- Email: [email protected]
Ion trap measurement of U64+ X-ray transition spectra
227
Nuclear Instruments and Methods in Physics Research B56/57 (1991) 227-231 North-Holland
Ion trap measurement of V4+ X-ray transition spectra N.K. Del Grande, and J.K. Swenson
P. Beiersdorfer,
J.R. Henderson,
A.L. Osterheld,
J.H. Scofield
University of California, Lawrence Luxrmore National Laboratov, Overmore, CA 94550, USA
Highly-charged uranium ions with a dominant nickel-like component (U@+ ) were produced using the electron beam ion trap (EBIT) with an electron bombardment energy of 7.4 keV. A comparison of the measured N = 4 to n = 3 X-ray transition spectra with calculations for U@+ gave excellent qualitative agreement. The low-energy region of the 4-3 spectrum for the Ni-like ions was characterized by a strong electric quadrupole 4s-3d transition, about as large as the leading dipole 4f-3d transition, which tagged the abundance of U64f tons. High resolution spectroscopy was used to measure 4f-3d transition energies for ten charge states: U60+-U69+ excited by 6.4-8.9 keV electrons. The ionization balance for 8.9 keV electron excitation was mostly from five charge m qualitative agreement with a separate analysis of extracted ions. states, U64+-U68+,
ion trap studies have focused on L-shell X-ray transitions for neon-like ions [l-3] and K-shell X-ray transitions for helium-like ions [4,5]. We report the first use of an ion trap to study M-shell X-ray transitions for nickel-like ions. Previous studies of n = 4 to n = 3 X-ray
1. Introduction The electron beam ion trap (EBIT) is proving to be a valuable source for studying the spectroscopy of highly charged ions in the electron-ion interactions. Previous Table 1 Measured and calculated 3d,,,-4f,,, (A) and 3d s,,-4f,,, the experimental uncertainty in determining line energies.
(B) X-ray line energies
Transition
Charge state
Designation
EBIT exp. a
(r exp.
A A
60t 61+
Ge-like Ga-like
3621.6 3647.7
0.5 0.8
A A A A A
62f 63+ 64+ 65+ 66+
Zn-like Cu-like Ni-like Co-like Fe-hke
3667.6 3686.9 3705.5 3762.5 3814.7
0.7 0.4 0.4 0.6 1.0
B B B B B B B B B B
60+ 61f 62f 63+ 64+ 65+ 66t 67+ 68+ 69+
Ge-like Ga-like Zn-like Cu-like Ni-like Co-like Fe-like Mn-like Cr-like V-like
3194.4 3814.6 3835.7 3854.7 3873.5 3935.7 3996.1 4055.8 4117.0 4182.4
0.3 0.7 0.3 0.5 0.2 0.4 0.5 0.6 1.1 1.2
in eV for uranium
Nova exp. b
GRASP talc. ’
HULLAC talc. d
3703
3687.3 3705.5 3761.1
3687.3 3706.8 3760.8
3870
3855.3 3873.5 3934.2
3856.4 3876.0 3936.8
a This measurement uses energies relative to the GRASP value for U64’. b Nova laser measurement; R.L. Kauffman, LLNL, private communication (1990). ’ Based on relativistic Hartree Fock code by I.P. Grant and co-workers implemented LLNL, private communication (1989). d Based on Hebrew Umversity codes by M. Klapisch and A. Bar-Shalom. e Based on the unresolved transition array (UTA) formalism and relativistic parametric Nucl. Instr. and Meth. B31 (1988) 153. 0168-583X/91/$03.50
0 1991 - Elsevler Science Pubhshers
ions U60+-U69+.
B.V. (North-Holland)
at LLNL
potential
by K.T. Cheng
method
0 represents
UTA calce
3671.3 3692.1 3709.8
3827.8 3849.1 3867.2
and M.H.
of C. Bauch-Amoult
I. ATOMIC/MOLECULAR
Chen;
et al.,
PHYSICS
228
N.K. Del Grande / Ion trap measurements of Uih4+
transitions for near nickel-like ions have been conducted using tokamaks, vacuum sparks, or laser-produced plasma sources [6-81. We have made measurements both with lower resolution Si(Li) detectors and with higher resolution Bragg crystal spectrometers to tag the abundance of nickel-like uranium with E2 transitions and to study the near nickel-like uranium ionization balance. Our study represents the first measurement of the 4f-3d transition energies for a series of near nickel-like (U64+) uranium ions: U60+-U69t, with the exception of the unpublished measurement for U64-c taken with the Nova laser [9]. We compare our results with this measurement and with calculations [lo-141. Further studies were conducted to determine the ionization balance for trapped ions within EBIT, which can be compared to the ion distribution reported for the extracted ions measured at an excitation energy near 9 keV [15].
2. Experimental The electron beam ion trap, described in detail elsewhere [1,16], was used to trap, ionize and excite uranium ions for our spectroscopic measurements. Ions were injected into the trap from a uranium metal vapor arc. The ion density was about lo9 cme3 and the electron density was approximately 5 x lOI cme3. Measurements were made of X-ray spectra using a windowless Si(Li) detector at one of the beam ports, a Ge detector at a second port, and a Bragg-diffraction spectrometer consisting of a flat Ge crystal and a position-sensitive proportional counter filled with a Xe-CH, gas mixture at a third port. The spectrometer was calibrated (i.e. the energy centroid and dispersion) using theoretical values for two Ni-like uranium lines (see table 1). In addition, ions were extracted from the trap and were mass and charge analyzed for comparison with the results obtained with X-ray spectroscopy [15].
3d 3,2-4f5,2 transitions.
(3873.5 ev);
and 3p,,,-4d,,,
(4152.0 eV)
4. Discussion of results An overview of dominantly nickel-like uranium 4-3 transitions measured with a Si(Li) detector is shown in fig. 1. A comparison of the measured spectrum with X-ray emission line intensities from calculations using the HULLAC codes gave excellent qualitative agreement. We note in particular the strong electric quadrupole 4s-3d transition. This E2 transition is a unique feature in nickel-like ions. It results from decay of the second lowest excited level in U64+, and is mostly fed by radiative cascades, as indicated in fig. 2. In contrast, the corresponding excited levels in copper-like U63’ and cobalt-like U6’+ decay by El intrashell transitions. The 4s-3d transition at 2.692 keV brackets the low energy side of the 4-3 transitions. Based on our empirical results, it appears to tag the charge state abundance of nickel-like U64’ ions. It is strongest at electron excitation energies near the ionization energy of U64+ (7.393 keV) where the distribution inferred from
600 *
“64+
measurement
I
u64+
,
calculation
1
r
A
3. Theory Several relativistic atomic configuration calculations for M-shell X-ray line energies are available for comparison with experimental measurements. Among the calculations considered were the relativistic Hartree Slater code [13], the Hebrew University-Lawrence Livermore Atomic Codes (HULLAC) developed by Klapisch and Bar-Shalom [ll], and the GRASP relativistic Hartree Fock code of Grant and co-workers [lo]. Further comparisons were made with published predictions for U62+, U63+ and U641- by Bauche-Arnoult and co-workers [12]. Our measurements were made relative to the GRASP code line energies for U64+ 3d,,,-4f,,, (3705.5 eV);
‘6 photon energy in keV Fig. 1. Comparison of X-ray spectrum measured on EBIT with a Si(Li) detector at a beam energy of E = 7.4 keV with calculated X-ray intensities from the HULLAC codes.
N. K. Del Grande / Ion trap measurements of
3p%d94p+ 3p63d84s 3p53d”+ 3p53d84s2
t not rn”Ch
e2
6 _-EL 3p63dg
Fig. 2. Decay schemes for highly charged uranium ions with copper-like,nickel-like and cobalt-like charge states.
crystal spectrometer measurements is approximately 59% nickel-like, 28% copper-like and 11% zinc-like uranium ions. It decreases in rough proportion to the percentage of U 64+ ions for a higher electron excitation energy at 8.89 keV where there are five dominant charge states: U64+, U65+, U66+, U67+ and U6’+. Another way to tag nickel-like uranium is by looking at radiative recombination spectra at the onset of the opening of a new shell. In this case, we used a Ge
lJ64t
229
detector, which is more efficient at higher energies than the Si(Li) detector, to observe radiative recombination from U65+ onto the n = 3 shell for U64+. Understanding the ionization balance when there are several charge states more ionized than U64t is a significant problem which required higher resolution than obtained with the Si(Li) detector used for fig. 1. Using the Bragg crystal spectrometer, we measured the 3d-4f X-ray transitions with a FWHM of about 5 eV. This was sufficient to resolve transitions from different charge states. The relative ion abundances could thus be inferred from the relative X-ray line intensities. The high resolution spectra shown in fig. 3 resolve U60+-U64+ ions at 6.40 keV U61+-U64+ ions at 7.19 keV, U63+-U 67t ions at 8.09’keV and U63’-U69f ions at 8.89 keV electron excitation energies. In fig. 4, we compare an X-ray spectrum taken at a beam energy of 8.9 keV with a measurement of the charge distribution of uranium ions extracted from EBIT. There are remarkable similarities between the two measurements,
64+ 7.19 keV
UJ 5 8
50 0 120
photon energy (keV) 6%”
U 3d-4f
1
67+ 64+ 8 09 keV I
I
80 40
65
63
magnet current (A)
photon energy (keV) Fig. 3. High resolution spectra showing the 3d-4f X-ray lines for ten charge states: U60+-U69t produced at electron excitation energiesvarying from 6.40 to 8.89 keV.
Fig. 4. Comparison of X-ray line intensities from near nickellike uranium ions trapped in EBIT (as shown in fig. 3) with charge distribution of extracted ions based on mass and charge analysis (from ref. [15]). I. ATOMIC/MOLECULAR PHYSICS
N.K. Del Grande / Ion trap measurements
230
Table 2 Measured and calculated 3d-4f splitting of lines: 3d,,,-4f,,, Charge state
Designation
EBIT exp.
(r exp.
60+ 61+ 62+ 63+ 64+ 65+ 66+
Ge-like Ga-like &r-like &-like Ni-like Co-like Fe-like
166.8 166.9 168.1 167.8 168.0 173.2 181.4
0.6 1.1 0.8 0.6 0.4 0.7 1.1
which suggest the possibility the future.
of detailed
comparisons
and 3d,,,-4f,,,
in
5. Summary and conclusion By way of summary, table 1 gives the measured and calculated 3d,,,-4f,,, and 3d,,,-4f,,, X-ray line energies for uranium ions U 60+-U6g+. The measmements are a composite of between one and two measurements at several excitation energies ranging from 6.4 to 8.9 keV. Since the measured lines had a FWHM of about 5 eV, we were unable to resolve the two C&like lines whose predicted excitation rates roughly add up to the excitation rate of the Ni-like line, but whose spacing is 0.3 or 0.4 eV. Similarly, we need better resolution to test the effect of configuration interaction in mixing the energy levels and line strengths among the Co-like lines.
Designation
60+ 61f 62+ 63+
Ge-like Ga-like Zn-Iike Cu-like
Average 0, - I 65+ 66-l67+ 68+ 69+ Average on-1
Co-like Fe-like Mn-like Cr-like V-like
EBIT exp.
in eV for uranium ions U60+-U66+.
Nova exp.
GRASP talc.
HULLAC talc.
167
168.0 168.0 773.1
169.1 169.2 176.0
UTA talc.
156.5 157.0 151.4
The GRASP and HULLAC calculations shown in tables 1-3 represent a weighted average based on the respective excitation rates. The UTA calculations represent a centroid of all the transitions that would be present in a dense plasma and include the effect of transitions not observed in EBIT. Table 2 compares the measured splitting of the 3d-4f transitions with calculations, whereas table 3 compares the measured and calculated energy shift per charge state for ions less ionized and more ionized than U64t. The EBIT experiment provides uranium ion X-ray line energies and energy shifts per charge state in good agreement with the GRASP and HULLAC calculations for U63c and U6’+. The behavior of U66+-U6g+ ions, which have a smaller energy shift per charge state for the 3d 5,2-4f7,2 transition than for the 3d,,,-4fs,, transition, may be indicative of complexities from energy level mixing. Spectra from these configurations become much more complex as the 3d shell opens up. Measure-
Table 3 Measured and calculated energy shift per charge state in eV for 3d,,,-4f,,, the line energies of nickel-lie uranium ions U64+. Charge state
of lJ64 ’
(A) and 3d,,,-
4f,,,
(B) X-ray line energies relative to
GRASP talc.
HULLAC talc.
UTA caIc.
A
B
A
B
A
B
A
B
-19.5 - 19.3 - 19.0 - 18.6
- 19.8 - 19.6 -18.9 -18.8
-18.2
- 18.2
- 19.5
- 19.6
- 19.2 - 17.7
- 19.7 -18.1
- 19.1 0.4
-19.3 0.5
- 18.4 1.1
-18.9 1.1
57.0 54.6
62.2 61.3 60.8 60.9 61.8
55.5 1.7
61.4 0.6
55.6
60.7
54.0
60.8
N K. Del Grande / Ion trap measurements of lJh4+
ments with higher energy resolution ter understand these complexities.
are needed
to bet-
Acknowledgements We are grateful for atomic physics support from W. Goldstein and M. Chen; for experimental work and useful conversations with M. Schneider, C. Bennett, D. Knapp, D. Schneider, M. Clark, and D. Dewitt; for technical support from D. Nelson and E. Magee; and for support and encouragement from R. Marrs, R. Fortner and A. Hazi. This work was performed at the Lawrence Livermore National Laboratory under the auspices of the U.S. Department of Energy under contract No. W-7405ENG-48.
References PI R.E. Marrs, M.A. Levme, D.A. Knapp and J.R. Henderson, Phys. Rev. Lett. 60 (1988) 1715. M.H. Chen and R.E. Marrs, Phys. Rev. A41 (1990) 3453. [31 P. Beiersdorfer, A.L. Osterheld, M.H. Chen, J.R. Henderson, D.A. Knapp, M.A. Levme, R.E. Marrs, K.J. Reed, M.B. Schneider and D.A. Vogel, Phys. Rev. Lett. 65 (1990) 1995. R.E. Marrs, M.A. Levine, CL. Bennett. I41 D.A. Knapp, M.H. Chen, J.R. Henderson, M.B. Schneider and J.H. Scofield, Phys. Rev. Lett. 62 (1989) 2104.
PI P. Beiersdorfer,
231
[5] J.R. Henderson. P. Betersdorfer. C.L. Bennett, S. Chantrenne. D.A. Knapp, R.E. Marrs, M.B. Schneider, K.L. Wong, G.A. Doschek, J.F. Seely, C.M. Brown, R.E. LaVilla, J. Dubau and M.A. Levine, Phys. Rev. Lett. 65 (1990) 705. [6] S. VonGoeler. P. Beiersdorfer, M. Bitter, R. Bell, K. Hill. P. LaSalle, L. Ratzan, J. Stevens, J. Trmberlake, S. Maxon and J. Scofield, J. Phys. (Paris) 49 (1988) Cl-181. [7] P. Burkhalter, D. Nagel and R. Whitlock. Phys. Rev. A9 (1974) 2331. J.-C. Gauthier, J.-P. PI J.-F. Wyart, C. Bauche-Arnoult, Geindre, P. Monier, M. KIapisch, A. Bar-Shalom and A. Cohn, Phys. Rev. A34 (1986) 701. LLNL Laser Program Report, UCRL [91 R.L. Kauffman, 50021-87 (1987) 3-139; private commumcation (1990). D.F. Mayers UOI I.P. Grant, B.J. McKenzie, P.H. Norrington. and N.C. Pyper, Comput. Phys. Commun. 21 (1980) 207. A. Bar-Shalom, P. Mandelbaum, J.L. ill1 M. KIapisch, Schwab. A. Zigler, H. Zmora and S. Jackel, Phys. Lett. 79A (1980) 67. C. Bauche-Arnoult, E. Luc-Koenig and J.-F. Wyart, Nucl. PI Instr. and Meth. B31 (1988) 153. [I31 J.H. Scofield, Phys. Rev. A9 (1974) 1041. P41 M.H. Chen, Phys. Rev. A31 (1985) 1449; private communication (1989). D. Dewitt, M.W. Clark, R. Schuch, CL. P51 D. Schneider, Cocke, R. Schmieder, K.J. Reed, M.H. Chen, R.E. Marrs, M. Levine and R. Fortner, Phys. Rev. A42 (1990) 3889. D.A. Knapp [I61 M.A. Levine, R.E. Marrs, J.R. Henderson, and M.B. Schneider, Phys. Scripta T22 (1988) 157.
I. ATOMIC/MOLECULAR
PHYSICS
Nuclear Instruments and Methods in Physics Research B56/57 (1991) 227-231 North-Holland
Ion trap measurement of V4+ X-ray transition spectra N.K. Del Grande, and J.K. Swenson
P. Beiersdorfer,
J.R. Henderson,
A.L. Osterheld,
J.H. Scofield
University of California, Lawrence Luxrmore National Laboratov, Overmore, CA 94550, USA
Highly-charged uranium ions with a dominant nickel-like component (U@+ ) were produced using the electron beam ion trap (EBIT) with an electron bombardment energy of 7.4 keV. A comparison of the measured N = 4 to n = 3 X-ray transition spectra with calculations for U@+ gave excellent qualitative agreement. The low-energy region of the 4-3 spectrum for the Ni-like ions was characterized by a strong electric quadrupole 4s-3d transition, about as large as the leading dipole 4f-3d transition, which tagged the abundance of U64f tons. High resolution spectroscopy was used to measure 4f-3d transition energies for ten charge states: U60+-U69+ excited by 6.4-8.9 keV electrons. The ionization balance for 8.9 keV electron excitation was mostly from five charge m qualitative agreement with a separate analysis of extracted ions. states, U64+-U68+,
ion trap studies have focused on L-shell X-ray transitions for neon-like ions [l-3] and K-shell X-ray transitions for helium-like ions [4,5]. We report the first use of an ion trap to study M-shell X-ray transitions for nickel-like ions. Previous studies of n = 4 to n = 3 X-ray
1. Introduction The electron beam ion trap (EBIT) is proving to be a valuable source for studying the spectroscopy of highly charged ions in the electron-ion interactions. Previous Table 1 Measured and calculated 3d,,,-4f,,, (A) and 3d s,,-4f,,, the experimental uncertainty in determining line energies.
(B) X-ray line energies
Transition
Charge state
Designation
EBIT exp. a
(r exp.
A A
60t 61+
Ge-like Ga-like
3621.6 3647.7
0.5 0.8
A A A A A
62f 63+ 64+ 65+ 66+
Zn-like Cu-like Ni-like Co-like Fe-hke
3667.6 3686.9 3705.5 3762.5 3814.7
0.7 0.4 0.4 0.6 1.0
B B B B B B B B B B
60+ 61f 62f 63+ 64+ 65+ 66t 67+ 68+ 69+
Ge-like Ga-like Zn-like Cu-like Ni-like Co-like Fe-like Mn-like Cr-like V-like
3194.4 3814.6 3835.7 3854.7 3873.5 3935.7 3996.1 4055.8 4117.0 4182.4
0.3 0.7 0.3 0.5 0.2 0.4 0.5 0.6 1.1 1.2
in eV for uranium
Nova exp. b
GRASP talc. ’
HULLAC talc. d
3703
3687.3 3705.5 3761.1
3687.3 3706.8 3760.8
3870
3855.3 3873.5 3934.2
3856.4 3876.0 3936.8
a This measurement uses energies relative to the GRASP value for U64’. b Nova laser measurement; R.L. Kauffman, LLNL, private communication (1990). ’ Based on relativistic Hartree Fock code by I.P. Grant and co-workers implemented LLNL, private communication (1989). d Based on Hebrew Umversity codes by M. Klapisch and A. Bar-Shalom. e Based on the unresolved transition array (UTA) formalism and relativistic parametric Nucl. Instr. and Meth. B31 (1988) 153. 0168-583X/91/$03.50
0 1991 - Elsevler Science Pubhshers
ions U60+-U69+.
B.V. (North-Holland)
at LLNL
potential
by K.T. Cheng
method
0 represents
UTA calce
3671.3 3692.1 3709.8
3827.8 3849.1 3867.2
and M.H.
of C. Bauch-Amoult
I. ATOMIC/MOLECULAR
Chen;
et al.,
PHYSICS
228
N.K. Del Grande / Ion trap measurements of Uih4+
transitions for near nickel-like ions have been conducted using tokamaks, vacuum sparks, or laser-produced plasma sources [6-81. We have made measurements both with lower resolution Si(Li) detectors and with higher resolution Bragg crystal spectrometers to tag the abundance of nickel-like uranium with E2 transitions and to study the near nickel-like uranium ionization balance. Our study represents the first measurement of the 4f-3d transition energies for a series of near nickel-like (U64+) uranium ions: U60+-U69t, with the exception of the unpublished measurement for U64-c taken with the Nova laser [9]. We compare our results with this measurement and with calculations [lo-141. Further studies were conducted to determine the ionization balance for trapped ions within EBIT, which can be compared to the ion distribution reported for the extracted ions measured at an excitation energy near 9 keV [15].
2. Experimental The electron beam ion trap, described in detail elsewhere [1,16], was used to trap, ionize and excite uranium ions for our spectroscopic measurements. Ions were injected into the trap from a uranium metal vapor arc. The ion density was about lo9 cme3 and the electron density was approximately 5 x lOI cme3. Measurements were made of X-ray spectra using a windowless Si(Li) detector at one of the beam ports, a Ge detector at a second port, and a Bragg-diffraction spectrometer consisting of a flat Ge crystal and a position-sensitive proportional counter filled with a Xe-CH, gas mixture at a third port. The spectrometer was calibrated (i.e. the energy centroid and dispersion) using theoretical values for two Ni-like uranium lines (see table 1). In addition, ions were extracted from the trap and were mass and charge analyzed for comparison with the results obtained with X-ray spectroscopy [15].
3d 3,2-4f5,2 transitions.
(3873.5 ev);
and 3p,,,-4d,,,
(4152.0 eV)
4. Discussion of results An overview of dominantly nickel-like uranium 4-3 transitions measured with a Si(Li) detector is shown in fig. 1. A comparison of the measured spectrum with X-ray emission line intensities from calculations using the HULLAC codes gave excellent qualitative agreement. We note in particular the strong electric quadrupole 4s-3d transition. This E2 transition is a unique feature in nickel-like ions. It results from decay of the second lowest excited level in U64+, and is mostly fed by radiative cascades, as indicated in fig. 2. In contrast, the corresponding excited levels in copper-like U63’ and cobalt-like U6’+ decay by El intrashell transitions. The 4s-3d transition at 2.692 keV brackets the low energy side of the 4-3 transitions. Based on our empirical results, it appears to tag the charge state abundance of nickel-like U64’ ions. It is strongest at electron excitation energies near the ionization energy of U64+ (7.393 keV) where the distribution inferred from
600 *
“64+
measurement
I
u64+
,
calculation
1
r
A
3. Theory Several relativistic atomic configuration calculations for M-shell X-ray line energies are available for comparison with experimental measurements. Among the calculations considered were the relativistic Hartree Slater code [13], the Hebrew University-Lawrence Livermore Atomic Codes (HULLAC) developed by Klapisch and Bar-Shalom [ll], and the GRASP relativistic Hartree Fock code of Grant and co-workers [lo]. Further comparisons were made with published predictions for U62+, U63+ and U641- by Bauche-Arnoult and co-workers [12]. Our measurements were made relative to the GRASP code line energies for U64+ 3d,,,-4f,,, (3705.5 eV);
‘6 photon energy in keV Fig. 1. Comparison of X-ray spectrum measured on EBIT with a Si(Li) detector at a beam energy of E = 7.4 keV with calculated X-ray intensities from the HULLAC codes.
N. K. Del Grande / Ion trap measurements of
3p%d94p+ 3p63d84s 3p53d”+ 3p53d84s2
t not rn”Ch
e2
6 _-EL 3p63dg
Fig. 2. Decay schemes for highly charged uranium ions with copper-like,nickel-like and cobalt-like charge states.
crystal spectrometer measurements is approximately 59% nickel-like, 28% copper-like and 11% zinc-like uranium ions. It decreases in rough proportion to the percentage of U 64+ ions for a higher electron excitation energy at 8.89 keV where there are five dominant charge states: U64+, U65+, U66+, U67+ and U6’+. Another way to tag nickel-like uranium is by looking at radiative recombination spectra at the onset of the opening of a new shell. In this case, we used a Ge
lJ64t
229
detector, which is more efficient at higher energies than the Si(Li) detector, to observe radiative recombination from U65+ onto the n = 3 shell for U64+. Understanding the ionization balance when there are several charge states more ionized than U64t is a significant problem which required higher resolution than obtained with the Si(Li) detector used for fig. 1. Using the Bragg crystal spectrometer, we measured the 3d-4f X-ray transitions with a FWHM of about 5 eV. This was sufficient to resolve transitions from different charge states. The relative ion abundances could thus be inferred from the relative X-ray line intensities. The high resolution spectra shown in fig. 3 resolve U60+-U64+ ions at 6.40 keV U61+-U64+ ions at 7.19 keV, U63+-U 67t ions at 8.09’keV and U63’-U69f ions at 8.89 keV electron excitation energies. In fig. 4, we compare an X-ray spectrum taken at a beam energy of 8.9 keV with a measurement of the charge distribution of uranium ions extracted from EBIT. There are remarkable similarities between the two measurements,
64+ 7.19 keV
UJ 5 8
50 0 120
photon energy (keV) 6%”
U 3d-4f
1
67+ 64+ 8 09 keV I
I
80 40
65
63
magnet current (A)
photon energy (keV) Fig. 3. High resolution spectra showing the 3d-4f X-ray lines for ten charge states: U60+-U69t produced at electron excitation energiesvarying from 6.40 to 8.89 keV.
Fig. 4. Comparison of X-ray line intensities from near nickellike uranium ions trapped in EBIT (as shown in fig. 3) with charge distribution of extracted ions based on mass and charge analysis (from ref. [15]). I. ATOMIC/MOLECULAR PHYSICS
N.K. Del Grande / Ion trap measurements
230
Table 2 Measured and calculated 3d-4f splitting of lines: 3d,,,-4f,,, Charge state
Designation
EBIT exp.
(r exp.
60+ 61+ 62+ 63+ 64+ 65+ 66+
Ge-like Ga-like &r-like &-like Ni-like Co-like Fe-like
166.8 166.9 168.1 167.8 168.0 173.2 181.4
0.6 1.1 0.8 0.6 0.4 0.7 1.1
which suggest the possibility the future.
of detailed
comparisons
and 3d,,,-4f,,,
in
5. Summary and conclusion By way of summary, table 1 gives the measured and calculated 3d,,,-4f,,, and 3d,,,-4f,,, X-ray line energies for uranium ions U 60+-U6g+. The measmements are a composite of between one and two measurements at several excitation energies ranging from 6.4 to 8.9 keV. Since the measured lines had a FWHM of about 5 eV, we were unable to resolve the two C&like lines whose predicted excitation rates roughly add up to the excitation rate of the Ni-like line, but whose spacing is 0.3 or 0.4 eV. Similarly, we need better resolution to test the effect of configuration interaction in mixing the energy levels and line strengths among the Co-like lines.
Designation
60+ 61f 62+ 63+
Ge-like Ga-like Zn-Iike Cu-like
Average 0, - I 65+ 66-l67+ 68+ 69+ Average on-1
Co-like Fe-like Mn-like Cr-like V-like
EBIT exp.
in eV for uranium ions U60+-U66+.
Nova exp.
GRASP talc.
HULLAC talc.
167
168.0 168.0 773.1
169.1 169.2 176.0
UTA talc.
156.5 157.0 151.4
The GRASP and HULLAC calculations shown in tables 1-3 represent a weighted average based on the respective excitation rates. The UTA calculations represent a centroid of all the transitions that would be present in a dense plasma and include the effect of transitions not observed in EBIT. Table 2 compares the measured splitting of the 3d-4f transitions with calculations, whereas table 3 compares the measured and calculated energy shift per charge state for ions less ionized and more ionized than U64t. The EBIT experiment provides uranium ion X-ray line energies and energy shifts per charge state in good agreement with the GRASP and HULLAC calculations for U63c and U6’+. The behavior of U66+-U6g+ ions, which have a smaller energy shift per charge state for the 3d 5,2-4f7,2 transition than for the 3d,,,-4fs,, transition, may be indicative of complexities from energy level mixing. Spectra from these configurations become much more complex as the 3d shell opens up. Measure-
Table 3 Measured and calculated energy shift per charge state in eV for 3d,,,-4f,,, the line energies of nickel-lie uranium ions U64+. Charge state
of lJ64 ’
(A) and 3d,,,-
4f,,,
(B) X-ray line energies relative to
GRASP talc.
HULLAC talc.
UTA caIc.
A
B
A
B
A
B
A
B
-19.5 - 19.3 - 19.0 - 18.6
- 19.8 - 19.6 -18.9 -18.8
-18.2
- 18.2
- 19.5
- 19.6
- 19.2 - 17.7
- 19.7 -18.1
- 19.1 0.4
-19.3 0.5
- 18.4 1.1
-18.9 1.1
57.0 54.6
62.2 61.3 60.8 60.9 61.8
55.5 1.7
61.4 0.6
55.6
60.7
54.0
60.8
N K. Del Grande / Ion trap measurements of lJh4+
ments with higher energy resolution ter understand these complexities.
are needed
to bet-
Acknowledgements We are grateful for atomic physics support from W. Goldstein and M. Chen; for experimental work and useful conversations with M. Schneider, C. Bennett, D. Knapp, D. Schneider, M. Clark, and D. Dewitt; for technical support from D. Nelson and E. Magee; and for support and encouragement from R. Marrs, R. Fortner and A. Hazi. This work was performed at the Lawrence Livermore National Laboratory under the auspices of the U.S. Department of Energy under contract No. W-7405ENG-48.
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I. ATOMIC/MOLECULAR
PHYSICS