Purpose
The ARRONAX cyclotron facility offers the possibility to deliver proton beams from low to ultra‐high dose rates (UHDR). As a good control of the dosimetry is a prerequisite of UHDR experimentations, we evaluated in different conditions the usability and the dose rate dependency of several radiochromic films commonly used for dosimetry in radiotherapy.
Methods
We compared the dose rate dependency of three types of radiochromic films: GAFchromic™ EBT3 and GAFchromic™ EBT‐XD (Ashland Inc., Wayne, NJ, USA), and OrthoChromic OC‐1 (OrthoChrome Inc., Hillsborough, NJ, USA), after proton irradiations at various mean dose rates (0.25, 40, 1500, and 7500 Gy/s) and for 10 doses (2–130 Gy). We also evaluated the dose rate dependency of each film considering beam structures, from single pulse to multiple pulses with various frequencies.
Results
EBT3 and EBT‐XD films showed differences of response between conventional (0.25 Gy/s) and UHDR (7500 Gy/s) conditions, above 10 Gy. On the contrary, OC‐1 films did not present overall difference of response for doses except below 3 Gy. We observed an increase of the netOD with the mean dose rate for EBT3 and EBT‐XD films. OC‐1 films did not show any impact of the mean dose rate up to 7500 Gy/s, above 3 Gy. No difference was found based on the beam structure, for all three types of films.
Conclusions
EBT3 and EBT‐XD radiochromic films should be used with caution for the dosimetry of UHDR proton beams over 10 Gy. Their overresponse, which increases with mean dose rate and dose, could lead to non‐negligible overestimations of the absolute dose. OC‐1 films are dose rate independent up to 7500 Gy/s in proton beams. Films response is not impacted by the beam structure. A broader investigation of the usability of OC‐1 films in UHDR conditions should be conducted at intermediate and higher mean dose rates and other beam energies.
Cesium-134 and -137 are prevalent, long-lived, radio-toxic
contaminants
released into the environment during nuclear accidents. Large quantities
of insoluble, respirable Cs-bearing microparticles (CsMPs) were released
into the environment during the Fukushima Daiichi nuclear accident.
Monitoring for CsMPs in environmental samples is essential to understand
the impact of nuclear accidents. The current detection method used
to screen for CsMPs (phosphor screen autoradiography) is slow and
inefficient. We propose an improved method: real-time autoradiography
that uses parallel ionization multiplier gaseous detectors. This technique
permits spatially resolved measurement of radioactivity while providing
spectrometric data from spatially heterogeneous samplesa potential
step-change technique for use after nuclear accidents for forensic
analysis. With our detector configuration, the minimum detectable
activities are sufficiently low for detecting CsMPs. Further, for
environmental samples, sample thickness does not detrimentally affect
detector signal quality. The detector can measure and resolve individual
radioactive particles ≥465 μm apart. Real-time autoradiography
is a promising tool for radioactive particle detection.
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