Measurement of photoneutrons in the output of 15 MV varian clinac 2100C LINAC using bubble detectors

Abstract

Photoneutron contamination in the output of Varian Clinac 2100C medical linear accelerator (LINAC) operated at 15 MV photon beam energy has been investigated using bubble detectors. Photoneutrons are produced from the photo-disintegration reaction of photons with materials of the head components with threshold energy of approximately 8 MeV. Measurements were conducted in the patient plane at 100 cm source-to-detector distance on beam axis and at stipulated distances outside the irradiated field for 5×5 cm2 to 40×40 cm2 field sizes for in-air and 5×5 cm2 to 20×20 cm2 for water phantom measurements. Neutron dose equivalent of 1.57±0.10 mSv·Gy−1 was measured for 10×10 cm2 field size for in-air. For in phantom, neutron dose equivalent of 1.42 mSv·Gy−1 was measured for 10×10 cm2 field size on the beam axis at a depth of 1 cm but independent of field size at depth >5 cm.