INST-94/RNPD-17 lUUUIIil BD0510001 Installation, Performance, Safety Aspects and Technical Data of the Triple Axis Spectrometer at TRIGA Reactor of AERE S. M. Yunus, I. Kamal, Т. К. Datta, А. К. М. Zakaria and aF. U. Ahmed REACTOR AND NEUTRON PHYSICS DIVISION "PHYSICAL SCIENCE DIVISION, BAEC INSTITUTE OF NUCLEAR SCIENCE & TECHNOLOGY ATOMIC ENERGY RESEARCH ESTABLISHMENT GANAKBARI, SAVAR, GPO BOX 3787, DHAKA-1000, BANGLADESH February 2004 INST-94/RNPD-17 CONTENTS Page 1. Introduction 1 2. Fundamentals of Neutron Scattering 1 3. Properties of Neutron 1 4. Triple Axis Neutron Spectrometer (TAS) at TRIGA Mark 2 II Reactor 4.1. Installation of TAS 2 5. Different Hardware Assemblies of TAS 6 6. The Control System of TAS 9 6.1. The IMDI Unit 9 6.2. IMDI status monitor 10 6.3. The data acquisition system 11 6.4. The on-line PC system 11 7. Sample Environment Control Devices for TAS 11 8. Data Analysis Software 11 9. Radiation Safety Features of TAS 11 9.1. Inbuilt shielding of TAS 11 9.2. Additional shielding around TAS and control room 12 9.3. Safety aspects of working personnel 14 10. Performance Test of TAS 14 10.1. Zero-Bragg-angle and wavelength of monochromatic neutron 14 beam 10.2. Spectrometer zero-line 16 10.3. Reproducibility test of diffraction pattern by TAS 16 11. Experimental Facilities with TAS 16 1.1. Neutron Diffraction 16 1.2. Small Angle Neutron Scattering 18 2. Conclusions 19 3. References 19 1NST-94/RNPD-17 Abstract The technical data of the Triple Axis Neutron Spectrometer installed at the 3 MW TRIGA Mark II research reactor has been described. These are the reference data required for the operation, maintenance and use of the spectrometer. The detail information of the installation of the spectrometer has been given. Radiation safety features of the spectrometer and around the radial piercing beam port (where the spectrometer is installed) are described elaborately. The quality test experiments and the performance of the spectrometer as found from these tests are also described. ш INST-94/RNPD-17 1. Introduction Commissioning of the TRIGA Mark 11 research reactor at the Atomic Energy Research Establishment, Savar is an important milestone for the promotion of science and technology in Bangladesh. The principal aim of installing the reactor is to create facilities for advanced research using neutrons as well as radioisotope production and training of researchers and students. The reactor became critical on 14 September, 1986 and the maximum attainable power level of the reactor is 3MW (thermal) providing a maximum thermal neutron flux of 6.87x1013 neutrons/cm2/sec. The reactor caters facilities for neutron beam research through its four beam tubes of which two are radial, one is radial piercing and the other is tangential. The installation of a Triple Axis Neutron Spectrometer (TAS) at the radial piercing beam port of the reactor is another important breakthrough that has opened the door of most modern material research opportunity in the country using the neutron beam from the reactor. This spectrometer was built in Bhabha Atomic Research Centre (BARC), India and procured under the technical assistance of International Atomic Energy Agency (IAEA), Vienna, Austria. The spectrometer provides neutron scattering research facility not only to the scientists of Bangladesh Atomic Energy Commission (BAEC) but also to the teachers and students of all the universities as well as researchers from other institutes of the country. 2. Fundamentals of Neutron Scattering Neutron scattering is a well established and important technique for understanding the structure and dynamics of condensed matter and is widely used in physics, chemistry, biology, materials science and engineering. It is the most versatile technique for scientific and technical applications, particularly for relating the bulk properties to the microscopic structure and dynamics for the development of new materials. The technique is also useful in quality assurance of manufactured products, optimization of process parameters and also in the study of texture, fatigue and stress phenomena. These aspects are particularly important for assisting manufacturing industries and to increase added value to indigenous raw materials. As a tool for the characterization of materials, thermal neutrons offer several unique advantages over other probes such as protons, electrons or X-rays. The range of wavelengths and energies covered by thermal neutrons corresponds to the interatomic distances and the lattice vibration energies in the crystalline materials. The magnetic moment of the neutron makes it a unique probe of magnetism on an atomic scale, since neutrons are scattered from the magnetic moments associated with the unpaired electron spins in magnetic samples. Thermal neutrons for condensed matter research are usually obtained by slowing down energetic neutrons produced through nuclear chain reactions in nuclear reactors. Various types of neutron spectrometers are employed for neutron scattering experiments at the reactor sites. 3. Properties of Neutron The unique properties of neutrons as regards to their penetration and ability to distinguish isotopes have made neutron scattering a very formidable technique in the study of materials in its different perspectives. Neutron is an elementary particle characterized by a mass 1.6675X10"27 kg, spin V2, magnetic moment -1.913 nuclear magneton, zero electrical charge and life time 10.68 ±0.13 minute. The important characteristics which make neutron a very unique probe for the study of materials are: 1. The absorption coefficient of solids for neutrons is so small that the loss of intensity by transmission through a few millimeters of constructional materials such as steel or INST-94/RNPD-17 aluminium is negligible. This makes possible to construct cryostats, furnaces, pressure vessels and the like to study samples under different environments without much loss of intensity. 2. The wavelength of thermal neutrons is of the same order of magnitude as the inter- atomic distance. Thus significant interference effects are produced between waves elastically or inelastically scattered from different scattering centers. 3. The wavelengths of neutrons can be varied over quite a large range to suit a desired length scale from a fraction of angstrom to few order of magnitudes using hot and cold moderators. 4. The most important and the unique property of neutron is that it is endowed with magnetic moment. Thus by virtue of its magnetic moment it can interact magnetically and is capable of giving the details of the magnetic structure of materials. 5. The average energy of thermal neutrons is comparable to the energy of atomic vibrations, magnetic excitations, molecular rotations etc. Hence neutrons can be used to measure energy of various excitations in solids and liquids from the change in neutron energy in the course of scattering from solids or liquids. 6. The scattering cross sections of neutrons for different elements differ in a random manner. Therefore, locations of atoms with close atomic numbers and even isotopes in alloys and other compounds can be identified by neutron scattering 7. It has no charge and its absorption in most of the elements is low, therefore, it can penetrate deeply into the bulk matter. This makes neutrons a good probe for the study of bulk or volume properties of matter. 8. The scattering amplitude of neutrons from the nucleus does not show any variation with angle and has no form factor dependence. On the other hand, in the case of X- rays one has to deal with form factor problems. 4. Triple Axis Neutron Spectrometer (TAS) at TRIGA Mark II reactor TAS is a general purpose spectrometer and it can be used for carrying out a variety of measurements covering elastic as well as inelastic scattering with the energy of incoming/outgoing neutrons selectable over a wide range. The possible uses of TAS are: -Neutron diffraction from powders and liquids. -Measurement of textures and internal strains in metals and alloys. -Small angle neutron scattering from various materials. -Inelastic neutron scattering to derive phonon/magnon dispersion curves and density of states of solids. The programs available on the control system allow the users to operate the instrument in constant momentum transfer or constant energy transfer or any general mode in (Q, со) space. 4.1 Installation of TAS Fig. 1 shows the arrangement of the four beam tubes in the cross-sectional view of the reactor. Out of the four beam ports of the TRIGA Mark II research reactor of AERE, Savar, Dhaka two are radial, one is radial piercing and the other is tangential. The radial piercing beam port terminates at the reflector of the reactor core. Considering the necessity of high flux, TAS has been installed at the radial piercing beam port since the neutron flux is higher at this port than that of the others. INST-94/RNPD-17 LEAD LINED GRAPHITE REFLECTOR RADIAL M PORT TANGENTIAL RADIAL PIERCING STEEL SHADOW BEAM PORT BEAM PORT SHIELD Fig. 1. Cut-way view of the TRJGA Mark II reactor showing the four beam tube facilities. 1NST-94/RNPD-17 (e) (f) Fig. 2. (a) Installation of the base plate, (b) the base plate along with the yoke assembly stand, (c) installation of the middle rotating drum and central pillar, (d) fixing of the monochromator axis and monochromator, (e) TAS in completely assembled form and (0 intelligence Motor Drive Interface (IMDI) and data acquisition system of TAS at the control room. INST-94/RNPD-17 (а) (b) Fig.3. (a) Demonstration of TAS to the then chairman, BAEC (3nl from the right) after installation and (b) sample mounting to the sample table of TAS and discussion among the scientists INST-94/RNPD-17 The installation of TAS was started in June, 1992 and was completed in few months. The installation work was done by the scientists of the neutron scattering group of BAEC with the help and advice from an engineer of BARC, India, the supplier of TAS.