Americium-241 has a half life of 432.7 years.
Source: TEPCO
Press Release (Jun 11,2011)
Detection of radioactive materials in the soil in Fukushima Daiichi Nuclear Power Station (16th release)
As part of monitoring activity of the surrounding environment, we conducted
an analysis of plutonium contained in the soil collected on March 21 and 22
at the 5 spots in Fukushima Daiichi Nuclear Power Station. As a result,
plutonium 238, 239 and 240 were detected.
(Previously announced)
As a result of plutonium analysis in the soil from the samples at the 3
periodic sampling spots collected on May 26, plutonium 238 was detected as
shown in the attachment 1.
In addition, as a result of nuclide analysis of the gamma ray contained in
the soil, radioactive materials were detected as shown in the attachment 2.
Since plutonium and uranium were detected from the samples at the 3
periodic sampling spots collected on April 11 and 25, we conducted
americium and curium analyses. As a result, americium 241, curium 242, 243,
and 244 were detected as shown in the attachment 3.
Today, we informed the Nuclear and Industrial Safety Agency and the
government of Fukushima Prefecture of the results.
We will continue conducting the similar analysis.
Attachment1: Fukushima Daiichi Nuclear Power Station:
Plutonium analysis result in the soil(PDF 9.34KB)
Attachment2: Result of gamma ray nuclide analysis of soil(PDF 10.9KB)
Attachment3: Fukushima Daiichi Nuclear Power Station:
Americium and curium analyses result in the soil(PDF 12.2KB)