A cyclotron neutron irradiation facility at IFIN-HH

U-120 Cyclotron facility is used for fast neutron field generation. The nuclear reaction produced by deuterons on Be is the best neutron source due to the high yield and angular distribution strongly peaked forward and low gamma ray production. A maximum 10μA beam of 13 MeV deuterons incident on the thick Be target (165 mg/cm2) produces a high neutron flux by stripping reactions. A dosimetric characterization of the neutron fields were performed prior to the radiation-damage studies. The threshold detectors (115 In, 197 Au), mica track detectors (Th and U), 6 LiF and 7 LiF dosimeters were used to determine the neutron fluence and photon doses and to measure the total absorbed dose angular distribution. The neutron flux at 0 angle (i.e. in the beam direction) was found to be equivalent to 2.13 x 108 neutrons/cm2sμA , at 10 cm distance from the Be target. The higher part of the energy spectrum was derived by time of flight (TOF) spectrometer. The neutron energy spectrum shows a mean energy of 5.2 MeV. The neutron and gamma components of the mixed radiation field give rise to 138 Gy/C and 2.38 Gy/C, respectively, at 90 cm distance from the Be target. In practice, a neutron fluence up to 1013 n/cm2 can be obtained in about two days over an area of 100 cm2. The beam power (maximum 100 W) released in the Be target is removed by a flow of cooling water. At full beam power, the highest temperature on the target does not exceed 50 deg C. Some precautions have been taken to maintain the Be disk electrically insulated, thus permitting on-line monitoring of the beam current on the target. During irradiations the neutron fluences were monitored by activated foil dosimetry (58 Ni (n,p)58 Co reaction) and mica track detectors. The absolute accuracy is ∼15% due to uncertainty in activation cross-sections, but the results are typically reproducible to within a few percent. The measured uniformity of neutron field in the region of irradiation (20 cm x 8 cm) is better than 25%. By measuring the integrated beam current, the time-stability of the neutron source was checked at 30 minute intervals during the irradiation. The current was roughly constant over the irradiation period. (authors)