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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
Collaborators
• Jim Lawler – University of Wisconsin
• Chris Sneden – University of Texas
• John Cowan –University of Oklahoma
Outline
• Review - transition probability effort at the University of Wisconsin
• Current work - progress in astrophysics
• Future work in aid of divertor diagnostics and modeling
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
u
A3
A2
A1
Transition probabilities are determined by combining branching fractions and radiative lifetimes.
A1 branching fraction
radiative lifetime
1
u
A1
A1 A2 A3
1
uA1 A2 A3
• Branching Fractions are determined from relative intensity measurements using Fourier-Transform Spectroscopy.
• Radiative Lifetimes provide the absolute normalization for determining transition probabilities.
• Combined techniques used to measure BF’s and ’s allows for large sets of data measured to good accuracy (’s 5%, gA’s 5-20%).
• In past ~9 years - > 1400 ’s published for 16 spectra, >3600 gA’s published for 13 spectra.
Techniques used are broadly applicable and efficient.
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 >2 s
• no collisional quenching or radiation trapping
Radiative lifetimes are measured using time-resolved laser-induced fluorescence on a slow atom/ion beam.
The experimental apparatus is simple and robust.
Triggergenerator
Pulsed power supply
dc power supply
Nitrogen laser
Tunable dye laser
Frequency doubling
(when needed)
Diffusion pump
cathode
anode
Atomic beam
side view
Schematic of Experiment - top view
PMT
Fused silica window
and lenses
Spectral filters
Transient digitizer
Tunablelaserradiation
Atomic beam
Fluorescence
Sample Fluorescence Data
Recorded fluorescence
1st analysisinterval
2nd analysisinterval
Data collection:
• begins after laser terminates
• each decay is divided into 2 analysis regions
• each region ~1.5 in length
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 - 1:108 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
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.
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
Update on Current Work - progress in Astrophysics
In past 6 months -
• completed a very large work on Sm II gA’s
(> 200 ’s, > 900 gA’s) and astrophysical Sm abundances
• ~3/4 through measurements of Gd II gA’s
• extension to the VUV progressing with the Spatial Heterodyne Spectrometer
Progress Report
All-Reflection Spatial Heterodyne Spectrometer -- optics mounts built- optical table purchased- initial tests this week using small detector array
Sm II gA measurements
• fairly extensive work on ’s in literature
• only 2 reported independent determinations of BF’s
• Saffman and Whaling - measured BF’s using a grating spectrograph
•Xu, et al - determined BF using HFR calculations
Sm II gf values - Comparison with other experimental measurements
Saffman L., & Whaling W. 1979, J. Quant. Spectrosc. Radiat. Transfer, 21, 93
SW BF’s measured using a grating spectrometer are combined with our measured lifetimes for comparison.
Sm II gf values - compared with HFR calculations
HFR Calculations: Xu, H. L., Svanberg, S., Quinet, P., Garnir, H. P., & Biémont, E. 2003b, J. Phys. B: At. Molec. Opt. Phys., 36, 4773
Xu, et al - BF determined with HFR combined with measured lifetimes
Comparisons of measured lifetimes
Radiative lifetimes are not a significant source of the discrepancy between measured and calculated gf values
Solar photosphere - scatter is much reduced from earlier determinations
log ε(A) = log10(NA/NH) + 12.0
Astrophysical Application to Sm II abundance
Application to a metal-poor halo star BD +17 3248
log ε(A) = log10(NA/NH) + 12.0
Many more lines employed and scatter reduced x3
Abundance determinations are improving element by element.
Metal-poor galactic halo stars are being studied to understand early galactic evolution and the details of nucleosynthesis.
Future work - UW contribution to CRP
• gA’s for W II, Mo II, UV/VIS gA’s for levels up to ~50,000 cm-1
• VUV gA’s for higher levels
• improved wavelengths as needed
Summary
• Large sets of gA’s (UV/VIS) are routinely measured to ± 5 - 20% for neutral and singly-ionized species.
• Sm II gA’s 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?).