Amplifiers are often the most critical parts of any detection system, especially for high-bandwidth and very low-noise measurement signals... more»
Within the amplification phase of any signal, especially for systems in need of very high gain, the noise criteria, dynamic range and analogue bandwidth are the crucial parameters characterizing amplifiers. According to these specifications the user can verify if the proposed solution suits best and will assure signals to be measured with enough precision, accuracy and speed. In Physics and Medical Applications, employing ionizing radiation for detection, disease diagnostics or treatments purposes, there is a high request for ultra-fast, precise and accurate detection systems in order to measure direction, dose, radiation profile or time structure of applied radiation. One of the most promising today's technology concerning radiation detectors are Diamond Detectors, especially Diamonds made artificially by CVD (Chemical Vapor Deposition) process. The CVD Diamond Detectors are incredibly fast devices (typical pulse duration <1 ns FWHM) and demonstrate very low noise level, however do require very low-noise electronics with wide analogue bandwidth. The CVD Diamonds are also widely used in Modern, Particle and Sub-atomic Physics Experiments (i.e. at CERN) especially where levels of radiation are considered very high.
For the CVD Diamond Detectors, the precision of time and amplitude measurements depend much on quality of the signal amplification, especially the noise-level, while maintaining wide bandwidth. Dedicated, very low-noise and wideband preamplifiers allow systems with CVD Diamond Detectors to measure even low-energy signals <100 keV without shaping filters, in order to preserve signal's time performance for time-critical applications.
The INS Instruments company has designed a novel PA Series Wideband Preamplifiers for CVD Diamond Detectors, capable of dealing with CVD Diamonds in highly-demanding applications as Particle Counting, Intensity Measurements for Radiation Profilometry and Low-energy Spectroscopy. The presented PA-10 and PA-20 models as the Low-noise Diamond Detectors Preamplifiers are employing cutting-edge technology solutions, verified in collaboration with scientific centers from Poland, Italy and Spain.
There are several applications where detection of single particle (i.e. protons, carbon ions, heavy ions or electrons) is of great importance, mostly because this would considerably improve measurement precision of ionizing radiation fields. Although the measurement and detection of heavier ions, even with reasonably thin (<50 µm of thickness) detectors positioned perperdicularly to the beam is technology-wise feasible, detection of high-energy protons is still an issue. The typical signal created by a single 70-MeV proton in a 50-µm thick Diamond Detector is only ~11000 electrons.
In Medical Applications and Physics Experiments there is a high request for detection systems capable of making intensity measurements in single particle counting mode, for high-energy, low-LET particles passing through thin (~µmeters thick) detectors.
Energy Spectroscopy is one of the most challenging measurements in Physics. Performance of measurement system to be used in particular experiment or application, is mostly defined by accuracy, precision and speed. Traditionally, the particle Energy Spectroscopy concerns measurement of entire particle energy by stopping it withing the detector volume. Hence, the detector thickness has to be chosen with care, according to radiation type and its energy range. The stopping power of the detector material (i.e. Germanium, NaI, LaBr3, CVD Diamond) causes the Bragg peak to appear inside of detector, assuring the measurement of full energy peak.
For the sake of high-resolution spectroscopy, the typical front-end electronics design contains a Charge Sensitive Preamplifier (CSA). CSA provides an improved S/N ratio by shaping a signal, however its time development is increased to tenths or hundreds of ns even in the case of CVD Diamond detectors.
For time-critical applications, as high-intensity particle beams of modern accelerators, the use of CSA can cause overlaps of consecutive signal pulses, thus preventing the system from working in a single-particle regime. The ideal solution to this problem would be a very low-noise, wideband amplifier, providing a high-enough precision of energy measurement, while preserving the signal pulse shape.
The presented figure demonstrates the performance of energy measurements with 100-µm scCVD detector with PA-20 amplifier by INS and the mixed-nuclide Alpha source: Pu-239, Am-241 and Cm-244 with energies of 5157 keV, 5486 keV and 5805 keV accordingly. The obtained energy resolution ~122 keV @ 5486 keV is comparable to results presented by different R&D groups with CVD Diamonds and CSA amplifiers. This is substantially due to the very-low noise level of the wide-band PA-20 preamplifier.
The method of energy measurement by using a Time-of-Flight (ToF) technique, can potentially assure even higher measurement precision. Employed detectors and front-end electronics has to be fast enough to satisfy time precision, which directly translates into particle energy, when a distance between two detectors is known.
Time Resolution of measurement system is directly proportional to signal-to-noise ratio (SNR) and inversly related to the rise time of the signal. The higher the SNR, the better the timing performance. The third component, affecting the time resolution, is the intrinsic detector time precision, which in the case of CVD Diamonds is considered very small, hovewer it sums up with square with other errors.
The PA-10 amplifiers by INS Instruments have been optimized for CVD Diamond Detectors and rapid signals (<1 ns) providing high SNR also for signals with low amplitude (i.e. generated by 70-MeV protons in 50-µm detector being ~11000 electrons). This implies a very low noise level ~15 µV RMS refered to amplifier's input and the gain of 45 dB, to provide a detectable signal even for low particle energy loss. The dynamic range of the PA-10 preamplifier is 5.5 MeV. For the sake of high-energy and heavy ion's spectroscopy the PA-20 amplifier has been developed to cover the energy range of up to 100 MeV. The noise level of PA-20, refered to the input is <20 µV RMS and the gain is 20 dB.
The figure shows the time performance of proton coincidence with two scCVD Diamond Detectors: 100-µm & 300-µm, positioned one after another and traversed by same, 70-MeV protons. The detector's signals amplified by PA-10 and 2x PA-20(to assure enough gain) preamplifiers, make possible to obtain the time resolution of <130 ps for the set of two detectors. Signal of each channel has been digitized at 20GS/s and registered by the LeCroy SDA5000 Data Analyzer. The time jitter introduced by both: PA-10 and PA-20 preamplifiers is well below 2 ps, which makes them appealing for timing and time-critical applications.
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