Decay of 85Sr

; im~rg. ,lu~t Chem, 1977, Vol, 39, pp, 919-920. Pergamon Press.

Printed in Great Britain

DECAY OF 85Sr WILLIAM W. PRATT Department of Physics, The Pennsylvania State University, University Park, PA 16802. U.S.A. (Received 9 August 1976) Abstract--A study of the decay of aSSrhas confirmed the presence of a weak transition with an energy of 868 keV in 8~Rb. The intensity of the de-excitation 3'-ray has been found to be (1.154-+0.063)× 10-4 relative to that of the 514keV y-ray.

INTRODUCTION

in an early scintillation spectrometer study of the decay of 85Sr, a weak ,/-ray with an energy of 878-+ 12 keV was found by Sattler[1], which he attributed to the deexcitation of a level at that energy in S~Rb. This ,/-ray was confirmed in a later scintillation spectrometer study by Vartanov et al.[2]; and the corresponding state in 85Rb has been well established by other means by numerous other investigators [3-7]. The energy of this state has been more accurately determined to be approx. 868.5 keV. The population of this state in the decay of SSSr has been called into question by Bubb et al.[8]. They carried out a measurement of the ,/-spectrum of 85Sr using a high resolution Ge(Li) detector and found that the 868 keV ,/-ray did not maintain a constant intensity when chemical purifications of the source were carried out. They accordingly attributed this ,/-ray to an impurity in the source. A more recent Ge(Li) study of 85Sr by Vatai et al.[9] has indicated that the intensity of this ,/-ray does remain constant when the source is chemically purified and leads these investigators to the conclusion that this y-ray is attributable to the decay of S~Sr. It is the purpose of the present paper to describe additional evidence that the 868keV ,/-ray does follow the decay of SSSr as originally proposed by Sattler. Sources of 8~Sr were prepared by sealing high purity samples of strontium compounds in polyethylene or quartz tubing and exposing them to thermal neutrons from

our nuclear reactor, thereby producing 85Sr via the (n, y) reaction in S4Sr. After a delay of at least one week to allow for the decay of short lived isomers of 85Sr and SYSrthe source was placed in front of a 35 cm 3 Ge(Li) detector with a 1.27 cm aluminum shield interposed to absorb /3-rays from the 51 day sgsr. The detector has a resolution of 3 keV for the 1333 keV y-ray of ~°Co. Each source was counted for a period ranging from 4 to 15 days. A total of 11 different measurements were made as follows: 2 measurements with a source prepared from SrCO,, 1 measurement with a source prepared from SrCI2, 6 measurements with a source prepared from Sr(NO3)2 and 2 measurements with a source prepared from Sr(NO3)2 in which the 8~Sr isotope had been enriched (by a factor of 136) to 76%. The time delays between source production and counting time mid-point varied from 12 to 375 days corresponding to a range of 5.6 half lives of S'Sr. Each measurement consisted of a determination of the ratio of the intensity of the 868 keV y-ray to that of the known 514 keV T-ray. A comparison of the results obtained with the different SSSr sources is shown in Table 1. The errors are standard deviations based on the consistency of different measurements using the same source. They do not include a 5% error associated with the intensity calibration, which was obtained using standard sources of ,/-rays of known relative intensity. This error will affect all ratios in the same way. The results shown in Table 1 indicate that there

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I

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I

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I

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400

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Fig. 1. Intensity ratio as a function of time. The solid line is a fit of the data to a curve of the form ae b'. 919

920

WILLIAM W. PRATT Table 1. Intensity ratios obtained with different sources Source SrCO3 SrC12 Sr(NO3)2 S'Sr(NO3)2

I(868 keV) × 10~ 1.146 -+0.058 1.268 -+0.082 1.158 -+0.034 1.095 -+0.058

obtain the best value for the intensity ratio the result is: 1(868 keV) = (1.154 -+0.063) x 10-' 1(514 keV) where the error includes an error of 5% associated with the intensity calibration. This result is in good agreement with those of both Sattler and Vatai et al. Acknowledgement--The assistance of the staff of the Breazeale Nuclear Reactor in performing neutron irradiations is gratefully acknowledged.

REI~RENCES is no significant difference in the intensity ratios obtained using different strontium compounds; nor does this ratio change to a significant extent when the enriched ~Sr isotope is substituted for normal strontium. Figure 1 shows the intensity ratio plotted as a function of the time delay between source production and counting time mid-point. The solid line represents a least squares fit of the data to a curve of the form ae b'. The value of b is found to be (1.64-+ 1.40) x 10-4 days-' which indicates that the half lives of both ~,-rays are the same within approx.

1.5%. All of the above measurements confirm the assignment of the 868 keV 3,-ray to the decay of 85Sr as originally proposed by Sattler. When all of the data are combined to

1. A. R. Sattler, Phys. Rev. 127, 854 (1%2). 2. N. A. Vartanov, P. S. Samoilov and Y. S. Tsaturov, Soviet J. Nucl. Phys. 3, 436 (1%6). 3. R. C. Ragaini, C. F. Smith and R. A. Meyer, Bull. Am. Phys. Soc. 17, 444 (1972). 4. R. P. Torti, V. M. Cottles, V. R. Dave, J. A. Nelson and R. M. Wilenzick, Phys. Rev. C6, 1686 (1972). 5. P. D. Bond and G. J. Kumbartzki, Nucl. Phys. A205,239 (1973). 6. E. Barnard, N. Coetzee, J. A. M. de Villiers, D. Reitmann and P. van der Merwe, Z. Phys. 260, 197 (1973). 7. J. R. Comfort, J. R. Duray and W. J. Braithwaite, Phys. Rev. C8, 1354 (1973). 8. I. F. Bubb, S. I. H. Naqvi and J. L. Wolfson, Nucl. Phys. A167, 252 (1971). 9. E. Vatai, A. C. Xenoulis, K. R. Baker, F. Tolea and R. W. Fink, Nucl. Phys. A219, 595 (1974).