The following table shows the energy ranges that correspond with the
gamma chart. Radioactive material from Japan could be
seen in various energy ranges, depending on the specific radionuclide.
Iodine-131 and cesium-137 would primarily be seen in ranges 3 and 5,
respectively, along with other naturally occurring radioactive
materials.

Please note that fluctuations in the gamma readings may be caused by a

number of factors, primarily naturally occurring radioactivity in the
environment. Two of the most prominent naturally-occurring radionuclides
in air are lead-214 and bismuth-214. Natural levels of these nuclides
fluctuate significantly in the environment and their primary gamma
energies are similar to those of cesium-137 and iodine-131. When the
RadNet computer system detects a reading from a monitor that is outside
the range of background levels typically seen by that monitor, those
data are flagged to be reviewed by an EPA scientist. The review includes
obtaining the gamma spectrum stored in the monitor and evaluating that
spectrum for both natural and man-made nuclides.

Energy Ranges

Energy | Gamma Energies
Range | (keV) Number |
---------+---------------------
1 | Reserved by
| software for
| instrument
| stabilization
---------+---------------------
2 | 100-200
---------+---------------------
3 | 200-400
---------+---------------------
4 | 400-600
---------+---------------------
5 | 600-800
---------+---------------------
6 | 800-1000
---------+---------------------
7 | 1000-1400
---------+---------------------
8 | 1400-1800
---------+---------------------
9 | 1800-2200
---------+---------------------
10 | 2200-2800