- Email: [email protected]
Precision measurements in 124Te following the decay of 124Sb
ARTICLE IN PRESS
Applied Radiation and Isotopes 64 (2006) 693–699 www.elsevier.com/locate/apradiso
Precision measurements in
124
Te following the decay of
124
Sb
Amol Patil, D. Santhosh, K. Vijay Sai, M. Sainath, K. Venkataramaniah Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthinilayam 515 134, India Received 14 April 2004; received in revised form 12 December 2005; accepted 12 December 2005
Abstract The decay of 124Sb (60 d half-life) to levels of 124Te has been studied using two HPGe detectors in singles and coincidence mode. We identify 75 transitions in this decay, including 14 gamma rays, the emission of which are being reported here for the first time. In confirming the existence of 26 well-established levels below 2900 keV excitation, we also introduce 5 other levels at 2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV. The data on energies of gamma transitions and the levels are reported at high precision. r 2006 Elsevier Ltd. All rights reserved. Keywords: Radioactivity;
124
Sb beta decay; Singles and coincidence studies;
1. Introduction The even–even isotope 124Te has been the subject of considerable interest (Auble and Ball, 1972; Lien et al., 1977) since it is the testing ground for different theoretical models. Till now, no complete understanding of nuclear structure of this nucleus has been achieved. Even many aspects of the low-lying spectrum are still puzzling (Warr et al., 1998). The level structure of 124Te has been investigated through the study of 124Sb (t1=2 ¼ 60:2 days) decay as well as through nuclear reactions (Iimura et al., 1997). Several levels in 124Te that were established in the decay studies of various workers (Meyer et al., 1969; Johnson and Mann, 1974; Sharma et al., 1979; Mardirosian and Stewart, 1984; Jianming et al., 1988; Goswamy et al., 1993) have not been supported unambiguously and they have never been reported by any of the reaction studies. Conversely, several levels which in view of the decay energy might have been studied by 124Sb decay, have only been reported in reaction studies (Bushnell et al., 1969; Christensen et al., 1970; Auble and Ball, 1972; Lien et al., 1977). Fourteen new gamma transitions and two new levels have been reported by Iimura et al. (1997). Jianming et al. (1988) have studied Corresponding author. Tel.: +91 8555287235; fax: +91 8555287474.
E-mail address: [email protected] (K. Vijay Sai). 0969-8043/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.12.010
124
Te level scheme
this decay through singles and coincidence measurements, reporting nine new gamma transitions, also trying to establish four new levels at 2512, 2550, 2808.8 and 2814.5 keV. Based on their coincidence data, Jianming et al. (1988) ruled out the presence of 34 of the previously reported gammas (Lederer et al., 1978; Sharma et al., 1979; Mardirosian and Stewart, 1984). Goswamy et al. (1993) confirmed the levels at 2808 and 2814 keV and nine gamma rays of energies 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9, and 2808.0 keV. Apart from the energies of the levels and the gamma transitions, the intensity values for many weak gamma rays measured by different workers are inconsistent with each other. The present work attempts to: (i) clarify the abovementioned discrepancies and to confirm the new results of Jianming et al. (1988) and Goswamy et al. (1993); (ii) determine the energies and intensities of gamma transitions, and (iii) propose a revised level scheme for 124 Te by a reinvestigation of the decay of 124Sb aiming at precision measurements (singles and coincidence studies). By looking for the weak transitions that could not be seen in earlier decay studies, an effort has been made to look for several of the energy levels that were proposed in particle transfer reaction studies (Auble and Ball, 1972; Lien et al., 1977) but which were not reported in the beta decay studies. This becomes possible with present precision
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gamma spectroscopy systems and has lead to very interesting results for other nuclei (Sainath et al., 1999, 2003). 2. Experimental procedure 2.1. Singles Gamma-ray measurements A carrier-free sample has been obtained of the radioactive source 124Sb, being produced by thermal neutron irradiation of 123Sb at the Bhabha Atomic Research Centre (Mumbai) in the form of antimony chloride (SbCl3) in dilute HCl solution. The 124Sb source was allowed to decay for about 8 months, primarily to rid the source of any short-lived impurities. Sources for acquiring spectra were prepared by drying the source solution on aluminized mylar foil supported by thin aluminium discs of 1 cm diameter. The count rate was kept at around 500 counts/s.
Table 1 Coincidence measurement results from decay of Energy (keV)
124
Sb
Singles gamma spectra were recorded with two 60 cm3 HPGe detectors (FWHM ¼ 1.80 keV at 1.33 MeV) coupled to an 8k PC-based Multichannel Analyser. Gamma singles spectra were acquired at a source to detector distance of 25 cm. The counting period lasted an average of 4.5 105 s/ spectrum. Efficiency calibration for HPGe detectors was done using standard radioactive sources obtained from the International Atomic Energy Agency, Vienna. The lowenergy spectrum was acquired using a Si(Li) detector (FWHM ¼ 180 eV at 5.9 keV). The gamma ray peaks were analysed using the computer codes FIT (Petkov and Bakaltchev, 1990) and Gamma Vision (version 5.10 EG&G ORTEC (1998)). 2.2. Gamma–gamma coincidence measurements Coincidence measurements were performed with the above mentioned two 60 cm3 HPGe detectors. A standard fast–slow coincidence system with the time resolution of 20 ns was used. The source to detector distance was maintained at 10 cm. Coincidence spectra were taken by setting gates at 602, 614, 709, 714, and 723 keV gamma energies, as summarized in Table 1.
Gate (keV)
3. Results and discussion 603 183 336 444 511 525 603 646 662 670 709 715 722 736 790 899 968 1045 1068 1178 1198 1263 1325 1355 1368 1376 1436 1445 1489 1526 1580 1690 1720 1919 2033 2091 2287
646
709
714
723
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Our typical gamma spectra are shown in Fig. 1(a–h). We explain the comparison with a ‘bench mark’ test to establish the credibility of our identification of as yet unconfirmed weaker transitions and their precise energies. The most recent energy calibration standard for 125Sb (IAEA, 1995; Firestone and Shirley, 1996; IAEA–TECDOC-619, 1991) have been compared with our results obtained in Table 2(a); a similar comparison with the additional transitions included in the ‘standardization analysis’ (Helmer, 1990) is presented in Table 2(b). It is seen that almost in all cases the deviations are comparable to the assigned uncertainties. The average deviation for the 16 transition energies is less than 8 eV. The excellent agreement of our measured gamma energies and accepted ‘benchmark values’ in the IAEA calibration tables and other similar measurements provides us with a firm basis for the identification of new transitions and also for the use of our measured gamma ray energies to arrive at a revised level scheme for 124Te through application of the Ritz combination principle (Mitropolsky I.A., 2003). A complete list of the energies and relative intensities of 75 gamma transitions observed in our study and shown in Fig. 1(a–h) is given in Table 3. In addition to a comparison of our intensity values, we also include results from Mardirosian and Stewart (1984); Jianming et al. (1988) and Goswamy et al. (1993). In accordance with the usual convention, intensities in the table are quoted relative to the intense 602.9 keV transition (in which it is assumed Ig ¼ 1000). We do not see the 148.4, 189.6 and 346.5 and 1054.0 keV transitions reported in a number of earlier studies. On the other hand, we observe 14 new gamma
ARTICLE IN PRESS A. Patil et al. / Applied Radiation and Isotopes 64 (2006) 693–699
Fig. 1. (a–h) Singles gamma-ray spectra. Fig 1(i) X-ray spectrum. Fig. 1(j) Coincidence spectrum (gate 602).
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Table 2 Comparison of our measured gamma energies with the corresponding adopted values for the transitions (IAEA-95; IAEA-91) and for other gamma energies precisely determined in ‘standardization’ studies by Helmer (1990) in the decay of 125Sb Gamma energies (keV) Present
(a) IAEA-95
Present
(b) Helmer-90
176.308(2) 380.454(8) 427.880(5) 463.368(4) 600.589(3) 606.700(2) 635.951(3) 671.445(6)
176.314(2) 380.454(8)a 424.874(4) 463.365(4) 600.597(2) 606.713(2) 635.950(3) 671.441(6)
35.489(4) 172.708(7) 198.631(14) 204.144(8) 208.074(10) 227.876(10) 408.069(12) 443.565(7)
35.489(5) 172.719(8) 198.654(11) 204.139(8) 208.079(4) 227.891(10) 408.065(10) 443.554(9)
Numbers within the parentheses denote the uncertainties in last digit(s). a Taken from R.G. Helmer (1990).
Table 3 Intensities of gamma rays emitted following the decay of Eg (keV)
27.741(15) 31.622(31) 148.4 186.100(185) 209.839(31) 254.529(48) 291.829(11) 336.220(16) 371.059(30) 400.339(21) 444.119(21) 469.089(25) 481.420(37) 525.510(21) 530.450(27) 572.070(57) 592.729(50) 602.900(25) 632.500(16) 646.070(9) 662.409(29) 709.590(42) 713.900(6) 722.849(8) 735.799(14) 743.200(82) 766.320(28) 775.270(73) 790.679(009) 795.310(15) 816.9 856.679(35) 899.229(28) 968.320(13) 976.640(22) 1045.420(11) 1053.8 1086.750(74)
transitions not given in NDS (1997) or any other report included in the table. Our measured energies and intensities for K X-rays and gamma rays which are weighted averages are found to be consistent and are found to be in general agreement with Goswamy et al. (1993) and Jianming et al. (1988). However the intensity values for many weak gamma rays differ. A few of these additional gamma energies had earlier been tentatively suggested, but they do not appear in the evaluated data set of NDS, 1997. Seven of the 14 new gamma transitions pertain to already existing levels and the other 7 gamma transitions are in connection with the 5 proposed levels.
4. Revised
124
Te level scheme
Using the precisely determined transition energies as input data for application of the Ritz combination
124
Sb
Ig Present
Goswamy et al. (1993)
Jianming et al. (1988)
Mardirosian et al. (1984)
3.681(55) 0.852(15) — 0.02(36) 0.147(5) 0.137(6) 0.070(6) 0.760(18) 0.257(15) 1.249(66) 1.830(10) 0.364(23) 0.205(10) 1.429(75) 0.421(12) 0.184(10) 0.14(2) 1000(10) 0.990(9) 76.85(52) 0.148(10) 13.94(16) 22.88(24) 108.77(118) 1.399(19) 0.058(11) 0.039(3) 0.119(12) 7.664(89) 0.368(11) — 0.216(11) 0.200(12) 21.051(225) 0.841(10) 20.257(95) — 0.358(16)
3.66 0.84 0.037(7) — 0.055(10) 0.163(8) 0.088(8) 0.75(2) 0.34(8) 1.24(13) 1.92(2) 0.47(3) 0.24(2) 1.4(2) 0.43(2) 0.193(13) — 1000(10) 1.07(1) 75.5(8) 0.32(2) 13.4(2) 22.7(3) 107.7(14) 1.29(2) — 0.124(2) 0.093(18) 7.52(9) — 0.74(2) — 0.175(14) 19.2(2) 0.845(17) 18.7(2) 0.05(2) 0.38(2)
— — 0.061(20) — 0.062(28) 0.214(41) 0.122(61) 0.86(6) 0.356(61) 1.55(13) 2.04(10) 0.53(3) 0.29(8) 1.65(10) 0.47(11) 0.25(10) — 1000(10) 1.01(6) 75.5(10) 0.35(11) 13.8(4) 22.9(5) 109.9(15) 1.45(21) — 0.092(41) 0.112(41) 7.53(11) — 0.74(7) — 0.2(6) 19.45(23) 0.88(5) 18.97(24) — 0.43(5)
— — — — — 0.3(66) — 0.78(7) 0.239(61) 1.68(12) 2.26(15) 0.79(5) 0.3(5) 1.78(12) — — — 1000 1.18(7) 78.2(22) 0.43(5) 14.9(7) 24.6 114.6(16) 1.42(5) — 0.09(5) 0.112(41) 7.66(8) — 0.86(8) — — 20.38(24) 0.88(12) 20.13(23) 0.07(1) 0.58(5)
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Table 3 (continued ) Eg (keV)
1263.489(69) 1301.119(86) 1325.800(8) 1355.420(58) 1368.369(32) 1376.089(9) 1385.339(34) 1418.599(124) 1436.859(37) 1445.189(49) 1489.00(44) 1509.630(151) 1526.329(15) 1565.9 1580.020(107) 1621.670(19) 1691.089(13) 1720.719(15) 1757.9 1852.170(42) 1918.829(28) 2016.349(61) 2039.810(27) 2079.929(52) 2091.350(22) 2099.379(94) 2108.330(13) 2145.060(29) 2172.2 2182.409(163) 2204.260(13) 2232.409(50) 2256.489(119) 2283.649(26) 2294.149(26) 2323.479(79) 2373.790(596) 2386.139(1619) 2455.300(108) 2490.600(199) 2515.189(3209) 2681.6 2693.300(633) 2746.179(253) 2807.420(257) 2814.370(449)
Ig Present
Goswamy et al. (1993)
Jianming et al. (1988)
Mardirosian et al. (1984)
0.482(14) 0.256(13) 17.07(19) 10.93(13) 27.00(21) 5.43 (5) 0.64 (2) 0.05(2) 12.70(12) 3.35 (32) 6.92 (5) 0.08 (1) 4.51(4) — 4.60 (4) 0.477(12) 466.27 (45) 0.97 (18) — 0.02 6(10) 0.58 (16) 0.090(9) 0.661(19) 0.741 (18) 53.97 (52) 0.572(12) 0.501(7) 0.0068(3) — 0.36 (7) 0.310 (6) 0.01(3) 0.006(2) 0.422(9) 0.56 (23) 0.060(3) 0.009(3) 0.0024(2) 0.092(1) 0.02 (1) 0.0049(1) — 0.003(1) 0.01(1) 0.093(4) 0.035(2)
0.42(2) 0.35(1) 16.1(2) 10.5(1) 26.4(3) 4.93(6) 0.62(3) — 12.5(1) 3.34(4) 6.87(6) — 4.14(5) 0.15(4) 4.27(5) 0.42(1) 493.2(55) 0.96(2) 0.049(23) 0.062(9) 0.55(2) 0.112(10) 0.66(2) 0.268(14) 57.4(7) — 0.45(2) — 0.021(5) 0.44(1) — — — 0.101(8) 0.76(5) 0.027(3) — — 0.081(2) — — 0.020(4) 0.047(5) — 0.015(2) —
0.43(5) 0.39(5) 16.45(23) 11.03(18) 26.96(31) 4.96(10) 0.71(6) — 12.36(17) 3.46(10) 7.09(54) — 4.34(9) 0.13(4) 4.19(41) 0.4(4) 487.3(61) 1.02(4) — 0.112(31) 0.6(3) 0.124(7) 0.68(2) 0.163(25) 56.9(9) 0.46(2) 0.44(2) — 0.022 0.45(2) — — — 0.076(14) 0.31(5) 0.025(7) — — 0.016(6) — — 0.018(6) 0.026(16) — 0.020(8) —
0.54(10) 0.61(8) 16.9(29) 11.08(22) 27.58(69) 5.31(46) 0.79(25) — 13.4(27) 3.29(14) 7.23(20) — 4.33(8) — 2.38(7) 0.47(4) 508.8(88) 1.01(5) 0.188(35) 0.025(25) 0.55(3) 0.112(25) 0.68(3) 0.371(87) 59.2(10) 0.37(5) 0.35(5) — 0.046(10) 0.48(2) — — — 0.097(20) 0.45(2) 0.04(1) — — 0.01(5) — — 0.025(10) 0.056(10) — — —
principle, we now proceed to construct the 124Te level scheme. Well-established undisputed features of this scheme as seen in the latest nuclear data sheets NDS 97 are used as cross checks in our procedure. Application of the energy sum rule using the software GTOL (program package, ENSDAT version 3.92 NNDC, Brookhaven, 1994) in different loops leads us to the placement of the observed transitions and to an evaluation of the level energies in the thus constructed level scheme. The results of this exercise are shown in Fig. 2, which incorporates all the 75 observed transitions.
All the 22 levels in the adopted scheme of NDS, 1997 and the 4 extra levels proposed by Jianming and Goswamy et al. appear in our level scheme with the excitation energies agreeing in each case. Our level scheme includes five additional levels with excitation energies 2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV. These new levels were proposed in the particle transfer studies (Auble and Ball, 1972; Lien et al., 1977) but were not reported in beta decay studies. Out of the 9 gamma rays observed by Jianming et al. (1988) and Goswamy et al. (1993), only 6 could be observed in the present work. The observed
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Fig. 2.
124
Sb b decay scheme.
gamma rays at 1565.9 and 2808 keV confirm the proposed levels at 2814.5 and 2807.427 keV. The level at 1747 keV of the NDS 97 could not be confirmed because of the absence of the 498 keV gamma emission. The newly observed 2490.6 keV gamma transition could be fitted as a transition to the ground state of 124Te from 2490.5 keV new level. Two gammas with energies 2016.34 and 1368.36 keV were reported by Goswamy et al. (1993) but the former does not find its place in their level scheme while the later was fitted between the 2693.80 and 1325.57 keV levels. However, in the present work both the gammas have been observed but could be fitted differently by proposing a new level. The decay gammas of 1368.36 and 2016.34 keV transition from a new level to 602.73 and 1248.0 keV levels yield an energy of 2618.4 keV for the new level. The 3rd level, proposed at 2747.05 keV with the observation of 2746.17 and 2145.06 keV gamma transitions connects the ground state and the 602.73 keV level with the new level. The decay gammas 795.0, 1509.63, and 2232.4 keV could be fitted using the GTOL program between 602.73, 1325.52, and 2039.303 keV levels and a level at 2834.99 keV energy.
A newly observed gamma emission of 2256.48 keV has been observed and could be fitted between 602.73 keV and a level at 2859.4 keV. All these 5 levels have been proposed in the particle transfer reaction studies (Auble and Ball, 1972; Lien et al., 1977). In the present work the precision measurements of energies and intensities have made it possible to establish and assign the exact level energies of the 5 new levels. 5. Summary We have carried out precise measurements of the X-ray and the gamma-ray energies and intensities following the 124 Sb decay. The precision of our data is established by comparing our results with the IAEA adopted international calibration standards and other similar benchmark measurements. The revised level scheme for 124Te is constructed based on summed energy rules for various loops incorporating 75 gamma transitions; the latter include 14 new transitions observed by us but not listed in the adopted data set of the latest (1997) Nuclear data sheets. The revised level scheme introduces 5 new levels at
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2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV with 7 out of 14 new transitions connecting these levels with the earlier established levels. It is expected that the presently reported more extensive gamma-ray data and the revised level scheme of 124Te taken together with the results from reaction studies produces a better data base for understanding the level structures in the transitional nuclei. Acknowledgements The authors acknowledge financial support provided by the Department of Atomic Energy, Government of India through the DAE-BRNS research project. References Auble, R.L., Ball, J.B., 1972. Energy levels of 122,124Te populated by (3He, d) and (p, t) reactions. Nucl. Phys. A 179, 353–370. Bushnell, A.H., Chaturvedi, R.P., Smither, R.K., 1969. Neutron-capture gamma-ray studies of the level structure of the Te124 nucleus. Phys. Rev. 179, 1113–1133. Christensen, P.R., Lovhoiden, G., Rasmussen, J., 1970. Elastic and inelastic deuteron scattering from 124Te and 146Nd. Nucl. Phys. A 49, 302–322. Gamma Vision-32, version 5.10 EG&G ORTEC, 1998. Goswamy, J., Chand, B., Mehta, D., Singh, N., Trehan, P.N., 1993. Study of the 124Sb decay. Appl. Radiat. Isot. 44, 541–546. GTOL Program package, ENSDAT version 3.92 NNDC, Brookhaven, 1994.
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Helmer, R.G., 1990. Selected gamma-ray energies and emission probabilities for the decay of 125Sb and 154Eu. Appl. Radiat. Isot. 41, 75–81. IAEA-TECDOC-619, 1991. Iimura, H., Katakura, J., Kitao, K., Tamura, T., 1997. Nuclear data sheets for A ¼ 124. Nucl. Data Sheets 80, 895–1068. Jianming, Y., Yunzuo, L., Dailing, H., 1988. Levels, in 124Te populated in the decay of 124Sb Z. Phys. A 331, 391–400. Johnson, J.R., Mann, K.C., 1974. The decay of 124Sb. Can J. Phys. 52, 406–419. Lederer, C.M., Shirley, V.S., Browne, E., Dairiki, J.M., Doebler, R.E., Shihab-Eldin, A.A., Jardine, L.J., Tuli, J.K., Buyrn, A.B., 1978. Table of Isotopes, seventh ed. Wiley, Inc., New York. Lien, J.R., Nilsen, C.L., Nilson, R., Vold, P.B., Graue, A., Lovhoiden, G., 1977. Spectroscopy of 121Te and 124Te from the 120,123Te(d, p)121,124Te reactions. Can. J. Phys. 55, 463–472. Mardirosian, G., Stewart, N.M., 1984. Low energy nuclear states in 124Te. Z. Phys. A 315, 213–222. Meyer, R.A., Walters, W.B., Ragaini, R.C., 1969. Decay of the 124Sb isomers to levels of 124Te. Nucl. Phys. A 127, 595–608. Mitropolsky, I.A., 2003. Level scheme construction and allocation of transitions on the basis of Ritz combination principle, http:// www.physics.mcmaster.ca/balraj/nsdd2003/indc-nds-456.pdf Petkov, V., Bakaltchev, N., 1990. FIT, a computer program for decomposition of powder diffraction patterns and profile analysis of pair correlation functions. J. Appl. Crystallogr. 23, 138–140. Sainath, M., Venkataramaniah, K., Sood, P.C., 1999. Beta decay of 125Sb and level structures in 125Te. Pramana J. Phys. 53, 289–305. Sainath, M., Venkataramaniah, K., Sood, P.C., 2003. Observation of high spin levels in 131Cs from 131 Ba. Pramana J. Phys. 61, 1157–1162. Sharma, A.K., Kaur, R., Verma, H.R., Suri, K.K., Trehan, P.N., 1979. Level structure of 124Te. J. Phys. Soc. Japan. 46, 1057–1066. Warr, N., Drissi, S., Garrett, P.E., Jolie, J., Kern, J., Lehmann, H., Mannanal, S.J., Vorlet, J.-P., 1998. Study of 124Te by the 122Sn(a, 2ng) reaction and by the decay of 124I. Nucl. Phys. A 636, 379–418.
Applied Radiation and Isotopes 64 (2006) 693–699 www.elsevier.com/locate/apradiso
Precision measurements in
124
Te following the decay of
124
Sb
Amol Patil, D. Santhosh, K. Vijay Sai, M. Sainath, K. Venkataramaniah Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthinilayam 515 134, India Received 14 April 2004; received in revised form 12 December 2005; accepted 12 December 2005
Abstract The decay of 124Sb (60 d half-life) to levels of 124Te has been studied using two HPGe detectors in singles and coincidence mode. We identify 75 transitions in this decay, including 14 gamma rays, the emission of which are being reported here for the first time. In confirming the existence of 26 well-established levels below 2900 keV excitation, we also introduce 5 other levels at 2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV. The data on energies of gamma transitions and the levels are reported at high precision. r 2006 Elsevier Ltd. All rights reserved. Keywords: Radioactivity;
124
Sb beta decay; Singles and coincidence studies;
1. Introduction The even–even isotope 124Te has been the subject of considerable interest (Auble and Ball, 1972; Lien et al., 1977) since it is the testing ground for different theoretical models. Till now, no complete understanding of nuclear structure of this nucleus has been achieved. Even many aspects of the low-lying spectrum are still puzzling (Warr et al., 1998). The level structure of 124Te has been investigated through the study of 124Sb (t1=2 ¼ 60:2 days) decay as well as through nuclear reactions (Iimura et al., 1997). Several levels in 124Te that were established in the decay studies of various workers (Meyer et al., 1969; Johnson and Mann, 1974; Sharma et al., 1979; Mardirosian and Stewart, 1984; Jianming et al., 1988; Goswamy et al., 1993) have not been supported unambiguously and they have never been reported by any of the reaction studies. Conversely, several levels which in view of the decay energy might have been studied by 124Sb decay, have only been reported in reaction studies (Bushnell et al., 1969; Christensen et al., 1970; Auble and Ball, 1972; Lien et al., 1977). Fourteen new gamma transitions and two new levels have been reported by Iimura et al. (1997). Jianming et al. (1988) have studied Corresponding author. Tel.: +91 8555287235; fax: +91 8555287474.
E-mail address: [email protected] (K. Vijay Sai). 0969-8043/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.12.010
124
Te level scheme
this decay through singles and coincidence measurements, reporting nine new gamma transitions, also trying to establish four new levels at 2512, 2550, 2808.8 and 2814.5 keV. Based on their coincidence data, Jianming et al. (1988) ruled out the presence of 34 of the previously reported gammas (Lederer et al., 1978; Sharma et al., 1979; Mardirosian and Stewart, 1984). Goswamy et al. (1993) confirmed the levels at 2808 and 2814 keV and nine gamma rays of energies 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9, and 2808.0 keV. Apart from the energies of the levels and the gamma transitions, the intensity values for many weak gamma rays measured by different workers are inconsistent with each other. The present work attempts to: (i) clarify the abovementioned discrepancies and to confirm the new results of Jianming et al. (1988) and Goswamy et al. (1993); (ii) determine the energies and intensities of gamma transitions, and (iii) propose a revised level scheme for 124 Te by a reinvestigation of the decay of 124Sb aiming at precision measurements (singles and coincidence studies). By looking for the weak transitions that could not be seen in earlier decay studies, an effort has been made to look for several of the energy levels that were proposed in particle transfer reaction studies (Auble and Ball, 1972; Lien et al., 1977) but which were not reported in the beta decay studies. This becomes possible with present precision
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gamma spectroscopy systems and has lead to very interesting results for other nuclei (Sainath et al., 1999, 2003). 2. Experimental procedure 2.1. Singles Gamma-ray measurements A carrier-free sample has been obtained of the radioactive source 124Sb, being produced by thermal neutron irradiation of 123Sb at the Bhabha Atomic Research Centre (Mumbai) in the form of antimony chloride (SbCl3) in dilute HCl solution. The 124Sb source was allowed to decay for about 8 months, primarily to rid the source of any short-lived impurities. Sources for acquiring spectra were prepared by drying the source solution on aluminized mylar foil supported by thin aluminium discs of 1 cm diameter. The count rate was kept at around 500 counts/s.
Table 1 Coincidence measurement results from decay of Energy (keV)
124
Sb
Singles gamma spectra were recorded with two 60 cm3 HPGe detectors (FWHM ¼ 1.80 keV at 1.33 MeV) coupled to an 8k PC-based Multichannel Analyser. Gamma singles spectra were acquired at a source to detector distance of 25 cm. The counting period lasted an average of 4.5 105 s/ spectrum. Efficiency calibration for HPGe detectors was done using standard radioactive sources obtained from the International Atomic Energy Agency, Vienna. The lowenergy spectrum was acquired using a Si(Li) detector (FWHM ¼ 180 eV at 5.9 keV). The gamma ray peaks were analysed using the computer codes FIT (Petkov and Bakaltchev, 1990) and Gamma Vision (version 5.10 EG&G ORTEC (1998)). 2.2. Gamma–gamma coincidence measurements Coincidence measurements were performed with the above mentioned two 60 cm3 HPGe detectors. A standard fast–slow coincidence system with the time resolution of 20 ns was used. The source to detector distance was maintained at 10 cm. Coincidence spectra were taken by setting gates at 602, 614, 709, 714, and 723 keV gamma energies, as summarized in Table 1.
Gate (keV)
3. Results and discussion 603 183 336 444 511 525 603 646 662 670 709 715 722 736 790 899 968 1045 1068 1178 1198 1263 1325 1355 1368 1376 1436 1445 1489 1526 1580 1690 1720 1919 2033 2091 2287
646
709
714
723
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Our typical gamma spectra are shown in Fig. 1(a–h). We explain the comparison with a ‘bench mark’ test to establish the credibility of our identification of as yet unconfirmed weaker transitions and their precise energies. The most recent energy calibration standard for 125Sb (IAEA, 1995; Firestone and Shirley, 1996; IAEA–TECDOC-619, 1991) have been compared with our results obtained in Table 2(a); a similar comparison with the additional transitions included in the ‘standardization analysis’ (Helmer, 1990) is presented in Table 2(b). It is seen that almost in all cases the deviations are comparable to the assigned uncertainties. The average deviation for the 16 transition energies is less than 8 eV. The excellent agreement of our measured gamma energies and accepted ‘benchmark values’ in the IAEA calibration tables and other similar measurements provides us with a firm basis for the identification of new transitions and also for the use of our measured gamma ray energies to arrive at a revised level scheme for 124Te through application of the Ritz combination principle (Mitropolsky I.A., 2003). A complete list of the energies and relative intensities of 75 gamma transitions observed in our study and shown in Fig. 1(a–h) is given in Table 3. In addition to a comparison of our intensity values, we also include results from Mardirosian and Stewart (1984); Jianming et al. (1988) and Goswamy et al. (1993). In accordance with the usual convention, intensities in the table are quoted relative to the intense 602.9 keV transition (in which it is assumed Ig ¼ 1000). We do not see the 148.4, 189.6 and 346.5 and 1054.0 keV transitions reported in a number of earlier studies. On the other hand, we observe 14 new gamma
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Fig. 1. (a–h) Singles gamma-ray spectra. Fig 1(i) X-ray spectrum. Fig. 1(j) Coincidence spectrum (gate 602).
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Table 2 Comparison of our measured gamma energies with the corresponding adopted values for the transitions (IAEA-95; IAEA-91) and for other gamma energies precisely determined in ‘standardization’ studies by Helmer (1990) in the decay of 125Sb Gamma energies (keV) Present
(a) IAEA-95
Present
(b) Helmer-90
176.308(2) 380.454(8) 427.880(5) 463.368(4) 600.589(3) 606.700(2) 635.951(3) 671.445(6)
176.314(2) 380.454(8)a 424.874(4) 463.365(4) 600.597(2) 606.713(2) 635.950(3) 671.441(6)
35.489(4) 172.708(7) 198.631(14) 204.144(8) 208.074(10) 227.876(10) 408.069(12) 443.565(7)
35.489(5) 172.719(8) 198.654(11) 204.139(8) 208.079(4) 227.891(10) 408.065(10) 443.554(9)
Numbers within the parentheses denote the uncertainties in last digit(s). a Taken from R.G. Helmer (1990).
Table 3 Intensities of gamma rays emitted following the decay of Eg (keV)
27.741(15) 31.622(31) 148.4 186.100(185) 209.839(31) 254.529(48) 291.829(11) 336.220(16) 371.059(30) 400.339(21) 444.119(21) 469.089(25) 481.420(37) 525.510(21) 530.450(27) 572.070(57) 592.729(50) 602.900(25) 632.500(16) 646.070(9) 662.409(29) 709.590(42) 713.900(6) 722.849(8) 735.799(14) 743.200(82) 766.320(28) 775.270(73) 790.679(009) 795.310(15) 816.9 856.679(35) 899.229(28) 968.320(13) 976.640(22) 1045.420(11) 1053.8 1086.750(74)
transitions not given in NDS (1997) or any other report included in the table. Our measured energies and intensities for K X-rays and gamma rays which are weighted averages are found to be consistent and are found to be in general agreement with Goswamy et al. (1993) and Jianming et al. (1988). However the intensity values for many weak gamma rays differ. A few of these additional gamma energies had earlier been tentatively suggested, but they do not appear in the evaluated data set of NDS, 1997. Seven of the 14 new gamma transitions pertain to already existing levels and the other 7 gamma transitions are in connection with the 5 proposed levels.
4. Revised
124
Te level scheme
Using the precisely determined transition energies as input data for application of the Ritz combination
124
Sb
Ig Present
Goswamy et al. (1993)
Jianming et al. (1988)
Mardirosian et al. (1984)
3.681(55) 0.852(15) — 0.02(36) 0.147(5) 0.137(6) 0.070(6) 0.760(18) 0.257(15) 1.249(66) 1.830(10) 0.364(23) 0.205(10) 1.429(75) 0.421(12) 0.184(10) 0.14(2) 1000(10) 0.990(9) 76.85(52) 0.148(10) 13.94(16) 22.88(24) 108.77(118) 1.399(19) 0.058(11) 0.039(3) 0.119(12) 7.664(89) 0.368(11) — 0.216(11) 0.200(12) 21.051(225) 0.841(10) 20.257(95) — 0.358(16)
3.66 0.84 0.037(7) — 0.055(10) 0.163(8) 0.088(8) 0.75(2) 0.34(8) 1.24(13) 1.92(2) 0.47(3) 0.24(2) 1.4(2) 0.43(2) 0.193(13) — 1000(10) 1.07(1) 75.5(8) 0.32(2) 13.4(2) 22.7(3) 107.7(14) 1.29(2) — 0.124(2) 0.093(18) 7.52(9) — 0.74(2) — 0.175(14) 19.2(2) 0.845(17) 18.7(2) 0.05(2) 0.38(2)
— — 0.061(20) — 0.062(28) 0.214(41) 0.122(61) 0.86(6) 0.356(61) 1.55(13) 2.04(10) 0.53(3) 0.29(8) 1.65(10) 0.47(11) 0.25(10) — 1000(10) 1.01(6) 75.5(10) 0.35(11) 13.8(4) 22.9(5) 109.9(15) 1.45(21) — 0.092(41) 0.112(41) 7.53(11) — 0.74(7) — 0.2(6) 19.45(23) 0.88(5) 18.97(24) — 0.43(5)
— — — — — 0.3(66) — 0.78(7) 0.239(61) 1.68(12) 2.26(15) 0.79(5) 0.3(5) 1.78(12) — — — 1000 1.18(7) 78.2(22) 0.43(5) 14.9(7) 24.6 114.6(16) 1.42(5) — 0.09(5) 0.112(41) 7.66(8) — 0.86(8) — — 20.38(24) 0.88(12) 20.13(23) 0.07(1) 0.58(5)
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Table 3 (continued ) Eg (keV)
1263.489(69) 1301.119(86) 1325.800(8) 1355.420(58) 1368.369(32) 1376.089(9) 1385.339(34) 1418.599(124) 1436.859(37) 1445.189(49) 1489.00(44) 1509.630(151) 1526.329(15) 1565.9 1580.020(107) 1621.670(19) 1691.089(13) 1720.719(15) 1757.9 1852.170(42) 1918.829(28) 2016.349(61) 2039.810(27) 2079.929(52) 2091.350(22) 2099.379(94) 2108.330(13) 2145.060(29) 2172.2 2182.409(163) 2204.260(13) 2232.409(50) 2256.489(119) 2283.649(26) 2294.149(26) 2323.479(79) 2373.790(596) 2386.139(1619) 2455.300(108) 2490.600(199) 2515.189(3209) 2681.6 2693.300(633) 2746.179(253) 2807.420(257) 2814.370(449)
Ig Present
Goswamy et al. (1993)
Jianming et al. (1988)
Mardirosian et al. (1984)
0.482(14) 0.256(13) 17.07(19) 10.93(13) 27.00(21) 5.43 (5) 0.64 (2) 0.05(2) 12.70(12) 3.35 (32) 6.92 (5) 0.08 (1) 4.51(4) — 4.60 (4) 0.477(12) 466.27 (45) 0.97 (18) — 0.02 6(10) 0.58 (16) 0.090(9) 0.661(19) 0.741 (18) 53.97 (52) 0.572(12) 0.501(7) 0.0068(3) — 0.36 (7) 0.310 (6) 0.01(3) 0.006(2) 0.422(9) 0.56 (23) 0.060(3) 0.009(3) 0.0024(2) 0.092(1) 0.02 (1) 0.0049(1) — 0.003(1) 0.01(1) 0.093(4) 0.035(2)
0.42(2) 0.35(1) 16.1(2) 10.5(1) 26.4(3) 4.93(6) 0.62(3) — 12.5(1) 3.34(4) 6.87(6) — 4.14(5) 0.15(4) 4.27(5) 0.42(1) 493.2(55) 0.96(2) 0.049(23) 0.062(9) 0.55(2) 0.112(10) 0.66(2) 0.268(14) 57.4(7) — 0.45(2) — 0.021(5) 0.44(1) — — — 0.101(8) 0.76(5) 0.027(3) — — 0.081(2) — — 0.020(4) 0.047(5) — 0.015(2) —
0.43(5) 0.39(5) 16.45(23) 11.03(18) 26.96(31) 4.96(10) 0.71(6) — 12.36(17) 3.46(10) 7.09(54) — 4.34(9) 0.13(4) 4.19(41) 0.4(4) 487.3(61) 1.02(4) — 0.112(31) 0.6(3) 0.124(7) 0.68(2) 0.163(25) 56.9(9) 0.46(2) 0.44(2) — 0.022 0.45(2) — — — 0.076(14) 0.31(5) 0.025(7) — — 0.016(6) — — 0.018(6) 0.026(16) — 0.020(8) —
0.54(10) 0.61(8) 16.9(29) 11.08(22) 27.58(69) 5.31(46) 0.79(25) — 13.4(27) 3.29(14) 7.23(20) — 4.33(8) — 2.38(7) 0.47(4) 508.8(88) 1.01(5) 0.188(35) 0.025(25) 0.55(3) 0.112(25) 0.68(3) 0.371(87) 59.2(10) 0.37(5) 0.35(5) — 0.046(10) 0.48(2) — — — 0.097(20) 0.45(2) 0.04(1) — — 0.01(5) — — 0.025(10) 0.056(10) — — —
principle, we now proceed to construct the 124Te level scheme. Well-established undisputed features of this scheme as seen in the latest nuclear data sheets NDS 97 are used as cross checks in our procedure. Application of the energy sum rule using the software GTOL (program package, ENSDAT version 3.92 NNDC, Brookhaven, 1994) in different loops leads us to the placement of the observed transitions and to an evaluation of the level energies in the thus constructed level scheme. The results of this exercise are shown in Fig. 2, which incorporates all the 75 observed transitions.
All the 22 levels in the adopted scheme of NDS, 1997 and the 4 extra levels proposed by Jianming and Goswamy et al. appear in our level scheme with the excitation energies agreeing in each case. Our level scheme includes five additional levels with excitation energies 2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV. These new levels were proposed in the particle transfer studies (Auble and Ball, 1972; Lien et al., 1977) but were not reported in beta decay studies. Out of the 9 gamma rays observed by Jianming et al. (1988) and Goswamy et al. (1993), only 6 could be observed in the present work. The observed
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Fig. 2.
124
Sb b decay scheme.
gamma rays at 1565.9 and 2808 keV confirm the proposed levels at 2814.5 and 2807.427 keV. The level at 1747 keV of the NDS 97 could not be confirmed because of the absence of the 498 keV gamma emission. The newly observed 2490.6 keV gamma transition could be fitted as a transition to the ground state of 124Te from 2490.5 keV new level. Two gammas with energies 2016.34 and 1368.36 keV were reported by Goswamy et al. (1993) but the former does not find its place in their level scheme while the later was fitted between the 2693.80 and 1325.57 keV levels. However, in the present work both the gammas have been observed but could be fitted differently by proposing a new level. The decay gammas of 1368.36 and 2016.34 keV transition from a new level to 602.73 and 1248.0 keV levels yield an energy of 2618.4 keV for the new level. The 3rd level, proposed at 2747.05 keV with the observation of 2746.17 and 2145.06 keV gamma transitions connects the ground state and the 602.73 keV level with the new level. The decay gammas 795.0, 1509.63, and 2232.4 keV could be fitted using the GTOL program between 602.73, 1325.52, and 2039.303 keV levels and a level at 2834.99 keV energy.
A newly observed gamma emission of 2256.48 keV has been observed and could be fitted between 602.73 keV and a level at 2859.4 keV. All these 5 levels have been proposed in the particle transfer reaction studies (Auble and Ball, 1972; Lien et al., 1977). In the present work the precision measurements of energies and intensities have made it possible to establish and assign the exact level energies of the 5 new levels. 5. Summary We have carried out precise measurements of the X-ray and the gamma-ray energies and intensities following the 124 Sb decay. The precision of our data is established by comparing our results with the IAEA adopted international calibration standards and other similar benchmark measurements. The revised level scheme for 124Te is constructed based on summed energy rules for various loops incorporating 75 gamma transitions; the latter include 14 new transitions observed by us but not listed in the adopted data set of the latest (1997) Nuclear data sheets. The revised level scheme introduces 5 new levels at
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2490.5, 2618.4, 2747.05, 2834.99, and 2859.4 keV with 7 out of 14 new transitions connecting these levels with the earlier established levels. It is expected that the presently reported more extensive gamma-ray data and the revised level scheme of 124Te taken together with the results from reaction studies produces a better data base for understanding the level structures in the transitional nuclei. Acknowledgements The authors acknowledge financial support provided by the Department of Atomic Energy, Government of India through the DAE-BRNS research project. References Auble, R.L., Ball, J.B., 1972. Energy levels of 122,124Te populated by (3He, d) and (p, t) reactions. Nucl. Phys. A 179, 353–370. Bushnell, A.H., Chaturvedi, R.P., Smither, R.K., 1969. Neutron-capture gamma-ray studies of the level structure of the Te124 nucleus. Phys. Rev. 179, 1113–1133. Christensen, P.R., Lovhoiden, G., Rasmussen, J., 1970. Elastic and inelastic deuteron scattering from 124Te and 146Nd. Nucl. Phys. A 49, 302–322. Gamma Vision-32, version 5.10 EG&G ORTEC, 1998. Goswamy, J., Chand, B., Mehta, D., Singh, N., Trehan, P.N., 1993. Study of the 124Sb decay. Appl. Radiat. Isot. 44, 541–546. GTOL Program package, ENSDAT version 3.92 NNDC, Brookhaven, 1994.
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Helmer, R.G., 1990. Selected gamma-ray energies and emission probabilities for the decay of 125Sb and 154Eu. Appl. Radiat. Isot. 41, 75–81. IAEA-TECDOC-619, 1991. Iimura, H., Katakura, J., Kitao, K., Tamura, T., 1997. Nuclear data sheets for A ¼ 124. Nucl. Data Sheets 80, 895–1068. Jianming, Y., Yunzuo, L., Dailing, H., 1988. Levels, in 124Te populated in the decay of 124Sb Z. Phys. A 331, 391–400. Johnson, J.R., Mann, K.C., 1974. The decay of 124Sb. Can J. Phys. 52, 406–419. Lederer, C.M., Shirley, V.S., Browne, E., Dairiki, J.M., Doebler, R.E., Shihab-Eldin, A.A., Jardine, L.J., Tuli, J.K., Buyrn, A.B., 1978. Table of Isotopes, seventh ed. Wiley, Inc., New York. Lien, J.R., Nilsen, C.L., Nilson, R., Vold, P.B., Graue, A., Lovhoiden, G., 1977. Spectroscopy of 121Te and 124Te from the 120,123Te(d, p)121,124Te reactions. Can. J. Phys. 55, 463–472. Mardirosian, G., Stewart, N.M., 1984. Low energy nuclear states in 124Te. Z. Phys. A 315, 213–222. Meyer, R.A., Walters, W.B., Ragaini, R.C., 1969. Decay of the 124Sb isomers to levels of 124Te. Nucl. Phys. A 127, 595–608. Mitropolsky, I.A., 2003. Level scheme construction and allocation of transitions on the basis of Ritz combination principle, http:// www.physics.mcmaster.ca/balraj/nsdd2003/indc-nds-456.pdf Petkov, V., Bakaltchev, N., 1990. FIT, a computer program for decomposition of powder diffraction patterns and profile analysis of pair correlation functions. J. Appl. Crystallogr. 23, 138–140. Sainath, M., Venkataramaniah, K., Sood, P.C., 1999. Beta decay of 125Sb and level structures in 125Te. Pramana J. Phys. 53, 289–305. Sainath, M., Venkataramaniah, K., Sood, P.C., 2003. Observation of high spin levels in 131Cs from 131 Ba. Pramana J. Phys. 61, 1157–1162. Sharma, A.K., Kaur, R., Verma, H.R., Suri, K.K., Trehan, P.N., 1979. Level structure of 124Te. J. Phys. Soc. Japan. 46, 1057–1066. Warr, N., Drissi, S., Garrett, P.E., Jolie, J., Kern, J., Lehmann, H., Mannanal, S.J., Vorlet, J.-P., 1998. Study of 124Te by the 122Sn(a, 2ng) reaction and by the decay of 124I. Nucl. Phys. A 636, 379–418.