DD226394A1 - ANALYTICAL MATERIAL FOR DOSIMETRY OF IONIZING RADIATION - Google Patents

Abstract

The previous disadvantage in the application of electron acceleration systems for irradiating a wide variety of products, the only inadequate quality or nonexistent dosimetry for analysis, control and monitoring of these systems, is eliminated by the use of new analytical materials. For the analysis of the radiation fields, these materials use polyethylene terephthalate films, the evaluation of which takes place via transmittance value differences. The films usable in the range of 0-2 500 kGy are characterized by the following parameters: density / cm31.3931.397Dickemm 951 tensile strengthN / mm2 20010 elongation% 10010crystallinity% 551.5Thermo shrinkage%%

Description

Substantially limiting conditions of use. Further advantages are the very good surface strength, which prevents scratches due to mechanical influences. Even with the range of 300 to 2500 kGy, which was previously not evaluable with dosimeter films, the described advantages are retained. It is also surprising that the films produced according to the strict technological and chemical regimes largely retain their good physical-mechanical characteristics and are not brittle by the radiation exposure. The films can be evaluated by changing their permeability, which is advantageously measured at 340 nm.

It is also unexpected that the resulting changes in the permeability of the films, as a result of the irradiation, remain constant under a wide variety of climatic conditions and that no time-dependent displacement of the measured values occurs. Thus, a problem-free evaluation is possible even after a variety of times. These slides can be easily archived and show even after months unchanged measured values, a significant advantage in production processes and measurements that run over longer periods. Other advantages are that even with the high radiation doses no degradation products are formed, the z. B. lead to contamination of the film and thus to influence the evaluation. Another important advantage of the films of the invention is their universal readability to a variety of photometers, due to the measuring wavelength and the easy preparation of the test samples z. B. by cutting. The invention will be explained in more detail below with reference to examples.

embodiments example 1

A polyethylene terephthalate film is produced, the physical parameters of which are given in Table 1.

Table 1

Parameter value

Density g / cm ³ 1.395

Thickness μιη 99

Tensile strength N / mm ² 204.5

Elongation% 108

Crystallinity% 55.8

Thermal shrinkage% * in both directions <0.8

* determined after 30 min at 150 ⁰ C.

Example 2

A polyethylene terephthalate film produced according to Example 1 is cut to size corresponding to the irradiation zone of an electron accelerator, arranged stationary in the radiation field and irradiated for an irradiation time of 10 seconds.

at a dose rate in the measurement plane of 8.3 kGy / sec. irradiated. The exact dose rate distribution in the entire radiation field of the electron accelerator is determined by simple point-by-point measurement of the transmittance value differences. For determination, test pieces are punched or cut out of the film. Table 2 shows the dose rate distribution of a radiation field of 2.0 0.5 m. The numerical values document the relative dose at the measuring point.

The high uniformity of the film makes it possible to easily analyze even larger radiation fields only a film of appropriate size.

Example 3

From the Dosimeterfolie invention according to Example 1 pieces are cut to 2 x 2 cm and from this a package of 120 superimposed pieces of film formed. After the short-term irradiation (irradiation time 4 s, dose rate in the measurement plane of 8.3 kGy / s) of this film package, the electron energy-dependent depth dose distribution is determined from the transmission value differences of the individual films. Table 3 and Figure 1 contain the results of an irradiation facility at 3 MeV.

Example 4

From a prepared according to Example 2 and irradiated polyethylene terephthalate film samples are cut and exposed to different humidities and temperatures. In the range up to 95% relative humidity and 100 ⁰ C, no changes in the measurement results are observed. Further film samples are measured within 6 months at intervals of 10 days. These results also show no deviation from the values determined in Example 2. This confirms the excellent properties of the dosimeter film.

Claims (1)

1. Analytical material for dosimetry of ionizing radiation based on polymer films, characterized in that it consists of polyethylene terephthalate having a density of 1.393 to 1.397 g / cm ³ , a film thickness of 99 ± 1 pm, a tensile strength of 200 ± 10 N / mm ² , an elongation of 100 ± 10%, a crystallinity of 55 ± 1.5% and a thermal shrinkage <1.5%. For this 1 sheet drawing Field of application of the invention The invention relates to an analytical material based on polymer films for dosimetry of systems for generating ionizing radiation. Characteristic of the known technical solutions In recent years, there has been a marked increase in the development and application of electron accelerators, X-ray and gamma irradiation equipment. These systems are used in production and research in a wide variety of application forms. The radiation-chemical treatment of products of different species offers tremendous advantages due to the significant quality gains, which are often achieved without harmful waste products, which in addition can usually only be achieved by this procedure. The development of the advantageous properties and their constant reproducible setting presupposes the knowledge of the absorbed dose and its distribution, or in addition to this information their constant control in continuous production processes. If one can determine today that the constructive conditions of powerful irradiation facilities were created, ie the procedure of a modern radiation technology is present, then the important field of metrological problems, so the reliable Strahlendosimetrie developed only inadequate. The few analytical materials known for this purpose generally use a very wide variety of polymer films which may also contain dyes (Kaindl, K., and Graul, EH "Radiation Chemistry Base Technology and Application" Hüthig-Verlag Heidelberg 1967; Boag, JW Radiation Res. 9 [1958 ], 559.) The action of, for example, electron beams destroys the dye molecule, so that the loss of dye density permits statements about the radiation dose (CH-PS 491394, DD-PS 124 082). using the dye dimethoxydiphenyl-bis-azo-8-amino-1-naphthol-5,7-disulfonic acid and the polymer cellulose acetate (Faterpaker, SA, Patnis SP Angew. Makromol., Chem. 90 [1980], 69-81) , The non-uniformity of the dye distribution in the polymer and the insufficient physical properties of these films have not been widely used. Higher doses of radiation could not be measured, since the resulting damage to the film led to uselessness. Furthermore, cellulose acetate films containing no dyes have been described. Their properties are such that they are suitable for higher radiation doses, eg. As when used on accelerators high performance, not satisfactory. Thus, these films significantly change their geometry, and the radiation exposure destroys the polymer structure, resulting in easily brittle and thus unusable films. This clear embrittlement should be avoided by the use of polyethylene films (Grünewald, Th., Rumpf, G. Atompraxis 11 [1965] 2, 95-98; Kügler, I. et al., Atomic Energy 4 [1959] 1,23). But even these films are not to be used for very high radiation doses. In addition, these films have insufficient surface hardness, which can cause mechanical damage during the measurement process. Other Dosimeterfolien can not be used in daylight, otherwise a premature destruction or activation of the detection agent would occur, a handling requirement that precludes a universal use. On this basis, for. B. Dosimeterfolien made of polymamide containing radiochromic Aminotriphenylderivate as a coloring substance (DD-PS 126 045). In addition to the disadvantages already described, an application is only possible in the range of 0 to 300 kGy. Another disadvantage of most previously known films is their high sensitivity to moisture, resulting in the expiring swelling processes changes in geometry and thus in the measurement accuracy. US Pat. No. 3,450,878 describes a dosimetric method in which the dose measurement is carried out by determining changes in the viscosity of irradiated polyester films and comparison with a calibration curve. A disadvantage of this analytical element is the considerable workload associated with the determination of the viscosity and the viscosity measurement of irradiated polyester films, which involves a relatively large error; since under the influence of high-energy radiation in addition to the chain degradation of the polymer body, the formation of functional groups takes place, which are capable of inter- or intramolecular interactions and thereby can influence the viscosity value undefined. Thus, at present, the state is reached worldwide that, with significant rates of increase in the construction and use of high power irradiation facilities for higher irradiation dosimeters, little useful film dosimeters are available for lack of suitable analytical elements. Object of the invention The object of the invention is to provide suitable analytical materials for the dosimetry of electron and beta as well as X-ray and gamma radiation up to energy doses of 2500 kGy. Explanation of the essence of the invention The object of the invention is the production and use of dosimeter films for dosimetry on irradiation facilities, these films should be applicable over the wide field of different amounts of energy and to maintain their geometry, their visual transparency and their good physico-mechanical properties in the measurement processes. According to the invention the object is achieved in that analytical material for dosimetry of ionizing radiation based on polymer films of polyethylene terephthalate having a density of 1.393 to 1.397 g / cm ³ , a film thickness of 99 ± 1 pm, a tensile strength of 200 ± 10 N / mm ² , an elongation of 100 ± 10%, a crystallinity of 55 ± 1.5% and a thermal shrinkage <1.5%. These films can be used in a hitherto inaccessible measuring range from 0 to 2500 kGy. These slides do not lose their visual transparency, and their geometry remains unchanged. This advantage of good geometry stability is maintained even at different humidities and temperatures. There are none