Pulse dosimetry

In the following text, a few dosimeter systems will be mentioned that are commonly used in radiation chemistry. For a more detailed treatment of chemical and physical dosimetry, see O Chap. 49 in Vol. 5 on Dosimetry Methods. However, more attention will be paid to pulse dosimetry that is used in pulse radiolysis investigations. 

A large variety of aqueous and a few nonaqueous solutions have been used or proposed as chemical dosimeters with respective dose ranges for use (Spinks and Woods, 1990 Draganic and Draganic, 1971). Of these, a special mention may be made of the hydrated electron dosimeter for pulse radiolytic use (l(h2 to 10+2 Gy per pulse). It is composed of an aqueous solution of 10 mM ethanol (or 0.7 mM H2) with 0.1 to 10 mM NaOH. Concentration of hydrated electrons formed in the solution by the absorption of radiation is monitored by fast spectrophotometry, which is then used for dosimetry with the known G value of the hydrated electron. 

The first pulse radiolysis experiments to measure G°(e ) directly were made in the 1970s, with reported values of 4.0 0.2 molecules (100 eV) at 30 psec [45] and 4.1 0.1 molecules (100 eV) at > 200 psec [46]. The latter value was subsequently revised to 4.6 0.2 molecules (100 eV) at 100 psec [47], and later a yield of 4.8 0.3 molecules (100 eV) at 30 psec was reported by Sumiyoshi et al. [48]. The method of evaluating G(e ) at these short times is either to use dosimetry [45,46] and the molar absorption coefficient of e, or to compare the optical absorbance at short times with that observed at 10 -10 sec and take G(e q) = 2.7 molecules (100 eV) at this time [48]. The causes of the discrepancies between these pulse radiolysis values have been reviewed recently by Bartels et al. [49], who have also made new measurements of the spur decay of e. ... 

Schuchmann H-P, Deeble DJ, Phillips GO, von Sonntag C (1991) Pulse radiolysis with conductometric detection two approaches to absolute dosimetry. Radiat Phys Chem 37 157-160 Schuchmann MN, Schuchmann H-P, von Sonntag C (1989) The pJCa value of the O2CH2CO2H radical the Taft a constant of the -CEi202 group. J Phys Chem 93 5320-5323 Schuler RH, Hartzell AL, Behar B (1981) Track effects in radiation chemistry. Concentration dependence for the scavenging of OH by ferrocyanide in N20-saturated solutions. J Phys Chem 85 192-199... 

The most commonly used sources of radiation are the 60 Co gamma source for continuous irradiation and pulsed high-energy (>1 MeV) electron beams for fast kinetic studies. Detailed descriptions of several such sources and accelerators are given in numerous books, as are the various methods used by radiation chemists for dosimetry, sample preparation and irradiation, and common product analysis. Several new developments in the analytical procedures, both in the determination of final products and in the direct observation of transient species, will be discussed below. 

Dosimetry. The dose given by each pulse was monitored with a secondary emission chamber (abbr. SEC). The SEC was calibrated by... 

Dosimetry. For dose measurements the adenine powder in the sample cup was replaced by a similar quantity of LiF powder (TLD 100). The thermoluminescence of the LiF was measured 24 hours after a single pulse irradiation on a commercial reader, the Madison Research S-2L. A typical dose was 10 to 15 Krad in water from a 1.6 /xsec. pulse. 

The Dosimetry of Very High Intensity Pulsed Electron Sources Used for Radiation Chemistry II. Dosimetry for Gaseous... 

Ion chambers, the common standard for dosimetry of gases at lower intensities, cannot be used. A 1 Mrad pulse in air produces about 2 X 10° esu. per cc. in 100 nsec., which is orders of magnitude higher than can be used in ion chambers (5). 

The use of calorimetry as a standard for radiation dosimetry is well established (9) and we have previously demonstrated that adiabatic calorimetry in stainless steel cells can be used for very high intensity electron pulses (16). The electron stopping parameters given in Table I are from experimental papers but agree within 1% with those calculated by Meisels (10) from Bethe s equations and any errors introduced by these must be insignificant. Calorimetry then, can be considered to be an acceptable standard for gas phase dosimetry of intense electron pulses. 

Hydrated Electron and Thermoluminescent Dosimetry of Pulsed X-ray Beams... 

Two dosimeters suitable for monitoring single pulses of x-rays with doses in the range 1 to 100 rads at dose rates greater than 103 rads/sec. are described. Both systems were independently referred to Fricke dosimetry as the absolute standard and cross checked under pulse conditions. In one system the transient hydrated electron absorption produced by the pulse is measured by kinetic spectrophotometry as an indication of the dose. In the other, doped LiF crystals of about 50 mg. are irradiated in sealed polyethylene bags under conditions of electronic equilibrium. Readout of the irradiated crystals was done on a standard commercial machine. Both methods were readily capable of 5% precision and with a little care better than 3% is obtainable. 

Comparison between TLD dosimetry and the hydrated electron absorption showed excellent linearity. Figure 4 shows a typical calibration curve the points on this curve represent data from two LiF crystals with their counts per pulse normalized to the same weight of crystal. 

TLD and Fricke dosimetry were also compared for x-ray pulses of 10 to 1000 X 10"9 sec. (nsec.) duration at low doses. The results are given in Table I. They show good agreement with the 60Co calibration and a dose rate independence from 0.90 rad/sec. up to 1.5 X 106 rad/sec. 

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