In Dortmund, planar silicon pixel sensors were designed with modified n+-implantations and produced in n+-in-n sensor technology. Baseline for these new designs was the layout of the IBL planar silicon pixel sensor with a 250 μm × 50 μm pitch. The different implantation shapes are intended to cause electrical field strength maxima to increase charge collection after irradiation and thus increase particle detection efficiency. To test and compare the different pixel designs, the modified pixel designs and the standard IBL design are placed on one sensor which can be read out by a FE-I4. After irradiation with protons and neutrons respectively the performance of several sensors is tested in laboratory and test beam measurements. The presented laboratory results verify that all sensors are fully functional after irradiation. The the test beam measurements show different results for sensors irradiated to the same fluence with neutrons in Sandia compared to sensors irradiated with neutrons in Ljubljana or with protons at CERN PS.

The accurate measurement of the beam range in the frame of quality assurance (QA) is a requirement for clinical use of a proton therapy machine. Conventionally used detectors mostly estimate the range by measuring the depth dose distribution of the protons. In this paper, we use pixel detectors designed for individual particle tracking in the high-radiation environment of the ATLAS experiment at LHC. The detector measures the deposited energy in the sensor for individual protons. Due to the limited dynamic energy range of the readout chip, several ways to measure the proton energy or range are examined. A staircase phantom is placed on the detector to perform an energy calibration relative to the NIST PSTAR stopping power database. In addition, track length measurements are performed using the detector aligned parallel with the beam axis to investigate the Linear Energy Transfer (LET) per pixel along the trajectory of individual protons. In this proof-of-principle study, we show that this radiation hardness detector can successfully be used to determine the initial proton energy for protons impinging on the sensor with an energy below 44 MeV after the range shifters. It becomes clear that an improvement of the energy resolution of the readout chip is required for clinical use.

A: Planar silicon pixel sensors with modified n + -implantation shapes based on the IBL pixel sensor were designed in Dortmund. The sensors with a pixel size of 250 µm × 50 µm are produced in n + -in-n sensor technology.The charge collection efficiency should improve with electrical field strength maxima created by the different n + -implantation shapes. Therefore, higher particle detection efficiencies at lower bias voltages could be achieved. The modified pixel designs and the IBL standard design are placed on one sensor to test and compare the designs. The sensor can be read out with the FE-I4 readout chip.At the iWoRiD 2018, measurements of sensors irradiated with protons and neutrons respectively at different facilities were presented and showed incongruent results. Unintended annealing during irradiation was considered as an explanation for the observed differences in the hit detection efficiency for two neutron irradiated sensors. This hypothesis will be examined and confirmed in this work, presenting first annealing studies of sensors irradiated with neutrons in Ljubljana.

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