The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation gamma-ray spectrometer. AGATA is based on the technique of gamma-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a gamma ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of gamma-ray tracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector-response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer.

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AGATA - Advanced GAmma Tracking Array

Euroball is a European project to build a highly efficient and powerful gamma-ray spectrometer for nuclear spectroscopy. The project represents an amalgamation of recent technical advances in detectors, electronics and data acquisition. These developments and the status of the project will be discussed.

The Euroball Spectrometer

The GREAT spectrometer is designed to measure the decay properties of reaction products transported to the focal plane of a recoil separator. GREAT comprises a system of silicon, germanium and gas detectors optimised for detecting the arrival of the reaction products and correlating with any subsequent radioactive decay involving the emission of protons, α particles, β particles, γ rays, X-rays or conversion electrons. GREAT can either be employed as a sensitive stand-alone device for decay measurements at the focal plane, or used to provide a selective tag for prompt conversion electrons or γ rays measured with arrays of detectors deployed at the target position. A new concept of triggerless data acquisition (total data readout) has also been developed as part of the GREAT project, which circumvents the problems and limitations of common dead time in conventional data acquisition systems.

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The GREAT spectrometer

In-beam and decay spectroscopy of transfermium nuclei

A new and innovative array, MUST, based on silicon strip technology and dedicated to the study of reactions induced by radioactive beams on light particles is described. The detector consists of 8 silicon strip – Si(Li) telescopes used to identify recoiling light charged particles through time of flight, energy loss and energy measurements and to determine precisely their scattering angle through X, Y position measurements. Each 60×60 mm 2 double sided silicon strip detector with 60 vertical and 60 horizontal strips yields an X – Y position resolution of 1 mm, an energy resolution of 50 keV, a time resolution of around 1 ns and a 500 keV energy threshold for protons. The backing Si(Li) detectors stop protons up to 25 MeV with a resolution of approximately 50 keV. CsI crystals read out by photo-diodes which stop protons up to 70 MeV are added to the telescopes for applications where higher energy particles need to be detected. The dedicated electronics in VXIbus standard allow us to house the 968 logic and analog channels of the array in one crate placed adjacent to the reaction chamber and fully remote controlled, including pulse visualization on oscilloscopes. A stand alone data acquisition system devoted to the MUST array has been developed. Isotope identification of light charged particles over the full energy range has been achieved, and the capability of the system to measure angular distributions of states populated in inverse kinematics reactions has been demonstrated.

Must: a silicon strip detector array for radioactive beam experiments

Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the Gamma Recoil Electron Alpha Tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time. Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experiment.

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The GREAT triggerless total data readout method

During 1992-1993 the Nuclear Structure Facility at Daresbury Laboratory hosted phase one of the EUROGAM experimental programme. These were the first nuclear physics experiments to make large scale use of the VXIbus standard for electronics and data acquisition. EUROGAM phase 1 was made up of an array of 45 escape suppressed Germanium (Ge) detectors. It was used for gamma-ray spectroscopy both standalone and in conjunction with external detectors including the Daresbury Recoil Separator (RS), isomer detectors and various particle detectors. An overview of the system, details of special VXI cards, the readout and trigger systems for EUROGAM have been previously reported at the 1991 IEEE-NSS. Here we report on how they worked in real experiments. >

Experience with VXI electronics and data acquisition for the EUROGAM spectrometer

A single-width D-sized VXI card has been designed and built to fully instrument one of the new Clover detectors designed for experiments with the EUROGAM array Each Clover detector consists of four individual germanium (Ge) crystals and an escape suppression shield comprising 16 bismuth germanate (BGO) crystals The Clover electronics card measures energy and timing data to 13-bit accuracy from each Ge crystal for spectroscopy and measures sum energy and timing for the BGO shield It also records a complete Ge and BGO hit pattern for each event and performs intelligent hardware escape suppression to exploit the segmented nature of the Clover detectors

VXI electronics for EUROGAM clover detectors

During 1992-1993 the Nuclear Structure Facility at Daresbury Laboratory hosted phase one of the EUROGAM experimental programme. These were the first nuclear physics experiments to make large scale use of the VXIbus standard for electronics and data acquisition. EUROGAM phase 1 was made up of an array of 45 escape suppressed Ge detectors. It was used for gamma-ray spectroscopy both stand-alone and in conjunction with external detectors including the Daresbury Recoil Separator, isomer detectors and various particle detectors. An overview of the system, details of special VXI cards, the readout and trigger systems for EUROGAM have been previously reported at the 1991 IEEE-NSS. Here we report an how they worked in real experiments. >

A single width D sized VXI card has been designed and built to fully instrument one of the new Clover detectors designed for experiments with the EUROGAM array. Each Clover detector consists of 4 individual germanium (Ge) crystals and an escape suppression shield comprising 16 bismuth germanate (BGO) crystals. The Clover electronics card measures energy and timing data to 13 bit accuracy from each Ge crystal for spectroscopy and measures sum energy and timing for the BGO shield. It also records a complete Ge and BGO hit pattern for each event and performs intelligent hardware escape suppression to exploit the segmented nature of the Clover detectors. >

I. Lazarus

Papers

The GREAT triggerless total data readout method

Experience with VXI electronics and data acquisition for the EUROGAM spectrometer

VXI electronics for EUROGAM clover detectors

Experience with VXI electronics and data acquisition for the EUROGAM spectrometer

VXI electronics for EUROGAM clover detectors