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FNPMLS Recent progress on the study of nuclear fission using laser spectroscopy Kieran Flanagan 6th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei, Chamrousse, March 2017 Overview Introduction to laser spectroscopy

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Recent progress on the study of nuclear fission using laser spectroscopy

Kieran Flanagan 6th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei, Chamrousse, March 2017

FNPMLS

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Overview

  • Introduction to laser spectroscopy and

considerations.

  • Highlights of recent work on heavy elements.
  • New technique developments
  • Shell structure studies on fission fragments
  • Summary and outlook
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SLIDE 3

Atomic spectroscopy for nuclear physics

F=J+I

Data using existing techniques

Composition, shape and size

  • f the nuclear wave function,

without introducing assumptions from nuclear models.

  • Production rates of 1 atom/second
  • r lower and are not accessible

with existing laser spectroscopy techniques in this region.

  • Goal region for CRIS

(far from a complete survey)

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SLIDE 4

Laser Spectroscopy Options

  • Choice of transition often lead by the constraints of the

technique (sensitivity to HFS/IS fortuitous).

  • More atomic physics input is required.

Flux and Fluence Modulated Light

Fluorescence (trapped, collinear …) State selective

  • B. Cheal, et al. Phys. Rev. Lett. 102, 222501 (2009)
  • L. Vermeeren, et al. Phys. Rev. Lett. 68, 1679 (1992)

Resonance Ionization

V.N. Fedosseev, Yu. Kudryavtsev and V. I. Mishin Phys. Scr. 85, 058104 (2012)

Wavelength A coefficient Dark states

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SLIDE 5

Transition choice for experiment (example of francium)

  • Ionization potential measured
  • Atomic theory available for 7s1/2, 7p1/2, and 7p3/2
  • HFS A(7p3/2)/(8p3/2) ~3.0 B(8p3/2)/(7p3/2) = ~3.4
  • Lifetime for 7p3/2 = 21 ns and 8p3/2 = 85 ns
  • But
  • 355+355 nm will non-resonantly ionization and

add significant background.

  • Multi-step scheme looked risky (original plan was

to Doppler tune)

  • Two step resonant ionization scheme
  • nm resonant step
  • nm non-resonant step

717.986 nm 355 nm 355 nm 355 nm

  • A. Voss et al., Phys. Rev. Lett. 111, 122501 (2013)
  • A. Voss et al., Phys. Rev. C. 91, 044307 (2015)

7s1/2-7p3/2 transition in 204-206Fr

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SLIDE 6

Status of Laser spectroscopy: 2016

Gaps in knowledge

Production of exotic nuclei Atomic physics Rare isotopes will require more sensitive techniques

  • P. Campbell, I.D. Moore, M.R. Pearson, Progress in Particle and Nuclear Physics 86 (2016) p127
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SLIDE 7

Heavy nuclei

191-210,216,218Po 182-189Pb 177-182Au 197,198,203,205,207,209,211,217At 202-206,214, 218,219,229,231Fr 179-185Tl

N=104 Shape Coexistence Intruder States Region of octupole deformation Permanent static ground state deformation Structure relevant to beta-delayed fission

239-244Pu

Fission

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SLIDE 8
  • B. A. Marsh et al., 20013 EMIS conference, NIM B317, p.550 (2013)

WM: A.Andreyev et al, Phys. Rev. Lett 105, 252502 (2010) MR-ToF MS: R. N. Wolf et al, NIM, A686, 82 (2012)

In-source laser spectroscopy

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Au? At? Hg?

Summary of charge radii in the Pb region

Andrei Andreyev

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Collinear resonance ionization spectroscopy

  • 1982: Outline of method proposed by Yu. A. Kudriavtsev and V. S. Letokhov, Appl.
  • Phys. B29 219 (1982)

Laser Laser

  • σ for non resonant ionization = 1-10

Mb (107-108 smaller than allowed atomic transitions)

  • Requires high power pulsed lasers
  • ns pulses & 10 Hz – 10 kHz
  • Flight time through interaction

region ~5-10 μs (depends on space and budget).

  • Necessitates 100-200 kHz repetition

rate laser or an ion trap.

  • UHV in the interaction to avoid

collisional ionization <10-8 mbar

  • Ion optic tuning required when

Doppler scanning

Promised

  • High resolution,
  • High efficiency
  • Low background
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CRIS laser laboratory Sep 2015

  • Increasing the available wavelengths we can produce for RIS schemes
  • M2 Ti:Sa laser and frequency-doubling cavity
  • Matisse dye laser and frequency-doubling cavity
  • Industrial Nd:YAG laser and (injection-seeded) Ti:Sa cavities
  • 200 Hz Nd:YAG laser and pulsed-dye laser
  • Fibre-couple or mirror-couple light downstairs to the beam line
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CRIS laser laboratory April 2016

  • Increasing the available wavelengths we can produce for RIS schemes
  • M2 Ti:Sa laser and frequency-doubling cavity
  • Matisse dye laser and frequency-doubling cavity
  • Industrial Nd:YAG laser and (injection-seeded) Ti:Sa cavities
  • 200 Hz Nd:YAG laser and pulsed-dye laser
  • Fibre-couple or mirror-couple light downstairs to the beam line

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CRIS laser laboratory

  • Increasing the available wavelengths we can produce for RIS schemes
  • M2 Ti:Sa laser and frequency-doubling cavity
  • Matisse dye laser and frequency-doubling cavity
  • Industrial Nd:YAG laser and (injection-seeded) Ti:Sa cavities
  • 200 Hz Nd:YAG laser and pulsed-dye laser
  • Fibre-couple or mirror-couple light downstairs to the beam line

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Status 2012

  • Francium run completed 202-231Fr
  • RILIS Narrowband laser used 1.5 GHz linewidth
  • ~1% total experimental efficiency estimated from 202,218,219Fr
  • Non-resonant ionization efficiency ~0.0003%. Background rate

0.002 counts/s 202Fr (arising from 202Tl).

  • At 9x10-9 mbar, 1pA of contaminant isobar reduced to 18cps
  • Laser on/off 218Fr alpha detection>330 (expected 3000-4000)
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High resolution CRIS: 2015

E I CRIS 2012 CRIS 2014

  • First experiments used a

1.5 GHz laser system.

  • New method of chopped

CW laser spectroscopy: 20(1) MHz linewidth.

  • Separating pulses

reduces coherent effects.

  • Same rate on 219Fr in

narrow linewidth mode.

  • R. de Groote Phys Rev. Lett. 115 (13), 132501 (2015)
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Comparison

  • Factor of 75 improvement in linewidth

219Fr 2012 219Fr 2014 206Fr 2012 206Fr 2014

  • R. de Groote Phys Rev. Lett. 115 (13), 132501 (2015)

K.M. Lynch Phys Rev C 93 (1), 014319 (2016)

Γ=20 MHz Γ=1.5 GHz

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Laser spectroscopy of shortlived

Exploratory check to during a break while high resolution laser system was “optimised”

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Fortuitous Spectroscopy

  • Low resolution (RILIS) 1.5 GHz
  • Started scan on resonance

(based on a best guess).

  • Alpha identification on

resonance confirmed ground state

  • Change in bunching rate from

200 Hz to 100 Hz also used.

  • Most exotic N=127 isotone

measured.

  • 5ms represents the shortest

lived isotope measured with laser spectroscopy on-line.

GJ Farooq-Smith et al, Physical Review C 94 (5), 054305 (2016)

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Departure from lead δ<r2>

  • Amazing overlap with the δ<r2>

trend in lead down to N=122.

  • Typically nuclei are deformed yet

the extended region around 208Pb remains spherical

  • Transition after 205,206Fr
  • Q moments suggest small change

in static deformation.

  • Can still describe magnetic

moments with using single particle coupling rules.

  • Suggestive of a ‘soft’ spherical

potential and zero point

  • scillations about the minimum.
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Shell evolution of fission fragments: Ni region

  • Nucleon-nucleon interaction: single-particle energies evolve as function of

nucleons in an orbit

  • Away from stability, this can lead to (dis)appearance of shell closures
  • Cu chain: Z=29: probe for the magicity of Z=28 and N=28,40,50
  • T. Otsuka et al, PRL 104, 012501 (2010)

K.T. Flanagan et al, PRL 103, 142501, 2009

ν in g9/2

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SLIDE 23

Moments of neutron-rich Cu (Z=29)

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Magnetic moments: sensitive to details of wave function

Does the deviation increase? Can we verify this prediction?

  • Theoretical reproduction: excitation across Z=28 required
  • Moment confirms dominant πf5/2 contribution for 72,74Cu

πf5/2 vg9/2

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Moments of neutron-rich Cu (Z=29)

Quadrupole moments: collectivity and deformation

  • Quadrupole moment is sensitive to E2 transitions
  • Neutrons across N=50 (not included in jj44b/JUN45) not

required up to A=75

Will the reproduction continue for A > 75?

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Initial Copper experiment

  • Low efficiency and high background only allowed us to

reach 71Cu.

  • Choice of scheme was sub optimal
  • Utilized novel frequency chopping method with a strong

transition (lifetime < 10 ns)

– Achieved resolution of 75 MHz Ex1 IP

266 nm

P3/2

GS

S1/2

324 nm

71Cu 25

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SLIDE 26

Second Attempt

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  • Laser ionization scheme:

249 nm + 314 nm

  • Laser system: injection locked

pulsed ti:sapphire laser (Jyvaskyla/Mainz) and pulsed dye laser

  • High efficiency (total ε~1%)
  • High resolution (70 MHz linewidth)
  • High background suppression
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SLIDE 27

Experimental spectra

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Count rate (Hz) Frequency detuning from centroid (MHz)

  • Data on 63-78Cu
  • 80hrs total of data taking

78Cu

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SLIDE 28

Future work at CRIS

  • Extending laser measurements to 79Cu.
  • Neutron-rich indium up to 134In (later neutron

deficient down to 100In)

  • Extending measurements in francium to 201Fr,

203mFr, 214mFr

  • 52,53K and testing the N=32,34 shell closures.
  • Neutron deficient tin towards 100Sn
  • Decay spectroscopy of 80mGa and laser

spectroscopy of 83Ga

  • High resolution measurements of neutron

deficient Po

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Summary

  • In source laser spectroscopy is in a harvesting

period (70 new measurements in the last decade).

  • In-source measurements have now extended

measurements in Au,Hg and At (and recently Bi)

  • CRIS has now demonstrated ultra-high

resolution combined with high efficiency laser spectroscopy across the nuclear chart.

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SLIDE 30

Windmill Collaboration ‘2016

Comenius University, Bratislava, Slovakia GANIL, Caen, France Helmholtz Institut Jena, Germany ILL, Grenoble, France Institut für Physik, Johannes Gutenberg-Universität Mainz, Germany IPN Orsay, France JAEA, Tokai, Japan KU Leuven, IKS, Belgium PNPI, Gatchina, Russian Federation RILIS and ISOLDE, CERN, Switzerland SCK-CEN, Mol, Belgium The University of Manchester, United Kingdom The University of York, United Kingdom

Special thanks to the MR-TOF@ISOLTRAP team and the GSI Target Laboratory

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SLIDE 31

kara.marie.lynch@cern.ch

The CRIS Collaboration

10th April 2013

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HIAS2013, Australia

  • J. Billowes, C. Binnersley, T.E. Cocolios, G. Farooq-Smith, K.T. Flanagan, W. Gins,

K.M. Lynch, S. Franchoo, V. Fedosseev, Á. Koszorús, B.A. Marsh, G. Simpson, M. Bissell, R.P. De Groote, R.F. Garcia Ruiz, H. Heylen, G. Neyens, A.J. Smith, , H.H. Stroke, R.E. Rossel, S. Rothe, A. Vernon, K. Wendt, S. Wilkins, X. Yang.

FNPMLS