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Study of the 124Sb decay
Appl. Radiar.hr. Vol. 44, No. 3, pp. 54-546, 1993 Printed in Great Britain
Study JATINDER
0883-2889/93 96.00+ 0.00 Pergamon Press Lid
of the 124Sb Decay
GOSWAMY, BAKHSHISH CHAND, DEVINDER NIRMAL SINGH and P. N. TREHAN
MEHTA,
Department of Physics, Panjab University, Chandigarh 160014, India (Received 18 February 1992; in revised form 30 July 1992) The energies and intensities of gamma-rays emitted following the ‘“Sb decay have been measured with better precision using three HPGe detectors. Two levels reported at 2808 and 2814 keV and nine gamma-rays of energy 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9, and 2808.0 keV in ‘*‘Te, proposed recently, have been confirmed. The intensities of x-rays emitted following the decay of ‘*%b have been reported for the first time. The results of the directional correlation measurements have been used to uniquely assign 4+ and 3- spins to the levels at 1958 and 2694 keV respectively. Also the multipole mixing ratios for 13 transitions in ‘24Tehave been deduced.
Keeping in view the above-mentioned status of the level structure of ‘*?e, the decay of ‘24Sb has been investigated through gamma-ray singles and gamma-gamma directional correlation measurements using high resolution spectrometers.
1. Introduction The radionucleus lz4Sb (tliz = 60.2 d) undergoes B decay to the excited states of ‘24Te which further de-excite to the ground state with the emission of gamma-rays and conversion electrons. The level structure of ‘*?e has been investigated through the study of radioactive decays as well as through nuclear reactions (Tamura et al., 1984). The singles measurements of gamma-rays following the decay of ‘*%b have been performed by many workers (Iwata et al., 1984; Jianming et al., 1988; Mardirosion and Stewart 1984), but these investigations are associated with controversies regarding the intensity values and existence of a large number of gamma-rays. Recently, Jianming et al. (1988) have studied this decay through singles and coincidence measurements. They have reported nine new gamma-rays and also established four new levels at 2512, 2550, 2808 and 2814 keV. They have ruled out the presence of 34 previously reported gamma-rays (Mardirosion and Stewart, 1984; Lederer and Shirley, 1978; Sharma et al. 1979). The multipole mixing ratios of many transitions and spin-parity assignments to some of the levels in ‘24Te have been done on the basis of angular correlation (Baker et al., 1972; Behar et al., 1976; Garbowski et al., 1971; Sharma et al., 1979) and conversion electron measurements (Johnson and Mann, 1974). Most of these measurements have been done by using either NaI(Tlwe(Li) or Ge(L+Ge(Li) coincidence set-ups having poor energy and time resolution, and low coincidence efficiency. A survey of the literature reveals that most of these measurements are limited only to few cascades. The spin assignments to a number of levels in ‘24Te are still uncertain as reported in the compilation by Tamura et al. (1984).
2. Experimental 2.1. Gamma-ray singles measurements The radioactive source of ‘“Sb was procured, in two instalments, from BARC, Bombay (India) in the
form of SbCl, dissolved in dilute HCl. The present intensity measurements have been performed using a set of three precisely calibrated HPGe detectors: HPGe detector (volume = (i) a vertical 28.27 mm* x 5.0 mm; FWHM = 459 eV at 122 keV) over the energy region 2&750 keV; and (ii) two coaxial HPGe detectors (volumes = 57 and 96 cm’; FWHM = 1.8 keV at 1332 keV) over the energy region 100-3800 keV. The 57 cm3 HPGe detector was placed in a heavy lead housing to reduce the detection of background radiations to 5 counts/s. Thin and uncovered sources, prepared by drying the source solution on thin mylar backing treated with insulin, were used with vertical HPGe detector and these sources yielded about 500 counts/s. For intensity measurements with coaxial HPGe detectors, the sources were covered with thin mylar and their counting rates were kept about 2000 counts/s at source-to-detector distance of 25 cm. The efficiency calibration of the vertical planar and the two coaxial HPGe detectors were performed using the radioactive sources of 24Na, “Co, @‘Co,“Se,
541
542
JATINDER
G~SWAMY
*‘Y, 94Nb, “OrnAg, ‘33Ba, 13’Cs, “‘Eu, 24’Am and a mixed standard containing ‘“Eu, IssEu, ‘25Sb and ‘25mTe sources. The details of efficiency calibration and interpolation procedures have been described in our earlier papers (Chand et al., 1989; Mehta et aI., 1986). Fifteen spectra were taken with each source and detector combination for the time duration ranging between 10-20 h. The spectra were analyzed by using a computer code which fits gamma-peaks as gaussians with a provision of including short and long exponential tails. The continuum under the peak can be approximated by a polynomial up to fourth order with the option of including a step function. The peaks at 189.4 and 210.4 keV were clearly distinguishable (on the basis of FWHM) from the broad backscattered peaks due to high energy intense gamma-rays falling in the energy region 18&230 keV. The summing corrections for various cascading and cross-over gamma-rays were calculated by the method suggested by Gehrke et al. (1977) and the present intensity results were corrected for these.
2.2. Directional correlation measurements The gamma-gamma directional correlation measurements were performed using a 96 cm3 HPGe-90 cm3 HPGe set up having time resolution = 7 ns for the 1173-1332 keV cascade from @‘Co decay and energy resolution = 1.8 keV at 1332 keV. The source-to-detector distance was kept to be 15.0 cm for both the detectors. A movable 90cm3 HPGe detector was used to gate the photopeaks at 603, 646 and 723 keV energy. The sources were prepared by putting the source solution in a perspex holder having a vertical cavity of 1.5 mm dia and depth of 4 mm. The coincidence spectra were recorded at seven angles from 90” to 180” at intervals of 15” for the 603 keV gate and at four angles at intervals of 30” for other two gates. The data were corrected for the miscentering (< 1%) of the source, the chance and the Compton contributions. Also the correlation coefficients were corrected for the finite angular resolution of HPGe detectors by the method of Krane (1972). The details of the method of analysis are described elsewhere (Sharma et al., 1979).
3. Results and Discussion 3.1. Gamma-ray singles measurements The present measured energies and intensities of K x-rays and gamma-rays emitted following the decay of ‘24Sb are presented in Table 1. The intensity values of gamma-rays, in the energy region above 100 keV, measured by using two different coaxial HPGe detectors, are found to be consistent, and their weighted
et
al.
average results are presented in Table 1. The uncertainties correspond to one standard deviation (la) and include contributions due to statistics and analysis (cc 1% for good peaks), efficiency calibration errors (l-3%) over the energy region 20-3800 keV, errors due to summing corrections (< 1.0%) and other systematic errors (0.5%). The intensity results of other workers (Iwata et al., 1984); Jianming et al., 1988; Mardirosion and Stewart, (1984) are also presented in Table 1 for comparison. The present intensity results are found to be in general agreement with those reported by Mardirosion and Stewart (1984), Jianming et al. (1988) and Iwata et al., (1984) for strong gamma-rays. However the intensity values for many weak gamma-rays measured by different workers (Iwata et al., 1984; Jianming et al., 1988; Mardirosion and Stewart, 1984) and by us are inconsistent with each other. Since we have collected good statistics for the weak peaks and the results obtained by using two coaxial HPGe detectors are well consistent with each other, we judge the present results therefore to be more reliable. Nine new gamma-rays of energy 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9 and 2808.0 keV, observed by Jianming et al. (1988), were clearly seen in the present measurements with general consistent intensity results. The observed gamma-rays at energy 1565.9 and 2808.0 keV confirm the proposed levels at 2814 and 2808 keV (Jianming et al., 1988). No gamma-ray was observed at 498 keV; consequently, the level at 1747 keV in Nuclear Data sheets (Tamura et al., 1984) decaying through this gamma-ray alone is discarded. The other gamma-rays at 283.6, 387.3, 476.5, 498.1, 621.5, 938.2, 997.2, 1014.6, 1163.4, 1195.9, 1199.2, 1204.5, 1248.1, 1254.0, 1272.4, 1389.0, 1428.6, 1557.2, 1709.5, 1730.1, 1733.0, 1752.7, 1795.2,2151.1,2204.2,2224.7, 2412.7, 2521.5 and 2642.2 keV reported previously (Mardirosion and Stewart, 1984; Sharma et al., 1979) could not be seen in the present measurements. Many other peaks reported in earlier measurements (Mardirosion et al., 1984; Sharma et al., 1979) were observed in the present measurements but could be identified as sum, escape or background peaks; or having decay rates different from the known gamma-rays from the ‘24Sb decay. The intensity of K x-rays emitted following the decay of ‘24Sb have been measured for the first time. These intensity results show good agreement with the evaluated results given in the Tables of Radioactive Isotopes (Browne and Firestone, 1986) using physical parameters associated with atomic processes subsequent to internal conversion process. The present photon emission probabilities (in the last column of Table I), deduced using formalism given by Browne (I 986), show good agreement with the values reported in Table of Radioactive ISOtopes (Browne and Firestone, 1986). The logft values and percentage b _ feeding to various levels of ‘24Te populated in 124Sb decay have been deduced
Study of the %b
decay
543
Table I.Intensities of K. and gamma-rays emittedfollowing the decay of "'Sb
27.4(Te-K,) 30.9(Te-K,) 148.4 189.7 210.4 254.4 291.5 335.8 346.5 370.8 400.0 444.1 468.8 481.1 525.5 530.3 571.6 602.8 632.4 645.9 662.3 709.3 713.8 722.8 735.6 735.9 766.2 775.2 790.7 816.9 857.0 899.4 968.2 976.4 1045.2 1053.8 1086.5 1263.4 1301.5 1325.6 1355.2 1368.3 1376.1 1385.1 1436.6 1445.2 1489.0 1526.3 1565.9 1579.8 1622.3 1691.0 1720.3 1757.9 1851.7 1918.6 2015.9 2039.4 2078.9 2091.0 2098.9 2107.9 2172.2 2182.6 2283.8 2293.8 2323.1 2454.5 2681.6 2693.8 2808.0
3.66(17) 0.84(5) 0.037(7) 0.066(13) 0.055(l0) 0.163(8) 0.088(8) 0.75(2) 0.060(13) 0.34(8) 1.24(13) 1.92(2) 0.47(3) 0.24(2) 1.40(2) 0.43(2) 0.193(13) 1000(10) 1.07(l) 75.5(8) 0.32(2) 13.4(2) 22.7(3) 107.7(14)
0.061(20) 0.062(22) 0.062(28) 0.214(41) 0.122(61) 0.86(6) 0.132(51) 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(S) 109.9(15)
1.29(2)
1.45(21)
0.124(2) 0.093(18) 7.52(9) 0.74(2) 0.24(l) 0.175(14) 19.212) 0.845(17) 18.7(2) 0.05(2) 0.38(2) 0.42(2) 0.35(l) 16.1(2) 10.5(l) 26.4(3) 4.93(6) 0.62(3) 12.5(l) 3.34(4) 6.87(6) 4.14(5) 0.15(4) 4.27(S) 0.42(l) 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) 0.47(l) 0.45(2) 0.021(5) 0.44(l) 0.101(8) 0.76(S) 0.027(3) 0.018(2) 0.020(4) 0.047(5) 0.015(2)
0.092(41) 0.112(41) 7.53(11) 0.74(7) 0.32(6) 0.20(6) 19.45(23) 0.88(5) 18.97(24) 0.43(5) 0.43(5) 0.39(5) 16.45(23) ll.O3(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) 0.40(4) 487.3(61) 1.02(4) 0.112(31) 0.60(3) 0.124(7) 0.68(2) 0.163(25) 56.9(9) 0.46(Z) 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)
0.51(9) 1.29(16) 2.05(10) 0.58(S) 1.17(12) lOOO(4) 1.14(6) 76.1(3) 0.16(S) 13.99(11) 23.38(12) 110.2(4) 1.33(9) 7.58(9) 0.79(6) 0.29(7) O.l6(9) 19.19(13) 0.88(8) 18.64(17) 0.39(9) 0.46(15) 0.41(15) 15.84(22) 10.42(27) 26.7(3) 5.01(20) 0.61(26) 12.25(24) 3.58(17) 6.79(19) 4.10(24) 0.35(12) 485.8(16) 0.97(7)
0.52(4) 0.093(26) 0.59(3) 0.157(14) 55.9(2) 0.45(6) 0.44(3) 0.40(2) 0.041(13) 0.31(10) O.G7(19) -
0.3G(66) 0.78(7) 0.239(61) 1.68(12) 2.26(15) 0.79(5) 0.30(5) 1.78(12)
1000 1.18(7) 78.2(22) 0.43(S) 14.9(7) 24.6 114.6(16) 1.42(S) 0.09(5) 0.112(41) 7.66(8) 0.86(8) 0.27(6) 20.3;(24) 0.88(12) 20.13(23) 0.07(l) 0.58(S) 0.54(10) 0.61(8) 16.90(29) 11.08(22) 27.58(69) 5.31(46) 0.79(25) 13.40(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(Z) 0.04(l) O.OlO(5) 0.025(10) 0.056(10)
'Errorin energyrange from O.lJsl.6 keV. tResultsevaluated theoretically in compilation in Browne and Firestone (1986)
0.357(17) 0.082(10) 0.0037(7) O.O065(I3) 0.0054(10) 0.0159(10) 0.0086(10) 0.073(3) 0.0059(13) 0.033(10) 0.121(3) 0.188(5) 0.046(3) 0.024(2) 0.137(3) 0.042(2) 0.0190(13) 97.8(17) 0.105(Z) 7.38(10) 0.031(2) 1.31(3) 2.22(4) 10.5(2) 0.126(3) 0.0121(5) 0.0091(18) 0.74(2) 0.072(3) 0.024(l) 0.0171(14) 1.88(3) 0.083(2) 1.83(3) 0.005(2) 0.037(2) 0.041(2) 0.034(2) 1.57(3) 1.03(2) 2.58(4) 0.48(l) 0.061(2) 1.22(2) 0.327(7) 0.671(14) 0.412(8) 0.015(4) 0.424(8) 0.041(2) 48.2(7) 0.094(3) 0.005(2) 0.0061(9) 0.054(2) 0.011(1) 0.065(2) 0.026(2) 5.62(10) 0.046(l) 0.044(2) 0.0021(5) 0.043(2) 0.0099(8) 0.057(3) 0.0026(3) 0.0018(2) 0.0020(4) 0.0046(7) O.OOl5(2)
0.373(8)t 0.079(10) <0.028 0.079(20) 0.020(7) 0.147(23) 0.193(22) 0.064(24) 0.029(12) 0.159(23) 97.8 0.098(23) 7.4(4) 1.35(6) 2.28(10) 10.9(4) 0.264(23) <0.06 <0.09 0.74(4) 0.078(23) 0.20(7) 0.016(5) 1.87(6) 0.075(12) 1.86(8) 0.033(12) 0.029(6) 0.034(7) 1.59(7) 1.05(9) 2.66(11) 0.52(8) 0.052(19) 1.25(11) 0.33(7) 0.69(7) 0.40(7) 0.41(7) 0.033(9) 47.1(14) 0.083(13) 0.020(7) 0.049(15) 0.0088(18) 0.068(5) 0.013(5) 5.49(19) 0.044(8) 0.039 0.0010(5) 0.039 0.0078(23) 0.0311(23) 0.0023(5) 0.0006(3) 0.0014(3) -0.15
544
from the present Fig. 1. 3.2. Directional
JATINDER GOSWAMY
intensity
results and are shown
in
correlation measurements
The present directional correlation coefficients for 17 cascades in ‘24Te along with the results of other workers are presented in Table 2. The present directional correlation results are in general agreement with those reported by other workers except for significant differences in 791-(646t603, and 1437603 keV cascades from previous measurements (Baker et al., 1972; Sharma et al., 1979; Garbowski et al., 1971). The directional correlation coefficients for the 7099(646)-603, 791-646, 1368-(723)-603, 1356603, 1045-646, 144-646, 1526646 and 1376 723 keV cascades have been measured for the first time. The directional correlation coefficients from the present work have been further used to deduce the multipole mixing ratios for various transitions in ‘24Te by the method described by Krane and Steffan
et al.
(1971) whose sign convention and notations have been used throughout. For whole of the analysis, the 603 keV transition has been assumed pure E2 on the basis of ICC measurements (Johnson and Mann, 1974). The multipole mixing ratios and deduced multipole admixture for different transitions in ‘24Te are presented in Table 3. The important results derived from these measurements are discussed below. 3.2. I. Spin of 2694 ke V level: The level at 2694 keV has two possible spin assignments of 2-and 3from the previous measurements (Baker et al., 1972; Garbowski et al., 1971) and the compilation in Nuclear Data Sheets (Tamura et al., 1984). The directional correlation results for 2091603 cascade were used to choose correct spin for 2694 keV level. The measured A,, coefficient was used for the analysis of 2091603 keV cascade with consideration of both the 2- & 3- spin assignments for the 2694 keV level. The following values of
Fig. 1. The decay scheme of ‘%b
Study of the ‘*‘Sb decay
545
Table 2. Gamma-gamma directional correlation coefficients Directional
correlation
results from ‘*‘Sb decay
coefficients
Cascade (kev) 64&603
709<646wo3 714-(723w3 723403
791-(646~03 104y646)-603
135&603 1368-(723HO3 1437-603 1691-603
209 I-603
709-646
791646 1045-646 1445-646 152&646 968-723
1376723
multipole mixing ratio for 2091 keV transition obtained:
0.019 * 0.007 0.003 f 0.011 0.005 f 0.010 0.010 f 0.030 0.0399 + 0.075 -0.039 f 0.034 0.245 + 0.009 0.270 f 0.015 0.295 + 0.020 0.283 k 0.007 -0.116 + 0.079 0.114 f 0.095 0.042 f 0.027 -0.052 f 0.046 0.064 * 0.060 0.026 f 0. I73 0.042 f 0.109 -0.214 + 0.086 0.340 f 0.100 -0.0088 f 0.0143 -0.005 + 0.025 -0.01 I * 0.011 0.009 i 0.016 -0.038 + 0.018 0.004 f 0.020 -0.009 + 0.138 0.011 f 0.033 -0.02 f 0.03 -0.187~0.044 -0.04 f 0.04 0.02 f 0.09 -0.02 f 0.07 -0.030 * 0.002 -0.023 f 0.026 0.058 f 0.027 -0.06 + 0.07
were
For J”(2694) = 3 6, = 0.031(6)
Ref.
,444
AZ, 0.110~0.005 0.095 * 0.01 I 0.100 f 0.005 0.121 + 0.025 0.23 f 0.06 0.094 +_0.025 0.128 + 0.006 0.135 f 0.009 0.130 + 0.015 0.101 f 0.005 0.104 f 0.058 0.307 f 0.065 -0.135~0.020 - 0. I75 + 0.032 -0.114+0.042 0.08+0.13 - 0.009 * 0.08 -0.112+0.064 -0.240 + 0.060 -0.065 i 0.01 I - 0.064 f 0.020 -0.068 f 0.005 -0.047 f 0.005 -0.067 + 0.012 -0.069 + 0.015 0.206+0.117 0.187 + 0.017 0.190 f 0.020 0.280 f 0.031 -0.10 f 0.03 -0.16 + 0.07 0.22 + 0.05 0.028 + 0.002 0.058 k 0.027 0.043 * 0.012 -0.03 + 0.06
6, = 4.96(16)
Present Baker et al. (1972) Behar el al. (1976) Garbowski ef al. (1971) Present Present Present Baker ef of. (1972) Garbowski et al. (1971) Sharma ef al. (1979) Present Sharma er a/. (1979) Present Baker et al. (1972) Sharma er 41. (1979) Present Present Present Baker er al. (1972) Present Garbowski er al. (1971) Baker et al. (1972) Present Baker el al. (1972) Garbowski ef al. (1971) Present Garbowski et al. (1971) Behar et al. (1976) Present Present Present Present Present Baker ef al. (1972) Sharma er al. (1979) Present
were used in analysis to deduce multipole mixing ratio of 709 keV transition assuming 3 + and 4+ spin values for the 1958 keV level. The possible multipole mixing ratios for the 709 keV transition are tabulated below.
For J”(2694) = 2 6, = 0.400(7)
Multipole
6, = 25.5+‘.’ 4.6
The experimental K conversion coefficient for 2091 keV transition is tlk = 0.00013(4) (Johnson and Mann, 1974) clearly indicates this transition to be pure El with possibly very small M2 component. Thus the only acceptable value of mixing ratio for 2091 keV transition is 0.031(6) which is consistent with 3- spin for 2694 keV level. It is concluded therefore that the 2694 keV level has 3- spin and multipole admixture for 2091 keV transition is El + (0.10 k O.O4)%M2 3.2.2. Spin of 1958keV level: There are two possible spin assignments (3 + and 4+) to the 1958 keV level from earlier measurements (Behar et al., 1976) and compilation in Nuclear Data Sheets by Tamura et al. (1984). In the present measurements the cascades 709-(646b603 keV, studied for the first time, and 70946 keV have been attempted to deduce the spin of the 1958 keV level. The A,, coefficients for both the cascades
P(l958) 3+ 3+ 4+ 4+
Cascade
6,
709-(646)-603 709-646 70!_(646fi603 709646
*Indicates the mixing measurements.
mixing ratio
ratio
6,
0.56>6 -4.2?’ 40 -0.75rp” -LO’;? acceptable
on
>0.13 +;:;~;[ O.O~~.~ the
basis
of
ICC
Thus for the 3+ spin assignment to 1958 keV level, the mixing ratio of 709 keV transition, determined from two cascades does not show any overlapping value. With the 4+ assignment to 1958 keV level, the multipole mixing ratio for 709 keV transition, exhibits good agreement for the two cascades. Consequently the spin value 4+ is confirmed from present directional correlation results. 3.2.3. Multipolarity of 1445keV transition. The cascade 1445-646 keV, following the spin sequence 3-4+-2+ was used to deduce the multipole mixing ratio of 1445 keV transition. The present measured
JATINDERGOSWAMY et al.
546
Table 3. Multipole mixing ratio for various Transition enerav (keV)
Cascade used
Spin sequence 4+-2+-0+ 4+_(4+-Z+fl+ 4+-4+-Z+ 2+<2+-2+~+ 2+-2+a+ 2+-(4+-2+)~3+ 2+4+-2f 3--2+-z+ 3-+4+-2+)-O+ 3--4+-Z+ 4+-2+AI+ 3.
646-603 709-(646t603 709-646 714-(723fi603 723603 791<646t603 791-646 968-723 104~(646t603 1041-646 1356-603 l368-(723t603 1376723 1376723 1437-603 1441-646 1691-603 2091-603
646 709 714 723 791 968 1045 1356 I368 I376 1437 1445 1691 209 I
2+-2+-o+ 3TA+-2+ 3--2+C1+ 3--2+-0+
A,, coefficients permit the following ratio for the 1445 keV transition. Multipole
mixing ratio
values of mixing
Multipole
0.015 f 0.080 4.8’;,:
admixture
El + (0.02+0’7)%M2 El + (95.8’::)%M2
However, the lower value of 6(1445) is supported by the presently measured value of A,. Thus the mixing ratio, 6(1445) = O.OlS(SO), i.e. a multipole admixture El + (<0.90)%M2 is accepted for the 1445 keV transition. 3.2.4. Multipole admixture of 791 keV transition. The multipole admixture of 791 keV transition, as deduced by Sharma et al. (1979) and later accepted in the compilation in Nuclear Data Sheets by Tamura et al. (1984) is Ml + E2 which is not permissible by the confirmed spin sequence 2 + 4 + of the initial and final levels of 791 keV transition. In the present work, two cascades i.e., 791-646, 7914646t603 were analysed to determine multipole mixing ratio for the 791 keV transition. This gave the following values for mixing ratios which are acceptable on the basis of ICC measurements (Johnson and Mann, 1974): Cascade 791-546 791<646)-603
Mixing
ratio
-0.15?;~: -0.32’;::
Multipole
admixture
E2 + (2.3’:;)%M3 E2 + (9.3:; ,)%M3
transitions
in “?e
Multipole mixing ratio 0.013 * 0.009 -0.8Y - l.O$ -0.65,;; 3.74kO.12 Po.3T;:: -0.15:;;: 0.038 f 0.003 -0.14’:; -0.054 (38) -0.32,;;; 0.17;?6’ 0.26~0.11 0.16’0” 0.51 +O -0 ”II 0.015 ? 0.08 -0.009 * 0.022 0.031 ? 0.006
Multipolarity E2 + (O.O2’:&)%M3 Ml + (36+;;)%E2 Ml + (50t’6)%E2 2” Ml + (30’,$%E2 E2 + (6.6’;;)%MI E2 + (9.3:8,;)%M3 E2 + (2.3’:;)%M3 El + (0.14 k O.O3)%M2 El +(1.9T$%M2 El + (0.29’:;;)%MZ E2 + (0.1 ‘:,:)%Ml El + (2.8”“)%M2 * El + (6.4’$)%M2 El + (2.6’:“)%MZ Ml + 20S’::)%E2 El + (<0.90)%M2 El + (O.O2’;‘$)%M2 El + (0.10 f O.O4)%M2
have been deduced. These directional correlation results have convincingly confirmed the spin assignment for the 2694 and 1958 keV levels and we have deduced the multipole mixing ratios for the 791 and 1445 keV transitions. Acknowledgements-Three of us JG (SRF, DAE), BC (SRF, PL-480 Project) and DM (Scientist’s Pool Officer, CSIR) acknowledge the financial support provided by Department of Atomic Energy, Bombay (India), Council of Scientific and Industrial Research, New Delhi (India) and Indo-US rupee fund.
References Baker K. R., Hamilton J. H., Rammaya A. V. and Highland G. (1972) Nucl. Phys. A 186, 493. Behar M., Bermudez Garcia G., Filevich A. and Cambiaggio M. C. (1976) Phys. Rev. C 13, 767. Browne E. (1986) Nucl. Instr. Methods A 249, 461. Browne E. and Firestone R. B. (1986)Tables of Radioactive Isotopes. Wiley, New York. Chand B., Goswamy J., Mehta D., Singh N. and Trehan P. N. (1989) Nucl. Instr. Methods A 284, 393. Garbowski Z. W., Krane K. S. and Steffen R. M. (1971) Phys. Rev. C 3, 1649. Gehrke R. J., Helmer R. G. and Greenwood R. C. (1977) Nucl. Instr. Methods A 147, 405. lwata Y., Masayuki Y., Maeda K. and Yoshizawa Y. (1984) Nucl. Insrr. Methods A 219, 123. Jianming Y., Yunzuo L. and Dailing H. (1988) Z. Phys. A 331, 391.
4. Conclusions The decay scheme, from present and previous works (Tamura et a/., 1984; Jianming et al., 1988) is shown in Fig 1. The energies of levels, logft values and Is(%) presented in Fig. 1. are deduced from the measurements. The present intensity present measurements, performed using precisely calibrated set of HPGe detectors, confirm all the nine new gamma-rays and the two levels proposed by Jianming et al. (1988). The present directional correlation measurements have been done for 17 cascades, of which 8 cascades, have been attempted for the first time and multipole mixing ratio for 13 transitions
Johnson J. R. and Mann R. C. (1974) Can. J. Phys. 52, 406.
Krane K. S. (1972) Nucl. Instr. Methods 98, 205. Krane K. S. and Steffan R. M. (1971) Phys. Rev. C 4, 1419.
Lederer C. M. and Shirley V. S. (1978) Tables of Isoropes 7th ed. Wiley, New York. Mardirosion G. and Stewart N. M. (1984) Z. Phys. A 235, 213.
Mehta D., Garg M. L., Singh J., Cheema T. S. and Trehan P. N. (1986) Nucl. Instr. Methods A 245, 447. Sharma A. K., Verma H. R., Singh N. and Trehan P. N. (1979) J. Phys. Sot. Japan 47, 1. Sooth S. S., Kaur R., Singh N. and Trehan P. N. (1983) J. Phys. Sot. Japan 52, 61.
Tamura T., Miyano K. and Ohya S. (1984) Nucl. Data Sheets 41, 413.
Study JATINDER
0883-2889/93 96.00+ 0.00 Pergamon Press Lid
of the 124Sb Decay
GOSWAMY, BAKHSHISH CHAND, DEVINDER NIRMAL SINGH and P. N. TREHAN
MEHTA,
Department of Physics, Panjab University, Chandigarh 160014, India (Received 18 February 1992; in revised form 30 July 1992) The energies and intensities of gamma-rays emitted following the ‘“Sb decay have been measured with better precision using three HPGe detectors. Two levels reported at 2808 and 2814 keV and nine gamma-rays of energy 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9, and 2808.0 keV in ‘*‘Te, proposed recently, have been confirmed. The intensities of x-rays emitted following the decay of ‘*%b have been reported for the first time. The results of the directional correlation measurements have been used to uniquely assign 4+ and 3- spins to the levels at 1958 and 2694 keV respectively. Also the multipole mixing ratios for 13 transitions in ‘24Tehave been deduced.
Keeping in view the above-mentioned status of the level structure of ‘*?e, the decay of ‘24Sb has been investigated through gamma-ray singles and gamma-gamma directional correlation measurements using high resolution spectrometers.
1. Introduction The radionucleus lz4Sb (tliz = 60.2 d) undergoes B decay to the excited states of ‘24Te which further de-excite to the ground state with the emission of gamma-rays and conversion electrons. The level structure of ‘*?e has been investigated through the study of radioactive decays as well as through nuclear reactions (Tamura et al., 1984). The singles measurements of gamma-rays following the decay of ‘*%b have been performed by many workers (Iwata et al., 1984; Jianming et al., 1988; Mardirosion and Stewart 1984), but these investigations are associated with controversies regarding the intensity values and existence of a large number of gamma-rays. Recently, Jianming et al. (1988) have studied this decay through singles and coincidence measurements. They have reported nine new gamma-rays and also established four new levels at 2512, 2550, 2808 and 2814 keV. They have ruled out the presence of 34 previously reported gamma-rays (Mardirosion and Stewart, 1984; Lederer and Shirley, 1978; Sharma et al. 1979). The multipole mixing ratios of many transitions and spin-parity assignments to some of the levels in ‘24Te have been done on the basis of angular correlation (Baker et al., 1972; Behar et al., 1976; Garbowski et al., 1971; Sharma et al., 1979) and conversion electron measurements (Johnson and Mann, 1974). Most of these measurements have been done by using either NaI(Tlwe(Li) or Ge(L+Ge(Li) coincidence set-ups having poor energy and time resolution, and low coincidence efficiency. A survey of the literature reveals that most of these measurements are limited only to few cascades. The spin assignments to a number of levels in ‘24Te are still uncertain as reported in the compilation by Tamura et al. (1984).
2. Experimental 2.1. Gamma-ray singles measurements The radioactive source of ‘“Sb was procured, in two instalments, from BARC, Bombay (India) in the
form of SbCl, dissolved in dilute HCl. The present intensity measurements have been performed using a set of three precisely calibrated HPGe detectors: HPGe detector (volume = (i) a vertical 28.27 mm* x 5.0 mm; FWHM = 459 eV at 122 keV) over the energy region 2&750 keV; and (ii) two coaxial HPGe detectors (volumes = 57 and 96 cm’; FWHM = 1.8 keV at 1332 keV) over the energy region 100-3800 keV. The 57 cm3 HPGe detector was placed in a heavy lead housing to reduce the detection of background radiations to 5 counts/s. Thin and uncovered sources, prepared by drying the source solution on thin mylar backing treated with insulin, were used with vertical HPGe detector and these sources yielded about 500 counts/s. For intensity measurements with coaxial HPGe detectors, the sources were covered with thin mylar and their counting rates were kept about 2000 counts/s at source-to-detector distance of 25 cm. The efficiency calibration of the vertical planar and the two coaxial HPGe detectors were performed using the radioactive sources of 24Na, “Co, @‘Co,“Se,
541
542
JATINDER
G~SWAMY
*‘Y, 94Nb, “OrnAg, ‘33Ba, 13’Cs, “‘Eu, 24’Am and a mixed standard containing ‘“Eu, IssEu, ‘25Sb and ‘25mTe sources. The details of efficiency calibration and interpolation procedures have been described in our earlier papers (Chand et al., 1989; Mehta et aI., 1986). Fifteen spectra were taken with each source and detector combination for the time duration ranging between 10-20 h. The spectra were analyzed by using a computer code which fits gamma-peaks as gaussians with a provision of including short and long exponential tails. The continuum under the peak can be approximated by a polynomial up to fourth order with the option of including a step function. The peaks at 189.4 and 210.4 keV were clearly distinguishable (on the basis of FWHM) from the broad backscattered peaks due to high energy intense gamma-rays falling in the energy region 18&230 keV. The summing corrections for various cascading and cross-over gamma-rays were calculated by the method suggested by Gehrke et al. (1977) and the present intensity results were corrected for these.
2.2. Directional correlation measurements The gamma-gamma directional correlation measurements were performed using a 96 cm3 HPGe-90 cm3 HPGe set up having time resolution = 7 ns for the 1173-1332 keV cascade from @‘Co decay and energy resolution = 1.8 keV at 1332 keV. The source-to-detector distance was kept to be 15.0 cm for both the detectors. A movable 90cm3 HPGe detector was used to gate the photopeaks at 603, 646 and 723 keV energy. The sources were prepared by putting the source solution in a perspex holder having a vertical cavity of 1.5 mm dia and depth of 4 mm. The coincidence spectra were recorded at seven angles from 90” to 180” at intervals of 15” for the 603 keV gate and at four angles at intervals of 30” for other two gates. The data were corrected for the miscentering (< 1%) of the source, the chance and the Compton contributions. Also the correlation coefficients were corrected for the finite angular resolution of HPGe detectors by the method of Krane (1972). The details of the method of analysis are described elsewhere (Sharma et al., 1979).
3. Results and Discussion 3.1. Gamma-ray singles measurements The present measured energies and intensities of K x-rays and gamma-rays emitted following the decay of ‘24Sb are presented in Table 1. The intensity values of gamma-rays, in the energy region above 100 keV, measured by using two different coaxial HPGe detectors, are found to be consistent, and their weighted
et
al.
average results are presented in Table 1. The uncertainties correspond to one standard deviation (la) and include contributions due to statistics and analysis (cc 1% for good peaks), efficiency calibration errors (l-3%) over the energy region 20-3800 keV, errors due to summing corrections (< 1.0%) and other systematic errors (0.5%). The intensity results of other workers (Iwata et al., 1984); Jianming et al., 1988; Mardirosion and Stewart, (1984) are also presented in Table 1 for comparison. The present intensity results are found to be in general agreement with those reported by Mardirosion and Stewart (1984), Jianming et al. (1988) and Iwata et al., (1984) for strong gamma-rays. However the intensity values for many weak gamma-rays measured by different workers (Iwata et al., 1984; Jianming et al., 1988; Mardirosion and Stewart, 1984) and by us are inconsistent with each other. Since we have collected good statistics for the weak peaks and the results obtained by using two coaxial HPGe detectors are well consistent with each other, we judge the present results therefore to be more reliable. Nine new gamma-rays of energy 148.4, 189.7, 210.4, 291.5, 346.5, 530.3, 571.6, 1565.9 and 2808.0 keV, observed by Jianming et al. (1988), were clearly seen in the present measurements with general consistent intensity results. The observed gamma-rays at energy 1565.9 and 2808.0 keV confirm the proposed levels at 2814 and 2808 keV (Jianming et al., 1988). No gamma-ray was observed at 498 keV; consequently, the level at 1747 keV in Nuclear Data sheets (Tamura et al., 1984) decaying through this gamma-ray alone is discarded. The other gamma-rays at 283.6, 387.3, 476.5, 498.1, 621.5, 938.2, 997.2, 1014.6, 1163.4, 1195.9, 1199.2, 1204.5, 1248.1, 1254.0, 1272.4, 1389.0, 1428.6, 1557.2, 1709.5, 1730.1, 1733.0, 1752.7, 1795.2,2151.1,2204.2,2224.7, 2412.7, 2521.5 and 2642.2 keV reported previously (Mardirosion and Stewart, 1984; Sharma et al., 1979) could not be seen in the present measurements. Many other peaks reported in earlier measurements (Mardirosion et al., 1984; Sharma et al., 1979) were observed in the present measurements but could be identified as sum, escape or background peaks; or having decay rates different from the known gamma-rays from the ‘24Sb decay. The intensity of K x-rays emitted following the decay of ‘24Sb have been measured for the first time. These intensity results show good agreement with the evaluated results given in the Tables of Radioactive Isotopes (Browne and Firestone, 1986) using physical parameters associated with atomic processes subsequent to internal conversion process. The present photon emission probabilities (in the last column of Table I), deduced using formalism given by Browne (I 986), show good agreement with the values reported in Table of Radioactive ISOtopes (Browne and Firestone, 1986). The logft values and percentage b _ feeding to various levels of ‘24Te populated in 124Sb decay have been deduced
Study of the %b
decay
543
Table I.Intensities of K. and gamma-rays emittedfollowing the decay of "'Sb
27.4(Te-K,) 30.9(Te-K,) 148.4 189.7 210.4 254.4 291.5 335.8 346.5 370.8 400.0 444.1 468.8 481.1 525.5 530.3 571.6 602.8 632.4 645.9 662.3 709.3 713.8 722.8 735.6 735.9 766.2 775.2 790.7 816.9 857.0 899.4 968.2 976.4 1045.2 1053.8 1086.5 1263.4 1301.5 1325.6 1355.2 1368.3 1376.1 1385.1 1436.6 1445.2 1489.0 1526.3 1565.9 1579.8 1622.3 1691.0 1720.3 1757.9 1851.7 1918.6 2015.9 2039.4 2078.9 2091.0 2098.9 2107.9 2172.2 2182.6 2283.8 2293.8 2323.1 2454.5 2681.6 2693.8 2808.0
3.66(17) 0.84(5) 0.037(7) 0.066(13) 0.055(l0) 0.163(8) 0.088(8) 0.75(2) 0.060(13) 0.34(8) 1.24(13) 1.92(2) 0.47(3) 0.24(2) 1.40(2) 0.43(2) 0.193(13) 1000(10) 1.07(l) 75.5(8) 0.32(2) 13.4(2) 22.7(3) 107.7(14)
0.061(20) 0.062(22) 0.062(28) 0.214(41) 0.122(61) 0.86(6) 0.132(51) 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(S) 109.9(15)
1.29(2)
1.45(21)
0.124(2) 0.093(18) 7.52(9) 0.74(2) 0.24(l) 0.175(14) 19.212) 0.845(17) 18.7(2) 0.05(2) 0.38(2) 0.42(2) 0.35(l) 16.1(2) 10.5(l) 26.4(3) 4.93(6) 0.62(3) 12.5(l) 3.34(4) 6.87(6) 4.14(5) 0.15(4) 4.27(S) 0.42(l) 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) 0.47(l) 0.45(2) 0.021(5) 0.44(l) 0.101(8) 0.76(S) 0.027(3) 0.018(2) 0.020(4) 0.047(5) 0.015(2)
0.092(41) 0.112(41) 7.53(11) 0.74(7) 0.32(6) 0.20(6) 19.45(23) 0.88(5) 18.97(24) 0.43(5) 0.43(5) 0.39(5) 16.45(23) ll.O3(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) 0.40(4) 487.3(61) 1.02(4) 0.112(31) 0.60(3) 0.124(7) 0.68(2) 0.163(25) 56.9(9) 0.46(Z) 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)
0.51(9) 1.29(16) 2.05(10) 0.58(S) 1.17(12) lOOO(4) 1.14(6) 76.1(3) 0.16(S) 13.99(11) 23.38(12) 110.2(4) 1.33(9) 7.58(9) 0.79(6) 0.29(7) O.l6(9) 19.19(13) 0.88(8) 18.64(17) 0.39(9) 0.46(15) 0.41(15) 15.84(22) 10.42(27) 26.7(3) 5.01(20) 0.61(26) 12.25(24) 3.58(17) 6.79(19) 4.10(24) 0.35(12) 485.8(16) 0.97(7)
0.52(4) 0.093(26) 0.59(3) 0.157(14) 55.9(2) 0.45(6) 0.44(3) 0.40(2) 0.041(13) 0.31(10) O.G7(19) -
0.3G(66) 0.78(7) 0.239(61) 1.68(12) 2.26(15) 0.79(5) 0.30(5) 1.78(12)
1000 1.18(7) 78.2(22) 0.43(S) 14.9(7) 24.6 114.6(16) 1.42(S) 0.09(5) 0.112(41) 7.66(8) 0.86(8) 0.27(6) 20.3;(24) 0.88(12) 20.13(23) 0.07(l) 0.58(S) 0.54(10) 0.61(8) 16.90(29) 11.08(22) 27.58(69) 5.31(46) 0.79(25) 13.40(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(Z) 0.04(l) O.OlO(5) 0.025(10) 0.056(10)
'Errorin energyrange from O.lJsl.6 keV. tResultsevaluated theoretically in compilation in Browne and Firestone (1986)
0.357(17) 0.082(10) 0.0037(7) O.O065(I3) 0.0054(10) 0.0159(10) 0.0086(10) 0.073(3) 0.0059(13) 0.033(10) 0.121(3) 0.188(5) 0.046(3) 0.024(2) 0.137(3) 0.042(2) 0.0190(13) 97.8(17) 0.105(Z) 7.38(10) 0.031(2) 1.31(3) 2.22(4) 10.5(2) 0.126(3) 0.0121(5) 0.0091(18) 0.74(2) 0.072(3) 0.024(l) 0.0171(14) 1.88(3) 0.083(2) 1.83(3) 0.005(2) 0.037(2) 0.041(2) 0.034(2) 1.57(3) 1.03(2) 2.58(4) 0.48(l) 0.061(2) 1.22(2) 0.327(7) 0.671(14) 0.412(8) 0.015(4) 0.424(8) 0.041(2) 48.2(7) 0.094(3) 0.005(2) 0.0061(9) 0.054(2) 0.011(1) 0.065(2) 0.026(2) 5.62(10) 0.046(l) 0.044(2) 0.0021(5) 0.043(2) 0.0099(8) 0.057(3) 0.0026(3) 0.0018(2) 0.0020(4) 0.0046(7) O.OOl5(2)
0.373(8)t 0.079(10) <0.028 0.079(20) 0.020(7) 0.147(23) 0.193(22) 0.064(24) 0.029(12) 0.159(23) 97.8 0.098(23) 7.4(4) 1.35(6) 2.28(10) 10.9(4) 0.264(23) <0.06 <0.09 0.74(4) 0.078(23) 0.20(7) 0.016(5) 1.87(6) 0.075(12) 1.86(8) 0.033(12) 0.029(6) 0.034(7) 1.59(7) 1.05(9) 2.66(11) 0.52(8) 0.052(19) 1.25(11) 0.33(7) 0.69(7) 0.40(7) 0.41(7) 0.033(9) 47.1(14) 0.083(13) 0.020(7) 0.049(15) 0.0088(18) 0.068(5) 0.013(5) 5.49(19) 0.044(8) 0.039 0.0010(5) 0.039 0.0078(23) 0.0311(23) 0.0023(5) 0.0006(3) 0.0014(3) -0.15
544
from the present Fig. 1. 3.2. Directional
JATINDER GOSWAMY
intensity
results and are shown
in
correlation measurements
The present directional correlation coefficients for 17 cascades in ‘24Te along with the results of other workers are presented in Table 2. The present directional correlation results are in general agreement with those reported by other workers except for significant differences in 791-(646t603, and 1437603 keV cascades from previous measurements (Baker et al., 1972; Sharma et al., 1979; Garbowski et al., 1971). The directional correlation coefficients for the 7099(646)-603, 791-646, 1368-(723)-603, 1356603, 1045-646, 144-646, 1526646 and 1376 723 keV cascades have been measured for the first time. The directional correlation coefficients from the present work have been further used to deduce the multipole mixing ratios for various transitions in ‘24Te by the method described by Krane and Steffan
et al.
(1971) whose sign convention and notations have been used throughout. For whole of the analysis, the 603 keV transition has been assumed pure E2 on the basis of ICC measurements (Johnson and Mann, 1974). The multipole mixing ratios and deduced multipole admixture for different transitions in ‘24Te are presented in Table 3. The important results derived from these measurements are discussed below. 3.2. I. Spin of 2694 ke V level: The level at 2694 keV has two possible spin assignments of 2-and 3from the previous measurements (Baker et al., 1972; Garbowski et al., 1971) and the compilation in Nuclear Data Sheets (Tamura et al., 1984). The directional correlation results for 2091603 cascade were used to choose correct spin for 2694 keV level. The measured A,, coefficient was used for the analysis of 2091603 keV cascade with consideration of both the 2- & 3- spin assignments for the 2694 keV level. The following values of
Fig. 1. The decay scheme of ‘%b
Study of the ‘*‘Sb decay
545
Table 2. Gamma-gamma directional correlation coefficients Directional
correlation
results from ‘*‘Sb decay
coefficients
Cascade (kev) 64&603
709<646wo3 714-(723w3 723403
791-(646~03 104y646)-603
135&603 1368-(723HO3 1437-603 1691-603
209 I-603
709-646
791646 1045-646 1445-646 152&646 968-723
1376723
multipole mixing ratio for 2091 keV transition obtained:
0.019 * 0.007 0.003 f 0.011 0.005 f 0.010 0.010 f 0.030 0.0399 + 0.075 -0.039 f 0.034 0.245 + 0.009 0.270 f 0.015 0.295 + 0.020 0.283 k 0.007 -0.116 + 0.079 0.114 f 0.095 0.042 f 0.027 -0.052 f 0.046 0.064 * 0.060 0.026 f 0. I73 0.042 f 0.109 -0.214 + 0.086 0.340 f 0.100 -0.0088 f 0.0143 -0.005 + 0.025 -0.01 I * 0.011 0.009 i 0.016 -0.038 + 0.018 0.004 f 0.020 -0.009 + 0.138 0.011 f 0.033 -0.02 f 0.03 -0.187~0.044 -0.04 f 0.04 0.02 f 0.09 -0.02 f 0.07 -0.030 * 0.002 -0.023 f 0.026 0.058 f 0.027 -0.06 + 0.07
were
For J”(2694) = 3 6, = 0.031(6)
Ref.
,444
AZ, 0.110~0.005 0.095 * 0.01 I 0.100 f 0.005 0.121 + 0.025 0.23 f 0.06 0.094 +_0.025 0.128 + 0.006 0.135 f 0.009 0.130 + 0.015 0.101 f 0.005 0.104 f 0.058 0.307 f 0.065 -0.135~0.020 - 0. I75 + 0.032 -0.114+0.042 0.08+0.13 - 0.009 * 0.08 -0.112+0.064 -0.240 + 0.060 -0.065 i 0.01 I - 0.064 f 0.020 -0.068 f 0.005 -0.047 f 0.005 -0.067 + 0.012 -0.069 + 0.015 0.206+0.117 0.187 + 0.017 0.190 f 0.020 0.280 f 0.031 -0.10 f 0.03 -0.16 + 0.07 0.22 + 0.05 0.028 + 0.002 0.058 k 0.027 0.043 * 0.012 -0.03 + 0.06
6, = 4.96(16)
Present Baker et al. (1972) Behar el al. (1976) Garbowski ef al. (1971) Present Present Present Baker ef of. (1972) Garbowski et al. (1971) Sharma ef al. (1979) Present Sharma er a/. (1979) Present Baker et al. (1972) Sharma er 41. (1979) Present Present Present Baker er al. (1972) Present Garbowski er al. (1971) Baker et al. (1972) Present Baker el al. (1972) Garbowski ef al. (1971) Present Garbowski et al. (1971) Behar et al. (1976) Present Present Present Present Present Baker ef al. (1972) Sharma er al. (1979) Present
were used in analysis to deduce multipole mixing ratio of 709 keV transition assuming 3 + and 4+ spin values for the 1958 keV level. The possible multipole mixing ratios for the 709 keV transition are tabulated below.
For J”(2694) = 2 6, = 0.400(7)
Multipole
6, = 25.5+‘.’ 4.6
The experimental K conversion coefficient for 2091 keV transition is tlk = 0.00013(4) (Johnson and Mann, 1974) clearly indicates this transition to be pure El with possibly very small M2 component. Thus the only acceptable value of mixing ratio for 2091 keV transition is 0.031(6) which is consistent with 3- spin for 2694 keV level. It is concluded therefore that the 2694 keV level has 3- spin and multipole admixture for 2091 keV transition is El + (0.10 k O.O4)%M2 3.2.2. Spin of 1958keV level: There are two possible spin assignments (3 + and 4+) to the 1958 keV level from earlier measurements (Behar et al., 1976) and compilation in Nuclear Data Sheets by Tamura et al. (1984). In the present measurements the cascades 709-(646b603 keV, studied for the first time, and 70946 keV have been attempted to deduce the spin of the 1958 keV level. The A,, coefficients for both the cascades
P(l958) 3+ 3+ 4+ 4+
Cascade
6,
709-(646)-603 709-646 70!_(646fi603 709646
*Indicates the mixing measurements.
mixing ratio
ratio
6,
0.56>6 -4.2?’ 40 -0.75rp” -LO’;? acceptable
on
>0.13 +;:;~;[ O.O~~.~ the
basis
of
ICC
Thus for the 3+ spin assignment to 1958 keV level, the mixing ratio of 709 keV transition, determined from two cascades does not show any overlapping value. With the 4+ assignment to 1958 keV level, the multipole mixing ratio for 709 keV transition, exhibits good agreement for the two cascades. Consequently the spin value 4+ is confirmed from present directional correlation results. 3.2.3. Multipolarity of 1445keV transition. The cascade 1445-646 keV, following the spin sequence 3-4+-2+ was used to deduce the multipole mixing ratio of 1445 keV transition. The present measured
JATINDERGOSWAMY et al.
546
Table 3. Multipole mixing ratio for various Transition enerav (keV)
Cascade used
Spin sequence 4+-2+-0+ 4+_(4+-Z+fl+ 4+-4+-Z+ 2+<2+-2+~+ 2+-2+a+ 2+-(4+-2+)~3+ 2+4+-2f 3--2+-z+ 3-+4+-2+)-O+ 3--4+-Z+ 4+-2+AI+ 3.
646-603 709-(646t603 709-646 714-(723fi603 723603 791<646t603 791-646 968-723 104~(646t603 1041-646 1356-603 l368-(723t603 1376723 1376723 1437-603 1441-646 1691-603 2091-603
646 709 714 723 791 968 1045 1356 I368 I376 1437 1445 1691 209 I
2+-2+-o+ 3TA+-2+ 3--2+C1+ 3--2+-0+
A,, coefficients permit the following ratio for the 1445 keV transition. Multipole
mixing ratio
values of mixing
Multipole
0.015 f 0.080 4.8’;,:
admixture
El + (0.02+0’7)%M2 El + (95.8’::)%M2
However, the lower value of 6(1445) is supported by the presently measured value of A,. Thus the mixing ratio, 6(1445) = O.OlS(SO), i.e. a multipole admixture El + (<0.90)%M2 is accepted for the 1445 keV transition. 3.2.4. Multipole admixture of 791 keV transition. The multipole admixture of 791 keV transition, as deduced by Sharma et al. (1979) and later accepted in the compilation in Nuclear Data Sheets by Tamura et al. (1984) is Ml + E2 which is not permissible by the confirmed spin sequence 2 + 4 + of the initial and final levels of 791 keV transition. In the present work, two cascades i.e., 791-646, 7914646t603 were analysed to determine multipole mixing ratio for the 791 keV transition. This gave the following values for mixing ratios which are acceptable on the basis of ICC measurements (Johnson and Mann, 1974): Cascade 791-546 791<646)-603
Mixing
ratio
-0.15?;~: -0.32’;::
Multipole
admixture
E2 + (2.3’:;)%M3 E2 + (9.3:; ,)%M3
transitions
in “?e
Multipole mixing ratio 0.013 * 0.009 -0.8Y - l.O$ -0.65,;; 3.74kO.12 Po.3T;:: -0.15:;;: 0.038 f 0.003 -0.14’:; -0.054 (38) -0.32,;;; 0.17;?6’ 0.26~0.11 0.16’0” 0.51 +O -0 ”II 0.015 ? 0.08 -0.009 * 0.022 0.031 ? 0.006
Multipolarity E2 + (O.O2’:&)%M3 Ml + (36+;;)%E2 Ml + (50t’6)%E2 2” Ml + (30’,$%E2 E2 + (6.6’;;)%MI E2 + (9.3:8,;)%M3 E2 + (2.3’:;)%M3 El + (0.14 k O.O3)%M2 El +(1.9T$%M2 El + (0.29’:;;)%MZ E2 + (0.1 ‘:,:)%Ml El + (2.8”“)%M2 * El + (6.4’$)%M2 El + (2.6’:“)%MZ Ml + 20S’::)%E2 El + (<0.90)%M2 El + (O.O2’;‘$)%M2 El + (0.10 f O.O4)%M2
have been deduced. These directional correlation results have convincingly confirmed the spin assignment for the 2694 and 1958 keV levels and we have deduced the multipole mixing ratios for the 791 and 1445 keV transitions. Acknowledgements-Three of us JG (SRF, DAE), BC (SRF, PL-480 Project) and DM (Scientist’s Pool Officer, CSIR) acknowledge the financial support provided by Department of Atomic Energy, Bombay (India), Council of Scientific and Industrial Research, New Delhi (India) and Indo-US rupee fund.
References Baker K. R., Hamilton J. H., Rammaya A. V. and Highland G. (1972) Nucl. Phys. A 186, 493. Behar M., Bermudez Garcia G., Filevich A. and Cambiaggio M. C. (1976) Phys. Rev. C 13, 767. Browne E. (1986) Nucl. Instr. Methods A 249, 461. Browne E. and Firestone R. B. (1986)Tables of Radioactive Isotopes. Wiley, New York. Chand B., Goswamy J., Mehta D., Singh N. and Trehan P. N. (1989) Nucl. Instr. Methods A 284, 393. Garbowski Z. W., Krane K. S. and Steffen R. M. (1971) Phys. Rev. C 3, 1649. Gehrke R. J., Helmer R. G. and Greenwood R. C. (1977) Nucl. Instr. Methods A 147, 405. lwata Y., Masayuki Y., Maeda K. and Yoshizawa Y. (1984) Nucl. Insrr. Methods A 219, 123. Jianming Y., Yunzuo L. and Dailing H. (1988) Z. Phys. A 331, 391.
4. Conclusions The decay scheme, from present and previous works (Tamura et a/., 1984; Jianming et al., 1988) is shown in Fig 1. The energies of levels, logft values and Is(%) presented in Fig. 1. are deduced from the measurements. The present intensity present measurements, performed using precisely calibrated set of HPGe detectors, confirm all the nine new gamma-rays and the two levels proposed by Jianming et al. (1988). The present directional correlation measurements have been done for 17 cascades, of which 8 cascades, have been attempted for the first time and multipole mixing ratio for 13 transitions
Johnson J. R. and Mann R. C. (1974) Can. J. Phys. 52, 406.
Krane K. S. (1972) Nucl. Instr. Methods 98, 205. Krane K. S. and Steffan R. M. (1971) Phys. Rev. C 4, 1419.
Lederer C. M. and Shirley V. S. (1978) Tables of Isoropes 7th ed. Wiley, New York. Mardirosion G. and Stewart N. M. (1984) Z. Phys. A 235, 213.
Mehta D., Garg M. L., Singh J., Cheema T. S. and Trehan P. N. (1986) Nucl. Instr. Methods A 245, 447. Sharma A. K., Verma H. R., Singh N. and Trehan P. N. (1979) J. Phys. Sot. Japan 47, 1. Sooth S. S., Kaur R., Singh N. and Trehan P. N. (1983) J. Phys. Sot. Japan 52, 61.
Tamura T., Miyano K. and Ohya S. (1984) Nucl. Data Sheets 41, 413.