Location Of Radiation Source Research Articles

Interferometric observations of a single stroke cloud‐to‐ground flash

VHF radiation source location measurements using an interferometric technique are presented for a single stroke cloud‐to‐ground lightning discharge. The discharge began with 100 ms of preliminary activity during which several horizontal streamers developed inside the cloud, one of which culminated in the development of a negative leader to ground and a return stroke. The return stroke was followed by a 10 ms quiet period in the radiation and by a single, fast ‘k‐type‧ event which appeared to transport negative charge horizontally into the region of initial breakdown, completing the flash.

The Image Establishing Theory in Track α-Autoradiography

The autoradiographic method consists in establishing the “true” location of nuclear radiation sources on the surface being analyzed with the aid of a two-dimensional image of their radiation field shown on the autoradiogram. The distribution of the density of the tracks can be described by the two-dimensional Fredholm integral equation of the 1st type through a convolution. Some assumptions of the proposed model are discussed and its application is shown by way of example.

The initial streamer of intracloud lightning flashes

The initial development of four vertical intracloud lightning flashes has been studied using time‐resolved measurements of the electric field change from 7–8 ground locations at Kennedy Space Center, Florida. The initial field changes of the flashes were analyzed with a unidirectional piecewise‐linear streamer model in an attempt to determine the direction and sign of the initial charge transfer. The results indicate that the discharges were initiated by an upward propagating negative streamer, rather than by a downward propagating positive streamer. The initial streamer appeared to progress upward at speeds between 1 and 3×105 m/s for durations of 10–30 ms and deposited 1 to 4 Coulombs per kilometer of extent. These results disagree with those of earlier studies which used the shape of the overall electric field change to infer the sense of the streamer, and which gave relatively low values for progression speeds (104 m/s). The results agree with observations of VHF radiation source locations by Proctor in South Africa.

Doppler Radar and Radio Observations of Thunderstorms

Three-dimensional motion fields in a thunderstorm are compared to measurements of the radar reflectivity structure of the storm and to the locations of VHF radiation from electrical discharges, in an attempt to determine the physical conditions which prevailed during the electrically active phase of the storm. The observations were obtained from a network of three Doppler radars and a long-baseline radiation source location system during the 1978 Thunderstorm Research International Program (TRIP 78) at Kennedy Space Center, FL. The analysis shows that two cells developed sequentially on the upshear side of the storm. In the second cell, the updraft velocity between 6- and 7-km altitude (-10 to -15°C) increased rapidly to greater than 20 ms-1; and coincided with a substantial increase in the VHF radiation burst rate. Growth of the updraft was accompanied by the simultaneous development of an upper level downdraft on its upshear side. Reflectivity values in excess of 50 dBZ were observed within the vicinity of the updraft, and have been attributed to graupel or hail that was suspended in the updraft and which grew by riming of supercooled water droplets. Initial source locations for each radiation burst formed an umbrella-like pattern above the high-reflectivity core. We interpret the results to be consistent with an ice-ice electrical charging interaction first investigated by Reynolds et al.

Quasi-Uniform Irradiation of Plane Surfaces Using Multiple Radiation Sources

The question of the optimum location of multiple radiation sources for quasi-uniform irradiation of plane surfaces is addressed, and the problem is studied numerically for the case of a square plane target surface and plane arrays of equal spherically symmetric (4?) radiation sources. The technique presented is also applicable to non-planar source arrays and non-planar targets as well as to the case of sources whose radiation pattern is not spherically symmetric. The square target problem is solved numerically for the case where the desired target surface flux uniformity is 80%. The optimum source location coordinates and the resulting target flux patterns are presented for a number of source arrays. The scaling with the number of sources used and the distance between the source and target planes is also given. The results show that a significant reduction in the total source strength required to produce a given quasi-uniform target fluence can be achieved by using multiple sources. For example, for an 80% uniformity constraint, four properly placed sources, So, are found to give ~19 times the average flux from a single source of strength So. This represents a gain factor of ~4.76 due to better utilization of the available source strength. Calculations show that gains in excess of an order of magnitude can be achieved in this manner by using a large number of properly placed sources.

A Scintillation Camera

A stationary radionuclide imaging system employs a planar scintillation crystal viewed by multiple photodetectors. A new positioning technique allows use of signal information that must be discarded by conventional cameras. A calibrator generates photodetector signal patterns characteristic of known radiation source locations. Unknown sources are positioned by matching signal patterns of their radiations with the stored calibration signal patterns. The integral of individual location is displayed as a corrected image.