Ovrednotenje silicijevih mikropasovnih detektorjev kot rentgenskih senzorjev za digitalno mamografijo

Background. Position sensitive silicon microstrip detectors are used as sensors for X rays in a digital imaging system. Silicon detectors were used inan edgeon geometry, yielding high X ray detection efficiency. Material and methods. A small detector system was assembled and tested. Images of a standard, 5 cm thick phantom were made and evaluated. It is demonstrated, thatthe use of silicon detectors in mammography could significantly contributeto a reduction of dose. All images were made with skin entrance doses lower than 1 mGy. Results and conclusion. Microcalcifications with a diameter of 350microm could still be detected with skin entrance doses of about 0.25 mGy. It was demonstrated that a 5 Ip/mm pattern can be detected. Image processing should further improve the image quality.Izhodišče. Pozicijsko občutljive silicijeve detektorje smo uporabili kot senzorje rentgenskih žarkov v sistemu za digitalno rentgensko slikanje. Silicijevi detektorje smo uporabili v t. i. geometriji "na rob", kjer rentgenski žarki zadenjejo detektor s strani, zato lahko dosežemo visok izkoristek detekcije - preko 80% pri energiji rentgenskih fotonov 20 keV. Material in metode. Sestavili in testirali smo majhen sistem. Posneli smo slike standardnega, 5 cm debelega fantoma in jih ovrednotili. Rezultati in zaključki. Silicijevi detektorji lahko znatno prispevajo k zmanjšanju doze primamografskih preiskavah. Vse slike so bile posnete pri vstopni kožni dozi do 1 mGy. Mikrokalcifikacije s premerom 350 microm so še vedno vidne z vstopnokožno dozo 0.25 mGy. Pokazali smo, da z našim sistemom uspešno zaznamo testni vzorec črt z gostoto 5 parov na mm. Z nadaljno digitalno obdelavo lahkoše dodatno izboljšamo kvaliteto slik

Neutron irradiation test of depleted CMOS pixel detector prototypes

Charge collection properties of depleted CMOS pixel detector prototypes produced on p-type substrate of 2 k$\Omega$cm initial resistivity (by LFoundry 150 nm process) were studied using Edge-TCT method before and after neutron irradiation. The test structures were produced for investigation of CMOS technology in tracking detectors for experiments at HL-LHC upgrade. Measurements were made with passive detector structures in which current pulses induced on charge collecting electrodes could be directly observed. Thickness of depleted layer was estimated and studied as function of neutron irradiation fluence. An increase of depletion thickness was observed after first two irradiation steps to 1$\cdot$10$^{13}$ n/cm$^{2}$ and 5$\cdot$10$^{13}$ n/cm$^{2}$ and attributed to initial acceptor removal. At higher fluences the depletion thickness at given voltage decreases with increasing fluence because of radiation induced defects contributing to the effective space charge concentration. The behaviour is consistent with that of high resistivity silicon used for standard particle detectors. The measured thickness of the depleted layer after irradiation with 1$\cdot$10$^{15}$ n/cm$^{2}$ is more than 50 $\mu$m at 100 V bias. This is sufficient to guarantee satisfactory signal/noise performance on outer layers of pixel trackers in HL-LHC experiments

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements