New constant-temperature operating mode for graphite calorimeter at LNE-LNHB

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Calorimetry

Background:

• The LNE-LNHB laboratory relies on graphite calorimetry for absorbed dose unit realization.
• The traditional quasi-adiabatic operating mode faces limitations in measurement frequency and potential temperature drift.
• Existing methods restrict radiotherapy dose rate measurements to fewer than ten per day.

Purpose of the Study:

• To introduce and evaluate a novel constant-temperature operating mode for graphite calorimetry.
• To enhance the flexibility, accuracy, and automation of absorbed dose measurements.
• To improve the efficiency of calorimetric calibrations in radiation dosimetry.

Main Methods:

• Implemented a constant-temperature operating mode where both calorimeter core and jacket are maintained at fixed temperatures.
• Utilized a digital PID regulator developed with LabView software for precise core temperature control.
• Measured the difference in electrical power required to maintain core temperature during irradiation versus steady state.

Main Results:

• The new constant-temperature mode demonstrated no significant difference (<0.09%) compared to the quasi-adiabatic mode in cobalt-60 beam measurements.
• Achieved equivalent reproducibility (1sigma < 0.06%) between the two operating modes.
• The constant-temperature mode allows for numerous, automated measurements and integrates electrical calibration efficiently.

Conclusions:

• The new constant-temperature operating mode is a viable and advantageous alternative for graphite calorimetry.
• This method improves measurement efficiency, automation, and accuracy in absorbed dose determination.
• The findings support the continued development and application of advanced calorimetric techniques in radiation dosimetry.