TheK-conversion coefficient of 108.2 keV (E3) transition in the decay of165Dy

IL NUOVO CIMENTO VOL. 105 A, N. 2 Febbraio 1992 The K-Conversion Coefficient of 108.2keV (E3) Transition in the Decay of lSSDy. K. RADHA KRISHNA(1), D. L. SASTRy(1), K. VENKATA REDDY(1) M. R. IYER(2) and S. G. SAHASRABHUDHE (2) (1) Swami Jnanananda Laboratories for Nuclear Research, Andhra University Visakhapatnam-530 003, India (2) Health Physics Division, Bhabha Atomic Research Centre - Bombay-400 085, India (ricevuto il 27 Febbraio 1991; approvato il 19 Aprile 1991) Summary. - - The K-conversion coefficient of the 108.2 keV E3 transition in the de- cay of 16SDy was measured using the X-ray peak to gamma method. The ~g value is found to be 2.92_+ 0.08 in agreement with the theoretical value 3.2. PACS 28.40.Nw - Experiments with nuclear reactors. 1. - Introduct ion. 165Dy is a typical odd-A deformed nucleus exhibiting rotational bands characteris- tic of the 150 < A < 190 region. The results of the levels of lSSDy were summarized in Nuclear Data Sheets[i]. The K-conversion coefficient, K/L ratio, K/(L +M) ra- tio, .... measurements have been carried out by several authors [3-6] and classified the present isomeric transition shown in fig. 1, taken from Lederer and Shirley [2], as E3 type. Jordan et al. [3] employed a 180 ~ photographic internal conversion spectro- meter and a scintillation coincidence spectrometer for the measurement of conversion electrons and to establish the coincidence relationships between gamma-rays in the E--decay of 165Dy to daughter 165Ho levels. Hardell and Nilsson [4] used scintillation counters, in singles and coincidence mode to study the decay scheme of 16SDy. Tor- nav[5] measured the ~A value using a scintillation spectrometer. Dutta et al. [6] measured the ~A- of the same isomeric transition with a beta spectrometer. The values due to the above authors [3-6] are summarized in table I together with the theoretical values [7, 8]. We have undertaken a careful measurement of the ~1,- of the 1/2- ---) 7/2 + isomeric transition using a different technique, namely X-ray peak to gamma (XPG) with a high-resolution hyperpure germanium (HpGe) detector system. 165 166 K. RADHA KRISHNA, D. L. SASTRY, K. VENKATA REDDY, ETC. > aJ r oo O 1/2- 7/2+' I 0 165 Dy 66 Fig. 1. - Decay scheme of l~SmDy from ref. [2]. 1.26m 2.33h TABLE I. - aK values (experimental and theoretical). Authors Conversion coefficient Tornav [5] 3.62 + 0.22 Dutta et al. [6] 2.70 + 0.80 Hardell and Nilsson [4] 3.40 _+ 0.20 Jordan et al. [3] 4 Present value 2.92 + 0.08 Theory Rosel et al. [7] 3.2 Hager and Seltzer [8] 3.3 2. - Exper imenta l details. A HpGe detector of coaxial type with an active diameter of 10 mm and depth 7 mm coupled to a microprocessor-based multichannel analyser was employed in the pre- 4.0 3.6 ~ - ,_.3.2 ~ o 52.8 ~2.4 2.0 1.6 1.2 ' ' 1 ' .o ' ' ' ' ' ' ' ' 0.6 0.8 1 2 1.4 1.6 1.8 2.0 2 2 2 4 2.6 2.8 log (energy) Fig. 2. - Efficiency calibration �9 57Co, x 241Am, ~ 152Eu, [] 133Ba. THE K -CONVERSION COEFF IC IENT OF 108.2keV (E3) TRANSIT ION ETC. 167 sent work. The energy and efficiency calibrations were accomplished using the stan- dard reference lines. The efficiency plot is shown in fig. 2. 3. - Source preparation and experimentation. For the present experiment natural dysprosium in its oxide form was uniformly pressed between a cello tape and an X-ray mylar film of thickness 0.00024". The target thickness was of the order of 5 mg/cm e. The target was irradiated at a ther- mal neutron flux of 1.5.109 neutrons/cme/s. The irradiation was carried out re- peatedly to facilitate data collection and used the pooled up counts in the calcula- tion of ~g- The experiment was conducted at the CIRUS reactor site, Bhabha Atomic Re- search Centre, Bombay, India in view of the short half-life (1.26 m) of the source. The source was kept in a close geometry at a distance of 2.2 cm from the detector. The spectrum was recorded for a period of 10 m for each irradiation and it was repeated for six irradiations. The pooled up counts were taken against each channel as shown in fig. 3. The figure shows besides the 108.2 keV gamma-peak, the K~ and K~ X-ray com- ponents arising out of the internal conversion of the 108.2 keV isomeric transition. The areas under the K~, Kz and gamma peaks were computed after subtracting the background. These areas were corrected for self absorption in the target using the relationship (1) I / Io = (1 - exp [-,,zt])/,~t, where 4 , is the thickness of the target and ~,,~, is the mass attenuation coefficient. The ,,~, values were taken from McMaster et al. [9] at each values of X and v-en- 80 70 60 50 cI1 40 S 321 2.8 oo F 2.4 - 30 i i i I i i 114 126 138 20 2.0 1.6 1 1.2 9.8 0.4 0 , i 260 268 10 0 I I I | , I 78 90 102 276 channel number Fig. 3. - Measured X-ray and v-ray spectrum from 165mDy. 1 I i 284 292 168 K. RADHA KRISHNA, D. L. SASTRY, K. VENKATA REDDY, ETC. ergies. The absorption factor for X and gamma lines is of the order of 0.995. After cor- recting for absorption the intensities were corrected for efficiency using fig. 2. The aK value was estimated using the following relationship: (2) aK = IgX/ I~ ~K �9 To get the K-X-ray intensity the corrected Ks and Kz intensities were added. The ~oK value was taken from Bambynek et al. [10]. A substitution of the values of different parameters in the above equation has yielded ~g as 2.92 + 0.08. The compounded er- ror arising out of counting statistics, background subtraction, self-absorption and ef- ficiency corrections is of the order of 3%. The present value is also included in table I for a comparison. 4. - Resu l t s and d i scuss ion . Table I shows that the present value of ~K governing the isomeric transition in 165Dy is in agreement with the theory due to Rosel et al. [7] and Hager and Seltzer [8] within nearly two standard deviations. From table I it can be seen that the value of Jordan et al. [3] is inconclusive. The value of aK due to Tornav [5] is not consistent with the recent theoretical prediction due to Rosel et al. [7] and shows an anomaly of 13%. The ag value reported by Hardell and Nilsson [4] agrees with the theory within experimental uncertainties. The ~K value due to Dutta et al. [6] has a large uncertain- ty of more than 30%. The E3 experimental transition probability of the 108.2 keV gamma transition was calculated and compared with the Moszkowski's [11~ single-particle estimate as given below: (3) T(E3)exp = (3.083 + 0.077)" 10 -4 s -~ , (4) T(E3)~p = 1650" 10 --4 s -1 , (5) E3 hindrance = T(E3)sp/T(E3)exp = 535.23 + 13.39. The present results on the ag measurement of the 108.2 keV transition shows its E3 character in accordance with the earlier studies due to different authors [3-6]. The spin-parity assignments to these states are consistent with the Nilssons model de- scription. The anomaly reported by Tornav [5] is not observed in the present work. The E3 hindrance with respect to the single-particle estimates is understood as 16~Dy belongs to the deformed region. The authors acknowledge the financial support given by the University Grants Commission to carry out the present work. One of the authors, K. Radha Krishna, ac- knowledges the financial assistance given by the Council of Scientific and Industrial Research in awarding him the Senior Research Fellowship. THE K-CONVERSION COEFFICIENT OF 108.2keV (E3) TRANSITION ETC. 169 REFERENCES [1] L. K. PEKER: Nucl. Data Sheets, 50, 137 (1987). [2] C. M. LEDERER and V. S. SHIRLEY (Editors): Table of Isotopes, VII edition (John Wiley, New York, N.Y., 1978), p. 983. [3] W. C. JORDAN, J. M. CORK and S. B. BURSON: Phys. Rev., 92, 1218 (1953). [4] R. HARDELL and S. NILSSON: Nucl. Phys., 39, 286 (1962). [5] R. TORNAV: Z. Phys., 159, 101 (1960). [6] B. C. DUTTA, T. V. EGIDY, TH. W. ELZE and W. KAISER: Z. Phys., 207, 153 (1967). [7] F. ROSEL, H. M. FRIES, F. ALDER and H. C. PAULI: At. Data Nucl. Data Tables, 21, 91 (1978). [8] R. S. HAGER and E. C. SELTZER: Nucl. Data, 4, 1 (1968). [9] W. H. MCMASTER, N. KERR DEL GRANDE, J. H. MALLETT andJ. H. HUBBELL: Compilation of X-Ray Cross Sections (Lawrence Radiation Laboratory, Livermore, 1969), p. 265. 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