[en] Differences and similarities between LiF-based LiF:Mg,Ti and LiF:Mg,Cu,P are discussed with respect to their dosimetric properties - sensitivity, non-linearity of dose-response and heavy charged particle efficiency, as related to the concentration and the individual role of the Mg, Ti, Cu and P dopants. To study further the role of these dopants, the properties of some new, 'hybrid' phosphors: LiF:Mg,Cu,Ti and LiF:Mg,P, specially developed for this purpose, are also discussed. In the glow-curve of LiF:Mg,Cu,P with a low concentration of Mg a new peak was found, which appears to be an analogue of peak 4 in LiF:Mg,Ti. Magnesium apparently controls most of the dosimetric properties of LiF-based phosphors. For instance, charged-particle efficiency appears to be anti-correlated with the concentration of Mg, being much less dependent on the content of other dopants. On the other hand, some properties of LiF-based systems seem to be correlated with changes in the emission spectra. It is suggested that Ti hampers the acceptance of an increased amount of Mg into more traps in LiF:Mg,Ti. The absence of Ti, not the presence of P or Cu, is therefore a key to the high sensitivity of LiF:Mg,Cu,P. (author)

[en] Environmental pollutants activated by UV sunlight may have contributed to the recent decline in frog populations and the concomitant increase in malformations in the USA and abroad. UV radiation is able to mutate DNA and to initiate photosensitization processes that generate mutagenic and biologically disruptive oxygen transients. We have examined water from selected sites in Minnesota and Vermont using singlet molecular oxygen (¹O₂), detected by its phosphorescence and free radicals detected by spin trapping, as markers for photosensitization. Water from a pond in Minnesota with malformed frogs, which also causes malformations in the laboratory, photosensitized more ¹O₂, even though it absorbed less UV light compared to water from a site that did not cause malformations. This suggested that unknown natural or pollutant agents were present, and that photosensitization may be involved. Although UV irradiation of the two Minnesota water samples in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) revealed the presence of the DMPO/·OH, DMPO/·H(e_aq^-) and DMPO/·C(unknown) adducts there were no qualitative or quantitative differences between them. We also examined water samples from several sites in Vermont, and compared them by measuring the quantum yield of ¹O₂ photosensitization. While all the Vermont samples produced a small amount of ¹O₂, there was no clear correlation with the incidence of frog malformations. However, the samples differed strongly in absorption spectra and the ability to quench ¹O₂. These factors may determine how much UV light is absorbed and converted into chemical reactions. Our results show that photochemical characterization of ¹O₂ photosensitization is possible in untreated natural water samples. Photosensitization falls into the category of global factors that may be closely associated with the effects of UV irradiation of the Earth's environments. Thus, photosensitization might be an important component in global amphibian malformation and decline. The observation of ¹O₂ emission directly from natural water may also provide new opportunities to investigate the involvement of ¹O₂ in other complex environmental processes

[en] Photon energy response of MTS-N (LiF:Mg,Ti) detectors (TLD Poland) and of MTS-N detectors sensitised with 200 Gy of ⁶⁰Co gamma rays, followed by UV irradiation (sMTS-N), has been determined using X rays with narrow energy spectra, in the energy range from 20 keV to 300 keV. The over-response of LiF:Mg,Ti detectors for X rays (relative TL efficiency ? = 1.1) can be explained as an ionisation density effect. Low energy X rays produce short electron tracks, which locally deposit a high radiation dose and, consequently, lead to an enhanced (supralinear) response. This over-response has not been observed in sensitised MTS-N where supralinearity in the response after gamma-ray doses above 1 Gy is not seen. Using the dose-response curves measured for MTS-N detectors after ¹³⁷Cs gamma ray irradiation and local doses calculated using Monte Carlo generated electron tracks, it was possible to predict the relative TL effectiveness for different X ray energies. The calculation procedure can be applied to predict the photon energy response of LiF:Mg,Ti detectors in an arbitrary photon field. (author)

[en] Lithium fluoride single crystals were successfully used for fluorescent imaging of single tracks of alpha particles. This was realized with a standard wide-field fluorescent microscope equipped with a 100× objective. Alpha particles create F_2 and F_3"+ color centers in LiF crystals. The subsequent illumination with the blue light (wavelength around 445 nm), excites these centers and produces fluorescence with a broad band peaked at 670 nm. The observed tracks of alpha particles have diameter of about 500 nm. Focusing of the microscope at different depths in a LiF crystal, enables imaging changes of shape and position of tracks, allowing for visualization of their paths. These encouraging results are the first step towards practical application of LiF as fluorescent nuclear track detectors.

[en] Measurements were performed with various LiF-based TLDs on board seven Polish aircraft, flying long-distance or middle-distance routes. All of the 7LiF detectors used (various types of ⁷LiF:Mg,Ti and ⁷LiF:Mg,Cu,P detectors), which measure the non-neutron component of the radiation field, produced consistent results. It was found that the characteristics of the TLD response (ratio of different detector responses, glow curve shapes) after doses of radiation at flying altitudes differ from those obtained after exposure at the CERN facility (CERF), suggesting a lower contribution of densely ionising radiation. The neutron induced TL signal was also more affected by the thickness of the holder, suggesting the presence of a softer neutron energy spectrum at flight altitudes. Further in-flight and CERF exposures of detectors are planned to resolve these issues. (author)

[en] There are two widely applied types of thermoluminescent detectors based on LiF:Mg luminophor: LiF,Mg,Ti and highly sensitive LiF:Mg,Cu,P. The role of luminescence centres in these materials is usually attributed to defects connected with, respectively, titanium and phosphorus dopants. In order to check how composition of dopants introduced into the LiF lattice influences emission spectra, measurements on a series of variously doped LiF:Mg samples were performed. Apart from LiF:Mg,Cu,P and LiF:Mg,Ti detectors with different concentration of activators, an experimental sample being a kind of a 'hybrid' between both standard materials was also prepared. It was synthesised with concentrations of magnesium and copper identical to those used for LiF:Mg,Cu,P preparation, but instead of phosphorus it was doped with titanium (LiF:Mg,Cu,Ti). The measurements of the emission spectra were performed by using a liquid nitrogen cooled CCD 1024E detector with an SP150 spectrograph. During the measurements the samples were placed inside a cryostat in a vacuum. Resulting data were numerically deconvoluted for individual peaks with respect to the wavelength and the temperature. The glow curve shape of this material resembles that of LiF:Mg,Cu,P while sensitivity is at the level of LiF:Mg,Ti. Preliminary results indicate that emission of the LiF:Mg,Cu,Ti sample is similar to that of LiF:Mg,Cu,P rather than to LiF:Mg,Ti, showing a maximum for wavelengths well below 400 nm. (author)

[en] Three different experimental methods of determination of TL light attenuation coefficients were compared using a specially prepared set of LiF detectors with different thickness. The three methods were: (1) a two-detector method in which an irradiated detector is covered during readout by another one; (2) a surface irradiation method in which a detector is twice irradiated with alpha particles and read out first with the irradiated side facing the PM and then upside-down; (3) a whole volume irradiation method in which detectors of different thickness are irradiated homogeneously with gamma rays. The two-detector method and the surface irradiation method produced consistent results, while values obtained with the whole volume irradiation method were quite different. In the surface irradiation method it is necessary to take into account the decrease in the distance between the source of light and the PM tube, when the detector is read out with its irradiated side facing the PM, with respect to the opposite position. Also light reflections from the side walls of the heater were found to play a role. The two-detector method produces the most reliable results and should be considered as the reference method. As established using this method, the attenuation factor for the white, opaque LiF : Mg,Ti detectors applied in all reported measurements was found to be μ=1.69±0.05 mm^-1

[en] The low energy component of the cosmic radiation field is strongly modified by the shielding of the spacecraft and it is time and location dependent. Thermoluminescent lithium fluoride detectors have been applied to determine the radiation doses inside the ESA-Facility BIOPAN. The BIOPAN facility was mounted outside and launched on a Foton spacecraft and opened to space to allow exposure of several experiments to open space. Standard TLD-600, TLD-700 chips, two layers MTS-Ns sintered pellets with different effective thickness of the sensitive layer and MTS-N of different thickness have been exposed with different shielding thickness in front of them. The measured TL signal in the 0.1 mm thick detector just shielded by an aluminised Kapton foil of 25 μm thickness in front yielded a dose of 29.8 Gy (calibrated with ¹³⁷Cs gamma rays) for an exposure time of 12.7 days; after 2.5 gcm^-2 shielding the doses dropped to 3 mGy. The monitoring of radiation doses and its depth dose distribution outside the spacecraft are of great interest for radiation protection of astronauts working in the open space. The knowledge of depth-dose distribution is a prerequisite to determine the organ doses an astronaut will receive during an extravehicular activity. The BIOPAN experiments are to be continued in the future. (author)

[en] Lithium aluminate (LiAlO₂) polycrystalline material showing high OSL sensitivity and linear dose response was prepared at IFJ Krakow. The kinetic parameters of OSL and TL processes were evaluated using various experimental techniques: LM-OSL deconvolution, TL glow-curve deconvolution, variable heating rate and isothermal decay. The OSL signal was found to consist of four components, one of them exhibiting a very slow decay. The TL glow-curve possesses two apparent peaks at approximately 85 °C and at 165 °C, which both seem to follow first order kinetics. These peaks seem to have a composite structure and as many as six peaks were found in the glow-curve. - Highlights: • LiAlO₂ components' photoionization cross sections for blue light was calculated. • Estimation of LiAlO₂ TL trap parameters using deconvolution. • Calculation of LiAlO₂ TL trap parameters using various heating rates. • Estimation of LiAlO₂ TL activation energy using isothermal decay measurements

[en] A novel method of determining two-dimensional (2-D) dose distributions was developed using in-house produced large-area thermoluminescent (TL) detectors based on LiF, read with a newly developed planar large-area TL reader equipped with a CCD camera. The detectors were developed by attaching, pressing and sintering thermoluminescent LiF:Mg,Ti or LiF:Mg,Cu,P powder on Al foil of 0.3 mm thickness. The detectors, of active area of a few square centimeters, read out using the large-area TL reader, were successfully used to map the 2-D dose distribution around an alpha source Am-241, a Ra-226 needle source and a Ru-106 ophthalmic applicator