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The negaton transition in 196Au
I
4.E
[ I
Nuclear Physics 31 (1962) 5 8 4 - - 5 8 6 ; ~ ) North-Holland Publishing Co., Amsterdam Not to be reproduced by photopriat or microfilm without written permission from the publisher
THE N E G A T O N T R A N S I T I O N IN t96Au E. W . A. L I N G E M A N , K . E. G. L O B N E R , G. J. N I J G H a n d A. H. W A P S T R A
Instituut voor Kernphysisch Onderzoek, Amsterdam, The Netherlands Received 23 O c t o b e r 1961 T h e end p o i n t e n e r g y of t h e n e g a t o n s p e c t r u m e m i t t e d b y 6-d 19eAu is m e a s u r e d to be 259 4-4 keV, as o b s e r v e d b y m e a s u r e m e n t s in coincidence w i t h t h e following 426 k e V g a m m a t r a n s i t i o n . F o r t h e half-life of l°6Au, a v a l u e 6.074-0.11 d w a s found.
Abstract:
1. Introduction In the preceding paper 1) measurements have been described on the decay of 6-d 19eAu. In that investigation the continuous beta spectrum due to transitions to the 426-keV level in 19eHg was found to be considerably disturbed by the presence of the strong conversion lines belonging to the electron capture branch. We have now tried to circumvent this difficulty by measuring coincidences between electrons and gamma rays, the electrons being detected by a magnetic spectrometer. The electrons belonging to the continuous beta spectrum are in coincidence with the 426-keV gamma transition in 19eHg, while the disturbing conversion electrons are coincident with the gamma rays of 333 and 356 keV in 19ept (and only very weakly with higher-energy transitions). The two groups of electrons can therefore be separated by analyzing the gamma spectra observed in coincidence with the electrons detected by the beta spectrometer in each energy setting used. In order to make this separation more clear-cut a lead absorber was inserted between the source and the gamma detector, so that the latter was made relatively less sensitive to the lower-energy gamma rays; this also made it possible to use a stronger source without overloading the gamma channel by the dominant 333-356 keV peak.
2. Equipment The present work was done with the lens type beta-ray spectrometer of this Institute 2). The strong K conversion line associated with the 356-keV gamma transition was used for energy calibration. The adjustments were such as to yield a line width (full width at half height) of approximately 4 %. As beta detector we used a conically shaped plastic scintillator, as gamma detector a 45 mm diam. × 50 mm NaI (TI) crystal (Quartz et Silice), both with E.M.I. 6097 photomultiplier tubes. This arrangement will be described in greater detail 584
NEGATON TRANSITION IN 196Au
585
in a forthcoming paper. The gamma spectra observed in coincidence with the electrons focused by the beta-ray spectrometer were displayed on one of the quadrants of an R I D L model 34-12 400-channel analyzer. The experiment was performed with one of the sources used for the work described in ref. 1), to which paper we refer for information about its preparation. 3. R e s u l t s a n d D i s c u s s i o n
Coincident gamma spectra were recorded for energy settings of the beta-ray spectrometer of 101, 127, 166, 196 and 229 keV, respectively. The intensity of the 426-keV photopeak in these spectra was determined after applying a correction for accidental coincidences, which was only small in the region of interest due to the low intensity of the 426-keV peak in the single spectrum. Two separate sets of data were collected under different conditions of coincidence resolving time, lead absorber thickness and source strength. The resulting Kurie diagrams were slightly curved upward at the low energy end, which can be attributed to scattering effects due to the thick backing of the available source and the geometric situation. We therefore determined the end point of the spectrum by straight-line extrapolation of the Kurie diagram using only the data at the highest three energy settings, by which procedure the influence of the scattering effects on the result should have been reduced to negligible proportions. The possibility of an energy dependent angular correlation in the betagamma cascade was neglected because the energy dependence is expected to be small due to the low endpoint energy and the high Z value and because moreover any angular correlation should be smeared out to a large extent under our geometric conditions. I x%.
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'
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2C)0
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250 kcV "E
Fig. 1. K u r i e d i a g r a m of t h e n e g a t o n s p r e c e d i n g t h e 426-keV g a m m a t r a n s i t i o n in t h e d e c a y of 6-d X98Au (average of b o t h sets of d a t a ) .
586
E.w.A.
LINGEMAN e~ al.
The two sets of data agreed well with one another and were averaged to give a final value for the maximum negaton energy of 259±4 keV, corresponding to a decay energy of 685-[-4 keV from the ground state of 19eAu to that of 19SHg. The averaged Kurie diagram is shown in fig. 1. Also, the half-life of the ground state of 196Au was determined from the intensity of the 333-356 keV peak in the single gamma spectrum. We found a value of 6.07:[:0.11 d, in good agreement with the result quoted in ref. 1). In view of the time elapsed between source preparation and the experiment described above (nearly three half-lives) we are led to believe that the shorter values quoted in earlier papers (see ref. 1) m a y have been the result of the presence of contaminating activities with a shorter half-life. It is a pleasure to thank Prof. Dr. P. C. Gugelot for his interest in this work, which is part of the research programme of the "Stichting voor Fundamenteel Onderzoek der Materie" (F.O.M.), financially supported by the "Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek" (Z.W.O.). One of us (K.E.G.L.) is indebted to Euratom for a grant enabling him to take part in this work. References 1) A. H. W a p s t r a , J. F. W. Jansen, P. F. A. G o u d s m i t and J. Oberski, Nuclear Physics 31 (1962) 575 2) N. F. Verster, G. J. Nijgh, R. van Lieshout and C. J. Bakker, Physica 17 (1951) 637
4.E
[ I
Nuclear Physics 31 (1962) 5 8 4 - - 5 8 6 ; ~ ) North-Holland Publishing Co., Amsterdam Not to be reproduced by photopriat or microfilm without written permission from the publisher
THE N E G A T O N T R A N S I T I O N IN t96Au E. W . A. L I N G E M A N , K . E. G. L O B N E R , G. J. N I J G H a n d A. H. W A P S T R A
Instituut voor Kernphysisch Onderzoek, Amsterdam, The Netherlands Received 23 O c t o b e r 1961 T h e end p o i n t e n e r g y of t h e n e g a t o n s p e c t r u m e m i t t e d b y 6-d 19eAu is m e a s u r e d to be 259 4-4 keV, as o b s e r v e d b y m e a s u r e m e n t s in coincidence w i t h t h e following 426 k e V g a m m a t r a n s i t i o n . F o r t h e half-life of l°6Au, a v a l u e 6.074-0.11 d w a s found.
Abstract:
1. Introduction In the preceding paper 1) measurements have been described on the decay of 6-d 19eAu. In that investigation the continuous beta spectrum due to transitions to the 426-keV level in 19eHg was found to be considerably disturbed by the presence of the strong conversion lines belonging to the electron capture branch. We have now tried to circumvent this difficulty by measuring coincidences between electrons and gamma rays, the electrons being detected by a magnetic spectrometer. The electrons belonging to the continuous beta spectrum are in coincidence with the 426-keV gamma transition in 19eHg, while the disturbing conversion electrons are coincident with the gamma rays of 333 and 356 keV in 19ept (and only very weakly with higher-energy transitions). The two groups of electrons can therefore be separated by analyzing the gamma spectra observed in coincidence with the electrons detected by the beta spectrometer in each energy setting used. In order to make this separation more clear-cut a lead absorber was inserted between the source and the gamma detector, so that the latter was made relatively less sensitive to the lower-energy gamma rays; this also made it possible to use a stronger source without overloading the gamma channel by the dominant 333-356 keV peak.
2. Equipment The present work was done with the lens type beta-ray spectrometer of this Institute 2). The strong K conversion line associated with the 356-keV gamma transition was used for energy calibration. The adjustments were such as to yield a line width (full width at half height) of approximately 4 %. As beta detector we used a conically shaped plastic scintillator, as gamma detector a 45 mm diam. × 50 mm NaI (TI) crystal (Quartz et Silice), both with E.M.I. 6097 photomultiplier tubes. This arrangement will be described in greater detail 584
NEGATON TRANSITION IN 196Au
585
in a forthcoming paper. The gamma spectra observed in coincidence with the electrons focused by the beta-ray spectrometer were displayed on one of the quadrants of an R I D L model 34-12 400-channel analyzer. The experiment was performed with one of the sources used for the work described in ref. 1), to which paper we refer for information about its preparation. 3. R e s u l t s a n d D i s c u s s i o n
Coincident gamma spectra were recorded for energy settings of the beta-ray spectrometer of 101, 127, 166, 196 and 229 keV, respectively. The intensity of the 426-keV photopeak in these spectra was determined after applying a correction for accidental coincidences, which was only small in the region of interest due to the low intensity of the 426-keV peak in the single spectrum. Two separate sets of data were collected under different conditions of coincidence resolving time, lead absorber thickness and source strength. The resulting Kurie diagrams were slightly curved upward at the low energy end, which can be attributed to scattering effects due to the thick backing of the available source and the geometric situation. We therefore determined the end point of the spectrum by straight-line extrapolation of the Kurie diagram using only the data at the highest three energy settings, by which procedure the influence of the scattering effects on the result should have been reduced to negligible proportions. The possibility of an energy dependent angular correlation in the betagamma cascade was neglected because the energy dependence is expected to be small due to the low endpoint energy and the high Z value and because moreover any angular correlation should be smeared out to a large extent under our geometric conditions. I x%.
\x\ x~
\
',6o'
'
,5o'
'
'
2C)0
'
250 kcV "E
Fig. 1. K u r i e d i a g r a m of t h e n e g a t o n s p r e c e d i n g t h e 426-keV g a m m a t r a n s i t i o n in t h e d e c a y of 6-d X98Au (average of b o t h sets of d a t a ) .
586
E.w.A.
LINGEMAN e~ al.
The two sets of data agreed well with one another and were averaged to give a final value for the maximum negaton energy of 259±4 keV, corresponding to a decay energy of 685-[-4 keV from the ground state of 19eAu to that of 19SHg. The averaged Kurie diagram is shown in fig. 1. Also, the half-life of the ground state of 196Au was determined from the intensity of the 333-356 keV peak in the single gamma spectrum. We found a value of 6.07:[:0.11 d, in good agreement with the result quoted in ref. 1). In view of the time elapsed between source preparation and the experiment described above (nearly three half-lives) we are led to believe that the shorter values quoted in earlier papers (see ref. 1) m a y have been the result of the presence of contaminating activities with a shorter half-life. It is a pleasure to thank Prof. Dr. P. C. Gugelot for his interest in this work, which is part of the research programme of the "Stichting voor Fundamenteel Onderzoek der Materie" (F.O.M.), financially supported by the "Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek" (Z.W.O.). One of us (K.E.G.L.) is indebted to Euratom for a grant enabling him to take part in this work. References 1) A. H. W a p s t r a , J. F. W. Jansen, P. F. A. G o u d s m i t and J. Oberski, Nuclear Physics 31 (1962) 575 2) N. F. Verster, G. J. Nijgh, R. van Lieshout and C. J. Bakker, Physica 17 (1951) 637