RRFM 2009 Transactions - European Nuclear Society

3.3 Materials Characterisation
3.3.1 Radiation hardness of electronic components
(fast neutron beam with additional filters)
CMOS sensors, also being referred to as Monolithic Active Pixel Sensors (MAPS),
demonstrated their ability to serve as sensors for minimum ionising particles (MIPs). They
represent a novel technology for charged particle tracking in high-energy particle and nuclear
physics. Small pixel sizes of down to 10x10 µm 2 allow unprecedented spatial resolutions and
a low material budget at the same time. The Technology Laboratory of the University
Frankfurt, Institute of Nuclear Physics, participates in the R&D, design and construction of
the vertex detector of the Compressed Baryonic Matter (CBM) experiment (FAIR at GSI
Darmstadt, Germany). An essential performance criterion in such applications is the radiation
tolerance of the pixel chip. The detectors are foreseen to operate in close vicinity to the
primary interaction vertex and exposed to the maximum track density. Moreover, the
experiments are optimized to measure rare probes such as open charm and, hence, cope
with very high integral particle fluences.
At FRM II, irradiations were performed with equivalent fluences up to 10 13 cm² (1 MeV
equivalent neutron fluence for silicon according to ASTM standard E 722-04). They proved
that the latest MAPS generation (MIMOSA-18) may stand more than 10 13 n eq /cm²
representing a progress of one order of magnitude with respect to previous designs [9].
3.3.2 Neutron computerised tomography and radiography (NECTAR)
Radiography and tomography using collimated fission neutrons on objects from different
fields of applications (e.g., technical objects like turbine blades, archaeological and art
historical objects, wooden samples as Fig. 5 left) have become a standard application at the
NECTAR facility located at the rear end of the SR10 beam [10].
Recently, preliminary measurements for investigation of real-time applications were
performed successfully using a lead filtered beam with no additional collimator unit [11]. The
abdication of the collimator results in a decreased spatial resolution (Fig. 5 right) by a factor
of about two, but an increased fission neutron flux by a factor of about 8.
Fig 5: Left: Cut through a 3D-CT of a timber using a collimated neutron beam.
Right: Radiography of a test sample consisting of a plastic can containing a thighbone
and a polyethylene rod, both covered by water in the lower part, using no collimator.
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