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The short-lived 127Sn isomer
J. Inorg. Nucl. Chem., 1965, Vol. 27, pp. 1713 to 1715. Pergamon Press Ltd. Printed in Northern Ireland
NOTES
T h e short-lived m S n i s o m e r
(Recewed 12January 1965) As a consequence of the proximity of the low-lying h11/2 and d3/~ (or sl/2) neutron states, nuclear isomerism is predicted and observed in most odd-A tin isotopes. In the case of l~Sn, the assignment of an approximate 2-hour half-life to this isotope is well established. ~l-st DROP~KY and OaTH {~t isolated this activity from fission products and found a half-life of 2-15 ± 0.10hr. and HAGEBO et al. cs~report a half-life of 2"2 ± 0'2 hr. By means of rapid milking of 1~7Sbfrom fission product tin, DROPtSKY and ORTH also observed a short-lived, 2.5 i 1.0 rain tsTSn activity whereas I-IAGE~ et al. found a half-life of 4"6 4- 0'4 min. No/~- or 7-spectroscopical data for the short lived 127Sn have so far been reported. In the present work, 1~7Sn was produced through the (n, ~) reaction from lS~l'e, and the decay of the short-lived mSn was directly observed after rapid chemical separation of the tin fraction. About 1 g of natural tellurium metal or 0.5 g of enriched tS°Te* was irradiated with 14 MeV neutrons for 4 min. The target was then rapidly dissolved in 3 N HCI containing 20 mg of tin carrier and bromine as oxidant.'[" The resulting solution was cooled with ice, I0 ml of 3 M NH,CNS was added, and the tin fraction was extracted with diethylether. After two washings with dilute HCI containing some NH,CNS the organic phase was ready for gamma counting. For beta measurements the tin was back-extracted with NaOH. The aqueous phase was acidified, tin hydroxide was precipitated with NH,OH, centrifuged and dissolved in HNOa. The tin was finally precipitated as phenylarsenate, which was rapidly filtered, washed, dried, covered with mylar and fl-counted. The 7-sources were ready in 5 min and fl-sources in 10 min after the end of irradiation. The enriched ~S°Te was recovered as metal and purified for re-use. The gross beta decay of the tin fraction from irradiated natural Te showed a strong 9"7 min component, obviously due to ~sSn, which is produced by the (n, ~) reaction from ~UTe. However, a more rapidly decaying fl-activity was clearly present, and was strongly favoured when enriched ~°Te was used as target material instead of natural Te. A half-life of 4"4 + 0'5 rain was estimated for the short-lived component from these experiments. ;,-spectra of the tin fractions showed the 326 KeV peak of 9-7 min ~25Sn, and another, more short-lived, peak at 495 + 5 KeV. No other short-lived 7-peaks were found; their intensity was certainly Jess than 10 per cent of the 495 KeV line. Also, no gammas in coincidence with the 495 KeV 7-ray were detected. The few long-lived ),-peaks could in most cases be identified with the ~,-spectrum of the 2" 15 hr ~27Sn. No Sb and only a very small amount of roTe gammas could be detected in these spectra. From successive ),-spectra the half-life of the 495 KeV peak was found to be 4.0 4- 0"3 min. This ),-ray could not be identified with any known 7-activity. By changing from the natural Te * The ~a°Tewas obtained from the Isotope Division of the Oak Ridge National Laboratory and it had the following composition: ~S°Te 96.03 :.~ 0-2; ~28Te 3"57 -'__0"2; ~6Te 0"40 and all other Te isotopes <0.1 atom per cent. HNO8 would have been much more convenient as oxidant, but Te tended to hydrolyze and tin recoveries were erratic in presence of nitrate. ct, H. Cx~r~A'rrl, I. FR.ANZ, R. RADICELLAand J. RODRIGUEZ, Z. Naturforschung 11 A 419 (1956). ~ B. J. DnOPES~Y and C. J. OR'rH, J. Inorg. Nucl. Chem. 7.4, 1301 (1962). ~*~E. H~GE~O, A. KJ~LBE~G and A. PAPPAS,J. Inorg. Nucl. Chem. 2,4, 117 (1962). 1713
326 key 9.7 minion
49,5 keV 4' I min~n
i0 ='
o,
!-/
id
i
i
t
i
200
i
400
1
600
FIG. l.--),-spectra of fin fractions, taken with 3 in. × 3 in. NaI (Tl) crystal. Fourminute countings were started 5 rain after the end of 4-min irradiations. Broken line: tin fraction from irradiated natural T¢. Solid line: tin from irradiated enriched *S°T¢. A = 127
A = 125
f3/2")
4"Jrain
(iw2")
~TSn (3/2°1 11/2"
2"15 hi\
9'7 rain
\ \ 066 ~ , v MeV 1'710 2.04 MeV\
1.9%
0-3 c
I 1-068 0'495
'3% 1 0.326 /
7/2* ~ ~ 9 9 r~Sb
f7 %
(7/2°) I
~b
2.7 y
FroG. 2.--Decay scheme of 9"7 ~ n m S n and proposed decay scheme for 4.! rain. l=~Sn. 1714
3.7d
Notes
1715
target to the enriched aWl'e, the emission rate of the 495 KeV y-ray was enhanced by a factor of 24.4 '___1.5 in relation to the 326 KeV gammas, while the abundance of lS°Te in relation to XUTe in these target materials differed by a factor of 24-8 -t- 1.4. The gamma-spectra of the two types of sources are shown in Fig. 1. Beta spectra were taken by means of a 1.5 in × 13/16 in. plastic scintillator. The endpoint energy of the short-lived/~-component was found to be 2.7 ± 0.1 MeV. A E-spectrum taken in coincidence with the 495 KeV y-rays showed the same endpoint energy, although the counting statistics were quite low in this case. It is concluded that the observed activity of approximately 4 minute half-life is, in fact, the short-lived 1~7Sn isomer, and that the decay of this isomer is connected with the emission of the 495 KeV ;,-ray. As a weighted mean, 4-1 :t: 0'3 min is given for the half-life. Fig. 2 shows the proposed simple decay scheme, giving a total decay energy of 3'2 :: 0" 1 MeV. Other low-intensity modes of decay are, of course, not excluded. The same figure also includes a slightly simplified decay scheme of the 9.7-min az~Sn.~ The similarity between the two decay structures suggests that the 4'l-min ~JTSn is the low spin isomer. It may also be pointed out, that, if the lowering of the h,,~ level in relation to the ds/2 level, that is taking place between A : : 117 and A = 125, continues at A - 127, the low-spin isomer also is the excited state.
Acknowledgements--This work was supported by the U.S. Atomic Energy Commission under contract AT-(40-1)-1313 and 3235. The author is grateful to Professor P. K. KURODA for his interest and encouragement. Department of Chemistry', Unit,ersity of ArkanscL~, Fa),etterille
P. KAURANEN+*
+*Present address: Department of Physics, University of Helsinki, Helsinki, Finland, c~ S. B. BURSON, J. M. Lr.BLA~C, and D. W. MARrlN, Phys. Rev. 105, 625 (1957).
J. lnorg. Nucl. Chem., 1965, Vol. 27. pp. 1715 to 1717. Pergamon Press Ltd. Printed in Northern Ireland
Pauling crystal radius of the hydride ion (ReceiL'ed 3 March 1965) I~ HiS table of crystal radii PAULINO'~} lists 2'08 /~ as the radius of the hydride ion H -. This magnitude refers to the free ion and is not appropriate to dimensions in crystalline compounds. Comparison of radial distribution functions for Li + and H - ions ~zl with the observed distance in crystalline lithium hydride shows that there is a considerable shortening of the internuclear separation when the oppositely-charged ions interact in the formation of the compound. It seems desirable, therefore, to consider the possibility of deriving a value for the radius of the hydride ion which can be collated with other crystal radii of PAULING. GIBBca' has recently proposed the value r a - ~ 1-40/~ for application with radii due to ZACHARIASEN. 14~ In producing his set of crystal radii of ions PAULI:qG~ took the salts NaF, KCI, RbBr and Csl as standard crystals and in these the cation :anion radius ratio p = r_/r_, was found to be ,-,-0-75 (the equilibrium distance r0 in the B 1 modification of CsI was assessed for use in the calculations). To explain divergences between observed distances and radius sums in other alkali halide crystals, PAULING corrected for a radius ratio effect. By multiplying requisite radius sums by F(p), a function of the radius ratio and of the Born repulsion exponent n, excellent agreement with observed distances was obtained (for full details see Ref. 1). " ' L. PAULING, The Nature of the Chemical Bond (3rd Ed.), Cornell University Press (1960). ~tJ E. HYLLEgAS, Proc. Rydberg Centennial Conf. Lund, Sweden, July 1954 p. 83; H. A. BETHE in GERLAG--SCHEEL'S Handbuch der Physik (2nd Ed.), 24, Part I Verlag Julius Springer, Berlin (1933). ~a~T. R. P. GraB, Progr. Inorg. Chem. 3, 315 (1962). t'~ W. H. ZACHARIASEN,Z. Krist. 80, 137 (1931).
NOTES
T h e short-lived m S n i s o m e r
(Recewed 12January 1965) As a consequence of the proximity of the low-lying h11/2 and d3/~ (or sl/2) neutron states, nuclear isomerism is predicted and observed in most odd-A tin isotopes. In the case of l~Sn, the assignment of an approximate 2-hour half-life to this isotope is well established. ~l-st DROP~KY and OaTH {~t isolated this activity from fission products and found a half-life of 2-15 ± 0.10hr. and HAGEBO et al. cs~report a half-life of 2"2 ± 0'2 hr. By means of rapid milking of 1~7Sbfrom fission product tin, DROPtSKY and ORTH also observed a short-lived, 2.5 i 1.0 rain tsTSn activity whereas I-IAGE~ et al. found a half-life of 4"6 4- 0'4 min. No/~- or 7-spectroscopical data for the short lived 127Sn have so far been reported. In the present work, 1~7Sn was produced through the (n, ~) reaction from lS~l'e, and the decay of the short-lived mSn was directly observed after rapid chemical separation of the tin fraction. About 1 g of natural tellurium metal or 0.5 g of enriched tS°Te* was irradiated with 14 MeV neutrons for 4 min. The target was then rapidly dissolved in 3 N HCI containing 20 mg of tin carrier and bromine as oxidant.'[" The resulting solution was cooled with ice, I0 ml of 3 M NH,CNS was added, and the tin fraction was extracted with diethylether. After two washings with dilute HCI containing some NH,CNS the organic phase was ready for gamma counting. For beta measurements the tin was back-extracted with NaOH. The aqueous phase was acidified, tin hydroxide was precipitated with NH,OH, centrifuged and dissolved in HNOa. The tin was finally precipitated as phenylarsenate, which was rapidly filtered, washed, dried, covered with mylar and fl-counted. The 7-sources were ready in 5 min and fl-sources in 10 min after the end of irradiation. The enriched ~S°Te was recovered as metal and purified for re-use. The gross beta decay of the tin fraction from irradiated natural Te showed a strong 9"7 min component, obviously due to ~sSn, which is produced by the (n, ~) reaction from ~UTe. However, a more rapidly decaying fl-activity was clearly present, and was strongly favoured when enriched ~°Te was used as target material instead of natural Te. A half-life of 4"4 + 0'5 rain was estimated for the short-lived component from these experiments. ;,-spectra of the tin fractions showed the 326 KeV peak of 9-7 min ~25Sn, and another, more short-lived, peak at 495 + 5 KeV. No other short-lived 7-peaks were found; their intensity was certainly Jess than 10 per cent of the 495 KeV line. Also, no gammas in coincidence with the 495 KeV 7-ray were detected. The few long-lived ),-peaks could in most cases be identified with the ~,-spectrum of the 2" 15 hr ~27Sn. No Sb and only a very small amount of roTe gammas could be detected in these spectra. From successive ),-spectra the half-life of the 495 KeV peak was found to be 4.0 4- 0"3 min. This ),-ray could not be identified with any known 7-activity. By changing from the natural Te * The ~a°Tewas obtained from the Isotope Division of the Oak Ridge National Laboratory and it had the following composition: ~S°Te 96.03 :.~ 0-2; ~28Te 3"57 -'__0"2; ~6Te 0"40 and all other Te isotopes <0.1 atom per cent. HNO8 would have been much more convenient as oxidant, but Te tended to hydrolyze and tin recoveries were erratic in presence of nitrate. ct, H. Cx~r~A'rrl, I. FR.ANZ, R. RADICELLAand J. RODRIGUEZ, Z. Naturforschung 11 A 419 (1956). ~ B. J. DnOPES~Y and C. J. OR'rH, J. Inorg. Nucl. Chem. 7.4, 1301 (1962). ~*~E. H~GE~O, A. KJ~LBE~G and A. PAPPAS,J. Inorg. Nucl. Chem. 2,4, 117 (1962). 1713
326 key 9.7 minion
49,5 keV 4' I min~n
i0 ='
o,
!-/
id
i
i
t
i
200
i
400
1
600
FIG. l.--),-spectra of fin fractions, taken with 3 in. × 3 in. NaI (Tl) crystal. Fourminute countings were started 5 rain after the end of 4-min irradiations. Broken line: tin fraction from irradiated natural T¢. Solid line: tin from irradiated enriched *S°T¢. A = 127
A = 125
f3/2")
4"Jrain
(iw2")
~TSn (3/2°1 11/2"
2"15 hi\
9'7 rain
\ \ 066 ~ , v MeV 1'710 2.04 MeV\
1.9%
0-3 c
I 1-068 0'495
'3% 1 0.326 /
7/2* ~ ~ 9 9 r~Sb
f7 %
(7/2°) I
~b
2.7 y
FroG. 2.--Decay scheme of 9"7 ~ n m S n and proposed decay scheme for 4.! rain. l=~Sn. 1714
3.7d
Notes
1715
target to the enriched aWl'e, the emission rate of the 495 KeV y-ray was enhanced by a factor of 24.4 '___1.5 in relation to the 326 KeV gammas, while the abundance of lS°Te in relation to XUTe in these target materials differed by a factor of 24-8 -t- 1.4. The gamma-spectra of the two types of sources are shown in Fig. 1. Beta spectra were taken by means of a 1.5 in × 13/16 in. plastic scintillator. The endpoint energy of the short-lived/~-component was found to be 2.7 ± 0.1 MeV. A E-spectrum taken in coincidence with the 495 KeV y-rays showed the same endpoint energy, although the counting statistics were quite low in this case. It is concluded that the observed activity of approximately 4 minute half-life is, in fact, the short-lived 1~7Sn isomer, and that the decay of this isomer is connected with the emission of the 495 KeV ;,-ray. As a weighted mean, 4-1 :t: 0'3 min is given for the half-life. Fig. 2 shows the proposed simple decay scheme, giving a total decay energy of 3'2 :: 0" 1 MeV. Other low-intensity modes of decay are, of course, not excluded. The same figure also includes a slightly simplified decay scheme of the 9.7-min az~Sn.~ The similarity between the two decay structures suggests that the 4'l-min ~JTSn is the low spin isomer. It may also be pointed out, that, if the lowering of the h,,~ level in relation to the ds/2 level, that is taking place between A : : 117 and A = 125, continues at A - 127, the low-spin isomer also is the excited state.
Acknowledgements--This work was supported by the U.S. Atomic Energy Commission under contract AT-(40-1)-1313 and 3235. The author is grateful to Professor P. K. KURODA for his interest and encouragement. Department of Chemistry', Unit,ersity of ArkanscL~, Fa),etterille
P. KAURANEN+*
+*Present address: Department of Physics, University of Helsinki, Helsinki, Finland, c~ S. B. BURSON, J. M. Lr.BLA~C, and D. W. MARrlN, Phys. Rev. 105, 625 (1957).
J. lnorg. Nucl. Chem., 1965, Vol. 27. pp. 1715 to 1717. Pergamon Press Ltd. Printed in Northern Ireland
Pauling crystal radius of the hydride ion (ReceiL'ed 3 March 1965) I~ HiS table of crystal radii PAULINO'~} lists 2'08 /~ as the radius of the hydride ion H -. This magnitude refers to the free ion and is not appropriate to dimensions in crystalline compounds. Comparison of radial distribution functions for Li + and H - ions ~zl with the observed distance in crystalline lithium hydride shows that there is a considerable shortening of the internuclear separation when the oppositely-charged ions interact in the formation of the compound. It seems desirable, therefore, to consider the possibility of deriving a value for the radius of the hydride ion which can be collated with other crystal radii of PAULING. GIBBca' has recently proposed the value r a - ~ 1-40/~ for application with radii due to ZACHARIASEN. 14~ In producing his set of crystal radii of ions PAULI:qG~ took the salts NaF, KCI, RbBr and Csl as standard crystals and in these the cation :anion radius ratio p = r_/r_, was found to be ,-,-0-75 (the equilibrium distance r0 in the B 1 modification of CsI was assessed for use in the calculations). To explain divergences between observed distances and radius sums in other alkali halide crystals, PAULING corrected for a radius ratio effect. By multiplying requisite radius sums by F(p), a function of the radius ratio and of the Born repulsion exponent n, excellent agreement with observed distances was obtained (for full details see Ref. 1). " ' L. PAULING, The Nature of the Chemical Bond (3rd Ed.), Cornell University Press (1960). ~tJ E. HYLLEgAS, Proc. Rydberg Centennial Conf. Lund, Sweden, July 1954 p. 83; H. A. BETHE in GERLAG--SCHEEL'S Handbuch der Physik (2nd Ed.), 24, Part I Verlag Julius Springer, Berlin (1933). ~a~T. R. P. GraB, Progr. Inorg. Chem. 3, 315 (1962). t'~ W. H. ZACHARIASEN,Z. Krist. 80, 137 (1931).