RADIATIVE LIFETIMES OF HIGHLY IONIZED AND FOIL-EXCITED Al.

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RADIATIVE LIFETIMES OF HIGHLY IONIZED AND FOIL-EXCITED Al.

B. Denne, D. Pegg, K. Ishii, E. Alvarez, R. Hallin, J. Pihl, R. Sjödin

To cite this version:

B. Denne, D. Pegg, K. Ishii, E. Alvarez, R. Hallin, et al.. RADIATIVE LIFETIMES OF HIGHLY

IONIZED AND FOIL-EXCITED Al.. Journal de Physique Colloques, 1979, 40 (C1), pp.C1-183-C1-

185. �10.1051/jphyscol:1979136�. �jpa-00218416�

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JOURNAL DE PHYSIQUE Colloque C 1, supplbment utr n

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2, Tome 40, fbvrier 1979, page

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183

RADIATIVE LIFETIMES OF HIGHLY IONIZED AND FOIL-EXCITED Al.

Department of Physics, University of Lund, S-223 62 Lund, Sweden E. ALVAREZ, R. HALLIN, J. PIHL, R. SJ6DIN

Department of Physics, University of Uppsala, S-751 21 Uppsala, Sweden + Permanent address: University of Tennessee, Knoxville, Tenn., U.S.A.

r Permanent address: Department of Engineering Science, Kyoto University, Kyoto 606, Japan.

~ d

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Des spectres d'atomes d'aluminium tr6s ionis6s par une cible de carbone ont et6 enre- ~ ~ ~ d gistrls dans le domaine spectral de 300 1 1000 A, 2 10, 20, 30 et 45 MeV d16nergie de

faisceau, en utilisant l'accdllrateur tandem d'uppsala. Les durles de vie de quelques niveaux bas de l'aluminium .3 3-, 4-, 5- electrons ont ltl mesurlesavec la m6thode faisceau- cible. Les forces d'oscillateurs ont ltl calculdes et compar6es avec les valeurs thdo- riques.

Abstract

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Foil-excited spectra of multiply charged A1 ions in the spectral range s300- 1000 A have been recorded at 10, 20, 30 and 45 MeV beam energies using the Uppsala tandem accelerator. Radiative lifetimes of some of the low-lying levels in 3-, 4- and 5-electron A1 were measured using the beam-foil time of flight method. Oscillator strengths have been derived from the measurements and will be compared with theory.

INTRODUCTION

Oscillator strengths for allowed transitions between low-lying levels of multiply charged ions are of interest for the study of high tempera- ture plasmas C1,23. In this work we have studied some An=O transitions in 3-, 4- and 5-electron A1 using the beam foil method. The experiment was per- formed at the Tandemaccelerator Laboratory in Upp- sala.

EXPERIMENTAL ARRANGEMENT

Fig. 1 shows the experimental arrangement. The monochromator used in the present work is a 1 m

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instrument of the Seya-Namioka type, desig- ned and built at the Uppsala laboratory. The pho-

tons were detected with a channeltron (Eendix/~ul- lard). In order to move the grating for spectral scans as well as translating the foil for lifetime measurement's, stepping motors were used, each step corresponding to a preset value of integrated beam current, collected in a Faraday cup behind the foil.

RESULTS

Spectral scans in the wavelength region

Fig. 1

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The experimental arrangement. The vaccum- monochromator was used in the present measurements.

%300-1000 A were made at four different beam energies

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10, 20, 30 and 45 MeV. Using the tabulations of Kelly and Palumbo C3 1 most of the lines seen in these spectra were identified with transitions in A1 IX-A1 XI. Some hydrogenic transitions were also

seen. They were classified using the simplified formula T = ~<'/n*.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979136

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JOURNAL DE PHYSIQUE

For the lifetime measurements a beam energy of 20 MeV was chosen. At this energy the transitions of interest in this study were strong- est and least affected by blends with transitions belonging to other charge states. Also, at the

1 2

higher cnergies was, for instance, the 2s2p PI-2p ID2 transition in A1 X (670.1 A) affected by the second order line of the hydrogenlike transition n=

4-5 in A1 XI, 334 A. Fig. 2 shows the spectrum at 20 MeV with the wavelengths for the investigated transitions indicated.

KIIL-EXCITED S P E C T W FRMl 2 0 k V Y r n E A M I N SPECTRAL REMOH -m-low&.

7

Fig. 2

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Spectrum of foil-excited A1 at 20 MeV beam energy.

The results of the lifetime measurements are compiled in Table I. Oscillator strengths, calculated from the measured lifetimes, are also given.

Theoretical oscillator strengths and lifetimes are given for comparison.

In A1 XI the lifetimes for the 2p L~312- and 2p 2 levels were determined. The decay curves are shown in Fig. 3. The lifetimes obtained are 1.19f0.05 ns for the 2p

level

and 1.35t0.06 ns for the 2p Pl12-level. These lifetimes correspond 2 to oscillator strengths of 0.076f0.003 and 0.036i 0.002. Our f-values for the doublet are compared and agrees well with the theoretical values given by Kim and Desclaux C41, Armstrong, Fielder and Lin

153, further with the values from Safronova et al.

1.C61; calckated from the multiplet oscillator strength, and also with the f-values given in Atomic Transition Probabilities, Vol. 11 C73.

in A1 X the transitions 2sZp 3~>2p2 3 ~ 2 , 401 A and 2s2p PI-2p2 ID2, 670.1 1 A were studied.

200

0 10 DISTANCE 20 F R X FOIL 30 ( M M I Lo 50

Fig. 3

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Intensity decay curves for the 2p 'P- levels in A1 XI.

3 0 3 3 o The 401 A-line is a mixture of the P ₂

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^{P and P}₂ ₁

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3~ transitions, 401.2

A

ar2 400.5

A

respectively.

1

The lifetime for the upper level is 0.19f0.03 ns, which corresponds to an f-value of 0.047f0.007. Our experimental value agrees well with theory 17,8,91.

The lifetime measured for the 2p 2 1 D2- level is 1.03+0.05 ns, which corresponds to an f - value of 0.109+0.005. Theoretical f-values have been obtained from the work of Muhlethaler and Nuss- baumer C91 by interpolation, of Victorov and Safro- nova C81 and also from Atomic Transition Probabili- ties, Vol. I1 C73. Our experimental value agrees very well with the theoretical values of refs. C83 and C91.

In A1 IX, finally, the transitions 2s2p 2 2 P ~ I Z - Z P ~ 2p712,~,2* 438

A

(mean wavelength of the two transitions) and 2s2p PlI2-2p3 'DO 3/2, 602.2 A, were investigated. Each one of the decay curves were decomposed into two exponentials, one short- lived component and one long-lived. The long-lived components can not be due to cascades from the levels within the L-shell; they are probably due to blends. The extracted lifetimes are 0.093i0.009 ns for the 2p3 2~o-levels and 0.19f0.02 ns for the 2p 3

-level, respectively. Since the

zp3

^{2 ~ 0 -}^and

Do-levels also have other decay channels than the one studied, it is not possible to calculate the oscillator strengths of the transitions. There- fore the lifetimes of the two levels are compared

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TABLE I. Radiative Lifetimes and Oscillator Strengths of Some Levels and Transitions in Mu1 tiply-Charged A1

.

Wavelength Lifetime of upper levels (ns) Oscillator Strength

Ion Transit ions ( A ) Present Theory Present Theory

a Kim et al. 141. Armstrong et al. C51. Safronova et al. C61. Atomic Trans. Prob. C71.

Victorov et al. 181. Miihlethaler et al. C91. Dankwort et al. [lo].

with theoretical lifetimes only. From the work of Dankwort and Trefftz C101 the theoretical lifetimes for 2p3 2 ~ 0 and 2p3 2 ~ 0 are obtained as 0.088 ns a d 0.21' ns respectively. Atomic Transition Probabili- ties, Vol. I1 171 gives the values 0.077 ns and 0.19 ns respectively.

CONCLUSION

On the whole, the agreement between our values and theory are fairly good; in some of the cases excellent.

3 3

We also observed the 2s S1-2p P0,1,2- transitions in He-like A1 at 35 MeV and higher beam

Ermolaev C111 give the following predicted wave-

3 3 3 3

lengths: 2s S1-2p P2, 899.18 A, 2s Sl-2p P1, 943.20 A and 2s Sl-2p '3 pO 953.93 A. Kelly and Pa- lumbo 131 give a predicted wavelength for the transition 2s 3~1-2p P2 of 847.4 3

A,

more than 50 A lower than our value. Because of the lack of nearby lines with well-determined wavelengths we have only been able to determine the relative spacings between the lines. These spacings agree with the wavelength differences obtained from the calculated values.

This work was supported by the National Swedish Board for Energy Source Development (NE) and the Swedish Natural Science Research Council (NFR).

energies. Our calculations and calculations by

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