Minami Soma's Assemblyman Koichi Ooyama says he simply took the sample to a laboratory in Minami Soma instead of waiting for the city officials to come back to work on Monday. The result, presented in his blog, was:
Germanium semiconductor detector for 600 seconds
718,000 becquerels/kg [of radioactive cesium]
margin of error 10%
He says the sample was from a different location than the sample that Professor Yamauchi had tested. Assemblyman Ooyama says he will be giving a press conference at 11AM on Monday February 19.
In his blogpost, Ooyama mentions OPCOM institute of isotopes. It is an arm of the NGO called HCR (Heart Care Rescue) which has been active in supporting people in the nuclear disaster since last March.
HCR's Facebook page has additional information of the surface radiation levels of this mysterious substance:
【今消されたツイート】「黒い粉」通報によりHCRの専門部会OPCOM Institute of Isotopes緊急出動、放射線測定を済ませて只今帰還。南相馬市営住宅の駐車場でγ＋β＋α：61.321μSv/h、γ＋β：15.622μSv/h,残り45.699μSv/h：α線！
(Tweet that just got deleted) Emergency survey by OPCOM Institute of Isotopes, special arm of HCR, upon the discovery of "black dust". In the parking lot of a public housing project of Minami Soma City, measurement was:
which means α: 45.699μSv/h
If this is the same public housing apartments that the blogger "Night that never ends" wrote about, then people, including children, have been living there.