Passive radiation sensors such as gamma ray spectrometers detect radiation given off directly by covert nuclear material, but these are expensive and can be fooled by shielding. Existing active sensors such as X-ray machines that probe a suspect volume looking for such material are also limited by shielding effects. What is needed for a next-generation active radiation sensor is a source of deeply probing radiation that is more penetrating than X-rays, and cheaper and easier to generate than existing X-ray machines. Cosmic rays from space may be just the ticket. As these enter Earth’s atmosphere they collide with air molecules and produce showers of muons. A typical cosmic-ray muon can pass through more than 10 metres of water and they are commonplace everywhere on earth; millions of them pass harmlessly through each of us every day. When they meet an object, the muons leave it at an angle that depends on the material – the denser the material, the bigger the angle. Los Alamos scientists are using this highly predictable scatter pattern to form the basis of a new, inexpensive type of detector for terrorist nuclear weapons.
They’d better hurry. The International Atomic Energy Agency (IAEA) says more than 100 countries lack the controls to prevent or even detect the theft of nuclear materials. Even in the United States, it says, nuclear regulators report that since 1996, companies have lost track of 1,500 sources of radioactivity, and less than half have since been recovered. The worst incident of involving lost radioactive sources took place in the Brazilian city of Goiania in 1987.
Scavengers dismantled a metal canister from a radiotherapy machine at an abandoned cancer clinic, and left it in a junkyard. This released the radioactive substance caesium 137 which contaminated more than 200 people in the city. Some children and adults even rubbed the deadly powder on their bodies, thinking it looked pretty as it glowed in the dark. Four subsequently died.
The threat is not just from so-called “dirty bombs” which would use conventional explosives to scatter radioactive waste. It turns out that pure plutonium and pure highly-enriched-uranium are not the only material from which a true fission explosion atomic-bomb may be made. The Oxford Research Group is working to highlight concern over so called “Metal Oxide (MOX) Fuel” which they say can be obtained from spent fuel pools at commercial power reactors and processed relatively easily into a fissionable weapon core.