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Background characterisation in γ - γ fast-timing measurements is of essential importance when lifetimes of the order of tens of picoseconds are being measured. In this work, the nature, composition and behaviour of the timing background is extensively discussed and an adaptation of the background subtraction method used in E γ -E γ -E γ cubes to the case of E γ -E γ - Δ T cubes, is presented. This is applied to 252 Cf fission data, showing very low peak-to-background ratios (less than 0.5), collected using a hybrid array made of 51 HPGe detectors from Gammasphere and 25 LaBr 3 (Ce) scintillators . Two different procedures are suggested: the “Interpolation” approach and the “Three Samples” approach. Both were used to measure the lifetime of the 2 + state in 110Ru, and gave τ = 483(38) ps and τ = 445(34) ps, respectively, both within one standard deviation of the literature value of τ l = 462(29) ps. The 2 + state in 114Pd was also measured using the three samples approach and the lifetime obtained was τ = 104(12) ps, consistent with the literature lifetime of τ l = 118(20) ps.

The NAtional Nuclear Array (NANA) is a LaBr 3 (Ce)-based coincidence gamma-ray spectrometer which can be used to identify, and enhance with respect to the background, signature gamma-ray emissions associated with particular radionuclide decays from a complex multi-component spectrum. Gamma-ray energy coincidence measurements using the NANA have been made using a digital data acquisition system based on CAEN V1751C 1 GHz digitizers. The improved time resolution offered by LaBr 3 (Ce) crystals compared to similar-sized solid state detectors can provide narrow time-correlated, gamma-ray energy coincidence matrices that can be interrogated to select discrete gamma-ray emissions associated with particular radionuclide decays. This paper provides an overview of the operational characteristics of the NANA spectrometer, including energy resolution and full-energy peak efficiency parameters, and provides an example of double and triple gamma-ray coincidence gating on decays associated with the nuclear fuel waste product 134 Cs. The full-energy peak efficiency response of the spectrometer is compared to Monte Carlo GEANT4 simulations.

C.M. Shand et al. -- 6 pags., 3 figs., tab. --Open Access funded by Creative Commons Atribution Licence 4.0, We report on the measurement of new low-lying states in the neutron-rich Zn nuclei via in-beam γ-ray spectroscopy. These include the 4 →2 transition in Zn, the 2 →0 and 4 →2 transitions in Zn, and low-lying states in Zn were observed for the first time. The reduced E(2 ) energies and increased E(4 )/E(2 ) ratios at N=52, 54 compared to those in Zn attest that the magicity is confined to the neutron number N=50 only. The deduced level schemes are compared to three state-of-the-art shell model calculations and a good agreement is observed with all three calculations. The newly observed 2 and 4 levels in Zn suggest the onset of deformation towards heavier Zn isotopes, which has been incorporated by taking into account the upper sdg orbitals in the Ni78-II and the PFSDG-U models., All UK authors are supported by the Science and Technology Facilities Council (STFC). The development of MINOS and the core MINOS team have been supported by the European Research Council through the ERC Grant No. MINOS-258567. A. Jungclaus was supported by the Spanish Ministerio de Economía y Competitividad under contract FPA2014-57196-C5-4-P. Authors from Cologne were supported by German BMBF Grant No. 05P15PKFNA. Authors from TU Darmstadt were supported by German BMBF Grant No. 05P12RDFN8 and 05P15RDFN1. L.X. Chung and B.D. Linh would like to acknowledge Vietnam Ministry of Science and Technology for the support, and Radioactive Isotope Physics Laboratory of the RIKEN Nishina Center for supporting their stay during the experiments.

The electronic γ–γ fast-timing technique using arrays consisting of many LaBr3(Ce) detectors is a powerful method to determine lifetimes of nuclear excited states with a lower limit of about 5 ps. This method requires the determination of the energy-dependent time walk of the zero time which is represented by the centroid of a prompt γ–γ time distribution. The full-energy peak versus full-energy peak prompt response difference which represents the linearly combined mean γ–γ time walk of a fast-timing array consisting of 8 LaBr3(Ce) detectors was measured using a standard 152Eu γ-ray source for the energy region of 40–1408 keV. The data were acquired using a “multiplexed-start and multiplexed-stop” analogue electronics circuitry and analysed by employing the generalized centroid difference method. Concerning the cylindrical 1.5 in.×1.5 in. LaBr3(Ce) crystals which are coupled to the Hamamatsu R9779 photomultiplier tubes, the best fast-timing array time resolution of 202(3) ps is obtained for the two prompt γ lines of 60Co by using the leading-edge timing principle. When using the zero-crossover timing principle the time resolution is degraded by up to 30%, dependent on the energy and the shaping delay time of the constant fraction discriminator model Ortec 935. The smallest γ–γ time walk to below 50 ps is obtained by using a shaping delay time of about 17 ns and an optimum “time-walk adjustment” needed for detector output pulses with amplitudes smaller than 400 mV.

The ν -ballspectrometer is an hybrid array combining high purity co-axial germanium detectors from the french-UK loan pool, clover detectors from the GAMMAPOOL, lanthanum bromide (LaBr3:Ce) scintillator detectors belonging to the FATIMA collaboration and phoswitches from the PARIS collaboration. The aim was to couple the excellent energy resolution of germanium detectors to the excellent time resolution of the LaBr3 detectors. We achieved a total photopeak efficiency of 6.7% at 1.3 MeV, and peak-to-total ratio of 50% for the germanium part of the array. Using the digital acquisition system FASTER, we achieved time resolution of about 250 ps for LaBr3. This acquisition system made also possible the use of the calorimetry for reaction selection. It makes ν -ball the first fully digital large fast timing spectrometer with time resolution similar to analogue electronics. The construction began in June 2017 and commissioning was performed in early November 2017. From November 2017 to June 2018, more than 3200 h of beam time were provided by the ALTO facility to perform eight experiments during the campaign. Among them, five weeks of beam time were dedicated to γ spectroscopy of fast neutron induced reactions. In this paper all the technical details about the spectrometer are presented. First steps of the data analysis process are also discussed.

The electronic γ–γ fast timing technique allows for direct nuclear lifetime determination down to the few picoseconds region by measuring the time difference between two coincident γ-ray transitions. Using high resolution ultra-fast LaBr3(Ce) scintillator detectors in combination with the recently developed mirror symmetric centroid difference method, nuclear lifetimes are measured with a time resolving power of around 5 ps. The essence of the method is to calibrate the energy dependent position (centroid) of the prompt response function of the setup which is obtained for simultaneously occurring events. This time-walk of the prompt response function induced by the analog constant fraction discriminator has been determined by systematic measurements using different photomultiplier tubes and timing adjustments of the constant fraction discriminator. We propose a universal calibration function which describes the time-walk or the combined γ–γ time-walk characteristics, respectively, for either a linear or a non-linear amplitude versus energy dependency of the scintillator detector output pulses.

The lifetime of the first excited 2 + state in 172W and 178W has been measured in fast timing experiments using the Cologne Double Orange Spectrometer for conversion electron spectroscopy. The B ( E 2 , 2 1 + → 0 1 + ) values of the isotopes 170–178W are compared to calculations in the Interacting Boson Model (IBM) employing the consistent Q formalism. An analysis of the B ( E 2 ) value systematics in the rare earth nuclei around mass A = 170 using the N p N n -scheme shows signatures of a structural change in the tungsten isotopes which is not reflected in the energy systematics.

The ultra-fast timing technique was introduced in the 1980s and is capable of measuring picosecond lifetimes of nuclear excited states with about 3 ps accuracy. Very fast scintillator detectors are connected to an electronic timing circuit and detector vs. detector time spectra are analyzed by means of the centroid shift method. The very good 3% energy resolution of the nowadays available LaBr3(Ce) scintillator detectors for γ -rays has made possible an extension of the well-established fast timing technique. The energy dependent fast timing characteristics or the prompt curve, respectively, of the LaBr3(Ce) scintillator detector has been measured using a standard 152Eu γ -ray source. For any energy combination in the range of 200 keV E γ 1500 keV , the γ – γ fast timing characteristics is calibrated as a function of energy with an accuracy of 2–4 ps. An extension of the centroid shift method providing very attractive features for picosecond lifetime measurements is presented. The mirror symmetric centroid difference method takes advantage of the symmetry obtained when performing γ – γ lifetime measurements using a pair of almost identical very fast scintillator detectors. In particular cases, the use of the mirror symmetric centroid difference method also allows the direct determination of picosecond lifetimes, hence without the need of calibrating the prompt curve.

Conversion electron spectroscopy constitutes an important tool in nuclear structure physics. A high efficiency iron-free Orange type electron spectrometer with an energy resolution of 1–2% has been installed at a beam line of the Cologne 10 MV FN Tandem Van-de-Graaff accelerator for in-beam studies of conversion electrons. In combination with a γ -ray detector array, high efficiency e - – γ -coincidences can be performed. The newly developed very fast LaBr 3 ( Ce ) scintillator detector with an energy resolution of about 4% makes it also possible to use e - – γ -coincidences for lifetime measurements of nuclear excited states. A second iron-free Orange spectrometer can be connected to perform e - – e - -coincidences. Because of the higher efficiency and the better energy resolution, the use of the Double Orange Spectrometer for lifetime measurements is more powerful. Lifetimes down to 100 ps and even less can be determined with an accuracy of about 10 ps. The working principle of the Orange spectrometer and the setup of the Double Orange Spectrometer are described. The performances are illustrated by examples of in-beam experiments with a main focus on high precision lifetime measurements.