H." Sato

Y. "Sakuma

National Institute for Fusion Science (NIFS-Repository)

§5. Development of a Neutron Man itor for DO Experiment by Means of LHD Sakuma, Y., Sato, H. (Inter. Univ. of Health and Welfare) We are developing a neutron monitor 00sed on a new concept for radiation protection of DD experiment by means of UID. The instnnnent measures the neutron dale rate in the unit of J1Sv/hour with approximately correct equiwlent dose response which is given by ICRP in the energy range from thermal to 20Me V without m<Xlerator [I]. The instnnnent is a complete measming assembly consisting of a neutron detection unit and of an electric unit and a memory unit combirm together. The detection unit consists of a NE-213 or BC-50lA liquid scintillator and of high neutron sensitivity smrounded with liquid scintillator with double layer ~ 1Ie ionization chamber without moderator. The JXllses from the liquid scintillator are 100 to a cirarit of n- y discrimination by the pulse shape method or by the digital charge COlllJlllison methcd The JX1lses from each layer of 1Ie ionization chambers are amplifioo in the charge sensitive amplifier. The process JX1lses are indicatoo on display unit in counting rates from each detector respectively and stored by memory. The memory JX1lses are analyzed into seprrate adequate energy ranges by a certain computer. <Sf 20.~ r 15 .~ · .: .~ .~ \ .. ~ Fig I Radiation weighting :factors for neutron The smooth anve is to be treated as an approximation 396 11 - 6 1 8 f---'- 6 9 f---5 I-- 7 10 Fig2 Block diagram of the neutron monitor. I.Liquid scintillator, 2.1Ie ionization chamber of second JXUt, 3. 1Ie ionization chamber of third Jlll1, 4.Photo-multipliers, 5.Preamplifier, 6.Pulse shape discriminators, 7.Charge sensitive amplifier, 8-1O.Display unit for fust, epitherrnal and thennal neutrons. I I Memory unit, 12.Computer The fimdamental dosimetric quantity in radiologiali protection is the absorbed dose D. Furthermore, ICRP recommended to evaluate in the equiwlent dale. The average and R radiation dose DTl{ in ~e T is given by the expression HT = }; ()JR ·DTl{ Where HT is the symbol of equiwlent dose, ()J R the radiation weighting :factor. For neutron, mdiation weighting :factors were given in Fig 1. The instnnnent is designed to detect the neutron from O.025eV-20MeV in counting rate and to analyze to absorbed dose based on the counting rate. The ultimate infonnation of the equiwlent dose is estimatoo from the product of the absorbed dose and the radiation weighing factor for neutron in each group respectively by micrqmx:;essor or computer. Reference [1] ICRPPublication60 (19~). 

Development of a Neutron Monitor for DD Experiment by Means of LHD

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