Activation Analysis of Several Rare Earth Elements A Comparison with Spectrophotometric Procedures W. WAYNE MEINKE and RICHARD E. ANDERSON Chemistry Department, University o f Michigan, A n n Arbor, M i c h .
I
Research Chemic&, Inc. , Burbank, Calif. Minimum purities listed by the suppliers were 99.9% for the samarium oxide and 99.8% for the europium oxide. The solutions of dysprosium nitrate and holmium nitrate were prepared from compounds supplied by Fairmount Chemical Co., Kewark, N. J. The dysprosium oxide r a s listed by the suppliers as being 98% pure; the major impurity n-as terbium and traces of holmium and yttrium were present. The holmium oxalate was listed as being 98y0 pure with some yttrium impurity. The solutions were prepared by dissolving the oxide in nitric acid, evaporating to dryness on a steam bath, and then dissolving the residue in water.
S A previous paper ( 3 ) the authors discussed the use of a
25-mg. radium-beryllium source as an analytical tool. They have shown graphically that the factors which determine whether neutron activation analysis is feasible for any given neutron flux are: ( a ) the half life of the isotope formed, (6) t,he atomic cross wction for the formation, and ( c ) the energy of the beta particles (or gamma rays) emitted by the isotope resulting from the reaction. The following changes should be made to Figure 1 of reference ( 3 ) to eliminate gross plotting errors: ( a ) replot Te’22 a t 0.025 barns and 1.5 X lo5 minutes, (6) replot Cd1I2a t 0.0048 barns and 2.7 X I O b minutes, (c) replot Ce14*a t 0.27 barns and 4.8 X lo4 minutes, ( d ) replot I&84a t 0.057 barns and 2.6 X lo2 minutes, ( e ) replot Ga” a t 1.35 barns and 8.6 X lo2 minutes, ( f ) replot Tala1at’ 21 barns and 1.6 X lo5 minutes, ( 9 ) delete “ E U ’ ~ ~replot ’ ’ ; as E r a t 1. barn and 4.5 X 102 minutes; and ( h ) underline L u ” 5 a t 35 barns and 222 minutes. On these plot3 the positions of a number of the rare earth elements are seen to be very favorable for activation analysis. It was felt that a comparison between this activation analysis method and the well-known spectrophotometric method for analysiP of single species or mixtures of several of t.hese rare earth elements rrould be of interest. The spectrophotometric method (4-6) is based on the fact that in the visible and ultraviolet regions of the spectrum many of the rare earth ions display characteristic absorption bands. Rodden (6, 6) has prepared spectral-transniittancy and transniittancyconcentration curves of a number of t.he rare eart,h ions. [This work has recently been extended by Sloeller and Brantly (,$).I Some of these ions such a$ cerium, gadolinium, and terbium show no absorption bands over the range from 350 to 1000 mp, while others like europium possess only shallow bands. The fact that absorption bands of some of the rare earth ions also may occur in the same region of the spectrum makes it difficult. to analyze mixtures of these ions. Figure 1 shows a typical overlapping of abporption bands in the spectra of europium and samarium nitrates. The rare earth elements used in this studj- xere samarium, europium, dysprosium, and holmium. This work was designed t o study the usefulness of neutron activation analysis for these elements in certain cases where spectrophotometric determinations are difficult or impossible.
PROCEDURE
The rai e earth solutions were analyzed spectrophotonietrically by taking an absorption curve on each of the samples. The wave length4 used for each determination and also the principal interfeiing elemeutq a t that nave length are shon-n in Table I . A calibration curve was constructed for those rare earth ions that do not folloir- Beer’s lav. As the absorbances of mixtures are additive, Iiy determining the tranFniittancy a t tn-o different wave
IO0
80
c
I
In
z K Y
i i
201
‘350
400
450 500 550 600 650 700 WAVE LENGTH- MILLIMICRONS
750 8 0 0
Figure 1. Spectral-Transmittaricy Curves of Europium Kitrate and Samarium Nitrate Solutions 0 E u r o p i u m n i t r a t e s o l u t i o n c o n t a i n i n g 0.18 g r a m of e u r o p i u m p e r 10 ml.
0 S a m a r i u m n i t r a t e s o l u t i e n c o n t a i n i n g 0.20 g r a m of
APPAR 4TUS
The activation analyses were carried out n ith a 25-mg. radium-beryllium neutron source enclosed in paraffin ( 3 ) to slow down the neutrons to thermal velocities. The maximum thermal flus obtainable with this source v a s about 100 neutrons per square centimeter per second. The irradiated samples xvere counted in a SIodel D46-.1 lead-shielded Nuclear Q-gas counter. This GeigerNuller flow counter used a mixture of 2% isobutane with helium as the counting gas. -4Model 165 scaling circuit, manufactured by the Suclear Instrument and Chemical Corp., Chicago, Ill, x a s used in conjunction with the counter. -1 Beckman Model DU quartz spectrophotometer with square cells of 0.998-cm. path length v a s used for the transmittancy measurements.
s a m a r i u m per 10 m l .
Table I.
Element Srn
Summary of Spectrophotometric Data (5, 6)
Principal Bands (Showing a Minim u m Transmittancy. mp)
402, 479, 950
Band Used, mp
402
Principal Interfering Elements E u , D y , Ho
Eu
396
396
Pm, Dy, H o
DY
508,910
910
Ho
Ho
452,540,643,910
643
...
REAGEhTS
The solutiolis of samarium nitrate and europium nitrate were prepared from oxides supplied hy
901
.4mount of Absorption a t Band Used Sm bands show less absorption t h a n a n y other element in cerium group except E u Amount of absorption a t 396 mp is very small 910 mp band shows strong a b sorption and is hardly affected by other members of ytterbium group 411 three bands show a b o u t same a m o u n t of absorption b u t 643 mp band is least affected b y ytterbium group members
ANALYTICAL CHEMISTRY
908
of samarium, samarium-154, has such a relatively low, Daughter atomic cross section (1.24 Atomic RadioEnergy of Range of PaiParent Abundance, Cross Sectlon, isotope Half Particles, tides in AI, barns) that very few atoms are Isotope % Barns Produced Life Radiation .\I E 1’. 31g.lSq. Clll. formed in an irradiation with 240 the low level neutron source. 0 . 8 0 i-33gj 300 SrnlL4 22.53 1 . 2 4 & 0.25 Srnlja 2 3 . 5 niin. @-, y 1.8 840 A stronger source such as an Eu161 47.77 669 5 143 Eui5? 9 . 2 hr. @-, y 1.88 890 733 f 8: DylSh 28.18 Dy16:”’ l.2binin. 14 e-,y 0.10 antimo n y-b e r yl1 i u m source Dyla4 28.18
