Seven European countries are reporting low but unusual levels of radiation for a second week running.
According to the United Nations nuclear agency, "the continued presence of trace levels of iodine-131 in the atmosphere" are being reported by the Czech Republic, Austria, Slovakia, Germany, Sweden, France and Poland.
The agencysaid the levels of iodine-131 that have been measured do not pose a public health risk. Although they do not yet know the cause of the radiation, it is not believed to have been caused by the Fukushima Daiichi nuclear accident in Japan.
Iodine-131 is a short-lived radioisotope that has a radioactive decay half-life of about eight days.
