GODOT: An introduction

Gamma-ray Observations During Overhead Thunderstorms (GODOT)

GODOT is an instrumentat to measure radiation from lightning from the ground


A GODOT detector unit consists of a scintillator coupled to a PMT (photomultiplier tube). When a gamma-ray or high energy electron interacts in the scintillator an amount of light proportional to the energy deposited is released. This light is converted to photoelectrons in the PMT that form a current which is read out as an analog voltage signal. An ADC (analog digital converter) reads in the analog voltage signal and returns an ADC amplitude, which is the integrated analog voltage signal (see figure). For a discussion of how this analog signal is calibrated to an equivelent incident particle energy, please read this.

Summary of Instrumentation


GODOT consists of five radiation detectors, summarized below.


Scintillator
Size
HVPS Emin Emax Description
SN
Plastic 5x5" 1100V 108keV 19MeV Fast timing (high count rates), poor energy resolution, very sensitive (easily saturated)
eRC1491
Plastic 1x1" 690V
102keV 6.1MeV Fast timing (high count rates), poor energy resolution, less sensitive (hard to saturate)
eRC1489
NaI(Tl) 5x5" 1000V 147keV 13MeV Slow timing (low count rates), excellent energy resolution
eRC1490
Empty 1x1" 690V - - No Scintillator, active PMT, noise check for HVPS
eRC1488
50 Ω Cable - No
- - 6" Cable, noise check for EMI interference
eRC1386

Summary of Electronics

ADCs

GODOT uses Bridgeport eMorpho Multichannel Analysers for the ADC of the detector outputs. Information about eMorphos is available here. A summary of the GODOT raw data file is discussed here.

Plastic NaI(Tl)
ADC Pulse Width (662keV Gamma)
~100ns
~1μs
Maximum Trigger Rate
1.84/μs 0.20/μs
Turnaround Pulse Rate
5/μs 0.56/μs

A table of the eMorpho DSP configurations on 15-12-30/00:58:26 is here.

Photos


Top-open view of GODOT. Lenovo records data from the 5 ADCs on the left. The metal box in the bottom left corner is a GPS unit that conditions the software clock on the computer. Upper right shows 50 Ohm terminated BNC cable serving as check against radio noise and other forms of EMI. The two small detectors on top sit above the two large detectors. The high voltage power supplies (HVPS) are under the metal tray holding the computer, ADCs, and GPS.