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In this work, an improved neutron spectrum unfolding code "Artificial Neural Network Iterative" (ANN_Iter), which utilizes the iterative method combined with artificial neural networks, is proposed for Bonner sphere spectrometer. 201 neutron energy spectra and the corresponding measured responses of Bonner spheres with 15 polyethylene shells of different diameter were provided by an IAEA report. In the process of unfolding, the pre-trained artificial neural network provides a guess spectrum according to the "knowledge" it has learned. The guess spectrum was used as the default initial spectrum in the iterative method, which unfolds the spectrum by the response function and the measured counts. The results show that the ANN_Iter's unfolded spectra have a good agreement with the desired spectra. In addition, their accuracy has improved compared with ANN's guess spectra. [ABSTRACT FROM AUTHOR]

Bonner sphere spectrometer (BSS) based on gold foils, as thermal neutron detectors, is one of the common device for neutron spectrometry. In this paper, the response functions of the Bonner spheres were determined for neutrons with energies ranging from thermal up to 20 MeV using Monte Carlo code. To verify the simulated response functions, the spheres of BSS were irradiated with Am-Be neutron source at the Ferdowsi University of Mashhad and the activities of the gold foils were measured. Then the artificial neural network was applied for neutron spectrum unfolding. The results showed a good agreement between unfolded and reference spectrum of ISO 8529-1. [ABSTRACT FROM AUTHOR]

Neutron spectrum and ambient dose equivalent has been measured around two 10 MV linear accelerators. Measurements were carried out in Mevatron and Primus model linacs, both made by Siemens. Main differences between those models are the beam collimator and the vault room. Here, Bonner sphere spectrometer with a passive thermal neutron detector has been utilized to measure the neutron spectrum inside the vault. Using an active detector the neutron spectrum was measured at the vault’s door of both accelerators. With a neutron area monitor the dose equivalent was measured by the door at both vault doors. Neutron strength, total fluence rate and ambient dose equivalent were compared, from this was found that shielding conditions are better in the Primus model. [ABSTRACT FROM AUTHOR]

Bonner sphere spectrometer with TLDs pairs has been utilized to measure the neutron spectrum 100 cm from isocenter of a 18 MV LINAC, simultaneously the ambient dose equivalent due to neutrons and photons was measured in the control room area with neutron and gamma-ray area monitors. Measurements were carried out when the LINAC was delivering a dose of 600 MU at the isocentre that was located at 5 cm depth of a head phantom. Undesired neutron field in the treatment room produce activation reactions with nuclei in different materials of LINAC, couch, air, and phantom. To determine the dose due to decay of activation nuclei the ambient dose due to gamma-rays was measured inside the treatment room immediately after dose was delivered. Measured spectrum has two peaks, one between 0.1–1 MeV and other in the thermal region, the ambient dose equivalent in the control room are 3.1 and 0.93 μSv h−1 for photons and neutrons, respectively. In the treatment room the ambient dose equivalent due to photons produced during decay of activation nuclei varies from 6 to 26.1 μSv h−1. [ABSTRACT FROM AUTHOR]