Thiocyanate dosimeter

Buxton GV, Stuart CR (1995) Re-evaluation of the thiocyanate dosimeter for pulse radiolysis. J Chem Soc Faraday Trans 91 279-281... 

The chemical dosimeter that is used most frequently is the thiocyanate dosimeter [119]. Other chemical dosimeters for pulse radiolysis are ferrocyanide [119], modified Fricke (Super-Fricke) [119], hydrated electron [120], 02-saturated solutions of potassium iodide [112], and N20-saturated solutions of methylviologen and formate [118]. The C(N02)4 (tetranitromethane, TNM) dosimeter is used in pulse radiolysis experiments with simultaneous optical and conductometric detection [121-124]. The composition and characteristics of the various chemical dosimeters used for pulse radiolysis with optical detection are listed in Table 8. 

The thiocyanate dosimeter is not suitable when the dose per pulse is large and/or the detector response time is long, because the product (SCN)2 decays in a fast self-reaction, the rate of which increases with increasing dose. For these conditions it is better to use the ferrocyanide dosimeter for high dose and the methylviologen dosimeter for low dose, because the respective products Fe(CN)6 and MV are stable. The hydrated electron dosimeter is suitable for low doses it should be used cautiously, since the G value changes with measurement time. 

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) ... 

In pulse radiolysis, the dose measurement should be carried out in the measuring cell under identical conditions with the experiments. Therefore, for dosimetry purposes it is advisable to use the same detection system that is also utilized in the measurements. In practice mostly the thiocyanate dosimeter and, less frequently, the hydrated electron dosimeter is used in pulse radiolysis studies (Fielden 1982). 

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. 

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