C. Fiorini

Silicon drift detectors for high resolution room temperature X-ray spectroscopy

New cylindrical silicon drift detectors have been designed, fabricated and tested. They comprise an integrated on-chip amplifier system with continuous reset, on-chip voltage divider, electron accumulation layer stabilizer, large area, homogeneous radiation entrance window and a drain for surface generated leakage current. The test of the 3.5 mm2 large individual devices, which have also been grouped together to form a sensitive area up to 21 mm2 have shown the following spectroscopic results: at room temperature (300 K) the devices have shown a full width at half maximum at the MnKα line of a radioactive 55 Fe source of 225 eV with shaping times of 250 to 500 ns. At −20°C the resolution improves to 152 eV at 2 μs Gaussian shaping. At temperatures below 200 K the energy resolution is below 140 eV. With the implementation of a digital filtering system the resolution approaches 130 eV. The system was operated with count rates up to 800 000 counts per second and per readout node, still conserving the spectroscopic qualities of the detector system.

Silicon drift detectors for high count rate X-ray spectroscopy at room temperature

Abstract Silicon Drift Detectors (SDDs) combine a large sensitive area with a small value of the output capacitance and are therefore well suited for high resolution, high count rate X-ray spectroscopy. The low leakage current level obtained by the elaborated processing technology makes it possible to operate them at room temperature or with moderate cooling. A brief description of the device principle is followed by the presentation of first results of a new production of large area SDDs with external electronics. Performance and applications of the already established SDDs with on-chip amplification are summarised. Various shapes of Multichannel Drift Detectors are introduced as well as their use in new experiments like X-ray holography and in new systems like an Anger camera for γ-ray imaging.

Prompt gamma imaging with a slit camera for real-time range control in proton therapy.

Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study reports on the development and test of a prompt gamma camera using a slit collimator to obtain a 1-dimensional projection of the beam path on a scintillator detector. A first prototype slit camera using the HICAM gamma detector, originally developed for low-energy gamma-ray imaging in nuclear medicine and modified for this purpose, was tested successfully up to 230 MeV beam energy. Results now confirm the potential of this concept for real-time range monitoring with millimeter accuracy in pencil beam scanning mode for the whole range of clinical energies. With the experience gained, a new prototype is under study for clinical beam currents. In this work, we present both the profiles obtained at 230 MeV using HICAM and the description of the new gamma camera prototype design.

A New Measurement of Kaonic Hydrogen X-rays

The KN system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the K-series x rays of kaonic hydrogen atoms at the DANE electron-positron collider of Laboratori Nazionali di Frascati, and have de- termined the most precise values of the strong-interaction energy-level shift and width of the 1s atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be ǫ1s = 283 ± 36(stat) ± 6(syst) eV and 1s = 541± 89(stat) ± 22(syst) eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy KN interaction.

Gamma ray spectroscopy with CsI(Tl) scintillator coupled to silicon drift chamber

A /spl gamma/-ray detector, designed around a silicon drift chamber having a diameter of 3 mm and coupled to a CsI(Tl) scintillator of the same diameter and 10 mm thick, has been realized and extensively tested. This detector may operate over a wide energy band with a minimum energy threshold that may be set around 10 keV at room temperature or at around 4 keV at 0/spl deg/C. At the typical energy of 662 keV used to characterize a /spl gamma/-ray spectrometer, an energy resolution of 4.4% full-width at half-maximum has been measured at room temperature. This detector shows high energy resolution over the full energy range explored, 6 keV-1.27 MeV, and to our knowledge the results reported are the best ever obtained with a scintillator.

Kaonic hydrogen X-ray measurement in SIDDHARTA

Abstract Kaonic hydrogen atoms provide a unique laboratory to probe the kaon–nucleon strong interaction at the energy threshold, allowing an investigation of the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. The SIDDHARTA Collaboration has measured the K -series X rays of kaonic hydrogen atoms at the DAΦNE electron–positron collider of Laboratori Nazionali di Frascati, and has determined the most precise values of the strong-interaction induced shift and width of the 1 s atomic energy level. This result provides vital constraints on the theoretical description of the low-energy K ¯ N interaction.

First clinical application of a prompt gamma based in vivo proton range verification system

BACKGROUND AND PURPOSE To improve precision of particle therapy, in vivo range verification is highly desirable. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically. Here we report on the worldwide first clinical application of prompt gamma imaging (PGI) based range verification. MATERIAL AND METHODS A prototype of a knife-edge shaped slit camera was used to measure the prompt gamma ray depth distribution during a proton treatment of a head and neck tumor for seven consecutive fractions. Inter-fractional variations of the prompt gamma profile were evaluated. For three fractions, in-room control CTs were acquired and evaluated for dose relevant changes. RESULTS The measurement of PGI profiles during proton treatment was successful. Based on the PGI information, inter-fractional global range variations were in the range of ±2 mm for all evaluated fractions. This is in agreement with the control CT evaluation showing negligible range variations of about 1.5mm. CONCLUSIONS For the first time, range verification based on prompt gamma imaging was applied for a clinical proton treatment. With the translation from basic physics experiments into clinical operation, the potential to improve the precision of particle therapy with this technique has increased considerably.

Gamma-ray spectroscopy with LaBr/sub 3/:Ce scintillator readout by a silicon drift detector

In this paper, the authors propose a gamma-ray spectrometer based on a LaBr3 :Ce scintillator coupled to a silicon drift detector (SDD). The SDD is a photodetector characterized by a very low noise thanks to the low value of output capacitance independent from the active area. With respect to a PMT, the SDD offers a higher quantum efficiency which reduces the spread associated to the statistic of photoelectrons generation. Also with respect to an APD, the SDD offers a lower photoelectrons statistic contribution, which, in the APD, is worsened by the excess noise factor with respect to pure Poisson statistics. Moreover, the SDD has a stable behavior, less sensitive to temperature and bias drift. In the past years, good energy resolutions were measured using a SDD coupled to a CsI:Tl crystal. However, the long shaping time, to be used with this scintillator to prevent ballistic deficit, was too far to exploit the best noise performances achievable with a SDD obtained at shaping times in the order of 1 mus. On the contrary, this optimum shaping time is fully compatible with the short decay time of the LaBr3 :Ce crystal (about 25 ns). The results of the experimental characterization of the LaBr3 :Ce-SDD gamma-ray spectrometer are presented in this work and are compared with the performances achieved with the same crystal coupled to a PMT and to a CsI(Tl) crystal coupled to the same SDD. The SDD has an active area of 30 mm2. Antireflective coatings have been implemented. Good energy resolutions were measured at room temperature, thanks to the low leakage current of the detector: 2.7% at the137 Cs 661.7 KeV line and 6.1% at the 57Co 122 KeV line. A resolution of 5.7% at 122 KeV line was measured at 0 degCIn this work we propose a gamma-ray spectrometer based on a LaBr/sub 3/:Ce scintillator coupled to a silicon drift detector (SDD). The SDD is a photodetector characterized by a very low noise thanks to the low value of output capacitance independent from the active area. With respect to a PMT, the SDD offers a higher quantum efficiency which reduces the spread associated to the statistic of photoelectrons generation. Also with respect to an APD, the SDD offers a lower photoelectrons statistic contribution, which, in the APD, is worsened by the excess noise factor with respect to pure Poisson statistics. Moreover, the SDD has a stable behaviour, less sensitive to temperature and bias drift. In the past years, good energy resolutions were measured using a SDD coupled to a CsI:Tl crystal. However, the long shaping time, to be used with this scintillator to prevent ballistic deficit, was far to exploit the best noise performances achievable with a SDD obtained at shaping times in the order of 1 /spl mu/s. On the contrary, this optimum shaping time is fully compatible with the short decay time of the LaBr/sub 3/:Ce crystal (about 25 ns). The results of the experimental characterization of the LaBr/sub 3/:Ce-SDD gamma-ray spectrometer are presented in the work and are compared with the performances achieved with other photodetectors, coupled to the same scintillator crystal. The SDD has an active area of 30 mm/sup 2/. Antireflective coatings have been implemented. Good energy resolutions were measured also at room temperature, thanks to the low leakage current of the detector: a resolution of 2.7% was measured at the /sup 137/Cs 661.7 KeV line and a resolution of 6.1% at the /sup 57/Co 122 KeV line. A discussion of the noise performances of the SDD is carried out in the last part of the paper.

A high resolution, 6 channels, silicon drift detector array with integrated JFET's designed for XAFS spectroscopy: first X-ray fluorescence excitation spectra recorded at the ESRF

We have investigated the performances of a 6 channel silicon drift diode (SDD) as a possible detector for X-ray fluorescence excitation spectroscopy. This detector, whose total active area is 21 mm2, combines the advantage of high counting rates with a remarkable energy resolution (ΔE). At room temperature, ΔE at the Mn-Kα line (5.895 keV) is 227 eV FWHM with 0.5 μs Gaussian shaping time constant whereas this value decreases to 139 eV at 150 K with a longer optimum shaping time (5 μs). The resolution at 150 K and 250 ns shaping time is 162 eV allowing high count rate measurements still with a good energy resolution. This paper reproduces the first XAFS spectra recorded in the fluorescence excitation mode with a silicon drift diode. These experiments have been carried out at the ESRF on beamline BL6/ID12A using diluted macrocyclic complexes of cerium (III) as test samples. This choice was motivated by the opportunity to check for the contamination of the LIII-EXAFS oscillations by the LII-edge signatures even though one is able to discriminate in energy between the Lα and Lβ emission lines.

Silicon drift detector with integrated p-JFET for continuous discharge of collected electrons through the gate junction

Abstract The paper describes the design and the performance of a silicon drift detector with integrated front-end electronics for large area, high resolution X-ray spectroscopy. The detector features a new type of p-JFET embedded in the collecting anode and operated with the gate-to-channel junction forward biased by the detector leakage current. This unusual condition performs, at the same time, the amplification of the signal and the continuous discharge of the collected charge eliminating any additional component or system for resetting. The particular design of the transistor allows the anode region to be very compact without affecting the collection of the charge. Using a test device with an active area of 3 mm 2 the detector has reached an energy resolution of 19 electrons rms at an operating temperature of 208 K.