9. 6  An Essential System for Wide Application of Ion Beams
- Development of an Induced Radioactivity Calculation Code Friendly to Accelerator Users
 


Fig. 9-12 Nuclear reactions in ion beam irradiation

Radioactivity is induced by nuclear reactions between incident ions and atoms in target materials. The reaction probability increases with the energy of the ions.


Fig. 9-13 Calculation flow of IRAC code

In this code, necessary data are automatically selected based on input data for incident particles and target nuclides. Radionuclides produced, radioactivity induced, and the gamma-ray dose equivalent are all calculated by means of simulation of the energy dissipation of incident particles and of nuclear reactions in the target materials.


Fig. 9-14 The relation between ion beam irradiation conditions and research field

Ion beams with a wide range of mass numbers and various target materials are of interest in the research fields of materials science and biotechnology. To suit each area of interest, the IRAC code system provides an isotope production cross-section library for 136 target nuclides from H to Bi and for incident particles covering acceleration energies up to 150 MeV for light ions and 500 MeV for heavy ions.

Recent technical progress with particle accelerators has made it easy to generate energetic ion beams and secondary neutrons. Research applications for ion beam irradiation are expanding broadly into the fields of materials science, medicine, biotechnology, and neutron science. Since radioactivity-inducing nuclear reactions occur when energetic ions and neutrons hit target materials and accelerator components, appropriate radiation safety control is required in order to minimize radiation exposure to personnel and the amount of radioactive waste. To conduct accelerator beam experiments safely and effectively, basic information about induced radioactivity and radionuclides produced should be available to accelerator users in the planning stage of such experiments, since induced radioactivity depends on the accelerated particle, acceleration energy, the material irradiated and experimental conditions.
In conventional practice, availability of the foregoing resource has not been required, because accelerator users were mostly nuclear scientists and the range of target materials was rather limited. In recent years, however, a number of non-nuclear users are conducting accelerator beam experiments with an extremely wide variety of target materials. Therefore, an induced radioactivity calculation system which can be easily accessed without expert knowledge is now essential.
The computer code system IRAC has been the first such calculation system to be developed. It allows us to easily calculate the radioactivity induced by ion beam irradiation over an energy range of several to several hundred MeV, where one only needs to provide the input parameters of the incident particles employed, and data on the target material (Fig. 9-14). It plays an especially important role for heavy ion beam irradiation, where the availability of induced radioactivity information from measured data is very limited.
The calculation code system has been successfully applied to an open system of facility management such as the screening of experiment proposals, the experimental programs, and safety control in the ion beam irradiation research facilities TIARA. The code system has also been applied to a wide range of research fields in accelerator science communities both inside and outside of the country.


Reference
S. Tanaka et al., The IRAC Code System to Calculate Activation and Transmutation in the TIARA Facility, J. Nucl. Sci. Technol., Supl. 1, 840 (2000).

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Persistent Quest - Research Activities 2001
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