Design of a rotational modulation collimator utilizing asymmetric masks for the gamma-ray/neutron dual imaging technique

We are currently developing a dual-particle imager based on the rotational modulation collimator (RMC) technique employing Cs2LiYCl6:Ce (CLYC) detector. A symmetric mask design has been conventionally used for RMC, however, it has an intrinsic problem of not being able to distinguish two symmetric sources located with respect to the rotation axis. In the present study, we propose a new design of collimator masks to solve the artifact problem in the source location estimation imposed by the symmetric pattern of collimator masks. We used the Monte Carlo N-Particle 6.1 (MCNP6) code to obtain modulation patterns, and we applied the maximum likelihood expectation maximization (MLEM) algorithm to reconstruct radiation images from the modulation patterns. The asymmetric mask design we proposed in this paper showed enhanced performance in image reconstruction by removing intrinsic artifacts from the symmetric mask design and will be used as a fundamental design for the future development of the dual-particle RMC system.