The GRETINA Spectrometer Cromaz, M
Journal of physics. Conference series,
05/2015, Letnik:
606, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The GRETINA spectrometer is a first generation, gamma-ray tracking spectrometer capable of determining the Compton scattering path of gamma-rays incident on the detector volume. This ability allows ...the Ge detectors to be close packed allowing the detector to be scaled to high efficiencies while maintaining good peak-to-total. GRETINA currently consists of 7 4-detector modules giving approximately 1π solid angle coverage with a calorimetric efficiency of 6.3% and tracked efficiency of 4.7% at 1.3 MeV. The array's sensitivity to the position of the gamma ray's first interaction point enables precision event-by-event Doppler correction which allows one to achieve 1% energy resolution even for sources moving at a large fraction of the speed of light such as those encountered at fragmentation facilities such as NSCL and the future FRIB.
The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is a new generation high-resolution γ-ray spectrometer consisting of electrically segmented high-purity germanium crystals. GRETINA is ...capable of reconstructing the energy and position of each γ-ray interaction point inside the crystal with high resolution. This enables γ-ray energy tracking which in turn provides an array with large photopeak efficiency, high resolution and good peak-to-total ratio. GRETINA is used for nuclear structure studies with demanding γ-ray detection requirements and it is suitable for experiments with radioactive-ion beams with high recoil velocities. The GRETINA array has a 1π solid angle coverage and constitutes the first stage towards the full 4π array GRETA. We present in this paper the main parts and the performance of the GRETINA system.
UCGretina, a geant4 simulation of the GRETINA gamma-ray tracking array of highly-segmented high-purity germanium detectors is described. We have developed a model of the array, in particular of the ...Quad Module and the capsules, that gives good agreement between simulated and measured photopeak efficiencies over a broad range of gamma-ray energies and reproduces the shape of the measured Compton continuum. Both of these features are needed in order to accurately extract gamma-ray yields from spectra collected in in-beam gamma-ray spectroscopy measurements with beams traveling at v∕c≳0.3 at the National Superconducting Cyclotron Laboratory and the Facility for Rare Isotope Beams. In the process of developing the model, we determined that millimeter-scale layers of passive germanium surrounding the active volumes of the simulated crystals must be included in order to reproduce measured photopeak efficiencies. We adopted a simple model of effective passive layers and developed heuristic methods of determining passive-layer thicknesses by comparison of simulations and measurements for a single crystal and for the full array. Prospects for future development of the model are discussed.
Recent results from RIKEN/RIBF on the low-lying level structure of 29F are interpreted within the Particle-Rotor Model. We show that the experimental data can be understood in the Rotation-aligned ...Coupling Scheme, with the 5/2+ ground state as the bandhead of a decoupled band. In this picture, the energy of the observed 1/21+ state correlates strongly with the rotational energy of the core and provides an estimate of the 2+ energy in 28O. Our analysis suggests a moderate deformation, ϵ2∼0.16, and places the 2+ in 28O at ∼ 2.5 MeV.
The structure of 71Zn was investigated by one-neutron transfer and heavy-ion induced complex (deep-inelastic) reactions using the GRETINA-CHICO2 and the Gammasphere setups, respectively. The observed ...inversion between the 9/2+ and 1/2− states is explained in terms of the role of neutron pairing correlations. Non-collective sequences of levels were delineated above the 9/2+ isomeric state. These are interpreted as being associated with a modest oblate deformation in the framework of Monte-Carlo shell-model calculations carried out with the A3DA-m Hamiltonian in the pfg9/2d5/2 valence space. Similarities with the structure of Ni402868 were observed and the shape-coexistence mechanism in the N=40 region of neutron-rich nuclei is discussed in terms of the so-called Type-II shell evolution, with an emphasis on proton–neutron correlations between valence nucleons, especially those involving the shape-driving g9/2 neutron orbital.
In this paper, we provide a formalism for the characterization of tracking arrays with emphasis on the proper corrections required to extract their photopeak efficiencies and peak-to-total ratios. ...The methods are first applied to Gammasphere, a well characterized 4π array based on the principle of Compton suppression, and subsequently to GRETINA. The tracking efficiencies are then discussed and some guidelines as to what clustering angle to use in the tracking algorithm are presented. It was possible, using GEANT4 simulations, to scale the measured efficiencies up to the expected values for the full 4π implementation of GRETA.
Measured- and simulated-pulse shapes in electrically segmented coaxial Ge detectors have been investigated. Three-dimensional position sensitivities have been determined experimentally and ...theoretically in a 36-fold segmented Ge detector. By using the two-dimensional segmentation in conjunction with pulse-shape analysis, a position sensitivity of better than 1 mm can be obtained in three dimensions at an energy of 374 keV. This is achieved by analyzing the shape of net charge signals of segments containing interactions and of transient image charge signals of neighboring segments. The ability to locate interactions in three-dimensions is one of the crucial properties in the proposed γ-ray energy tracking array (GRETA). The concept of γ-ray tracking will not only increase the efficiency in detecting γ radiation but also enables the localization and characterization of unknown γ-ray sources with much higher accuracy than is possible with current instruments.
The position resolution of a highly segmented coaxial germanium detector was determined by analyzing the 2055
keV
γ
-ray transition of
Zr
90
excited in a fusion–evaporation reaction. The high ...velocity of the
Zr
90
nuclei imparted large Doppler shifts. Digital analysis of the detector signals recovered the energy and position of individual
γ
-ray interactions. The location of the first interaction in the crystal was used to correct the Doppler energy shift. Comparison of the measured energy resolution with simulations implied a position resolution (root mean square) of 2
mm in three-dimensions.
Performance of the GRETA prototype detectors Vetter, K.; Kuhn, A.; Lee, I.Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2000, Letnik:
452, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A working, two-dimensionally segmented Ge detector is one of the crucial elements in the development of GRETA – a next-generation 4π germanium detector array that uses three-dimensional positions and ...energies to of individual interactions of γ rays in the detector to reconstruct the full energies and direction vectors of the individual γ rays by employing tracking algorithms. The three-dimensional position and the energy of interactions will be determined by using a two-dimensionally segmented Ge detector along with pulse-shape analysis of the signals. The current prototype is a 36-fold segmented HP-Ge detector in a closed-ended coaxial geometry. Preamplifiers with a compact design, low noise, and very good response properties have been built and implemented. An integrated noise level of about 5 keV has been measured for the segment channels. The average energy resolution of this detector was measured to be 1.14 and 1.93 keV at 60 and 1332 keV, respectively. Using pulse-shape analysis, a three-dimensional position sensitivity of 0.2 to 0.5 mm (R.M.S) has been obtained at 374 keV, dependent on the position and the direction. The results represent a major step towards the feasibility of a γ-ray tracking detector.
PDF
