Debasis Ghose

Network of seismo-geochemical monitoring observatories for earthquake prediction research in India

Present paper deals with a brief review of the research carried out to develop multi-parametric gas-geochemical monitoring facilities dedicated to earthquake prediction research in India by installing a network of seismo-geochemical monitoring observatories at different regions of the country. In an attempt to detect earthquake precursors, the concentrations of helium, argon, nitrogen, methane, radon-222 (222Rn), polonium-218 (218Po), and polonium-214 (214Po) emanating from hydrothermal systems are monitored continuously and round the clock at these observatories. In this paper, we make a cross correlation study of a number of geochemical anomalies recorded at these observatories. With the data received from each of the above observatories we attempt to make a time series analysis to relate magnitude and epicentral distance locations through statistical methods, empirical formulations that relate the area of influence to earthquake scale. Application of the linear and nonlinear statistical techniques in the recorded geochemical data sets reveal a clear signature of long-range correlation in the data sets.

Radon as a tracer for helium exploration in geothermal areas

Abstract High heat flow and weak structural features in geothermal areas allow easy passage for release of subsurface gases to the atmosphere. In particular, radon and helium are constantly transported from the earths interior and vented out through exhalation points in permeable fault zones. At some places unusually large concentrations of helium may be encountered in soil airs. The possibility of trapping the released helium for bulk use has recently emerged. Because of its highly dispersive nature, helium is a difficult gas to detect during field explorations. Radon monitoring is thus taken up to locate structurally weak zones that allow helium permeation. The technique was recently adopted to determine high helium exhalation points in the Birbhum–Santhal Paragana geothermal area.

Observed mass distribution of spontaneous fission fragments from samples of lime—an SSNTD study

SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements.

SSNTD study of the probable influence of alpha activity on the mass distribution of 252Cf fission fragments

Abstract The SSNTD has come a long way in its application for the study of nuclear phenomena. Spontaneous fission of transuranic elements is one such phenomena wherein use of SSNTD offers easy registration of the signature of the fission fragments. The object of the present study is to explore whether any one of the track parameters such as the diameter can be used to estimate the atomic mass ratios of the spontaneous fission fragments. The spontaneous fission data from 252 Cf recorded almost at the end of one and four half-life periods for alpha decay are analysed, taking a plot of the number of tracks versus the track diameter. From these plots it is seen that initially, when significant alpha activity of 252 Cf persists, the fission fragments appear to cluster into two predominant groups as indicated by two peaks. The ratio of the diameters at these peak positions appear to be related to the ratio of average mass numbers of the light and heavy groups of fission fragments. However, absence of two peaks for similar plots at the end of about four half-life periods for alpha decay suggests that presumably the presence of alphas influence the mass distribution of the fission fragments.

Fractal pattern in hydrothermal emission

The thermal spring Agnikunda, in eastern India, is characterized by spontaneous emission of helium bearing natural gases. Temporal variation of the concentration of this helium has been observed for a fairly long period of time and seen to be random in nature. This irregular variation of helium emanation with time has been studied by fractal statistics, Hursts rescaled range analysis. The temporal variation of concentration of helium shows persistent behaviour with Hurst coefficient about 0.6. Various causes for the observed fractal nature of the temporal variation of helium is discussed in this paper.

Observed branching ratios of alpha to fission fragments of Cf252 using CR-39

Abstract There has been a rapid growth in the application of SSNTD to the study of nuclear phenomena in the recent past. The considerable ease introduced in recording the signature of heavy ions in the presence of alpha particles has made them particularly suitable for the study of spontaneous fission of transuranic elements. It is the object of the present study to explore the response of CR-39 for the determination of the branching ratios of alpha to fission fragments of Cf 252 at the end of almost one and four half-life periods for alpha decay. The results more or less confirm the expected values.

An SSNTD study of spontaneous fission fragments from the soil-gas samples of Bakreswar thermal springs

During the course of investigations on the radon and stable gas migration around the hot spring zone at Bakreswar, Birbhum in India, it was noticed that CR-39 plastic detectors used for the detection of radon revealed tracks with much bigger diameters than usual for alpha particle tracks. Exposed CR-39 detectors etched adapting sequential etching technique confirmed the presence of bigger diameter tracks similar in nature to the tracks formed by spontaneous fission fragments. This paper presents the results of these observations along with the histogram plots of the track number versus track diameter that indicate an asymmetric distribution as was seen for mass distribution of spontaneous fission fragments.

Helium Extraction from Thermal Spring Gases

Publisher Summary Helium, the second most abundant element in the universe, is scarce in the earths atmosphere because of thermal diffusion to outer space. It is far more plentiful within the solid earth due to continuous generation through present day radioactivity, retention of fossil helium left by short-lived extinct radioactivity, and the existence of primordial helium trapped deeper within. The solid earth therefore, automatically provides source of commercial helium. Helium concentration in natural gases is highly uneven and anomalous. Known natural gas sources in India are lean in it, making recovery uneconomical. On the other hand, many Indian thermal springs contain a high percentage of helium in their emanations, so that it becomes practicable for extraction. A pilot recovery plant has been set up at Bakreswar, West Bengal, about 250 km NW of Calcutta. This chapter presents the purification process adopted and future scope of work in this direction.

A Study on Ionizing Emissions from Limestone Samples using CR-39 Solid State Nuclear Track Detector

Limestone is an item most commonly consumed by the people in the Barak Valley area of Assam along with betel leaves. Also limestone chips are extensively used for water treatment in filter beds of these areas. A preliminary investigation on the activity of the samples of limestone, collected from the local market at Silchar, Assam, indicated the presence of beta and gamma-ray activity, prompting further investigations for the presence of alpha particle emitting radionuclides. Also the study of the ionising emissions from these samples using solid state nuclear track detector (SSNTD) has revealed the presence of spontaneous fission fragments along with alpha particles. This paper presents an account of the results obtained from the SSNTD studies of these limestone samples.