Kalyani, V D M L

Prasad, N V S Vara

Rao, M V S Chandrasekhar

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j  phys. 71A (4), 493-500 (1997)IndianI J P  A— an international journalStudies on K -electron  capture probability  in the  decay o f 95T c an d  139CeV D M L  Kalyani, N V S Vara Prasad, M V S  Chandrasekhar Rao, N R Mishra, G S K  Murthy*, G Satyanarayana and D L SastrySwann Jnanananda Laboratories for Nuclear Research, Andhra University,Visnkhaputnam-530 003, IndiaandS N ChintalapudiIntel University Consortium for DAE facilities. Salt Lake, Calcutta-700 091,IndiaReceived II October 1996, accepted 30 January 1997Abstract : The electron capture probability measurements were performed in the decay of y4STc to the 1073.8 and 765.79 keV levels in the daughter 95Mo using a x-y internal sum coincidence technique for the first time. The experimental Pk values of the transitions were estimated to be 0.868 ± 0.052 and 0.870 ± 0 040 in agreement with the theoretical values 0.879 and 0.880, respectively The Pk value of the allowed transition in the decay of 1:19La was also measured employing the same technique. The experimental Pk value was found to be 0 714 ± 0 025 in agreement with the theoretical value 0.723.Keywords : K-electron capture probability, allowed transitions x-y  internal sum coincidence, HPGc system.TAGS Nos. : 23 40.Hc, 27.60 +j1- IntroductionSludies on electron capture probabilities are not only of interest in Nuclear Science but also in Astrophysics, Nuclear Medicine, Nuclear masses e t c .  We have taken up a systematic piogrjnimc on these measurements following the jc-ysum coincidence technique proposed hy Das Mahapatra and Mukherjee [1]. Our recent results in l68Tm and ,83Re were reported hy Vara Prasad e l  a l  \ 2 \ .  The same paper includes references to our earlier studies. We have employed a similar experimental technique to undertake the present measurements also and <‘'llowcd identical experimental procedures to determine P K (expt.) values. .ThePresent Address : Department of Radiology, UMDNJ, 185 S. Orange Avenue, Newark NJ-07 103, U$A© 1997 I ACS494 V D M L Kalyani et alexperimental arrangement essentially consists of a high resolution (220 eV at 5.9 kcV 0f Mn Ka line) HPGe detector coupled to a computer controlled multi channel analyser. The experiments were performed with a source at a distance of 5 cm from the surface of the detector, so as to reduce the detector dead time. The relative efficiency calibration of the system was performed in the usual manner and is shown in Figure 1.Figure 1. The relative efficiency of the HPGe system.2. 95Tc (Ti/2 = 20 h)A partial decay scheme of 95Tc which is of present interest is shown in Figure 2, taken from Lederer and Shirley [3]. Figure 2 shows that 93% of electron capture decay of 9STc proceeds to the 765.79 keV level while 4.5% to the 1073.8 keV level. The decay of these levels v i a  765.79 and 1073.8 keV transitions to the lower ones are shown in Figure 2 hy wide lines. Both transitions appear to be allowed beta transitions following the spin sequence 7/2+ —> 5/2+. No previous measurements are available on the /\  values of these two transitions though the other spectroscopic parameters are known. Thus, it is felt worthwhile to undertake the present study on the'P* values in the decay of wTc.C O J NT 5Studies on K-electron capture probability etc 495The radioisotope 95Tc was produced at the Variable Energy Cyclotron Centre, Calcutta, India v ia  92Mo (a,p) at a beam energy of 15 McV and current 200 nA. The largett iECTC0.5 *44.5 •/.93*420hFigure 2. A partial decay scheme of 95Tc.thickness was 1.2 mg/cm2. After withdrawing the source from the site of irradiation, a ns ai ling period of about one day was allowed before commencing the data collection to i m n u n i / c  interferences due to short lived activities. The jc-y spectrum was collected using ihc HPCie (system) and is shown in Figure 3. The data was collected over a time period so600bOO1.003007001 0 0i !04ii1.0Figure 3. The X-ray, gamma and sum spectrum from w Tcas ensure a good statistical accuracy (< 1%) in singles and y + x  sum lines. From f igurc 3, it may be seen that the gamma transitions of present interest 765.79 and 1073.8 keV and the corresponding sum lines (y*-K X-ray) show up in Figure 3.496 V D  M L  K a lyan i e ta l2. /. Computation of the experimental Pk value to the 765.79 keV level:The experimental Pk value was computed using the following relationship taken from Bambynek et al 14).f/7 8 6 a 786 ' r /"786 T^765 7<»+K ~  a ) k £ k \ ' jT 6 5 / > ' 5 5 1  8 + ** 1 +  a ™ 6 +  -P k 's, ( X s  and f ' s  represent the K-electron capture probabilities, Internal Conversion Coefficients and intensities of the respective transitions respectively, 765T represents the total intensity of the gamma rays decaying from the 765 KeV level, N's represent the intensities of gamma and gamma + K X-ray lines and £k is the absolute efficiency of the K X-ray. The intensities of the individual gamma and sum lines were obtained from Figure 3 using the fitting routines after subtracting the linear background. The intensities thus obtained, were corrected for efficiency using Figure 1 and self-absorption (lies within experimental errors). The sum peak intensity was also corrected for chance coincidences ar's were taken from Rosel et al [5]. In the above equation the K-fluorescent y\eld, was taken from the tables of Bambynek et al [ 6 ] P ]k551'* is due to the interference from thip upper1551.8 keV level and the P ]551 8 theoretical value was computed using the relationships ot Behrens and Janecke [7). The absolute efficiency of the K X-ray was determined in the following manner.The spectra of 81 keV and 356 keV reference lines from ,33Ba were studied in a separate experiment in an identical geometry. The absolute efficiency of the 356 keV transition was determined with the help of the following relationship.-  8^1 , + a 356 '356 ( 2 )Here, i and V8, are the intensities of the sum 356 + 81 and 81 keV lines, respective!) and ls lhe absolute efficiency of the 356 keV line. The value of Rosel et  al [5| was used in the above equation. A substitution of 56+8|, /Vgj and a ” 6 in eq. (2) gives the absolute efficiency (£3 5 6 ) of the 356 line. The absolute efficiency of the K X-ray that appears in eq. (I) is related to the absolute efficiency of the 356 keV transition hy the following relationship.K)ubs (3)The relative efficiency values of K X-ray and 356 keV gamma transitions were obtained from Figure I. The values of different parameters that occur in eq. (1) are summarized in Table I. The different parameters thus obtained, were substituted in eq. (1) to gel (expt). The Pk (theory) was also computed using the relatioship of Behrens and Janecke 17]Studies on K-electron capture probability etc 497and the Q zc  value £*uc to Wapstra and Bos [8]. The experimental and theoreticalPj65 79 values are summarized in Table 2. The compounded error assigned to P* (expt.) is due to lhe individual errors in ^intensities (~ 0.5%), e* (4.2%) and ek (2%).Table I. Values of different parameters used to obtain the Pk (expt) values of ihe 765.79 keV level and 1073.8 keV level of present interest in the electron capture decay of 95Tc and 165.85 keV level in the electron capture decay of '™ C e .Nucleus Parameter Value(Ok 0.764 ± 0  032€k 0.084910,0017«T c ^765.79 26826321 1739^765.79+K 1514201509^1073 1651741605W|07.3+K 93061 349€k 0J 009 1  0 0020l'V e ** 0 906 1  0.026^165 8 16963601 1630^1658+K 1107181890Table 2. Fa  peri mental and theoretical Pk values in 95Tc and ,?9Ce.Pk valueNucleus Level energy in the daughter (keV)Transition Expt Theory765.79 7/2+ -> 5/2+ 0.8701 0.040 0 8801073.8 in* -* sn* 0 868 10.052 0 879n 9 Cc 165.8 V2+ - > m* 0 .71410  025 0 723- - Computation o f  experimenta l p£073 H ;The experimental value of P k to the 1073.8 keV level was computed just as in the previous Laxc and with the help of the following relationship,N,1073 8+ K p,1551.8 +a 477l +  a :TFT + P,1 -f477  r l073 8 1073 8 ’ (4)which also includes contribution from the EC decay of the upper 1551.8 keV level.Alter applying the usual corrections to the observed 1073.8 gamma and 1073.8 + X hne intensities in Figure 3, the final values of gamma and sum peak intensities were determined A substitution of different parameters in eq. (4) has yielded the experimental P k498 V D M L Kalyani et alvalue as 0 . 8 6 8  ± 0.052. The errors were estimated just as in the case of P k of the 765.79 keV level. The theoretical value of P k was computed to be 0.879. The different values of P k and the corresponding theoretical values are summarized in Table 2.Table 2 shows that the present experimental values of P k agree with the theory. We have also computed the theoretical values using Q EC values due to different mass relationships. We have found that the P k values are not sensitive to the variation in QKC. The present value of P \ m  8  is in good agreement with the Q EC value due to Wapstra and Bos 18].3. *-wCe (T , / 2  = 137.2 d)The decay of ,39Cc is v ia  electron capture to the daughter , 3 9 La. It is a simple decay scheme and well studied as shown in Figure 4. The K-electron capture probability was measured by\3 /2 ‘ 137.2 ans58CeEC5/2 r 1 A 8 n s -------keV16 5.85 165 85 100 V.7lLMl1)957LaFigure 4. The decay scheme of * 3\ ’e0several authors |3] employing different experimental techniques. However, one sees discrepancies in the P k values ranging from 0.65 to 0.87. Hence, we felt that it was worthwhile to undertake a rcmcasurement of the same accurately by using the sum coincidence technique.The ,3l,Cc source was produced v i a  ngLa (a, p3n) reaction at a beam energy of 55 MeV and a current of 200 nA at the Variable Energy Cyclotron Centre, Calcutta, India. Alter allowing a wailing time ol one week to eliminate the short lived activities, the experimental data were collected in the same geometry employed for wTc. The gamma transition of present interest, namely, 165.8 keV follows the spin sequence of 5/2* —» 7/2* while the corresponding K X-ray energy, a weighted average of Ka and fy , is 34.18 keV. The gamma and the .v-ysum lines are shown in Figure 5 . The final values of y + x  sum intensities weie determined in the usual manner after applying the necessary corrections. In the case of sum peak intensity, the 5/2* level half-life of 1.48 ns is of no consequence in theStudies on K-electron capture probability1 etc 499present measurement in as much as the resolving time of the detector system is 2 |xs. The p ' M  h (expt.) was determined using the following relationship.N 165.8+K a ke t Fi N 165.8* (5)The absolute efficiency of the K X-ray line (weighted average of Ka and Kp) was determined following the procedure given for 95Tc. The different parameters used for theCHANNEL N U M B E RFigure 5. The X-ray, gamma and sum spectrum from ,39Ce.calculation of P k (expt.) are also given in Table 1. After a substitution of (Oh  £k> N | 658 and A/U,s K+K in eq. (5), the experimental P k value was calculated and is found to be 0.714 ± 0 025. The error to the experimental P k value is assigned after taking into account the individual errors as mentioned in the case of 95Tc. The P k (theory) was computed using the Q i c  value due to the mass relationship of Wapstra and Bos [8] and the theoretical value ihus obtained, is 0.723. These values are included in Table 2. The present experimental value is seen to be in good agreement with the theory due to Behrens and Janecke [7].4. ConclusionsThe experimental values of the electron capture probabilities in the decay of 95Tc and M9Ce are measured using ajc-ysum coincidence method. The relevant transitions following the same spin sequence 7/2+ —> 5/2+ in the decay of 95Tc to the daughter (9SMo) levels 765.79 keV and 1073.8 KeV are found to be 0.870 ± 0.040 and 0.868 ± 0.052 respectively in agreement with the theory within the experimental uncertainties. The P k value governing the EC transition (5/2* -> 7/2+) in the decay of ,39Ce to the daughter (,39La) level165.8 keV is measured to be 0.714 ± 0.025, consistent with the theoretical value. The present experimental P k values are seen to be in accordance with the mass relationship due lo Wapstra and Bos.500 V DM  L Kalyani et alAcknowledgmentsThe authors acknowledge the Inter-University Consortium for DAE Facilities, under the University Grants Commission (UGC), Calcutta centre for the financial support and facilities provided to carry out the present studies. Three of the authors NVSVP, MVSCR, GSKM convey their thanks to the Council of Scientific and Industrial Research (CSIR), India for giving them the fellowship grant.References[ I ] B K Das Mahapatra and P Mukherjee J. Phys A7 388 (J974)12] N V S Vara Prasad, G Sree Krishna Murty, M V S  Chandrasekhar Rao, S Bhuloku Reddy, G Saryanarayana, D L Sastry and S N Chimalpudi J Phys. G20 451 (J 994)[3] C M Ledercr and V S Shirley Table of Isotopes (New York : Wiley Interscience) 7th edn ( I97H)(4) Bainbynek etal. Rev Mod Phys. 49 141 (1977)|5] F Rosel, H M Fries, K Alder and H C Pauli At. Data Nucl. Data Tables 21 110 (1975)[6] W Bambynck, B Crasemann, R W Fink, H U Freund, H Mark, C D Swift, R E Price and P V Rao Rev Mod Phys. 44 716 (1972)|7] H Behrens and J Janecke Numerical Data and Functional Relationships in Science and Technolof>\. Nanicruul Data Table* for a-decay and electron capture (Landolt l-Bdrnstein Senes) 4 (Beilin Springer) (1969)[8] A H Wapstra and K Bos At Data Nucl Data Tables 17 474 ( 1976)

Studies on K-Electron Capture Probability in the Decay of 95tc and 139Ce

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Studies on K-Electron Capture Probability in the Decay of 95tc and 139Ce

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