Radiation Field Components Research Articles

Calculation of total absorbed doses in research reactors / Berechnung von totalen Energiedosen in Forschungsreaktoren

A methodology for calculating the absorbed doses in samples irradiated in research reactors which permits to know the contribution of each radiation field component is presented. The calculation of partial doses due to neutrons is based on average kerma factors and experimental neutron fluxes at the irradiation position, whereas the calculation of the dose due to gamma radiation is based on the experimental dose rate with subsequent use of a correction factor for converting doses in different media. It is assumed that the size of the samples and/ or the boundary conditions ensure to a reasonable degree that the charged particle equilibrium condition is fulfilled, in which case the kerma is practically equal to the absorbed dose. In order to use the present method, only the knowledge of the elemental composition of the samples and of the characteristics of the radiation field are required, because other data necessary for the calculation are already gathered in the present work.

Current and electric field derivatives in triggered lightning return strokes

Forty simultaneous, submicrosecond time‐resolved measurements of triggered lightning returnstroke current (I), current derivative (dI/dt), and electric field derivative (dE/dt) were made in Florida and France in 1985 and 1986. Peak currents ranged from about 5 to 50 kA, peak dI/dt amplitudes from 60 to 260 kA/μs in 1985 and from 20 to 140 kA/μs in 1986. The mean peak dI/dt values, 111 kA/μs (1985) and 68 kA/μs (1986), are 2–3 times higher than data from instrumented towers, and peak I and dI/dt appear to be positively correlated. The dE/dt and dI/dt waveform pairs have similar shapes, and the peak amplitudes are linearly proportional. Return‐stroke velocity, computed from the ratio of peak dE/dt and dI/dt signal amplitudes using an expression derived from the radiation field term of the transmission line model (TLM), averaged 2.9×108 m/s and 3.0×108 m/s in 1985 and 1986, respectively, which is about 2 times higher than most optical measurements. The TLM velocity may be erroneous because (1) the dE/dt measurement was made only 50 m from the lightning channel, where fields other than the radiation field component, that is near fields, may contribute to the total dE/dt and (2) fine structure on the measured E fields was not consistent with a single upwardly propagating return‐stroke current wave assumed by the TLM (two waves are more consistent).

Raman emission in an external resonator with nonlinear absorption at the Stokes frequency

An analysis is made of cw generation of the fundamental and first Stokes components of stimulated Raman emission in an optical resonator excited by an external monochromatic beam under conditions of efficient narrow-band nonlinear absorption at the Stokes frequency. Some features of this laser action are studied and a dependence of the oscillation intensity of the radiation field components on the exciting beam intensity is determined. It is found that nonlinear absorption substantially changes the character of the laser action in the system. In particular, it results in the establishment of a hysteretic dependence of the amplitudes of the radiation field oscillations on the pump wave amplitude, which may be of considerable practical interest. For example, these systems may be used as generators of tuned (Stokes) frequency rectangular pulses.

A probabilistic model for the initial peaks of ground wave atmospherics generated by lightning return strokes

By using a previously developed statistical model of the lightning discharge the probability density function for the initial peaks of the ground wave electric field generated by the return strokes was developed. The variation of the probability density function with the distance to the source is expressed analytically for the range of approximately 25–500 km in which the ground wave predominates. Since the statistical simulation model can include the frequency response of the receiving circuitry, the model can be used to predict the performance of threshold sensitive devices which operate on the initial peaks of the electric field. An example is given which illustrates the application of the results to a device similar to a lightning flash counter. Although only the induction and radiation field components were included in this study, it should be possible to modify the results to include the electrostatic component which would then allow calculation of the effective range of lightning flash counters.

Complementary field component of radiation from a Cassegrain subreflector

The effect of the induced currents on the subreflector can be evaluated by the method of stationary phase and gives, to a first approximation, the specularly reflected radiation. The radiation at an angle of interest, as thus calculated, is found to be supplemented by the backlobe of the radiation directed at the complementary angle.

Radiation Field and Q of a Resonant Cylindrical Plasma Column

A cylindrical plasma column displays a series of resonant responses when it is excited by an electromagnetic wave with its electric field and direction of propagation both perpendicular to the axis of the column. In the principal member of the mode spectrum, the electrons are taken to move in phase in a direction transverse to the axis of the column. The diameter of the column is small compared to wavelength. In this paper, for the transverse electronic motion described, an expression for the vector potential in the region about the column is derived and thence the electromagnetic field components. The radiation field components Eφ and Hz vary as ρ−½. The effect of radiation damping is calculated by deriving an expression for the selectivity factor Q. The expression is Q = (λ/a)2/2π3, when the radius a is much less than a wavelength.