Lifetimes of the 15/2-1 and 13/2-1 levels in 129Sn have been measured using gamma -gamma fast timing technique which come out to be 10(3) ps and 6(4) ps, respectively. The excited states were populated through internal transition decay of higher lying mu s isomers in 129Sn produced as fission fragments and mass separated by the Lohengrin separator at Institut Laue-Langevin. The generalized centroid difference method was applied with four LaBr3(Ce) detectors, placed at the focal plane of the separator. The measured lifetimes and absolute transition probabilities are discussed in the light of large scale shell model calculations to interpret the single particle configurations and their mixing.

Low-lying excited states in Tc-93 and Ru-94 were populated using the two fusion-evaporation reactions Zr-90(Li-6, 3n) Tc-93 and Mo-92(alpha, 2n) Ru-94 at the Cologne FN Tandem accelerator and their lifetimes were measured using a hybrid setup of high-purity germanium and fast cerium doped lanthanum bromide detectors for gamma-gamma fast-timing. The measured lifetimes fill gaps in the experimental data for electromagnetic transition probabilities B(sigma lambda) along the N = 50 isotonic chain and provide more insight for ambiguous cases, such as the lifetime of the 4(1)(+) state in Ru-94. The experimental data are compared with theoretical B(E2) values from a single-j approximation, with state-dependent effective charges derived from Mo-92 and with the results from shell-model calculations performed using the SR88MHJM interaction in the pi(1p(1/2), 0g(9/2)) model space.

Background: gamma -ray spectroscopy studies of the Sn isotopes provide important information on nuclear structure and shell evolution across the long isotopic chain between the doubly-magic Sn-100 and Sn-132 nuclei. These studies also offer great value to test and tune nuclear models which can then be applied to other regions of the nuclear chart. Purpose: We aim to expand the level scheme of Sn-118 by populating low-spin states in the range of 3-5 MeV and determine their angular momentum for the possible connection of these states to pygmy quadrupole Resonances, a new phenomenon observed in the neighboring Sn-112,Sn-114,Sn-124 isotopes as a resonance-like structure in the 3-5 MeV range. Method: Excited states in Sn-118 were populated via the Sn-117(n, gamma)Sn-118 reaction at the Institut Laue-Langevin in Grenoble, France. The FIssion Product Prompt gamma-ray Spectrometer (FIPPS), an array of eight n -type high purity Germanium clover detectors augmented with eight additional clover detectors from IFIN "Horia Hulubei" were used to detect gamma rays from excited states in Sn-118. The array provides a superior efficiency for gamma -ray detection and nearly 4 pi coverage for the measurements of angular correlations for spin assignment of excited nuclear levels. Results: Through gamma -gamma coincidences, 112 excited states were identified with 57 being newly placed in the level scheme. From these states, 567 gamma -ray transitions were observed with 501 being newly identified. Many levels were identified in the 3-5 MeV region. Further, an indirect measurement of the E0 transition which decays from the 0(3)(+) state to the 2p -2h, 0(2)(+) state was performed and the q(K)(2)(E0/E 2) and X(E0/E2) for this transition were determined to be 12.7(11) and 6.3(5), respectively. The 10(3) x rho(2)(E0) was determined to be >38 based on a half-life limit of <200 ps of the 2057-keV, 0(3)(+) level. Conclusions: The abundant spectroscopic information on Sn-118 obtained in the present experiment is an important input to the theoretical description of nuclei in the region and highlights the capabilities of the FIPPS array at ILL in conjunction with neutron capture reactions. Many states identified in the 3-5 MeV region could very likely have J = 2(+) and contribute to the pygmy quadrupole resonances.

Excited states in 193Os were populated using a 192Os(nth., gamma ) 193Os thermal neutron capture reaction, with neutrons provided by the high-flux reactor of the Institut Laue-Langevin in Grenoble, France. Lifetimes of low-spin excited states were measured using the generalized centroid difference method. A total of eight mean lifetimes of low-lying excited states were determined for the first time, and limits for the lifetimes of three further excited states were established. Additionally, gamma -gamma angular correlations were analyzed to assign spins to previously known excited states up to 1 MeV, and extract multipole mixing ratios for several transitions. The new spectroscopic information is compared to calculations in the framework of the interacting boson-fermion model, based on the nuclear density functional theory, to investigate the prolate-to-oblate shape phase transition, predicted to occur in the neutron rich A 190 region.

The excited structure of the single-hole nucleus 131 Sn populated by the beta - decay of 131 In was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited nu h 11 / 2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyv & auml;skyl & auml;. The level scheme of 131 Sn was notably expanded with the addition of 31 new gamma-ray transitions and 22 new excited levels. The gamma-emitting excited levels above the neutron separation energy in 131 Sn were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in 131 Sn and the beta-decaying 131 In state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct beta feeding to the 3/2+ / 2 + ground and 11/2- / 2 - isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in log ft for first-forbidden transitions observed in previous studies, and to determine the beta-delayed neutron decay probability (Pn) P n ) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in 131 Sn was performed in this work. A short T 1 / 2 = 18(4)-ps value was measured for the 1/2+ / 2 + neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M 1 behavior for the nu 3 s - 1 1/2 / 2 -> nu 3 d - 13 / 2 transition. The measured half-lives of high-energy states populated in the beta decay of the (21/2+) / 2 + ) second isomeric state ( 131 m 2 In) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic 132 Sn.

Lifetimes of the $15/{2}_{1}^{\ensuremath{-}}$ and 13/${2}_{1}^{\ensuremath{-}}$ levels in $^{129}\mathrm{Sn}$ have been measured using $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ fast timing technique which come out to be 10(3) ps and 6(4) ps, respectively. The excited states were populated through internal transition decay of higher lying $\textmu{}\mathrm{s}$ isomers in $^{129}\mathrm{Sn}$ produced as fission fragments and mass separated by the Lohengrin separator at Institut Laue-Langevin. The generalized centroid difference method was applied with four ${\mathrm{LaBr}}_{3}$(Ce) detectors, placed at the focal plane of the separator. The measured lifetimes and absolute transition probabilities are discussed in the light of large scale shell model calculations to interpret the single particle configurations and their mixing.

Reduced transition probabilities have been extracted between excited, yrast states in the N=Z+2 nucleus 94Pd. The transitions of interest were observed following decays of the Iπ=14+, Ex=2129-keV isomeric state, which was populated following the projectile fragmentation of a 124Xe primary beam at the GSI Helmholtzzentrum für Schwerionenforschung accelerator facility as part of FAIR Phase-0. Experimental information regarding the reduced E2 transition strengths for the decays of the yrast 8+ and 6+ states was determined following isomer-delayed Eγ1−Eγ2−△T2,1 coincidence method, using the LaBr3(Ce)-based FATIMA fast-timing coincidence gamma-ray array, which allowed direct determination of lifetimes of states in 94Pd using the Generalized Centroid Difference (GCD) method. The experimental value for the half-life of the yrast 8+ state of 755(106) ps results in a reduced transition probability of B(E2:8→+6+) = 205−25+34 e2 fm4, which enables a precise verification of shell-model calculations for this unique system, lying directly between the N=Z line and the N=50 neutron shell closure. The determined B(E2) value provides an insight into the purity of (g9/2)n configurations in competition with admixtures from excitations between the (lower) N=3pf and (higher) N=4gds orbitals for the first time. The results indicate weak collectivity expected for near-zero quadrupole deformation and an increasing importance of the T=0 proton-neutron interaction at N=48.

We present a review of the electronic γ-γ “fast-timing” technique in combination with LaBr3(Ce) scintillator detectors. The γ-γ fast-timing technique has increased in popularity since the commercial introduction of the LaBr3(Ce) scintillators in 2005. The use of LaBr3(Ce) for measurements of lifetimes of nuclear excited states has rapidly spread out over the world and also the setups have grown from a few detectors to large-scale fast-timing arrays. The LaBr3(Ce) is one of the fastest scintillators available with good relative energy resolution of about 3%. Due to high energy selectivity, lifetimes of nuclear excited states down to 1 ps in the best case can be determined directly via electronic γ-γ time-difference measurements. The use of the high-performance LaBr3(Ce) detectors made it possible to systematically investigate the γ-γ fast-timing technique over the total dynamic range corresponding to γ-ray energies of 40 keV up to 6.8 MeV with precision of 2(1) ps. A non-linear energy-dependent time difference between the signals of full-energy peak and Compton events is given. Related to this finding, a new procedure to calibrate the time response of full-energy peak events has been introduced as well as time-correction formulae to account for the Compton contributions in the total experimental γ-γ time-difference distribution. We present a review of the γ-γ fast-timing technique including the performance of the LaBr3(Ce) detectors, the electronic timing principles, the methods to analyze the experimental γ-γ time-difference distributions and the possible energy-dependent time deviations that can be observed using the γ-γ fast-timing technique with many LaBr3(Ce) detectors. The use of a centrally symmetric detector arrangement with respect to the center of an extended γ-ray emission area reduces any possible energy-dependent time shifts rapidly to negligible values with the number of detectors. Moreover, a transition from the conventional analog to the digital timing technique is observed, worldwide. We present the promising results of nowadays available digitzers, where the programmable timing algorithm is used onboard to extract timing information with comparable or even better accuracy than the use of analog-electronic timing modules.

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research () Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian. Published by the American Physical Society 2024

The excited structure of the single-hole nucleus Sn131 populated by the β− decay of In131 was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited νh11/2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. The level scheme of Sn131 was notably expanded with the addition of 31 new γ-ray transitions and 22 new excited levels. The γ-emitting excited levels above the neutron separation energy in Sn131 were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in Sn131 and the β-decaying In131 state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct β feeding to the 3/2+ ground and 11/2− isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in logft for first-forbidden transitions observed in previous studies, and to determine the β-delayed neutron decay probability (Pn) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in Sn131 was performed in this work. A short T1/2=18(4)−ps value was measured for the 1/2+ neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M1 behavior for the ν3s1/2−1→ν3d3/2−1 transition. The measured half-lives of high-energy states populated in the β decay of the (21/2+) second isomeric state (In131m2) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic Sn132. Published by the American Physical Society 2024

The performance of two implementations of digital real-time interpolating constant fraction discriminator algorithms with respect to fast-timing lifetime measurements are investigated. The implementations integrated in two different digitizers were evaluated in terms of the effects of tuning parameters of the digital CFDs and the influence of different input amplitudes on the time resolution and time walk characteristics. Reference is made to the existing analog standard of fast-timing techniques. The study shows, that the timing performance of both modules is comparable to established fast-timing setups using analog constant fraction discriminators, but with the added benefit of digital processing. Both digitizer modules were found to be highly effective and user-friendly instruments for modern fast-timing requirements.

A 152Eu source was measured for 28 days using an experimental setup consisting of four LaBr3(Ce) detectors, connected to a CAEN V1730 digitizer, implementing online interpolation constant fraction discrimination for picosecond-precise timestamp determination. Using the definition of the time-walk curve, the lifetime of the 2+1 (344 keV) state in 152Gd was re-measured, resulting in r(2+1 ) = 46.9(3) ps. Compared to the previously adopted lifetime the uncertainty is reduced by an order of magnitude. This improved lifetime is of significant importance for electronic fast-timing lifetime measurements, and the impact on the systematic correction procedure and lifetime measurements in the low picosecond regime are discussed.

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2^+ state and the increase in the transition strength B(E2; 2^+_1→ 0^+_1) going from ^98 Zr to ^100 Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γγ -coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in ^98-104 Zr carried out to extract reduced transition probabilities. The new lifetime values in γγ -coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

A 152Eu source was measured for 28 days using an experimental setup consisting of four LaBr3(Ce) detectors, connected to a CAEN V1730 digitizer, implementing online interpolation constant fraction discrimination for picosecond-precise timestamp determination. Using the definition of the time-walk curve, the lifetime of the 21+ (344 keV) state in 152Gd was re-measured, resulting in τ(21+)=46.9(3) ps. Compared to the previously adopted lifetime the uncertainty is reduced by an order of magnitude. This improved lifetime is of significant importance for electronic fast-timing lifetime measurements, and the impact on the systematic correction procedure and lifetime measurements in the low picosecond regime are discussed.

Excited states in the yrast and negative parity bands in 92Mo were populated in two different experiments using the 90Zr(alpha, 2n) 92Mo and 93Nb(p, 2n) 92Mo fusion-evaporation reactions at the Cologne FN Tandem accelerator and measured using a hybrid setup of high purity germanium and lanthanum bromide detectors. Lifetimes of the excited 2+ 1 , 4+ 1 , 6+ 1 , 8+ 1 , 5- 1 , 7- 1 , and 9- 1 states were measured using the gamma -gamma fast-timing technique. The newly measured lifetime of the 4+ 1 state differs from the recently published value measured using the recoil distance Doppler shift method. Experimental B(E2) strengths of excited states in 92Mo are used to predict theoretical B(E2) values in the N = 50 isotones from 93Tc up to 95Rh using semiempirical calculations in the single-j orbital 0g9/2 for the protons.

In this work, we present recent lifetime measurements in exotic nuclei performed at Institut Laue-Langevin in different 235U neutron-induced fission campaigns, using the Lohengrin spectrometer and a hybrid setup made of HPGe clover detectors and LaBr3(Ce) scintillators. In particular, results on the neutron -rich 131Sb and 96Rb isotopes will be discussed, which have implications on the origin of collectivity around the doubly magic 132Sn nucleus and the shape-coexistence phenomenon around N = 60, respectively.

The timing performance of the integrated digital constant fraction discriminators of the two digitizer modules V1730 and V1751 from CAEN are systematically investigated with respect to fast-timing lifetime measurements. Systematic and parameter-dependent knowledge of the time walk behavior and the time resolution of the digital constant fraction discriminators is obtained. Understanding these dependencies is crucial for properly calibrating individual fast-timing systems and a comparable investigation of these digitizers was never conducted before. Reference is made to the existing analog standard for fast-timing techniques and recent digital developments. The study shows, that the timing performance of both modules is comparable to other digital fast-timing implementations and established fast-timing setups using analog constant fraction discriminators, but with the added benefit of digital processing. The peculiarities of the modules are pointed out and described. Both digitizer modules were found to be highly effective and user-friendly instruments for modern fast-timing requirements. Best parameter sets for both digitizers as well as best energy application ranges are provided.

The A approximate to 100 mass region is of special interest due to a rapid shape transition, observed by going from neutron number 58 to 60, especially pronounced in the Zr isotopes, where 98Zr is weakly and100Zr is strongly deformed. To further examine this intricate phenomenon, in this work lifetimes of low-lying excited states in the nuclei 99Zr and 99Nb were determined using fast-timing techniques and an experimental setup consisting of four LaBr3(Ce) detectors. Neutron rich A = 99 fragments were produced in neutron induced fission and separated by the spectrometer LOHENGRIN at the Institut Laue-Langevin in Grenoble, France. Experimental values are compared to two different calculations in the framework of the interacting boson-fermion model and discussed in the context of shape coexistence.