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Angular correlation of the 460 keV-27.7 keV gamma-gamma cascade in 129I
3.A
[
Nuclear Physics A138 (1969) 583--587; (~) North-Holland Publishing Co., Amsterdam
Not to be reproduced by photoprintor microfilmwithout written permission from the publisher
ANGULAR CORRELATION GAMMA-GAMMA
OF T H E 460 keV-27.7 keV
C A S C A D E I N 129I
R. SANDERS t Natuurkundi 9 Laboratorium der RUksuniversiteit, Groningen, The Netherlands Received 19 September 1969 Abstract: Normalized expansion coefficients A2z = --0.01484-0.0029 and A44 = --0.006810.0043 have been found for the angular correlation of the 460 keV-27.7 keV cascade in ~291, in contra-
diction with some earlier measurements. These results are consistent with a spin t or ~ assignment of the 487 keV level. For both spins the E2/M 1 mixing ratio of the 460 keV transition is given. Unfortunately, no conclusion can be drawn about the sign of the mixing ratio of the 27.7 keV transition. E [
I
RADIOACTIVITY lza'I'e [from 12aTe(n,7)]; measured ~r),(0). x291 level deduced J, ),-mixing ratio. Enriched target.
1. Introduction
Only a few measurements o f the angular correlation o f the 460 keV-27.7 keV g a m m a - g a m m a cascade in t29I have been reported. Kaplan et al. 1) measured no anisotropy within 2 % for this cascade. G u p t a and Saha 2), however, found `422 -0.160+_0.033 (and .444 = 0.022+0.060) for the normalized expansion coefficients o f the correlation function W(O) = ~ kk=4 = O, eve,.4kkPk (COS0), in which ek(cos 0) are Legendre polynomials of order k, while Arya and Nicholson 3) obtained A22 = - 0 . 0 4 8 9 +0.0090 and A44 = 0.0230+-0.0100. As pointed out by Dickinson et al. 4) this result favours a spin :~ for the 487 keV level. We have remeasured the 460 keV-27.7 keV g a m m a - g a m m a angular correlation and obtain A22 = -0.0148+-0.0029 and A44 = - 0 . 0 0 6 8 + 0 . 0 0 4 3 . These results are consistent with both spin ½ and ~. The 27.7 keV transition of 129[ is extensively used for M6ssbauer investigations. Since the relative intensities of the hyperfine components o f M6ssbauer spectra of a mixed E 2 - M I transition depend on the mixing ratio 6, an accurate knowledge o f 6 is important for the interpretation of such spectra. The value of fiz of the 27.7 keV transition o f 129I is k n o w n from the conversion ratio measurements of Bemis and Fransson 5). Unfortunately, it is impossible to derive the sign of 6 from our angular correlation results. t Present address: Development Laboratories, N.V. Philips Gloeilampenfabrieken, Drachten. 583
584
R. SANDERS
2. Experimental results and discussion The measurements were performed with an angular correlation apparatus, using a fixed and a movable scintillation counter, in a normal fast-slow coincidence arrangement. The positioning of the movable counter and the printing of the scaler readouts were controlled by an electronic programming unit. The performance of the apparatus was checked by measuring the well-known angular correlation of the 356 keV-81 keV g a m m a - g a m m a cascade in 133Cs from the decay of 7.2 y 133Ba' as well as the isotropic distributions of the 31 keV-356 keV X-rayg a m m a cascade accompanying the electron capture decay of 133Ba, and the 31 keV668 keV X - r a y - g a m m a cascade from 6.5 dt32Cs ' that mainly decays by electron capture to the 668 keV level in 132Xe.
,
.....
~- ..........
.... r - -
1
~
1
-~1
1 . o o _-
l I
]
0.95 90
°
150 °
2i0 ° angle
270 °
0
Fig. I. Angular correlation of the 460 keV-27.7 keV gamma-gamma cascade in a291. The lz9mTe source was produced by irradiating about 100 mg of 128Te, enriched to 93 o/ for three weeks in a flux of 1.2 × 1014 neutrons/cmZsec of the H F R of the Reactor Centrum at Petten. A drop of a solution of the activity in HNO3 was forced into a glass capillary by centrifuging. The open end was sealed off in order to prevent evaporation. In this way we obtained a cylindrical source of 27 m m length. A perspex disc was placed in front of a 1 m m thick NaI(TI) crystal used for detection of the 27.7 keV g a m m a rays to avoid detection of beta particles. A thickness of 4 mm will absorb all electrons, and only about 10 ol, of the 27.7 keV g a m m a rays. The 460 keV g a m m a ray was detected in a 4.4 cm × 5.1 cm NaI(TI) crystal. A contribution in this channel of gamma rays with higher energy that are coincident with the 27.7 keV transition is expected to be negligible, because the intensity of these gammas is small compared to that of the 460 keV transition.
1 2 9 1 ~'-7 C A S C A D E
585
Our measurements are more extensively described in ref. 6). Fig. 1 shows the angular correlation function that was measured. F r o m our data we find the normalized expansion coefficients .422 = -0.01484-0.0029, .444 = - 0.0068 ___0.0043. The errors given are standard deviations. The E2 admixture of the 27.7 keV transition 622 = 0.016-t-0.011 that follows from the work of G u p t a and Saha (based on a spin ½ for the 487 keV level and a pure
2,A4
0
3 5
12 -~ -~)
1.0
0~
q 15=1
,-,-i
.
-.
,.:.
.., ......
.
02:.0
,-
~ . -
A2(exp)~. 8 =OD,,
,/3,
61>0
t
-1.0 -
O
L
t
,
,
I
0.5
L
,
,
,
10
/ /
O
L
~
,
,
L
0.5
,
,
K
1O
Q1
Fig. 2. Theoretical coefficients A~1) as a function of the quadrupole content QI of the 460 keV transition in 129I. The shaded bands give the experimental results for A~ ~.
460 keV E2 transition) is in disagreement with the accurate value c5,2 = (2.80+0.22) x 10-3 that follows from L-subshell measurements by Bemis and Fransson 5). We have carried out a conversion coefficient measurement 7) which is in agreement with this
586
R. SANDERS
value*. We therefore a d o p t it as the correct value. We can use it for an A r n s and W i e d e n b e c k ~o) analysis o f o u r a n g u l a r c o r r e l a t i o n m e a s u r e m e n t s to o b t a i n i n f o r m a tion a b o u t the E 2 / M I mixing r a t i o 61 o f the 460 keV transition. Before p e r f o r m i n g this analysis we discuss the possible spins o f the 487 keV level. The spins o f the g r o u n d state and the first excited state o f 1291 are k n o w n to be -i a n d -~. respectively. T h e spin o f the level at 487 keV that decays m a i n l y by the 460 keV t r a n s i t i o n to the 27.7 keV level, can be ~, 3 or ~ because it is p o p u l a t e d by an allowed b e t a t r a n s i t i o n i t - 1 3 ) from the 129Te g r o u n d state which has spin ~. H u r l e y and M a t h i e s e n 14) s h o w e d first that transitions from the 487 keV level to the first excited state a n d the g r o u n d state do occur. This was confirmed by the work o f B o r n e m e i c r et al. [rcf. ~3)], that o f Berzins et al. i5) a n d that o f D i c k i n s o n et al. 4). On this basis we may conclude a spin a s s i g n m e n t 3 or ~ for the level at 487 keV. TABLE 1 Mixing ratio ,~t of the 460 keV transition for both signs of the mixing ratio tSz of the 27.7 keV transition in ~2'~I Spin of 487 kcV lcvel
hi ,3~ > 0-. . . . . . . . . . . . . . . . . . .
......
--0.325:=0.014 or
4.20:-'-0.24
0.231:!.0.008 or --16.39+-1.90
62-< 0
--0.171-±0.014 or 2.52-_': 0.10 0.325~:0.011 or 41
-::13
Using the value 6_~ = +_(0.0529_+0.0021) o f Bemis a n d F r a n s s o n for the E 2 / M I mixing ratio o f the 27.7 keV transition, we find from the tables o f a n g u l a r correlation F-coefficients 16):
and
A~2~ = 0.2078 _+0.0030
for
62 > 0,
r ~"~ . =
for
62 < 0,
0.0613 _+0.0029
At4-'j = 0.00033+0.00003
for b o t h signs o f ~2.
F r o m these values a n d o u r e x p e r i m e n t a l values o f ,,422 and coefficients A~ ~ = A k k /,-(2~ A k o f the 460 keV t r a n s i t i o n :
A44
A~ 1~ = -0.0712___0.0140
for di2 > 0,
A~ l~ = - 0 . 2 4 1 4 - t - 0 . 0 1 5 4
for 62 < 0,
A~~) = - 2 2 +
for both signs o f ~52.
14
~,:c
derive for the
Physically, the value of,4(41) has o f course no meaning. In fig. 2 the A(21)coefficients a r e p l o t t e d as a function o f the q u a d r u p o l e c o n t e n t Q1 = ~2/(1 + 6 2 ) o f t h e 4 6 0 k e V t Our value for the total conversion coefficient at = 5.3 :=0 3, given in ref. 7) was based on Rose's s) value for the M-conversion coefficient of the 106 keV isomeric transition in t29Te. Rose neglected screening of the M-electrons. More recent calculations of Hager and Seltzer 9) take this effect into account. Using their tables and rccent data on the decay scheme of ~2¢"Te [ref. 4) ], we find a corrected value at == 4.8-:.0.4.
129[ Y-7 CASCADE
587
t r a n s i t i o n for spins ~ a n d ~ of the 487 keV level. We see that our results are consistent with both spin assignments. The possible mixing ratios 6t that follow from this analysis are given in table 1 for both possible spins of the 487 keV level. U n f o r t u n a t e l y n o n e of the values of 61 for 129[ c a n be excluded o n the basis of the value of A~t). It is clear that o u r a n g u l a r correlation experiments do not favour a particular sign of 32. "Ihus the sign of the mixing ratio of the 27.7 keV t r a n s i t i o n in 1291 is as yet unknown. The a u t h o r wishes to t h a n k Professor H. de W a a r d for his stimulating interest.
References 1) 2) 3) 4) 5) 6) 7) 8) 9)
N. Kaplan, S. Ofer and H. Zmora, Nucl. Phys. 52 (1964) 249 S. L. Gupta and N. K. Saha, Nucl. Phys. 73 (1965) 461 A. P. Arya and N. Nicholson, Bull. Am. Phys. Soc. 10 (1965) 588 W. C. Dickinson, S. D. Bloom and L. G. Mann, Nucl. Phys. A123 (1969) 481 C. E. Bemis and K. Fransson, Phys. Lett. 19 (1965) 567 R. Sanders, thesis, Groningen, 1969 R. Sanders and H. de Waard, Phys. Rev. 146 (1966) 907 M. E. Rose, Internal conversion coefficients (North-Holland Publ. Co., Amsterdam, 1958) R. S. Hager and E. C. Seltzer, Internal conversion tables, part I; K-, L-, M-shell conversion coefficients, AEC Research and Development Report CALT-63-60, Pasadena, California, 1967 10) R. G. Arns and M. L. Wiedenbeck, Phys. Rev. 111 (1958) 163 l l ) S. H. Devare and H. G. Devare, Phys. Rev. 134 (1964) B705 12) A. V. Ramayya, Y. Yoshizawa and A. C. G. Mitchell, Nucl. Phys. 56 (1964) 129 13) D. D. Bornemeier, V. R. Potnis, L. D. Ellsworth and C. E. Mandeville, Phys. Rev. 138 (1965) B525 14) J. P. Hurley and J. M. Mathiesen, Nucl. Phys. 73 (1965) 328 15) G. Berzins, L. M. Beyer and W. H. Kelly, W. B. Walters and G. E. Gordon, Nucl. Phys. A93 (1967) 456 16) Nuclear Spectroscopy Tables, eds. A. H. Wapstra, G. J. Nijgh and R. van Lieshout (NorthHolland Publ. Co., Amsterdam, 1959)
[
Nuclear Physics A138 (1969) 583--587; (~) North-Holland Publishing Co., Amsterdam
Not to be reproduced by photoprintor microfilmwithout written permission from the publisher
ANGULAR CORRELATION GAMMA-GAMMA
OF T H E 460 keV-27.7 keV
C A S C A D E I N 129I
R. SANDERS t Natuurkundi 9 Laboratorium der RUksuniversiteit, Groningen, The Netherlands Received 19 September 1969 Abstract: Normalized expansion coefficients A2z = --0.01484-0.0029 and A44 = --0.006810.0043 have been found for the angular correlation of the 460 keV-27.7 keV cascade in ~291, in contra-
diction with some earlier measurements. These results are consistent with a spin t or ~ assignment of the 487 keV level. For both spins the E2/M 1 mixing ratio of the 460 keV transition is given. Unfortunately, no conclusion can be drawn about the sign of the mixing ratio of the 27.7 keV transition. E [
I
RADIOACTIVITY lza'I'e [from 12aTe(n,7)]; measured ~r),(0). x291 level deduced J, ),-mixing ratio. Enriched target.
1. Introduction
Only a few measurements o f the angular correlation o f the 460 keV-27.7 keV g a m m a - g a m m a cascade in t29I have been reported. Kaplan et al. 1) measured no anisotropy within 2 % for this cascade. G u p t a and Saha 2), however, found `422 -0.160+_0.033 (and .444 = 0.022+0.060) for the normalized expansion coefficients o f the correlation function W(O) = ~ kk=4 = O, eve,.4kkPk (COS0), in which ek(cos 0) are Legendre polynomials of order k, while Arya and Nicholson 3) obtained A22 = - 0 . 0 4 8 9 +0.0090 and A44 = 0.0230+-0.0100. As pointed out by Dickinson et al. 4) this result favours a spin :~ for the 487 keV level. We have remeasured the 460 keV-27.7 keV g a m m a - g a m m a angular correlation and obtain A22 = -0.0148+-0.0029 and A44 = - 0 . 0 0 6 8 + 0 . 0 0 4 3 . These results are consistent with both spin ½ and ~. The 27.7 keV transition of 129[ is extensively used for M6ssbauer investigations. Since the relative intensities of the hyperfine components o f M6ssbauer spectra of a mixed E 2 - M I transition depend on the mixing ratio 6, an accurate knowledge o f 6 is important for the interpretation of such spectra. The value of fiz of the 27.7 keV transition o f 129I is k n o w n from the conversion ratio measurements of Bemis and Fransson 5). Unfortunately, it is impossible to derive the sign of 6 from our angular correlation results. t Present address: Development Laboratories, N.V. Philips Gloeilampenfabrieken, Drachten. 583
584
R. SANDERS
2. Experimental results and discussion The measurements were performed with an angular correlation apparatus, using a fixed and a movable scintillation counter, in a normal fast-slow coincidence arrangement. The positioning of the movable counter and the printing of the scaler readouts were controlled by an electronic programming unit. The performance of the apparatus was checked by measuring the well-known angular correlation of the 356 keV-81 keV g a m m a - g a m m a cascade in 133Cs from the decay of 7.2 y 133Ba' as well as the isotropic distributions of the 31 keV-356 keV X-rayg a m m a cascade accompanying the electron capture decay of 133Ba, and the 31 keV668 keV X - r a y - g a m m a cascade from 6.5 dt32Cs ' that mainly decays by electron capture to the 668 keV level in 132Xe.
,
.....
~- ..........
.... r - -
1
~
1
-~1
1 . o o _-
l I
]
0.95 90
°
150 °
2i0 ° angle
270 °
0
Fig. I. Angular correlation of the 460 keV-27.7 keV gamma-gamma cascade in a291. The lz9mTe source was produced by irradiating about 100 mg of 128Te, enriched to 93 o/ for three weeks in a flux of 1.2 × 1014 neutrons/cmZsec of the H F R of the Reactor Centrum at Petten. A drop of a solution of the activity in HNO3 was forced into a glass capillary by centrifuging. The open end was sealed off in order to prevent evaporation. In this way we obtained a cylindrical source of 27 m m length. A perspex disc was placed in front of a 1 m m thick NaI(TI) crystal used for detection of the 27.7 keV g a m m a rays to avoid detection of beta particles. A thickness of 4 mm will absorb all electrons, and only about 10 ol, of the 27.7 keV g a m m a rays. The 460 keV g a m m a ray was detected in a 4.4 cm × 5.1 cm NaI(TI) crystal. A contribution in this channel of gamma rays with higher energy that are coincident with the 27.7 keV transition is expected to be negligible, because the intensity of these gammas is small compared to that of the 460 keV transition.
1 2 9 1 ~'-7 C A S C A D E
585
Our measurements are more extensively described in ref. 6). Fig. 1 shows the angular correlation function that was measured. F r o m our data we find the normalized expansion coefficients .422 = -0.01484-0.0029, .444 = - 0.0068 ___0.0043. The errors given are standard deviations. The E2 admixture of the 27.7 keV transition 622 = 0.016-t-0.011 that follows from the work of G u p t a and Saha (based on a spin ½ for the 487 keV level and a pure
2,A4
0
3 5
12 -~ -~)
1.0
0~
q 15=1
,-,-i
.
-.
,.:.
.., ......
.
02:.0
,-
~ . -
A2(exp)~. 8 =OD,,
,/3,
61>0
t
-1.0 -
O
L
t
,
,
I
0.5
L
,
,
,
10
/ /
O
L
~
,
,
L
0.5
,
,
K
1O
Q1
Fig. 2. Theoretical coefficients A~1) as a function of the quadrupole content QI of the 460 keV transition in 129I. The shaded bands give the experimental results for A~ ~.
460 keV E2 transition) is in disagreement with the accurate value c5,2 = (2.80+0.22) x 10-3 that follows from L-subshell measurements by Bemis and Fransson 5). We have carried out a conversion coefficient measurement 7) which is in agreement with this
586
R. SANDERS
value*. We therefore a d o p t it as the correct value. We can use it for an A r n s and W i e d e n b e c k ~o) analysis o f o u r a n g u l a r c o r r e l a t i o n m e a s u r e m e n t s to o b t a i n i n f o r m a tion a b o u t the E 2 / M I mixing r a t i o 61 o f the 460 keV transition. Before p e r f o r m i n g this analysis we discuss the possible spins o f the 487 keV level. The spins o f the g r o u n d state and the first excited state o f 1291 are k n o w n to be -i a n d -~. respectively. T h e spin o f the level at 487 keV that decays m a i n l y by the 460 keV t r a n s i t i o n to the 27.7 keV level, can be ~, 3 or ~ because it is p o p u l a t e d by an allowed b e t a t r a n s i t i o n i t - 1 3 ) from the 129Te g r o u n d state which has spin ~. H u r l e y and M a t h i e s e n 14) s h o w e d first that transitions from the 487 keV level to the first excited state a n d the g r o u n d state do occur. This was confirmed by the work o f B o r n e m e i c r et al. [rcf. ~3)], that o f Berzins et al. i5) a n d that o f D i c k i n s o n et al. 4). On this basis we may conclude a spin a s s i g n m e n t 3 or ~ for the level at 487 keV. TABLE 1 Mixing ratio ,~t of the 460 keV transition for both signs of the mixing ratio tSz of the 27.7 keV transition in ~2'~I Spin of 487 kcV lcvel
hi ,3~ > 0-. . . . . . . . . . . . . . . . . . .
......
--0.325:=0.014 or
4.20:-'-0.24
0.231:!.0.008 or --16.39+-1.90
62-< 0
--0.171-±0.014 or 2.52-_': 0.10 0.325~:0.011 or 41
-::13
Using the value 6_~ = +_(0.0529_+0.0021) o f Bemis a n d F r a n s s o n for the E 2 / M I mixing ratio o f the 27.7 keV transition, we find from the tables o f a n g u l a r correlation F-coefficients 16):
and
A~2~ = 0.2078 _+0.0030
for
62 > 0,
r ~"~ . =
for
62 < 0,
0.0613 _+0.0029
At4-'j = 0.00033+0.00003
for b o t h signs o f ~2.
F r o m these values a n d o u r e x p e r i m e n t a l values o f ,,422 and coefficients A~ ~ = A k k /,-(2~ A k o f the 460 keV t r a n s i t i o n :
A44
A~ 1~ = -0.0712___0.0140
for di2 > 0,
A~ l~ = - 0 . 2 4 1 4 - t - 0 . 0 1 5 4
for 62 < 0,
A~~) = - 2 2 +
for both signs o f ~52.
14
~,:c
derive for the
Physically, the value of,4(41) has o f course no meaning. In fig. 2 the A(21)coefficients a r e p l o t t e d as a function o f the q u a d r u p o l e c o n t e n t Q1 = ~2/(1 + 6 2 ) o f t h e 4 6 0 k e V t Our value for the total conversion coefficient at = 5.3 :=0 3, given in ref. 7) was based on Rose's s) value for the M-conversion coefficient of the 106 keV isomeric transition in t29Te. Rose neglected screening of the M-electrons. More recent calculations of Hager and Seltzer 9) take this effect into account. Using their tables and rccent data on the decay scheme of ~2¢"Te [ref. 4) ], we find a corrected value at == 4.8-:.0.4.
129[ Y-7 CASCADE
587
t r a n s i t i o n for spins ~ a n d ~ of the 487 keV level. We see that our results are consistent with both spin assignments. The possible mixing ratios 6t that follow from this analysis are given in table 1 for both possible spins of the 487 keV level. U n f o r t u n a t e l y n o n e of the values of 61 for 129[ c a n be excluded o n the basis of the value of A~t). It is clear that o u r a n g u l a r correlation experiments do not favour a particular sign of 32. "Ihus the sign of the mixing ratio of the 27.7 keV t r a n s i t i o n in 1291 is as yet unknown. The a u t h o r wishes to t h a n k Professor H. de W a a r d for his stimulating interest.
References 1) 2) 3) 4) 5) 6) 7) 8) 9)
N. Kaplan, S. Ofer and H. Zmora, Nucl. Phys. 52 (1964) 249 S. L. Gupta and N. K. Saha, Nucl. Phys. 73 (1965) 461 A. P. Arya and N. Nicholson, Bull. Am. Phys. Soc. 10 (1965) 588 W. C. Dickinson, S. D. Bloom and L. G. Mann, Nucl. Phys. A123 (1969) 481 C. E. Bemis and K. Fransson, Phys. Lett. 19 (1965) 567 R. Sanders, thesis, Groningen, 1969 R. Sanders and H. de Waard, Phys. Rev. 146 (1966) 907 M. E. Rose, Internal conversion coefficients (North-Holland Publ. Co., Amsterdam, 1958) R. S. Hager and E. C. Seltzer, Internal conversion tables, part I; K-, L-, M-shell conversion coefficients, AEC Research and Development Report CALT-63-60, Pasadena, California, 1967 10) R. G. Arns and M. L. Wiedenbeck, Phys. Rev. 111 (1958) 163 l l ) S. H. Devare and H. G. Devare, Phys. Rev. 134 (1964) B705 12) A. V. Ramayya, Y. Yoshizawa and A. C. G. Mitchell, Nucl. Phys. 56 (1964) 129 13) D. D. Bornemeier, V. R. Potnis, L. D. Ellsworth and C. E. Mandeville, Phys. Rev. 138 (1965) B525 14) J. P. Hurley and J. M. Mathiesen, Nucl. Phys. 73 (1965) 328 15) G. Berzins, L. M. Beyer and W. H. Kelly, W. B. Walters and G. E. Gordon, Nucl. Phys. A93 (1967) 456 16) Nuclear Spectroscopy Tables, eds. A. H. Wapstra, G. J. Nijgh and R. van Lieshout (NorthHolland Publ. Co., Amsterdam, 1959)