Pulsed Neutron Powder Diffraction for Materials Science


The accelerator-based neutron diffraction began in the end of 60's at Tohoku University which was succeeded
by the four spallation neutron facilities with proton accelerators at the High Energy Accelerator Research Organization (Japan), Argonne National Laboratory and Los Alamos Laboratory (USA), and Rutherford Appleton Laboratory (UK). Since then, the next generation source has been pursued for 20 years, and IMW-class spallation neutron sources will be appeared in about three years at the three parts of the world: Japan, UK and USA. The joint proton accelerator project (J-PARC), a collaborative project between KEK and JAEA, is one of them. The aim of the talk is to describe about J-PARC and the neutron diffractometers being installed at the materials and life science facility of J-PARC. The materials and life science facility of J-PARC has 23 neutron beam ports and will start delivering the first neutron beam of 25 Hz from 2008 May. Until now, more than 20 proposals have been reviewed by the review committee, and accepted proposal groups have started to get fund. Those proposals include five poly crystalline diffractometers: a super high resolution powder diffractometer (SHRPD), a 0.2 %-resolution powder diffractometer of Ibaraki prefecture (IPD), an engineering diffractometers (Takumi), a high intensity S(Q) diffractometer (VSD), and a high-pressure dedicated diffractometer. SHRPD, Takumi and IPD are being designed and constructed by the joint team of KEK, JAEA and Ibaraki University, whose member are originally from the KEK powder group. These three instruments are expected to start in 2008. VSD is a super high intensity diffractometer with the highest resolution of Mid = 0.3%. VSD can measure rapid time-dependent phenomena of crystalline materials as well as glass, liquid and amorphous materials. The pair distribution function will be routinely obtained by the Fourier transiformation of S(Q) data. Q range of VSD will be as wide as 0.0IA-1 Q 100A-1. IPD is fully funded by Ibaraki prefecture for the promotion of new industries based on advanced science and technologies. It is for the first time in neutron facilities in Japan that a prefecture owns neutron instruments as well as neutron beam will be provided widely to industrial users. To make it successful, the user system is quite important because those users are expected to use IPD like chemical analyzers in their materials development process. Based on questionnaire data to several hundreds industries, IPD is designed as a versatile diffractometer including texture measurement, small angle scattering and total scattering as well as usual powder diffraction. IPD covers d range 0.15 d (A) 4 with Mid = 0.15 %, and covers 4 d (A) 60 with gradually changing resolution. Q range of IPD will be as wide as 0.0IA-1 Q 50A-1 to be utilized for varieties of structures: local structure, nano structure and crystal structure analyses. Typical measuring time for the typical Rietveld-quality data is several minutes with the sample size of laboratory X-ray: 0.4 cc. SHRPD is designed to be the world highest resolution with Mid = 0.03% without sacrificing intensity. The combination of the high quality data from HRPD and their high-precision analysis gives us information on tiny structural changes which have been overlooked. After careful examination with the moderator group five years ago, we have decided to develop a high-resolution & good SIN moderator to achieve the 0.03 % resolution within 100 m flight path. This development was almost successful up to now. Instrumental simulation and radiation analysis were almost completed. The d range 0.5 d (A) 4 with Mid = 0.03 %, and covers 4 d (A) 45 with gradually changing resolution. Takumi is the first priority instrum_entin IAEA for stress mapping inside structure materials with the highest resolution of Mid = 0.2% (corresponding to 105 to 106 strain precision). The typical gauge volume will be 1 mm3. JED has transmission radiography detectors to support stress mapping. Software group is planning so that basic software to cover data acquisition and data treatment should be common. Since 1 Gbyte data are typically obtained for single experiment in an instrument, the basic software is quite important. International TV conference between ISIS, lPNS, SNS has been held every month to exchange information on each development. KEK developed manyo-lib to help basic analysis. ArJalysis software development including powder diffraction is strongly related with the activity of the software group. However, users of IPD will be from various field of science and their background is different. It should cover wide topics and help both beginners and well-trained users. We have started with neutron intensity database, peak-search software, peak-match software, pattern simulation, whole pattern fitting, PDF and RDF analysis, and now start coding Rietveld software. Keywords: Pulsed neutron, powder diffractometer, crystalline, glass, amorphous. T. Kamiyama Materials and Lift Science Facility, J-PARC Center, High Energy Accelerator Research Organization, Tsukuba, lbaraki 305-0801 JAPAN