Indian Journal of Pure and Applied Physics

 

___________________________________________________________________________________

VOLUME 40                         NUMBER 1                JANUARY  2002

__________________________________________________________________________________________

CONTENTS

 

Nuclear Physics

40K, 137Cs and 232Th activities in Brazilian milk samples measured by gamma ray spectrometry

F L Melquiades* & C R Appoloni

 

5

Atomic and Molecular  Physics

Spectroscopic study of pentacene assembled in Langmuir-Blodgett film mixed with stearic acid

      Somobrata Acharya, Tapan Kr Parichha & G B Talapatra*

 

12

Vibational assignments of 2,6-di(p-methoxyphenyl)-3-methyl piperidone, 2,6-di(p-methyl phenyl)-3-

      methyl piperidone, 2,6-di(o-hydroxy phenyl)-3-methyl piperidone and 1-methyl-2,6 (p-methoxy

      phenyl) piperidone

      T Chithambarathanu, V Umayorubagan & V Krishnakumar*

72

Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics and Fluid Dynamics

Ultrasonic studies  on charge transfer complexes of iodine with certain aromatic compounds in n-hexane

      solution

V Kannappan* & S Kothai

 

17

Physics of Gases, Plasmas and Electric Discharges

Unified empirical model for collective oscillations of asymmetric positive space charge sheath

      Ram Prakash, A Sarma, C B Dwivedi*, U Deka, B Singha, S Bujarbarua & J C Upadhyaya

 

24

Condensed Matter: Structure, Mechanical and Thermal Properties

Evaluation of partial and total structure factors, Bhatia-Thornton correlation functions, compressibility 

      and diffusion coefficient of Pb-Pd alloy at different compositions and temperatures

      Sumita Bandyopadhyay, R Venkatesh & R V Gopala Rao*

 

32

Applicability of Van’t Hoff equation in calculation of impurities in liquid crystalline materials

      Ravindra Dhar*, R S Pandey & S L Srivastava

42

Studies of Mn0.5Cr0.5Fe2O4 ferrite by neutron diffraction at different temperatures in the range 768 K ³ T ³ 13K

A K M Zakaria*, M A Asgar, F U Ahmed, A K Azad, S M Unus, S K Paranjpe & A Das

46

Thermally stimulated conductivity and evaluation of some parameters of CaS:Pr phosphors

      R N Dubey O N Awasthi, V Singh* & M Tiwari

54

X-ray analysis of 2-methyl-4-phenyl-3,4-dihydro-quinazolinium chloride

      Rajnikant*, V K Gupta, O P Suri & M Lal

59

Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties

Micro-crystallographic and spectral response studies of CdSe1-xTex alloyed thin films

PD More, G Shahane, L P Deshmukh*, P N Bhosale, A A Belhekar & M K Dongare

 

62

Dielectric relaxation of some rigid polar molecules and their binary mixture in benzene solution

      A D Vyas* & V A Rana

69

____________

*The corresponding author has been indicated by (*) mark in case of papers with more than one author

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 5-11

40K, 137Cs and 232Th activities in Brazilian milk samples

measured by gamma ray spectrometry

F L Melquiades & C R Appoloni

 

This work deals with the measurement of radioactivity in powdered milk, with high-resolution gamma-ray spectrometry, using a HPGe detector. Preliminary measurements were accomplished to define the kind of the system shield, the geometry of the sample recipient, the size of the sampling and the self-absorption correction. It was possible to measure the radionuclides 40K, 137Cs and 232Th. Tukey’s average comparison test was used to check the repeatability of the measurements.

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 12-16

Spectroscopic study of pentacene assembled in

Langmuir-Blodgett film mixed with stearic acid

Somobrata Acharya, Tapan Kr Parichha & G B Talapatra

Langmuir Blodgett (LB) films of non-amphiphilic pentacene mixed with stearic acid have been prepared and its photo-physical properties are reported here. Surface pressure versus area-per-molecule isotherms (p-A) at different compositions are measured. Spectroscopic properties (UV-Visible absorption, emission and Scanning Electron Micrograph) of pentacene in LB film have been reported. The blue-shifted absorption and red shifted emission suggest the formation of H-type of aggregates.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 72-74

NOTE

Vibrational assignments of 2,6-di(p-methoxy phenyl)-3-methyl piperidone, 2,6-di(p-methyl phenyl)-3-methyl piperidone,

2,6-di(o-hydroxy phenyl)-3-methyl piperidone and

1-methyl-2,6(p-methoxy phenyl) piperidone

T Chithambarathanu, V Umayorubagan & V Krishnakumar

The FTIR spectra of the title compounds were recorded in the region 400–4000 cm-1 and the detailed vibrational assignments have been proposed based on the functional group frequency approach.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 17-23

Ultrasonic studies on charge transfer complexes of iodine with certain aromatic compounds in n-hexane solution

V Kannappan & S Kothai

Ultrasonic velocities, densities and viscosities have been measured in n-hexane solutions containing iodine (acceptor) and diphenyl (DP), diphenyl amine (DPA) or diphenyl ether (DPE) (donor) at various equimolar concentrations at 303 K. Acoustical parameters such as adiabatic compressibility (b), linear free length (Lf), relaxation time (t), free volume (Vf), molecular interaction parameter (c), acoustical impedance (Z), absorption coefficient (a/f2), Rao’s constant (R), cohesive energy (CE), internal pressure (pi) and Van der Waal’s constant (a) are evaluated. These parameters indicate the formation of charge-transfer complexes between iodine and the aromatic compounds. The stability constant (K), the free energy of activation (DG*), the standard free energy of formation (DG°) values are reported for the donor-acceptor complexes. These investigations reveal that the stability of the charge transfer complex depends on the structure of the aromatic compound.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 24-31

Unified empirical model for collective oscillations of asymmetric positive space charge sheath

Ram Prakash, A Sarma, C B Dwivedi, U Deka, B Singha, S Bujarbarua & J C Upadhyaya

Hypothesis for a comprehensible unification of the previous physical models for the collective oscillation dynamics and its driving mechanism for an asymmetric positive space charge sheath has been proposed. Under diode-like circuit approximations of the sheath, the asymmetry driven beam-plasma interaction model provides a source mechanism to produce an internal rf resonator to transform the diode-like sheath into a system of an active oscillator. The LCR components and the resonant frequency of the equivalent diode-like circuit of the sheath are estimated for real experimental plasma parameters. The numerical values of the resonant eigen frequency of the equivalent circuit for different grid biasing voltages are validated against the real experimental values within some error limit. The resonant eigen frequency agrees well with that of the internal rf source of ion beam-plasma model origin.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 32-41

Evaluation of partial and total structure factors, Bhatia-Thornton correlation functions, compressibility and diffusion coefficient of Pb-Pd alloy at different compositions and temperatures

Sumita Bandyopadhyay, R Venkatesh & R V Gopala Rao

The partial and total structure factors of Pd-Pb alloy have been computed using Lebowitz solution of hard spheres with a square well attractive tail. The calculated values of the total structure factors and also that of the reduced radial distribution function are in excellent agreement with experiment. It is found that the partial structure factors show peculiarities due to the formation of a compound Pb2Pd as reported by Christian et al.[J Noncryst Solids, 156(1993)38]. Bhatia-Thornton correlation functions are also calculated, namely, SNN(k), which show strong correlation in k-space while SCC(k) and SNC(k) do not show such correlation. The partial and total radial distribution functions (RDF) are also calculated from which first coordination numbers are obtained. The RDFs show for all compositions the first peaks at 3.35 Å. Exactly the same value has been obtained by Christian et al. This value is in no way nearer to the first nearest neighbour distances in pure Pb or Pd. Thus, the small value of 3.35 Å, which corresponds to the first peak position, has been attributed to the formation of a compound Pb2Pd, which in crystalline form shows exactly the same distance between unlike neighbouring atoms. The values of compressibility have also been calculated, which show a bigger value of 41.6 ´ 10-12 cm2/dyne at 60 atomic percent of Pb. This also indicates the formation of a compound. The diffusion coefficients have been calculated through Helfand’s prescription. No observable sudden changes are seen in the case of diffusion coefficient. As suggested by Christian et al.,  the  authors also calculated the total sum of the partial structure factor Ss(k), namely that of SPb-Pb(k) and SPb-Pd(k) and a strong right hand shoulder at 60 atomic percent of Pb has been found and this perhaps is a characteristic of compound formation and the shoulder is obtained at 2.8 Å while in Pb2Pd an exact distance is found in its crystalline form between unlike atoms. It may be pointed out Pd-Pb distance in amorphous Pb2Pd compound is exactly 2.83 Å while the present shoulder is obtained at 2.8 Å. Hence it is concluded that Lebowitz solution with a square well attractive tail reproduced several characteristics shown in the experiment and also clearly indicate the formation of a compound.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 42-45

Applicability of Van't Hoff equation in calculation of impurities in liquid crystalline materials

Ravindra Dhar & R S Pandey

 

Van't Hoff equation has been applied to the binary mixtures of cholesteryl pelargonate (ChP) with nonyloxybenzoic acid (NOBA) and of cholesteryl myristate (ChM) with dodecyloxybenzoic acid (DDOBA) for different mole concentrations of pure components. The calculated and added impurities have been compared. The applicability of the Van't Hoff equation depends upon the degree of miscibility of impurity with the pure component. This equation has also been applied to calculate the radiation-induced impurities in ChP and ChM.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 46-53

Studies of Mn0.5Cr0.5Fe2O4 ferrite by neutron diffraction at different temperatures in the range 768K ³ T ³ 13K

A K M Zakaria, M A Asgar, F U Ahmed, A K Azad, S M Yunus, S K Paranjpe & A Das

 

Neutron diffraction studies of a polycrystalline manganese-chromium-ferrite with composition Mn0.5Cr0.5Fe2O4 have been performed at a number of temperatures in the range 768K ³ T ³ 13K. The cation distributions, oxygen position parameter (u) and lattice constant (ao) have been determined from the analysis of the higher angle neutron diffraction data. The temperature response of the lattice constant has also been investigated and a slight anomalous expansion has been found around the magnetic transition temperature. Sublattice as well as net ferrimagnetic moments of the specimen have been found out from the analysis of the neutron diffraction data at different temperatures. A randomly canted ordering of spins has been observed in the B sublattice, while the A sublattice moments appear to exhibit collinear Néel type ordering at all temperatures.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 54-58

Thermally stimulated conductivity and evaluation of

some parameters of CaS:Pr phosphors

R. N. Dubey, O N Awasthi, V Singh & M Tiwari

Thermally stimulated conductivity (TSC) of CaS:Pr microcrystalline phosphors studied in the temperature range of 300-330 K. One TSC was observed in the range 311-318 K. Trap depths relaxation times, attempts to escape frequency and initially filled traps are evaluated using Bucci-Fischi [Bucci c, fischi r and guide G, Phys rev, 148(1956)816] and Cowell-Woods methods [cowell T A T and woods j, brit j appl phys, 18(1967)1045]. An attempt is made to explain initially filled trap density using ozawa model [ozawa L-j, Elec Chem Soc, 120, 140 (1981)] of luminescent center.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 59-61

X-ray analysis of 2-methyl-4-phenyl-3,

4-dihydro-quinazolinium chloride

Rajnikant, V K Gupta, O P Suri & M Lal

The crystal structure of the title compound (C15H14N2.HCl) has been determined by X-ray crystallographic techniques. The compound crystallizes in the monoclinic space group P21/c with unit cell parameters: a = 9.682(1), b = 10.532(1), c = 13.139(1)Å, b = 90.82(2)°, Z = 4. The structure has been solved by direct methods and refined to R = 0.057 for 1204 observed reflections and wR(F2) = 0.154. The dihedral angle between the planes of phenyl ring C and the quinazoline moiety is 79.3(1)°. The Cl- anion is located 3.109(4) Å from the N3 atom.

 

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 62-68

Micro-crystallographic and spectral response studies 
of CdSe1-xTex alloyed thin films

P D More, G S Shahane, L P Deshmukh, P N Bhosale, A A Belhekar & M K Dongare

Chemical deposition of CdSe1-xTex solid solution thin films from salt solutions of cadmium, selenium and tellurium derivatives of sodium sulphite at 70 °C temperature has been presented. The quantitative analyses (EDS and spectro-photometric) showed that the film deposits are Cd rich and compared to the Te, Se content is larger. The variation of xfilm with xbath is non-linear. The XRD studies show composites to be crystalline in nature and both CdSe and CdTe existed in both hexgonal wurtzite and cubic zinc blende structures whereas CdSe1-xTex alloys were hexgonal dominating. Both wurtzite (0 £ x £ 0.08) and zinc blende (0 £ x £ 0.15) phases undergo solid solution and variation in lattice parameters followed Vegard’s law. The surface topography showed diffused grain polycrystalline texture with an overgrowth developed in some cases. The spectral studies of these films gave a continuous change in the optical gap (Eg = 1.76 to 1.45 eV ) with a band to band direct type of transitions.

Indian Journal of Pure & Applied Physics

Vol. 40, January  2002, pp. 69-71

Dielectric relaxation of some rigid polar molecules

and their binary mixture in benzene solution

A D Vyas & V A Rana

 

Dielectric absorption of rigid polar molecule pyridine and its mixture with benzonitrile in benzene solution has been studied at microwave frequency 9.1 GHz and at different temperatures (20-47ºC). The relaxation time (t0) and distribution parameter (a) were evaluated using Higasi’s single frequency method. The thermodynamical parameters were calculated using Eyring’s rate equations. From the dielectric relaxation and activation energies it is found that the molecules retain their characteristic behaviour in the mixture.