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General Information
Introduction
1
1-1
Section 1
General Information
1.1 Introduction
The Model 35040 Therapy Dosimeter is designed for calibration dosimetry of therapeutic radiation
treatment machines including high-energy accelerators,
60
Co, and brachytherapy equipment. The
instrument can be used for calibration, government compliance testing, installation and set-up of new
equipment, and troubleshooting.
The Model 35040 Therapy Dosimeter is a reference grade instrument that exceeds calibration
laboratories’ 1993 recommendations for linearity, long-term stability, and zero drift. The instrument uses
calibrated ion chambers to simultaneously measure and display dose and dose rate in the user specified
radiological units. At the user’s discretion, the reading may be corrected for air density by user entered
ambient temperature and barometric pressure readings.
• The highly regulated, precision electronic bias is continuously monitored. The bias voltage may be
selected from the front panel.
• The Model 35040 Therapy Dosimeter provides a timer for performing timed charge and dose
measurements. A typical application of the timer is for measuring brachytherapy sources. The
instrument supplies four timed measurement quantities, which may be added to any of the
measurement displays with the Customization software
• Triaxial ion chamber input connectors are furnished on both the front and rear of the instrument to
make it easier to set up and use.
• For the first time in a therapy dosimeter, the effective exposure time for
60
Co source is determined
from a single exposure.
1.2 Features
• Low leakage current in the instrument.
• All front panel settings are stored at power down and recalled at power up.
• A wide variety of measurements are available simultaneously; including charge, dose, current, dose
rate, accumulated charge, accumulated dose, and effective exposure time.
• Timer for performing timed charge, predicted time charge and corresponding dose measurements.
• The user may select one of 32 ion chamber calibration factors for direct readout of dose or dose
rate units.
• Dose measurement values may be displayed in units of Roentgens, rads, Sieverts, or Grays. Dose
rate measurement values may be displayed in dose units per second, minute or hour. For
brachytherapy applications, the instrument may be configured to read in Curies, becquerles, or
kerma.
• The user may enter ambient temperature and pressure for air density correction of dose and dose
rate measurements. Air density correction may be turned on or off from the front panel.
• The user may select the dose rate time divisor from the front panel.