From the samples taken on March 27, from the same places where plutonium and uranium were detected. Now they tell us one month later.
From TEPCO's press release on April 27, 2011 (English):
As part of monitoring activity of the surrounding environment, we conducted an analysis of plutonium contained in the soil collected on March 21st and 22nd at the 5 spots in Fukushima Daiichi Nuclear Power Station. As a result, plutonium 238, 239 and 240 were detected.
As the result of the plutonium analysis in the soil from the sample from the 3 periodic sampling spots on April 14th, plutonium 238, 239 and 240 were detected as shown in Attachment 1. In addition, as the result of gamma ray nuclide analysis from the same sample, radioactive materials were detected as shown in Attachment 2.
Besides, as the result of the americium and curium analysis in the soil from 2 samples among the 3 periodic sampling spots in which plutonium was detected on March 28th amerium [sic] 241, curium 242, 243, and 244 were detected.
We have reported the results of analyses to the Nuclear and Industrial Safety Agency and the government of Fukushima Prefecture.
We will continue to conduct the similar analysis.
Here's the Attachment 3 that shows the analysis:
Americium and curium do not exist in nature. Half-life of the nuclides are as follows:
Am-241: 432 years
Cm-242: 162.8 days
Cm-243: 29.1 years
Cm-244: 18.1 years