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Preparation and characterisation of some Np(VII) compounds
INORG. NUCL. CHEM. LETTERS Vol. 7, pp.
145-151, 1971.
PergamonPress.
Printed in Great Britain.
PREPARATION ARD CHARACTERISATION OF SOME Np(VII) COMPOUNDS 8.K. Awasthi*, L. Martinot, J. Fuger and G. Duyckaerts Laboratory of Nuclear Chemistry Rue A. St6vart I 2, B - ~ O O Li&ge (Belgium) (Received 6 October 1970)
ABSTRACT
The following Np(VII) compounds
:
LisNp06, Ba3(NPO5)2~ Ba2NaNpO 6 and
Ba2LiNpO 6 have been prepared by reactions between solids at high temperature. From powder diffraction data~ the lattice parameters of L~sNp06, Ba2NaNpO 6 and Ba2LiNpO 6 have been calculated. These compounds appear to be isomorphous with the corresponding technetium and rhenium compounds.
INTRODUCTION The oxidation of Np(VI) to Np(VII) in alkaline solutions was first observed by Krot and Gelman (I). Spitsyn et al. (2) recently discussed the role of various oxidizing agents to obtain Np(VII) in solution and also prepared a few solid Np(VII) compounds. They believe Np(VII) to exist in solution as NpO~-, the anionic form of the amphoteric hydroxide NPO2(OH) 3. The present paper describes the preparation by solid state reactions of a few Np(VII) compounds analogous to the corresponding Re(VII) and Tc(VII) compounds. Powder X-rays diffraction data of these compounds are also
reported.
EXPERIMENTAL 1.
Compounds. The experimental
* On O . C . D .
fellowship.
conditions
Present
for
the
address
preparation
of
: Radiochemistry
the
Division,
Radiolo~ical labs., B.A.R.C., Trombay, Bombay - 85, India. 145
compounds
146
SOME Np(Vll) COMPOUNDS
LisNPO6, NasNp06, results
Ba3(Np05)2,
Vol. 7, No. 2
Ba2LiNpO6
Ba2NaNpO6 and
of spectrophotonetric observations of their
a l o n g with the
solution in 1 - 2 M
NaOH are given in Table I. T A B L E
I
P r e p a r a t i o n o f Np(VII) compounds Compounds
Method o f p r e p a r a t i o n
t(°C)
Time (hrs)
Spectrophotonetric results
2.5 Li202 + NPO3.H20
400
16
Np(VZZ)
2.5 Na202 + NpO3.H20
500,600
24
Np(VI) + Np(VII)
2 BaO 2 + 1/2 Li202 + Np03. H20
42o
~6
Np(VZZ)
2 BaO 2 + I/2 Na202
450
3o
Np(VZZ)
2 BoO 2 + 1/2 Na202 + NpO 2
45o
15
Np(Wl)
3 BaO 2 + 2 NpO3.H20
4OO~5OO
20
Np(VII)
02 LisNpO 6
2Na p06
+ NpO3.H20 - ~
The s t a r ~ i n g m a t e r i a l NpO3.H20 was p r e p a r e d by t h e method r e p o r t e d by Bagnall state.
(10)
and was found t o c o n t a i n o n l y neptunium i n the h e x a v a l e n t
O t h e r o x i d e s were a n a l a r g r a d e . The d i f f e r e n t
oxides in stoich~netric
p r o p o r t i o n s as r e p r e s e n t e d by
the equa~ions i n Table I were mixed and ground i n an a g a t e p e s t l e m o r t a r i n a day n i t r o g e n g l o v e box. The m i x t u r e s were h e a t e d i n p l a t i n u m c r u c i b l e s k e p t i n s i d e q u a r t z t u b e s under one a t n o s p h e r e o f oxTgen. S e v e r a l a t t e n p s to p r e p a r e Ba2LiNpO 6 with NpO2 i n s t e a d o f NpO3.~O have f a i l e d .
The conpounds KsNpO6 and Ba2KNpO6 c o u l d n e v e r be o b t a i n e d
under t h e e x p e r i n e n t a l c o n d i t i o n s d e s c r i b e d above f o r the c o r r e s p o n d i n g Na compounds.
Vol. 7. No. 2
SOME Np(VID COMPOUNDS
147
2. ~-ra~ techniques and calculations The X-ray generator is a Philips unit equipped with a "fine focus" tube. The camera is a ~7.54 mm diameter, Philips Debye-Scherrer
type,
using Straumanis film mounting. To minimize random errors, lines positions on the films are read 2 or 3 times by different experimenters and their results averaged. After indexing the various reflections,
the lattice parameters were
calculated by the least squares method, using the LCR-2 program developed by Willi~ms
(3). The Nelson-Riley
extrapolation
function was used in the
calculations. Theoretical intensities were calculated for Ba2NaNpO 6 and Ba2LiNpO 6 on the basis of a cubic symmetry
(0~, space group Fn3m), using the program
written by Smith (4). All the observed intensities were estimated visually. For each compound, all the calculations were carried out on results obtained from two independent preparations and the error limits we report in thi~ paper represent twice the standard deviation. 3. 8~ectro~hotometric
data
All the samples were dissolved in I - 3 M NaOH and the presence of Np(VII) was checked from the absorption spectrum taken on a Cary 14 H recording spectrophotometer.
RESULTS The characteristic
absorption peaks of Np(VI7) at 410 and 625 m~ (2)
were observed in all samples but in the system Na202 - NpO3.H20 the oxidation was not complete even when Na202 was taken in excess. This unreacted Ma202 could also be observed in the diffraction pattern. The intensities calculated for Ba2MaNpO 6 and Ba2LiNpO 6 are given in Table If. The data for LisNpO 6, Ba2LiNpO 6 and Ba2NaNpO 6 are reported in Table III along with the values for the corresponding Tc(VII) and Re(VII)
148
SOME Np(Vil) COMPOUNDS
Vol. 7, No. 2
T A B L E II Lines list and indexing for cubic compounds
(1) B a a N ~
6
hkl
2ecalc .
111 200 220 311 222 400 331 420 422
17.77 20.57 29.3O 34.53 36.12 41.97 45.96 47.23 52.07 55.5O 60.92 64.05 65.07
33 44 531
6o }
44 620 533 622 444 711 551 64O 642
55 8OO 733
82 } 64 822} 660
55 662 840 75 842 664 931 844 77 75
2Cobs.
Icalc.
lobs.
17.68
3.?5 0.03 lO.OO 2.25 0.40 3.53 1.04 0.01 4.20
4.0
29.32
34.50 42.oo 45.92 52.07 55.48 60.96 64.03
69.09
69.08 72.o2 72.99 76.81 ?9.64 80.58 84.3o
8?.o8
87.24
91.7o 94.48
91.79
100
127.63
86
132.45
1.5 2.5 1.5 3.5 0.5
76.73
o.72
?9.78
0.46
1.5 1.0
84.35
0.~ 2.24
0.5? o.~
3.0 1.0 0.5
0.17 0.00
99.23
102.91
110.63 114.63 117.76 123.088 126.46
4.0
1.83 0.29 0.08
101.96 106.72 109.64
2.20 0.81 0.00
2.5 1.5
72.01
95.41 99.13
o.81
10.0 2.0
107.04
lO9.75 114.39 122.73
1.31 0.~ 0.03 1.25 0.48 0.~ 0.88 0.~ 1.~ 0.5?
2.0
m
1.0 0.5 1.0 1.0
0.00 132.46
3-33
2.0
V,,I. 7, No. 2
SOME Np(VII) COMPOUNDS
149
(2) Ba2LiNI~O6 h k 1 1 1 20 22 31 22 4O 33 42 42 51 33 44 53 6O 44 62 53 62 44 71 55 64 64 73 55 80 73 82 64 82 66 75 55 66 84 91 75 84 66 93 84 93 77 75 10 0 86 10 2 86
2@calc.
2@obs.
I 0 0 1 2 0 1 0 2
18.37 21.24 30 •22 35-59 37.23 43.26 47.36 48.67 53.67
18.27
i}
0}
57-21 62.83 66.06 67.12
0 3 2 4 1}
71.29 74.~ 75.35 79 •34 82.29
79.35 82.33
0 2
83.27 87.18
87.22
1
;}
30.19 35.60 37.21 43.22 47.36 53.69 57.28 62.84 66.07 71.25
90.08 95.00
Ic alc.
lobs.
5.06 0.00 10.00 2.99 0.56 3.57 1.36 0.00 4.17 1.04 2.21 1.03 0.00
5.0
1.84 0.37 0.11 o.74 0.58 o.oo 2.3o o.74 0.38 0.22 0.00
10.0 3.0 0.5 4.0 2.0 3.0 0.5 2.0 1.0 1.5 0.5 0.5 2.5 0.25 0.1
0 3 ~}
94.97 97.90
2}
102.85
lo2.78
1.41
1.5
~} 2 0
lO5.85 lO6.88 110.99 114.15 115.22 119.61 123.02 129.04
lO5.84
0.49 0.05 1.40
o.25
0.66 0.00 0.84 0.20 0.93
0.5
;} 2 4 I 4
98.89
111.o2 114.15 119.61 [email protected] 129.19
1.0
1.o 0.25 1.5
0.03
0.29 139.83
I.78
2.0
compounds for the purpose of comparison. During the progress of this work, Keller et al. (5) also prepared
150
SOME Np(VII) COMPOUNDS
T A B L E Lattice parameters
Vol. 7, No. 2
III
for some Np(VII),
Re(VII),
Tc(VII)
compounds
M
Hexagonal
LisMO 6
Np
Re
Tc
Compounds~
(6)
Hexagonal
Hexagonal
(9)
o
o
a = (5.04 ±O.01)A
a = (5.053_+ O.OO1)A
c =(1 4 . 1 0 ! 0 . 0 2 ) Ao
c
(5)
o
a = (5.21+ O.03)A
@
o
= (14.21 + O.01)A
c = (14.61 + 0.05)A
(.)
o
a = (5.21+ O.02)A o c= (14.69 +O.06)A
F.C.C.
Ba2LiMO 6
(7)
F.c.c.
(8)
F.C.C.
(')
o
o
o
a = (8.092 _+ O.O02)A
a = ( 8 . 1183_+ O.OO03)A
a = (8.367+ 0.O03)A
F.C.C.
Ba2NaMO 6
(7)
F.C.C.
(8)
F.C.C.
(')
o
a = ( 8 . 2 9 2 + 0.002),~,
a = (8.2963_+ O.OO09)A
o
a = (8.590+ O.O06)A
* This work LI5NpO 6 with NpO 2 as starting material
and the cell parameters
obtained
by these authors are also included. The diffraction
pattern of Ba3(Np05) 2 is similar to that obtained
Ba3(Tc05) 3 by Wassilopulos
for
(7) and has not been indexed so far.
The ease of formation of Ba2(Na , Li)NpO 6 with Np(VII) in six-fold coordination
with oxygen may be understood by the high lattice energy of
the perovskite
(8) arrangement
and the large charge difference between
neptunium and the alkali metal. On the other hand, from our experimental to accomodate
results,
it seems difficult
in this type of structure a larger univalent ion such as
potassium. The structural
similarity
of these compounds with compounds
of
technetium and rhenium which are in the VII subgroup of the periodic arrangement
is in accordance
with the general observations
that in many
Vol. 7, No. 2
SOME Np(VII) COMPOUNDS
compounds t h e f i r s t
few members e f t h e a c t i n i d e s
ressemble the elements of the III,
151
series
Ac~ Th, P a , U
I V , V, VI eubKroupe o f t h e p e r i o d i c
arrangement respectively.
A similar work with plutonium compouds is in progress in oar Laboratory. ACENO~.~GE~HTS The a u t h o r s e x p r e s s t h e i r
thanks to the I.I.S.N.
and t h e y a r e a l s o
t h a n k f u l t o t h e B e l g i a n Government f o r t h e f e l l o w s h i p g i v e n t o one o f us 'S.K.A.).
REFERENCES (1)
N. KROT and A. GELMAN, Dokh. kk.ad. Nauk. S.S.S.R.,
177 , 124 (1967).
(2)
V. SPITSYN st al., J. Inorg. Mucl. CHem. 31, 2753 (1969).
(3)
D. WILLIAMS, Ames Laboratory Report, 18-1052 (1964).
(4)
D. SMITH, Report U.C.R.L. - 7196 (1963).
(5)
C. ~ E R
(6)
C. ~ W . ~ R and B. K A ~ L A K O P U L O S ,
(7)
M. WASSILOPULOS, Report K.F.K. - 341 (1965).
(8)
A. SLEIGHT and R. WARD, J.A.C.S., 83, 1088 (1961).
(9)
R. SCHOLDER and K.L. HUPPERT, Zeits. Anorg. Allg. Chemic 3 ~ ,
and H. SEIFFF~T, I.N.C.L. ~, 51 (1969). J. Inorg. Muel. Chem. 27, 78? (1965).
(qO) K.W. BAGNALL and J.B. LAIDLER, J. Chem. See., 2693 (1964).
209 (1964).
145-151, 1971.
PergamonPress.
Printed in Great Britain.
PREPARATION ARD CHARACTERISATION OF SOME Np(VII) COMPOUNDS 8.K. Awasthi*, L. Martinot, J. Fuger and G. Duyckaerts Laboratory of Nuclear Chemistry Rue A. St6vart I 2, B - ~ O O Li&ge (Belgium) (Received 6 October 1970)
ABSTRACT
The following Np(VII) compounds
:
LisNp06, Ba3(NPO5)2~ Ba2NaNpO 6 and
Ba2LiNpO 6 have been prepared by reactions between solids at high temperature. From powder diffraction data~ the lattice parameters of L~sNp06, Ba2NaNpO 6 and Ba2LiNpO 6 have been calculated. These compounds appear to be isomorphous with the corresponding technetium and rhenium compounds.
INTRODUCTION The oxidation of Np(VI) to Np(VII) in alkaline solutions was first observed by Krot and Gelman (I). Spitsyn et al. (2) recently discussed the role of various oxidizing agents to obtain Np(VII) in solution and also prepared a few solid Np(VII) compounds. They believe Np(VII) to exist in solution as NpO~-, the anionic form of the amphoteric hydroxide NPO2(OH) 3. The present paper describes the preparation by solid state reactions of a few Np(VII) compounds analogous to the corresponding Re(VII) and Tc(VII) compounds. Powder X-rays diffraction data of these compounds are also
reported.
EXPERIMENTAL 1.
Compounds. The experimental
* On O . C . D .
fellowship.
conditions
Present
for
the
address
preparation
of
: Radiochemistry
the
Division,
Radiolo~ical labs., B.A.R.C., Trombay, Bombay - 85, India. 145
compounds
146
SOME Np(Vll) COMPOUNDS
LisNPO6, NasNp06, results
Ba3(Np05)2,
Vol. 7, No. 2
Ba2LiNpO6
Ba2NaNpO6 and
of spectrophotonetric observations of their
a l o n g with the
solution in 1 - 2 M
NaOH are given in Table I. T A B L E
I
P r e p a r a t i o n o f Np(VII) compounds Compounds
Method o f p r e p a r a t i o n
t(°C)
Time (hrs)
Spectrophotonetric results
2.5 Li202 + NPO3.H20
400
16
Np(VZZ)
2.5 Na202 + NpO3.H20
500,600
24
Np(VI) + Np(VII)
2 BaO 2 + 1/2 Li202 + Np03. H20
42o
~6
Np(VZZ)
2 BaO 2 + I/2 Na202
450
3o
Np(VZZ)
2 BoO 2 + 1/2 Na202 + NpO 2
45o
15
Np(Wl)
3 BaO 2 + 2 NpO3.H20
4OO~5OO
20
Np(VII)
02 LisNpO 6
2Na p06
+ NpO3.H20 - ~
The s t a r ~ i n g m a t e r i a l NpO3.H20 was p r e p a r e d by t h e method r e p o r t e d by Bagnall state.
(10)
and was found t o c o n t a i n o n l y neptunium i n the h e x a v a l e n t
O t h e r o x i d e s were a n a l a r g r a d e . The d i f f e r e n t
oxides in stoich~netric
p r o p o r t i o n s as r e p r e s e n t e d by
the equa~ions i n Table I were mixed and ground i n an a g a t e p e s t l e m o r t a r i n a day n i t r o g e n g l o v e box. The m i x t u r e s were h e a t e d i n p l a t i n u m c r u c i b l e s k e p t i n s i d e q u a r t z t u b e s under one a t n o s p h e r e o f oxTgen. S e v e r a l a t t e n p s to p r e p a r e Ba2LiNpO 6 with NpO2 i n s t e a d o f NpO3.~O have f a i l e d .
The conpounds KsNpO6 and Ba2KNpO6 c o u l d n e v e r be o b t a i n e d
under t h e e x p e r i n e n t a l c o n d i t i o n s d e s c r i b e d above f o r the c o r r e s p o n d i n g Na compounds.
Vol. 7. No. 2
SOME Np(VID COMPOUNDS
147
2. ~-ra~ techniques and calculations The X-ray generator is a Philips unit equipped with a "fine focus" tube. The camera is a ~7.54 mm diameter, Philips Debye-Scherrer
type,
using Straumanis film mounting. To minimize random errors, lines positions on the films are read 2 or 3 times by different experimenters and their results averaged. After indexing the various reflections,
the lattice parameters were
calculated by the least squares method, using the LCR-2 program developed by Willi~ms
(3). The Nelson-Riley
extrapolation
function was used in the
calculations. Theoretical intensities were calculated for Ba2NaNpO 6 and Ba2LiNpO 6 on the basis of a cubic symmetry
(0~, space group Fn3m), using the program
written by Smith (4). All the observed intensities were estimated visually. For each compound, all the calculations were carried out on results obtained from two independent preparations and the error limits we report in thi~ paper represent twice the standard deviation. 3. 8~ectro~hotometric
data
All the samples were dissolved in I - 3 M NaOH and the presence of Np(VII) was checked from the absorption spectrum taken on a Cary 14 H recording spectrophotometer.
RESULTS The characteristic
absorption peaks of Np(VI7) at 410 and 625 m~ (2)
were observed in all samples but in the system Na202 - NpO3.H20 the oxidation was not complete even when Na202 was taken in excess. This unreacted Ma202 could also be observed in the diffraction pattern. The intensities calculated for Ba2MaNpO 6 and Ba2LiNpO 6 are given in Table If. The data for LisNpO 6, Ba2LiNpO 6 and Ba2NaNpO 6 are reported in Table III along with the values for the corresponding Tc(VII) and Re(VII)
148
SOME Np(Vil) COMPOUNDS
Vol. 7, No. 2
T A B L E II Lines list and indexing for cubic compounds
(1) B a a N ~
6
hkl
2ecalc .
111 200 220 311 222 400 331 420 422
17.77 20.57 29.3O 34.53 36.12 41.97 45.96 47.23 52.07 55.5O 60.92 64.05 65.07
33 44 531
6o }
44 620 533 622 444 711 551 64O 642
55 8OO 733
82 } 64 822} 660
55 662 840 75 842 664 931 844 77 75
2Cobs.
Icalc.
lobs.
17.68
3.?5 0.03 lO.OO 2.25 0.40 3.53 1.04 0.01 4.20
4.0
29.32
34.50 42.oo 45.92 52.07 55.48 60.96 64.03
69.09
69.08 72.o2 72.99 76.81 ?9.64 80.58 84.3o
8?.o8
87.24
91.7o 94.48
91.79
100
127.63
86
132.45
1.5 2.5 1.5 3.5 0.5
76.73
o.72
?9.78
0.46
1.5 1.0
84.35
0.~ 2.24
0.5? o.~
3.0 1.0 0.5
0.17 0.00
99.23
102.91
110.63 114.63 117.76 123.088 126.46
4.0
1.83 0.29 0.08
101.96 106.72 109.64
2.20 0.81 0.00
2.5 1.5
72.01
95.41 99.13
o.81
10.0 2.0
107.04
lO9.75 114.39 122.73
1.31 0.~ 0.03 1.25 0.48 0.~ 0.88 0.~ 1.~ 0.5?
2.0
m
1.0 0.5 1.0 1.0
0.00 132.46
3-33
2.0
V,,I. 7, No. 2
SOME Np(VII) COMPOUNDS
149
(2) Ba2LiNI~O6 h k 1 1 1 20 22 31 22 4O 33 42 42 51 33 44 53 6O 44 62 53 62 44 71 55 64 64 73 55 80 73 82 64 82 66 75 55 66 84 91 75 84 66 93 84 93 77 75 10 0 86 10 2 86
2@calc.
2@obs.
I 0 0 1 2 0 1 0 2
18.37 21.24 30 •22 35-59 37.23 43.26 47.36 48.67 53.67
18.27
i}
0}
57-21 62.83 66.06 67.12
0 3 2 4 1}
71.29 74.~ 75.35 79 •34 82.29
79.35 82.33
0 2
83.27 87.18
87.22
1
;}
30.19 35.60 37.21 43.22 47.36 53.69 57.28 62.84 66.07 71.25
90.08 95.00
Ic alc.
lobs.
5.06 0.00 10.00 2.99 0.56 3.57 1.36 0.00 4.17 1.04 2.21 1.03 0.00
5.0
1.84 0.37 0.11 o.74 0.58 o.oo 2.3o o.74 0.38 0.22 0.00
10.0 3.0 0.5 4.0 2.0 3.0 0.5 2.0 1.0 1.5 0.5 0.5 2.5 0.25 0.1
0 3 ~}
94.97 97.90
2}
102.85
lo2.78
1.41
1.5
~} 2 0
lO5.85 lO6.88 110.99 114.15 115.22 119.61 123.02 129.04
lO5.84
0.49 0.05 1.40
o.25
0.66 0.00 0.84 0.20 0.93
0.5
;} 2 4 I 4
98.89
111.o2 114.15 119.61 [email protected] 129.19
1.0
1.o 0.25 1.5
0.03
0.29 139.83
I.78
2.0
compounds for the purpose of comparison. During the progress of this work, Keller et al. (5) also prepared
150
SOME Np(VII) COMPOUNDS
T A B L E Lattice parameters
Vol. 7, No. 2
III
for some Np(VII),
Re(VII),
Tc(VII)
compounds
M
Hexagonal
LisMO 6
Np
Re
Tc
Compounds~
(6)
Hexagonal
Hexagonal
(9)
o
o
a = (5.04 ±O.01)A
a = (5.053_+ O.OO1)A
c =(1 4 . 1 0 ! 0 . 0 2 ) Ao
c
(5)
o
a = (5.21+ O.03)A
@
o
= (14.21 + O.01)A
c = (14.61 + 0.05)A
(.)
o
a = (5.21+ O.02)A o c= (14.69 +O.06)A
F.C.C.
Ba2LiMO 6
(7)
F.c.c.
(8)
F.C.C.
(')
o
o
o
a = (8.092 _+ O.O02)A
a = ( 8 . 1183_+ O.OO03)A
a = (8.367+ 0.O03)A
F.C.C.
Ba2NaMO 6
(7)
F.C.C.
(8)
F.C.C.
(')
o
a = ( 8 . 2 9 2 + 0.002),~,
a = (8.2963_+ O.OO09)A
o
a = (8.590+ O.O06)A
* This work LI5NpO 6 with NpO 2 as starting material
and the cell parameters
obtained
by these authors are also included. The diffraction
pattern of Ba3(Np05) 2 is similar to that obtained
Ba3(Tc05) 3 by Wassilopulos
for
(7) and has not been indexed so far.
The ease of formation of Ba2(Na , Li)NpO 6 with Np(VII) in six-fold coordination
with oxygen may be understood by the high lattice energy of
the perovskite
(8) arrangement
and the large charge difference between
neptunium and the alkali metal. On the other hand, from our experimental to accomodate
results,
it seems difficult
in this type of structure a larger univalent ion such as
potassium. The structural
similarity
of these compounds with compounds
of
technetium and rhenium which are in the VII subgroup of the periodic arrangement
is in accordance
with the general observations
that in many
Vol. 7, No. 2
SOME Np(VII) COMPOUNDS
compounds t h e f i r s t
few members e f t h e a c t i n i d e s
ressemble the elements of the III,
151
series
Ac~ Th, P a , U
I V , V, VI eubKroupe o f t h e p e r i o d i c
arrangement respectively.
A similar work with plutonium compouds is in progress in oar Laboratory. ACENO~.~GE~HTS The a u t h o r s e x p r e s s t h e i r
thanks to the I.I.S.N.
and t h e y a r e a l s o
t h a n k f u l t o t h e B e l g i a n Government f o r t h e f e l l o w s h i p g i v e n t o one o f us 'S.K.A.).
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V. SPITSYN st al., J. Inorg. Mucl. CHem. 31, 2753 (1969).
(3)
D. WILLIAMS, Ames Laboratory Report, 18-1052 (1964).
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D. SMITH, Report U.C.R.L. - 7196 (1963).
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C. ~ E R
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C. ~ W . ~ R and B. K A ~ L A K O P U L O S ,
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