Ferrous Sulfate Dosimeter Research Articles

Calibration of the Absorbed Dose Produced in Water by Betatron Electrons with the Benzoic-Acid Dosimeter

Monitoring of betatron electron beams used for therapy in the United States during the past decade has most frequently been done with a transmission ionization chamber, the output of which is calibrated periodically in terms of the reading of a Victoreen ionization chamber surrounded by sufficient additional plastic material to obtain the maximum response (1, 2). These monitor measurements may be converted to absorbed dose by calculation (3) or by calibration with the absorbed dose calorimeter (4). This conversion is more conveniently accomplished through the use of a suitable chemical dosimeter. Such an approach is also more direct than the use of calculated conversion factors, which necessarily involve major assumptions. In the experiments to be described here the benzoic-acid dosimeter has been used to determine the absorbed dose rate produced by betatron electrons at the depth of relative maximum dose in water. These measurements have been related to the conventional and arbitrary specification of betatron electron exposure in terms of the reading of a Victoreen thimble chamber inserted in a polystyrene block. Chemical yield and Victoreen chamber readings have been obtained for all field sizes and energies (6 to 20 Mev) used in therapeutic applications of the betatron electron beam. Replicate determinations of energy absorbed with the Fricke ferrous sulfate dosimeter for all combinations of field sizes and energies would be very time-consuming at therapeutic dose rates. Achemical dosimeter in which benzoic acid is oxidized to salicylic acid is at least ten times more sensitive than the Fricke dosimeter (5), and its use permits considerable saving of time. Since the absolute yield of this dosimeter for electrons is not known, it was calibrated in terms of the Fricke dosimeter for 10- and 20-Mev electrons, on the basis of 15.5 ferricions per 100 e.v. absorbed for the absolute yield of the Fricke dosimeter. The Fricke dosimeter solution was irradiated in the identical geometry, as described below, and in the same containers as the benzoic acid dosimeter. The irradiation field size was 6 × 8 cm. for both 10- and 20-Mev electrons. The ferrous sulfate solutions were irradiated to 5,200 rads and the benzoic acid solutions to 250 rads. The irradiations were monitored by a special transmission ionization chamber and integrating circuit of very good reproducibility (2). Three samples of each chemical dosimeter were irradiated, in alternating sequence, at each energy. A direct calorimetric determination of this yield for a variety of electron energies is now in progress in our laboratory. Experimental Twice recrystallized reagent grade benzoic acid was used throughout. The dosimeter solution consisted of an aqueous solution 1 millimolar in benzoic acid and 10 millimolar in sodium hydroxide. A large cylindrical tank of water 20 cm. deep and 15 cm. in diameter was irradiated.

The Relative Biological Effectiveness of 22-Mevp X-Rays, Cobalt-60 Gamma Rays, and 200-Kvcp X-Rays: II. The Use of the Ferrous Sulfate Dosimeter for X-Ray and Gamma-Ray Beams

The Fricke ferrous sulfate dosimeter (1) has served as a verification of the method of dose measurement in the experiments reported in this series of papers. Irradiations of the chemical dosimeter were performed in the same exposure apparatus and with the same method of dose measurement as was used for the RBE experiments (paper I of this series). The ferric yields (G-ferric ions oxidized from the ferrous state per 100 ev) so determined are in fair agreement with others in the literature. For the successful use of the ferrous sulfate dosimeter for X-ray and y-ray beams it is necessary to know the yield of ferric ions and the method of converting from energy absorbed in the dosimeter to energy absorbed in a sample (say, of water or tissue) for which the dosimeter has been substituted. These questions will be considered, and the answers will be presented in a form convenient for practical use.

Investigation of the Spectrophotometric Method of Measuring the Ferric Ion Yield in the Ferrous Sulfate Dosimeter

The sensitivity of the spectrophotometric method of measuring the ferric ion yield in the ferrous sulfate dosimeter was increased by measuring the absorbance of the radiation produced ferric ions at 224 m mu , instead of at 304 m mu . The higher sensitivity is due to the higher raolar extinction coefficient at 224 m mu which is 4565 liter mole/sup -1/ cm/sup -1/, compared with 2196 liter mole/sup -1/ cm/sup -1/ at 304 m mu . By this method, the measuring range of the ferrous sulfate dosimeter can be extended to smaller doses. The much smaller tcmperature dependence and smaller acidity dependence of the molar extinction coefficient at 224 m mu , compared with those observed at 304 m mu , increase the reproducibility of dose measurements. (auth)

Nitrous Oxide as a Dosimeter for Ionizing Radiations

Absolute measurements of the radiolytic yields of O/sub 2/, N/sub 2/, and oxides of nitrogen (NO + N0/sub 2/) from gaseous nitrous oxide, with tritium as internal source, have been compared with the yields obtained by irradiation with Co/sup 60/ gamma rays and 4-Mev x rays based on the ferrous and ceric sulfate dosimeters. Of the three products measured, nitrogen gives the most reliable results, with G(N/sub 2/) = 11.0 plus or minus 0.4. The oxygen and oxides of nitrogen yields are affectsd by foreign gases and by the analytical methods employed. Under certain conditions a liquid dosimeter solution can be used in conjunction with electron density ratios to calculate energy absorption in a gas irradiated in the same vessel. (auth)

The Relative Biological Efficiency of 20-Mev Electrons and 180-Kvp X-Rays in Escherichia coli Inactivation

The RBE of 20-Mev electrons as compared with 180 kvp x rays was determined from dose-survival curves for E. coli B/r, irradiated in the resting state. Absorbed doses produced by the 180-kvp x rays were measured with the Fricke ferrous sulfate dosimeter on the basis of Victoreen chamber measurements with correction and conversion factors applied as described. The absorbed dose of electrons was determined with the Fricke ferrous sulfate dosimeter and a G value of 15.5 molecules of ferric ion produced per 100 ev. The RBE was determined to be 0.82 hr at 1500 deg 0.01 with E. coli B/r.

Radiation-Induced Changes in Susceptibility of Substrates to Enzymatic Degradation

Albumin (bovine) fraction V, hemoglobin (bovine), and Hammerstein casein were obtained from the Nutritional Biochemicals Co.; soluble starch from the Merck Co.; and cellulose gum from the Hercules Powder Co. Recrystallized deoxyribonuclease I, trypsin (twice recrystallized, salt-free), and cellulase were purchased from the Worthington Biochemicals Co. Nuclei, isolated from rat liver by the method of Dounce et al. (4), were suspended in distilled water. Conditions of Irradiation The samples of substrate or isolated rat liver nuclei were irradiated with y-rays from a cobalt source (approximately 400 curies) at room temperature. The dose rate was 4600 r/min as measured by a ferrous sulfate dosimeter.

Chemical Dosimetry of Gamma Rays, Neutrons and Accelerated Electrons

A ferrous sulfate dosimeter solution was irradiated in pyrex glass capsules from several laboratory Co/sup 60/ sources. The results are plotted in a graph. The standardized sources were then used to determine the effect of formic acid as an organic impurity on the ferrous sulfate dosimeter. (OID)

A Theoretical Interpretation of the Effect of Radiation Quality on Yield in the Ferrous and Ceric Sulfate Dosimeters

Data are tabulated on the assumed and calculated yield values for ferrous sulfate and ceric sulfate dosimeters exposed to cobalt-60 gamma radiation and to polonium-210 alpha particles. Results are compared with predictions for tritium beta particles. The basic Jaffe formula for combination between radicals diffusing from a cylindrical column is adapted to allow for back and competitive reactions. The adaptation of the Jaffe formula, application of combination formulas, experimental data on the hydrogen and hydrogen peroxide yield, and the formation of water by recombination are discussed. LET are also presented and discussed. Theoretical predictions and experimental data are compared. (C.H.)

Ferric Ion Yields in Ferrous Sulfate Solutions Irradiated with Low-Energy X-Rays

A ferrous sulfate dosimeter was used to measure the absorbed doses in a study of changes induced in aqueous gel systems by low-energy x rays. The procedure used is described and results are tabulated. (J.R.D.)

Alpha-Particle Irradiation Apparatus

An apparatus having up to four Po210 sources suitable for radiation chemistry studies in liquids is described. Each unit consists of a source and housing that supplies a collimated beam of α particles, a variable speed stirrer, and an irradiation cell holder. Energy output is measured with the ferrous sulfate dosimeter.

Determination of the absorbed dose in radiation therapy.

The adoption of basic energy units for the expression of the absorbed dose of radiation (1) makes desirable a means for determining absorbed dose in rads under conditions simulating clinical radiation therapy and in actual clinical therapy. The ferrous sulfate dosimeter provides a means for determining absorbed dose under the first of these conditions (2). The ferrous sulfate dosimeter has been used to determine the average absorbed dose (rads) both within and outside of the geometric beam of a 2-fEV Van de Graaff accelerator, using a multiple compartment Lueite tank. The volume of solution irradiated is known, and the integral absorbed dose (gram rads) is the product of the average absorbed dose and the mass irradiated. The tank is filled with the solution, and the geometric beam is directed into one of the tank compartments for the determination of the average absorbed dose within the beam. The remaining compartments, also filled with the solution, provide a scattering medium and permit the determinatio...

Advances Toward a Stable Sensitive Iron Dosimeter

Utilization of the conventional ferrous sulfate dosimeter indicates the desirability of a chemical system which exhibits greater stability and is more sensitive to energy absorbed from radiation. Greater apparent sensitivity has been achieved (a) by comparing with a potentiometer the single electrode potentials of irradiated against unirradiated solutions, (b) by concentrating the ferric ion in a solution on an ion exchange column, and (c) by using aqueous solutions other than that proposed by Fricke. The potentiometer method is somewhat more difficult than that using the DU spectrophotometer and has not been exploited. The column concentration is successful, although in at least one case the resin in the column appears to cause a small amount of oxidation of ferrous to ferric ion. Most of our work to date is concerned with other solutions. A cursory examination of many metal cations showed that iron exhibited the greatest sensitivity and it has been adopted throughout. To stabilize the system, additive chemicals have been sought which would form complexes both with ferrous and with ferric ions. Addition of inorganic anions generally produces a dosimeter not more sensitive than that of Fricke. Addition of organic acids can produce a dosimeter of greater or lesser sensitivity, apparently depending on the groups contained in the acid, as well as on spectral considerations. Some of these dosimeters also exhibit long-term stability. Our current standard has a G of 40 or so and has exhibited no observable change in the absence of irradiation since being mixed in June 1956. The composition is as follows: To 1 N H2SO4 add 7 × 10−4 molar benzoic acid and then 7 × 10−4 molar Fe+2 as FeSO4. The optical density is read at 2715 Å. Having stabilized the ferrous system, for example with benzoic acid, further additions of aliphatic organic acids can increase or decrease the sensitivity. Oxalic acid (1.5 gm./liter) gives a G ∼ 60. Tartaric acid (0.4 gm./liter) can give G ∼ 130 under suitable conditions. There appear to be drift considerations with systems investigated to date when G > 45. Wavelengths of absorption and transmission, pH range to provide known complexing and to keep the iron from adhering to container walls, temperature control of solutions, and the kind of groups being added are all items of importance. Some insight is being gained as to the effect on sensitivity of some of the functional groups in the additive organic acids.

Chemical Yields of Ionizing Particles in Aqueous Solutions: Effect of Energy of Protons and Deuterons

Chemical effects produced in aqueous solutions by ionizing radiations are known to depend on the energy and mass of the ionizing particles. Light-particle radiations yield predominantly free radicals, whereas heavy-particle radiations yield principally hydrogen and hydrogen peroxide (1-4). According to current theory, hydrogen and hydrogen peroxide originate by a recombination of the primary hydrogen and hydroxyl free radicals in the track before appreciable diffusion takes place. As the density of ionization along the particle track increases, the greater becomes the probability of recombination, and consequently the yield of hydrogen and hydrogen peroxide is greater. The present work was undertaken to supply ferric ion yields for protons in the energy range from 0.3 to 2.0 Mev and for deuterons in the range from 3.5 to 21.2 Mev. This work was carried out with the Fricke and ferrous sulfate-cupric sulfate dosimeters. In the former dosimeter the free radical plus molecular hydrogen peroxide yields are measured, whereas in the latter dosimeter only the hydrogen perodixe formed in equimolar amounts with hydrogen is measured (5). G(Fe+++) and G(Fe+++ Cu++) experimental quantities obtained by the use of these dosimeters are interpreted in terms of free radical and molecular product yields for the decomposition of water by protons and deuterons.

Energy Required to Produce One Ion Pair for Several Gases

The absolute values of $W$, the energy required to produce one ion pair, for electrons have been determined for several gases. A parallel plate extrapolation ionization chamber in conjunction with a ferrous sulfate dosimeter was used. The gases investigated were air, nitrogen, oxygen, carbon dioxide, argon, methane, and ethylene; and the absolute values of $W$ were 33.9, 34.8, 30.9, 32.6, 25.5, 26.8, and 26.3 ev, respectively.