Sonochemistry in non-aqueous liquids

The chemical effects of high-intensity ultrasound on organic liquids are reported. In order to probe the factors which affect sonochemistry in non-aqueous solvents, two very different chemical dosimeters have been used: radical trapping by diphenylpicrylhydrazyl and decomposition of Fe(CO)₅. In both cases, good correlation is found between the logarithm of the sonochemical rate and the solvent vapour pressure. This result is justifiable in terms of the cavitation ‘hot-spot’ mechanism of sonochemistry. Thus, decreasing solvent vapour pressure increases the intensity of cavitational collapse, the peak temperature reached during such collapse, and, consequently, the rates of sonochemical reactions.     

Magnetic resonance imaging of spatially resolved acrylamide photopolymerization

Magnetic resonance imaging was employed to examine spatially and temporally resolved photopolymerization of acrylamide gels. Fast exchange between free and bound water results in single exponential T₂ decay, where 1/T₂ scales linearly with polymer concentration. Measured T₂s are sensitive to the experimental conditions; however, the 1/T₂ relationship to polymer concentration allows a straightforward interpretation of image contrast changes during photopolymerization. The polymer appears to form at a nearly constant rate until the monomer concentration is significantly depleted. Conventional spin‐echo images and quantitative CPMG‐weighted spin‐echo images were acquired. Photopolymerization of a partially masked sample produced a sharp transition (1 mm width) between polymer and monomer regions of the sample. The image intensity is uniform throughout the illuminated region of the sample, indicating uniform polymer formation. Interrupting the illumination quenches polymer formation. Copyright © 2003 John Wiley & Sons, Ltd.     

Computer simulation of the processes in a CR-39 neutron detector

The application of CR-39 as a fast neutron dosimeter, based on counting elastic recoil nuclei tracks of H, C and O nuclei in a geometrically matched pair of detectors, was studied. A computer simulation of the processes during the exposure of a detector pair to neutrons is presented. The energy and spatial distribution of the recoil nuclei was calculated with the MCNP 4B program package. On the basis of this distribution, a Monte-Carlo procedure for the generation of latent tracks in the CR-39 detectors was run. Additionally, a procedure for calculation of the chemical track etching for revealing the visible track parameters was performed to obtain the detector response.     

Determination of an Absorbed Radiation Dose by the EPR Method from the Concentration of the Centers Produced

A method to determine the absorbed radiation dose that is based on the spin-resonance dosimetry is suggested. It rests on the fact that under irradiation additional centers that absorb UHF radiation are generated in substance. This leads to a change in the time of longitudinal relaxation of a Zeeman subsystem and dipole-dipole reservoir as well as in the time of transverse relaxation because of the dipole-dipole interaction, which in turn causes a change in the shape of the line and in the saturation parameter. It is possible to determine the minimum absorbed dose at which the minimum deformation of the shape of the line is registered. A method is also suggested to determine an absorbed dose in the absence of absorbing centers in the substance before irradiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 335–338, May–June, 2005.     

Possible Use of Polymethylmethacrylate Doped with Hg Dithizonate as a Dosimeter in the Mrad Range

It is the found that the 3 μ thin film polymethylmethacrylate (PMMA) doped with Hg dithizonate can be used for dosimetry in a range of adsorbed dose from about 1 … 4 Mrad from which the decrease of optical density of the main absorption band at 485 … 490 nm decreases exponentially by increasing absorbed dose. The effects of post storage irradiation and storage temperature on the radiation induced visible spectrum were investigated.     

Ein Halbleiter-Szintillationsdosimeter zur Dosimetric von Röntgen- und Gammastrahlung

Durch Kombination geeigneter CdS-Photowiderstände mit langwellig fluoreszierenden organischen Plastszintillatoren lassen sich Miniatur-Szintillationssonden geringer Energieabhüngigkeit zur Dosimetric von Röntgen- und γ-Strahlung herstellen. Die beschreibene Sonde enthält einen Photowiderstand vom Typ Cl 905 HLL zur Szintillationslichtmessung und einen Polystyrolszintillator mit den lumineszierenden Komponenten PBD und PNB (γ_max = 493 nm) als Strahlungsdetektor. Aufbau und Eingenschaften eines Halbleiter-Szintillationsdosimeters mit einem Meβbereich von 1 bis 1000 R/h werden beschriben, insbesondere werden Maβnahmen zur Verringerung der Energieabhängigkeit der Sondenanzeige diskutiert.     

The 24Na Induced Activity as a Neutron Dosimeter for Radiobiologial Experiments

Measurement of the ²⁴Na induced activity as a part of a dosimetric system for radiobiological experiments was found to be an approach characterized by its proper reliability, reproducibility (relative error less than 8-5%) and high sensitivity (activities of about 0-01 μCi may be detected).     

Anwendung von Radionukliden in der Elektrotechnik

The effect of etching conditions on the energy resolution was studied. In the present work cellulose nitrate CN-85 films were used as Solid State Nuclear Track Detectors. There exists a relation between the etching condition and the energy resolution.     

Development of an improved dosemeter for assessments of risk to the eye

To develop an improved dosemeter to assess photon and beta exposures of the eye lens, and in response to issues surrounding the preferred values of H_lens to be used for guiding operational radiation protection, a programme of re-optimization of the current PHE thermoluminescence dosemeter has been performed. In particular, refinements of the filter located in front of the sensitive ⁷LiF:Mg,Cu,P element have been considered, so that the dose response characteristics of the device provide a better and more conservative estimate of risk. The investigation was performed using the Monte Carlo modelling software MCNP5, to produce a final design that featured a filter containing a 9.5 mm diameter polypropylene hemisphere truncated to a maximum thickness of 3.0 mm. The responses of this design in photon and electron fields are presented here, contrasted against those of the existing PHE eye dosemeter, with respect to the operational quantity H_p(3,E,θ) and both current and suggested values for the absorbed dose per fluence risk profile for the lens of the eye.     

Emergency OSL dosimetry with commonplace materials

Several commonplace materials were studied as possible emergency optically stimulated luminescence (OSL) dosimeters. The materials included: paper currency (banknotes) and coins of different denomination and from different countries; plastic cards of different types (credit and debit cards, driver's license cards, membership cards, etc.), parts and details of clothing and shoes as well as samples of different fabrics.The samples displayed significant variability in their OSL properties. They differed in the intensity of the initial ‘native’ signal; the bleaching time of the OSL signal; the sensitivity to light of different wavelengths; the fading rate of OSL signals, etc. Procedures of OSL analysis were proposed to account for this variety.Values of the minimum measurable dose (MMD) were below 2 Gy for most tested samples if OSL measurements were conducted within one week of exposure and the samples were kept in dark since exposure (except samples of shoes that were kept under environmental light).The OSL signals in banknotes appear to originate from compounds containing aluminum, silicon, calcium and titanium – these elements were detected using X-ray microanalysis. For coins, the source of the OSL signals is speculated to be small particles of quartz, which were detected on the coins' surfaces. The X-ray microanalysis spectra from fabrics and shoes revealed sodium, aluminum, titanium, iron and nickel as elements that appeared to be responsible for the radiation sensitivity of those samples.It was concluded that, under certain constrained circumstances, paper and metallic money, personal plastic cards, clothing and shoes could be used as emergency OSL dosimeters in triage applications.