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Abstract
The Medipix detector is the first device dedicated to measuring mixed-field radiation in the CMS (Compact Muon Solenoid) experiment cavern and able to distinguish between different particle types. Medipix2-MXR chips bump bonded to silicon sensors with various neutron conversion layers developed by the IEAP CTU in Prague were successfully installed for the 2008 LHC start-up in the CMS experimental and services caverns to measure the flux of various particle types, in particular neutrons. They have operated almost continuously during the 2010 run period, and the results shown here are from the proton run between the beginning of July and the end of October 2010. Clear signals are seen and different particle types have been observed during regular LHC luminosity running, and an agreement in the measured flux is found with the simulations. These initial results are promising, and indicate that these devices have the potential for further and future LHC and high energy physics applications as radiation monitoring devices for mixed field environments, including neutron flux monitoring. Further extensions are foreseen in the near future to increase the performance of the detector and its coverage for monitoring in CMS.
Highlights
The Medipix2-MXR chip [13] was developed by the Medipix collaboration [14, 15], and contains 256 × 256 pixels with an edge length of 55 μm
Whereas one strip at the bottom of the detector is left uncovered, the rest of the surface is covered by layers. 6Li in the form of 6LiF powder sputtered to the bottom of a 50 μm thick aluminium foil covers the upper left corner and creates a layer aimed at the conversion of thermal neutrons into α-particles via the reaction 6Li + n → α + 3H
The Medipix detector is the first device dedicated to measuring mixed-field radiation in the CMS cavern and able to distinguish between different particle types
Summary
The Medipix2-MXR chip [13] was developed by the Medipix collaboration [14, 15], and contains 256 × 256 pixels with an edge length of 55 μm. At CMS, the Medipix2-MXR chip bump bonded to a 300 μm thick silicon sensor was used in combination with a USB 1.1 readout [16]. Due to cable lengths of more than 5 meters a USB to Ethernet extender had to be used, which required an additional power supply. Measurements with the Medipix2-MXR can be fine-tuned by setting certain parameters or DAC values. Among those are a coarse and fine lower energy threshold THL and a coarse and fine higher energy threshold THH. For all measurements at CMS and in the laboratory Pixelman [17], a software package for Medipix detectors, has been used to set the measurement parameters and to acquire the data
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