A detailed analysis of neutral kaons decaying to (cid:25) + (cid:25)(cid:0)(cid:25) 0 is presented based on the complete data set containing half a million events. Time-dependent decay rate asymmetries are measured between initially tagged K 0 and K 0 and for different regions of the phase space. These asymmetries, resulting from the interference between the CP-conserving decay amplitude of K L and the decay amplitude of K S – either CP-violating or CP-conserving – allow the determination of the K S parameters (cid:17)+ (cid:0) 0 (CP-violating) and (cid:21) (CP-conserving), and also of the main isospin components of the K S decay amplitude. The branching ratio of K S ! (cid:25) + (cid:25)(cid:0)(cid:25) 0 (CP-conserving) is deduced directly from (cid:21) . In addition, we extract the slope parameters describing the energy dependence of the K L ! (cid:25) + (cid:25)(cid:0)(cid:25) 0 Dalitz plot. The whole set of our results fits well within the current phenomenological picture of the neutral-kaon system including CP violation and Chiral Perturbation Theory (ChPT).

State-of-the-art inorganic scintillators are discussed. After a short introduction to light sensors, more basic aspects of the scintillation process are addressed. These are the relevant aspects of interaction with radiation, energy transfer to the luminescence center (LC) of a scintillator, and problems related to the actual luminescence. Next, the specific case of lanthanide LCs and some application-related topics, viz. aspects of time and energy resolution, and detection efficiencies of x-rays, gamma rays, and thermal neutrons are studied. Subsequently, gamma-ray, x-ray, and thermal-neutron scintillators and their relation to the biomedical field are discussed. The chapter concludes with a section on storage phosphors and organic scintillators.

We present a detailed investigation of the intrinsic activity of LaBr3 scintillators from the natural abundance of radioactive isotope 138La. Compared to earlier studies of lanthanum halides intrinsic activity, we gained a sharper insight by using samples of different sizes, ranging from 0.16cm3 to 347cm3, and by applying in our recent analysis results on the non-proportionality of scintillation response. In addition, we took advantage of the fact that LaBr3 spectrometers offer a unique opportunity, never available before, to study the characteristics of the 138La electron capture and β radioactive decays that are 2nd order unique forbidden transitions. The observed shape of the β continuum, measured down to the energy of 2keV, is found to be different than expected from standard nuclear theory, indicating a possible underestimation of the screening effect for β energies below 75keV.

A review is presented of R&D of inorganic scintillators for position-sensitive thermal neutron detectors to be used at new spallation neutron sources.

Neutron resonance capture analysis (NRCA) has been applied to determine the elemental compositions of three valuable, precious and very well preserved ancient bronze objects from the National Museum of Antiquities in Leiden (NL). For this study it was not allowed to use analytical methods, for which samples should be taken from objects. For this reason they were studied by NRCA using epithermal neutron beams from the pulsed neutron source of the GELINA facility of the EC-JRC-IRMM in Geel (Belgium). Neutrons can penetrate thick layers of materials, and therefore this method provides bulk compositions. NRCA is a fully non-destructive method. Since thermal neutrons are removed from the beam, the activation of the objects is low already directly after the measurement and fully negligible after a short waiting period. This research is part of the European ANCIENT CHARM project.

PURPOSEPreviously, we demonstrated the potential of positron emission tomography detectors consisting of monolithic scintillation crystals read out by arrays of solid-state light sensors. We reported detector spatial resolutions of 1.1-1.3 mm full width at half maximum (FWHM) with no degradation for angles of incidence up to 30 degrees, energy resolutions of approximately 11% FWHM, and timing resolutions of approximately 2 ns FWHM, using monolithic LYSO:Ce3+ crystals coupled to avalanche photodiode (APD) arrays. Here we develop, validate, and demonstrate a simple model of the detector point spread function (PSF) of such monolithic scintillator detectors.METHODSA PSF model was developed that essentially consists of two convolved components, one accounting for the spatial distribution of the energy deposited by annihilation photons within the crystal, and the other for the influences of statistical signal fluctuations and electronic noise. The model was validated through comparison with spatial resolution measurements on a detector consisting of an LYSO:Ce3+ crystal read out by two APD arrays.RESULTSThe model is shown to describe the measured detector spatial response well at the noise levels found in the experiments. In addition, it is demonstrated how the model can be used to correct the measured spatial response for the influence of the finite diameter of the annihilation photon beam used in the experiments, thus obtaining an estimate of the intrinsic detector PSF.CONCLUSIONSDespite its simplicity, the proposed model is an accurate tool for analyzing the detector PSF of monolithic scintillator detectors and can be used to estimate the intrinsic detector PSF from the measured one.

Much research is being conducted on position-sensitive scintillation detectors for medical imaging, particularly for emission tomography. Monte Carlo simulations play an essential role in many of these research activities. As the scintillation process, the transport of scintillation photons through the crystal(s), and the conversion of these photons into electronic signals each have a major influence on the detector performance; all of these processes may need to be incorporated in the model to obtain accurate results. In this work the optical and scintillation models of the GEANT4 simulation toolkit are validated by comparing simulations and measurements on monolithic scintillator detectors for high-resolution positron emission tomography (PET). We have furthermore made the GEANT4 optical models available within the user-friendly GATE simulation platform (as of version 3.0). It is shown how the necessary optical input parameters can be determined with sufficient accuracy. The results show that the optical physics models of GATE/GEANT4 enable accurate prediction of the spatial and energy resolution of monolithic scintillator PET detectors.

Neutron resonance capture analysis (NRCA) is a method used to determine the bulk composition of various kinds of objects and materials. It is based on analyzing direct capture resonance peaks. However, the analysis is complicated by scattering followed by capture effects in the object itself. These effects depend on the object’s shape and size. In this paper the new Delft elemental analysis program (DEAP) is presented which can automatically and quickly analyze multiple NRCA spectra in a practical and simple way, yielding the elemental bulk composition of an object, largely independent of its shape and size. The DEAP method is demonstrated with data obtained with a Roman bronze water tap excavated in Nijmegen (The Netherlands). DEAP will also be used in the framework of the Ancient Charm project as data analysis program for neutron resonance capture imaging (NRCI) experiments. NRCI provides three-dimensional visualization and quantification of the internal structure of archaeological objects by performing scanning measurements with narrowly collimated neutron beams on archaeological objects in computed tomography based experimental setups. The large amounts (hundreds to thousands) of spectra produced during a NRCI experiment can automatically and quickly be analyzed by DEAP.

We developed positron emission tomography (PET) detectors based on monolithic scintillation crystals and position-sensitive light sensors. Intrinsic depth-of-interaction (DOI) correction is achieved by deriving the entry points of annihilation photons on the front surface of the crystal from the light sensor signals. Here we characterize the next generation of these detectors, consisting of a 20 mm thick rectangular or trapezoidal LYSO:Ce crystal read out on the front and the back (double-sided readout, DSR) by Hamamatsu S8550SPL avalanche photodiode (APD) arrays optimized for DSR. The full width at half maximum (FWHM) of the detector point-spread function (PSF) obtained with a rectangular crystal at normal incidence equals approximately 1.05 mm at the detector centre, after correction for the approximately 0.9 mm diameter test beam of annihilation photons. Resolution losses of several tenths of a mm occur near the crystal edges. Furthermore, trapezoidal crystals perform almost equally well as rectangular ones, while improving system sensitivity. Due to the highly accurate DOI correction of all detectors, the spatial resolution remains essentially constant for angles of incidence of up to at least 30 degrees . Energy resolutions of approximately 11% FWHM are measured, with a fraction of events of up to 75% in the full-energy peak. The coincidence timing resolution is estimated to be 2.8 ns FWHM. The good spatial, energy and timing resolutions, together with the excellent DOI correction and high detection efficiency of our detectors, are expected to facilitate high and uniform PET system resolution.

For the first time results obtained from gamma-ray excitation of a low-dimensional lead-halide-based perovskite-type organic-inorganic scintillator crystal are presented. Scintillation and luminescence properties have been studied of a 5 × 6 × 1 mm3 single crystal of bis(phenethylammonium) tetrabromoplumbate(II), (C6H5(CH2)2NH3)2PbBr4. Excitation, emission, pulse-height and decay-time spectra are presented. The light yield is 10,000 photons per MeV, measured at 662 keV gamma-ray energy. The main decay time under pulsed x-ray excitation is 9.4 ns.

A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed for pre-treatment verification of dose distributions in particle therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two gas electron multiplier (GEM) structures are mounted (Seravalli et al 2008b Med. Phys. Biol. 53 4651–65). Photons emitted by the excited Ar/CF4 gas molecules during the gas multiplication in the GEM holes are detected by a mirror–lens–CCD camera system. The intensity distribution of the measured light spot is proportional to the 2D dose distribution. In this work, we report on the characterization of the scintillating GEM detector in terms of those properties that are of particular importance in relative dose measurements, e.g. response reproducibility, dose dependence, dose rate dependence, spatial and time response, field size dependence, response uniformity. The experiments were performed in a 150 MeV proton beam. We found that the detector response is very stable for measurements performed in succession (σ = 0.6%) and its response reproducibility over 2 days is about 5%. The detector response was found to be linear with the dose in the range 0.05–19 Gy. No dose rate effects were observed between 1 and 16 Gy min−1 at the shallow depth of a water phantom and 2 and 38 Gy min−1 at the Bragg peak depth. No field size effects were observed in the range 120–3850 mm2. A signal rise and fall time of 2 µs was recorded and a spatial response of ⩽1 mm was measured.

A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth–dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb (‘Lanex’) screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

We investigated gamma- and neutron-scintillation properties of A(2)LiLnX(6) : Ce3+ (A = Cs, Rb, K, Na, Li; Ln = La, Y, Lu, Sc; X = Br, I) with the aim to develop new scintillators with high neutron detection efficiencies. Among the investigated thermal neutron scintillators, Rb2LiYBr6 : Ce3+ shows an excellent neutron peak resolution of 3.6%. This is the best neutron peak resolution ever reported. Together with the large alpha/beta ratio of 0.74, Rb2LiYBr6 : Ce3+ offers the possibility of excellent neutron/gamma discrimination. The highest thermal neutron scintillation light yield of 83,000 pbotons/neutron is also reported for Rb2LiYBr6 : Ce3+.

In recent years, a number of new gamma-ray scintillators are commercially available. These scintillators are either derived from known scintillators, e.g. Lu1-xYxAlO3: Ce (LuYAP) from LuAlO3:Ce and Lu(2(1-x))Y2xSiO5:Ce (LYSO) from Lu2SiO5:Ce or are the result of new discoveries, e.g. LaCl3:Ce and LaBr3:Ce. The first two materials are primarily of interest because of the relatively high detection efficiency and fast response; LYSO has found application in time-of-flight (TOF) positron-emission tomography (TOF PET) and the LuYAP-LYSO combination is used in small-animal PET. The halide scintillators have an excellent energy resolution of approximately 3% at 662 keV and they have a relatively high light yield. LaBr3:Ce is being studied for application in TOF PET. At the same time, the search for and research on new scintillator materials are going on. For example, LuI3:Ce is a new material with a very high light yield (approximately 90,000 photons MeV(-1)). Other examples of new materials are (C6H13NH3)2PbI4 and (C3H7NH3)2PbBr4, organic-inorganic hybrid compounds, of which the former has a very fast sub-nanosecond response. The new scintillators show great promise for new developments in medical applications, in particular, for PET systems.

We investigated and neutron-scintillation properties of A LiLnX Ce (A Cs, Rb, K, Na, Li; Ln La, Y, Lu, Sc; Br, I) with the aim to develop new scintillators with high neutron detection efficiencies. Among the investigated thermal neutron scintillators, Rb LiYBr Ce shows an excellent neutron peak resolution of 3.6%. This is the best neutron peak resolution ever reported. Together with the large ratio of 0.74, Rb LiYBr Ce offers the possibility of excellent neutron/ discrimination. The highest thermal neutron scintillation light yield of 83,000 photons/neutron is also reported for Rb LiYBr Ce .

A two-dimensional position-sensitive dosimetry system based on a scintillating gas detector is being developed with the aim of using it for pre-treatment verification of dose distributions in charged particle therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. In such a system, light quanta are emitted by the scintillating gas mixture during the electron avalanches in the GEM holes when radiation traverses the detector. The light intensity distribution is proportional to the energy deposited in the detector's sensitive volume by the beam. In the present work, we investigated the optimization of the scintillating GEM detector light yield. The light quanta are detected by means of a CCD camera or a photomultiplier tube coupled to a monochromator. The GEM charge signal is measured simultaneously. We have found that with 60 µm diameter double conical GEM holes, a brighter light signal and a higher electric signal are obtained than with 80 µm diameter holes. With an Ar + 8% CF4 volume concentration, the highest voltage across the GEMs and the largest light and electric signals were reached. Moreover, we have found that the emission spectrum of Ar/CF4 is independent of (1) the voltages applied across the GEMs, (2) the x-ray beam intensity and (3) the GEM hole diameter. On the other hand, the ratio of Ar to CF4 peaks in the spectrum changes when the concentration of the latter gas is varied.

The monolithic scintillator block, read out by an APD array, is a very promising detector concept for PET. Some recent results demonstrating this are presented. Furthermore, using experimental information, we performed a simulation study of the position resolution of the monolithic blocks as a function of gamma-ray energy. The best resolution is obtained in the 140 –250 keV region, i.e. for 99mTc and 111In, while at 364 keV (131I) the resolution is still good. Consequently the monolithic block approach can also be applied for SPECT. We discuss a combined PET/SPECT system employing monolithic scintillator block detectors.