Nucl. Tracks, VoL 3, pp. 213-218 Pergamon Press Ltd. 1979. Printed in Great Britain R A D I O A C T I V E S U R V E Y O F K I R A N A HILLS U S I N G S O L I D STATE N U C L E A R TRACK D E T E C T O R S N. A. KHAN,N. A. MAHMOODand M. A. KHALIQ Physics Department, Talim-ul-Islam College, Rabwah, Pakistan (Received 14 March 1979; in revised form 21 June 1979) Abstract--Radioactive survey of an area of Kirana hills (Pakistan) has been carried out by using Solid State Nuclear Track Detectors (SSNTDs). The track density has been observed to indicate contour variations. The results have been compared with the count rate obtained by using a G-M counter, and an excellent agreement has been obtained. 1. I N T R O D U C T I O N SOLID State Nuclear Track Detectors (SSNTDs) have been employed for the initial exploration of uranium and other radioactive elements. The method essentially consists in the detection of the three radon isotopes which are the products of decay of the naturally-occurring radioactive series. Only one of these isotopes of radon, namely 222Rn, which is one of the daughters of uranium decay, is really helpful since the other two isotopes are short-lived and cannot diffuse out of the rock surface from the entrapped mineral. Tanner (1975) has estimated that 222Rn, diffusing from a plain source through dry sand, can travel about 7 m before suffering a hundredfold decrease in concentration by radioactive decay. Miller (1973) has pointed out that, since radon prospecting is concerned with a dynamic system depending upon a number of variables, interpretation of results is difficult. Before 1960, exploration of uranium was mainly carried out by the application of surface gamma radioactivity measurement. The discovery of new deposits in further uranium exploration is going to be more difficult, since they may be buried deep down and there may not be any appreciable surface gamma activity. New methods of investigation must be developed, including those involving radon measurements, which can be applied even to ore bodies having very little sur- face gamma activity. Since radon does not combine with other elements, its free migration through pore spaces in rock and soil is possible. A radon atom diffuses through the enclosing mineral if the parent radium is close to the grain surface. Having escaped from a mineral, radon will diffuse through the ground air in pore spaces, and the long-lived 222Rn may travel up to several metres. Besides diffusion, there are other means by which radon is transported, such as low pressure and strong winds which may draw ground air out of the pore spaces, thus causing an upward movement of the gas from depth. Previously, alpha detection was done by chambers coated with alpha-sensitive phosphors. Probes and pump monitors for measuring radon in soil air have been described by Miller (1973). Detection of alpha activity by solid state nuclear track detectors has the advantages of simplicity, low cost and greater sensitivity. Also these detectors are insensitive to beta particles, gamma rays and light. 2. APPLICATION O F PLASTIC DETECTORS Gamma-sensitive techniques are effective only where the uranium mineralization is at, or very near, the surface. In many areas of the world where uranium is being explored, surface scintillation techniques are not effective, because all targets of interest are deeply buried. The only effective method 213 214 N. A. KHAN, N. A. M A H M O O D and M. A. KHALIQ of exploring in these areas are drilling techniques, which require thorough interpretation of the subsurface geology. Radon-detecting techniques offer an inexpensive prospection method of uranium mineralization buried several hundred metres deep (Gingrich and Fisher, 1973). The track-etch method based on the utilization of small or-radiation-sensitive solid-state plastic detectors gives an accumulated picture of changing radon soil-gas concentration and produces a reading indicative of the long-term average. To obtain the maximum amount of information from track-etch reading, the data are presented in the form of radon contour maps or graphs. Gingrich and Fisher (1973) have estimated that radon is an extremely small component of soil gas (0.66x 10 -18 1 Rn/l). Transport velocities of the order of (4-6 × 10-3cm s-~ or approximately 3-5 m per day have been suggested. Using the lower figure of 3 m per day and a soil containing 1 ppm U overlying 2000 ppm ore body, an anomaly 3 times the value of the background should be produced over the ore body if it were buried 120 m deep. Gingrich and Fisher (1973) have surveyed the use of the track-etch system for uranium exploration in about 300 programmes in a wide variety of geological environments. Most of the initial surveys were made in the sedimentary deposits area of Western United States, and in the vein type deposits of Australia. Several successful programmes are also reported to have been carried out in Canada and Africa. The track-etch technique for uranium has been found to be particularly attractive for preliminary survey, and for conducting exploration in remote areas where only a limited amount of field support is available. This system can result in significant savings in exploration drilling costs, and has been found to operate in any terrain from tropical areas of Australia to permafrost-covered arctic regions of Canada. 3. FIELD C O N D I T I O N S IN KIRANA HILLS We have chosen an area for investigation which is situated in Rachna and Chhaj Doabs on either side of river Chenab (32 ° North latitude). This level plain is largely made of fertile alluvium deposited by the river. Most of the area is 600-650 ft *Manufactured by Kodak-Path~ of France. (~200m) above sea-level. The average gradient is 1 ft to 1 mile (i.e. ~ 20 cm to 1 kin). The only breaks in the alluvial monotony of the plain are the little groups of arid, broken hills of sedimentary rocks near Sangla, Chiniot, Rabwah and Sargodha. These are known as Kirana Hills and are only ~ 100 km from the Salt Range. Their rigidity is shown by the occurrence of horst structure. These are very small in extent, but rise in jagged pinnacles 300m above the plains and are geomorphologically of great interest, as they provide an evidence of the extension of the old Gondwana Block (Wadia, 1966). The Kirana Hills belong to the Aravalli range which starts from Delhi and covers a part of Rajasthan province in India. Uranium--copper mineralization has been found on the western bank of Aravalli meta-sediments in Udaipur District of Rajasthan. Uranium ore occurs as lenses of variable size on the foot-wall side of the copper zone. The deposit is, however, economically unimportant. Low-grade uranium has also been found in the Alwar District. But this, again, is not fit for exploitation, as the grade goes only from 0.01 to 1.33% equivalent U30 8. The Jhunjhunu District also contains some uranium mineralization, but the analysed samples contain only up to 0.07 % equivalent U30 s. In the Kulu District of the Indian Punjab, which lies at the foot of the Himalayas, uranium in quartzite was found recently on the western slopes of the Shakiran Dhar. A full review of uranium and thorium deposits in India has been made by Bhola et al. (1975). They estimate large deposits of monazite in Rajasthan, which contain from 8 to 10'% ThO2 and up to 0.3'~ U 3 0 8. The use of thorium in breeder reactors opens up possibilities of utilizing monazite in connection with nuclear power plants. Since Kirana Hills are a part of the Aravalli range, there is a possibility of these hills containing uranium/thorium mineralization. The initial survey of a small area of these hills has indicated the presence of some interesting anomalies. Further tests are in progress. 4. EXPERIMENTAL RESULTS A N D DISCUSSION Nuclear track detectors CA80-15", and rarely LR115", were placed in a grid of approx. 3 0 x 3 0 m RADIOACTIVE SURVEY OF KIRANA HILLS USING SSNTDs anomalies found in the first survey were confirmed on subsequent measurements. T h e Fig. 1 contour map shows the result of these measurements. It can be seen that alpha activity in some of the rocks is greater by a factor of six than activity at other points. The anomaly may indicate the presence of uranium mineralization at some depth below the surface of these rocks. The part marked × in the contour map (Fig. 1) shows an additional area surveyed recently, for the purpose of comparing radon concentration in plain surface consisting of sand and clay with the values in rocks. within a maximum distance of about 1000m from the Nuclear Research Laboratory of the Talim-ul-Islam College. An exposure of 60 days was made, the average depth of holes being about 7080cm. Plastic detectors were attached to the lower sides of the roof surface of inverted small sampling' cups of diameters varying from 2.5 to 3cm that were placed in holes in the ground. At the end of the exposure time, the cups were recovered and the detectors were etched in 40% NaOH solution for 120 rain at a temperature of (50+2)°C. After etching, the detectors were placed under a high magnification microscope for counting the track density. A maximum track density of 2.2× l0 s cm -2 has been found. Places where radon activity was found higher than that of other points were subjected to this radioactive survey several times, both in winter and in summer. Track density was found to be higher in summer than in winter. The difference in the maximum values was as high as 30%. The object of repeated surveys was to locate positions where the radon activity is maximum. The Chemical composition Samples of rock and soil were sent for analysis to the Atomic Energy Minerals Centre at Lahore. The rock sample was found to be of quartzite with 95 % SiO 2 and minor quantities of Fe, Ca, K, Na, etc. Soil samples appeared to be mostly high-alumina clay. No appreciable amounts of radioactive elements were detected by gamma-spectrometry. The AhrnadNagar ~ / I - / ~ ~, 215 i r C._.q~__ Shah / ~ 0 C~) NuclearResearchLaboratory o ,oo 200 300 Metres FIG. 1. Contour map showing alpha activity (using plastic SSNTDs) over the area under survey. 216 N.A. KHAN, N. A. MAHMOOD and M. A. KHALIQ Ahmad Nagar Kot Amir Shah yard [, ~f I ~ SargodhaRood ~ ~ Railway line S X FIG. 2. 0 ,,~ 0 I00 200 300 Metres NuclearResearchLaboratory Contour m a p showing g a m m a activity (using G - M counter) over the area under survey. 220 For alpha activity -'- 180 For gamma activity 140 g I00 20 I I I 1 I I 300 400 500 600 700 800 Distance, meters FIG. 3. Variation of g a m m a and alpha activity with distance. G a m m a activity: 102N rain-~; alpha activity: 103N c m - 2 ; where N is the number of counts shown, RADIOACTIVE SURVEY OF KIRANA HILLS USING SSNTDs composition of these sedimentary rocks may be compared with Arenaceous type (Davies, 1949; Pettijohn, 1949). Gamma activity The anomalies found in the investigation mentioned above were interesting, and we wanted to know if there were corresponding variations in gamma activity. The area surveyed was therefore subjected to the measurement of its gamma activity by a Geiger-M011er counter assembly. The results of this measurement are shown in the Fig. 2 contour map. We have plotted in Fig. 3 the values of alpha activity measured by the plastic detectors as well as the gamma activity determined with the G M counter. The correspondence between the two activities is striking. The same correlation is expressed in another way in Fig. 4. The origin in the graphs as well as in the contour maps is the position of the Nuclear Research Laboratory, of the Department of Physics at the New Campus of our College. 80095 =70 084 5o2.65 217 5. CONCLUSION The initial survey of a small part of Kirana Hills shows interesting anomalies in radon concentration in these rocks and may indicate the presence of significant amounts of radioactive minerals. Moreover, the alpha activity has been found generally to be more in rock than in soil. Also, there is a marked effect of weather shown by a 30% increase in track density in summer as compared with that in winter. The continuous dust storm and strong winds in the hot summer months, which are characteristic of this area, may be responsible for the increased migration upward of radon from the subsurface rock and soil. Since the chemical analysis of the upper-surface rock and soil did not show marked presence of radioactive substances, the close correspondence between alpha and gamma activity in the area under survey is an important point needing further investigation. The area surveyed is small. Need for a full-scale investigation is obvious. We propose to cover the whole Kirana range as far as possible. N u~ 4°5"4o9.45 60 4o,5e65 4565 ®056 50 . 0 8 0 48 - 800 o For alpha particles 8 75 50.7o ® For gamma particles E Q .m %8p8- 6oo o o e70 65 56 • IO00o 92 40 , o 921 Nuclear Research Laboratory o9_ 150 __ 4b o ®rb 6 3, o6o.88 o ~ 5 ~ " 4 0 0 " o160 162o ®67 7 8 . o 900 ®465 ioo ~ 1 ~%o ,..®~o56 1201 v'* 70 66o o ® 70 ® ~-6o2o~®38 8o 223 ° 4O -- 2 0 0 ® 049 4o3 42o • 48 e45 o,o%2 C ~) l 200 351 400 I I I 1 I 600 800 I000 1200 1400 Distance, E meters 4008042a0%8050 s A°7°t7°6° FIG. 4. Correlation between gamma and alpha activity. Numerical figures represent number of counts. Gamma activity: 102Nmin- 1; alpha activity: 103Ncm-2; where N is the number of counts. 218 N. A. K H A N , N. A. M A H M O O D We have submitted a research project to the P a k i s t a n Science F o u n d a t i o n (PSF) for financial support. The project is under the active consideration of P S F and we hope to start a systematic survey of the entire range. Acknowledgements--We thank Dr Hameed Ahmad Khan and Mr Riaz Ahmed Akbar of PINSTECH for their help in the form of detectors and useful information at the initial stages of our work. We gratefully acknowledge the donation of two boxes of detectors and some literature by the Fund for Physics for Developing Countries established by Professor Abdus Salam, Director, International Centre for Theoretical Physics, Trieste, Italy. Mr Hamid Ali, M.A., lecturer in geography at the T.I. College is thanked for many useful discussions. a n d M. A. K H A L I Q REFERENCES Bhola K. L., Dar K. K., Rama Y. A., Sastor C. and Mehta N. R. (1975) A review of uranium and thorium deposits in India. In Proc. Uranium and Thorium Research and Resources Conf. (8-10 December 1975). U.S. Geological Survey, pp. 86-93. Davies G. M. (1949) A Student's Introduction to Geology. Thomas Murby and Co., London. Gingrich J. E. and Fisher J. C. (1973) Uranium explorations using the track-etch method. IAEA-SM208/19, pp. 213-227. Miller J. M. and Ostle D. (1973 Radon measurement in uranium prospecting. In Proc. Uranium Exploration Methods Panel (1972) IAEA, Vienna. Pettijohn F. J. (1949) Sedimentary Rocks. Harpers and Bros. Publishers, New York. Tanner A. B. (1975) Radon migration as applied to prospecting for uranium. In Proc. Uranium and Thorium Research and Resources Conf. (8 10 December 1975) U.S. Geological Survey. Wadia D. N. (1966) Geology of India. MacMillan, London.