[en] The implosion dynamics and fusion parameters of a high density θ-pinch plasma driven by a multicascade liner Z-pinch is investigated. The imploding multicascade liner Z-pinch plasma traps an axial magnetic field, compressing it to several megagauss in an extremely short time. The fast changing magnetic flux then induces an azimuthal θ-current on the fiber surface, with a rise time an order of magnitude smaller than the applied Z-pinch current. Numerical simulation shows that for optimum choice of shell thickness of the multicascade liner system, high-densities and temperatures can be realized for fibers seeded with some high-Z impurities. At peak compression the fuel densities of the order of 10²⁶/cm³ and temperature about 10 keV can be achieved on a time scale of the order of 0.5 ns, yielding the Lawson criterion parameter n_τ = 10¹⁴ s/cm³ for DT-plasma

[en] Full text: The optical actinometric technique is used to investigate the addition of impurities in the argon and helium microwave discharges during the wall conditioning process of the MT-I spherical tokamak. This technique normalizes the change occurring in the electron energy distribution function with changing plasma conditions through the emission intensity of the selected Ar/He lines. Any change in relative spectral intensities correlates with the group of electrons involved in the electron impact excitation and the concentration of the plasma species involved in the optical emission. The study investigates the impurity level and the change that occurred in the electron temperature and electron density by using relative intensities, Boltzmann plots, and stark broadening of the selected Ar/He lines. Optimization of the pre-ionization phase is also necessary to step forward to the main tokamak operation. The spectroscopic characterization is performed in terms of plasma parameters, with the sequential imaging of the electron cyclotron resonance (ECR)- heated plasma zones displaying their growth and progression. At lower fill pressure, plasma imaging illustrates the two distinct ECR-heated plasma zones corresponding to the first and second harmonics. The studies provide insights into the physics of preferential plasma heating in space and time-varying magnetic fields producing ECRH zones.

[en] Triple Langmuir probe (TLP) diagnostic system with its necessary driving circuit is developed and successfully applies for time-resolved measurement of plasma parameters in the negative glow region of pulsating-dc discharge. This technique allows the instantaneous measurement of electron temperature [T₋], electron number density [n₋] as well as plasma fluctuations without any voltage or frequency sweep. In TLP configuration two probes are differentially biased and serve as a floating symmetric double probe whereas the third probe is simply floating into plasma to measure floating potential as a function of time and thus incorporates the effect of plasma fluctuations. As an example of the application to time-dependent plasmas, basic plasma parameters such as floating potential, electron temperature, and electron number density in low pressure air discharge are determined as a function of time for different fill pressure. The results demonstrate temporal evolution of plasma parameters and thus plasma generation progression for different fill pressures

[en] An improved methodology is presented for simulation of coolant activation due to corrosion products and impurities in a typical pressurized water reactor (PWR) under power perturbations. Using time dependent production and losses of corrosion products in the primary coolant path an approach has been developed to calculate the coolant specific activity. Results for ²⁴Na, ⁵⁶Mn, ⁵⁹Fe, ⁶⁰Co and ⁹⁹Mo show that the specific activity in primary loop approaches equilibrium value under normal operating conditions fairly rapidly. Predominant corrosion product activity is due to ⁵⁶Mn. Flow rate has been assumed to follow power changes and different types of power perturbations are introduced after the equilibrium activity has been achieved. In particular the effects of linear changes in reactor operating power and power peaking on the corrosion product activity of the primary coolant have been studied

[en] The implosion dynamics of a dense θ-pinch plasma driven by a double gas-puff z-pinch is re-examined in the presence of kinetic pressure. A modified snow-plow model has been used to describe the dynamics of such a staged pinch plasma. The inclusion of kinetic pressure introduces the usual plasma β-term. Numerical results demonstrate that the thermonuclear fusion parameters can be achieved in a dense θ-pinch Deuterium-Tritium (D-T) fiber plasma for an optimum choice of density ratio of the test to driver gas at the interface position (α-parameter) of imploding z-pinch plasma and kinetic to magnetic pressure ratio (β-factor). Thus double gas-puff staged pinch device can be a more feasible approach to achieve fusion conditions with an enhanced stability

[en] On-site radon concentration has been measured in soil gas and ground water using AlphaGUARD PQ2000 PRO (Saphymo, Germany) radon monitor at the west coastal area of Bangladesh. The measured radon concentration in ground water samples is in the range of 1.41 ± 0.29 to 3.2 ± 0.59 Bq/l with the mean value of 2.33 ± 0.50 Bq/l, which lies within the safe limit recommended by UNSCEAR (2008). The total annual effective dose estimated due to radon concentration in ground water ranges from 3.85 to 8.74 μSv/y with the mean value of 6.37 μSv/y, which is lower than the safe limit set by WHO (2004) and EU (1998). In soil samples, radon concentration has been measured at three different depths (0, 20 and 40 cm) in each location. The highest and the lowest concentrations are 4790 ± 51 and 10 ± 04 Bq/m³ at 40 and 0 cm (surface) depth, respectively, which lie within the natural background levels. (authors)

[en] Naturally occurring radon-222 was evaluated for its use in estimating annual effective dose exposure in groundwater samples of the southeast coastal area of Bangladesh. On-site radon concentration was measured in groundwater using AlphaGUARD PQ2000 PRO (Saphymo, Germany) radon monitor. The measured values range 0.36-15.70 Bq per l, which lies within the safe limit of 4-40 Bq per l recommended by UNSCEAR. On the contrary, few samples show radon concentration above the safe limit of 11.1 Bq per l recommended by USEPA. The mean annual effective doses due to ingestion and inhalation resulting from radon in groundwater vary from 0.99 to 42.87 μSv per y with an average value of 12.45 μSv per y, which is far below the safe limit 100 μSv per y recommended by WHO and EU. Results reveal that there is no significant public health hazard due to radon ingestion and inhalation from groundwater in the study area. (authors)

[en] Coastal sediments and marine fish from a region with high natural radioactivity in Cox Bazar Bangladesh, were analyzed in order to investigate the levels of naturally occurring radionuclides. Sediment from the sea shore in high ambient radiation dose rate areas contained naturally occurring radionuclides at high concentrations. These sediments displayed ²²⁶Ra, ²³²Th and ²³⁵U activity concentrations of 2184 ± 88 Bq kg^-1 dry weight (d.w.), 3808 ± 200 Bq kg^-1 (d.w.) and 123 ± 15 Bq kg^-1 (d.w.), respectively. In contrast with these high values, radionuclide concentrations in sand from other areas of the Cox's Bazar coast were as low as 42 ± 3, 70 ± 4 and < 8 Bq kg^-1 (d.w.) for the same radionuclides, respectively, which are comparable to concentrations determined in many coastal areas elsewhere. The presence of sand deposits with high concentration of uranium series radionuclides could potentially originate high accumulation of alpha emitting radionuclides such as ²¹⁰Po in marine biota, and food chain transfer to man. ²¹⁰Po is a major contributor to the radiation dose both in marine organisms and sea food consumers. Determination of ²¹⁰Po in marine fish and shrimp from the area lead to concentration values ranging from 4.5±0.3 to 124±3 Bq kg^-1 (d.w.) in fish and 82.9±1.6 Bq kg^-1 (d.w.) in shrimp. Similar concentrations are commonly reported in marine biota from several regions. Therefore, in spite of the deposits of heavy mineral sands containing high concentrations of radionuclides such as ²¹⁰Pb and ²¹⁰Po no significant raise in the accumulation of these radionuclides in biota seems to occur, which suggests that radionuclides are tightly bound in sediment grains and are not significantly bioavailable. (author)

[en] Distribution of the natural radionuclides ( "2"3"8U, "2"3"2Th, and "4"0K) and their specific activities in sands and sediments of the Brahmaputra (Jamuna) river of Bangladesh together with mineral characteristics has been studied to assess the radiation levels as well as to develop a baseline database for comparison in the future in case of any change in the area under study due to anthropogenic activities. The radiological parameters of natural radioactivity were assessed calculating the radium equivalent activity, hazard index, the absorbed dose rate, and annual effective dose. The average activity concentrations of "2"2"6Ra ("2"3"8U), "2"3"2Th, and "4"0K in sand and sediment were found to be 59 ± 2 and 60 ± 2 Bq/kg, 113 ± 5 and 135 ± 5 Bq/kg, and 983 ± 42 and 1002 ± 43 Bq/kg, respectively. The calculated average absorbed dose rate and annual effective dose were found to be 150 nGy/h and 0.18 mSv/year respectively. These high values are associated with mineral content of the sediment. X-ray diffraction peaks of sand and sediment samples identify quartz, feldspar, rutile, zircon, monazite, uranium fluoride, hematite, kyanite, and uranium arsenide minerals to be present in the samples. (author)