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Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape -- AUG 26-SEP 02, 2018 -- Zakopane, POLAND, WOS: 000463866500047, A new neutron multiplicity filter NEDA, after a decade of design, R&D and construction, was employed in its first physics campaign with the AGATA spectrometer. Properties and performance of the array are discussed., Swedish Research CouncilSwedish Research Council [VR 2014-6644]; Scientific and Technological Research Council of Turkey (TUBITAK project)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [117F114, 114F473]; National Science Centre, Poland (NCN) [2017/25/B/ST2/01569, 2016/22/M/ST2/00269, 2014/14/M/ST2/00738, 2013/08/M/ST2/00257]; UK STFCScience & Technology Facilities Council (STFC) [ST/J000124/1, ST/L005727/1, STL005735/1, ST/P003885/1]; Generalitat Valenciana, SpainGeneralitat Valenciana; MICIU, Spain [PROM-ETEO II/2014/019, FPA2017-84756-C4, SEV-2014-0398]; E.C. FEDER fundsEuropean Union (EU), This study was supported by the Swedish Research Council (contract number VR 2014-6644), the Scientific and Technological Research Council of Turkey (TUBITAK project Nos. 117F114 and 114F473), the National Science Centre, Poland (NCN) (grants Nos. 2017/25/B/ST2/01569, 2016/22/M/ST2/00269, 2014/14/M/ST2/00738 and 2013/08/M/ST2/00257) the UK STFC under grant Nos. ST/J000124/1, ST/L005727/1, STL005735/1, ST/P003885/1, the Generalitat Valenciana and MICIU, Spain, grants PROM-ETEO II/2014/019, FPA2017-84756-C4, Severo Ochoa SEV-2014-0398 and by the E.C. FEDER funds.1

The paper focuses on a comparison of different positioning methods provided by free and open source software (FOSS) package called RTKLIB. The RTKLIB supports real-time and post-processed positioning. The most important modes of operation tested by the authors are Kinematic, Static, Fixed and Precise Point Positioning (PPP). The data for evaluation were obtained from low-cost Global Navigation Satellite System (GNSS) receiver. The tested receiver was based on the u-blox's LEA-6T GNSS module. This receiver provides different types of information including raw carrier phase measurements. It gives the possibility for centimeter-level precision of positioning. As the supporting source of data ASG-EUPOS system was used. ASG-EUPOS is a Polish network of GNSS reference stations providing the real-time corrections and post processing services for the entire territory of Poland.

A fast charge-to-digital converter, FQDC, based on a flash ADC is described. In order to test the FQDC independent of the experimental arrangement a special testing system was designed using CAMAC and an IBM PC. Results of tests of 20 dual FQDC cards are presented which show the ability of the design for future application.

The study of the single photoelectron time resolution as a function of the wavelength of the incident light was performed for a 56 CVP photomultiplier having an S-1 photocathode. The light flash from the XP22 light emitting diode generator was passed through passband filters and illuminated the 5 mm diameter central part of the photocathode. A significant increase of the time resolution above 30% was observed when the wavelength of the incident light was changed from 790 nm to 580 nm. This gives experimental evidence that the time jitter resulting from the spread of the initial velocity of photoelectrons is proportional to the square root of the maximal initial energy of photoelectrons. Based on this conclusion the measured time jitter of C31024, RCA8850 and XP2020 photomultipliers with the use of the XP22 light emitting diode at 560 nm light wavelength was recalculated to estimate the time jitter at 400 nm near the maximum of the photocathode sensitivity. It shows an almost twice larger time spread at 400 nm for the C31024 and RCA8850 with a high gain first dynode and an about 1.5 times larger time spread for the XP2020 photomultiplier, than those measured at 560 nm.

The not-ideally compensated space charge of donors and acceptors in lithium-drifted coaxial Ge(Li) detectors can modify the electric field distribution in the detector depleted volume, and influence in this way the charge collection process. Observations of the capacity, the time of charge collection (transit time), and the relative efficiency characteristics vs. detector bias voltage, showed that in conventional pin+ coaxial structures an undercompensation near the inner p-type core was typical. It was found that such an undercompensation had negligible consequences from the charge collection point of view. However, one case was observed where the modification near the outer electrode was present. In that case the charge pulses with remarkably increased rise-times were observed, as compared to the predictions based on the assumption of the classical, E∞1/r, electric field distribution. The pulses expected from not-ideally compensated detectors were calculated using the Variable Velocity Approximation, and much better agreement with the observed pulses was obtained. The calculated and observed dependencies of the charge transit times vs. reciprocal of the detector bias voltage exhibited, in the absence of the outer-electrode modification, linear parts. Measurement of their slopes permitted to find experimentally the depletion layer width provided the charge carriers mobility value was known, or vice versa.

Pulse-height resolution of thin scintillator foils prepared from plastic scintillators NE 111 and NE 102A was experimentally tested. Since the intrinsic energy resolution was not observed it was found that the overall resolution of the detector is due to the properties of the photomultiplier only. From the discussion of the dependence of energy resolution on foil thickness and mean number of photoelectrons released per scintillation it was concluded that this phenomenon can be related to the good optical properties of scintillator foils and their unusual optical coupling to the photomultiplier tube face, but not to the mechanism of light generation.

The scintillation efficiency of two different thin film detector designs was compared. The better design was chosen to perform studies on scintillation efficiency, light pulse shape and time resolution of NE 111 and NE 102A scintillator foils. The influence of the surface quenching effect on the scintillation efficiency was observed. Interesting phenomena such as the decay time constant and the pulse width decrease for very thin scintillator foils were measured. The dependence of the time resolution of thin scintillator foils on thier thickness and the mean number of photoelectrons released on a photocathode by a light flash were examined. On the basis of the modified Hyman theory of timing with scintillator counters it was concluded that in the case of very thin scintillator foils made of ternary-solution plastic scintillator, the role of the second scintillating species in the energy transfer process is strongly limited.

A detailed study of the NORDBALL Ge-BGO Compton suppression spectrometers has been performed. Special emphasis has been given to photoelectron yields of the scintillators, optimisation of charge integration in the electronics and the low energy thresholds of the BGO detectors. The time relation between the Ge detector and the BGO scintillator logic pulses has been studied in detail. Maximum Compton suppression factors of 12.0 and 12.7 have been measured for 60Co and 137Cs γ-rays respectively. Photon events observed between the full energy peak and the Compton edge suggest that other effects than multiple Compton scattering are involved. Such effects are usually not included in Monte Carlo simulations and could be the explanation of the factor of 2 deficiency between calculated and measured suppression ratios.

The light pulse shapes from the anthracene and stilben scintillators were studied by the single photon method with use of the C31024 photomultiplier to detect single photons. The slow initial rise of the light pulses as that observed before for plastic scintillators was found and the light pulse shapes were well described analytically by the convolution of the clipped Gaussian and exponential functions. The study of the light pulses from several stilben samples of different thickness with use of the pass-band wavelength filters of the light leads to the conclusion that the light pulse from the stilben scintillators is composed of two components with the decay time constant equal to 2.5 ns and 7.3 ns.

The study of time resolution as a function of the triggering fraction C / R for the scintillation counter consisting of an XP1021 photomultiplier and a 1.25 cm × 0.2 cm NE111 scintillator was performed. The scintillator was irradiated by β-rays of 60 Co. The C / R curves measured for some selected energy windows between 25 keV and 200 keV were normalized and compared with the calculated curve according to Hyman theory. The good fit of the theoretical curve to the experimental one shows that Hyman theory describes well the timing properties of the plastic scintillation counters.

The practically measured capacitance vs voltage ( C - V ) characteristics of coaxial Ge(Li) detectors show that the compensation of donors and acceptors in the depleted region of the detector is not ideal. Assuming a slightly p-type character of the “intrinsic” region the space-charge distribution and the electric-field distribution can be calculated with the help of the C - V characteristic. In the very often encountered case of the characteristic of the type: straight line in a log-log scale with a plateau for voltages greater than a certain value ( U 0 ), the electric field is shown to fall down near the p-contact of the detector. For voltages below U 0 — analogically to p-n junction detectors the field at the boundary of the depleted region is equal to zero, and the depleted-region width is dependent on the bias voltage. The type of the postulated electric-field distribution seems to be confirmed qualitatively by the drift theory and timing experiments.

The logic diagram principle of operation and some details of the design of the multiplicity logic unit are presented. This unit was specially designed to fulfil the requirements of a multidetector arrangement for gamma-ray multiplicity measurements. The unit is equipped with 16 inputs controlled by a common coincidence gate. It delivers a linear output pulse with the height proportional to the multiplicity of coincidences and logic pulses corresponding to 0, 1, … up to ⩾5-fold coincidences. These last outputs are used to steer the routing unit working with the multichannel analyser.

The stretching of pulses by a high-saturated transistor is considered. This phenomenon is applied for the pulse shaping in a slow coincidence circuit. An instrument with four coincidence channels and one anticoincidence channel is described.

A timing system working with plastic scintillation counters is described. It gives the best time resolution of 130 ps and 195 ps for 20% and 90% windows, respectively, at 60 Co Compton spectra, using NE 111 scintillators and XP 1021 photomultipliers. The time resolutions obtained using XP 1021 and XP 1023 photomultipliers did not show any difference. 56 DUVP photomultipliers working with 2.5 cm × 1 cm NE 111 scintillators, in spite of the twice larger time spread, gave a time resolution only 20% worse for 60 Co owing to higher quantum efficiency of the bialkali photocathode. It was shown that for larger scintillators, especially when NE 111 cannot be used because of light attenuation, the time resolution obtainable with 56 DUVP is better than with XP 1021.

The paper presents the results of investigations of the shape of an ses generated by α-particles in silicon drifted detectors having an active area 0.7 to 2.4 mm thick, under room and liquid nitrogen temperatures. It has been found, by fitting the analytical form of the pulse to an experimental shape, that the electric field distribution in such a detector is a parabolic function of depth. The distribution of concentration of donor impurities has been determined. Pulse risetimes have been determined as a function of the average value of the electric field and the thickness of the detector active area. Some information has also been obtained about the influence of short-term trapping on the process of charge collection.

An investigation of 172 Hf (T 1 2 = 5 y ) decay carried out after the sample was chromatographically purified of the daughter 172Lu (6.5 d) isotope. The half-lives of the 110 keV (2+) and 192 (1+) states of 172Lu were measured to 2.30±0.12 ns and ≦ 0.5 ns, respectively. The B(E2) of the 44 keV transition is calculated assuming the theoretical conversion coefficient αT = 1.31. The value obtained for B(E2)↑ is (5.60±0.28) × 10−48e2cm4. Assuming no band mixing, the intrinsic quadrupole moment of the { 7 2 + [404] p ; 7 2 + [633] n }K=0 rotational band was deduced as Q02 = 7.50±0.20 b. The γ-ray intensities measured with a Ge(Li) detector confirm the decay scheme of Valentin et al. and Harmatz and Handley1, 2).

Results of a study of time spreads of pulses from silicon drifted detectors, irradiated by 976 keV (207Bi) electrons at their positive electrode side are presented. A number of 0.8–2.4 mm thick detectors were tested at room temperature and at liquid nitrogen temperature. Two components of the time spreads have been found to exist; one of them being proportional to the detector pulse rise time and inversely proportional to the reduced average range of the beta particles, and the other one independent on these quantities, however, characteristic for the individual detector. Initial risetimes of the pulses (up to 20% of the total amplitude) were determined. The results are in disagreement with the predictions of the available approximate theory of charge collection in detectors.

The application of the many-layer tray of counters in a time-of-flight slow neutron spectrometer increases the luminosity of the spectrometer but simultaneously deteriorates its time resolution. This undesirable effect results from the time delay between the pulses produced in various layers of the tray. To overcome this difficulty a simple electronic device has been constructed. Its principle of operation is as follows: the pulses from the extreme layer come to the time-analyser directly, whereas the pulses produced in the other layers are automatically delayed according to the velocity of the neutrons which produce those pulses. The application of the correcting device described in the paper improves the time resolution of the spectrometer considerably.

An analysis of the charge collection process in a silicon drifted detector is presented, under the assumption that the distribution of the electric field in the detector is represented by a second order polynomial. The shape of the pulses induced by a point charge and a linearly-distributed charge is discussed in terms of the place of their generation. Agreement is found between experimentally determined time spreads of pulses generated by mono-energetic electrons, with those calculated using the present analysis of the charge collection process, in contrast to the theory of charge collection in a detector with uniform electric field.