Medipix3RX neutron camera for ambient radiation measurements

Precise evaluation of composition and spectral characteristics of radiation in and around the Compact Muon Solenoid (CMS) on the LHC are necessary to ascertain the performance of various detector systems as well as to predict their useful lifetimes. The CMS-NZ collaboration is planning to deploy Medipix detectors in the CMS cavern for these measurements. Medipix3RX is the latest version of the hybrid pixelated detectors developed at CERN for medical imaginary but widely used in high energy physics experiments. These detectors will be capable of delivering real-time images of fluxes and spectral composition of different particles including slow and fast neutrons. The detector consists of a semiconductor sensor layer made of silicon, which is bump bonded to the front-end electronics ASIC. Electronics and readout of these detectors, which were originally developed for the MARS spectral x-ray scanner at the University of Canterbury, Christchurch, were suitably adapted for their deployment in the cavern. Neutrons are detected by using conversion layers such as lithium fluoride or polyethylene to produce charged particles, which are then detected by the sensor. We studied the mixed-field radiation at seven Medipix detector proposed locations in the cavern by scoring particle tracks using FOCUS, a CMS FLUKA tool and analysed their energy as well as angular distributions. Good agreement was observed between average fluxes predicted by standard FLUKA methods and those obtained by integrating over FOCUS output data. The response function of the Medipix detectors with different neutron conversion layers has been simulated using Monte Carlo methods. A post-processing algorithm was developed for track reconstruction and recognition using cluster analysis techniques, which labels and determines the density of clusters formed by groups of particles. We will present overall scope of this work, it's status and the results obtained so far.