جستجوی مقالات مرتبط با کلیدواژه "scattering" در نشریات گروه "فیزیک"

The stopping power, penetration and scattering of high energy electrons with different energy distribution functions into dense fuel and hot-spot (fuel core) have been considered for a fast-shock ignition scenario. The analytical calculations indicate that fast electrons with two-temperature energy distribution function penetrate more into the dense fuel, in comparison with the monoenergetic and exponential function, where it is consistent with the MCNPX simulation results. Furthermore, the scattering of energetic electron beams toward the outer surface of the fuel for five various fuel density and two fast ignitor wavelengths of 0.53 and 0.35 micron have been investigated. The results show that for the fuel mass smaller than  2 mg, the scattering of electrons reduce for the electrons with smaller energies and fast ignitor of smaller  wavelengths. Meanwhile, for the electrons with energy of the order ~3.5 MeV, two-temperature and monoenergetic energy distribution function deliver the highest and lowest energy to the main fuel and the central hot-spot, respectively.

In this paper, the impacts of air, argon, helium and neon ambient gases under different gas pressures on radiations, emphasizing in the signal to radiation background and the expansion of laser induced plasma from laser metal interaction have been experimentally studied using spectroscopy, probe beam absorption, and scattering methods. The results show that the plasma radiations and its expansion behavior depend strongly on the ambient gas presure. The highest intensity of the copper spectral lines occurred in argon, neon, air, and helium, respectively. For all gases, by increasing the gas pressure from 5 to 100 mbar the plasma spectral radiation increases and then it saturates at the higher gas pressure. The continuum radiation also increases with the pressure and has the highest value for Ar, air, Ne and He gases, respectively. Plasma in He, Ne, air and Ar has the best singnal to backgrourd (S/B) ratio, respectively, and decreases with the pressure. The probe beam absorption and scattering results have also been compared with the Sedov-Taylor strong shock wave model. The maximum speed of the plasma plume expansion, occurred near the target surface under 750 mbar gas pressure, and was determined for helium to be about 25200 m/s, and through neon, air and argon gases, amounted to about 15625, 13900 and 11860 m/s, respectively, as they reduced significantly when they were far from the target surface and reached 2550, 1000, 700 and 690 m/s at 6 mm from the target for helium, neon, air and argon, respectively.

Seismic waves when crossing the Earth in heterogeneous and anisotropic environments, having interaction. Recognizing the impact of these factors on the seismograms help us to find out more information about interior of the Earth. Coda waves are the main reason for the random heterogeneities in earth. Local earthquakes in the northeast region of Iran with epicentral distance less than 200 km is used with magnitude range of 2 - 6 recorded in period 2006 to 2013. Finally, data for five stations which have (15441 earthquakes) were chosen. In this study, the attenuation parameters, Q, were estimated using the single scattering models. Aki and Chouet (1975) proposed a single backscattering model to explain the coda waves as a superposition of secondary waves from randomly distributed heterogeneities. The decrease of coda wave amplitude with lapse time at a particular frequency is due to energy attenuation and geometrical spreading, and is independent of earthquake source, path effect and site amplification (Aki, 1969). Generally, the Q factor increases with frequency (Mitchell, 1981) following the relation where Q0 is the quality factor at the reference frequency f0 (generally 1 Hz) and n is the frequency parameter, which is close to 1 and varies from region to region depending on the heterogeneity of the medium (Aki, 1980). This relation indicates that the attenuation of seismic waves with the passage of time (distance from source) is different for different frequencies. Hence, the seismic data are first bandpass-filtered to calculate the attenuation. In the present study, the attenuation of the S-coda wave (Figure 5) is calculated at seven central frequencies after getting bandpass-filtered using a Butterworth four pole filter as given in Table 1.The amplitude of the coda wave at lapse time t seconds from the origin time for a bandpass-filtered seismogram at central frequency f is related to the attenuation parameter Q by the following equation: Where C(f) is the coda source factor at frequency f, which is independent of time and radiation pattern, α is the geometrical spreading parameter and is equal to 1.0, 0.5 or 0.75 for body waves, surface waves or diffusive waves, respectively (Sato and Fehler, 1998), Qc(f) is the quality factor of coda waves. As coda waves are backscattered body waves, α= 1. Equation (1) can then be rewritten as: is determined from the slope (b) of a least-squares straight-line fit between versus t, using the relation Shows different steps involved in the computation of Qc (f) from the RMS values of amplitude with time. According to Rautian and Khalturin (1978), the above relation is valid for lapse times greater than twice the S-wave travel time for avoiding the data of the direct S-wave. Sato (1977) introduced the source receiver offset in a single scattering model so that the coda analysis begins after the arrival of the shear wave. In the present study, the time envelope for the coda decay observation is taken at twice the time of S-wave (2ts) from the origin time of the event. Q0 and n values indicate the average values for each station in the surroundings of the station. As an outcome, average of quality factors and frequency-dependents, is given by: In addition, to evaluate the variation in depth direction, we used the quality factor of 18 Coda windows from five to 90 seconds by 5 seconds step. Low values of Q0 in the initial Q-coda windows, indicating strong heterogeneity in the shallow layers of the Earth. The results in studying region have been compared with another zone in Iran (SSZ) (Figure 8).

Reflection spectra of four porous silicon samples under etching times of 2، 6، 10، and 14 min with current density of 10 mA/cm2 were measured. Reflection spectra behaviors for all samples were the same، but their intensities were different and decreased by increasing the etching time. The similar behavior of reflection spectra could be attributed to the electrolyte solution concentration which was the same during fabrication and reduction of reflection spectrum due to the reduction of particle size. Also، the region for the lowest intensity at reflection spectra was related to porous silicon energy gap which shows blue shift for porous silicon energy gap. Roughness study of porous silicon samples was done by scattering spectra measurements، Rayleigh criteria، and Davis-Bennet equation. Scattering spectra of the samples were measured at 10، 15، and 20 degrees by using spectrophotometer. Reflected light intensity reduced by increasing the scattering angle except for the normal scattering which agreed with Rayleigh criteria. Also، our results showed that by increasing the etching time، porosity (sizes and numbers of pores) increases and therefore light absorption increases and scattering from surface reduces. But since scattering varies with the observation scale (wavelength)، the relationship between scattering and porosity differs by varying the observation scale (wavelength).

The shadow cone technique is one of the methods which is used for determining the contribution of scattered particles on the response of neutron detectors. This technique is used for neutron field calibration in Agriculture, Medicine and Industry Research School (AMIRS). In this investigation, we have designed and constructed an optimized shadow cone. According to the calculated neutron dose equivalent attenuation factors, a cone with 20 cm of iron and 30 cm of polyethylene has been found as optimum. For this cone, the neutron dose equivalent attenuation factor for 241Am/Be neutron source, is 0.00035 for which the contribution of scattered neutrons in AMIRS neutron calibration laboratory according to the calculation and measurement results, can be evaluated with less than 0.5% of error.