I received key for gamma rays and normal ranges for each element from EPA

Thank you for contacting the U.S. Environmental Protection Agency. We
appreciate your concern. It’s important to know that the U.S. Nuclear
Regulatory Commission has said we do not expect to see radiation at
harmful levels reaching the U.S. from damaged Japanese nuclear power
plants.

The Environmental Protection Agency maintains a nationwide radiation
monitoring system known as RadNet. This system continuously monitors the
nation's air and regularly monitors drinking water, milk and
precipitation for environmental radiation. As of 3:00pm (EDT) April 19,
2011, EPA's RadNet radiation air monitors across the U.S. show typical
fluctuations in background radiation levels. The levels detected are far
below levels of concern.

Data from each fixed RadNet monitor are transmitted to EPA’s National
Air and Radiation Environmental Laboratory hourly. These data include
the gamma radiation measured during that hour. The data are screened
against pre-set values for each monitor to identify unusual readings,
particularly elevated radiation levels. In order to increase sensitivity
for screening the spectrum for small increases in gamma radiation, EPA
divides the gamma radiation measurement data into nine different gamma
energy ranges that collectively cover the energy spectrum where
essentially all of the nuclides of concern will be detected by our
monitors.

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 a trained EPA scientist. The
review includes obtaining the gamma spectrum stored in the monitor and
evaluating that spectrum for both natural and man-made nuclides.

EPA scientists use a science called gamma spectrometry to evaluate the
complete spectrum of the monitor’s specific calibration to detect the
type and amount of gamma emitting radioactive material at that location.
In this way, EPA scientists are able to determine what specific isotopes
are present in the air at any given time.

For information on the energy ranges for the gamma charts:
The following table shows the energy ranges that correspond with the
gamma charts on our website. 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

As part of the federal government's continuing effort to make our
activities and science transparent and available to the public, the
Environmental Protection Agency will continue to keep all RadNet data
available in the current online database. Please see
www.epa.gov/japan2011 for more information.