Abstract
To establish a methodology for neutron spectrum measurement at the CERN High energy AcceleRator Mixed field facility (CHARM), neutron spectra were measured using an NE213 scintillator on top of the CHARM roof shielding where is the CERN Shielding Benchmark Facility (CSBF). The spectra were derived as fluences into the scintillator by the unfolding method using an iterative Bayesian algorithm. The methodology was verified based on the agreement of two spectra measured for different positions and directions of incident neutrons by changing the detector orientation. Since the spectra on the roof-top were obtained within a reasonable beam-time, this methodology is suitable for measuring the spectrum when there is less shielding material. Thus, experimental data for neutron transition can be obtained as a function of shielding thickness using this facility.
Highlights
The energy spectra and attenuation lengths of secondary neutrons, which are generated through hadronic cascade reactions in a target, in a beam line tunnel, and shielding structure are of primary importance for the shielding design of high-energy and high-power hadron accelerators
The effective detector surface area A was derived from the following equation [25]: Fig. 11 shows the neutron energy spectra for the vertical and horizontal setups, as well as the ratio of the spectra for horizontal setup to vertical setup
The neutron energy spectra were measured by using an NE213 detector on the roof top of CERN High energy AcceleRator Mixed field facility (CHARM)
Summary
The energy spectra and attenuation lengths of secondary neutrons, which are generated through hadronic cascade reactions in a target, in a beam line tunnel, and shielding structure are of primary importance for the shielding design of high-energy and high-power hadron accelerators These quantities have recently been estimated using Monte Carlo codes such as FLUKA [1,2], GEANT4 [3], MARS [4], and PHITS [5], which are based on theoretical models and parameters for a simple bulk geometry and complex maze structures. Neutron energy spectra behind shielding have been measured at the CERF using Bonner spheres [10,11] and an NE213 scintillator [12] with the unfolding technique, and at the FNAL pbar using 120 GeV protons with Bonner spheres [13] According to these experiments, there are notable differences between calculation and experimental results. To explore the reasons for these differences experimentally, a facility is needed to measure neutron energy spectra and attenuation under various-conditions, such as different target and shielding materials, and its thicknesses, with various types of neutron detectors
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