1358 J. Opt. Soc. Am. B/Vol. 4, No. 9/September 1987
Energy levels of neutral and singly ionized berkelium,2 4 9Bk I and 249Bk II
Earl F. Worden
Lawrence Livermore National Laboratory, University of California, Livermore, California 94550
John G. Conway
Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
Jean Blaise
Centre National de la Recherche Scientifique, Laboratoire Aim6 Cotton, 91404 Orsay, France
Received May 14,1987; accepted June 8,1987
Energy-level analyses of the observed emission spectrum of berkelium have yielded 179 odd and 186 even levels ofneutral berkelium, Bk I, and 42 odd and 117 even levels of singly ionized berkelium, Bk II. The levels are tabulatedwith the J value, the g value, the configuration and hyperfine constants A and B, and the width given for many of thelevels. The ground states of Bki and Bk II are [Rn]5f97s2 6H5 /2 and [Rn]5f97s 7H;, respectively. A table lists thelowest level of each identified electronic configuration of Bk I and Bk II.
INTRODUCTION
Berkelium (Bk) is element number 97 in the periodic table.It was discovered in December of 1949 by S. G. Thompson,A. Ghiorso, and G. T. Seaborg by means of a cyclotronbombardment of 241Am with helium ions.' The first reportof the observation of the berkelium spectrum was by R. G.Gutmacher, E. K. Hulet, and R. Lougheed in 1965.2 Obser-vation of the hyperfine structure in high-resolution emissionspectra of 249Bk and confirmation of the nuclear spin of2491k as 7/2 were reported in 1967.3 Subsequently we re-ported the emission lines observed in the infrared 4 and thevisible-ultraviolet 5 as well as energy levels for neutral berke-lium, 49Bk I, and singly ionized berkelium, 4 9Bk II. Para-metric studies of the 5f97S2 and 5f86d7s2 configurations ofBk I and of the 5f 97s and 5f 96d configurations of Bk II havebeen made.67 We report here an extended list of energylevels of 249 Bk I and 249Bk II.
EXPERIMENT
The experimental conditions to obtain the two sets of emis-sion spectra used to find the levels reported here are coveredin the original papers.3 -5 All spectra were observed using249Bk. Detailed experimental information may be found inRef. 8. Briefly, the visible and ultraviolet lines were photo-graphed at Lawrence Livermore National Laboratory(LLNL) on a 3.4-m Ebert spectrograph with the grating athigh angles (high orders) near 60° and 300. The infrareddata were obtained with a Fourier-transform spectrometerat the Laboratoire Aim6 Cotton (LAC). Both works usedelectrodeless discharge lamps (EDL's) containing of the or-der of 30 to 100 Alg of Bk as the iodide. Zeeman spectra wereobtained using the 9.15-m Paschen-Runge spectrograph
and a magnetic field of 2.4 T at the Argonne National Lab-oratory (ANL).
RESULTS
As a result of the nuclear spin of 7/2 and the relatively largemagnetic moment, A = +2.0 i 0.4 nuclear magnetons of24 9 Bk,7,9 most lines show flag patterns of 8 diagonal compo-
nents and many with as many as 14 off-diagonal components(for transitions between levels with J _ 7/2). Except for lowJ values, the center of gravity of the pattern is close to thefourth component, which was taken as the wave number ofthe line. The widths of some Bk II hyperfine patterns wereobserved to be as large as 6 to 8 cm-'. Most of the lines havewidths of the order of 1 to 4 cm-'. This makes it difficult tomeasure Zeeman structures, particularly in the Bk II spec-trum. For this reason, the analyses of the Bk I and Bk IIspectra have been carried out mainly with the aid of thehyperfine structure. Figures 1-3 illustrate how hyperfinestructure can serve to confirm levels found by constant sumor difference procedures or in some cases to find new levelsand help to assign J values. Figures 1 and 2 are tracings ofthe Bk I lines at 11 204.260 and 11 024.046 cm-', respective-ly, taken on the Fourier-transform spectrometer. The pat-tern in Fig. 1 is characteristic of a transition between levelswith J's differing by one, while the pattern in Fig. 2 is for atransition between levels with the same J. The frequenciesof the resolved components of these lines permit the deter-mination of the hyperfine structure of the levels involved inthese transitions. Here one of the levels is common to bothtransitions, as shown in Fig. 3.
No isotope-shift experiments were possible because onlyone isotope was available in sufficient quantities to make
Vol. 4, No. 9/September 1987/J. Opt. Soc. Am. B 1359
10-11 9-10 8-9 7-8 6-7 5-6 4-5 3-4
10-10 9-9 8-8 7-7 6-6 5-5 4-4
EDL's. For this reason, the interpretation of the levels isbased on parametric studies for the lower configurations 6 ofeach spectrum and on empirical considerations such as thestrengths of transitions from levels without definite configu-ration assignment to the levels that already had configura-tion assignment. Land6 g values, when available, helped toestablish energy levels and in their interpretation. Usingthese methods, we have been able to identify nine configura-tions in Bk I and six configurations in Bk II. Table 1 lists thelowest levels of these 15 identified configurations along withthe hyperfine widths and designations. In Bk I we haveidentified levels belonging to all nine configurations expect-ed from Brewer's predictions to be found below 35 000cm-'. Bk II levels that belong to six of the eight configura-tions expected" below 37 000 cm-' have been identified.
34114, J = 13/2
11202.02 11204.02 11206.02
Wave number (cm-1 )Fig. 1. Tracing of the 249Bk line at 11 204.260 cm-' taken on theFourier-transform spectrometer at Laboratoire Aime Cotton. Thetransition is from the odd level 34 114.485 cm-', 5f9(6R 5/2 )7s8s(3S,), J = 13/2, to the even level 22 910.225 cm-', 5f
9(6i 51 2 )
7s7p(3P;), J = 15/2. The F values (F = I + J) are shown across thetop of the figure.
10-10 9-9 8-8 7-7 6-6 5-5 4-4 3-3
9-10 8-9 7-8 6-7 5-6 4-5 3-4
10-9 9-8 8-7 7-6 6-5 5-4 4-311
10
23090, J = 13/2
22910, J = 15/2
11024.02
Wave number (cm- 1)
Fig. 2. Fourier-transform spectrometer tracing of the 249Bk line at11 024.046 cm-1 . The transition is from the odd level 34 114.485cm-', 5f9(6H~,12)7s8s(3S$), J = 13/2, to the even 23 090.450 cm',5f 9(6H, 1 92)7s7p(3P;), J = 13/2. The same upper level as in Fig. 1 isinvolved. The F values are shown across the top of the figure.
I I I 111111 I1I 1 l I I I1 III IIIFig. 3. Energy-level diagram of transitions 11 204.260 and11 024.046 cm'1 shown in Figs. 1 and 2. The upper level is commonto both transitions and has a sign opposite that of the two lowerlevels. The number beside each hyperfine level indicates the Fvalue.
3-4
-5L 67
8
10
10
9
8
7
6
5
4
3
-
Worden et al.
I
1360 J. Opt. Soc. Am. B/Vol. 4, No. 9/September 1987
Table 1. Lowest Levels of the Identified Configurations of Neutral and Singly Ionized Berkelium, 249 Bk I and 249Bk iI
Level A B Width(cm-') J g Configuration (mK) (mK) (mK)
The known energy levels of Bk I and Bk II are listed inTables 2-5. In Tables 1-5, column 1 is the energy of thelevel in inverse centimeters, column 2 the J value, and col-umn 3 the Land6 g factor. The configuration designation is
given in column 4 and follows the notation convention usedin Ref. 12. Columns 5 and 6 contain the A and B hyperfinevalues4 and column 7 the overall width of the level in milli-kaysers, where 1 mK = 10-3 cm-'. Energy levels given to
1368 J. Opt. Soc. Am. B/Vol. 4, No. 9/September 1987
three significant figures (except those ending in 0 or 5) areuncertain to +0.003 cm-', and those ending in 0 or 5 areuncertain to +0.01 cm-'. Levels given to two significantfigures have uncertainties of +0.02 cm-' or more. Land6 gvalues with three significant figures have an uncertainty of+0.01 cm'1, while those given to two figures are uncertain by+0.03 cm-1 or more.
Table 2 lists 179 odd levels of Bk I. One hundred seven ofthese levels have been assigned to the odd configurationslisted in Table 1. Table 3 lists the known information forthe 186 Bk I even levels. There are 88 even levels assigned tothe even configurations listed in Table 1. Tables 4 and 5 listthe information for the 42 Bk II odd levels and 117 Bk II evenlevels.
CONCLUSIONS
We have identified 15 electronic configurations in Bk I and IIand have determined the lowest level of each. We havefound 385 levels of Bk I and 159 levels of Bk II. For Bk I 53%of the observed levels have been assigned to configurations,and for Bk II 35% have been assigned. The number of levelsfound represents a small fraction of the levels expected forBk I and II. In order for the analysis to progress further itwill be necessary to observe the spectrum again to increasethe total number of lines. It is especially important toreinvestigate the visible-ultraviolet region, taking advan-tage of the increased precision available with modern Fouri-er-transform spectrometers.
ACKNOWLEDGMENTS
We want to thank Mark Fred for the use of the equipment atthe ANL and Ron Lougheed and E. K. Hulet (LLNL) for thepreparation of the pure sample of 249Bk. We also thankPaul Linus (LLNL) for handling the radioactive samplesand R. G. Gutmacher and M. Jepson (LLNL) for help withthe experimental work. Our thanks to P. Camus (LAC) forderiving the hyperfine values.
This research was supported by the U.S. Department ofEnergy under contract W-7405-ENG-48 at the LLNL, by
the Director, Office of Energy Research, Office of BasicEnergy Sciences, Chemical Sciences Division, under con-tract DE-AC03-76SF00098 at the Lawrence Berkeley Lab-oratory, and by the Centre National de la Recherche Scienti-fique at the Laboratoire Aim6 Cotton, Orsay, France. JeanBlaise wishes to acknowledge a grant from NATO that madepossible a visit to the Lawrence Berkeley Laboratory.
REFERENCES
1. S. G. Thompson, A. Ghiorso, and G. T. Seaborg, "Element 97,"Phys. Rev. 77, 838-839 (1955).
2. R. G. Gutmacher, E. K. Hulet, and R. Lougheed, "Spark spec-trum of berkelium," J. Opt. Soc. Am. 55, 1029-1030 (1965).
3. E. F. Worden, E. K. Hulet, R. Lougheed, and J. G. Conway,"Nuclear spin of 249Bk from the hyperfine structure in its emis-sion spectrum," J. Opt. Soc. Am. 57, 550 (1967).
4. J. G. Conway, E. F. Worden, J. Blaise, P. Camus, and J. Verges,"The i.r. spectrum of berkelium-249," Spectrochim. Acta 32B,101-106 (1977).
5. E. F. Worden and J. G. Conway, "The emission spectrum ofberkelium," At. Data Nuclear Data Tables 22, 329-366 (1979).
6. J. Blaise, J. F. Wyart, J. G. Conway, and E. F. Worden, "Gener-alized parametric study of 5p, and 5p7s configurations," Phys.Scr. 22, 224-230 (1980).
7. J. Blaise, P. Luc, J. Verges, J. F. Wyart, J. G. Conway, and E. F.Worden, "Term analysis of the spectra of neutral (Bk ) andsingly-ionized berkelium (Bk II)," presented at the TwelfthConference of the European Group Atomic Spectroscopy, Pisa,Italy, September 2-5,1980 (Europhys. Conf. Abstr. 4E, abstract3).
8. E. F. Worden and J. G. Conway, "Energy levels of the firstspectrum of curium," J. Opt. Soc. Am. 66, 109-121 (1976).
9. L. A. Boatner, R. W. Reynolds, C. F. Finch, and M. M. Abraham,"Electron paramagnetic resonance of 249Bk 4+ in ThO4 singlecrystals," Phys. Lett. 42, 93-94 (1972); V. S. Shirley and C. M.Lederer, "Table of nuclear moments," LBL-3450 (LawrenceBerkeley Laboratory, Berkeley, Calif., 1974).
10. L. Brewer, "Energies of the electronic configurations of thelanthanide and actinide neutral atoms," J. Opt. Soc. Am. 61,1101-1111 (1971).
11. L. Brewer, "Energies of the electronic configurations of thesingly, doubly and triply ionized lanthanides and actinides," J.Opt. Soc. Am. 61, 1666-1682 (1971).
12. W. C. Martin, R. Zalubas, and L. Hagan, Atomic Energy Lev-els-The Rare Earth Elements, NSRDS-NBS 60 (U.S. Govern-ment Printing Office, Washington, D.C., 1978).
