Dosimetry Fricke dosimeter

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. 

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. 

Dosimetry. The dose rate of 2.0 X 1018 e.v. grams"1 min."1 in water vapor was based on the yield of hydrogen from ethylene, using G(H2) = 1.31 (23). Using this dosimetry, the yield of nitrogen from 700 torr N20 irradiated in the same experimental set-up at room temperature was G(N2) = 10.0 0.3. The relative dose rate was checked periodically with the Fricke dosimeter. The energy absorbed by each component in a mixture was calculated, assuming it to be directly proportional to the electron density of that component. 

Dosimetry is the measurement of absorbed dose. The unit of absorbed dose is the gray (Gy). Because dose is a measure of absorbed energy, calorime-try is the fundamental method of measurement. However, calorimetry suffers from being insensitive, complex, slow and highly demanding in technical skills and experience. Primary dose measurement is usually done with substances that are chemically changed quantitatively in response to the amount of radiation absorbed. For most purposes the standard primary system is the Fricke or ferrous sulfate dosimeter. In this system, which consists of a solution of ferrous sulfate in dilute sulfuric acid, ferrous ions Fe are oxidized by absorbtion of radiation to ferric ions Fricke dosimeters are usually presented in glass... 

Whatever the source of radiation used, the dose delivered to the biological samples is determined by the time of exposure to radiations. Thus the dose delivered by the radiation source must be measured with precision. Dosimetry can be performed with a ferrous sulfate solution (Fricke and Morse, 1927), thermoluminescent dosimeters, bleaching of films (Hart and Fricke, 1967), Perspex dosimetry (Berry and Marshall, 1969), or calibration with standard enzymes (Beauregard et al., 1980 Beauregard and Potier, 1982 Lo et al., 1982). In many laboratories, control enzymes with known D37 are added to protein preparations as internal standards so that any variation between experiments could be corrected for. Because of the better precision of dose rate in Gammacell irradiators, this precaution is not necessary. 

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. 

Figure 1. X-irradiation set-up for simultaneous Fricke or LiF and hydrated electron dosimetry. Left to right Linac, tungsten target, an 11.3 cm. water container with dosimeter bulb on the beam axis and a multiple reflexion cell for transient absorption spectrophotometry. From the multiple reflexion cell the light beam passes into a monochromator-photomultiplier assembly...

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