Three new projects for the CERN Dosimetry Service

The measures for the protection of personnel against ionising radiation at CERN are very strict. As soon as a new directive is issued by EURATOM, the Laboratory ensures it is adopted quickly. Since every system can be perfected, Pierre Carbonez and the Dosimetry Service team are working on three new projects aimed at improving the safety of workers exposed to ionising radiation in the course of their work on the CERN sites.




The two types of dosimeters currently in use at CERN.

4,700 people at CERN have a dosimeter. Every month, they have to have their dosimeter scanned by one of the 45 readers installed at various strategic locations around the Laboratory. Each month, the dosimetry team led by Pierre Carbonez exchanges around 450 dosimeters to recalibrate them and prepare them for further use. “These dosimeters are passive detectors which record the doses caused by beta, gamma and neutron radiation," explains Pierre Carbonez. "Using the digital readers installed in 2005, we can regularly check the gamma radiation dose that each worker receives on the site. This way, we can act immediately to ensure the maximum dose is not exceeded.”

The annual dose limit for most CERN employees and professional contractors is 6 mSv. However, as soon as the dosimeter shows a value of 2 mSv, the Dosimetry Service alerts the person concerned and their supervisor in order to reduce the time the person spends in controlled areas. "Our aim is for the dose received to be as low as possible. Over the past five years, 99% of personnel who have a dosimeter received less than 1 mSv per year," says Pierre Carbonez.

But settling for a decent score is a good strategy, especially when you're talking about radioprotection. So Pierre Carbonez and his team are working on three innovative projects, the first of which relates to training. "Anyone wishing to obtain a dosimeter must follow a theoretical course about radiation protection,” explains Pierre Carbonez.  "We will modify the content and presentation of the course in order to more effectively inform workers supplied by outside contractors.  In general, external contractors may be very familiar with the working environment of nuclear power plants, but are not familiar with the very specific environment of particle accelerators. So, from next year onwards, we will set up a practical class as a complement to the theoretical one.”



In addition to passive dosimeters, personnel are required to wear so-called “active” dosimeters in some areas, which continually display the accumulated dose received, for instance, during work on an accelerator. "Currently, personnel wearing this type of dosimeter must register the read-out values in a log book," explains Pierre Carbonez. "This data is then entered manually into the databases by the Radiation Protection service. This process will be improved with the introduction of the digital readout of dosimeters. There will no longer be any delay between dose accumulation and data acquisition, thus improving the safety of personnel and giving us better statistics on dose distribution at CERN."





After one year of use, all dosimeters must be checked. Any dosimeter showing an error higher than 5% is rejected. "We're working on a project for the construction of a new calibration laboratory. The current laboratory operates well but relies on ageing instruments, and in the field of dosimetry it is important to remain at the forefront of technology. The new building will house state-of-the-art equipment which will allow us to perform faster and more precise calibration measurements," Pierre Carbonez concludes. "The Dosimetry Service is accredited by the Swiss authorities. Our aim is for the calibration laboratory to receive the same accreditation."

The three projects have already been launched and the results will start to emerge in the coming months.


Understanding our radiation dose limits

In Europe, the maximum admissible dose is defined by the authorities in each country and regulated by EURATOM. Over the past five years at CERN, not a single member of the personnel has exceeded 6 mSv.  The legal limits are: 6 mSv for Category B workers, and 20 mSv for Category A workers. The majority of CERN personnel are Categroy B workers, and onnly around 100 people are classified in Category A, including the fire-fighters and members of the radiation protection team.

It's useful to recall, by comparison, that the average natural dose of ionising radiation accumulated every year by an individual living in Switzerland is 3.5 mSv. An airline pilot on long-haul flights can easily accumulate an annual dose higher than 3 mSv. Medical scanners emit a single dose close to 10 mSv, while astronauts regularly accumulate doses of up to 50 mSv during missions in space.


Read the new HSE Advice section for more information regarding the proper usage of your dosimeter.

by CERN Bulletin