@misc{oai:repo.qst.go.jp:00071132,
 author = {Takada, Masashi and et.al and 高田 真志},
 month = {Jun},
 note = {1.
Neutron dosimeters have been widely used in nuclear reactors and accelerator facilities; however, there is no real-time personal neutron dosimeter for aircrews and astronauts. Their exposure doses are larger than radiation workers in nuclear reactors and accelerator facilities. Using typical neutron dosimeters, we
experimentally obtained larger values of neutron doses than the calculated doses.
These large values were attributed to detection of high-energy neutrons and protons
at high altitudes. To measure cosmic neutron doses for aircrews and astronauts, we
studied the neutron response of dosimeters and developed a neutron dosimeter. The response functions of neutron dosimeters cannot be simulated by evaluating the energy deposited in the depletion layer by charged particles. We observed Funneling phenomena were observed at the detection of high energy protons. Owing to Funneling phenomena, higher energies were measured than deposited energies in the original depletion layer. Measurement and simulation of neutron response functions for 252Cf neutron sources were compared as shown below. The previous model has never simulated a 2.2-MeV neutron peak in the measured pulse height; however, by introducing Funneling phenomena, a neutron peak at 2 MeV and a high energy region of 3-7 MeV are well simulated. In addition, simulations of response functions for 5 and 15 MeV neutrons agreed well with measurements. Cosmic protons produce background for
neutron measurements in aircrafts and spacecrafts. We developed a neutron sensor with
a 60-micron-thick silicon matrix in order to decrease cosmic proton detection and Funneling phenomena. When using this neutron sensor, beta and neutron pulse heights are independent of bias voltages and are unaffected by Funneling. Photon and proton sensitivities of this neutron sensor are decreased, and therefore, it has the
potential to measure neutron doses in aircrafts.
2.
It is important to evaluate the biological effects of neutrons because the public is
exposed to neutrons in a variety of environments, for example, around nuclear reactors and accelerators and at nuclear accidents. Despite the importance of neutron protection, available data about the biological effects of neutrons are insufficient. To investigate a variety of biological objectives with regards to neutron exposure, the National Institute of Radiological Sciences (NIRS) in Japan constructed the neutron exposure accelerator system for biological effect experiments (NASBEE). NASBEE produces fast neutrons by bombarding a thick beryllium target with 4-MeV deuteron beams. Precise data are necessary over the entire range of the neutron spectrum for biological analysis and quality assurance of the neutron field. However, experimental data covering entire range of the neutron spectrum are very limited.
We measured the neutron energy spectrum using a time-of-flight method at Tohoku University. Neutron beams were produced with 3-MeV deuteron beams bombarding a 3-mm-thick beryllium target. Neutron angular spectra were obtained at angles of 0-60 degree with respect to the incident beam line, using an organic liquid scintillator (EJ-399-06, Eljen Technology, TX, USA) with a neutron-photon discriminator. The neutron detection efficiencies of this scintillator were obtained using the MCNPX Monte Carlo radiation transport code [2]. The measured neutron energy spectra are shown below. The neutron energy spectrum at 0 degree has four peaks at around 1.2, 1.8, 3, and 5.5 MeV. Neutrons from 0.5 to 2.5 MeV may be produced from stripping reactions, and those from 2.5 to 8 MeV are from the 9Be(d,n)10B reaction (Q=+4.36 MeV). The average neutron energy is 1.7 MeV. Present results show forward and isotropic angular distributions at energies of 0.5-2.5 MeV and 4-8 MeV, respectively. These neutron spectra are used to evaluate the neutron field at NASBEE by considering the target shield and room configuration. The neutron energy spectrum was found to be a few percent of the 1/E spectrum from thermal energy to 0.5 MeV at the biological irradiation position in NASBEE., Neutron and Ion Dosimetry Symposium},
 title = {Simulation of Response Functions of Fast Neutron Sensors, Neutron Energy Spectra Produced by 3-MeV Deuterons Bombarding a Thick Beryllium Target},
 year = {2013}
}