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The AGATA Detector Library (ADL) was developed for the calculation of signals from highly segmented large volume high-purity germanium (HPGe) detectors. ADL basis sets comprise a huge amount of ...calculated position-dependent detector pulse shapes. A basis set is needed for Pulse Shape Analysis (PSA). By means of PSA the interaction position of a
-ray inside the active detector volume is determined. Theoretical concepts of the calculations are introduced and cover the relevant aspects of signal formation in HPGe. The approximations and the realization of the computer code with its input parameters are explained in detail. ADL is a versatile and modular computer code; new detectors can be implemented in this library. Measured position resolutions of the AGATA detectors based on ADL are discussed.
The lifetimes of the low-lying excited states 2+ and 4+ have been directly measured in the neutron-deficient 106,108Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the ...lifetime measurement was performed employing a differential plunger device. The emitted γ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2;21+→0g.s.+) values and it describes well the experimental pattern for 104−114Sn; the B(E2;41+→21+) values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in 108Sn.
The first implementation of the AGATA spectrometer consisting of five triple germanium detector clusters has been installed at Laboratori Nazionali di Legnaro, INFN. This setup has two major goals, ...the first one is to validate the
γ
-
tracking
concept and the second is to perform an experimental physics program using the stable beams delivered by the Tandem–PIAVE-ALPI accelerator complex. A large variety of physics topics will be addressed during this campaign, aiming to investigate both neutron and proton-rich nuclei. The setup has been designed to be coupled with the large-acceptance magnetic-spectrometer PRISMA. Therefore, the in-beam prompt
γ
rays detected with AGATA will be measured in coincidence with the products of multinucleon-transfer and deep-inelastic reactions measured by PRISMA. Moreover, the setup is versatile enough to host ancillary detectors, including the heavy-ion detector DANTE, the
γ
-
ray
detector array HELENA, the Cologne plunger for lifetime measurements and the Si-pad telescope TRACE. In this paper the design, characteristics and performance figures of the setup will be described.
The space charge distribution inside highly segmented large volume HPGe detectors determined from capacitance–voltage (CV) measurements is investigated. A computer code was developed to understand ...the impact of impurity concentrations on the resulting capacitances between core contact and outer contact for HPGe detectors biased at different high voltages. The code is intended as a tool for the reconstruction of the doping profile within irregularly shaped detector crystals. The results are validated by comparison with the exact solution of a true coaxial detector. Existing methods for space charge parameter extraction are briefly reviewed. The space charge reconstruction under cylindrical symmetry is derived. An extension of this scheme to higher dimensions for inhomogeneous space charge distributions is illustrated for a two-dimensional segmented coaxial detector.
Electric quadrupole matrix elements, Mp, for the Jπ=2+→0+, ΔT=0, T=1 transitions across the A=46 isobaric multiplet 46Cr-46V-46Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows ...direct insight into the isospin purity of the states of interest by testing the linearity of Mp with respect to Tz. Pairs of nuclei in the T=1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The Mp values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for 46Cr and 46Ti; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in 46V and 46Ti. A constant value of Mp across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T=1 isospin triplets is presented.
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The performance of the Pulse-Shape Analysis (PSA) in AGATA HPGe detectors was investigated and improved employing a
γ
-ray source measurement based on
e
+
e
-
annihilation radiation after decays of
...22
Na by
β
+
decay. The first interaction positions of the two 511keV
γ
rays were determined and the connecting line of these two positions was compared to the known source position as a measure for the PSA performance. The position resolution and its dependence on the PSA parameters were investigated by varying most relevant input quantities: the charge carrier mobility of the holes, the response of the employed measuring electronics especially the preamplifier rise time. The relative statistical weight of charge signals and transient signals was scrutinized. The optimal distance metric of the grid-search algorithm and its impact on the position resolution were determined.
Background: Levels fulfilling the seniority scheme and relevant isomers are commonly observed features in semimagic nuclei; for example, in Sn isotopes (Z = 50). Seniority isomers in Sn, with ...dominantly pure neutron configurations, directly probe the underlying neutron-neutron (vv) interaction. Furthermore, an addition of a valence proton particle or hole, through neutron-proton (v pi) interaction, affects the neutron seniority as well as the angular momentum. Purpose: Benchmark the reproducibility of the experimental observables, like the excitation energies (E-x) and the reduced electric-quadrupole transition probabilities B(E2), with the results obtained from shell-model interactions for neutron-rich Sn and Sb isotopes with N < 82. Study the sensitivity of the aforementioned experimental observables to the model interaction components. Furthermore, explore from a microscopic point of view the structural similarity between the isomers in Sn and Sb, and thus the importance of the valence proton. Methods: The neutron-rich Sb122-131 isotopes were produced as fission fragments in the reaction Be-9(U-238, f) with 6.2 MeV/u beam energy. A unique setup, consisting of AGATA, VAMOS++, and EXOGAM detectors, was used which enabled the prompt-delayed gamma-ray spectroscopy of fission fragments in the time range of 100 ns to 200 mu s. Results: New isomers and prompt and delayed transitions were established in the even-A Sb122-131 isotopes. In the odd-A Sb122-131 isotopes, new prompt and delayed gamma-ray transitions were identified, in addition to the confirmation of the previously known isomers. The half-lives of the isomeric states and the B(E2) transition probabilities of the observed transitions depopulating these isomers were extracted. Conclusions: The experimental data was compared with the theoretical results obtained in the framework of large-scale shell-model (LSSM) calculations in a restricted model space. Modifications of several components of the shell-model interaction were introduced to obtain a consistent agreement with the excitation energies and the B(E2) transition probabilities in neutron-rich Sn and Sb isotopes. The isomeric configurations in Sn and Sb were found to be relatively pure. Furthermore, the calculations revealed that the presence of a single valence proton, mainly in the g(7/2) orbital in Sb isotopes, leads to significant mixing (due to the v pi interaction) of (i) the neutron seniorities (upsilon(v)) and (ii) the neutron angular momentum (I-v). The above features have a weak impact on the excitation energies, but have an important impact on the B(E2) transition probabilities. In addition, a constancy of the relative excitation energies irrespective of neutron seniority and neutron number in Sn and Sb was observed.
The γ-ray emission from the nuclei 62,64Fe following Coulomb excitation at bombarding energy of 400-440 AMeV was measured with special focus on E1 transitions in the energy region 4-8 MeV. The ...unstable neutron-rich nuclei 62,64Fe were produced at the FAIR-GSI laboratories and selected with the FRS spectrometer. The γ decay was detected with AGATA. From the measured γ-ray spectra the summed E1 strength is extracted and compared to microscopic quasi-particle phonon model calculations. The trend of the E1 strength with increasing neutron number is found to be fairly well reproduced with calculations that assume a rather complex structure of the 1− states (three-phonon states) inducing a strong fragmentation of the E1 nuclear response below the neutron binding energy.
Double-sided silicon strip detectors (DSSSD) are commonly used for event-by-event identification of charged particles as well as the reconstruction of particle trajectories in nuclear physics ...experiments with stable and radioactive beams. Intersecting areas of both p- and n-doped front- and back-side segments form individual virtual pixel segments allowing for a high detector granularity. DSSSDs are employed in demanding experimental environments and have to withstand high count rates of impinging nuclei. The illumination of the detector is often not homogeneous. Consequently, radiation damage of the detector is distributed non-uniformly. Position-dependent incomplete charge collection due to radiation damage limits the performance and lifetime of the detectors, the response of different channels may vary drastically. Position-resolved charge-collection losses between front- and back-side segments are investigated in an in-beam experiment and by performing radioactive source measurements. A novel position-resolved calibration method based on mutual consistency of p-side and n-side charges yields a significant enhancement of the energy resolution and the performance of radiation-damaged parts of the detector.
A lifetime measurement of the 19/2− state in 207Pb has been performed using the Recoil Distance Doppler-Shift (RDDS) method. The nuclei of interest were produced in multi-nucleon transfer reactions ...induced by a 208Pb beam impinging on a 100Mo enriched target. The beam-like nuclei were detected and identified in terms of their atomic mass number in the VAMOS++ spectrometer while the prompt γ rays were detected by the AGATA tracking array. The measured large reduced transition probability B(E3,19/2−→13/2+)=40(8) W.u. is the first indication of the octupole phonon at high spin in 207Pb. An analysis in terms of a particle-octupole-vibration coupling model indicates that the measured B(E3) value in 207Pb is compatible with the contributions from single-phonon and single particle E3 as well as E3 strength arising from the double-octupole-phonon 6+ state, all adding coherently. A crucial aspect of the coupling model, namely the strong mixing between single-hole and the phonon-hole states, is confirmed in a realistic shell-model calculation.
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