Shante, V K S

Sud, S P

Trehan, P N

English

IACS Institutional Repository

India. J. Phy •. 43, 40-44 (1969) A note on the spin of the 1970 keV level in Ba1l4• S. P. SUD, V. K. S. SHANT!! AND P. N. TREHAN PhY8ios Department, Pan jab University, Ohandigarh·U. India. (Received 16 December 1968) The directional correlation of the 802·1168 keY gamma rav cascade in ~e decay of CS1~" to Ba,·l" has been measured by sum-peak coincidence spectra eter to check the recently proposed (Ramo Mohan d al 1967) spin assignment 3 to he 1970 ke V level of Bau4, The present investigations fovour a spin 4 to this lev I. The 602 kc V gamma transition has been found to be pure El. , 1. INTRODUCTION In a reccnt study of the directional correlation of some cascades in Ba'" (Rama Mohan et aI1967), a spin 3 has been proposed for the 1970 keY level of Bam (figure la) on the basis of results for the 802·1168 keY cascade. These authors observed a negative asymmetry, whereas previous investigators (Everett & Glaubman 1955, Segaert et al1963) had observed a positive asymmetry for this cascade. A spin assignment 3 to the 1970 ke V level is in contradIction wIth the hereto·fore accepted spin 4 for this level. Hence it was considered worthwhile to reinvestigate the directional correlation of the 802·1168 keY cascade so as to verify the spin assignment to the 1970 keY level of Bam. The measurement of the directional correlation of the 802·1168 keY cascade is complicated by the presence of a strong 563.605 ke V cascade de.exciting the 1168 ke V level in competition with the weak 1168 ke V cross·over transition. Therefore, it is desirable to use large source·to· crystal distance for the detector selecting the 1168 keY transition so as to reduce the detection of the cascade sum (563+605 keY) compared to the cross·over gamma ray. An increase in the source-ta·crystal distance, however, also reduces the detectIOn efficiency for 1168 keY gamma ray, making it very time con· suming to measure the directional correlation of 802·1168 keY cascade with conventioal slow.fast coincidence spectrometer. The sum.peak coincidence spectrometer (Kantele & Fink 1962) has more than twice the coincidence detection efficiency compared to a conventional slow.fast coincidence • Work supported by National Bureau of Standard., Washington D. C., IJ. S. A. and Dep"tment of Atomic Energy. Government of India, Indio. A 1IOte on the Bpin oJ the 1970 keV level etc. 41 '0.1 (bl M ..... --------IfL...-.... ," II., ... II'. ," J ... .. , " 0' k" " " •• .. Flaure 1. (0) Partial Level Scheme of B.lIl popul.ted in the decay of C. "'. (h) Plot oi angul.r correlation function W (0) V. 8 for the 802·1168 KeV cascade of Ba11&, spectrometer and has proved useful in the measurement of angular correl.> tion of weal<: gamma ray cascades (Sud ee a! 1%8). Therefore a sum peak peak coincidence spectrometer has been utilized in the present study. 2. MEASUREMENTS AND RESULTS . The experimental arrangement was the same as described elsewhere (Sud eI' a! 1'968) except the cletectors which were a matched pair of Harshaw Integral lme aeemblies with 3' 4Ia and 3" lIhick Na I (T1) Cl"'/stals. These cferectors Iiave tresolution of 7,6 % for 662 ke V gamma r.ys. . A '42 S, p, Sud, V. K. S. Skante and P. N. Trehan moderately strong liquid source of radioisotope Csm was prepared in a cylin. derical perspex holder with a vertical cavity of 1.5 mm dia X 4 mm depth. This source was mounted vertically at the inter.section of the axes of the two detectors at a distance of 14 em from each crystal. The face of either crystal was covered with 7 mm of lead. This geometry reduced the detec· tion of cascade sum (563.605 ke V) compared to the 1168 ke V crossover gamma ray to less than 2 %. Compton graded lead cylinders and lea~ cones were used to eliminate crystal.to·crystal scattering. The source C~ld be centred to within less than 0.5% variation In the singles rate of m vable detector, The integral biases of the two single channel analysers w re set at 700 keY to completdy blas out the 605 keY gamma ray, The sum· peak cOlUCldence spectrum was tecorded on a 256·channel pulse h ight analyser at seven angles from 90" to ISO" at intervals of 15' each, This spectrum after substraction of random coincidences shows a peak at 1970 keY correspondmg to the sum of 802 and 1168 keY cascade. The area under thiS peak directly gave the coincidences between the 8020 and 1168 keV gamma rays. After a least squares fit of the data (Rose 1953) the correia. tion coefficients were corrected for finite angular resolution cJ the detectors (Yates 1965), The corrected correlation coefficients (an average of two independent measurements) are given in table 1 along with the results of previous investigators, The present results are in good agreement with the results of Everett and Glaubman (1955) and Segaert e! a! (1963) but do not agree with the results of Rama Mohan et a! (1967). 3. DISCUSSION The spin and parity of ground state of even·even nucleus Bal31 is 0+. The experimental K-conversion coefficient for the 1168 keY gamma ray (Brown & Ewan 1965) assigns a character 2+ to the 1168 keV level of Bam. The 86 keY beta group from the 4+ ground state of Csl3l feeding the 1970 keY level of Bam is an allowed transition (Nuclear data sheets), This suggests a character Y, 4+ or 5+ to the 1970 keY level, The lifetime consideration for this level, however, rules out the 5+ assignment, leaving only two possibilities 3+ or 4+. A spin assignment 3 requires ~,:;; 0 for all values of mixing ratio ( 0 ) for the a02 ke V transition. The definite positive value of A., from the present measurements favours a 4+ assign· ment for the 1970 keV level. Therefore the spin sequence for the 802·1168 keV cascade is 4 (2,3) 2(2) 0, Figure 2 shows a graphical analysis of the present results in terms of the above spin sequence for determining the mixing ratio (0) for the 802 keV transition. This analysis gives 6':;;-0.01 i.e, 802 ke V transition is pure EZ, This conclusion is in agreement with A note on tke apin 0/ the 1910 ke V level etc. 43 008 0'04 ~o I 0'04 AZ Figure 1. Parametric plot of A, V. A. for the .pin ,equonce 401·0 (or detenninillll .he mlx!lIIIratio in tho 801 keV umBitlon. Th. ,hided area correspond. to the I!lIJIOrlmenral •• 1., of A. and A.. the results based on internal conversion coellicient for the 802 Ice V gamma ray (Brown &. Ewan 1965) which shows this transition to be pure E2. TABLE 1. A SUMMAB.Y Of THE RBSULTS Of DIRECTIONAL CORRELATION MEASUREMEPTS ON THE 802-1168 KEV CASCADE IN Balli. Refeton .. AI A. Everett Ill. Glaubroan. 1955 0.095 0.006 Sep~ 11011963 O.lHO.Ol .o.Ol9±0.001 Rsma Mohon eI 011967 .0.1235±0.OOlS 0.OOO9±0.OOl Preaen.t DlOa8urements O.108l±o,o025 0.0091±0.OO40 -. 44 S. P. Sud, V. K. S. S4u,nJe and P. N. Trektue REFER'ENCES Brown, R.A. 51. Ewan, G.T. 1965 Nuol. Phy •. 68, lZS·36. Everett, A.E. 51. Gisubm.n. M.J. 1955 Pkg •. Re •. 100. 955A. Kantele, j. 51. Fink. R.W. 1962 Nvcl. IMr. and Matk. 15, 69·73. Ram. Moh.n, R. V .• Reddy. K.V .• R.ju. B.B.V .• & Jnnananda, S. 1967 Indial' J. Pky •. 41, 30·S. Rose, M.E. 1953 Pky., Re •. 91, 610·15. \ Segaert, O. j., Oemuynck, J. L., Ooriken,·Vanp"et, L. V., Oorlkon., M. 196~ N .. l. Pky •. 43, 76·91. \ Sud, S. P., Mang.l, P. C., Sur!, K. K" 51. Tr.han, P. N. 1968 Ind'an. J. Ph~ •. 4Z 167·176. Way, K. 1961 Noel .ar Data Shu", Nat. Acad. Sci., Nat. Research Council Waohington O. C., NRB·61.2·97. Yates, M. J. L. 1965 Alpha, B,ta and Gama Ray Spear.cony Ed. by K, Siegbohn North Holland Publishing Co. Amsterdam North Holland p. 1691·1703. 

A Note on the Spin of the 1970 KeV Level in Ba134

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A Note on the Spin of the 1970 KeV Level in Ba134

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