Murty, M Sriramachandra

Parthasaradhi, K

Rao, J Rama

English

IACS Institutional Repository

516 F. P . H a n n a , A . A . Y e h ia  a n d  A , A b o u -B a k rThe rubber vulcanizato obtained by formula 4 has good physico-mechanical projx'rties, t.q. samples vulcanized at 160°C for 10 minutes give tensile strength 106 kg/cm®, elongation 730%, modulus 300% elongation 9kg/cm- and pei'manent set 5%.The effect of cure time on e' and e" was also studied. Three cure times were used namely 10, 15 and 25 minutes. As shown in figure 2, e' does not change w ith the cure time, Avhile c" is changes slightly. Since the cure time affects nuiiiK the physico-meclianical properties of vulcanizates, it is recommended to use the cine time Avhicli gives optimum physjco-inechanical jnoperties, as its effect on the dielectric projicrties is negligible.This study leads to the conclusion that the ingredients which are nornully added to improve the physical properties of raw’ rubber, specially in the described proportions, do not practically change the dielectric propertiesWe should like to thank Prof Dr. 11. N. Sodra, Cairo University, for his kind interest in this work The facilities offei ed to us by the Transport and Engineer- mg (Jo. in preparing those samples arc Amry much appreciated.R e f e r e n c e s(Jlaik F M. 1902 JitNuLudiKj Matenala for  Demyti and J^tajinnerinif Now Yoik, 92.‘)Hiimui F. F & Cdioinoiri A IM 1970 Z  Plii/s. (hem  (lu thr iiiobb). ^Smylli C. r. lOSf) J)iclectnr Bchnrmn and SUndinr Nl'^  ^ Yoik JSS,Indian J. Phys. 44, 51G-518, (1970)Comparison of experimental and theoretical pair cross- sections near the thersholdBy  J- R ama R a o , M. 8rtramachandra M u rty  A nd  K. ParthasaradhiTfip. Laboratories for Nuckar Ra«carcht Andhra Vnivmsity,Waliair, India{ R e c e i v e d  4 D e c e m b e r  1970)I t  is  w e ll k n o w n  t h a t  t h e  e x p e r im e n t a l  p a i r  c r o s s - s e o t i o n s  o f  g a m m a  ra y s  v ery  n e a r  t h e  t h r e s h o ld  a r e  n o t  in  a g r e e m e n t  w it h  t h e  p r e d i c t e d  v a l u e s  fr o m  BetliC ' H e i t le r  t h e o r y  (1934) o i  Avilb t h e  e x t r a p o l a t e d  v a l u e s  f r o m  J a e g e r  &  Jluliik ' (1936) c a lc u la t io n s .  R e c e n t l y ,  h o A v e v o r , m o r e  a c c u r a t e  t h e o r e t i c a l  p a ir  wxiss- s e c t io n s  a re  l e p o r t e d  b y  O v e r b o  e t  al (1968) c l a i m in g  a  b e t t e r  a g r e e m e n t  Avith t h e  e x p e i im c i i t a l  A 'a lu os  n e a r  t h e  t h r e s h o ld  I n  t h e  p r e s e n t  c o m m u n ic a t io n  c o i n p a r i s o i i  is m a d e  o f  e x p e r im e n t a l  c r o s s - s e o t io n s  a t  1.119 MoV re p o r te d  ljvRama Rao et al (1963) with Overbo’s (1968) theory. In additioiij the pair cross-BectioJiB in germanium recently reported by Yamazaki et al (1965) are compared with Overbo s theory with a view to tost its validity near the threshold.Rama Rao et al (1963) measured the pair cross-sections absolutely at the energy 1.119 MeV in eight elements from copper to lead, using a Goiiicidenoo method. Yamazaki et al (1965) determined the pair cross-sections in germanium in the energy range 1.007 to 2.754 MeV by using a Ge(Li) crystal both as the target a.s well as detector. Those latter cross-sections were measured relatively and then normalized to the Jaeger & Hulmes’ (1936) value at 2.754 MeV which is 4% higher than the Bethe-Heitler (1934) value. It must be noted that this method implies tlio agreement between the experimental value and the theoretical value of Jaeger & Hulme at 2.754 MeV in gei maniuin. The ('xperimontal values of Yamazaki et al and those of Rama Rao et al along with the tlieoretical values of Overbo et al are given in tables 1 and 2.it can be seen from the table 1 that the agreement between theory and experi- ineni- is satisfactory fi-om 2.754 MeV down to 1.5 MeV. Below this energy there is deviation. The deviation cannot, however, be ascribed to an error arising from normalization pi-ocedure since the discrepanc}?’ increases with atomic number. It may also be noted that the theoretical values are always smaller than the experimental values wdiorever there is a discrepancy. The inclusion of screening uoTi'cction, neglected in the theory of Overbo et al, would however, still decrease the theoretical cross-section. The trend of deviation, increasing with atomic number toward the pair thresliold, suggests that adequate refinements are neces­sary in the theory of Overbo ct al in these directions.T a b l e  1 Experimental pair cross-sections in germanium (milliharns per atom)Comparison of experimental and theoretical p a ir  etc. 517Energy (MeV) ExperimentalValueTheoreticalValue(Overbo et al 1968)1.007 0.342±0.029 0.2661.115 1.38.h0.10 1.141.173 4 06±0.17 3.851.276 1 5 .6 ± 0 .5 13.61.332 2 4 .8 ± 0 .8 21.91.368 3 0 .7 ± 1 .0 26.61.407 3 7 .7 i2 , l 33.11.477 5 6 .7 ± 2 .5 47.31.506 7 fl.3 ±4 .2 75.01.837 145.0* is.185 263 ±10 246.02.318 284±8 282.02.754 451 ± 1 4 447.0Table 2. Pair crosa-soctions of 1.119 MeV gamma rays (millibarns per atom)518 K a o , M u rty  a n d  P a rth a sa ra d h iElomoni Expoi'imontalValueTheoreticalValue(Overbo et al 1968)C li 1 42 t o  09 1 02Zr 2 95-to . 18 2.16Rb .3 90 t o  23 2 79Sn 5.00 d-0.3 .3.43T t i 11 .40-1-0,6 O-.TPt 13.20:t0 7 0.92A n 13 40-1-0 7 7.0PI) 14.80dr0.7 7.24A c k n o w l e d g e m e n t sOne of the auihora (M.S.R.) is grateful to the C.S.I.R. Government of Tntjia, for the award of a Government Research Fellowship.R e f e r e n c e sBetho H. A. & Hoiilev W. 1934 Proo. R oy. Soc. A146, 83- Jaeger J. C. &, Hulmo, H. B. 1936 Proc. R oy. Soc. A153f 443.Oborbo T., Mork K, J. & OlHen H. A. 1968 Phya. Rev, 175, 1978.Rama Rao J. Lakshminarayana V. & Swami Jnanananda 1963 Proc. Phya. Soc. A81, 949. Yamazaki T. & Hollander J. M, 1965 Phya. Rev. 140B, 630.Indian J. Phya. 44, 518-519 (1970).Some comments on exact partition function of Ising model in Magnetism in one, two sind three dimensions in non-zero fieldB y  V . P . D e s a iSaJm Institute of Nudeur Physics, CalctUta-9 {Received 6 September 1971)In a recent paper on Ising model, Das (1970) comes to the surprising conclusion that Onsager’s (1944) and Yang’s (1952) results o f two dimensional Ising model are not reliable ! A closer look at the paper reveals that Das’s approach to the problem is basioally erroneous• The basic fallacy m

Comparison of Experimental and Theoretical Pair Cross-Sections Near the Threshold

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Comparison of Experimental and Theoretical Pair Cross-Sections Near the Threshold

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