  Due to the muon tomography's capability of imaging high Z materials, some
potential applications have been reported on inspecting smuggled nuclear
materials in customs. A compact Cosmic Ray Muons (CRM) imaging prototype,
Lanzhou University Muon Imaging System (LUMIS), is comprehensively introduced
in this paper including the structure design, assembly, data acquisition and
analysis, detector performance test, and material imaging commissioning etc.
Casted triangular prism plastic scintillators (PS) were coupled with Si-PMs for
sensitive detector components in system. LUMIS's experimental results show that
the detection efficiency of an individual detector layer is about 98%, the
position resolution for vertical incident muons is 2.5 mm and the angle
resolution is 8.73 mrad given a separation distance of 40.5 cm. Moreover, the
image reconstruction software was developed based on the Point of Closest
Approach (PoCA) to detect lead bricks as our target. The reconstructed images
indicate that the profile of the lead bricks in the image is highly consistent
with the target. Subsequently, the capability of LUMIS to distinguish different
materials, such as Pb, Cu, Fe, and Al, was investigated as well. The lower
limit of response time for rapidly alarming high-Z materials is also given and
discussed. The successful development and commissioning of the LUMIS prototype
have provided a new solution option in technology and craftsmanship for
developing compact CRM imaging systems that can be used in many applications.
