RESUMO
INTRODUCTION: This laboratory plans to establish neutron reference radiation fields with three neutron sources to calibrate neutron-measuring devices. To perform calibration at multiple dose rates, neutron ambient dose equivalent rate HË*(10) needs to range 1 µSv/h to 10 mSv/h. The lower limit requires that the maximum available calibration distance should be at least 4.5 m. METHODS: To reduce room-scattered neutrons and extend the available calibration distance, MC simulations were conducted to determine the material and size of the irradiation room. A 3â³ Bonner sphere and a LB6411 environmental neutron dosimeter were used to characterize the irradiation room. RESULTS: A 14.32 × 14.32 × 12.00 m3 irradiation room was built based on simulation results. Floor, roof, and walls are made of 75 cm concrete covered by a coating layer of 2 cm BPE and 3 cm PE. Experimental maximum available calibration distance reaches 4.65 m. The range of HË*(10) for calibration covers 1 µSv/h to 10 mSv/h. Neutron and photon HË*(10) outside the room are within 0.19 µSv/h and 0.22 µSv/h, respectively.
RESUMO
An experiment of 12C(16O,16O â 4α)12C was performed at a beam energy of 96 MeV. A large number of 4-α events were recorded in coincidence and with full particle identification (PID). This was made possible by employing a series of silicon-strip-based telescopes that provided excellent position and energy resolutions. Four narrow resonances just above the 15.1 MeV state were firmly identified in the α + 12C(7.65 MeV; Hoyle state) decay channel. Combined with the theoretical predictions, these resonant states provide new evidence for the predicted possible Hoyle-like structure in 16O above the 4-α separation threshold. Some very high-lying 4-α resonant states have also been observed and need to be further investigated.