Heavy Elements Transition Probability Data of Interest in Astrophysics and Divertor Physics

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Heavy Elements Transition Probability Data of
Interest in Astrophysics and Divertor Physics

• Betsy Den Hartog
• University of Wisconsin - Madison
• Madison, WI USA

IAEA RCM Heavy Element Data Needs
Vienna 14 - 15 Nov 2005
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Collaborators

• Jim Lawler University of Wisconsin
• Chris Sneden University of Texas
• John Cowan University of Oklahoma

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Outline

• Review - transition probability effort at the
  University of Wisconsin
• Current work - progress in astrophysics
• Future work in aid of divertor diagnostics and
  modeling

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Transition Probability Effort at the University
of WisconsinMadison
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Large sets of transition probabilities have been
measured at UW for 1st and 2nd spectra of many
heavy elements.

• gA values are determined from a combination of
  techniques to measure radiative lifetimes and
  branching fractions.
• Current focus is on elements of astrophysical
  interest Sm II and Gd II

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Transition probabilities are determined by
combining branching fractions and radiative
lifetimes.
u
A3
A2
A1

• Branching Fractions are determined from relative
  intensity measurements using Fourier-Transform
  Spectroscopy.
• Radiative Lifetimes provide the absolute
  normalization for determining transition
  probabilities.

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? and gA measurements at Wisconsin - 47 spectra
measured - most elements could be measured
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Techniques used are broadly applicable and
efficient.

• Combined techniques used to measure BFs and ?s
  allows for large sets of data measured to good
  accuracy (?s 5, gAs 5-20).
• In past 9 years - gt 1400 ?s published for 16
  spectra, gt3600 gAs published for 13 spectra.

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Radiative lifetimes are measured using
time-resolved laser-induced fluorescence on a
slow atom/ion beam.

• Advantages of LIF Technique
• ?5 uncertainty for most levels
• selective excitation - no cascade repopulation
• broad applicability - most elements of periodic
  table accessible
• broad accessibility - levels from 15,000 -
  60,000 cm-1 can be studied (using UV/VIS laser)
• wide dynamic range - 2 ns to gt2 ?s
• no collisional quenching or radiation trapping

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The experimental apparatus is simple and robust.
anode
Trigger generator
Pulsed power supply
side view
Nitrogen laser
dc power supply
Tunable dye laser
cathode
Frequency doubling (when needed)
Atomic beam
Diffusion pump
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Schematic of Experiment - top view
Atomic beam
Tunable laser radiation
Fluorescence
Fused silica window and lenses
Spectral filters
Transient digitizer
PMT
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Sample Fluorescence Data

• Data collection
• begins after laser terminates
• each decay is divided into 2 analysis regions
• each region 1.5? in length

Recorded fluorescence
1st analysis interval
2nd analysis interval
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Branching fractions are determined from spectra
recorded using a 1 m Fourier-transform
spectrometer.

• Advantages of Technique
• excellent resolution - resolution is Doppler
  limited, reducing blending in rich spectra
• excellent accuracy - 1108 wavenumber accuracy
• fast collection rate - 1 million point spectrum
  in 30 minutes
• broad spectral coverage - UV to Infrared
• simultaneous collection - data collected in all
  spectral elements of interferogram simultaneously
  - crucial for relative intensity measurements

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Sample FTS spectrum
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In near future, VUV spectrometry capability will
be in place at UW.

• VUV lifetime experiment already in place.
• Spatial Heterodyne Spectrometer is currently
  under development (NASA funding).
• SHS will be used for VUV Branching Fractions
  (300 nm - 150 nm this year 300 nm - 100 nm next
  year).
• SHS suitable for multiply ionized species.

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Advantages - SHS

• preserves advantages of Michelson FTS - high
  spectral resolution, étendue, high data
  collection rates, and simultaneous collection on
  all spectral elements
• reflecting beam splitter - eliminates the VUV
  optics issues of the transmitting beam splitter
  by use of a grating operated in Echelle mode as
  beam splitter
• no moving parts - can be used in flash mode
  making it suitable for multiply-ionized species

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Update on Current Work - progress in Astrophysics

• In past 6 months -
• completed a very large work on Sm II gAs
• (gt 200 ?s, gt 900 gAs) and astrophysical Sm
  abundances
• 3/4 through measurements of Gd II gAs
• extension to the VUV progressing with the
  Spatial Heterodyne Spectrometer

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Progress Report All-Reflection Spatial
Heterodyne Spectrometer -- optics mounts built-
optical table purchased- initial tests this week
using small detector array
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Sm II gA measurements

• fairly extensive work on ?s in literature
• only 2 reported independent determinations of
  BFs
• Saffman and Whaling - measured BFs using a
  grating spectrograph
• Xu, et al - determined BF using HFR calculations

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Sm II gf values - Comparison with other
experimental measurements
SW BFs measured using a grating spectrometer are
combined with our measured lifetimes for
comparison.
Saffman L., Whaling W. 1979, J. Quant.
Spectrosc. Radiat. Transfer, 21, 93
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Sm II gf values - compared with HFR calculations
Xu, et al - BF determined with HFR combined with
measured lifetimes
HFR Calculations Xu, H. L., Svanberg, S.,
Quinet, P., Garnir, H. P., Biémont, E. 2003b,
J. Phys. B At. Molec. Opt. Phys., 36, 4773
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Same comparison vs log(gf) value
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Same comparison vs Eupper
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Comparisons of measured lifetimes
Radiative lifetimes are not a significant source
of the discrepancy between measured and
calculated gf values
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Astrophysical Application to Sm II abundance
Solar photosphere - scatter is much reduced from
earlier determinations
log e(A) log10(NA/NH) 12.0
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Application to a metal-poor halo star BD 17 3248
Many more lines employed and scatter reduced x3
log e(A) log10(NA/NH) 12.0
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Metal-poor galactic halo stars are being studied
to understand early galactic evolution and the
details of nucleosynthesis.
Abundance determinations are improving element by
element.
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Future work - UW contribution to CRP

• gAs for W II, Mo II, UV/VIS gAs for levels up
  to 50,000 cm-1
• VUV gAs for higher levels
• improved wavelengths as needed

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Summary

• Large sets of gAs (UV/VIS) are routinely
  measured to 5 - 20 for neutral and
  singly-ionized species.
• Sm II gAs and astrophysical application recently
  finished, Gd II underway
• Near-future capabilities include VUV branching
  fractions and lifetimes
• We hope to expand the gA and ? database for
  species of interest for diagnostics and modeling
  of the edge plasma (W II, Mo II, others?).