M. Fransen

A Radiation Imaging Detector Made by Postprocessing a Standard CMOS Chip

An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. This letter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing. Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3D radiation tracks on the spot.

A UV sensitive integrated micromegas with timepix readout

This article presents a detector system consisting of three components, a CMOS imaging array, a gaseous-detector structure with a Micromegas layout, and a UV-photon sensitive CsI reflective photocathode. All three elements have been monolithically integrated using simple post-processing steps. The Micromegas structure and the CMOS imaging chip are not impacted by the CsI deposition. The detector operated reliably in He/isobutene mixtures and attained charge gains with single photons up to a level of 6x104. The Timepix CMOS array permitted high resolution imaging of single UV-photons. The system has an MTF50 of 0.4lp/pixel which corresponds to approximately 7lp/mm.

Applications of GridPix detectors

GridPix detectors provide an excellent tracking and vertex determination for internal radioactive sources with a 4p angular acceptance. In both WIMP search and neutrinoless double beta decay experiments, we expect that GridPix detectors have the ability to significantly improve the measurements.

New results from GridPix detectors

GridPix detector prototypes have been made using a TimePix pixel chip and a PSI 46 pixel chip. A system of discharge protection has been successfully tested. GridPix detectors have been tested using cosmic rays, a 90Sr source and the T9 test beam facility at CERN. GridPix detectors perform well for 3D track reconstruction, dE/dx measurements and transition radiation detection.

Results from MPGDs with a protected timepix or medipix-2 pixel sensor as active anode

The functioning of a high-resistive, hydrogenated amorphous Silicon layer as a protection against discharges for Micoomegas-based pixel readout gaseous detectors, has been investigated. Chips, protected with a 3 mum thick layer, still broke, but a 20 mum thick layer has proven to be adequate. Images from discharge events disclose their geometrical parameters, enabling to further optimize the discharge protection.

The gridpix detector: history and perspective

In 2000, the requirements for a large TPC for experiments at a new linear collider were formulated. Both the GEMand Micromegas gas amplification systems had matured, such that they could be practically applied. With the Medipix chip, a pixel-segmented anode readout became possible, offering an unprecedented level of granularity and sensitivity. The single electron sensitive device is a digital detector capable to record and transfer all information of the primary ionization, provided that it can be made discharge proof.

Charge protection characterisation and drift time resolution improvement for GridPix

A GridPix detector is a gaseous detector capable of detecting single primary electrons from ionising particles. Such a detector consists of a pixel chip as active anode covered with a thin layer of silicon rich silicon nitride (SiRN) for protection against discharges. A layer of 8 µm SiRN, and according recent tests even 4 µm, is sufficient to protect against discharges. The effect of the thickness of the SiRN layer on the operation of a detector has been determined.

DICE (Delft Internal Conversion Experiment)

GridPix detectors are thin μTPCs, they provide an excellent vertex determination for internal radioactive sources and they have a 4π angular acceptance. Gridpix detectors are ideal to study anomolies in Internal Pair Conversion signaling elusive light neutral bosons.