Transfer dosimeter

Table 6.4 lists some categories of improved and future dosimetry systems, their analytical methods, and several examples of each. This list includes both reference and routine dosimeters, as well as some of those suitable for transfer dosimeters, all three of these being defined in Chapter 5 of McLaughlin et al. (1989). 

One of the most promising dosimeters, which may under careful preparation and calibration, qualify as a reference dosimetry system, is L-a alanine as measured by EPR spectrometry (Regulla et al., 1993). It is also proving to be useful as a transfer dosimeters, as shown by its application in the IAEA International Dose Assurance Service (IDAS) (Nam and Regulla, 1989) and in the reference dosimetry service to industry by the National Physical Laboratory (NPL). 

L-a-alanine has been employed as an ESR dosimeter since 1962 [26], Regulla et al. [7, 27] have reported detailed studies on its dosimetric properties. It is the most commonly used material in the field of ESR dosimetry being accepted by the International Atomic Energy Agency (IAEA) [28] and other agencies as a secondary reference and transfer dosimeter for high (industrial) dose irradiation. 

Studies in indoor environments of dermal contact transfer required an estimate, and a tight-fitting whole-body dosimeter was adopted and initially considered as a surrogate for skin (Krieger et al., 2000). Contact with treated surfaces was limited to feet, hands, limbs, and torso. Standardized Jazzercize to represent daily human activities and maximum contact was incorporated into protocols for indoor exposure studies (Ross et al., 1990,1991). Comparative studies will be reported elsewhere (Krieger et al., 2000). 

A short-handled modification of the CDFA (or California) roller was passed over an all-cotton dosimeter (1711 cm2) (Ross et al., 1991) to collect transferable chlorpyrifos at the University Club. All results were expressed as pg chlorpyrifos per cm2 of the collection surface. 

Alanine dosimeters are based on the ability of 1-a alanine (a crystalline amino acid) to form a very stable free radical when subjected to ionizing radiation. The alanine free radical yields an electron paramagnetic resonance (EPR) signal that is dose dependent, yet independent of the dose rate, energy type, and relatively insensitive to temperature and humidity. Alanine dosimeters are available in the form of pellets or films and can be used for doses ranging from 10 Gy to 200 kGy. A reference calibration service using the alanine EPR system was developed and the scans were sent to the service center by mail. Currently the available system allows transferring the EPR scan to a NIST server for a calibration certificate. This way the procedure has been shortened from days to hours. ... 

Fang X, Mark G, von Sonntag C (1996) OH-Radical formation by ultrasound in aqueous solutions, part I. The chemistry underlying the terephthalate dosimeter. Ultrason Sonochem 3 57-63 Fang X, Schuchmann H-P, von Sonntag C (2000) The reaction of the OH radical with pentafluoro-, pentachloro-, pentabromo- and 2,4,6-triiodophenol in water electron transfer vs. addition to the ring. J Chem Soc Perkin Trans 2 1391-1398... 

LaVerne JA, Schuler RH. (1996) Radiolysis of the Ericke dosimeter with 58Ni and 238Lf ions Response for particles of high linear energy transfer. J Phys Chem 100 16034-16040. 

Another possible probe could be the Michael addition of diethyl malonate to chalcone (Scheme 7) [192], This dosimeter operates in a toluene solution of chalcone and diethyl malonate with suspended powdered potassium hydroxide. Under sonication and in the presence of a phase transfer agent this reaction is too fast, but its rate can be conveniently controlled by adjusting the reagent concentrations in the absence of the phase transfer agent. Interestingly, the size of the KOH particles is not an important parameter since this solid is rapidly disrupted down to an average size of ca. 60 pm. 

The Thiocyanate Radiolysis Dosimeter. The thiocyanate dosimeter is a reliable, accurate, and convenient means of dose calibration in pulse radiolysis experiments, when coupled with a physical dosimeter of the type described earlier. An aqueous solution of KSCN (10 mmol dm" ) is saturated with N2O. The eaq are quantitatively converted to HO within about 3 ns, as described above (reaction 29). The hydroxyl radicals then oxidize SCN", transferring the radical center to the thiocyanate radical (SCN ) (reaction 30). The SCN radical rapidly couples with a thiocyanate ion, producing (SCN)2 ", a relatively stable radical with a high molar absorptivity (reaction 31) ... 

It is illustrative to consider the ratio of the dose ds(r) in a dosimeter with an energy transfer coefficient —s to the dose d (r) in water with... 

Let us assume that we want to measure the G-value, number of molecular changes per 100 e.v., of Ce4+ — Ce3+ in a ceric-sulfate solution as a function of the concentration. We measure the dose in a Fricke dosimeter vial or ferrous-cupric dosimeter vial at the same place as the vial containing the ceric solution, and then, as is usual, we correct for the difference in the energy transfer coefficient at 1.25 Mev. and for the difference in density of the solutions. However, as shown in Equation 14 and in Table V and Figures 3 and 4, these corrections are entirely inadequate because of the large difference in buildup factors. For 0.4M ceric sulfate solution, the correction caused by the buildup factor is 72% at fit r = 1 122% at /At r = 2 and 155% at fit r = 4. 

Photographic emulsions are sensitized by ionizing radiation resulting in darkening upon development. This is used in the film dosimeter for measurement of 0-, y-, or n-doses. In order to differentiate between various types of radiation, the film is siUTOunded by filters or transfer screens. Although any type of film may be used, special nuclear emulsions have been designed. The dose received is directly proportional to the optical daisity of the exposed film. Film dosimeters are useful in the same range as the pen dosimeter, and both are used for personnel measurements. While the pen dosimeter can be read directly, the film dosimeter requires development. 

The requirement to access cells for maintenance purposes and to transfer full product containers to the vitrified product store offers the potential for >1-Sv doses to operators under fault conditions. In order to prevent such incidents, entries to cells are controlled via inner and outer shield doors that are interlocked to gamma monitors. Additionally Operating Rules and Instructions place requirements on operators with regard to man entries to cells and prohibit the presence or introduction of active product containers to specified cells. Personal Alarmed Dosimeters are routinely worn during cell entries to provide an immediate indication of high dose rates. 

The monitoring of dose can be performed with different techniques chemical systems (Fricke and ceric solutions [31]), radiochromic compounds (dyes [32, 33]), polymeric tapes (polyethylene [34], poly(vinyl chloride) [35, 36], poly(methyl methacrylate) [37-40], epoxy resin [41]), radiation thermoluminescence phosphors [42, 43]. Several requirements are imposed for a proper dosimeter similarity with processed material in respect with linear energy transfer, reproducibility, sensitivity, lack of the influence of humidity, stability after irradiation, easy to calibrate, appropriate dose range and dose rate, linearity and independency on the type of radiation, the response being constant in time, lack of post-irradiation modification. 

In case (1) in gamma facilities the dose vs. irradiation time (in plants with no product transport system) or the dwell time (in plants with product transport system) can be measured by using different reference standard, transfer standard, or routine dosimeters. In EB facilities, the dose vs. conveyor speed relationship can be measured mainly with process calorimeters, but other dosimetry systems with quick dose evaluation capabilities after irradiation can also be used for this purpose. 

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