[en] This thesis presents experimental studies of ion-molecule reactions at low collision energies using two drift tube mass spectrometer apparatus. The reactions studied are (i) proton transfer from HeH⁺ to ArH⁺, (ii) charge and ion transfer reactions of O₂²⁺ with NO, CO₂, Ne and O₂⁺(⁴π_u) with CO₂, (iii) oxidation reactions of Zr⁺ and ZrO⁺ with NO, CO₂ and O₂, (iv) vibrational quenching reactions of H₃⁺ with He, (v) termolecular clustering reactions of H₂CN⁺ and H₂CN⁺(HCN) (with He as the third body), (vi) three body association reactions of H⁺ and D⁺ with He (with He as the third body) and (vii) termolecular association reaction of NO⁺ with NO (with Ne as third body). All the reactions were studied at thermal energies (at room temperature), reactions of O₂²⁺ with NO and CO₂, Zr⁺ with NO/CO₂/O₂ were also studied at center-of-mass energies higher than thermal and the association reactions of H₂CN⁺/H₂CN⁺(HCN) with HCN and H⁺/D⁺ with He were studied at low temperatures. In addition, the thesis presents model calculations for the sweep-out effect which is an instrumental effect. A super Langevin rate constant is introduced which is a higher-order correction to the Langevin model. A theoretical model for the three-body ion-atom association rate constant is presented in the appendix of the thesis

[en] Short communications only

[en] Superheated drops are known to vaporise when exposed to energetic nuclear radiation since the discovery of bubble chamber. The application of superheated drops in neutron research especially in neutron dosimetry is a subject of intense research for quite sometime. As the degree of superheat increases in a given liquid, less and less energetic neutrons are required to cause nucleation. This property of superheated liquid makes it possible to use it as a neutron spectrometer. Neutron detection efficiency of superheated drops made of R12 exposed to Am-Be neutron source has been measured over a wide range of temperature -17-60 deg. C and the results have been utilised to construct the energy spectrum of the neutron source. This paper demonstrates that a suitable neutron spectrometer may be constructed by using a single liquid and varying the temperature of the liquid suitably at a closer grid

[en] Detection of neutrons through use of superheated emulsions has been known for about two decades. The minimum neutron energy (threshold) required to nucleate drops of a given liquid has a dependence on the temperature of the liquid. The basic principle of nucleation has been utilized to find the relationship between the operating temperature and threshold neutron energy for superheated emulsions made of R-114 liquid. The threshold energy thus determined for different temperatures has been compared with accurate experimental results obtained using monoenergetic neutron sources. The agreement is found to be satisfactory and confirms the applicability of the present simple method to other liquids

[en] The γ-ray detection threshold temperatures of superheated drops of refrigerant liquid R-12 is presented here for the three γ-ray energies 59.54 keV (²⁴¹Am, 500 mCi), 662 keV (¹³⁷Cs, 32.5 mCi) and 1250 keV (⁶⁰Co, 0.45 mCi). Nucleation was detected with an active device by counting the number of drops vaporized per minute as a function of the temperature of the detector over a wide range. The results show that the threshold temperature for detection increases with the energy of the incident photons. (author)

[en] The basic principle that has been used in the application of superheated drops in neutron spectrometry is its dependence of threshold energy of nucleation on temperature. In the present work, superheated drops of R114 suspended in a visco-elastic gel were irradiated at different temperatures by neutrons obtained from an ²⁴¹Am-Be source. The temperature of the detector was converted to the energy of the incident neutrons following the method developed by us to unfold the neutron energy spectrum. The threshold energy obtained by us agrees well with other results obtained using monochromatic neutron sources, clearly demonstrating the validity of our principle of spectrometry. (author)

[en] The present work relates to a sensitive neutron dosimeter, a device for monitoring neutron dose in some accelerator and reactor sites. This device is capable of measuring a neutron dose as small as 0.1 μSv using superheated liquid as a sensitive liquid. The nucleation was measured by the volumetric method developed in our laboratory. The dose response of superheated drops of four liquids having boiling points of 8.92, -29.79, -40.75 and -45.6 deg. C, irradiated by a 3 Ci Am-Be neutron source has also been presented in this article

[en] It has been reported that superheated drops made of R-12 at room temperature are sensitive to neutrons yet insensitive to photons. This property makes its use attractive as one of the most useful neutron dosimeters. The photon sensitivity of R-12 at room temperature (25 deg. C) when exposed to 59.54 keV photons obtained from radioactive ²⁴¹Am has been noted for the first time in our laboratory. This discovery is of importance not only from the point of view of basic science but also to the users of R-12 in neutron dosimetry in assessing the neutron dose correctly. This discovery also indicates a new direction of investigation with R-12 detector

[en] Tabulated values of differential elastic scattering cross sections of photons for fourteen elements (16 ≤ Z ≤ 87) for energies above K-shell photoeffect threshold (up to 1332 keV) are presented. These values are derived by interpolation from the published state-of-the-art precise theoretical values. (author). 4 refs., 14 tabs

[en] The effect of heat treatment on lyoluminescence has been studied for saccharides and the experimental observations have been explained using a rate kinetic model of lyoluminescence. The model is found to be capable of explaining the observed effect of heat treatment when possible reaction mechanism due to heating are included. (author). 9 refs., 1 fig