New instruments for measuring x-rays from rocket-triggered lightning
Abstract
We have previously reported the observations of energetic radiation from rocket-triggered lightning made in the summer of 2002. These observations used one 12.7 cm diameter NaI(Tl)/PMT detector and one identical control detector (with no scintillator), housed in a container designed to operate in the electromagnetically noisy environment near lightning. Since then, we have constructed four new instruments, using seven 7.6 cm diameter NaI(Tl)/PMT detectors plus one control detector. The instruments were each housed in a heavy aluminum box. The sides of the boxes were 1.27 cm thick, except for a 0.32 cm thick Al window on the top that allowed x-rays with energies down to 30 keV to enter. The boxes were welded and RF gaskets and O-rings were used on all access doors to prevent RF noise, moisture and light from entering. The instruments were battery powered, and controlled on and off through fiber optic signals. In addition, the data were transmitted through fiber optic cables to a receiver in a shielded metal trailer and saved on the hard drives of three PCs. Data acquisition was initiated by an external trigger derived from the lightning current, signaling the time of the leading edge of the return strokes or other large current pulses. The entire waveforms from seven of the PMT detectors were then digitized with 0.2 microsecond resolution for 220 msec with 20 msec of pre-trigger sampling. For three detectors the waveforms were digitized with 10 nanosecond resolution for 10 msec with 1 msec of pre-trigger sampling. Measurements were made using these instruments at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL during the summer of 2003, and 10 flashes were observed with a total of 28 dart leader/return strokes sequences and two initial continuous current intervals. For the first five lightning flashes, 1.7 cm thick bronze collimators were placed around and in front of the detectors in order to study the intensity and arrival time of the x-rays as a function of height above the ground. The collimators had an opening angle of about plus or minus 15 degrees and were pointed in the direction of the lightning channel at 0, 15, 30 and 45 degrees from vertical. For the remaining five flashes, the collimators were replaced with bronze attenuators to study the energy spectra and electron and photon components of the energetic radiation. In a final experiment, the spacing and distance of the instruments were varied to study the spatial extent of the x-rays. In this report we shall describe the x-ray instruments, the observations made, and give a brief overview of the results.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFMAE21A1099A
- Keywords:
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- 3300 METEOROLOGY AND ATMOSPHERIC DYNAMICS;
- 3304 Atmospheric electricity;
- 3324 Lightning;
- 3329 Mesoscale meteorology;
- 3394 Instruments and techniques