Michiya Sasaki

Measurement of deep penetration of neutrons produced by 800-MeV proton beam through concrete and iron at ISIS

Abstract A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), UK. ISIS is an 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, which is shielded with approximately 3-m thick iron and 1-m thick ordinary concrete in the upward direction. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2-m and 0.6-m thicknesses, respectively, using the activation detectors of graphite, bismuth, aluminum and the multi-moderator spectrometer inserted indium. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV produced at 90° to the proton beam were obtained from the 12 C ( n ,2 n ) 11 C reaction rates of graphite. The neutron spectra through concrete and iron were obtained by the unfolding analysis of the reaction rates of the 12 C ( n ,2 n ) 11 C , 27 Al ( n , α ) 24 Na , 209 Bi ( n ,x n ) 210−x Bi (x=4–10) and 115 In ( n , γ ) 116m In in the energy range of thermal to 400 MeV.

Measurements of High-Energy Neutrons Penetrated Through Concrete Shields Using Self-TOF, NE213, and Activation Detectors

Abstract Neutron energy spectra penetrated through concrete shields were measured using three types of high-energy neutron detectors: the Self-TOF detector, an NE213 organic liquid scintillator, and Bi and C activation detectors, which have been newly developed by a group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) facility of the National Institute of Radiological Sciences, Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ions on a thick (stopping-length) copper target. The neutron spectra were obtained through an unfolding code with their response functions and compared with LAHET and MCNPX calculations combined with the LA150 cross-section library. The calculations tend to overestimate with increasing the shielding thickness compared to the experimental results. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX code, and the contribution of the room-scattered neutrons was evaluated. The neutron fluence attenuation length was obtained from the experiment for each detector and the calculation in the energy range of 20 to 800 MeV.

Measurements of the response functions of an NE213 organic liquid scintillator to neutrons up to 800 MeV

Abstract The neutron response functions of 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator have been measured in the energy range from 50 to 800 MeV at the Heavy-Ion Medical Accelerator in Chiba (HIMAC). Neutrons were generated by the 800 MeV / nucleon Si ion and 400 MeV / nucleon C ion bombardment on a thick carbon target. Neutron energy was determined by the time-of-flight method with using the beam pick-up scintillator. The maximum light outputs were gradually increased with increasing incident neutron energy and the variation of the response functions have been observed up to 800 MeV . The experimental results show good agreement with other experimental results and the calculated values for incident neutron energy below about 200 MeV .

Measurements of high energy neutrons penetrated through iron shields using the Self-TOF detector and an NE213 organic liquid scintillator

Neutron energy spectra penetrated through iron shields were measured using the Self-TOF detector and an NE213 organic liquid scintillator which have been newly developed by our group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS), Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ion on a thick (stopping-length) copper target. The neutron spectra in the energy range from 20 to 800 MeV were obtained through the FORIST unfolding code with their response functions and compared with the MCNPX calculations combined with the LA150 cross section library. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX, and evaluated the contribution of the room-scattered neutrons. The calculations are in fairly good agreement with the measurements. Neutron fluence attenuation lengths were obtained from the experimental results and the calculation.

Neutron Energy and Time-of-flight Spectra Behind the Lateral Shield of a High Energy Electron Accelerator Beam Dump,Part I: Measurements

Neutron energy and time-of-flight spectra were measured behind the lateral shield of the electron beam dump at the Final Focus Test Beam (FFTB) facility at the Stanford Linear Accelerator Center. The neutrons were produced by a 28.7 GeV electron beam hitting the aluminum beam dump of the FFTB which is housed inside a thick steel and concrete shield. The measurements were performed using a NE213 organic liquid scintillator behind different thicknesses of the concrete shield of 274 cm, 335 cm, and 396 cm, respectively. The neutron energy spectra between 6 and 800 MeV were obtained by unfolding the measured pulse height spectrum with the detector response function. The attenuation length of neutrons in concrete was then derived. The spectra of neutron time-of-flight between beam on dump and neutron detection by NE213 were also measured. The corresponding experimental results were simulated with the FLUKA Monte Carlo code. The experimental results show good agreement with the simulated results.

Feasibility studies of the self-TOF detector for high-energy neutron measurements in shielding experiments

Abstract The feasibility of a new type of neutron detector was studied. The detector consists of a radiator, a start counter and a stop counter. The radiator is composed of 20 thin plastic-scintillation detectors and the stop counter is segmented into nine plastic-scintillation detectors. Neutrons impinging on the radiator emit charged particles. The time of flight of protons emitted at a forward angle is measured using the start and stop counters, therefore, we call the detector the “self-TOF detector”. The proton time-of-flight spectrum is converted to the energy spectrum of neutrons using a measured response function. The basic properties of the detector, such as detection efficiency, signal-to-noise ratio, particle identification capability, and energy resolution, were studied.

Response Function Measurements of the Self-TOF Neutron Detector for Neutrons up to 800 MeV

The Self-TOF detector has been developed for high energy neutron spectrometry behind a shield. This detector consists of a radiator, a start counter and a stop counter. The radiator is composed of 20 thin plastic-scintillation detectors and the stop counter is segmented into nine plastic-scintillation detectors. The response functions of the Self-TOF detector for high energy neutrons up to 800 MeV were measured at the HIMAC (Heavy Ion Medical Accelerator in Chiba) of the National Institute of Radiological Sciences (NIRS). The measured responses were compared with those calculated using the LCS (LAHET Code System). The LCS results considerably overestimate the measuremental results with an increase in the neutron energy. It was found that this detector can give the neutron energy spectrum by using the FERDO-U unfolding code combined with the measured response functions, and is useful for high energy neutron spectrometry because of the almost constant efficiency for neutrons above 100 MeV.

Measurements of Neutron Attenuation through Iron and Concrete at ISIS

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory. ISIS is an 800MeV-200 μ A proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3m thick iron and 1 m thick ordinary concrete. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2 m and 0.6 m thicknesses, respectively, using activation detectors of carbon, aluminum and bismuth, and also indium-loaded multi-moderator spectrometer. The dose attenuation was simultaneously measured with the neutron and photon survey meters. The attenuation lengths of concrete and iron for high energy neutrons above 20MeV were obtained from the 12C(n,2n) reaction of carbon, and the neutron spectra penetrated through the additional shield and on the target shield top were obtained from the 12C(n,2n), 27Al(n,α) and 209Bi(n, xn) reactions, and multi-moderator spectrometer. We are now analyzing the measured results to compare with the shielding calculation.

Development of Self-TOF Neutron Detector and its Application to Shielding Experiment at HIMAC

A new type detector, called ‘Self-TOF detector’, has been developed for high energy neutron spectrometry behind a shield by our group. The detector consists of a veto counter, a set of radiators with 20 thin detectors, a start counter and a stop counter of nine segments. The measurement of the detector response function for high energy neutrons and the concrete shielding experiment were done at the HIMAC(Heavy-Ion Medical Accelerator in Chiba) of NIRS(National Institute of Radiological Sciences), Japan. Neutron spectra were also compared with the LCS(LAHET Code System). Both results are in rather good agreement within a factor of 2.

Development of Self-TOF neutron detector and its application to concrete and iron shielding experiments

Abstract A new type detector, called ‘Self-TOF detector’, has been developed for high energy neutron spectrometry behind a shield. The detector consists of a veto counter, a set of radiators with 20 thin detectors, a start counter and a stop counter of nine segments. The measurement of the detector response function for high energy neutrons and the concrete and iron shielding experiments were done at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS), Japan. By using the response functions, neutron spectra behind shield were obtained by unfolding and the results were compared with the LAHET Code System (LCS).