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Chromosome changes after exposure to neutron radiation

The question of how harmful neutron radiation is plays an important role in radiation protection. In a project jointly carried out by PTB and other research institutes a new lower detection limit for chromosome changes in human lymphocytes has been achieved.

The arrow points to a dicentric chromosome developed after neutron irradiation. The additional constriction is clearly visible.

Different kinds of radiation fields induce different effects in living cells, even if the cumulative dose is the same. The varying relative biological effectiveness is described by the RBE factor. It indicates the ratio of the dose in a reference field (frequently the 60Co photon field) to the dose in the radiation field to be investigated, which leads to the same biological effect. RBE factors thus provide information about radiation-induced risks. Especially high RBE factors are obtained in the case of neutron irradiation in the energy range between 10 keV and 2 MeV.

In a cooperation between PTB and the Forschungszentrum für Umwelt und Gesundheit (GSF, Research center for environment and health) in München-Neuherberg, human lymphocytes were irradiated in a neutron field and, parallel to this, in a 60Co photon field. Lymphocytes are especially well-suited to yield information in the low-dose range (< 0,2 Gy).

After irradiating the cells in the PTB’s reference fields, the number of damaged chromosomes in human lymphocytes was determined in vitro (in cell cultures) at GSF as a function of the neutron dose. As dicentric chromosomes impede or even suppress the regular process of cell division, fewer changes are observed in each successive cell cycle. Using modern methods of analysis, the GSF has, however, succeeded in determining correction factors which allow to extrapolate the number of dicentric chromosomes shortly after irradiation. This has led to a new lower detection limit in the case of dicentric chromosome changes in human lymphocytes to such an extent that even at low dose values between 26 mGy and 145 mGy a linear dose-effect-relation was detectable. An RBE factor of roughly 70 was related to neutrons with energies of about 200 keV. This has been confirmed by investigations on other cell cultures carried out in cooperation with the universities of Münster and Göttingen.

The results are of considerable importance for the assessment of neutron radiation in radiation protection.