A microfluidic dosimetry cell to irradiate solutions with poorly penetrating radiations: a step towards online dosimetry for synchrotron beamlines

Abstract

Synchrotron radiation can induce sample damage, whether intended or not. In the case of sensitive samples, such as biological ones, modifications can be significant. To understand and predict the effects due to exposure, it is necessary to know the ionizing radiation dose deposited in the sample. In the case of aqueous samples, deleterious effects are mostly induced by the production of reactive oxygen species via water radiolysis. These species are therefore good indicators of the dose. Here the application of a microfluidic cell specifically optimized for low penetrating soft X-ray radiation is reported. Sodium benzoate was used as a fluorescent dosimeter thanks to its specific detection of hydroxyl radicals, a radiolytic product of water. Measurements at 1.28 keV led to the determination of a hydroxyl production yield, G(HO . ), of 0.025 ± 0.004 µmol J−1. This result is in agreement with the literature and confirms the high linear energy transfer behavior of soft X-rays. An analysis of the important parameters of the microfluidic dosimetry cell, as well as their influences over dosimetry, is also reported.

Superoxide Production under Soft X-ray Irradiation of Liquid Water

“…Unlike the γ irradiation experiments, the soft X-ray irradiation experiments (using the soft X-ray branch of the METROLOGIE beamline at synchrotron SOLEIL) were performed using a dedicated microfluidic setup to solve the problem of the poor penetration of soft X-rays in liquid media. This setup consists of a microfluidic cell that was placed at a 1 mm air gap from the exit window of the IRAD setup. ,, The IRAD setup is a differential pumping system that terminates with a 150 nm-thick silicon nitride window, 1 mm × 1 mm large (FASTEC, Northampton, U.K.). The entire irradiation setup, including the irradiation microfluidic cell, is described in detail in a previous article .…”

“…Soft X-ray are strongly attenuated in liquid media and this limitation was overcome by the use of a microfluidic setup, with a microfluidic channel depth of 5.3 μm (described by Huart et al), 17 ensuring a much more homogeneous dose distribution. The soft X-ray beam, traveling in the vacuum chamber, was extracted in air to irradiate the sample flowing in the microfluidic cell, using the IRAD setup 17 described in Section 2.3. An inline UV detection scheme was implemented that allowed the use of standard superoxide probes 18 in the context of low dose and poorly penetrating radiations.…”

“…The entire irradiation setup, including the irradiation microfluidic cell, is described in detail in a previous article. 17 Irradiations were conducted at 21 °C.…”

“…A modified version of the previously used microfluidic cell 17 However, two modifications were introduced: First, a Si 3 N 4 membrane (exit membrane) was added to the back silicon chip and this exit membrane was 200 nm thick and 1 mm × 300 μm large. It was rotated by 90°with respect to the Si 3 N 4 membrane of the front silicon chip.…”

“…Our primary goal was to detect and quantify the HO 2 ° production from the direct pathway. We took advantage of our microfluidic cell adapted to perform irradiation measurements under anoxic conditions . In addition, as the reductive conditions in the ionization track are unknown, we performed irradiation measurements under oxic conditions to measure the indirect pathway as well.…”