Keeping in view the kinetic treatment for plasma particles, the electrostatic twisted dust-acoustic (DA) and dust-ion-acoustic (DIA) waves are investigated in a collisionless unmagnetized multi-component dusty plasma, whose constituents are the electrons, singly ionized positive ions, and negatively charged massive dust particulates. With this background, the Vlasov–Poisson equations are coupled together to derive a generalized dielectric constant by utilizing the Laguerre-Gaussian perturbed distribution function and electrostatic potential in the paraxial limit. The dispersion and damping rates of twisted DA and DIA waves are analyzed with finite orbital angular momentum states in a multi-component dusty plasma. Significant modifications concerning the real wave frequencies and damping rates appeared with varying twisted dimensionless parameter and dust concentration. In particular, it is shown that dust concentration enhances the phase speed of the DIA waves in contrary to DA waves, whereas the impact of twisted parameter reduces the frequencies of both DA and DIA waves. The results should be useful for the understanding of particle transport and trapping phenomena caused by wave excitation in laboratory dusty plasmas.

A generalized response (dielectric) function for twisted electrostatic waves is derived for an un-magnetized self-gravitating thermal dusty plasma, whose constituents are the Boltzmann-distributed electrons and positive ions in the presence of negatively charged micrometre-sized massive dust particulates. For this purpose, a set of Vlasov-Poisson coupled equations is solved along with the perturbed Laguerre-Gauss distribution function, as well as the electrostatic and gravitational potentials in the limit of paraxial approximation. For plane wave solution, the wavefronts of the dust-acoustic (DA) wave are assumed to have a constant phase with electric and gravitational field lines propagating straight along the propagation axis. On the other hand, non-planar wave solutions show helical (twisted) wavefronts, in which field lines spiral around the propagation axis owing to the azimuthal velocity component to account for the finite orbital angular momentum (OAM) states. The dispersion relation and damping rate for twisted DA waves are studied both analytically and numerically. It is shown that finite OAM states, the dust to electron temperature ratio, and dust self-gravitation effects significantly affect the linear dispersion and Landau damping frequencies. In particular, the phase speed of twisted DA waves is reduced with the variation of the twist parameter (= k/lq ), dust concentration (= n d0 /n i0 ), and dust self-gravitation (= Jd / pd ). The relevance of our findings to interstellar dust clouds is also discussed for micrometre-sized massive dust grains. KEYWORDS dusty plasma, electrostatic twisted waves, landau damping, orbital angular momentum INTRODUCTIONLight beam exchanges its energy and momentum [1] with matter upon interaction with it. The total angular momentum of the light beam can be composed of spin and orbital parts due to planar and helical wavefronts, respectively. In other words, the spin and orbital angular momenta have their origin from the polarization states and azimuthal phase structure, which are the well-known properties of polarized light beams. Using a specific experimental set-up, Beth [2] was the first to verify Poynting's idea and measure the mechanical torque of circularly polarized light by transferring the angular momentum to a half-wave plate. Later, Allen et al. [3] ) discussed a theoretical model for calculating the average angular momentum density per unit power and studied the well-defined orbital angular momentum (OAM) states due to the Laguerre-Gaussian (LG) light beams. In 2011, Yao and Padgett [4] presented a historical background of the angular momentum to explain various aspects of the OAM states, e.g. the generation of helical beams, the origin and behaviour of OAM, its transformation and possible applications, mode conversion and beam coherence, etc. Recently, several investigations [5][6][7][8][9][10][11][12] have been made with reference to the plasma physics to study the importance of the plasma modes and instabilities with finite OAM, e.g. nonlinear wave couplin...

Indoor radon concentrations have been measured in a limited

Results of indoor radon survey in the dwellings of district Bhimber are presented. Current study is continuation of our preceding studies aiming to setup baseline indoor radon data for the state of Azad Jammu & Kashmir, Pakistan. In this context, 60 representative houses were carefully selected and CN-85 based box type radon detectors were installed in bedrooms and living rooms of each house. The detectors were exposed to indoor radon for 90 days. After etching CN-85 detectors in 6M NaOH at 70°C for 3 hours, the observed track densities were related to the indoor radon concentration using calibration factor of 0.0092 tracks cm2/h per Bq/m3. The measured indoor radon concentration ranged from 29 ± 11 to 58 ± 8 Bq/m3, 40 ± 9 to 60 ± 7 Bq/m3, and 29 ± 12 to 66 ± 7 Bq/m3 in the regions of Bhimber, Samani, and Barnala, respectively. Excess relative risk factors were calculated using measured indoor radon concentrations, by using the risk model reported in the Biological Effects of Ionizing Radiation (BEIR VI, 1999) report. Excess relative risk was calculated for age groups of 35 and 55 years. Using local occupancy factor, average excess lung cancer risk for the population group of 35 and 55 years of age was found to be 0.42 ± 0.09 and 0.34 ± 0.08. The mean annual effective dose for Bhimber, Samani, and Barnala regions were found to be 1.05 ± 0.17 mSv, 1.09 ± 0.17 mSv, and 1.16 ± 0.17 mSv, respectively. These values are within in the safe limits recommended by the international organizations