Archived Information from the 2011 Japan Radiation Event
This information is no longer being updated as this is not considered a local hazard at this time.
On this page:
Radiation from the damaged nuclear reactors in Japan is not a public health risk in Oregon. Oregon Public Health Division’s Office of Environmental Public Health, records frequent measurements from EPA monitors in two Oregon locations: Corvallis and Portland. This page will be updated Mondays and Thursdays with the most current measurements. The radiation levels have been decreasing and most recently are at less than detectable levels.
The monitoring stations have continually shown normal background levels of radiation. The radiation levels would have to be hundreds of thousands of times higher than these readings before Oregonians need to take any protective actions, according to the U.S. Environmental Protection Agency.
In a typical day, Americans receive doses of radiation from natural sources like rocks, bricks and the sun that are about 100,000 times higher than what we have detected coming from Japan. For example, the levels we're seeing coming from Japan are 100,000 times lower than what you get from taking a roundtrip international flight.
Public Health officials don’t anticipate significant increases in gross beta as a result of the Japanese disaster. State health physicists are analyzing Portland air monitor filters and, as had been expected, detected shortly after the March 11 events in Japan, the presence of trace amounts iodine 131 and cesium 137, isotopes connected with Japan’s nuclear emergency. There is no health risk at this time due to events in Japan. The trace amounts of radioactive iodine and cesium that had been detected are far lower than levels that would be a health concern. These isotopes are a subset of the gross beta measurements.
The radiation monitoring results are consistent with findings reported by federal, California, Washington and Canadian partners. As expected, because of the nearly 5,000 mile distance from Japan and air diffusion, radiation reaching our state is so diluted there is no health risk here, making protective action unnecessary.
For example, the amount of radiation from iodine 131 on March 21 was about 80 nanorems, or .00008 millirems. This is a small amount; a chest x-ray is about 10 millirems. For example at the level from the March 21 sampling, a person would have to be exposed to that amount of radiation for 80,000 years before needing to take potassium iodide (KI) to decrease radiation risk.
The chart below shows radiation measures called a “gross beta” count. It tracks how much radioactive material that emits beta radiation is in the environment. Gross beta counts are used because they give us the fastest indication of any change in radiation levels. They’re measured in “counts per minute.”
Gross Beta Count Levels
Location |
Most Recent
Daily Average
05/12/2011 |
Last
month
average |
Last
month
highest |
last
month
lowest |
Last
year
average |
Last
year
highest |
Last
year
lowest |
|---|
All measurements in gross beta (counts per minute). |
| Portland, OR+ |
19.6 |
14.6 |
49 |
8 |
* |
* |
* |
| Corvallis, OR+ |
22.0 |
19.2 |
44 |
7 |
* |
* |
* |
| Eureka, CA+ |
7.0 |
10.7 |
42 |
5 |
* |
* |
* |
+ As you view the data, be aware that there are often large differences in normal background radiation among the monitoring locations because background radiation levels depend on altitude and the amount of naturally occurring radioactive elements in the local soil. What is natural in one location is different from what is natural in another.
* * Electrical interference can cause spikes, shown on graphs, as one point significantly higher than the rest of the data.
* Data unavailable from EPA.
Daily data since March 1, 2011
Gamma Spectroscopy Analysis, Portland Station
The estimated overall maximum biological effect from the trace amounts of radiation currently detected in Oregon from the events in Japan is about 0.000160 mrem per day. To put this into perspective, a person would need to be exposed to this level all day, everyday for over 100 years to equal the exposure from ONE chest X-ray.
| |
Cesium - 137 |
Iodine - 131 |
Date |
Activity
pCi/m3 |
Bio Effect
mrem |
Activity
pCi/m3 |
Bio Effect
mrem |
| 05/09 - 05/12/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
| 05/05 - 05/09/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
05/02 - 05/05/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
| 04/28 - 05/02/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
| 04/25 - 04/28/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
| 04/21 - 04/25/2011 |
<MDA* |
<MDA* |
<MDA* |
<MDA* |
| 04/18 - 04/21/2011 |
<MDA* |
<MDA* |
0.000678 |
0.000003 |
| 04/14 - 04/18/2011 |
<MDA* |
<MDA* |
0.0003085 |
0.000002 |
| 04/11 - 04/14/2011 |
<MDA* |
<MDA* |
0.002863 |
0.000011 |
| 04/07 - 04/11/2011 |
0.000594 |
0.000002 |
0.001129 |
0.000006 |
| 04/04 - 04/07/2011 |
0.00177 |
0.000005 |
0.0062 |
0.000023 |
| 04/01 - 04/04/2011 |
0.0011327 |
0.000003 |
0.00583362 |
0.000022 |
| 03/31 - 04/01/2011 |
<MDA* |
<MDA* |
0.0008 |
0.000001 |
| 03/30 - 03/31/2011 |
<MDA* |
<MDA* |
0.012 |
0.000015 |
| 03/29 - 03/30/2011 |
<MDA* |
<MDA* |
0.0008 |
0.000001 |
| 03/28 - 03/29/2011 |
<MDA* |
<MDA* |
0.003 |
0.000004 |
| 03/25 - 03/28/2011 |
<MDA* |
<MDA* |
0.002 |
0.000006 |
| 03/24/2011 |
<MDA* |
<MDA* |
0.0521 |
0.000066 |
03/23/2011 |
<MDA* |
<MDA* |
0.0986 |
0.000125 |
03/22/2011 |
0.0019 |
0.000002 |
0.12 |
0.000153 |
03/21/2011 |
<MDA* |
<MDA* |
0.065 |
0.000083 |
*Minimal Detectable Activity
Units
- Picocurie (pCi): Measures the rate of decay of a sample of radioactive material.
- Millirem (mrem): Equals 1/1000 of a rem (Roentgen equivalent man). Measures the biological effect (risk of illness) of a dose of radiation on a person.