The objective of this study is to design an elastic neutron scattering system according to the angle with a sample using thermal neutron beam at the Dalat Nuclear Reactor (DNR). The system is used for research and training in the field of material structure analysis by neutron scattering and diffraction technique s . It is designed on the basis of inheriting the neutron measurement spectrometer systems at the DNR and the scattered neutron measurement systems in the world. The measuring system, which was installed at the horizontal channel 4 of the DNR, consists of 5-helium-3 detectors and a fully electronic system to record the scatter counts and a mechanical system with the possibility of rotating at 15 ˚ - 75 ˚ angles. The constructed system is tested for evaluation of the accuracy, stability and reliability of the mechanical and electronic systems of moving detector s by angles.
The neutron scattering technique is playing a crucial part in determining properties and structures of solid, liquid, gaseous materials, nanomaterials, crystals, crystal lattice dynamics, etc. There are four neutron measurement techniques: transmission, inelastic scattering, elastic scattering, and echo-spin neutron. The elastic scattering technique is a measure of the intensity of scattered neutrons through angles to determine the properties and structure of materials. Diffraction, reflection, and Small-Angle Scattering Systems (SANS) operating effectively at JAEA of Japan, at Dubna JINR in Russia, etc., are also based on those methods [
The design model of the neutron scattering measurement system is shown in
The system is designed in the shape of a semicircle with a diameter of 2.0 m. The
circular arc is fabricated from U-shaped steel 200 mm wide, 75 mm high and 9.0 mm thick. The mechanical part moving the detector includes a mechanical system for the detector holder; a drive system rotates the detector holder at angle, a stepper motor and controller, Microcontroller (Pic 16f877) that controls the mechanical system via wireless RS232 communication, cooling fan, a small stepper motor to rotate the sample tray. The rotary system uses a small motor (12V/17RPM) to rotate the sample tray and a large industrial motor (86BYGH450C) to rotate the entire probe system at angles.
The block diagram of electronic system is shown in
The neutron scattering system is installed in space with a rotation radius of 1 m. Therefore, shielding of neutron and gamma radiation is essential. The radiation shielding system consists of two parts: a shield around the sample location and a shield behind the detector chamber.
- The shielding around the sample location is composed of High Density Polyethylene (HDPE) sheets containing 5% boron (SWX-201) 75 × 34 cm in size, 3.0 cm thick to shield neutron and lead radiation, size 5 × 40 cm, thickness 3.0 cm outside for gamma radiation shielding.
- The shield behind the detector chamber consists of 2 HDPE sheets containing 5% boron (SWX-201) high density polyethylene (SWX-201) with dimensions of 12.2 × 12.2 × 2.5 cm, each. These shields are mounted on a steel frame with wheels for mobility.
The control system for the neutron scattering measurement system consists of a PIC controller board (PIC 16F886) [
The neutron scattering measurement system was installed and tested on the channel 4 Dalat nuclear reactor. To improve the accuracy when setting measuring angles for the scattering system, the project team designed and manufactured an automatic detector moving system and accompanying YAT control software. The YAT program is used to control the drive system to rotate in an angle. The interface of the program is shown in
To check the accuracy and stability of the motor and the rotary system, the test steps are performed in turn.
From the results in
The Helium-3 counters are connected to a CANBERRA Model 2006 preamp and connected voltage 1000 V from a 3 kV CANBERRA Model 3002D high voltage block. The preamplifier output signal is amplified and pulsed through a CANBERRA Model 2022 amplifier and connected to a Multi-port II block (6 units). The GENNIE2K program was used to acquire the spectrum.
In this experimental configuration, the reaction between thermal neutron and He-3 counter is shown as follows:
H 3 e + n → H 1 + H 3 + 764 keV
For proportional counter, the dead time of the measuring system is usually high > 10% due to the signal from gamma rays and pulse superposition of low energy region. To reduce the dead time of the measurement system, the LLD cut off of the amplifier is used. In this experiment, the LLD threshold set at 3% corresponds to a dead time of about 0.1%.
The installation and testing of the entire system was carried out on the channel 4 of DNR. The result above shows the mechanical system rotates at angles;
| Order | Angle (degree) | Average rotational speed (second/degree) | Position needle (degree) | Graduated ruler (degree) | Difference (degree) | |
|---|---|---|---|---|---|---|
| Go | Back | |||||
| 1 | 0 - 180 | 0.77 | 0.68 | 180.00 | 180.40 | 0.40 |
| 2 | 0 - 15 | 0.77 | 0.68 | 15.00 | 15.00 | 0.00 |
| 3 | 30 | 0.77 | 0.68 | 30.00 | 30.00 | 0.00 |
| 4 | 45 | 0.77 | 0.68 | 45.00 | 45.00 | 0.00 |
| 5 | 60 | 0.77 | 0.68 | 60.00 | 60.00 | 0.00 |
| 6 | 75 | 0.77 | 0.68 | 75.00 | 75.00 | 0.00 |
| 7 | 90 | 0.77 | 0.68 | 90.00 | 90.00 | 0.00 |
| 8 | 105 | 0.77 | 0.68 | 105.00 | 105.50 | 0.50 |
| 9 | 120 | 0.77 | 0.68 | 120.00 | 120.50 | 0.50 |
| 10 | 135 | 0.77 | 0.68 | 135.00 | 135.15 | 0.15 |
| 11 | 150 | 0.77 | 0.68 | 150.00 | 135.20 | 0.20 |
| 12 | 165 | 0.77 | 0.68 | 165.00 | 165.25 | 0.25 |
| 13 | 180 | 0.77 | 0.68 | 180.00 | 180.40 | 0.40 |
the electronic control system and the neutron measurement system with 5 He-3 counters operate accurately, stably and reliably.
Recommendations for future research directions will include as follows:
- Continue design shielding and reducing background;
- Measure some neutron beams with different energies.
- Currently, the scattering neutron in a cylinder with a diameter equal to the detector diameter of 2.5 cm, which has not been collimated. The scattered neutron can only reach the detector in a narrow gap. Therefore; angular measurement error also need to be corrected.
A neutron scattering spectrometer system is fully installed at channel 4 of the Dalat nuclear reactor. However, there is still no scattering data when measuring with the samples. The research groups only checked the stability of the mechanical and electronic systems. The aim in the near future is to measure the elastic scattering cross-section with different samples and calculate the elastic neutron scattering cross-section.
The authors declare no conflicts of interest regarding the publication of this paper.
Quy, D.H.N., Son, P.N., Hieu, P.B.Q. and Van Cuong, T. (2021) Design and Manufacture an Elastic Neutron Scattering Spectrometer at the Dalat Nuclear Reactor. Journal of Analytical Sciences, Methods and Instrumentation, 11, 23-28. https://doi.org/10.4236/jasmi.2021.113003