Radiation over Atlantic October 8, 2008Posted by dorigo in personal, physics, science, travel.
Tags: cosmic rays, dosimetry, radiation
Swamped by last-minute obligations before leaving to Fermilab for an owl shift as a Scientific Coordinator in the CDF control room, I was prevented from contributing to the recent discussions on the Nobel prize in Physics, other than providing the original post below. After an uneventful trip, I find myself jet-lagged this afternoon in my good-old office in the CDF portakamps. Everything looks and feels as always: home.
Anyway, I want to report on a small scientific experiment here. I brought with me in my trip a digital dosimeter, which records exposure to ionizing radiation as a function of time. The device (which I described here) is a nifty little thing I bought some time ago, and still carry around when I work around particle physics experiments. It measures radiation in milliRem, but is actually very sensitive – it can signal doses in increments as small as 100 nanoRems, which I figured out correspond to about a dozen minimum-ionizing particle hits.
So, about the experiment: I set integration times of 3600 seconds, and turned the device on before leaving Munich with LH434, a flight departing to Chicago at 9AM this morning. The plane actually left with a half hour delay, and finally arrived at O’Hare at about noon local time, ten full hours later. Below are the radiation doses recorded by the instrument during the flight.
As you immediately notice, the purple points describe a quickly rising function, which levels off and finally goes back down. The maximum instantaneous levels of radiation recorded by the instrument appear in line with what one would expect: as the plane takes off and gains elevation, the screening effect of our atmosphere is reduced, and the radiation increases. Local effects may have an impact in the distribution, and they thus depend on time, while the plane traveled above Europe, Greenland, Canada, and the north-western US; but they are not observable given the uncertainty in the points -0.1 mRem is the smallest digit provided when rates are measured in the logs.
The blue line instead puzzles me. It is the integrated dose per hour, and it should be a much more accurate description of the radiation field. But it bounces back and forth, after leveling at about 0.25 mRem/h. What are the causes of this funny behavior ? Here is what I can think of:
- a real fluctuation in the flux of cosmic rays, due to magnetic field effects
- an erroneous recording of data by the instrument, specifically at 14h and 16h (Munich time)
I instead discard the option that the fluctuations are statistical in nature: 0.01 mRem corresponds, as I noted above, to roughly a thousand hits.
Any other idea ?
PS (mainly for the record): another simple experiment I performed with the dosimeter is discussed here.