1 year of the RADOS DIS1 Dosimetry System at CERN

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1 year of the RADOS DIS-1 Dosimetry System at CERN

• Thomas Otto, SC-RP, CERN
• and
• Personnel of the Individual Dosimetry Service

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Personal Dosimetry at CERN

• A service of the Radiation Protection Group
• Distribution and evaluation of passive dosimeters
  to 5000 persons/year (3000 regular customers)
• Operation under authorisation by the Swiss
  federal office for public health, following both
  Swiss and French regulations.
• Categories
• Regular personnel, must have med. fitness
  certificate (Staff, contractors, Regular users)
• Short term visitors, med. certificate waived for
  one visit of not more than 2 months per year

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Reading the future

• Number of dosimeter users is fluctuating,
  depending on experimental programme
• A dosimeter is obligatory for work in designated
  areas
• Major experiments are not (yet) able to give
  reliable figures for personnel working in
  designated areas
• For procurement, the service can only make an
  overestimated projection into the future

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Dosimetry by photographic film

• CERN the last Dosimetry Service in Switzerland
  to have used film dosimeters
• Film dosimeter failed to fulfil requirements of
  CH dosimetry ordinance (1999)
• linearity in dose, energy
• detection threshold

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Subscription-based Service

• Subscription of the user to regular
  distribution of a new film dosimeter
• Distribution by internal mail
• Service free for CERN clients important number
  of unnecessary dosimeters

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Film-Dose Relationship

• Direct relationship User-Film-Dose
• An unused film generates a 0 dose record

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Replacement of Film-Dosimetry
The technology of personal dosimetry is not a
CERN core competence. It can be bought from
other, more competent partners. The special
irradiation conditions make it desirable, that
the service is under close control by CERN

• We were looking for
• A dosimetry system owned by CERN (no
  subscription)
• A manpower-un-intensive technology (excludes
  TLD-based dosimeters)
• A tailored system to the special needs (lots of
  visitors with short term presence, suitable
  neutron detector)

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A new dosimeter type

• Technical/ Commercial Market Survey (2003)
• PSI and RADOS inform CERN of the DIS-1 dosimeter
• Already in small-scale use at PSI
• Received approval by Authorities
• Introduction prepared at Beznau NPP

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RADOS DIS-1 Dosimeter

• Measurement principle
• Ionisation chamber
• Physical storage of charge, infalsifiable
• User triggers conversion to dose in reader station

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DIS System at CERN

• History
• Spring 2004 Contract signature
• July 2004 40 Reader Stations installed
• Sept. 2004 First 800 dosimeters in use
• Jan. 2005 Changeover completed, 3000 dosimeters
  in use
• Feb. 2005 1st periodic call back of 400
  dosimeters for annual calibration check
• Sept. 2005 Fully regular service taken up

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The CERN dosimeter

• Owned by CERN
• 5500 DIS-1
• 40 DBR-1 readers
• Software, computers
• DBR Maintenance
• Raditec AG
• Fast Neutron dosimeter
• annual delivery and evaluation by PSI

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Connection of Databases
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The CERN DIS Network
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The DIS-Dose relationship

• One DIS-1 dosimeter will deliver many dose values
  during its use.
• An unused dosimeter generates no reading.

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The Challenge

• An approved dosimetry service must report
  personal dose once per month for every monitored
  individual
• At CERN, many persons access controlled radiation
  areas infrequently
• Researchers are not at CERN during the full year
• How to assure periodic dose records ?

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Distributionof 40 reader stations

• At accelerator access points
• and places of large public frequentation

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Direct contact with users

• Basic information is maintained on the services
  website
• Mass-e-mailing of certain groups of users,
  selected by SQL from the dosimetry database
• All e-mail from users will be answered within a
  working day.
• Reminder schedules

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Hunting late readings

• Reminder by e-mail (SQL-selected in database)
• After 3rd reminder
• Blocking of access to controlled radiation areas
  with automatic access control
• Requesting return of the obviously unneeded
  dosimeter

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Feedback from users

• Positive attitude towards the new technology
• Alerting of failing readers
• Suggestions for improvement
• Closer contact (by e-mail)

• Unwillingness to take responsibility for
  dosimeter and/or its periodic readout
• Analysis of the ?Sv

• User satisfaction poll
• Users appreciate
• Modern system
• Availability of service
• Communication with service

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Summary

• DIS-1 system introduced at CERN
• to respond to requests from authorities
• to reduce technical complexity of dosimetry
• The setup of DIS-1 at CERN
• DIS-1 represents a shift to the usual
  dosimeter-dose paradigm
• Maintaining close contact to users
• First experiences and user feedback are presented
• Some problems with calibration (reproducibiliyty,
  Hp(0.07))

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Thank you

• The helpful staff of RADOS, Raditec AG and PSI
  for delivering and installing the dosimetry
  system
• The personnel of the CERN dosimetry service, for
  assigning and handing out 1000s of CERN
  dosimeters
• The CERN personnel fortheir interest and
  forplaying the game