Dosimeter Fricke

Repeating unit of polymer chain including solvation Mn of samples not irradiated based on GPC in NMP with polystyrene standards, or by NMR end-group analysis if so indicated Measured net G value after cesium-137 irradiation corrected relative to Fricke dosimeter... 

The quantitative aspects of track reactions are involved some details will be presented in Chapter 7. The LET effect is known for H2 and H202 yields in aqueous radiation chemistry. The yields of secondary reactions that depend on either the molecular or the radical yield are affected similarly. Thus, the yield of Fe3+ ion in the Fricke dosimeter system and the initiation yield of radiation-induced polymerization decrease with LET. Numerous examples of LET effects are known in radiation chemistry (Allen, 1961 Falconer and Burton, 1963 Burns and Barker, 1965) and in radiation biology (Lamerton, 1963). 

Several authors have made restricted comparisons between experiment and calculations of diffusion theory. Thus, Turner et al. (1983, 1988) considered G(Fe3+) in the Fricke dosimeter as a function of electron energy, and Zaider and Brenner (1984) dealt with the shape of the decay curve of eh (vide supra). These comparisons are not very rigorous, since many other determining experiments were left out. Subsequently, more critical examinations have been made by La Verne and Pimblott (1991), Pimblott and Green (1995), Pimblott et al. (1996), and Pimblott and LaVeme (1997). These authors have compared their... 

The chemical change in the Fricke dosimeter is the oxidation of ferrous ions in acidic aerated solutions. It is prepared from a -1 mM solution of ferrous or fer-roammonium sulfate with 1 mM NaCl in air-saturated 0.4 M H2S04. Addition of the chloride inhibits the oxidation of ferrous ions by organic impurities, so that elaborate reagent purification is not necessary. Nevertheless, the use of redistilled water is recommended for each extensive use. Absorption due to the ferric ion is monitored at its peak -304-305 nm. The dose in the solution is calculated from the formula... 

Figure 7 Effect of ion energy on the response of the Fricke dosimeter. The solid lines and filled...

Hydrated electron yields decrease with increasing MZ jE, but they do not seem to decrease to zero. Experiments have been performed on aerated and deaerated Fricke dosimeter solutions using Ni and ions [93]. One half of the difference in the ferric ion yields of these two systems is equal to the H atom yield. The Fricke dosimeter is highly acidic so the electrons are converted to H atoms and to a first approximation the initial H atom yield can be assumed to be zero (see below). There is considerable scatter in the data of the very heavy ions, but they seem to indicate that hydrated electron yields decrease to a lower limit of about 0.1 electron/100 eV. The hydrated electron distribution is wider than that of the other water products because of the delocalization due to solvation. This dispersion probably allows some hydrated electrons to escape the heavy ion track at even the highest value of MZ jE. 

Watanabe, R. Usami, N. Takakura, K. Hieda, K. Kobayashi, K. Water radical 5uelds by low energy vacuum ultraviolet photons as measured with Fricke dosimeter. Radiat. Res. 1997,148, 489-490. 

Experimental approaches to measure the radial dose distribution are also in progress [119], and it was found that the distribution follows r law in the inner region of a critical distance and obeys r law outside of that region. LaVerne and Schuler reported the considerable decrease in the radiation chemical yield for ferric production in the Fricke dosimeter, suggesting a model of a deposited energy density in an ion track, which depends on the LET and the atomic number of an irradiation particle [120,121]. 

Product analysis of y-R was carried out in a Pyrex tube with an inner diameter of 1.0 cm at room temperature (r.t.). After y-R, the reaction mixtures were directly analyzed by GC and GC-MS. The G values were calculated from the product yields, and the absorbed dose measured by the ferrous sulfate dosimeter (Fricke dosimeter). 

The coolant water at around 300 °C is irradiated mainly at the core of the reactor. At the initial stage to determine the G-values of water decomposition products at elevated temperatures, the Fricke dosimeter was chosen [10-14] because the mechanism of the reaction has been established. Since the reactions in neutral solution are of practical interest, intensive measurement of the G-values of water decomposition products at elevated temperatures in neutral solutions has been done [15 21]. 

Dosimetry was based either directly on the Fricke Dosimeter (I) (using GFes+ = 15.5) or on an n-on-p solar cell (18) that was frequently calibrated against the Fricke dosimeter. 

A.S.T.M., Standard Method of Test for Adsorbed Gamma Radiation Dose in the Fricke Dosimeter, D 1671-63. 

HPhe Fricke dosimeter (ferrous sulfate solutions) has been used to measure A the radiation intensity of various types of ionizing radiation sources since its development by Fricke and Morse in 1927 (2). It is widely accepted because it yields accurate and reproducible results with a minimum of care. This system meets many of the requirements specified for an ideal dosimeter (5, 9) however, it has a limited dose range, and for our applications it has been necessary to develop a dosimeter covering larger doses. Of the systems reviewed (6, 7), two (ferrous sulfate-cupric sulfate and ceric sulfate) showed the most promise for use with the radiation sources at the U. S. Army Natick Laboratories (8). Of these, the ferrous-cupric system has received the most use, and this paper describes our experience in using this system and suggests procedures by which it may be used by others with equal success. 

The time required to raise or lower the source is 1.5 minutes, comparable to an irradiation dose in the irradiation position of approximately 35,000 rads (transient dose). The dose rate in the irradiation position is approximately 60,000 rads per minute. Calibration of the ferrous-cupric dosimeter is determined by comparison with the Fricke dosimeter, when irradiated at a position in the cell having a lower dose rate. The dose rate in the calibration position is approximately 5 X 103 rads per minute with a transient dose of approximately 3 X 103 rads. Calibrations made at such a position when using a G(Fe3+) = 15.6 for the Fricke dosimeter gave a G(Fe3+) of 0.66 for the ferrous-copper dosimeter. 

It has been established (5, Jf) that by adding cupric sulfate to modify the Fricke dosimeter, it is possible to reduce the ( (Fe3+) drastically from 15.6 to 0.66. 

Effect of Ferrous Ion Concentration. The reactions involved in the ferrous-cupric dosimeter, as described by Hart (1) are independent of oxygen concentration, and one would not expect to observe a change in the ferric yield ( (Fe3+) in this system when increasing the dose, as occurs in the Fricke dosimeter. This would indicate that the dose limit of this dosimeter is a function of the initial ferrous ion concentration and is not influenced by the oxygen concentration. To explore this idea, we increased the ferrous ion concentration from 0.001M to 0.01M while keeping the... 

Dosimetry with high-energy particles is a sensitive point because there are not enough experimental data for each type and energy of ion beams and the calculated yields depend strongly on the dose. The evaluation of the dose cannot be as accurate as for y or high energy electron beams for which a few secondary dosimeters have been determined such as Fricke dosimeter, thiocyanate and ceric systems, for example. 

Fig. 3. Compilation of radiolytic yields of the Fricke dosimeter in aerated conditions for various ions and energy. The squares are unpublished results obtained from 34 MeV protons, 1 GeV carbon ions and 2 GeV argon ions.

A shutter and cutoff filters are usually placed between the light source and the irradiation cell to minimize photolysis effects. For example, when the MV +/ formate dosimeter is used (see Table 8), it is essential to exclude UV light to prevent photolytic generation of MV+, which is also the product of this dosimeter system. Similar considerations apply to the ferrocyanide and Fricke dosimeters where photo-oxidation of Fe to Fe can occur. Different filters are sometimes mounted on a wheel that can be remotely controlled, possibly by a computer, as it is done for the shutter. 

One of the earliest devices for the measurement of radiation dosage, the Fricke dosimeter, is based on the oxidation of the ferrous ion by OH radicals produced in the radiolysis of a dilute aqueous solution of ferrous sulfate ... 

Source of 7-radiation. We applied a cylinder of Co with an activity of about 6 to 7 curies. The dose rates in reaction vessel I were 1.1 to 1.3 X 10 rad per hour (Fricke dosimeter). The dose rates in the dilatometers were 200, 50, and 22.2 rad per hour, depending on the distance from the source. These values were determined by an electrostatic dosimeter, which was dipped in the dilatometers. The absolute error in this case may be it 20% the proportions between the three values are exact. 

Several methods exist for the identification and quantification of the HO and H02 radicals generated by the sonolysis of water. These species can oxidize ionic moieties e.g. Fe2+ into Fe3+ (the Fricke dosimeter) and I- into iodine. In addition, either can dimerize to form hydrogen peroxide (Schemes 2 and 3), which can then be titrated using conventional techniques. The HO will also react with terephtha-late anion in aqueous solution to produce hydroxyterephthalate anion, a fluorescent material which can then be estimated using fluorimetry. 

Price and Lenz [188] compared the TA probe with the Fricke dosimeter (Fe2+ — Fe3+), using a Sonics and Materials VC 600 horn operating at 20 kHz. 

Since this chapter appears in a volume devoted to sonochemistry, chemical probes would appear to be the most attractive since they could allow direct comparisons with other chemical reactions. Chemical dosimeters are generally used to test the effect of an ultrasonic device on the total volume of the reactor. Local measurements can however be made with very small cells containing the dosimeter which could be moved inside the reaction vessel as with a coated thermocouple. Most of these chemical probes are derived from reactions carried out in an homogeneous medium, e.g. Weissler s solution, the Fricke dosimeter, or the oxidation of terephthalate anions. Among these the latter shows promise in that despite the fact that to date it has been much less used than Weissler s reaction it seems to have higher sensitivity and better reproducibility. 

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