This article provides an insight into the world of Polish development workers operating in South Sudan. It shows that the conceptualisations of aid work in terms of a 'mission', a unique job with a ...special, ethical goal, a difficult, risky operation requiring specific skills are not incidental. Instead, the point is made, that such ways of thinking about foreign aid and distant locations are strongly institutionalised sets of values and behavioural patterns, here defined as 'work in crisis'. This specific notion is shaped by aid organisations who actively promote this rhetoric firstly through producing 'truth' about the aid work and project locations, and secondly through governing lived realities of the aid workers. The 'work in crisis' rhetoric helps to draw people into a development movement as devoted and allegiant followers. It also enables the management of these employees who are the most crucial for the industry - project coordinators - but who are separated from the organisational headquarters and NGO management by thousands of miles. Finally, it assists in the promotion of foreign aid among wider audiences in donor societies.
A micro photomultiplier (microPMT or μPMT) works like a classic photomultiplier but the whole device is made directly in a silicon wafer sandwiched between two glass layers. A microPMT has dimensions ...of only 13x10x2 mm and its photocathode has a size of 3x1 mm. The aim of the work is to check usefulness of a microPMT in gamma spectrometry with scintillators and fast timing. In the first part of the study analysis of the energy resolution obtained with 3x3x1 mm LSO, BGO and CsI(Tl) scintillators is made. The recorded values for 662 keV are equal to 22.9% and 13.5% for CsI and LSO, respectively. The light pulse shapes of a single photoelectron and scintillation signal of LSO are also shown. The important part of the study is measurement of the number of photoelectrons and estimation of the excess noise factor. Only 2200 phe/MeV were obtained for LSO coupled with the tested microPMT. The calculated excess noise factor is equal to 1.4. In the second part, measurements of the time jitter and timing resolution with LSO crystal for 511 keV annihilation quanta are reported. The timing characteristics of the tested device is poor. Its time jitter equals to 1.5 ns, whereas timing resolution for 22 Na is 620 ps. All the results are compared with data obtained with classic PMTs.
In spite of the excellent performance of SiPMs in the application of time-of-flight PET detectors, the development of better photomultipliers for PET detectors is still worth considering. Fast timing ...with detectors based on the PMT light readout depends mainly on the time jitter and the quantum efficiency of the PMTs. Several studies in the past showed that a screening grid at the anode significantly improves the time resolution when measured with scintillation detectors. ADIT Co. has started a development of a 1" diameter fast PMT with the screening grid at the anode to be applied in the block detectors in TOF PET scanners. In the presented studies, we report the first comparative study of the L25, a classical PMT, with one that is equipped with a screening grid. Adding the screening grid yielded a large improvement in the time resolution, up to a factor of 1.2.
According to the present knowledge, the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution. However, several observations collected ...in the last 15 years on the influence of slow components of the light pulses on energy resolution suggest more complex processes in the scintillators. The presented study of undoped CsI crystals shows a large deterioration of the intrinsic resolution of the crystal, when most of the light, including slow component was integrated. Moreover, it was confirmed by a large difference of the non-proportionality characteristics measured at short peaking time, corresponding to the integration of the fast intrinsic emission of the CsI, and that observed with a long peaking time, when the slow component was integrated.
In this paper, five detectors (EJ-270 — single plastic scintillator, EJ-309B5 — single liquid scintillator, and 3 phoswich detectors: EJ-276+GS20, GS20+EJ-276, EJ-309+GS20) were studied in terms of ...simultaneous detection of gamma-rays and slow and fast neutrons. The measurements were carried out in a mixed field of neutron and gamma radiation from an intense (∼106 neutrons/s/4π) PuBe source. The PuBe neutron source was placed in an 18 cm diameter paraffin ball in order to increase the number of slow neutron detections. This paper covers the measurements of the neutron/gamma discrimination, photoelectron yield and analysis of the light pulse shapes originating from events related to gamma-rays, slow neutrons and fast neutrons. Sensitivity to slow neutrons is also briefly discussed. A comparison of n/γ discrimination for all of the tested detectors shows excellent performance of all phoswich detectors. Phoswich configurations tested within the scope of this study allow unambiguously resolve all three types of radiation and show superior performance in comparison with single loaded plastic or liquid scintillators.
Recently, a silicon photomultiplier (SiPM) became one of the strongest candidates for application in PET–MR or SPECT–MR dual-modality scanners. However, optimization of the scintillation detectors ...with SiPM light readout requires different approach than in the case of classic photomultipliers. The finite number of micro-cells in a SiPM creates nonlinear response for high number of incident photons. Moreover, the size and total number of micro-cells defines fill factor, which in turn affects the photon detection efficiency (PDE). Response of SiPMs is also highly sensitive to bias voltage causing changes in PDE and excess noise factor (ENF). Finally, each cell posses an effective dead time needed to fully recharge that cell after the photon detection. In this work the listed above unique features of SiPMs are overviewed. The reported data also contain measurements of energy resolution and 22Na time resolution.
The aim of this work is to provide the characteristics of MPPC arrays with an active area of 6 × 6 mm 2 in gamma-ray spectrometry with CsI:Tl, LSO:Ce:Ca, LaBr 3 :Ce and BGO scintillators. The chosen ...scintillators have significantly different decay times of the scintillation pulses and different wavelengths of emission peaks. This allowed an investigation into the dependence of MPPC readout features on the MPPC and scintillator characteristics. The study of influence of effective dead time and the number of MPPC pixels on a readout response in relation to the brightness and speed of the scintillator were performed. The measurements covered a selection of MPPC optimum operating voltage, verification of the linearity range for a given decay time of the crystals, verification of the excess noise factor for the optimal voltage and evaluation of the Photon Detection Efficiency (PDE). The results of energy resolution and non-proportionality obtained with the MPPC array readout of CsI:Tl and BGO were compared to those obtained for the same crystals with the XP2020Q PMT readout. The results show that an MPPC can be used as effectively as a PMT for gamma spectrometry measurements in the whole tested energy ranges (up to 1.3 MeV) and for many types of scintillation crystals (BGO, CsI:Tl).
Characterization of CsI:Tl at a wide temperature range (−40°C to +22°C) Grodzicka, M.; Moszyński, M.; Szczęśniak, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2013, Letnik:
707
Journal Article
Recenzirano
The aim of this work is the characterization of a ∅ 9×9mm CsI:Tl scintillator at a wide temperature range of −40°C to +22°C. A tested crystal with dimensions of ∅ 9×9mm was coupled to a 16mm diameter ...large area Avalanche photodiode (LAAPD). The crystal and the LAAPD were cooled down in a cryostat with a built-in Peltier element. Properties such as the number of electron–hole pairs per 1MeV, the nonproportionality, the energy resolution and the intrinsic resolution were inspected with eight different peaking times – i.e., 0.6μs, 1.2μs, 2.4μs, 4.8μs, 7.2μs, 9μs, 14.4μs, 28.8μs – and discussed in terms of the light pulse shapes measured by a single photon method.
MCORD - MPD Cosmic Ray Detector a new features Bielewicz, M.; Milewicz-Zalewska, M.; Grodzicka-Kobylka, M. ...
EPJ Web of Conferences,
2019, Letnik:
204
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The main detector system at the Nuclotron-based Ion Collider fAcility (NICA) located in Dubna, Russia is the Multi-Purpose Detector (MPD). For better calibration reason, the MPD needs an additional ...trigger system for an off-beam calibration of MPD sub-detectors and for rejection (veto) of cosmic muons. The system should also be useful for practical astrophysics observations of cosmic showers. The consortium NICA-PL group defines goals and basic assumptions for the MPD Cosmic Ray Detector (MCORD). This article describes the conceptual design and simulation plans of the MCORD detector based on plastic scintillators with SiPM photodetectors and electronic digital system based on the MicroTCA crate.
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