Ordinary table salt can be used to measure radiation from radioactive substances, provided that it is stored in the dark. This has been shown in a new thesis from Lund University in Sweden, where the method has been enhanced and tested on fallout from the nuclear disasters in Fukushima and Chernobyl.
“Salt is readily available and very cheap, which gives it an advantage over the retrospective dosimeters that are currently used”, said Maria Christiansson, a doctoral student at the Department of Clinical Sciences, Lund University.
In her doctoral thesis, salt has been tested with the help of radiation safety workers in Fukushima. The staff carried small, light-tight packets of salt while they worked. The measurements corresponded well with the results from more traditional dosimeters.
The advantages of salt also include the fact that it is stored in large or small quantities almost everywhere. It is therefore possible to use it to estimate radiation exposure at the site of accidents or terrorist attacks involving radioactive substances.
“Salt is best suited to estimating radiation levels at a general level, for example in a district or housing estate, because we don’t usually carry salt around with us. However, if someone had a packet of salted nuts in their handbag, for instance, it would be possible to estimate their personal exposure”, explained Maria Christiansson.
Salt’s function as a radiation detector has also been verified through tests carried out in Svetilovichi, Belarus. This is one of the places affected by large amounts of nuclear fallout following the nuclear disaster in Chernobyl in 1986. Different types of salt packets were placed in the kitchen cupboards of local residents for just over four months.
The results showed that the salt preserved the radiation signal very well – even for low measurements – as long as it was stored in the dark. Out in the daylight, strong cardboard packaging is therefore required, whereas for salt stored in a cupboard, plastic containers also work.
The interest in measuring radiation signals in salt began in the 1980s, but the method was initially used only as a way of dating geological samples. Since then, a number of different materials and substances, including household chemicals, have been evaluated to assess whether they can be used to measure radiation from different sources. Unlike many other substances, sea salt and rock salt (the raw materials for table salt) can be used as a measurement source directly, without chemical preparation.
The measurement technique used in the thesis is optically stimulated luminescence, in which a special light from LEDs is used to determine the radiation dose. The research on the suitability of salt for use as a dosimeter is continuing, with more field studies and laboratory tests.
“At present there are not many good types of dosimeters for certain types of radiation, such as neutron radiation, which is the type that will be generated at the materials research facility ESS in Lund. Perhaps salt would work better, but it is still too early to say”, explained Maria Christiansson.