An extensive indoor Rn/Rn monitoring in North-East India

The behaviour of ubiquitous radon (), thoron () and their progeny in the indoor atmosphere generally reflect a complex interplay between a number of processes, the most important of which are radioactive -decay, ventilation, attachment to aerosols and deposition on the surfaces. The present work involved a long-term (1997–2000) passive monitoring of and in the indoor environment of the North-Eastern region of India. This region being a zone of high seismicity, the indoor radon and thoron measurement of the region will provide a better insight and a valuable database for any study related to radon and thoron anomalies.     

Measurement of indoor radon levels in Erbil capital by using solid state nuclear track detectors

Radon alpha activity concentration has been measured in 28 homes in the Erbil Capital-Iraqi Kurdistan region during the autumn season by using time-integrated passive radon dosimeters containing CR-39 solid state nuclear track detectors “SSNTDs”. The radon activity concentrations in these homes range from (10.33–90.34) with an average of . The average absorption effective dose equivalent for a person living in homes for which the investigation were done was found to be , obtained by using an equilibrium factor of 0.5 and an occupancy factor of 0.8. The average lung cancer cases per year per 10⁶ person was found to be 23±12.     

Measurement of neutron fluence with CR-39 using a UV spectrophotometer

Measurement of the correct neutron fluence in various energy intervals in and around the neutron sources is important for the purpose of personnel and environmental neutron dosimetry. In the present paper we present a method for the measurement of neutron fluence using a CR-39 plastic track detector. The samples exposed to fission neutrons from a reactor with 10¹²– fluence and to fast neutrons from a ²⁴¹Am–Be source with a fluence of were etched for 14 time intervals starting from 10 to 570 min in 6 N NaOH at . The etched samples were exposed to the monochromatic light signal from an iodine–tungsten lamp and the transmittance was measured after each etching time interval using a UV Spectrophotometer. An exponential decay of the transmittance has been observed with increasing etching time. The behaviour of the fission neutrons having four different values of fluence has been observed to be distinctly different from that of the fast neutrons. It has also been observed that there is a linear relationship between the transmittance decay constant and fission neutron fluence.     

Studies of UV-cured CR-39 recording properties in view of its applicability in radiobiological experiments with alpha particles

In radiobiology, low doses of high-LET radiation correspond to a few particle traversals through the cell population. Therefore, for studies on cell monolayers irradiated with a low dose of -particles, it is extremely useful if the number and position of particle traversals can be determined. In this study we describe a new method, based on UV-curing, to obtain a thick CR-39 grafted onto a thick PolyEthylene Terephtalate (PET). This thin double polymeric layer, used as a dish base, has a regular and reproducible detector thickness which can be traversed by 3.5 MeV -particles, with a sufficient residual energy to traverse mammalian cells attached to the base. The recording properties of a PET-CR-39 dish, together with a demonstration of its use for radiobiological experiments, are presented. This new tool allows the precise determination of single-track impact parameters at a sub-cellular level.     

Search for intermediate mass magnetic monopoles and nuclearites with the SLIM experiment

SLIM is a large area experiment (440 m²) installed at the Chacaltaya cosmic ray laboratory since 2001, and about 100 m² at Koksil, Himalaya, since 2003. It is devoted to the search for intermediate mass magnetic monopoles (10⁷–10¹³ GeV/c²) and nuclearites in the cosmic radiation using stacks of CR-39 and Makrofol nuclear track detectors. In four years of operation it will reach a sensitivity to a flux of about 10^-15 cm^-2 s^-1 sr^-1. We present the results of the calibration of CR-39 and Makrofol and the analysis of a first sample of the exposed detector.     

Thermochronology of the South American platform in the state of São Paulo, Brazil, through apatite fission tracks

The fission-track method (FTM) in apatite was applied to 45 samples collected in the Serra da Mantiqueira (Mantiqueira mountain range), the Serra do Mar (Mar mountain range), regions next to these mountain ranges and the coastal region between Ubatuba and Santos in the State of São Paulo, Brazil, to study the thermochronology of the South American Platform in southeast Brazil and its influence on Santos and Campos basins. The data presented in this work complement the previously presented data on the same region (Tello Saenz et al., 2003. J. S. Am. Earth Sci. 15, 765–774) with 31 new samples analyzed. The weighted mean of the corrected ages from high Mantiqueira (around 1000 m), , coincides with the South Atlantic opening. The fact that its thermal history starts at a relatively low temperature suggests that the age of would be the formation age of Serra da Mantiqueira due to a rapid pulse, in which tracks had no time to be retained at the closure temperature, that is . The Serra do Mar presents a more complicated thermal history, with several reactivations indicated by the changes in the slope of its cooling curve. The thermal histories obtained in the regions next to these mountain ranges are compatible with the results mentioned above. The Santos Basin has unconformities that agree with changes in the slope thermal histories of the studied region.     

Radon activity and exhalation rates measurements in fly ash from a thermal power plant

Radon exhalation rate from fly ash samples and from the homogeneous mixture of fly ash of different proportions additive in soil and cement samples to study the effect of the addition was measured by cup dosimeter using SSNTDs. Radon activities were found to vary from (1018±38) to ( whereas the radon exhalation rate varied from (366±14) to . A gradual increase has been observed in samples having fly ash as an additive in cement samples whereas a gradual decrease was observed in soil samples after the addition of fly ash. ²³⁸U in fly ash was measured by a low-level NaI (Tl)-based gamma ray spectrometer. The results show enhancement in U concentration in fly ash as compared to coal samples, whereas radon exhalation rate is less in fly ash samples.     

Production of heavy fragments in the fission mass region in C+U, Bi, Au and Ag reactions at 26.5 GeV

Formation of heavy fragments in the fission mass region in the interaction of 26.5 GeV with U, Bi, Au and Ag is studied using a sandwich configuration of the Makrofol polycarbonate track detector. Events in which at least one heavy fragment in the fission mass region is detected are analyzed. Fragments produced in these events are identified and an event-by-event model-free analysis is performed in order to separate different production mechanisms. We have identified the events produced in fission, deep spallation and fragmentation processes. The cross sections and experimental features are determined for these reaction mechanisms, and their variations as a function of the target mass have been investigated. The results show that in the interactions of with U the dominant process is fission, while in the interactions of with lighter target nuclei the dominant processes are deep spallation and fragmentation.     

U and Th thin film neutron dosimetry for fission-track dating: application to the age standard Moldavite

Neutron dosimetry based on U and Th thin films was used for fission-track dating of the age standard Moldavite, the central European tektite, from the Middle Miocene deposit of Jankov (southern Bohemia, Czech Republic). Our fission-track age () agrees with a recent ⁴⁰Ar/³⁹Ar age, , based on several determinations on Moldavites from different sediments, including the Jankov deposit. This result indicates that the U and Th thin film neutron dosimetry represents a reliable alternative for an absolute approach in fission-track dating.     

Relation between radon concentrations and morphotectonics of the Dead Sea transform in Wadi Araba, Jordan

Radon concentrations were measured along six profiles crossing three morphotectonic features of the Dead Sea transform fault in Wadi Araba. Two profiles of detectors were placed across a fault scarp, a sag pond and a pressure ridge formed along the active Wadi Araba strike-slip fault. The maximum radon peak was measured in the pressure ridges . This high concentration may be due to the up squeezing and heterogeneous fracturing of the Cretaceous and the Pleistocene Lisan beds beneath the pressure ridges. The minimum radon readings were measured in the sag pond floor , the fractures are concentrated at the pond borders and not in the pond floor. The sag ponds are filled with fine sediments, which decreases the porosity and hence the upward radon migration. The fault scarp has intermediate radon radiation, with concentration values ranging between 1.1 and .     

Development of a high speed imaging microscope and new software for nuclear track detector analysis

Automated digital imaging optical microscopy is widely used for diagnostic applications in the health care and biology fields and for routine inspection in industrial applications such as semiconductor fabrication. These applications require the imaging of large areas at high speed in order to obtain sufficient data for image processing with good statistics. Track detector analysis also benefits from the rapid acquisition of large areas on the detector surface. We have developed a new microscope system, the HSP-1000, for high speed image acquisition that uses a line sensor camera in place of a traditional CCD camera. Continuous, automatic focusing of the microscope is achieved by means of an optical pick-up system that provides fast feedback for control of distance between the objective and the image surface. Using transmitted light illumination, the microscope is able to digitize a area at resolution in . As a result of continuous stage motion and continuous focusing, we have attained image acquisition speeds that are 50–100 times faster than conventional CCD-based microscope systems. In this paper, we describe a number of aspects of the microscope system including the use of the line sensor and the automatic focus system.     

Investigation of free radicals induced by light ions in CR-39 using ESR spectroscopy

In previous investigations the formation of radicals induced by γ-irradiation in CR-39 samples has been studied by electron spin resonance (ESR) spectroscopy. On the other hand, all attempts fail to detect radicals in samples irradiated by particles (p, and neutrons). The present work succeeded in detection of radicals produced by charged particle radiation in CR-39 (TASTRAK). The detectors were irradiated with protons of 7 MeV and -particles of 3 MeV with fluences in the order of 10¹¹–10¹² particles/cm². The observed ESR signal is composed of at least four different resonance lines for each of which we determined the amplitudes, g-factors, lifetimes and the G-value. The amplitude of the total ESR signal decreases rapidly with a short and a longer lifetime. About 5 days after irradiation the ESR intensity decreased to an undetectable value. The lowest detectable dose (LDD) is of the order of 1 kGy.     

Dose distribution of carbon ions in air assessed using imaging plates and ionization chamber

A system to expose biological specimens to medium-energy (2.6–6.0  MeV/u) irradiation has been developed at the NIRS-HIMAC. In order to determine the beam energy or LET at the irradiation position in air, the dose distribution for 6.0  MeV/u carbon beam has been obtained using a secondary electron monitor and a flat-type ionization chamber by using air as the energy absorber. Imaging plates were applied to assess the beam profile distribution. The intensity of photo-stimulated luminescence (PSL) was found to be almost proportional to the energy deposited within the sensitive layer of the imaging plate. It has been confirmed that a uniform irradiation field can be produced (about ±5% within 20 mm in diameter) at low-intensity exposure from 10¹ to . Long-term beam stability in the low-intensity condition has also been demonstrated. As a consequence, the methodology for uniform, stable and low-intensity beam exposure has been established, and the continuously variable linear energy transfer (LET) values have also been obtained by changing the distance from the endcap of beamport, for biological studies.     

: Hadronic molecules in effective field theory

We consider the implications from the possibility that the recently observed state X(3872) is a meson–antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We explore the consequences of the assumption that X(3872) is a molecular bound state of D^*0 and mesons for the existence of bound states in the and channels.     

Molecular data for a biochemical model of DNA damage: Electron impact ionization and dissociative ionization cross sections of DNA bases and sugar-phosphate backbone

As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of - and -deoxyribose-phosphate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the - and -deoxyribose-phosphate cross sections, differing by less than 10%, an indication that a building-up principle may be applicable. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-H1)⁺, with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 16.9 eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage.     

Radiator design for detecting high-energy neutrons with a nuclear track detector

Subsequent to the proposal of a two-layer structured radiator for more efficient detection of high-energy neutrons with a plastic nuclear track detector (PNTD), its availability has been investigated both experimentally and theoretically. An inner deuterized hydrocarbon (CD₂) layer adjacent to PNTD should play the role of both a radiator of deuterons recoiled there and a degrader for energetic protons recoiled in the outer layer of a CH₂ material. It was found that the energy dependence of the efficiency was changed sensitively by the thickness of the CD₂ layer. A best combination of CH₂ and CD₂ thickness was estimated under a condition of a constant total thickness. For example, the sensitivity could be flattened within 20% between about 5 and 70 MeV by using -CD₂ and -CH₂.     

Quadrupole collectivity of Ne and the boundary of the island of inversion

The excitation of the neutron-rich nucleus ²⁸Ne has been investigated via heavy-ion inelastic scattering in reversed kinematics. The value was determined to be , which is smaller than expected from the low excitation energy of the first state. A comparison with theoretical predictions suggests that the suppressed collectivity in ²⁸Ne is characteristic of nuclei lying on the boundary of the ‘island of inversion’.     

Alpha-recoil track densities in mica and radiometric age determination

Recoiling daughters of -decaying U and Th impurities in mica and other minerals produce localised lattice damage: alpha-recoil tracks. The age of a sample can be calculated from the number of tracks per unit volume (N_ART). To this end, the mica is etched and the etch pits at the sites of recoil-tracks are counted under the optical microscope. Because the measured track densities increase with etching time, N_ART is calculated from the fitted regression line. A number of problems inherent in this approach are overcome by the etch–anneal–etch and the mirror-image methods. The track densities determined with these methods are independent of etching time. Although both methods need improvement, they hold the potential of a precise determination of N_ART from a single measurement in future recoil-track dating.     

Upgrading of LET track-etch spectrometer calibration: Calibration and uncertainty analysis

The spectrometer of linear energy transfer (LET) was developed several years ago. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are determined through track parameters determination and analysis by an automatic optical image analyser LUCIA G. For the past few years, we have used three materials, Page, 0.5 mm thick and Tastrak, 1 and 0.5 mm thick. To upgrade and determine their calibration curves, we have performed irradiation in high-energy heavier charged particle beams at Dubna, Russia and at Chiba, Japan. We were able to irradiate detectors by means of particles from ¹²C to ⁵⁶Fe with LET in water from 7.9 to . Upgraded calibration curves were obtained through a regression analysis, including systematic uncertainty estimation. The results obtained were combined with statistical uncertainty treatment and were used to analyse recently and previously obtained data. Examples of the results are presented and analysed.     

Search for Uranium Source in Warcha Sandstone, Salt Range, Pakistan, using SSNTD Technique

The similarity in sedimentary depositional characteristics of the Warcha Sandstone of Nilawahan Group in the Salt Range to the uranium bearing sandstones of Siwalik Group in the foot hills of Himalaya and Sulaiman Ranges, Pakistan, tempted geologists to investigate the former group for the occurrence of uranium deposits in it. Like volcanic ash beds in Siwaliks, phosphatic nodules may be a possible source of uranium mineralization in Warcha Sandstone. Samples of phosphatic nodules occurring in the Warcha sandstone near Chakwal were collected and subjected to the solid state nuclear track detection technique for the determination of their uranium concentration. The uranium concentration in these samples ranges from (434±32) to (964±74) with an average of . The high uranium content indicates that the phosphatic nodules may be the possible source of uranium mineralization in Warcha Sandstone. These results are quite encouraging and favor the idea of exploring the area in detail for any possible occurrence of uranium deposits.