The Advanced Gamma Ray Tracking Array AGATA

New accelerator facilities for radioactive–ion beams will enter into operation in the next few years, providing the opportunity to explore unknown territories of the nuclear landscape. The foreseen harsh experimental conditions require the construction of a new generation of γ–ray detector arrays based on the emerging technique of γ–ray tracking. The "Advanced GAmma Tracking Array" (AGATA), proposed in Europe, will be built out of 120 or 180 highly segmented Ge crystals operated in position sensitive mode by means of digital data techniques and pulse shape analysis of the segment signals. AGATA will be capable of measuring γ radiation in a large energy range (from ∼ 10 keV to ∼ 10 MeV), with the largest possible photopeak efficiency (25% at M γ = 30 ) and with good spectral response. The very good Doppler correction and background rejection capability of this γ–ray tracking array will allow to perform γ–ray spectroscopy experiments using fragmentation beams with sources moving at velocities up to β ∼ 0.5

Simulation and analysis of pulse shapes from highly segmented HPGe detectors for the γ-ray tracking array MARS

A flexible program to calculate the pulse shapes from highly segmented HPGe detectors of various geometrical shapes has been developed. Signals originating from single points of interaction in both the quasi-true-coaxial and the closed-end part of the detector are discussed. In order to present the main features of these signals, we have introduced simplified characteristic curves. These curves are analysed with regard to the application of pulse shape analysis for three-dimensional position determination in detectors for a g-ray tracking array. # 2001 Elsevier Science B.V. All rights reserved

Performance of the Fully Digital FPGA-based Front-End Electronics for the GALILEO Array

In this work we present the architecture and results of a fully digital Front End Electronics (FEE) read out system developed for the GALILEO array. The FEE system, developed in collaboration with the Advanced Gamma Tracking Array (AGATA) collaboration, is composed of three main blocks: preamplifiers, digitizers and preprocessing electronics. The slow control system contains a custom Linux driver, a dynamic library and a server implementing network services. The digital processing of the data from the GALILEO germanium detectors has demonstrated the capability to achieve an energy resolution of 1.53 per mil at an energy of 1.33 MeV.Comment: 5 pages, 6 figures, preprint version of IEEE Transactions on Nuclear Science paper submitted for the 19th IEEE Real Time Conferenc

Extending the dynamic range of nuclear pulse spectrometers

Using an innovative time-varying front-end electronics in conjunction with a bulky coaxial high-purity germanium detector, we were able to extend the range of the radionuclide spectra well beyond the analog to digital converter (ADC) saturation point. The electronics automatically conditions the signal for digital-filtering optimization if it is in the ADC voltage range and for time-over-threshold analysis if it exceeds the ADC range. A high spectroscopic resolution has been achieved in both operation ranges. An unprecedented wide energy range from 5 keV to 150 MeV of equivalent energy, or 90 dB, has been obtained using a single acquisition chain, while maintaining a high-energy resolution in the whole spectrum. For example, with an ADC range of 3 MeV a resolution has been obtained of 1.3/2.2 keV full width at half maximum on the 122/1332 keV gamma-ray lines of Co-57 and Co-60, and of <0.4% in the time-over-threshold region, or for energy deposits beyond 3 MeV. (C) 2008 American Institute of Physics

Co-existing structures in 105Ru

New positive-parity states, having a band-like structure, were observed in 105Ru. The nucleus was produced in induced fission reaction and the prompt gamma-rays, emitted from the fragments, were detected by the EUROBALL III multi-detector array. The partial scheme of excited 105Ru levels is analyzed within the Triaxial-Rotor-plus-Particle approach

πNN\pi NN coupling determined beyond the chiral limit

Within the conventional QCD sum rules, we calculate the $\pi NN$ coupling constant, $g_{\pi N}$, beyond the chiral limit using two-point correlation function with a pion. We consider the Dirac structure, $i\gamma_5$, at $m_\pi^2$ order, which has clear dependence on the PS and PV coupling schemes for the pion-nucleon interactions. For a consistent treatment of the sum rule, we include the linear terms in quark mass as they constitute the same chiral order as $m_\pi^2$. Using the PS coupling scheme for the pion-nucleon interaction, we obtain $g_{\pi N}=13.3\pm 1.2$, which is very close to the empirical $\pi NN$ coupling. This demonstrates that going beyond the chiral limit is crucial in determining the coupling and the pseudoscalar coupling scheme is preferable from the QCD point of view.Comment: 8 pages, revtex, some errors are corrected, substantially revise

AGATA, Technical Proposal for an Advanced Gamma Tracking Array for the European Gamma Spectroscopy Community

International audienceAn Advanced GAmma-ray Tracking Array, AGATA, is proposed for high-resolution γ-ray spectroscopy with exotic beams. AGATA will employ highly segmented Ge detectors as well as fully digital electronics and relies on newly developed pulse-shape analysis and tracking methods. The array is being designed in a way that it provides optimal properties for nuclear structure experiments in a wide range of beam velocities (from stopped to v/c ≈ 50%), almost independent of beam quality and background conditions. Selectivity and sensitivity of AGATA will be superior to any existing γ-array by several orders of magnitude. Hence, it will be for a long time a rich source for nuclear structure physics providing the means for new discoveries and opening challenging new perspectives. This document is the initial proposal sent to the European Commission to obtain the necessary funds for the project

Effects of Pairing in the Pseudo-SU(3) Model

An extended version of the pseudo-SU(3) model which includes both spin and proton-neutron degrees of freedom is used to study the influence of the pairing interaction on K-band mixing, B(E2) values and quadrupole moments. Using the asymmetric rotor model as a backdrop, specific consequences of a many-particle shell-model based description of these collective properties are demonstrated and fundamental limits of the collective model's approach are investigated. Finally, the pseudo-SU(3) model, including representation mixing induced by pairing, is used to calculate the energies of 140Ce and the results are compared to experimental data and other theories.Comment: 21 pages, Latex, 11 figures available on request via mail or fax, accepted by Nucl. Phys.

Identification and rejection of scattered neutrons in AGATA

Gamma rays and neutrons, emitted following spontaneous fission of 252Cf, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36-fold segmented high-purity germanium crystals), placed at a distance of 50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high-purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and gamma rays and which was used to optimise the gamma-ray tracking-based neutron rejection methods. It was found that standard gamma-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points due to recoiling Ge nuclei after elastic scattering of neutrons. Standard tracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the tracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the gamma ray, figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with Geant4 simulations