p-4h Potential Energy Surface for 186 Pb K. Heyde et al., Phys. Rep. 102 (1983) 291 J.L. Wood et al., Phys. Rep. 215 (1992) 101 A. Andreyev et al., Nature 405 (2000) 430 K. Heyde and J. Wood, Review of Modern Physics, 2012

Pre-2012: Charge Radii in Au-Po isotopes ? 85 At? 2011: Tl isotopes: IS511 ISOLDE and IRIS (Gatchina) Pb ISOLDE, PRL98, (2007) H. De Witte et al. Po ISOLDE, T. Cocolios et al., PRL106, (2011)

R. N. Wolf et al., Nucl. Instr. and Meth. A 686, (2012), S. Kreim et al., INTC-P-299, IS 518 (2011) Multi-reflection time-of-flight mass separator (MR-ToF MS) In-Source Spectroscopy with MR-ToF MS ~1000 revolutions, ~35 ms, m/Δm ~ 10 5

Isomer selectivity enable us to measure masses of 197g,198g At and receive nuclear spectroscopic information for pure g.s. Isomer selectivity for 197,198 At

Astatine HFS spectra 1 st step is better for Δ extraction 2 nd step is better for hfs resolution (Q and μ determination) 216 nm 795 nm 532 nm IP

197g 197m g 198m 217 Isotope shift δ A,A : Δσ for different transitions should lie on the straight line with a slope F λ1 / F λ2 King plot for 216 nm and 795 nm lines in At

IS534 October 2012: Charge radii of At isotopes 211 At(N=126)

85 At vs 84 Po charge radii N=126

October 2012: IS534 experiment at ISOLDE – Au isotopes Are the light Au isotopes deformed? What are the spins of ground and isomeric states?

IS534: Hyperfine Structure Scans for 177,179 Au 179 Au narrowband measured (WM) 179 Au 3/2 + calculated 179 Au 1/2 + calculated 177 Au narrowband measured (WM) Ground state spins of 177,179 Au are experimentally determined as 1/2 +

Why is 1/2 + 1/ Tl 177 Au decay hindered? Plot from A.Andreyev et al., PRC 80, (2009) 1/2 + ~1.6 N, pure sph. 3s 1/2, (as in the heavier Tls) ~1.1 N, (preliminary) mixed/def/triaxial 3s 1/2,/d 3/2

IS534: Charge Radii of Au isotopes, ISOLDE 2012 Deformation jump toward less deformed shapes in the light Au isotopes Shape staggering in 178 Au (large deformation difference between 2 states)

Summary: Charge Radii in Pb region IS/charge radii for 10 At nuclei were measured Back to sphericity in the lightest Au isotopes Magnetic/quadrupole moments will be deduced Large amount of by-product nuclear spectroscopic information on At and Au and their daughter products

Hyperfine structure anomaly for Au isotopes

1.Измерено асимметричное массовое распределение осколков запаздывающего деления 178 Tl и определена вероятность такого распада. Получены значения барьеров деления для 178,180 Hg. 2.Для исследования ядер At найдена эффективная схема фотоионизации, обнаружено около 20 ранее не известных атомных переходов, впервые определен потенциал ионизации At. 3.Обнаружено запаздывающее деление 196,194 At. Предварительный анализ свидетельствует о его симметричном характере. 4.Измерены изотопические сдвиги и сверхтонкое расщепление для 10 изотопов (изомеров) At на двух переходах, 216 nm и 795 nm, что позволит получить новые данные о μ, Q, δ и деформации этих изотопов (изомеров). Впервые для детектирования фотоионов использована установка MR-ToF. 5.Измерены изотопические сдвиги и сверхтонкое расщепление (μ, δ ) для 9 изотопов (изомеров) Au на переходе nm. Впервые обнаружен «обратный скачок деформации» возвращение к сферичности ядер с N

What is the ground state spin of 179 Au: 1/2 +,3/2 + or 5/2 - ? GS+FMA: W.F. Muller et al, PRC 69, (2004) 5.85 MeV 179 Au 183m Tl 53.3 ms RITU: A. Andreyev et al., R35 experiment (+ISOLDE data) M. Venhart et al, PLB 695, 82 (2011) Extensive ISOLDE data for g.s. of 183 Tl are available, analysis underway

What is the ground state spin of 177 Au: 1/2 + or 3/2 + ? GS+FMA: F.G. Kondev et al., PLB 512, 268 (2001) SHIP: A.Andreyev et al., PRC 80, (2009) Why is decay of 1/2 + gs of 181 Tl hindered, HF>3? Extensive ISOLDE data for g.s. of 181 Tl are available, analysis underway