Phase diagram of water confined in MCM-41 up to 700 MPa.

On the basis of measurements of NMR signal intensity and T1 and T2(*) relaxation times as a function of temperature (290 K-170 K) and pressure (0.1 MPa-700 MPa), the p-T phase diagram was made for the sample containing water inside and outside MCM-41 pores of 1.81 nm in radius. The temperature of nucleation of water confined in nanopores under normal pressure was 230 K. With increasing pressure this temperature decreased to 200 K under 300 MPa, but with further increase in pressure it did not change.

Exploring the molecular reorientations in amorphous rosuvastatin calcium.

Molecular reorientations in rosuvastatin calcium, a drug that is widely used to prevent cardiovascular disease, were explored thoroughly by means of solid state nuclear magnetic resonance (1H and 13C NMR) combined with calculations of steric hindrances. The experimental results reveal rich internal reorientational dynamics. All relaxation processes were tested in a broad range of temperatures and described in terms of their type and the associated energy barriers. The internal molecular mobility of rosuvastatin calcium can be associated with the reorientational dynamics of four methyl groups, accompanied by reorientation of the isopropyl group. The energy barriers of methyl and isopropyl group reorientation depended on the type of E/Z isomers, while the water content also had a strong influence on the dynamics of the isopropyl group. In the paper, a consistent picture of the molecular dynamics is provided, facilitating our understanding of molecular mobility in this important pharmaceutical solid.

OPTICALLY STIMULATED LUMINESCENCE OF LiF:Mg,Cu,P POWDER-INFLUENCE OF THERMAL TREATMENT.

It was recently found that LiF:Mg,Cu,P, which is a very well-known thermoluminescent (TL) material, exhibits also quite substantial optically stimulated luminescence (OSL). In the present work a study on the influence of thermal treatment on the LiF:Mg,Cu,P OSL intensity has been performed. The results revealed that the well-known 'gold standard' of 240°C annealing is not appropriate for OSL measurements. The annealing at lower temperatures produced significantly higher OSL intensity. The highest enhancement of the OSL signal, reaching 95% (compared to the initial signal after standard annealing at 240°C/10 min) was obtained after annealing at about 190-200°C/30 min. The OSL emission spectrum of LiF:Mg,Cu,P was also measured and found to be peaked at 360 nm.

Validation of modelling the radiation exposure due to solar particle events at aircraft altitudes.

Dose assessment procedures for cosmic radiation exposure of aircraft crew have been introduced in most European countries in accordance with the corresponding European directive and national regulations. However, the radiation exposure due to solar particle events is still a matter of scientific research. Here we describe the European research project CONRAD, WP6, Subgroup-B, about the current status of available solar storm measurements and existing models for dose estimation at flight altitudes during solar particle events leading to ground level enhancement (GLE). Three models for the numerical dose estimation during GLEs are discussed. Some of the models agree with limited experimental data reasonably well. Analysis of GLEs during geomagnetically disturbed conditions is still complex and time consuming. Currently available solar particle event models can disagree with each other by an order of magnitude. Further research and verification by on-board measurements is still needed.

Optical and thermal pre-readout treatments to reduce the influence of fading on LiMgPO4 OSL measurements.

TL (Thermoluminescent) and OSL (Optically Stimulated Luminescence) techniques are both luminescent techniques widely applied in several areas into radiation dosimetry. The main difference between them are related to the employed stimulus (thermal or optical) for luminescent emission, as well as the advantages of each technique. Due to simplicity and not to be required heating, the OSL technique has been continuously improved and new researches in materials to be used with this technique have grown in the last decades. Nowadays the main problems in the application of the developed new materials are the poor stability and loss of OSL signal over time (fading). In this study, we performed a sequence of thermal (preheat) and optical (OSL with infra-red light stimulus) pre-readout treatments immediately before OSL readouts of LiMgPO4 based detectors (LMP), aiming the applicability of novel materials, contributing to find solutions to minimize the influence of fading. Moreover, it was demonstrated that the influence of fading is minimized and the stability of OSL signal from LMP is achieved using just optical process, without heating the material.

LITHIUM FLUORIDE CRYSTALS AS FLUORESCENT NUCLEAR TRACK DETECTORS.

Radiophotoluminescence signal of LiF crystals was found to be sufficiently strong to visualize tracks of a single charged particle. This was achieved with a wide-field fluorescent microscope equipped with a ×100 objective and LiF single crystals grown with the Czochralski method at IFJ PAN. The tracks of alpha particles, protons, as well as products of 6Li(n,α)3H reaction with thermal neutrons (moderated Pu/Be source), were observed. These encouraging results are the first steps towards practical use of LiF as fluorescent nuclear track detectors. The most promising dosimetric application seems to be neutron measurements.

IMAGING OF PROTON BRAGG PEAKS IN LiF.

Lithium fluoride (LiF) is one of the most common thermoluminescent phosphors routinely used in radiation protection services. Another advantageous property of LiF is radiophotoluminescence, whose occurs after its irradiation due to the creation of color centers. Excitation of LiF samples with a blue light causes the emission of photoluminescence, which spectrum consists of two peaks at ~520 and ~670 nm. The work was focused on imaging of Bragg peaks of proton beams routinely applied at the proton eye radiotherapy facility operating at the Institute of Nuclear Physics Polish Academy of Sciences (IFJ PAN) in Krakow by the measurement of the fluorescence light in LiF crystals excited with a 445 nm blue light after their previous irradiation with the proton beams of energies of 28, 30, 40 and 50 MeV. The range of proton beams in LiF crystals for different energies was calculated by Monte Carlo simulations.

Dosimetric properties of new cards with high-sensitivity MCP-N (LiF:Mg,Cu,P) detectors for Harshaw automatic reader.

A new configuration for a thermoluminescent dosimetric card has been developed through collaboration between the Institute of Nuclear Physics in Kraków and several commercial dosimetric companies. The card is based on high-sensitivity LiF:Mg,Cu,P circular pellets (MCP-N) welded inside synthetic foils. The basic configuration consists of two pellets of 3.6 mm diameter and thicknesses from 0.25 up to 0.38 mm. The cards can be processed in a standard 6600 or 8800 Harshaw automatic TLD reader. The dosemeters demonstrate very high sensitivity, low background and good stability. This article presents results of the performance tests of the new dosimetric cards in the automatic TLD readers and a comparison of their properties.

The problems associated with the monitoring of complex workplace radiation fields at European high-energy accelerators and thermonuclear fusion facilities.

The European Commission is funding within its Sixth Framework Programme a three-year project (2005-2007) called CONRAD, COordinated Network for RAdiation Dosimetry. The organisational framework for this project is provided by the European Radiation Dosimetry Group EURADOS. One task within the CONRAD project, Work Package 6 (WP6), was to provide a report outlining research needs and research activities within Europe to develop new and improved methods and techniques for the characterisation of complex radiation fields at workplaces around high-energy accelerators, but also at the next generation of thermonuclear fusion facilities. The paper provides an overview of the report, which will be available as CERN Yellow Report.

Dosimetry of densely ionising radiation with three LiF phosphors for space applications.

A new method of thermoluminescence dosimetry of densely ionising radiation based on the ratio of different efficiency-LET functions of three thermoluminescent detectors (TLDs) has been developed. The applied TLD types are: MTS-7 ((7)LiF:Mg,Ti), MCP-7 ((7)LiF:Mg,Cu,P) and MTT-7 (a newly developed (7)LiF:Mg,Ti with modified activator composition and increased response to high-LET radiation). The tests of this method, performed with high-energy ion beams at the HIMAC accelerator within the ICCHIBAN project, proved that good agreement with the true dose values may be achieved even in very complicated mixed fields. The proposed method will be applied for analysis of several thousand TLDs used for the determination of organ doses in an anthropomorphic phantom orbiting outside the International Space Station within the MATROSHKA experiment.

On the dose response of some CVD diamond thermoluminescent detectors.

The linearity of dose response of chemical vapour deposition (CVD) diamonds grown at the Institute for Materials Research at Limburg University, Belgium, was investigated over a dose range relevant for radiotherapy. The following CVD diamonds were investigated: (1) a batch of square 3 x 3 mm2 detectors cut from a CVD wafer and (2) an as-grown CVD wafer of 6 cm diameter. A total of 20 CVD square detectors were irradiated with 137Cs gamma rays over the dose range from 200 mGy to 25 Gy. The CVD wafer, used as a large-area thermoluminescent (TL) detector, was exposed to a 226Ra needle. Very few square detectors showed linearity over a limited dose range, followed by saturation of the TL signal. The dose range of linearity was found to be strongly affected by the thermal annealing procedure of the detector. Owing to its high sensitivity and homogeneity of response, the large CVD diamond wafer was found to be very suitable as a large-area detector for 2-D dose mapping of the 226Ra brachytherapy source, possibly for Quality Assurance purposes.

Application of different TL detectors for the photon dosimetry in mixed radiation fields used for BNCT.

Different approaches for the measurement of a relatively small gamma dose in strong fields of thermal and epithermal neutrons as used for Boron Neutron Capture Therapy (BNCT) have been studied with various thermoluminescence detectors (TLDs). CaF(2):Tm detectors are insensitive to thermal neutrons but not tissue-equivalent. A disadvantage of applying tissue-equivalent (7)LiF detectors is a strong neutron signal resulting from the unavoidable presence of (6)Li traces. To overcome this problem it is usual to apply pairs of LiF detectors with different (6)Li content. The experimental determination of the thermal neutron response ratio of such a pair at the Geesthacht Neutron Facility (GeNF) operated by PTB enables measurement of the photon dose. In the experimental mixed field of thermal neutrons and photons of the TRIGA reactor at Mainz the photon dose measured with different types of (7)LiF/(nat)LiF TLD pairs agree within a standard uncertainty of 6% whereas the CaF(2):Tm detectors exhibit a photon dose by more than a factor of 2 higher. It is proposed to determine suitable photon energy correction factors for CaF(2):Tm detectors with the help of the (7)LiF/(nat)LiF TLD pairs in the radiation field of interest.

Two-dimensional thermoluminescence dosimetry using planar detectors and a TL reader with CCD camera readout.

A novel method of determining two-dimensional (2-D) dose distributions is presented, using in-house developed, large-area (a few cm(2)) thermoluminescent (TL) detectors based on LiF powder plated on Al foil. An in-house developed planar large-area TL reader equipped with a coupled charge device (CCD) camera is used for readout, providing digital images of 2-D dose distributions on the surface of these large-area TL detectors. The capability of the newly developed system is demonstrated by mapping 2-D dose distributions around a brachytherapy source, at dose ranges and source geometries relevant for clinical radiotherapy. Examples of local and dynamic evaluation of TL output from conventional TL detectors are also shown.

Microdosimetric modelling of the response of thermoluminescence detectors to low- and high-LET ionising radiation.

The microdosimetric one hit detector model was applied to calculate the dose response, energy response and relative thermoluminescence (TL) efficiency, eta, of high sensitive LiF:Mg,Cu,P and Al(2)O(3):C detectors after their irradiations by X rays, gamma rays, beta electrons and heavy charged particles (HCP). Microdosimetric distributions in 60 nm targets for photons and beta rays were calculated using the TRION MC track structure code, for HCP using the analytical model of Xapsos with modified transport of secondary electrons and the model of Olko & Booz. The calculated values of eta compare favourably with a broad spectrum of experimental data, including ICHIBAN experiments with HCP. The model offers a method for calculating the thermoluminescence response of TL foils applied to 2-D dosimetry of radiotherapeutic proton beams.

On the relationship between dose-, energy- and LET-response of thermoluminescent detectors.

Measurements of the response of thermoluminescent (TL) detectors after gamma ray doses high enough to observe signal saturation provide input to microdosimetric models which relate this gamma-ray response with the energy response after low doses of photons (gamma rays and low-energy X rays) and after high-LET irradiation. To measure their gamma ray response up to saturation, LiF:Mg,Ti (MTS-7 and MTT), LiF:Mg,Cu,P (MCP-7), CaSO4:Dy (KCD) and Al2O3:C detectors were irradiated with 60Co gamma rays over the range 1-5000 Gy. The X-ray photon energy response and TL efficiency (relative to gamma rays) after doses of beta rays and alpha particles, were also measured, for CaSO4:Dy and for Al2O3:C. Microdosimetric and track structure modelling was then applied to the experimental data. In a manner similar to LiF:Mg,Cu,P, the experimentally observed under response of alpha-Al2O3:C to X rays <100 keV, compared with cross-section calculations, is explained as a microdosimetric effect caused by the saturation of response of this detector without prior supralinearity (saturation of traps along the tracks). The enhanced X-ray photon energy response of CaSO4:Dy is related to the supralinearity observed in this material after high gamma ray doses, similarly to that in LiF:Mg,Ti. The discussed model approaches support the general rule relating dose-, energy- and ionisation density-responses in TL detectors: if their gamma ray response is sublinear prior to saturation, the measured photon energy response is lower, and if it is supralinear, it may be higher than that expected from the calculation of the interaction cross sections alone. Since similar rules have been found to apply to other solid-state detector systems, microdosimetry may offer a valuable contribution to solid-state dosimetry even prior to mechanistic explanations of physical phenomena in different TL detectors.

Evaluation of the relative TL efficiency of the thermoluminescent detectors to heavy charged particles.

The relative thermoluminescence efficiency, η, is in general not constant but depends on ionisation density. Evaluation of the η is therefore important especially for correct interpretation of measurements of densely ionising radiation doses in proton radiotherapy or in space dosimetry. The correct determination of the η is not always straightforward especially when more strongly ionising radiation is to be measured. In the present work, the process of calculation of the η based on two kinds of heavy charged particles was studied. Several factors which may influence the value of the η and their significance for the final result were discussed. These include for example non-uniform deposition of the dose within the detector volume, self-attenuation of thermoluminescent light, choice of the reference radiation, etc. The presented approach was applied to the experimental results of η of LiF:Mg,Ti detectors irradiated with two kinds of heavy charged particles, protons and alpha particles.

Photosensitized oxidation of 2',7'-dichlorofluorescin: singlet oxygen does not contribute to the formation of fluorescent oxidation product 2',7'-dichlorofluorescein.

2',7'-Dichlorofluorescin (DCFH) is often employed to assess oxidative stress in cells by monitoring the appearance of 2',7'-dichlorofluorescein (DCF), its highly fluorescent oxidation product. We have investigated the photosensitized oxidation of DCFH in solution and elucidated the role played by singlet molecular oxygen (1O(2)) in this reaction. We used rose bengal (RB), protoporphyrin, and DCF as photosensitizers. Irradiation (550 nm) of RB (20 microM) in 50 mM phosphate (pH 7.4) in the presence of DCFH (50 microM) resulted in the rapid formation of DCF, measured as an increase in its characteristic absorbance and fluorescence. The oxidation rate was faster in deoxygenated solution, did not increase in D(2)O, and even increased in the presence of sodium azide. The presence of antioxidants that react with 1O(2), thus removing oxygen, accelerated DCF formation. Such results eliminate any potential direct involvement of 1O(2) in DCF formation, even though DCFH is an efficient (physical) quencher of 1O(2) (k(q) = 1.4 x 10(8) M(-1)s(-1) in methanol). DCF is also a moderate photosensitizer of 1O(2) with a quantum yield of circa phi = 0.06 in D(2)O and phi = 0.08 in propylene carbonate, which unequivocally indicates that DCF can exist in a triplet state upon excitation with UV and visible light. This triplet can initiate photo-oxidization of DCFH via redox-and-radical mechanism(s) similar to those involving RB (vide supra). Our results show that, upon illumination, DCF can function as a moderate photosensitizer initiating DCFH oxidation, which may prime and accelerate the formation of DCF. We have also shown that, while 1O(2) does not contribute directly to DCF production, it can do so indirectly via reaction with cellular substrates yielding peroxy products and peroxyl radicals, which are able to oxidize DCFH in subsequent dark reactions. These findings suggest that DCFH should not be regarded as a probe sensitive to singlet molecular oxygen, and that care must be taken when using DCFH to measure oxidative stress in cells as a result of both visible and UV light exposure.

Free radical reactions photosensitized by the human lens component, kynurenine: an EPR and spin trapping investigation.

We have undertaken electron paramagnetic resonance and spin trapping investigations of the photochemistry of kynurenine (KN), a natural component of the human eye and close analog of the principal chromophore in the young human lens 3-OH-kynurenine O-glucoside (3HKG). 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) was employed as a spin trap. We found that upon UV irradiation (> 300 nm) KN photoreduces oxygen to superoxide radical (in DMSO) and nitromethane (CH3NO2) to a nitromethane radical anion (CH3NO2.-) (in air-free buffers, pH 7 and 9.5). KN also sensitized photooxidation of cysteine, NADH, EDTA, azide, and ascorbate; oxygen greatly accelerated this process. Oxidation of cysteine, NADH, and EDTA was accompanied by superoxide radical formation. Cysteinyl and azidyl radicals were detected as DMPO adducts. We also observed that KN undergoes photodegradation to a product(s) whose photosensitizing capacity is greater than that of KN itself. We postulate that: (i) 3HKG may be able to photoinitiate free radical reactions in vivo, and (ii) oxygen is an important factor determining the yields of free radical processes initiated by lenticular chromophores.

Interaction of singlet molecular oxygen with double fluorescent and spin sensors.

Double fluorescent and spin sensors were recently used to detect transient oxidants via simultaneous fluorescence change and production of the nitroxide radical detected by electron paramagnetic resonance. One such oxidant, singlet molecular oxygen ((1)O(2)), was detected in thylakoid membrane using these probes. In the present study, we investigated the total (physical and chemical) quenching of (1)O(2) phosphorescence by sensors composed of the 2,5-dihydro-2,2,5,5-tetramethyl-1H-pyrrole moiety attached to xanthene or dansyl fluorophores. We found that the quenching rate constants were in the range (2-7) x 10(7) M(-1)s(-1) in acetonitrile and D(2)O. Quenching of (1)O(2) is usually an additive process in which different functional groups may contribute. We estimated that the (1)O(2) quenching by the amine fragments was ca. one to two orders of magnitude lower than that for the complete molecules. Our data suggest that the incorporation of a fluorescent chromophore results in additional strong quenching of (1)O(2), which may in turn decrease the nitroxide yield via the (1)O(2) chemical path, possibly having an effect on quantitative interpretations. We have also found that probes with the dansyl fluorophore photosensitized (1)O(2) upon UV excitation with the quantum yield of 0.087 in acetonitrile at 366 nm. This result shows that care must be taken when the dansyl-based sensors are used in experiments requiring UV irradiation. We hope that our results will contribute to a better characterization and wider use of these novel double sensors.

Photoproduction and direct spectral detection of singlet molecular oxygen (1O2) in keratinocytes stained with rose bengal.

In vivo, keratinocyte skin cells are exposed to photooxidative processes, some of which can be mediated by singlet molecular oxygen (1O2), a species that is very difficult to detect spectrally in cells. We photosensitized 1O2 in cultured HaCaT keratinocytes stained with rose bengal (RB) that localizes exclusively inside the keratinocyte hydrophobic regions, as evidenced by strongly red-shifted absorbance and intense fluorescence. We used keratinocytes grown in a monolayer on a plastic coverslip and in suspension. The phosphorescence spectrum (1200-1350 nm) from 1O2 was strongest when the coverslip containing RB-stained keratinocytes was irradiated in air. The spectral intensity decreased when the coverslip was immersed in D2O during irradiation and was almost completely quenched when it was irradiated while immersed in water. Water not only shortens the 1O2 lifetime but also reabsorbs part of the 1O2 phosphorescence, processes that do not occur when 1O2 is produced in a keratinocyte layer exposed to air. Because the RB was inside keratinocytes, singlet oxygen must also be produced inside the keratinocytes. However, the sensitivity to the extracellular environment suggests that most of the detectable 1O2 phosphorescence originates from those 1O2 molecules that escaped from the cell through its membrane into D2O or into the air, where 1O2 has longer lifetimes. Our results confirm directly that 1O2 is indeed photosensitized in living cells by RB. They also suggest that keratinocyte monolayers may be a good cell model to examine in vitro the production of 1O2 by other photosensitizers of environmental and photomedical interest.