Radiological risk assessment of outdoor ²²²Rn and ²²⁰Rn around rare earth element and uranium mines from Northern Vietnam.

The outdoor ²²²Rn and ²²⁰Rn concentrations at 320 sampling points at 1m above the ground in different sites surrounding rare earth element (REE) and uranium mines from northern Vietnam were measured using the RAD7. Results showed that ²²²Rn concentrations were always higher than ²²⁰Rn concentrations with large variation ranges from 25.7 to 573 Bq/m3 and from 18.5 to 385 Bq/m3, respectively. The high correlation between ²²⁰Rn and ²²⁸Ra concentrations in surface soil of the studied sites were observed. The highest ²²⁰Rn and ²²²Rn concentrations are found at the sampling points of the REE NX-Lai Chau site. The ²²⁰Rn and ²²²Rn activities surrounding the REE mines were found to be higher than those surrounding the uranium mines. The average annual committed effective doses originated from the inhalation of ²²⁰Rn and ²²²Rn outdoor concentrations is about five times higher than the worldwide average value as reported in UNSCEAR (2000).