Development of a neutron beam monitor with a thin plastic scintillator for nuclear data measurement using spallation neutron source
- A neutron detector for nuclear data measurement using a spallation neutron source has been developed.
- A detection system was designed and fabricated. A test experiment was conducted using a neutron beam to evaluate its validity as a detection method.
- Results of the test experiments showed that the present detector system was capable of monitoring an intense neutron beam for nuclear data measurement.
A neutron monitoring detection system was developed for neutron capture cross section measurement using a spallation neutron source. A combination of a plastic scintillator and a thin 6LiF foil was adopted for the detector. The detector system was tested to study the feasibility of the system. Neutron irradiation experiments were conducted with the Accurate Neutron-Nucleus Reaction Measurement Instrument in the Materials and Life Science facility of the Japan Proton Accelerator Research Complex. A neutron time-of-flight spectrum was successfully measured without significant count loss or detector paralysis.
Spallation neutron sources [Term 1] have extended nuclear data measurement into new frontiers. An intense neutron beam from a spallation neutron source enables nuclear data measurement of radioactive samples and small cross-section reactions. However, traditional neutron detectors are not suitable to measuring an intense neutron beam from a spallation neutron source due to its high counting rate. In the present work, a new neutron detector to monitor a neutron beam from a spallation neutron source was developed.
Detector system design and assembly
Figure 1 shows a schematic diagram of the present neutron detector. The detector consists of an aluminum foil with a thin 6Li layer, a thin plastic scintillator and a photomultiplier tube. Triton and alpha particles emitted from the 6Li(n,t)4He reaction are detected with the plastic scintillator. The thin 6Li layer gives an enough small detection efficiency, allowing the detector to be used to measure a high-intensity neutron beam without paralysis.
The neutron detector system was tested with a neutron beam from the spallation neutron source of J-PARC. Experiments were carried out at the ANNRI beamline of MLF. The detector system was placed at a neutron flight length of 28.6 m from the neutron source. Neutron energy was measured with time-of-flight (TOF) method .[Term 2]
Measurements were made for both 6LiF and natLiF deposited Al foils. The counting rate with the enriched 6LiF foil is much higher than that with the natLiF foil because of the 6Li abundance difference. The neutron TOF spectrum was successfully measured from 3.5 meV to 275 keV without significant count loss or detector paralysis. The statistical uncertainty reached 0.7% at neutron energies around 6 meV. To verify the applicability of the present detector system, the energy dependence of the neutron spectrum was compared with a previous measurement. The neutron energy spectrum was in good agreement with a different method. Thus, it is concluded that this detector system can be used to monitor an intense neutron beam for nuclear data measurement.
Figure 1. Schematic diagram of the present neutron detector.
- [Term 1] Spallation neutron source：
- When a particle of high energy in the order of GeV collides with an atomic nucleus, a spallation reaction occurs that breaks the nucleus into pieces. The spallation reaction produces a large number of neutrons, and is used as an efficient way to generate neutrons. Spallation neutron sources are being operated and constructed in many countries around the world to produce high-intensity neutron beams.
- [Term 2] Time-of-flight method：
- A method to measure the energy of neutrons. The neutron energy is determined by measuring the time of flight of a neutron over a certain distance.
- Journal :
- Journal of Nuclear Science and Technology
- Title :
- Development of a neutron beam monitor with a thin plastic scintillator for nuclear data measurement using spallation neutron source
- Authors :
- Nakano H 1) , Katabuchi T 1), Rovira G 1) , Kodama Y 1) , Terada K 1) , Kimura A 2), Nakamura S 2), Endo S 2)
- Affiliation :
- 1) Laboratory for Zero-Carbon Energy, Institute of Innovative Research, Tokyo Institute of Technology
2) Department of Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency