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Study of 82Br decay
Vol. 45, No. 3, pp. 309-315, 1994 Copyright 0 1994 Elsevier Science Ltd
Appl. Rodiat. ht.
Pergamon
Printed in Great Britain. All rights reserved 0969-8043/94 $6.00 + 0.00
Study J. GOSWAMY,
of 82Br Decay
A. SHARMA, D. MEHTA, P. N. TREHAN*
Department
of Physics,
(Received 14 December
Panjab
University,
B. CHAND,
Chandigarh,
N. SINGH
and
India
1992; in revised form 30 July 1993)
The decay of 82Br has been investigated through gamma-ray and conversion electron measurements. A level at 2172 keV in 82Kr has been proposed to place the newly observed gamma-rays of 215 and 1395 keV. The presence of gamma-rays of energies 280, 470, 599 and 932 keV has been confirmed. The K conversion coefficients for 8 transitions and (L + M + .) conversion coefficients for 4 transitions are reported. The gy-directional correlation measurements have been used to determine the mixing ratio of 10 transitions, of which the multipolarities for 221 and 273keV transitions have been deduced.
2. Experimental
1. Introduction The radionucleus **Br (t,,, = 35.4 h) undergoes p decay to the excited states of ‘*Kr which further de-excite through gamma-ray and conversion electron emission. The decay of **Br has been investigated previously by many workers through gamma-ray singles measurements (Sooth et al., 1980; Meyer et al., 1983) but there remains controversy regarding the existence and placement of gamma-rays of energy 280.3, 470.3, 599.5, 836.7 and 932.1 keV. Directional correlation measurements have been performed previously (Sooth et al., 1980; Cooper, 1977; Gardulski and Wiedenbeck, 1973; Gupta and Bajaj, 1968; Etherton and Kelly, 1966) but most of these measurements have been done using NaI(TltGe(Li) set-ups having poor time and energy resolution. The directional correlation results for many cascades exhibit significant variation which has, in some cases, led to different mixing ratio values. Also, spin-parity assignments to many levels are uncertain or have been made on weak arguments. Only one report regarding the total conversion coefficient measurements is available in the literature (Waddell, 1956). To the best of our knowledge, no measurements of intensities of K xrays, emitted following the **Br decay have been reported in literature. With the above-mentioned status of *‘Br decay in view, it was felt desirable to reinvestigate this decay through gamma-ray and conversion electron measurements.
*Author
Procedures
2.1. Singles measurements The present were measured detectors:
K x-ray and gamma-ray intensities using a set of three semiconductor
(i) a horizontal Si(Li) detector (volume = 28.27 mm* x 5.0 mm, fwhm = 180 eV at 5.96 keV) over the energy region 5-100 keV; and (ii) two coaxial HPGe detectors (volumes = 57.1 and 96.0 cm3, fwhm = 1.8 keV at 1332 keV) over the energy region 8&3000 keV. The conversion electron measurements were performed using a mini-orange electron spectrometer (fwhm = 1.8 keV for 624.5 keV conversion electrons from 13’Cs decay) (Goswamy et al., 1991). The radioactive source of 82Br was procured in four instalments from BARC, Bombay (India) in the form of NH,Br dissolved in dilute NH,OH solution. For K x-ray measurements, thin and uncovered sources yielding 500 counts/s were prepared by drying a drop on mylar backing treated with insulin. For measurements with coaxial HPGe detectors, the sources were prepared by the same method but were covered with mylar. The sources for conversion electron measurements were prepared by drying the source solution on aluminized mylar and then covering with thin mylar. These sources were made thin so as to avoid undue tailing at the leading edge of the conversion peaks. The efficiency calibration of two coaxial HPGe detectors, in the energy region 8&3000 keV, was performed using radioactive sources of 24Na, 6oCo, 88~ '%Nb, "hAg, ,)'Ba , “‘Cs, ‘52E~ and a mixed NIST
for correspondence. 309
J.
310
et al
GOSWAMY
HPGe-96 cm’ HPGe detectors set-up having time resolution of 7 ns for the 1173-1332 keV cascade following 6oCo decay. The source-to-detector distance was kept at 13.5 cm for each detector. For directional correlation measurements, the movable 90 cm’ HPGe detector was used to gate photopeaks at 554.5, 698.4, 776.5 and 1044.0 keV. Sources were prepared by putting NH,Br solution in perspex holders having a vertical cavity of 4 mm x 1.5 mm $J. The coincidence spectra were recorded at four angles (i.e. 90”, 120”, 150” and 180”). The data were corrected for the miscentering (< 1%) the chance and Compton contributions. The directional correlation coefficients were also corrected for the finite angular resolution of the HPGe detectors by the method suggested by Krane (1992) and by Krane and Steffen (1971). The details of the method of analysis are described elsewhere (Sharma et al., 1979). The yy-coincidence spectra, with gates on the photopeaks at 554.4, 698.4, 776.5 and 1044.0 keV, of very long durations were generated by adding the spectra taken during directional correlation measurements. These spectra at different angles were corrected for the chance and Compton contributions
(National Institute of Standards and Technology) standard containing ‘*‘Sb, lzSmTe, ‘j4Eu and “‘Eu sources. The efficiency calibration of the horizontal Si(Li) detector, in the energy region 5-100 keV, was performed using the radioactive sources of “Co, ‘jSe, *‘OPb, 24’Am and the above mentioned mixed standard. For efficiency calibration below 15 keV, K xray yields from thin target foils excited by ““Cd excitor source in a special EDXRF set-up, were measured. The details of the efficiency calibration and interpolation procedures have been described elsewhere (Chand et al., 1989; Mehta et al., 1986; Garg et aI., 1984). The mini-orange electron spectrometer was calibrated for its transmission in the energy region 20&1800 keV by using the radioactive sources of 54Mn, aCo, 65Zn, “Y, lz5Sb, “‘Cs, “*ELI, ‘921r and 19’Au. The details of transmission calibration have been described in our earlier paper (Goswamy et al., 1991). 2.2. yy-Coincidence
and
directional
correlation
measurements
The yy-coincidence measurements were
and directional correlation performed using a 90cm’ Table I. Intensitiesof K
x- and gamma-rays
emitted following the decay of "'Br
Relative mtensity Photon Energy
of
Sooth
radiation (kev)
PreseIlt
Meyer
e, ul.
e, al.
(1980)
(1983)
12.6(Kr-K,)
0.370(12)
14.2(Kr-Kp)
0.052(S)
92.2
0.87(l)
0.86(3)
0.90(3)
100.9
0.081 (5)
0.073(7)
129.3
0.017(3)
137.4
emission probability per 100 decays
Presell1
Browne
(1986)
0.308(11)
0.41 (15).
0.043(6)
0.065(30)'
0.73(7)
0.75(3)
0.084(8)
0.068(6)
0.070(7)
0.025(5)
0.036(7)
0.014(2)
0.030(6)
0.108(3)
0.13(l)
0.182(2)
0.089(3)
179.8
0.020(3)
O.Oll(4)
0.012(9)
0.017(3)
214.8
0.013(5)
221.5
2.71 (3)
2.61(3)
2.72(8)
2.26(3)
2.21(7)
0.96(l)
0.95(2)
l.OO(5)
0.80(l)
0.84(4)
280.3
273.5
0.152(3) -0.010
0.011 (4)
0.029(8)
0.016(3)
332.9
0.018(6)
0.023(7)
0.108(5)
0.015(S)
0.090(4)
401.2
0.107(6)
0.109(7)
0.109(9)
0.089(S)
0.091 (8)
470.3
0.047(8)
0.032(10)
554.4 599.5 606.4
85.2(6)
85.0(X)
0.020(6) 1.47(2)
0.024(7)
0.039(7) 84.8 (16) 0.016(9)
1.42(7)
70.9(10) 0.016(5)
70.9(14) -0.013
I.23 (2)
619.1
52.2(4)
51.9(5)
51.6(16)
43.5(6)
43.1(13)
698.4
33.9(4)
33.8(4)
33.8(4)
28.2(4)
28.2(8)
735.4 716.5 827.8
0.081 (8) loa 2X.8(4)
932.1
0.014(6)
952.0
0.44(l)
1007.6
1.53(2)
1044.0
33.9(4)
0.09(3) 100 28.9(3)
0.09(l) 100 28.7(9)
0.06X(7)
0.075(S)
83 3(8)
X3.6
24.0(4)
24.0(8)
O.Ol2(5,
0.012(S)
O.OlO(4)
0.45(l)
0.44(2)
0.37(l)
0.37 (2)
1.53(2)
1.57(4)
1.28(2)
33.4(3)
32.8(5)
28.2(4)
I.31 (3) 27.4(6)
1072.9
0.09(l)
0.11 (I)
O.lO(2)
0.08(l)
0.08(l)
1081.3
0.79(7)
0.76(2)
0.74(2)
0.66(l)
0.62(2)
1099.9
0.011 (6)
0.007(3)
0.009(S)
0.006(3)
1174.0
0.082(6)
0.04(2)
0.021(9)
0.068(5)
0.018(8)
1180.1
0.129(5)
0.11 (I)
0.103(9)
0.108(4)
1317.5 1395.2 1474.9
32.1 (4)
32.5(4)
32.2(6)
0.086(S) 26.9(5)
O.Oll(2)
0.014(2) 19.9(2)
26.7(4)
19.8(3)
19.9(3)
16.6(2)
16.6(3)
1650.3
0.90(l)
0.87(l)
0.95 (2)
0.75(l)
0.79 (2)
1719.7
0.134(3)
0.136(4)
0.138(15)
0.112(3)
0.115(13)
1871.6
0.059(2)
0.05(2)
0.049 (2)
1956.8
0.045(2)
W43(L)
0.03(l) _^. _ 0.04(L)
*Theoretical evaluated values.
0.038(2)
0.025(8)
’-0.033
Study of 82Br decay 3. Results and Discussion
3.1. Gamma-ray singles measurements The present measured intensities of K x-rays and gamma-rays emitted following the decay of ‘*Br are shown in the Table 1. The intensity values of gammarays, in the energy region 80_3000keV, measured by using two coaxial HPGe detectors, are found to be in close agreement and their weighted averages are presented in Table 1. The uncertainties shown in the intensity values correspond to one standard deviation (1 CT)and include contributions due to statistics and fitting (< 1% for good peaks), efficiency calibration (l-3% over the energy region 5-3000 keV), errors due to summing corrections ( < 1%) and other systematic errors (
311
version electron intensities were normalized to yield the theoretically predicted us value for 776 keV (2+ -O+) pure E2 transition (Rose1 et al., 1978). The K conversion coefficients for 554.4, 619.1, 698.4, 827.8, 1044.0, 1317.5, 1474.9 and (L + M + . .) conversion coefficients for 554.4, 619.1 and 698.4 keV transitions are being reported for the first time. The measured total conversion coefficients exhibit good agreement with the values reported by Waddell and Jensen (1956) (see Table 2). The present conversion coefficients for different transitions have been compared with the theoretically predicted values for various possible multipolarities (Rose1 et al., 1978) in Table 2. The multipolarities assigned to various transitions are also shown in this table. 3.3. yy Coincidence/directional ments
correlation measure-
The directional correlation coefficients for 25 cascades measured by us are presented in Table 3 along with the results of other workers (Sooth et al., 1980; Cooper, 1977; Gardulski and Wiedenbeck, 1973; Gupta and Bajaj, 1968; Etherton and Kelly, 1966). The directional correlation coefficients from the present work have been used to deduce the multipole mixing ratio for various transitions in ‘*Kr by the method described by Krane and Steffen (1971) whose notation and sign conventions are followed throughout (Krane, 1972). For whole of the analysis, the 776.5 keV transition was assumed to be pure E2 (Waddell, 1956). The mixing ratio for various transitions are presented in Table 4. Important results from yy coincidence and directional correlation measurements, which have led to addition of new information, are discussed below: 3.3. I. Existence of a level at 2172 ke V. The gammarays of energy 214.8 and 1395.2 keV have been observed with consistent intensities by using both the coaxial HPGe detectors (see Fig. 2). These gammarays were observed in coincidence with 776.5 keV transition (see Fig. 3) and were absent in coincidence spectra taken with gates on 554, 619, 698 and 1044 keV transitions. This suggests the possibility of 1395-776 and 215%(1180~776 keV cascades. Therefore, a new level at 2172 keV is proposed to fit these gamma-rays in the decay scheme of ‘*Br. 3.3.2. Multipolarity of the 221 keV transition. The mixing ratio of the 221 keV transition has been deduced using the directional correlation results of the 221-(1650)-776 keV cascade which follows the spin sequence 4--(4+-2+)4)+ (Muller, 1987). the spin for the 2426 keV level has been taken to be 4+ on the basis of Coulomb excitation measurements (Kemnitz et al., 1984). The analysis using A,, coefficient yields two possible values of 6 (221), which are 6,(221) = - 1.0:;:;; 6,(221) = 0.04’;::; The two possible mixing ratios and their corresponding multipole admixtures are tabulated over:
J. GOSWAMK
312
et
al
P’8hS 6’bLbI
.e 19 ;h )I -8 -
z Zh b ‘001 ‘IZZ
-9
.bSE
-
LZ8
-
.
-
* -
-
%
d
2 1
/’ + N
Study Table 2. Conversion
coefficients
for various transitions in the decay of “Br
Internalconversion Energy/ conversion shell 554.4/K /(L+M+..) 619.1/K /(L+M+..) 698.4/K /(L+M+..) 176.5/K /(L + M + 827.8/K 1044.0/K 1317.5/K 1474.9/K
6.59 (37) 0.91 (21) ll.O2(51) 2.96 (35) 9.9(12) 0.99 (42) 8.23 (35) 0.72(13) 2.96 (32) 4.0 (4) 2.53 (19) I .97 (24)
.)
*Total conversion
coefficients
698-776
619.698
55&(619w98 92-(1779t776 22l+l650)-776 273+1044)-776 554-(1317t776 60&( lO44)-776 619<698)-776 828<1044t776
1008&(1044)-776 1044776
1317-776
1650-776
1779-776 1871-776 554273 5546619 554-1317
2214606tl044 273-1044
60&1044
828-1044
1008-1044
Multipolarity
Riisel e, a/. (1978)
El
El: 6.78; M2: 46.15
6.9 (7)
E2: 15.37; Ml:
l5(2)
11.75
E2+(MI) EZ+MI
E2: 10.95; Ml: 8.97
9.0(13)
E2: 8.23
8.5 (9)
E2
-
1 2.9 (4) 3.8 (3) 2.03 (3) 2.0 (3)
measured
Table 3. Directional Cascade (keV)
coefficients (x lOe4)
Waddell* and Jensen (1956)
Present
313
of *‘Br decay
by Waddell
correlation
,422 -0.321 (33) -0.313(16) -0.297 (35) 0.094 (61) 0.088 (6) 0.069 (21) -0.020(17) - 0.54 (49) 0.14(18) 0.022 (41) 0.003 (14) 0.140(13) 0.000 I ( 149) -0.016(8) 0.200(17) 0.171 (17) 0.190(22) 0.03 (23) 0.055 (31) 0.131(31) 0.117(20) -0.047(13) -0.030(11) -0.025(19) 0.056 (63) -0.03 (5) 0.29 (7) 0.043 (15) 0.29 (46) 0. I I (45) 0.202 (80) -0.074(18) -0.064 (44) -0.046 (24) 0.09 (3) -0.048 (25) -0.026(31) -0.031 (17) 0.32 (31) 0.18(8) -0.45 (21) -0.32 (4) 0.33 (IO) 0.28 (33) 0.15(8) 0.02 (4) 0.20 (23) 0.179(15) 0.199(19) 0.04 (14) -0.03 (4) -0.13 (4)
El: 2.79; M2: E2: 3.99; M3: E2: 2.40; Ml: E2: 1.90
El E2 EZ+MI E2
15.60 17.80 2.35~ -
(1956).
coefficients A4
0.254(15) 0.171 (21) 0.214 (54) 0.049 (84) 0.028 (9) 0.10 (5) -0.009 (23) 0.44 (55) 0.02 (26) -0.74 (67) 0.010(19) -0.045(18) 0.004 (21) 0.037 (IO) 0.015 (24) 0.010 (27) 0.00 (4) 0.04 (31) 0.048 (43) 0.084 (31) 0.000 (3) -0.026(18) -0.033(15) - 0. IO4 (29) -0.161 (87) -0.02 (7) -0.01 (I I) -0.05 (3) -0.01 (67) 0.01 (7) -0.268 (15) -0.034 (21) -0.023 (60) -0.01 (4) 0.03 (5) 0.01 I (34) -0.01 (4) 0.028 (29) 0.20 (46) 0.13(12) 0. I7 (25) 0.13 (6) -0.24(16) 0.13 (44) O.OO(l2) 0.05 (62) 0.023 (32) 0.022 (22) 0.001 (29) -0.11 (19) -0.02 (6) 0.02 (6)
for various
transitions
in “Kr
Reference Present Sooth (1980) cooper (I 977) Present Gardulski and Wiedenbxk Gupta and Bajaj (1968) Present Present Present Present Present Present Present Gardulski and Wiedenbeck Present Sooth (1980) Cooper (I 977) Present Present Sooth ( 1980) Cooper (1977) Present Sooth (1980) Cooper (I 977) Present Sooth (1980) Coooer (1977) Gupia and Bajaj (1968) Present Present Present Present Present Sooth (1980) Cooper (1977) Present Sooth (I 980) Etherton and Kelly (1966) Present Sooth (I 980) Present Sooth (1980) Cooper (1977) Present Sooth (1980) Cooper (1977) Present Sooth (1980) cooper (I 977) Present Sooth (1980) cooper (1977)
(1973)
(1973)
J. GOSWAMY et al.
314 Table 4. The multipole Energy 221 213 554 606 619 698 828 1008 1044 1317 1650 1871
Mixing
ratio
6,(221) = - l.ot-;$ &(221) = 0.04:;:;
Cascade
admixtures
for various
Spin sequence 4%(4+__2+
221+1650t776 273-1044 273&( IO44t_776 554(619fi1474 554-(6193-698 60&((1044fi776 606-1044 6 I 9-698 55&6 I9 698-716 828-1044 828~( I044t776 1008&1044 I OOS-( 1044t776 1044776 1317-776 554-1317 l65&776 1871-776
Multipole
Mixing ratio
to+
El + (50;:;) %M2 El + (O-t!“) %M2
in “‘Kr Multipole admixture El + (0+!4)%M2
3+ 4+-2f 3+___(4+L2+)AJ’ 4 -(3+-2+ @+ 4 -(3+-2+)-2+ 4+-(4+-2’H’ 4+4+-Z+ 3+-2+-2+ 4 -3+-2+ 2+-2+-0+ 4 4+-2’ 4-(4+-Z+)AI+ 5 4+-Z+ 5S-(4’-2+)Al+ 4+-2+tl+ 3+-2+-0+ 4--3’L2+ 4+-2+Il+ 4 -2+-0+
admixture
transitions
Ml + (< 14%) E2 El + (0,04i;;)%M2 Ml + (63.5 f 3.O)%E2 Ml +(2.5X +“)%E2 08 2.ll+Q79 -061
MI + (81.7+::,)%E2
1.54;;:;
Ml +(70,3+;:;)%EZ
-0.02
k 0.06
El + (O.O4’?“)%M2
0.03,:;:
El + (0,1+;4)%M2
-0.075’;;:
E2 + (0.62’;::)%M3
I 4.95,;:
Ml + (96.1 i 0.7)%E2
> -0.07 + 0.05 6, = 0.0 f 0.8 6, = l.6,06
E2 + (O.SC;:)%M3 M2 + 0.0 k 0.4)%E3 M2 + (71.9,? 9)%E3
The multipole admixtures corresponding to S, (221) yields a large M2 component which implies that 221 keV transition should have large conversion coefficient. However, no conversion peak corresponding to 221keV transition is seen in the present
106
600
800
1000
? ‘f
L 1200
1000
1400
1600
Energy Fig. 2. A typical
gamma-ray
spectrum
following
1800
2000
(keV)
the decay
of 82Br taken using 96cm’
HPGe
detector.
315
Study of r2Br decay
600
400
200
Energy Fig. 3. The coincidence
y-ray spectrum
following
Thus we conclude that 221 keV transition should have small M2 component, i.e. 6,(221) can be accepted. 3.3.3. Multipolarity of the 273keV transition. The mixing ratio of the 273 keV transition has been deduced using the directional correlation results of 273-(1044)-776 and 273-1044 keV cascades. The analysis for these cascades yields 0.2 < 6 (273) < 0.4 as the overlapping range of the mixing ratio of 273 keV transition i.e. a multipole admixture of Ml + (< 14%) E2.
measurements.
References Browne E. (1986) Nucl. Instrum. Methods A 249, 361. Browne E. and Firestone R. B. (1986) Tables of Radioactiue Isotopes. Wiley, New York. Chand B., Goswamy J., Mehta D., Singh N. and Trehan P. N. (1989) Nucl. Instrum. Methodr A 284, 393. Cooper E. L. (1977) Diss. Abst. Int. 38B, 2173. Etherton E. C. and Kelly W. H. (1966) Nucl. Phys. 84, 129. Gardulski P. L. and Wiedenbeck M. L. (1973) Phys. Rev. C 7. 2080.
800
1000
(keV)
the 8’Br decay taken with gate on 776 keV transition.
Garg M. L., Singh J., Verma H. R., Singh N., Mangal P. C. and Trehan P. N. (1984) J. Phys. B; At. Mol. Phys. 17, 577. Gehrke R. J., Helmer R. G. and Greenwood R. C. (1977) Nucl. Instrum. Methods A 147, 405. Goswamy J., Chand B., Mehta D., Singh N. and Trehan P. N. (1991) Appl. Radial. Isot. 42, 1025. Gupta S. L. and Bajaj M. M. (1968) Aust. J. Phys. 21, 649. Kemnitz P., Ojeda P., Doring J., Funke L., Kostov L. K., Rotter H., Will E. and Winter G. (1984) Nucl. Phys. A 425, 493. Krane K. S. (1972) Nucl. Instrum. Methods 98, 205. Krane K. S. and Steffen R. M. (1971) Phys. Rev. C4, 1419. Mehta D., Garg M. L., Singh J., Singh N., Cheema T. S. and Trehan P. N. (1986) Nucl. Instrum. Methods A 245, 447. Meyer R. A., Wild J. F., Eskola K., Leino M. E., Vaisala S., Forresten K., Kaup U. and Gelberg A. (1983) Phys. Rev. C 27, 22 17. Muller H. W. (1987) Nuclear Data Sheets 50. Rose1 F., Fries H. M., Alder K. and Pauli H. C. (1978) AI. Data Nucl. Data Tables 21, 91. Sharma A. K., Verma H. R., Singh N. and Trehan P. N. (1979) J. Phys. Sot. Japan 47, I. Sooth S S., Verma H. R., Kaur R., Sharma A. K., Singh N. and Trehan P. N. (1980) J. Phys. Sot. Japan 49, 1222. Waddell R. C. and Jensen E. N. (1956) Phys. Rev. 102, 816.
Appl. Rodiat. ht.
Pergamon
Printed in Great Britain. All rights reserved 0969-8043/94 $6.00 + 0.00
Study J. GOSWAMY,
of 82Br Decay
A. SHARMA, D. MEHTA, P. N. TREHAN*
Department
of Physics,
(Received 14 December
Panjab
University,
B. CHAND,
Chandigarh,
N. SINGH
and
India
1992; in revised form 30 July 1993)
The decay of 82Br has been investigated through gamma-ray and conversion electron measurements. A level at 2172 keV in 82Kr has been proposed to place the newly observed gamma-rays of 215 and 1395 keV. The presence of gamma-rays of energies 280, 470, 599 and 932 keV has been confirmed. The K conversion coefficients for 8 transitions and (L + M + .) conversion coefficients for 4 transitions are reported. The gy-directional correlation measurements have been used to determine the mixing ratio of 10 transitions, of which the multipolarities for 221 and 273keV transitions have been deduced.
2. Experimental
1. Introduction The radionucleus **Br (t,,, = 35.4 h) undergoes p decay to the excited states of ‘*Kr which further de-excite through gamma-ray and conversion electron emission. The decay of **Br has been investigated previously by many workers through gamma-ray singles measurements (Sooth et al., 1980; Meyer et al., 1983) but there remains controversy regarding the existence and placement of gamma-rays of energy 280.3, 470.3, 599.5, 836.7 and 932.1 keV. Directional correlation measurements have been performed previously (Sooth et al., 1980; Cooper, 1977; Gardulski and Wiedenbeck, 1973; Gupta and Bajaj, 1968; Etherton and Kelly, 1966) but most of these measurements have been done using NaI(TltGe(Li) set-ups having poor time and energy resolution. The directional correlation results for many cascades exhibit significant variation which has, in some cases, led to different mixing ratio values. Also, spin-parity assignments to many levels are uncertain or have been made on weak arguments. Only one report regarding the total conversion coefficient measurements is available in the literature (Waddell, 1956). To the best of our knowledge, no measurements of intensities of K xrays, emitted following the **Br decay have been reported in literature. With the above-mentioned status of *‘Br decay in view, it was felt desirable to reinvestigate this decay through gamma-ray and conversion electron measurements.
*Author
Procedures
2.1. Singles measurements The present were measured detectors:
K x-ray and gamma-ray intensities using a set of three semiconductor
(i) a horizontal Si(Li) detector (volume = 28.27 mm* x 5.0 mm, fwhm = 180 eV at 5.96 keV) over the energy region 5-100 keV; and (ii) two coaxial HPGe detectors (volumes = 57.1 and 96.0 cm3, fwhm = 1.8 keV at 1332 keV) over the energy region 8&3000 keV. The conversion electron measurements were performed using a mini-orange electron spectrometer (fwhm = 1.8 keV for 624.5 keV conversion electrons from 13’Cs decay) (Goswamy et al., 1991). The radioactive source of 82Br was procured in four instalments from BARC, Bombay (India) in the form of NH,Br dissolved in dilute NH,OH solution. For K x-ray measurements, thin and uncovered sources yielding 500 counts/s were prepared by drying a drop on mylar backing treated with insulin. For measurements with coaxial HPGe detectors, the sources were prepared by the same method but were covered with mylar. The sources for conversion electron measurements were prepared by drying the source solution on aluminized mylar and then covering with thin mylar. These sources were made thin so as to avoid undue tailing at the leading edge of the conversion peaks. The efficiency calibration of two coaxial HPGe detectors, in the energy region 8&3000 keV, was performed using radioactive sources of 24Na, 6oCo, 88~ '%Nb, "hAg, ,)'Ba , “‘Cs, ‘52E~ and a mixed NIST
for correspondence. 309
J.
310
et al
GOSWAMY
HPGe-96 cm’ HPGe detectors set-up having time resolution of 7 ns for the 1173-1332 keV cascade following 6oCo decay. The source-to-detector distance was kept at 13.5 cm for each detector. For directional correlation measurements, the movable 90 cm’ HPGe detector was used to gate photopeaks at 554.5, 698.4, 776.5 and 1044.0 keV. Sources were prepared by putting NH,Br solution in perspex holders having a vertical cavity of 4 mm x 1.5 mm $J. The coincidence spectra were recorded at four angles (i.e. 90”, 120”, 150” and 180”). The data were corrected for the miscentering (< 1%) the chance and Compton contributions. The directional correlation coefficients were also corrected for the finite angular resolution of the HPGe detectors by the method suggested by Krane (1992) and by Krane and Steffen (1971). The details of the method of analysis are described elsewhere (Sharma et al., 1979). The yy-coincidence spectra, with gates on the photopeaks at 554.4, 698.4, 776.5 and 1044.0 keV, of very long durations were generated by adding the spectra taken during directional correlation measurements. These spectra at different angles were corrected for the chance and Compton contributions
(National Institute of Standards and Technology) standard containing ‘*‘Sb, lzSmTe, ‘j4Eu and “‘Eu sources. The efficiency calibration of the horizontal Si(Li) detector, in the energy region 5-100 keV, was performed using the radioactive sources of “Co, ‘jSe, *‘OPb, 24’Am and the above mentioned mixed standard. For efficiency calibration below 15 keV, K xray yields from thin target foils excited by ““Cd excitor source in a special EDXRF set-up, were measured. The details of the efficiency calibration and interpolation procedures have been described elsewhere (Chand et al., 1989; Mehta et al., 1986; Garg et aI., 1984). The mini-orange electron spectrometer was calibrated for its transmission in the energy region 20&1800 keV by using the radioactive sources of 54Mn, aCo, 65Zn, “Y, lz5Sb, “‘Cs, “*ELI, ‘921r and 19’Au. The details of transmission calibration have been described in our earlier paper (Goswamy et al., 1991). 2.2. yy-Coincidence
and
directional
correlation
measurements
The yy-coincidence measurements were
and directional correlation performed using a 90cm’ Table I. Intensitiesof K
x- and gamma-rays
emitted following the decay of "'Br
Relative mtensity Photon Energy
of
Sooth
radiation (kev)
PreseIlt
Meyer
e, ul.
e, al.
(1980)
(1983)
12.6(Kr-K,)
0.370(12)
14.2(Kr-Kp)
0.052(S)
92.2
0.87(l)
0.86(3)
0.90(3)
100.9
0.081 (5)
0.073(7)
129.3
0.017(3)
137.4
emission probability per 100 decays
Presell1
Browne
(1986)
0.308(11)
0.41 (15).
0.043(6)
0.065(30)'
0.73(7)
0.75(3)
0.084(8)
0.068(6)
0.070(7)
0.025(5)
0.036(7)
0.014(2)
0.030(6)
0.108(3)
0.13(l)
0.182(2)
0.089(3)
179.8
0.020(3)
O.Oll(4)
0.012(9)
0.017(3)
214.8
0.013(5)
221.5
2.71 (3)
2.61(3)
2.72(8)
2.26(3)
2.21(7)
0.96(l)
0.95(2)
l.OO(5)
0.80(l)
0.84(4)
280.3
273.5
0.152(3) -0.010
0.011 (4)
0.029(8)
0.016(3)
332.9
0.018(6)
0.023(7)
0.108(5)
0.015(S)
0.090(4)
401.2
0.107(6)
0.109(7)
0.109(9)
0.089(S)
0.091 (8)
470.3
0.047(8)
0.032(10)
554.4 599.5 606.4
85.2(6)
85.0(X)
0.020(6) 1.47(2)
0.024(7)
0.039(7) 84.8 (16) 0.016(9)
1.42(7)
70.9(10) 0.016(5)
70.9(14) -0.013
I.23 (2)
619.1
52.2(4)
51.9(5)
51.6(16)
43.5(6)
43.1(13)
698.4
33.9(4)
33.8(4)
33.8(4)
28.2(4)
28.2(8)
735.4 716.5 827.8
0.081 (8) loa 2X.8(4)
932.1
0.014(6)
952.0
0.44(l)
1007.6
1.53(2)
1044.0
33.9(4)
0.09(3) 100 28.9(3)
0.09(l) 100 28.7(9)
0.06X(7)
0.075(S)
83 3(8)
X3.6
24.0(4)
24.0(8)
O.Ol2(5,
0.012(S)
O.OlO(4)
0.45(l)
0.44(2)
0.37(l)
0.37 (2)
1.53(2)
1.57(4)
1.28(2)
33.4(3)
32.8(5)
28.2(4)
I.31 (3) 27.4(6)
1072.9
0.09(l)
0.11 (I)
O.lO(2)
0.08(l)
0.08(l)
1081.3
0.79(7)
0.76(2)
0.74(2)
0.66(l)
0.62(2)
1099.9
0.011 (6)
0.007(3)
0.009(S)
0.006(3)
1174.0
0.082(6)
0.04(2)
0.021(9)
0.068(5)
0.018(8)
1180.1
0.129(5)
0.11 (I)
0.103(9)
0.108(4)
1317.5 1395.2 1474.9
32.1 (4)
32.5(4)
32.2(6)
0.086(S) 26.9(5)
O.Oll(2)
0.014(2) 19.9(2)
26.7(4)
19.8(3)
19.9(3)
16.6(2)
16.6(3)
1650.3
0.90(l)
0.87(l)
0.95 (2)
0.75(l)
0.79 (2)
1719.7
0.134(3)
0.136(4)
0.138(15)
0.112(3)
0.115(13)
1871.6
0.059(2)
0.05(2)
0.049 (2)
1956.8
0.045(2)
W43(L)
0.03(l) _^. _ 0.04(L)
*Theoretical evaluated values.
0.038(2)
0.025(8)
’-0.033
Study of 82Br decay 3. Results and Discussion
3.1. Gamma-ray singles measurements The present measured intensities of K x-rays and gamma-rays emitted following the decay of ‘*Br are shown in the Table 1. The intensity values of gammarays, in the energy region 80_3000keV, measured by using two coaxial HPGe detectors, are found to be in close agreement and their weighted averages are presented in Table 1. The uncertainties shown in the intensity values correspond to one standard deviation (1 CT)and include contributions due to statistics and fitting (< 1% for good peaks), efficiency calibration (l-3% over the energy region 5-3000 keV), errors due to summing corrections ( < 1%) and other systematic errors (
311
version electron intensities were normalized to yield the theoretically predicted us value for 776 keV (2+ -O+) pure E2 transition (Rose1 et al., 1978). The K conversion coefficients for 554.4, 619.1, 698.4, 827.8, 1044.0, 1317.5, 1474.9 and (L + M + . .) conversion coefficients for 554.4, 619.1 and 698.4 keV transitions are being reported for the first time. The measured total conversion coefficients exhibit good agreement with the values reported by Waddell and Jensen (1956) (see Table 2). The present conversion coefficients for different transitions have been compared with the theoretically predicted values for various possible multipolarities (Rose1 et al., 1978) in Table 2. The multipolarities assigned to various transitions are also shown in this table. 3.3. yy Coincidence/directional ments
correlation measure-
The directional correlation coefficients for 25 cascades measured by us are presented in Table 3 along with the results of other workers (Sooth et al., 1980; Cooper, 1977; Gardulski and Wiedenbeck, 1973; Gupta and Bajaj, 1968; Etherton and Kelly, 1966). The directional correlation coefficients from the present work have been used to deduce the multipole mixing ratio for various transitions in ‘*Kr by the method described by Krane and Steffen (1971) whose notation and sign conventions are followed throughout (Krane, 1972). For whole of the analysis, the 776.5 keV transition was assumed to be pure E2 (Waddell, 1956). The mixing ratio for various transitions are presented in Table 4. Important results from yy coincidence and directional correlation measurements, which have led to addition of new information, are discussed below: 3.3. I. Existence of a level at 2172 ke V. The gammarays of energy 214.8 and 1395.2 keV have been observed with consistent intensities by using both the coaxial HPGe detectors (see Fig. 2). These gammarays were observed in coincidence with 776.5 keV transition (see Fig. 3) and were absent in coincidence spectra taken with gates on 554, 619, 698 and 1044 keV transitions. This suggests the possibility of 1395-776 and 215%(1180~776 keV cascades. Therefore, a new level at 2172 keV is proposed to fit these gamma-rays in the decay scheme of ‘*Br. 3.3.2. Multipolarity of the 221 keV transition. The mixing ratio of the 221 keV transition has been deduced using the directional correlation results of the 221-(1650)-776 keV cascade which follows the spin sequence 4--(4+-2+)4)+ (Muller, 1987). the spin for the 2426 keV level has been taken to be 4+ on the basis of Coulomb excitation measurements (Kemnitz et al., 1984). The analysis using A,, coefficient yields two possible values of 6 (221), which are 6,(221) = - 1.0:;:;; 6,(221) = 0.04’;::; The two possible mixing ratios and their corresponding multipole admixtures are tabulated over:
J. GOSWAMK
312
et
al
P’8hS 6’bLbI
.e 19 ;h )I -8 -
z Zh b ‘001 ‘IZZ
-9
.bSE
-
LZ8
-
.
-
* -
-
%
d
2 1
/’ + N
Study Table 2. Conversion
coefficients
for various transitions in the decay of “Br
Internalconversion Energy/ conversion shell 554.4/K /(L+M+..) 619.1/K /(L+M+..) 698.4/K /(L+M+..) 176.5/K /(L + M + 827.8/K 1044.0/K 1317.5/K 1474.9/K
6.59 (37) 0.91 (21) ll.O2(51) 2.96 (35) 9.9(12) 0.99 (42) 8.23 (35) 0.72(13) 2.96 (32) 4.0 (4) 2.53 (19) I .97 (24)
.)
*Total conversion
coefficients
698-776
619.698
55&(619w98 92-(1779t776 22l+l650)-776 273+1044)-776 554-(1317t776 60&( lO44)-776 619<698)-776 828<1044t776
1008&(1044)-776 1044776
1317-776
1650-776
1779-776 1871-776 554273 5546619 554-1317
2214606tl044 273-1044
60&1044
828-1044
1008-1044
Multipolarity
Riisel e, a/. (1978)
El
El: 6.78; M2: 46.15
6.9 (7)
E2: 15.37; Ml:
l5(2)
11.75
E2+(MI) EZ+MI
E2: 10.95; Ml: 8.97
9.0(13)
E2: 8.23
8.5 (9)
E2
-
1 2.9 (4) 3.8 (3) 2.03 (3) 2.0 (3)
measured
Table 3. Directional Cascade (keV)
coefficients (x lOe4)
Waddell* and Jensen (1956)
Present
313
of *‘Br decay
by Waddell
correlation
,422 -0.321 (33) -0.313(16) -0.297 (35) 0.094 (61) 0.088 (6) 0.069 (21) -0.020(17) - 0.54 (49) 0.14(18) 0.022 (41) 0.003 (14) 0.140(13) 0.000 I ( 149) -0.016(8) 0.200(17) 0.171 (17) 0.190(22) 0.03 (23) 0.055 (31) 0.131(31) 0.117(20) -0.047(13) -0.030(11) -0.025(19) 0.056 (63) -0.03 (5) 0.29 (7) 0.043 (15) 0.29 (46) 0. I I (45) 0.202 (80) -0.074(18) -0.064 (44) -0.046 (24) 0.09 (3) -0.048 (25) -0.026(31) -0.031 (17) 0.32 (31) 0.18(8) -0.45 (21) -0.32 (4) 0.33 (IO) 0.28 (33) 0.15(8) 0.02 (4) 0.20 (23) 0.179(15) 0.199(19) 0.04 (14) -0.03 (4) -0.13 (4)
El: 2.79; M2: E2: 3.99; M3: E2: 2.40; Ml: E2: 1.90
El E2 EZ+MI E2
15.60 17.80 2.35~ -
(1956).
coefficients A4
0.254(15) 0.171 (21) 0.214 (54) 0.049 (84) 0.028 (9) 0.10 (5) -0.009 (23) 0.44 (55) 0.02 (26) -0.74 (67) 0.010(19) -0.045(18) 0.004 (21) 0.037 (IO) 0.015 (24) 0.010 (27) 0.00 (4) 0.04 (31) 0.048 (43) 0.084 (31) 0.000 (3) -0.026(18) -0.033(15) - 0. IO4 (29) -0.161 (87) -0.02 (7) -0.01 (I I) -0.05 (3) -0.01 (67) 0.01 (7) -0.268 (15) -0.034 (21) -0.023 (60) -0.01 (4) 0.03 (5) 0.01 I (34) -0.01 (4) 0.028 (29) 0.20 (46) 0.13(12) 0. I7 (25) 0.13 (6) -0.24(16) 0.13 (44) O.OO(l2) 0.05 (62) 0.023 (32) 0.022 (22) 0.001 (29) -0.11 (19) -0.02 (6) 0.02 (6)
for various
transitions
in “Kr
Reference Present Sooth (1980) cooper (I 977) Present Gardulski and Wiedenbxk Gupta and Bajaj (1968) Present Present Present Present Present Present Present Gardulski and Wiedenbeck Present Sooth (1980) Cooper (I 977) Present Present Sooth ( 1980) Cooper (1977) Present Sooth (1980) Cooper (I 977) Present Sooth (1980) Coooer (1977) Gupia and Bajaj (1968) Present Present Present Present Present Sooth (1980) Cooper (1977) Present Sooth (I 980) Etherton and Kelly (1966) Present Sooth (I 980) Present Sooth (1980) Cooper (1977) Present Sooth (1980) Cooper (1977) Present Sooth (1980) cooper (I 977) Present Sooth (1980) cooper (1977)
(1973)
(1973)
J. GOSWAMY et al.
314 Table 4. The multipole Energy 221 213 554 606 619 698 828 1008 1044 1317 1650 1871
Mixing
ratio
6,(221) = - l.ot-;$ &(221) = 0.04:;:;
Cascade
admixtures
for various
Spin sequence 4%(4+__2+
221+1650t776 273-1044 273&( IO44t_776 554(619fi1474 554-(6193-698 60&((1044fi776 606-1044 6 I 9-698 55&6 I9 698-716 828-1044 828~( I044t776 1008&1044 I OOS-( 1044t776 1044776 1317-776 554-1317 l65&776 1871-776
Multipole
Mixing ratio
to+
El + (50;:;) %M2 El + (O-t!“) %M2
in “‘Kr Multipole admixture El + (0+!4)%M2
3+ 4+-2f 3+___(4+L2+)AJ’ 4 -(3+-2+ @+ 4 -(3+-2+)-2+ 4+-(4+-2’H’ 4+4+-Z+ 3+-2+-2+ 4 -3+-2+ 2+-2+-0+ 4 4+-2’ 4-(4+-Z+)AI+ 5 4+-Z+ 5S-(4’-2+)Al+ 4+-2+tl+ 3+-2+-0+ 4--3’L2+ 4+-2+Il+ 4 -2+-0+
admixture
transitions
Ml + (< 14%) E2 El + (0,04i;;)%M2 Ml + (63.5 f 3.O)%E2 Ml +(2.5X +“)%E2 08 2.ll+Q79 -061
MI + (81.7+::,)%E2
1.54;;:;
Ml +(70,3+;:;)%EZ
-0.02
k 0.06
El + (O.O4’?“)%M2
0.03,:;:
El + (0,1+;4)%M2
-0.075’;;:
E2 + (0.62’;::)%M3
I 4.95,;:
Ml + (96.1 i 0.7)%E2
> -0.07 + 0.05 6, = 0.0 f 0.8 6, = l.6,06
E2 + (O.SC;:)%M3 M2 + 0.0 k 0.4)%E3 M2 + (71.9,? 9)%E3
The multipole admixtures corresponding to S, (221) yields a large M2 component which implies that 221 keV transition should have large conversion coefficient. However, no conversion peak corresponding to 221keV transition is seen in the present
106
600
800
1000
? ‘f
L 1200
1000
1400
1600
Energy Fig. 2. A typical
gamma-ray
spectrum
following
1800
2000
(keV)
the decay
of 82Br taken using 96cm’
HPGe
detector.
315
Study of r2Br decay
600
400
200
Energy Fig. 3. The coincidence
y-ray spectrum
following
Thus we conclude that 221 keV transition should have small M2 component, i.e. 6,(221) can be accepted. 3.3.3. Multipolarity of the 273keV transition. The mixing ratio of the 273 keV transition has been deduced using the directional correlation results of 273-(1044)-776 and 273-1044 keV cascades. The analysis for these cascades yields 0.2 < 6 (273) < 0.4 as the overlapping range of the mixing ratio of 273 keV transition i.e. a multipole admixture of Ml + (< 14%) E2.
measurements.
References Browne E. (1986) Nucl. Instrum. Methods A 249, 361. Browne E. and Firestone R. B. (1986) Tables of Radioactiue Isotopes. Wiley, New York. Chand B., Goswamy J., Mehta D., Singh N. and Trehan P. N. (1989) Nucl. Instrum. Methodr A 284, 393. Cooper E. L. (1977) Diss. Abst. Int. 38B, 2173. Etherton E. C. and Kelly W. H. (1966) Nucl. Phys. 84, 129. Gardulski P. L. and Wiedenbeck M. L. (1973) Phys. Rev. C 7. 2080.
800
1000
(keV)
the 8’Br decay taken with gate on 776 keV transition.
Garg M. L., Singh J., Verma H. R., Singh N., Mangal P. C. and Trehan P. N. (1984) J. Phys. B; At. Mol. Phys. 17, 577. Gehrke R. J., Helmer R. G. and Greenwood R. C. (1977) Nucl. Instrum. Methods A 147, 405. Goswamy J., Chand B., Mehta D., Singh N. and Trehan P. N. (1991) Appl. Radial. Isot. 42, 1025. Gupta S. L. and Bajaj M. M. (1968) Aust. J. Phys. 21, 649. Kemnitz P., Ojeda P., Doring J., Funke L., Kostov L. K., Rotter H., Will E. and Winter G. (1984) Nucl. Phys. A 425, 493. Krane K. S. (1972) Nucl. Instrum. Methods 98, 205. Krane K. S. and Steffen R. M. (1971) Phys. Rev. C4, 1419. Mehta D., Garg M. L., Singh J., Singh N., Cheema T. S. and Trehan P. N. (1986) Nucl. Instrum. Methods A 245, 447. Meyer R. A., Wild J. F., Eskola K., Leino M. E., Vaisala S., Forresten K., Kaup U. and Gelberg A. (1983) Phys. Rev. C 27, 22 17. Muller H. W. (1987) Nuclear Data Sheets 50. Rose1 F., Fries H. M., Alder K. and Pauli H. C. (1978) AI. Data Nucl. Data Tables 21, 91. Sharma A. K., Verma H. R., Singh N. and Trehan P. N. (1979) J. Phys. Sot. Japan 47, I. Sooth S S., Verma H. R., Kaur R., Sharma A. K., Singh N. and Trehan P. N. (1980) J. Phys. Sot. Japan 49, 1222. Waddell R. C. and Jensen E. N. (1956) Phys. Rev. 102, 816.