Neutron monitor calibration with 241AmBe(α, n), 252Cf and 238PuBe(α, n) used in dose evaluation near LINAC

Full text: The use of linear accelerators in Radiotherapy is increasingly becoming more common. From the Radiation Protection point of view, these instruments represent an advance relative to cobalt and caesium irradiators, mainly due to the absence of radioactive material. On the other hand, accelerators with energies over to 10 MeV contaminate with neutrons the therapeutic beam. These neutrons are generated when high-energy photons interact with high-atomic-number materials present in the accelerator itself. Photo-neutrons can also interact with other materials, present in the treatment room, consequently modifying the initial spectrum and causing other types of interactions which privilege the gamma capture. In this way, the measurement of the photo-neutron spectrum can be necessary in a radiometric survey. For this neutron measurement it is important to verify the response of the commercially available detectors used in radiation protection, this verification being done ahead of the spectrum measurement. The present work carries through measurements in a linear accelerator of 15 MeV using three neutron area monitors calibrated using three radioactive sources: two ISO reference sources, 241AmBe(α, n) and 252Cf, and a 238PuBe(α, n) source. As the two first sources, this last one was standardized in the LMNRI/IRD manganese bath system. Comparison and evaluation of the response of these instruments were thereby made, analyzing whether the standard source response is adequate. In conclusion, the analysis of the response of neutron area calibrated detectors enable the employment of 238PuBe (α, n) source to calibrate neutron survey area monitors to be used in others measurements. (author)