Chromosome aberration frequencies in human lymphocytes irradiated in a phantom by a mixed beam of fission neutrons and gamma-rays.
OBJECTIVE
To provide further information on the existence of a significant quadratic component of the dose response relationship for the production of dicentrics in human lymphocytes by mixed fission neutron and gamma-ray irradiation, which has been observed previously employing the same beam under free-in-air conditions.


METHODS
Irradiation of blood samples and dosimetry was performed at 2 cm depth in a polymethyl methacrylate (PMMA) phantom of 16 cm side-length where the PMMA material fully surrounded the blood specimen. Chromosome analysis was carried out exclusively in complete first division metaphases.


RESULTS
Dicentric yields induced by absorbed doses between 0.043 and 2.68 Gy fit a linear-quadratic model with a quadratic coefficient significantly different from zero. The distribution of dicentrics is overdispersed compared to Poisson at lower doses, but is poissonian at higher doses.


CONCLUSIONS
The presence of a significant quadratic dose response coefficient for dicentrics, both for free-in-air and phantom irradiation, is caused by the various degraded fission spectra that produce neutrons or recoil protons over a broad energy range, rather than by the gamma-ray component of the beam.
Schmid
E
E
Institute of Radiobiology, GSF, National Research Center for Environment and Health, Neuherberg, Germany.
Schraube
H
H
Bauchinger
M
M
D002478:Cells, Cultured; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005214:Fast Neutrons; D005720:Gamma Rays; D006801:Humans; D008214:Lymphocytes / Q000528:radiation effects*; D008953:Models, Anatomic; D019047:Phantoms, Imaging