Peak overlapping and its de-convolution in TOF diffraction data from neutron biological diffractometer in J-PARC

The TOF neutron biological diffractometer in J-PARC proposed by Ibaraki prefectural government is designed to cover the sample crystals which have their cell edges up to 135 Å, and to realize the efficiency which is more than 50 times larger than the present high performance diffractometers, BIX-3 and BIX-4 in JRR-3 reactor in JAERI. To achieve this performance, the diffractometer will be installed on a coupled moderator which has more intense peak and integrated intensity but wider pulse shape than a decoupled moderator. It is expected that some neighbor Bragg spots will overlap partially each other along the time-axis. It is necessary to de-convolute the overlapped spots in order to obtain a data set which has a quality good enough to identify hydrogen atoms in biological macromolecules. The original simulation programs of TOF diffraction data with designed parameters of the diffractometer were developed to obtain information of spot-overlapping and then to find the best procedure to de-convolute the overlapped spots. The strategy of de-convoluting overlapped Bragg spots will be reported based on the results of the simulations.