A new satellite in the L-X-ray emission spectrum of erbium-68

ANAND N. NIGAM A N D RAKESH B. MATHUR X-Rrip Lrrborotories. Depo~.rnlenr of Pllysics, University of Jodl~pirr, Jodllpiir, Indiri

Received July 30, 1975l

Using a 40 cm curved mica crystal spectrograph of the transmission (Cauchois) type, a new satellite LaS at h = 1769.0 xu has been reported for the first time in the L emission spectrum of erbium. On the basis of Wentzel's multiple ionization theory, the satellite has been assigned to the transition L 3 M L +

M I M s . The presence of the satellites a", p,', p,', and y , ' , reported by earlier workers, has been con- firmed. The assignnient of the transitions to these satellites by Nigam er cil. has been critically examined and finally these have been assigned to the transitions L3M, + M,M,, L,M, + M,M4, L3M5 +

M S N s , and L,M, + M,N4 respectively.

En utilisant Lln spectrographe a transmission (type Cauchois), a cristal de mica courbe de 40 cm, on a observe pour la premiere fois un nouveau satellite La5, situe a h = 1769.0 xu, dans le spectre d'ernis- sion L de I'erbium. En se basant sur la thkorie d'ionisation niultiple de Wentzel, on a identifie le satel- lite avec la transition L 3 M L + M l M 5 . La presence des satellites a", PI' , p,' et yl ' , rapportts ante- rieurement par d'autres chercheurs, a ete confirmee. La designation par Nigam el a/. des transitions correspondait h ces satellites a fait I'objet d'un examen critique, et on a finalement conclu que ces transitions etaient L3M2 + M,M5, L z M l + MIM,, L 3 M s + M5N5 et LZM4 + M4N4 respective- rnent.

[Traduit par le journal] Can. J. Phys., 54,2193 (1976)

Introduction High frequency satellites in X-ray emission

spectra have now been known for a long time. Cauchois and Hulubei (1947) have compiled the experimental data on satellites. However, most of these satellites have not been assigned to specific transitions on the basis of the generally accepted Wentzel's theory of their origin. In re- cent years Kapoor et al. (1969) made assignments for ax and a' satellites in some rare-earth ele- ments. Nigam and Mathur (1972) have com- pleted this task in a systematic manner.

Satellites in the L emission spectrum of 6 8 ~ r have been reported by several workers (1947). A survey of the literature showed that several prominent satellites were not reported in this spectrum. We report in this paper the results of our investigations on 68Er.

Experimental Procedure The experimental set-up was similar to the one

described earlier (Nigarn et ul. 1968). However, the copper anticathode was replaced by an iron anticathode and in place of tungsten, a tantalum filament was used. Spectrographically standard- ized Er,O, powder (supplied by M/s Johnson Matthey & Co., London) was used for preparing

'Revision received June 21, 1976.

the erbium target. The hot cathode demountable X-ray tube was operated at 20 kV, 4 mA, and the exposure time ranged from 15 to 30 h. A 40 cm curved muscovite mica crystal spectrograph of the transmission (Cauchois) type, with the (100) planes of mica reflecting in the first order, was used to record the spectrum on the industrial X-ray films. The dispersion achieved was about 12 xu/mm in the region under study. Line wave- lengths were measured directly on the negatives with a Hilger Comparator of least count 0.0001 cm. Our measured values represent the mean of a large number of separate and independent mea- surements and their accuracy is 0. l xu.

Calculational Procedure for Transition Assignment

Out of the various theories proposed to ex- plain the origin of high frequency satellites in X-ray spectra, the one which has survived to date is that of Wentzel (1921). According to this theory, these satellites result from single elec- tronic transitions in atoms with 2 electrons mis- sing from the inner shells. The double-jump theory of Richtmyer (1928) which initially at- tracted attention on the basis of semi-Moseley plots for some satellites, has been discarded mainly on intensity considerations. Later on, it was found that even the semi-Moseley plots were not valid for many satellites.

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2 194 CAN. J. PHYS. VOL. 54, 1976

Druyvesteyn (1928) suggested the mode of cal- culations for energy differences in atoms with two vacancies. This is as follows: the second inner shell vacancy necessarily reduces the screening of the nuclear charge as compared to the case when this vacancy is not there. In the absence of exact calculations for screening by electrons in different levels, it was suggested that an atom with ( 2 ) protons, having two vacancies in the inner shells, may be approximately repre- sented by an atom with atomic number ( Z + 1) and possessing one vacancy. Obviously this is a crude approximation, but since energy values are available in integral steps for all these elements, this mode was followed.

For example, take the transition L,M, +

M , M , for a particular satellite. This a t once shows that the extra vacancy exists in the sub- shell M I while the transition L, + M, (La,) takes place. The energy difference will then be calculated as

where (L,), represents the energy value of the level L, in atom of atomic number Z , etc.

Results The present study has revealed, for the first

time, the existence of the satellite La, at 1769.0 xu in the spectrum of 6sEr. It has been assigned to the transition L 3 M l + M i M s . The presence of the satellites ax, PI', P2' and y ,' reported earlier in the L-spectrum of erbium has been con- firmed. These have been assigned to the transi- tions L3M2 + M2M5, L2M1 + M1M4, L,M, -t

M,N,, and L3M4 + M4N4 respectively. Table 1 summarizes our results. The new transitions, as well as those reported by previous workers have also been included for the sake of comparison.

Discussion (i) The Satellite La, (L3Ml + M,M,) ; h =

1769.0 xu The satellite La, has been reported by earlier

workers (Cauchois and Hulubei 1947) in the spectra of most of the elements with 37 5 Z 5 52. We report, for the first time, the existence of this satellite in the erbium spectrum. Taking Er La, (h = 1792.02 xu) and Fe KP, (h = 1753.04 xu) as reference lines, the measured value of the wavelength comes out t o be 1769.0 xu. Ruling out all other possibilities, this line is

t t t t t sssss 6 '49S3

- 0 - m ?w .6w6 e b b - * r - r - r - o m r - r - m m m 3 - m ' -

?=!"Y': o \ m w - m w r - t - o m r - r - m m m e m - - -

m a - N ? 6 ? ?

I ;=:a: r - m m m - ---

I G G - m r - r - o m r - m m m - - -- +%?

IEEg I - - - hhhhh 3 3 3 3 3 X X X X X

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NlGAM AND MATHUR 2 195

identified as La,, a high frequency satellite of La,. This has been assigned to the transition L 3 M l + M I M,. The calculated (h,,, = 1771.99 xu) value of the wavelength shows a fair agree- ment with the experimental value (h = 1769.0 xu). Out of the various double vacancy transi- tions, this gives the best numerical agreement (Table 2).

( i i) Tlze Satellite Lax (L3M2 + M 2 M 5 ) ; h = 1773.9 xu

We have observed the satellite Lax at 1773.9 xu. Kapoor et al. (1969) have assigned the transi- tion L3M, + M , M , to this satellite. The calcu- lated value according to their assignment is 1771.99 xu. However, we prefer to assign the transition L3M2 + M 2 M , t o this satellite, since the value (h,,, = 1774.66 xu) calculated from our assignment is in closer agreement with the ob- served value (h = 1773.9 xu) (Table 2). Further, Kapoor et al. (1969) restricted their studies to the rare earths only, whereas we have taken into con- sideration all the elements of the Periodic Table and have found that the transition suggested by the authors gives excellent matching with the experimental values of wavelengths of this satel- lite in all the elements of the Periodic Table. Not only this, we have also been able to conclude that for the elements from Z = 26 to 52, the satellite La, is also due to the transition L3M2 +

M2M5 which is assigned to the satellite Lax, re- ported in the heavier elements.

(iii) Tile Satellite LP, ' ( L 2 M , + M,M,) ; h = 1576.6 xu

Taking Er LP, (h = 1597.5 xu) and Er LP3 (h = 1558.35 xu) as reference lines the wave- length of this satellite is found to be 1576.6 xu. We have assigned the transition L 2 M , + M I M, (h,,, = 1577.40 xu) to t h ~ s satellite. The same transition has also been assigned to this satellite by earlier workers (Garg et al. 1972) (Table 3).

(io) T11e Satellite LPZ1 (L3M, + M,N,); h =

1501.5 xu The satellite observed by us at h = 1501.5 xu

has been assigned to the transition L3M, +

M5N5 (h,,, = 1501.61 xu). The transition as- signed by Garg et al. (1971) is L3M4 + M,N, (h,,, = 1501.61 xu). Although the calculated value of wavelength from both the transitions comes out to be the same in the case of erbium. it

TABLE 2. All the possible transitions for satel- lites of parent Lal (h = 1780.68 XLI)

Wavelength, Transition h (XU)

TABLE 3. All the possible transitions for satel- lites of parent L(3, (?, = 1584.09 xu)

Transition Wavelength,

h (xu)

TABLE 4. All the possible transitions for satel- lites of parent LDz (h = 1510.94 xu)

Transition Wavelength,

h (XU)

TABLE 5. All the possible transitions for the sat- ellites of parent Ly, (h = 1361.11 xu)

Wavelength, Transition A (xu)

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2196 CAN. I. PHYS.

was not so in other elements. The transition sug- gested by us is found more appropriate (Table 4) taking all the elements into account as against the assignment of Garg et a/. (1971) which con- cerns only rare earths.

(u) The Satellite Ly , ' ( L 2 M 4 -, M4N,) ; h = 1353.7 xu

We report the presence of this satellite in the spectrum of erbium at h = 1353.7 xu. We have assigned the transition L 2 M 4 -, M4N4 (h,,, = 1354.43 xu) t o it. Kapoor et al. (1970) have re- ported the existence of this satellite in the spec- trum of erbium at h = 1353.0 xu and have as- signed it to the transition L 2 M 3 -, M 3 N , (h,,, = 1352.02 xu). Our assignment is better on the same grounds as discussed in Sect. (ii) (Table 5).

VOL. 54, 1976

C ~ u c ~ o r s , Y. and H U L U B E I , H. 1947. Tables des lon- gueurs d'ondes des emission x et des discontinuites d'absorption x (Herman, Paris).

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Phys. B, 4,739. 1972. J . Phys. B , 5,2152.

KAPOOR, Q. S. , GARG, K. B . , and NIGAM, A. N . 1969. Phys. Lett. A , 30, 228.

1970. J . Phys. B . 3 , 1180. NIGAM, A. N. and MATHUR, R. B. 1972. Proc. Inter. Conf.

on Inner Shell Ionization Phenomena and its Applica- tions, Atlanta, GA (U.S. Atomic Energy Commission), p. 1698.

1974. Chem. Phys. Lett. 28,41. NIGAM, A. N.; GARG, K . B. , and KAPOOR, Q. S. 1968. J.

Phys. B , 1,492. RICHTMYER, F. K . 1928. Philos. Mag. 6 , 6 4 . SIEGBAHN, M. 1931. Spektroskopie der rontgenstrahlen

(Berlin), p. 216. WENTZEL, G. 1921. Ann. Phys. (Leipz.), 66,437.

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