Have you ever wondered why people visiting the site of the Fukushima nuclear accident are only dressed up in coveralls and masks?  In my post on December 18th entitled ‘Hiding in the Basement’, I explained that gamma radiation requires a sheet of lead to stop it so the coveralls are clearly not protecting Fukushima visitors against radiation.

Our bodies cope with low levels of radiation everyday because we absorb about 0.024 Sieverts per year from the natural environment and the same amount is absorbed during a full-body scan in hospital.  One Sievert is equivalent to 1 Joule absorbed per kilogram of body mass. If you hold a tennis ball as high above your head as you can reach and let it fall to the ground, then the ball hits the ground with about 1 Joule of kinetic energy.  Your heart uses about 1 Joule of energy per beat.

The estimated maximum dose received by residents living close to Fukushima was 0.068 Sieverts or about three annual doses.  The visitors’ coveralls and mask are protecting them from ‘hot’ particles that are often produced during a nuclear accident. ‘Hot’ particles can be inhaled or ingested and continue to emit radiation when inside the body thus delivering a large concentrated dose to a relatively small number of surrounding cells, which are disrupted and destroyed by the high-levels of energy.  ‘Hot’ particles are small pieces of radioactive material and vary in size from tens of nanometres to a few millimetres, so that they don’t have high penetrating power and can be detected using a Geiger counter.