- 46 Views
- Uploaded on
- Presentation posted in: General

NIST Spectroscopic Research on Heavy Elements 2005 - 2009

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

NIST Spectroscopic Research on Heavy Elements 2005 - 2009

Wolfgang L Wiese

National Institute of Standards and Technology (NIST), USA

General Objective: Determine experimentally and theoretically the atomic structure of heavy element atoms and ions of importance for magnetic fusion energy research

Main approaches:

- Measurements of heavy element spectra with vacuum sparks, lasers and the Electron Beam Ion Trap (EBIT). (This device reaches now charge state 68+.)
- Supporting analysis with pertinent plasma codes.
- Comprehensive critical compilations of atomic energy levels, wavelengths and transition probabilities os selected heavy elements
- Atomic structure calculations with sophisticated Hartree-Fock and Dirac-Fock programs
- Calculations of ionisation and excitation cross sections with the Binary Encounter Bethe (BEB) model and derivatives
- Analysis of the neutral chlorine spectrum with a wall-stabilized arc

Experimental Research: J. Reader, G. Nave,

J. Gillaspy, M. Bridges,*

W. Wiese*

Theoretical Approaches: Ch. Froese-Fischer,*

Y. Ralchenko,*

Y.-K. Kim , P. Stone*

Data Assessment andJ. Reader, E. Saloman,*

Compilations:J. Fuhr,* D. Kelleher,*

L. Podobedova,*

A. Kramida,* W. Wiese*

Database Development: Y. Ralchenko,*

A. Kramida*

R. Ibacache

*indicates Contractors or Guest Researchers

General Objective: Determine experimentally and theoretically the atomic structure of heavy element atoms and ions of importance for magnetic fusion energy research

Main approaches:

- Measurements of heavy element spectra with vacuum sparks, lasers and the Electron Beam Ion Trap (EBIT). (This device reaches now charge state 68+.)
- Supporting analysis with pertinent plasma codes.
- Comprehensive critical compilations of atomic energy levels, wavelengths and transition probabilities os selected heavy elements
- Atomic structure calculations with sophisticated Hartree-Fock and Dirac-Fock programs
- Calculations of ionisation and excitation cross sections with the Binary Encounter Bethe (BEB) model and derivatives
- Analysis of the neutral chlorine spectrum with a wall-stabilized arc

The EBIT not only creates a highly charged ions, but can hold their center of mass at rest.

This overcomes the primary limitation of large HCI facilities for precision spectroscopy.

EBIT size

~ 1 m

To first order, the relative Doppler shift is

Dl/l =v/c

107 K plasma

EBIT Internal View

EBIT on a table top

Ion production, trapping, and excitation

http://physics.nist.gov/ebit

A simplified EBIT:

Intense Electron Beam (4,000 A/cm2)

Strong magnetic field (3 tesla)

Highly Charged Ions (up to Bi72+at NIST).

2 cm

Ultrahigh vacuum (~10-10 torr)

Creates (by electron impact ionization) Traps (by electric and magnetic fields) Excites (electron impact)

Ion cloud width ~ 150 mm

Quantum Microcalorimeter

- operates at 65 mK

- absorber: a foil of
- superconducting tin

- thermistor: neutron
- transmutation-doped
- (NTD)germanium

“Crystal-quality” resolution, wide bandwidth and 100% efficiency.

Ar

L-shell

K-shell

Spectra and wavenumbers, as a function of element (Z)

Spectra as a function of electron beam energy

(Only a small subset shown. We have done this for several elements, extending as high as 24 keV for some)

Tungsten Data Tables from Recent Publications of the NIST EBIT Team

Includes new lines, and corrects misidentification from other groups.

Preliminary tables for >100 new lines presented at HCI and DAMOP conferences in 2006-2008

General Objective: Determine experimentally and theoretically the atomic structure of heavy element atoms and ions of importance for magnetic fusion energy research

Main approaches:

- Measurements of heavy element spectra with vacuum sparks, lasers and the Electron Beam Ion Trap (EBIT). (This device reaches now charge state 68+.)
- Supporting analysis with pertinent plasma codes.
- Comprehensive critical compilations of atomic energy levels, wavelengths and transition probabilities os selected heavy elements
- Atomic structure calculations with sophisticated Hartree-Fock and Dirac-Fock programs
- Calculations of ionisation and excitation cross sections with the Binary Encounter Bethe (BEB) model and derivatives
- Analysis of the neutral chlorine spectrum with a wall-stabilized arc

Already in the database:

1.Total ionization cross sections of neutral atoms and molecules, singly charged molecular ions (about 100)

2.Differential ionization cross sections of H, He, H2

3.Excitation cross sections of light atoms

Recent Results:

4.Total ionization cross sections (direct + excitation-autoionization) of Mo, Mo+, W, W+ (joint work with KAERI, see graphs)—BEB model plus BE/E scaling of Born cross sections [Mo/Mo+ in Kwon, Rhee & Kim, Int. J. Mass Spectrometry, 245, 26 (2005)]

5.Excitation cross sections of H2 (see graphs)—BE scaling of Born cross sections

6.Ionization cross sections of Si, Ge, Sn, Pb, Cl, Br, I, Cl2, Br2, I2

Ionisation cross sections from the 3p54s levels

Ionisation cross sections from the 2p53s levels

Ar I

Excitation cross section from the metastable level 3p54s to 3p55p

Main approaches:

- Supporting analysis with pertinent plasma codes.
- Atomic structure calculations with sophisticated Hartree-Fock and Dirac-Fock programs
- Analysis of the neutral chlorine spectrum with a wall-stabilized arc

Wall-Stabilized Arc

Wall-Stabilized Arc

Maxi Arc

- Arc Plasma operates at atmospheric pressure, electron density is about 1017 cm-3
- Local Thermodynamic Equillbrium (LTE) applies
- Line intensities I are measured to determine relative transition probabilities Ar initiating in atomic states m
I~(gm/λ) Ar exp(-Em/kT)

- Normalization to absolute A by one (or more) radiative lifetimes τ
τm =

and τm when there is one dominant transition

Bengtson et al (shock tube) vs NIST

±34%

Oliver a. Hibbert (CIV 3 Calc.) vs NIST

± 15%

Fischer (MCHF calc.) vs NIST

± 15%

An Example:

A-values for the 4s 2P -4p 2S doublet of Cl I

Experiments

C a l c u l a t i o n s

d (l-v) is the relative difference between the dipole-length and velocity results

Summary of principal NIST contributions to the

IAEA CRP on Heavy Elements

Investigations of spectra of heavy elements:

Cl I, Ar I, Fe IV, Kr I, Xe VII to Xe XLIV, W XL to W XLVIII, W LV to W LXIV

Calculations of cross sections:

Ar I(ionization, BEB), Ar I(excitation, plane wave Born)

Compilations of Reference Data:

Energy Levels, Wavelengths: Kr I to Kr XXXVI, W I to WLXXIV(510 pages!)

Ionization Energies: WIII to W LXXII

Transition Probabilities: Al I to Al XIII, Si I to Si XIV, Fe I and Fe II