[time-nuts] Boeing 787 GPS reception trouble

[Jim Lux]

On 6/3/14, 5:51 AM, Chuck Harris wrote:
> nuts wrote:
> ....
>> Regarding radiation, I've used my Geiger counter at mile high altitudes
>> in Nevada and never got a count per second, even with the gamma shield
>> not used. You can look at the DOE CEMP stations:
>
> 1 Mile high is still on the ground compared to an airplane's 8 miles high.
> Those 7 additional miles of altitude result in an atmosphere that is very
> sparse with the air molecules necessary to block cosmic radiation.

A handy number to remember is 18,000 ft or 6,000 meters: that's the 
"halving height" where the air pressure is 50% of sea level, so at 
36,000 ft, the air pressure is 25%, etc.



>
> TVB's readings correlate well with graphs I have seen on other websites.

http://www.acd.ucar.edu/Events/Meetings/HEPPA/pdf_files/Aviation_Hazards/Shea.pdf


makes an interesting point that a number calculated back in the 60s 
(orders of magnitude too high) has achieved urban legend status.


page 17 has some plots.. for 9449 m (31000 ft), 2 uSv/hr, for 11,887 
m(FL390) >5 uSv/hr  (pretty big change for only 2000 meter change in 
elevation)  (1 uSv = 0.1 mrem)

another source (DoE http://lowdose.energy.gov) gives 25 mrem/yr at 427 
ft, 40 mrem/yr in Denver(5,280ft), 130 mrem/yr in Leadville (10,157 ft)

Yet another source shows (for Galactic Cosmic Rays)
0 ft	31 mrem/yr (310 uSv/yr = 1 uSv/day)
5000 ft	55 mrem/yr
10k ft	137 mrem/yr
30k ft	1.9 rem/yr  (2.1 uSv/hr)
50k ft	8.75 rem/yr (87500 uSv/yr = 10 uSv/hr)
80k ft	12.2 rem/yr


I note that this doesn't follow a nice exponential curve (e.g. it's a 
big jump from 0.14 to 1.9 with a change of from 10k to 30k ft). The Shea 
presentation from UCAR makes the point that there's a fairly complex 
radiation transport process with scattering and secondary emissions.