Pages scientifiques 2004

Topic 1 : Effects of Extreme Conditions in Radiation Chemistry

In numerous real situations, radical reactions occur with extreme thermodynamic conditions like temperature over 300°C, with pressure over 100 MPa, or triggered by nuclear reactions which produce elevated Linear Energy Transfer (LET) ionizing particles[1]. These parameters can induce drastic changes in the production and in the reactivity of radical species in water. The most recent data bases[2]  show a lack of knowledge. Therefore the effect of the combinations of extreme values of these conditions has never been considered: high temperature water submitted to high LET particles for instance.

In the context of the generation 4 nuclear power plant systems in which temperatures of fluid transfer should increase in order to improve the thermal-cycle yield, one system expected to be developed will involve supercritical water (374°C, 22 MPa). Consequently many fundamental questions on water radiolysis in these conditions appeared since Arrhenius extrapolation could not be applied. How to predict water decomposition in these conditions? That was essentially the aim of Dimitri Saffré PhD (2008-2011) who has performed experiments and MC simulations in a large range of temperature and LET in order to determine radiolytic yields and rate constants through an extreme condition-resistant chemical system: HBr. In situ analysis of Br-, Br₂- and Br₃- species allowed the determination of HO^Ÿ yields in various conditions of irradiation: X-rays at ESRF (FAME Line, J.L. Hazeman), ns-electron pulses from ALIENOR accelerator in LRAD, ps-electron pulses from ELYSE in LCP/Orsay (M. Mostafavi), pulsed heavy ions in GANIL (E. Balanzat), helion beam in ARRONAX at Nantes (M. Fattahi). During this study a novel high temperature/high pressure cell has been designed and used with high LET particles (figure 1). Only a part of the work was published[3]. Publications of valuable results (figure 2) are still on the way because they are waiting for the comparison with MC simulations performed in collaboration with B. Gervais (CIMAP Caen) and M. Beuve (IPN Lyon). In parallel implementation of water radiation chemistry has been performed in the open source program GEANT4 in the ANR named GEANT4-DNA (2009-2012) by collaborating with S. Incerti (CENBG Bordeaux)[4].

Another high pressure system has been designed recently to reach 400 MPa with a flow and optical windows for pulse radiolysis experiments[5]. This system is devoted to the analysis of protein such as myoglobine under pressure stress in order to probe their tertiary structure and their reactivity towards water radical. (see topic 2)

Fig.1: Picture of the optical cell designed for high LET particle irradiations.

Fig.2: Transient signals at 357nm for various high temperatures of Br₂- (formation) and Br- (bleaching) in a 10mM NaBr solution irradiated by 130µs pulses of C⁶⁺ of 975MeV.

We are currently developing a new approach to analyze the fundamental aspects of the energy Deposition of swift Heavy Ions in Liquid Water (SIRMIO project 2012-2014). It should induce application in real time microdosimetry during hadrontherapy. This project consists in using fluorescence of molecule produced during radiolysis and observed by optical microscopy and fast detection of fluorescence induced by laser excitation. We expect to get images of energy deposition of energetic ions at micrometer scale with high time resolution as well.

After 6 months of work[6] the 4 partners got strong knowledge of the molecules to use, in terms of toxic effect in living cells, of radiolytic mechanisms and also purity, radiolytic yields. During these investigations, new methods in radiation chemistry should be available such as pulse radiolysis method with fluorescence induced by laser, and also a method to obtain the fluorescence lifetime coupled to alpha ionization (developed at IPHC Strasbourg). We expect to use very soon the microscopy in line with Van de Graaf accelerator, microprobe at LEEL in Saclay to reach our objectives.

Topic 1 : Effects of Extreme Conditions in Radiation Chemistry

In numerous real situations, radical reactions occur with extreme thermodynamic conditions like temperature over 300°C, with pressure over 100 MPa, or triggered by nuclear reactions which produce elevated Linear Energy Transfer (LET) ionizing particles[1]. These parameters can induce drastic changes in the production and in the reactivity of radical species in water. The most recent data bases[2]  show a lack of knowledge. Therefore the effect of the combinations of extreme values of these conditions has never been considered: high temperature water submitted to high LET particles for instance.

In the context of the generation 4 nuclear power plant systems in which temperatures of fluid transfer should increase in order to improve the thermal-cycle yield, one system expected to be developed will involve supercritical water (374°C, 22 MPa). Consequently many fundamental questions on water radiolysis in these conditions appeared since Arrhenius extrapolation could not be applied. How to predict water decomposition in these conditions? That was essentially the aim of Dimitri Saffré PhD (2008-2011) who has performed experiments and MC simulations in a large range of temperature and LET in order to determine radiolytic yields and rate constants through an extreme condition-resistant chemical system: HBr. In situ analysis of Br-, Br₂- and Br₃- species allowed the determination of HO^Ÿ yields in various conditions of irradiation: X-rays at ESRF (FAME Line, J.L. Hazeman), ns-electron pulses from ALIENOR accelerator in LRAD, ps-electron pulses from ELYSE in LCP/Orsay (M. Mostafavi), pulsed heavy ions in GANIL (E. Balanzat), helion beam in ARRONAX at Nantes (M. Fattahi). During this study a novel high temperature/high pressure cell has been designed and used with high LET particles (figure 1). Only a part of the work was published[3]. Publications of valuable results (figure 2) are still on the way because they are waiting for the comparison with MC simulations performed in collaboration with B. Gervais (CIMAP Caen) and M. Beuve (IPN Lyon). In parallel implementation of water radiation chemistry has been performed in the open source program GEANT4 in the ANR named GEANT4-DNA (2009-2012) by collaborating with S. Incerti (CENBG Bordeaux)[4].

Another high pressure system has been designed recently to reach 400 MPa with a flow and optical windows for pulse radiolysis experiments[5]. This system is devoted to the analysis of protein such as myoglobine under pressure stress in order to probe their tertiary structure and their reactivity towards water radical. (see topic 2)

Fig.1: Picture of the optical cell designed for high LET particle irradiations.

Fig.2: Transient signals at 357nm for various high temperatures of Br₂- (formation) and Br- (bleaching) in a 10mM NaBr solution irradiated by 130µs pulses of C⁶⁺ of 975MeV.

We are currently developing a new approach to analyze the fundamental aspects of the energy Deposition of swift Heavy Ions in Liquid Water (SIRMIO project 2012-2014). It should induce application in real time microdosimetry during hadrontherapy. This project consists in using fluorescence of molecule produced during radiolysis and observed by optical microscopy and fast detection of fluorescence induced by laser excitation. We expect to get images of energy deposition of energetic ions at micrometer scale with high time resolution as well.

After 6 months of work[6] the 4 partners got strong knowledge of the molecules to use, in terms of toxic effect in living cells, of radiolytic mechanisms and also purity, radiolytic yields. During these investigations, new methods in radiation chemistry should be available such as pulse radiolysis method with fluorescence induced by laser, and also a method to obtain the fluorescence lifetime coupled to alpha ionization (developed at IPHC Strasbourg). We expect to use very soon the microscopy in line with Van de Graaf accelerator, microprobe at LEEL in Saclay to reach our objectives.