Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their ...capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard 'International Electrotechnical Commission' (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures ( approximately 0.1-400 microGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than approximately 5000 photons has been found, corresponding to exposures above approximately 110 microGy and approximately 50 microGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses ( approximately 3, 30 and 300 microGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of approximately 1, thanks to its high efficiency ( approximately 100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is approximately 0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.
A detailed analysis is presented of the diffractive deep-inelastic scattering process ep→eXY, where Y is a proton or a low mass proton excitation carrying a fraction 1-xIP>0.95 of the incident proton ...longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies |t|<1 GeV2. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range 3.5≤Q2≤1600 GeV2, triple differentially in xIP, Q2 and β=x/xIP, where x is the Bjorken scaling variable. At low xIP, the data are consistent with a factorisable xIP dependence, which can be described by the exchange of an effective pomeron trajectory with intercept αIP(0)=1.118±0.008(exp.)+0.029-0.010(model). Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the Q2 and β dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the Q2 range studied. Total and differential cross sections are also measured for the diffractive charged current process e+p→ν̄eXY and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current ep cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on Q2 at fixed xIP and x or on x at fixed Q2 and β.
The charge sharing effect in the single photon counting hybrid pixel detector XPAD3-S is studied. Several figures of merit are measured, both in the case of Si and CdTe sensors. Data are compared to ...a Monte Carlo simulation that models the main sources of charge migration.
A measurement of the inclusive deep inelastic neutral current
e
+
p
scattering cross section is reported in the region of four-momentum transfer squared, 12 GeV
2
≤
Q
2
≤150 GeV
2
, and Bjorken
x
, ...2×10
−4
≤
x
≤0.1. The results are based on data collected by the H1 Collaboration at the
ep
collider HERA at positron and proton beam energies of
E
e
=27.6 GeV and
E
p
=920 GeV, respectively. The data are combined with previously published data, taken at
E
p
=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3–2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
Neutron imaging with the XPAD3-S hybrid pixel detector Cassol Brunner, F.; Kardjilov, N.; Clémens, J.-C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2011, Letnik:
634, Številka:
1
Journal Article
Recenzirano
The X-ray photon counting hybrid pixel camera XPAD3-S is a promising detector for small animal X-ray radiography and tomography. The increasing interest in neutron imaging as a complementary approach ...to X-ray imaging motivates the study of the potentialities of this device for neutrons. To investigate this issue, we have studied the response of XPAD3-S to alpha particles and cold neutrons. The neutron detection was obtained with passive converters placed in front of the sensor. This choice permits to easily assemble 2D neutron sensitive imagers without size constraints; it penalizes however the detector efficiency with respect to other solutions. In this paper, we first analyze the detector response to alpha particles under several conditions, then we investigate its imaging performances and its detection efficiency for cold neutrons. Finally, we present the first XPAD3-S neutron tomography. Most of the results are validated by Monte Carlo simulations that will also permit to extrapolate the detector response to thermal neutrons.
PIXSCAN: Pixel detector CT-scanner for small animal imaging Delpierre, P.; Debarbieux, F.; Basolo, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2007, Letnik:
571, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The PIXSCAN is a small animal CT-scanner based on hybrid pixel detectors. These detectors provide very large dynamic range of photons counting at very low detector noise. They also provide high ...counting rates with fast image readout. Detection efficiency can be optimized by selecting the sensor medium according to the working energy range. Indeed, the use of CdTe allows a detection efficiency of 100% up to 50
keV. Altogether these characteristics are expected to improve the contrast of the CT-scanner, especially for soft tissues, and to reduce both the scan duration and the absorbed dose. A proof of principle has been performed by assembling into a PIXSCAN-XPAD2 prototype the photon counting pixel detector initially built for detection of X-ray synchrotron radiations. Despite the relatively large pixel size of this detector (330×330
μm
2), we can present three-dimensional tomographic reconstruction of mice at good contrast and spatial resolution. A new photon counting chip (XPAD3) is designed in sub-micronique technology to achieve 130×130
μm
2 pixels. This improved circuit has been equipped with an energy selection circuit to act as a band-pass emission filter. Furthermore, the PIXSCAN-XPAD3 hybrid pixel detectors will be combined with the Lausanne ClearPET scanner demonstrator. CT image reconstruction in this non-conventional geometry is under study for this purpose.
A measurement of the derivative (∂ lnF2/∂ lnx)Q2≡−λ(x,Q2) of the proton structure function F2 is presented in the low x domain of deeply inelastic positron–proton scattering. For 5×10−5⩽x⩽0.01 and ...Q2⩾1.5GeV2, λ(x,Q2) is found to be independent of x and to increase linearly with lnQ2.
We investigate the capability to perform K-edge imaging with the newly developed micro-CT PIXSCAN based on the XPAD3 hybrid pixel detector. The XPAD3 detector surface of 8 cm ×11 cm makes it possible ...to perform whole body mouse imaging. We present a proof of principle of K-edge imaging of mouse-size phantoms filled with Silver and Iodine solutions. Results are compared with standard X-ray absorption tomography for several solution densities.
Elastic J/ψ production at HERA Aktas, A.; Andreev, V.; Anthonis, T. ...
The European physical journal. C, Particles and fields,
06/2006, Letnik:
46, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Cross sections for elastic production of J/ψ mesons in photoproduction and electroproduction are measured in electron proton collisions at HERA using an integrated luminosity of 55 pb-1. Results are ...presented for photon virtualities Q2 up to 80 GeV2. The dependence on the photon-proton centre of mass energy Wγp is analysed in the range 40≤Wγp≤305 GeV in photoproduction and 40≤Wγp≤160 GeV in electroproduction. The Wγp dependences of the cross sections do not change significantly with Q2 and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon density of the proton in the domain of low Bjorken x and low Q2. Differential cross sections dσ/dt, where t is the squared four-momentum transfer at the proton vertex, are measured in the range |t|<1.2 GeV2 as functions of Wγp and Q2. Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/ψ production and decay angular distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudinally and transversely polarised photons is measured as a function of Q2 and is found to be described by perturbative QCD based models.
The production of isolated photons in deep-inelastic scattering ep→eγX is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer ...squared 4<Q
2
<150 GeV
2
and a mass of the hadronic system W
X
>50 GeV. The analysis is based on a total integrated luminosity of 227 pb
-1
. The production cross section of isolated photons with a transverse energy in the range 3<E
T
γ
<10 GeV and pseudorapidity range -1.2<η
γ
<1.8 is measured as a function of E
T
γ
, η
γ
and Q
2
. Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.
PDF
