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Absorbed dose is a dose quantity which is the measure of the energy deposited in matter by ionizing radiation per unit mass. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection (reduction of harmful effects), and radiology (potential beneficial effects, for example in cancer treatment). It is also used to directly compare the effect of radiation on inanimate matter such as in radiation hardening. The SI unit of measure is the gray (Gy), which is defined as one Joule of energy absorbed per kilogram of matter. The older, non-SI CGS unit rad, is sometimes also used, predominantly in the USA. Conventionally, in radiation protection, unmodified absorbed dose is only used for indicating the immediate health effects due to high levels of acute dose. These are tissue effects, such as in acute radiation syndrome, which are also known as deterministic effects. These are effects which are certain to happen in a short time. The time between exposure and vomiting may be used as a heuristic for quantifying a dose when more precise means of testing are unavailable. radiation therapy The measurement of absorbed dose in tissue is of fundamental importance in radiobiology as it is the measure of the amount of energy the incident radiation is imparting to the target tissue. The absorbed dose is equal to the radiation exposure (ions or C/kg) of the radiation beam multiplied by the ionization energy of the medium to be ionized. For example, the ionization energy of dry air at 20 °C and 101.325 kPa of pressure is 33.97J/C. (33.97 eV per ion pair) Therefore, an exposure of 2.58e-4C/kg (1 roentgen) would deposit an absorbed dose of 8.76e-3J/kg (0.00876 Gy or 0.876 rad) in dry air at those conditions. When the absorbed dose is not uniform, or when it is only applied to a portion of a body or object, an absorbed dose representative of the entire item can be calculated by taking a mass-weighted average of the absorbed doses at each point.

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Innovative Lab on Fiber dosimeters for ionizing radiation monitoring at ultra-high doses

Georgi Gorine, Federico Ravotti

We report on a innovative Lab on Fiber (LOF) dosimeter for ionizing radiation monitoring at ultra-high doses. The new dosimeter consists in a metallo-dielectric resonator at sub-wavelength scale supporting localized surface plasmon resonances realized on the optical fiber (OF) tip. The resonating structure involves two gold gratings separated by a templated dielectric layer of poly(methyl methacrylate) (PMMA). Two LOF prototypes have been manufactured and exposed, at the IRRAD Proton Facility at CERN in Geneva, to 23 GeV protons for a total fluence of 0.67x10(16) protons/cm(2), corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrate the "radiation resistance" feature of the LOF devices and a clear dependence of the reflected spectrum on the total dose, expressed by a cumulative blue-shift of similar to 1.4 nm of the resonance combined with a slight increase of 0.16 dBm in the reflected spectrum. According to the numerical analysis and the literature, the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for High Energy Physics (HEP) experiments.

SPIE-INT SOC OPTICAL ENGINEERING2019

In this work, we report on the first demonstration of Lab on Fiber (LOF) dosimeter for ionizing radiation monitoring at ultra-high doses. The new dosimeter consists in a metallo-dielectric resonator at subwavelength scale supporting localized surface plasmon resonances realized on the optical fiber (OF) tip. The resonating structure involves two gold gratings separated by a templated dielectric layer of poly(methyl methacrylate) (PMMA). Two LOF prototypes have been manufactured and exposed at the IRRAD Proton Facility at CERN in Geneva to 23 GeV protons for a total fluence of 0.67 x 10(16) protons/cm(2,) corresponding to an absorbed dose of 1.8 MGy. Experimental data demonstrated the "radiation resistance" feature of the LOF devices and a clear dependence of the reflected spectrum versus the total dose, expressed by a cumulative blue-shift of similar to 1.4 nm of the resonance combined with a slight increase of 0.16 dBm in the reflected spectrum. The numerical analysis carried out to correlate the experimental results with the dimensional and physical properties of the resonator, expected to be tightly connected to the absorbed dose, suggests that the main phenomenon induced by exposure to proton beam and able to explain the measured spectral behavior is the reduction of the PMMA thickness, which is also consistent with past literature in the field. Preliminary results demonstrated the potentiality of the proposed platform as dosimeter at MGy dose levels for high energy physics experiments.

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