M. Pomorski

Radiation hardness of diamond and silicon sensors compared

The radiation hardness of silicon charged particle sensors is compared with single crystal and polycrystalline diamond sensors, both experimentally and theoretically. It is shown that for Si- and C-sensors, the NIEL hypothesis, which states that the signal loss is proportional to the Non-Ionizing Energy Loss, is a good approximation to the present data. At incident proton and neutron energies well above 0.1 GeV the radiation damage is dominated by the inelastic cross section, while at non-relativistic energies the elastic cross section prevails. The smaller inelastic nucleon-carbon cross section and the light nuclear fragments imply that at high energies diamond is an order of magnitude more radiation hard than silicon, while at energies below 0.1 GeV the difference becomes significantly smaller.

Ultra-thin optical grade scCVD diamond as X-ray beam position monitor

Results of measurements made at the SIRIUS beamline of the SOLEIL synchrotron for a new X-ray beam position monitor based on a super-thin single crystal of diamond grown by chemical vapor deposition (CVD) are presented. This detector is a quadrant electrode design processed on a 3 µm-thick membrane obtained by argon-oxygen plasma etching the central area of a CVD-grown diamond plate of 60 µm thickness. The membrane transmits more than 50% of the incident 1.3 keV energy X-ray beam. The diamond plate was of moderate purity (∼1 p.p.m. nitrogen), but the X-ray beam induced current (XBIC) measurements nevertheless showed a photo-charge collection efficiency approaching 100% for an electric field of 2 V µm(-1), corresponding to an applied bias voltage of only 6 V. XBIC mapping of the membrane showed an inhomogeneity of more than 10% across the membrane, corresponding to the measured variation in the thickness of the diamond plate before the plasma etching process. The measured XBIC signal-to-dark-current ratio of the device was greater than 10(5), and the X-ray beam position resolution of the device was better than a micrometer for a 1 kHz sampling rate.

Diamond thin film detectors for beam monitoring devices

Diamonds offer radiation hard sensors, which can be used directly in primary beams. Here we report on the use of a polycrystalline CVD diamond strip sensor as beam monitor of heavy ion beams with up to ∼10 9 lead ions per bunch. The strips allow for a determination of the transverse beam profile to a fraction of the pitch of the strips, while the timing information yields the longitudinal bunch length with a resolution of the order of a few mm.

Diamond Start Detectors

In this paper we describe the operation principles and the in-beam performance of Start Detector (SD) assemblies consisting of various diamond detectors (DDs) and special Front End Electronics (FEE) adapted to the requirements of different applications. In the framework of the European Joint Research Activity NoRHDia (Novel Radiation Hard Diamond detectors for hadron research) we optimized different sensor and FEE designs, particularly aiming at the development of relativistic proton SDs for the GSI experiments FOPI (Four PI detector) and HADES (High Acceptance Di-electron Spectrometer) as well as for the upcoming FAIR experiment CBM (Compressed Baryonic Matter). The limiting parameter in minimum-ionizing particles (mip) is the high pair-production energy of diamond (?r ~ 13eV/e-h pair), which leads to a rather small signal amplitude (a factor of ~2.5 smaller than the one of silicon sensors). We present the result from various SD assemblies obtained with relativistic heavy ions and protons. An excellent heavy-ion time resolution (?i <30ps) was obtained using the broadband preamplifier-discriminator plate FEE-1 with both, polycrystalline (pc) and single crystal (sc) devices. Good results are obtained with PADI-1, a preamplifier-discriminator ASIC designed for timing RPCs. In contrast, due to the small signal amplitude in the case of relativistic protons a more elaborated solution is needed to increase the S/N ratio and to improve the time resolution by the decrease of the total capacitance of the detector-FEE ensemble. The segmentation of the detector area and hence lowering of the input capacitance of the amplifier led to a proton time resolution of ?i =100ps. For this application a microwave BJT in common-emitter configuration was used for the FEE, which was mounted near the detecting sector of the DD. For micro-patterned DD applications the PADI-4 ASIC was designed, a four-channels variant of PADI-1 optimized to match low capacitance detectors.

Characterisation of CVD Diamond devices as XBPMs at SOLEIL

Single crystal CVD diamonds have been developed for use as XBPMs on the beamlines of the French synchrotron SOLEIL. These devices have been calibrated and characterized directly on the beamline following an elaborate protocol. An example is given for an XBPM installed on PROXIMA 2. This device has shown a charge collection efficiency of 100% for only 0.2V/μm with total signal-to-noise ratio better than 105. A complete 2D scan gives the homogeneity of the scale factors over the active surface with a very low error corresponding to 0.6μm (beam off-center and maximum calibration error). The current sensitivity measurement shows a fluctuation less than 0.02% and the responsivity is calculated to measure the incident flux. And finally, the spatial resolution for these XBPMs is better than 1μm rms at 1kHz and 100 nm rms at 5 Hz.

X-ray position-sensitive duo-lateral diamond detectors at SOLEIL

The performance of a diamond X-ray beam position monitor is reported. This detector consists of an ionization solid-state chamber based on a thin single-crystal chemical-vapour-deposition diamond with position-sensitive resistive electrodes in a duo-lateral configuration. The detectors linearity, homogeneity and responsivity were studied on beamlines at Synchrotron SOLEIL with various beam sizes, intensities and energies. These measurements demonstrate the large and homogeneous (absorption variation of less than 0.7% over 500 µm × 500 µm) active area of the detector, with linear responses independent of the X-ray beam spatial distribution. Due to the excellent charge collection efficiency (approaching 100%) and intensity sensitivity (0.05%), the detector allows monitoring of the incident beam flux precisely. In addition, the in-beam position resolution was compared with a theoretical analysis providing an estimation of the detectors beam position resolution capability depending on the experimental conditions (X-ray flux, energy and readout acquisition time).

Single Crystal CVD Diamond Detectors: Position and Temporal Response Measurements using a Synchrotron Microbeam Probe

Ultrapure, homoeptaxially grown CVD single crystal diamond is a material with great potential for the fabrication of ionizing radiation detectors for high energy, heavy ion physics, and realtime dosimetry for radiotherapy. Only diamond has suitable transmission properties and can offer the required radiation hardness for synchrotron X-ray beam monitoring applications. We report on experiments made using a synchrotron X-ray microbeam probe to investigate the performance of single crystal diamonds operated as position sensitive, solid state ‘ionization chambers’. We show that for a wide range of electric fields >0.3Vµm −1 , suitably prepared devices give excellent spatial response uniformity and time stability. With an applied field of 2Vµm −1 complete charge collection times are ∼1nsec for a diamond plate thickness of 100µm. Position sensitivity was obtained for an X-ray beam incident on the isolation gap between adjacent electrodes of a quadrant device: here, a crossover response region that results from charge carrier diffusion extends over ∼20µm. Using GHz bandwidth signal processing electronics, the signal charge collection process was measured with spatial and temporal resolutions of 1µm and

Diamond thin Film Detectors for Beam Monitoring Devices

Diamonds offer radiation hard sensors, which can be used directly in primary beams. Here we report on the use of a polycrystalline CVD diamond strip sensor as beam monitor of heavy ion beams with up to ∼10 9 lead ions per bunch. The strips allow for a determination of the transverse beam profile to a fraction of the pitch of the strips, while the timing information yields the longitudinal bunch length with a resolution of the order of a few mm.