Neutron Count at Different Altitudes
Calgary, Alberta, Canada
|The following observations were all
taken in the vicinity of Calgary, Alberta, Canada. All were taken
within a three hour period, starting at 3:45 PM on Sunday, July 30,
2006. The altitudes were derived from a handheld GPS, and the highest
and lowest altitudes were verified with topographical maps.
The neutron readings were taken with a Reuter Stokes RS-P4-0820-103 Helium 3 detector tube and a Ludlum model 2000 scaler, using a voltage of 1700 volts. No moderator was used with the tube.
Note that since this equipment has not been calibrated, the absolute values are meaningless. However a valid comparison can be made of the relative magnitude of the counts recorded. (Calibration would allow us to convert the readings obtained to the actual number of neutrons per cm. per minute. It would take into account the size of the active area of the tube and the tube's efficiency.)
365 Counts in the First 10 Minutes
402 " " " 2nd " "
417 " " " 3rd " "
Average count at 6500 Feet: 39.5 CPM
265 Counts in the First 10 Minutes
277 " " " 2nd " "
288 " " " 3rd " "
Average count at 4800 Feet: 27.7 CPM
193 Counts in the First 10 Minutes
225 " " " 2nd " "
203 " " " 3rd " "
Average count at 3550 Feet: 20.7 CPM
|UPDATE: On November 10, 2007, two flights
were taken on a commercial airliner, and background neutron counts were
recorded on a Bubble Technology Industries bubble neutron detector, a
thermally compensated PND model, with a calibrated sensitivity of 28
bubbles per mRem. Unlike the He3 tube, the BTI bubble neutron detectors
react only to high energy neutrons.
The first flight, fron Calgary to Vancouver B.C. was about 1 hour and 15 minutes at a cruising altitude of about 39,000 feet, per GPS. By the end of the flight, 4 bubbles had appeared. The bubble detector was then re-pressurised for two hours, until the start of the second flight.
The second flight, from Vancouver to Honolulu, was slightly under 6 hours, at an altitude that ranged from 34,000 feet to 38,000 feet, per GPS. At the end of the flight, 20 bubbles had appeared.
The return flight from Honolulu to Vancouver on November 18, 2007 was around 5 hours duration, and there were 10 bubbles at the end of the flight. Altitude per GPS (IIRC) was around 35,000 feet.
Note that there is no easy way to convert from the number of bubbles in a bubble detector to the CPM that would have been recorded by the He3 neutron detector. For one thing, the bubble detector reacts only to high energy neutrons, and the He3 tube reacts only to thermal (very low energy) neutrons. However,a moderator could be placed around an He3 tube to slow high energy neutrons enough to be counted by the He3 tube.
If we assumed that our He3 tube was shielded from ambient thermal neutrons, then equipped with a moderator to slow the high energy neutrons, an educated guess would be an average of around 500 CPM on the 6 hour flight described above. There is no way of calculating what the count would have been if the tube had not been shielded from the ambient thermal neutrons.
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