B. Roy

Superheated drop as a neutron spectrometer

Abstract 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°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.

PHOTOELECTRIC CROSS-SECTIONS DERIVED FROM MEASURED TOTAL ATTENUATION COEFFICIENT OF PHOTONS NEAR ABSORPTION EDGES OF HEAVIER ATOMS

Abstract A complete analysis of the estimated photoelectric cross-sections from the measured total photon attenuation coefficients of several atoms (41 ≤ Z ≤ 92) at two photon energies, 43 and 59.5 keV, has been presented. These energies fall close to K-absorption edges of some of the elements studied. In this paper, we examine the role of using coherent scattering cross-sections derived from various sources such as the state-of-the-art precise theoretical calculations, commonly used form factor approximations and form factors with anomalous corrections in estimating the photoelectric cross-section. Comparison of theorectical and other available experimental results are also made with our measured and estimated values. It has been found that an overall change of 5% in the total mass attenuation is expected while using the precise coherent scattering cross-sections.

An accurate method of measuring lifetime of superheated drops using differential manometer

A novel method of measuring the rate of nucleation of superheated drops and also the lifetime of metastable superheated drops accurately has been developed. The lifetime of superheated drops of Freon-12 has been determined by measuring the time dependence of the volume of vapour formed due to spontaneous nucleation of the drops using a relative water manometer. The time dependence of the nucleated volume of vapour indicates the presence of two lifetimes of decay of superheated droplets by spontaneous nucleation.

How high can the temperature of a liquid be raised without boiling

How high the temperature of a liquid can be raised beyond its boiling point without vaporizing (known as the limit of superheat) is an interesting subject of investigation. A different method of finding the limit of superheat of liquids is presented here. The superheated liquids are taken in the form of drops suspended in a dust free gel. The temperature of the superheated liquid is increased very slowly from room temperature to the temperature at which the liquid nucleates to boiling. The nucleation is detected acoustically by a sensitive piezoelectric transducer, coupled to a multichannel scaler, and the nucleation rate is observed as a function of time. The limit of superheat measured by the present method supersedes other measurements and theoretical predictions in reaching the temperature closest to the critical temperature of the liquids.

Use of basic principle of nucleation in determining temperature-threshold neutron energy relationship in superheated emulsions

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.

Efficiency of neutron detection of superheated drops of Freon-22

Abstract Neutron detection efficiency of superheated drops of Freon-22 for neutrons obtained from a 3 Curie Am-Be neutron source has been reported in this paper. Although Freon-22 having lower boiling point than many other similar liquids (e.g., Freon-12, Freon-114, Isobutane) is expected to be more sensitive to neutrons, it has not been reported so far and therefore this paper constitutes the first report on the subject. Neutron detection efficiency of both Freon-22 and Freon-12 have been determined from the measured nucleation rate using the volumetric method developed in our laboratory. The result shows that the neutron detection efficiency of Freon-22 for the neutron energy spectrum obtained from an Am–Be source, is almost double, while the life time is 58.6% smaller than that of Freon-12, for a particular neutron flux of that source.

A sensitive neutron dosimeter using superheated liquid

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 microSv 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 degrees C, irradiated by a 3 Ci Am-Be neutron source has also been presented in this article.

Superheated drops of R114—as a neutron spectrometer

Abstract 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 241 Am–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.

Study of nucleating efficiency of superheated droplets by neutrons

Superheated droplets are proven to be excelent detectors for neutrons and could be used as a neutron dosimeter. To detect accurately the volume of the vapour formed upon nucleation and hence to observe the nucleation quantitatively an air displacement system has been developed.

Strange interface deformation pulses in the flow of layered liquids

The interface in acoustically driven layered liquids, in an enclosed geometry, was found to be unstable to the production of spatially localized, quasi-periodic pulses of deformation. The most interesting property of these pulses is that they propagate in a direction opposite to that of the axial streaming velocity of both liquids. Experimental data are presented describing aspects of the phenomenon which occur only when both the interfacial tension and the density difference are small