A new method is proposed which allows the building of a signal basis, i.e. a matrix of traces corresponding to identified locations of gamma interactions with the crystal, directly from a set of ...signals delivered by the detector. The usual on-line algorithms dedicated to the location of the hits can apply this basis to perform signal decomposition. The method also provides Jacobian transforms that can be used to compute very quickly the hit locations in situations when signals are not overlapping.
Random Graphs and Mean Field Percolation are two names given to the most general mathematical model of systems composed of a set of connected entities. It has many applications in the study of real ...life networks as well as physical systems. The model shows a precisely described phase transition, but its solution for finite systems was yet unresolved. However, atomic nuclei, as well as other mesoscopic objects (e.g. molecules, nano-structures), cannot be considered as infinite and their fragmentation does not necessarily occur close to the transition point. Here, we derive for the first time the exact solution of Mean Field Percolation for systems of any size, as well as provide important information on the internal structure of Random Graphs. We show how these equations can be used as a basis to select non-trivial correlations in systems and thus to provide evidence for physical phenomena.
Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers A=35, 36, 37, and 38 have been measured using the differential recoil-distance method. The ...isotopes of sulfur were populated in binary grazing reactions initiated by a beam of 36S ions of energy 225 MeV incident on a thin 208Pb target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ-ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For 35S, the lifetime was determined for the first 1/2+ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the 3− state of 36S at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (6+) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For 37S, the states for which lifetime limits were established were those at 646 keV with Jπ=3/2− and at 2776 keV with Jπ=11/2−; there are no previously published lifetime values for excited states of 37S. Finally, a lifetime limit was established for the Jπ=(6+) state of 38S at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.
The kinetic energy of a neutron is determined experimentally by measuring its time-of-flight and flight distance from the source to the detector. However, this determination is vitiated by errors ...since the exact location of the interaction of the neutron within the detector is unknown. Moreover, more than one interaction may be necessary for the deposited energy to reach the detector threshold. We compare the different existing energy determination methods and introduce the method which gives the minimum-variance unbiased estimator of the neutron energy. The method is based of the inversion of the detector response function, for which we propose a universal algorithm. It is shown that the precision of the new method does not deteriorate with the length of the detector, which opens the possibility of conceiving detectors with a higher efficiency.
Lifetimes of excited states of the phosphorus isotopes 33 , 34 , 35 , 36 15 P have been measured by using the differential recoil-distance method. The isotopes of phosphorus were populated in binary ...grazing reactions initiated by a beam of 36 S ions of energy 225 MeV incident on a thin 208 Pb target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ -ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were made within the range from about 1 to 100 ps. The number of states for which lifetime measurements were possible was limited by statistics. For 33 P , lifetime limits were determined for the first 3/2+ and 5/2+ states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first 2+ state of 34 P at 429 keV was determined and compared with earlier measurements. For 35 P , the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with Jπ values of 3/2+, 5/2+, 7/2− 1 , and 7/2− 2 , respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched π ( 1 f 7 / 2 ) ⊗ ν ( 1 f 7 / 2 ) J π = ( 7 + ) state of 36 P at 5212 keV and a lifetime limit was established for the stretched π ( 1 d 3 / 2 ) ⊗ ν ( 1 f 7 / 2 ) J π = ( 5 − ) state at 2030 keV. There are no previously published lifetimes for states of 36 P . Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF effective interaction. In addition, measured branching ratios, published mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. In general, there is good agreement between experiment and the shell model; however there is evidence that the shell-model values of the M1 transition rates for the 3/2+1→ 1 / 2 + (ground state) and 5/2+1→ 3 / 2 + 1 transitions in 33 P underestimate the experimental values by a factor between 5 and 10. In 35 P there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited 7/2− states. In particular, there is a serious disagreement for the decay characteristics of the second 7/2− state at 4493 keV, for which the shell-model counterpart lies at 4754 keV. In this case, the shell-model competing electromagnetic decay branches are dominated by E1 and M1 transitions.
A new method to determine the positions and energies of the gamma -interactions in a segmented HPGe crystal of the AGATA detector is presented. The procedure is able to decompose multi-hit events, ...even if hits occur in the same segment. We tested the method with simulated signals; noise and the finite bandwidth of the preamplifier have been considered.
New setup for the characterisation of the AGATA detectors Ha, T.M.H.; Korichi, A.; Le Blanc, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2013, Letnik:
697
Journal Article
Recenzirano
A crucial step in the process of γ-ray tracking is related to the location of the interaction points of all the γ-rays within the AGATA (Advanced GAmma Tracking Array) segmented detectors. This ...requires a full understanding of the sensitivity of each highly segmented high-purity germanium (HPGe) detectors via the characterisation of the 2D and 3D position response. In this paper, we describe the experimental scanning setup that we developed at Orsay for the AGATA detectors. A collimated 137Cs source on an automated x–y positioning table was used for the front face scanning of the AGATA symmetric prototype detector. The 3D scanning measurement is performed using coincidence techniques based on γ-ray Compton scattering from the AGATA detector into an ancillary coupled detector. In our setup, TOHR (high resolution tomograph developed for small animal imaging) is used as an ancillary detector. The data is collected using TIGRESS cards for digital signal processing. The data flow, readout and storage is NARVAL as used for the full AGATA project. The analysis of the collected data and the obtained results is shown to illustrate our device performances.
An abnormal production of events with almost equal-sized fragments was theoretically proposed as a signature of spinodal instabilities responsible for nuclear multifragmentation in the Fermi energy ...domain. On the other hand finite size effects are predicted to strongly reduce this abnormal production. High statistics quasifusion hot nuclei produced in central collisions between Xe and Sn isotopes at 32 and 45 A MeV incident energies have been used to definitively establish, through the experimental measurement of charge correlations, the presence of spinodal instabilities. N/Z influence was also studied.
Agata characterisation and pulse shape analysis Boston, A. J.; Crespi, F. C. L.; Duchêne, G. ...
European physical journal. A, Hadrons and nuclei,
09/2023, Letnik:
59, Številka:
9
Journal Article
Recenzirano
Odprti dostop
The AGATA and GRETA spectrometers are large arrays of highly segmented HPGe detectors that use the technique of gamma ray tracking to reconstruct the scattering path of gamma rays interacting within ...the active material. A basic requirement is a precise reconstruction of the individual interaction locations within the detectors. This is possible through the use of pulse shape analysis which has to be conducted in real time due to the high data rates generated by the spectrometer. The methodologies that have been evaluated to perform this for AGATA are discussed along with the approaches used to calculate the pulse shape databases required by these algorithms. Finally, the performance and limitations of the existing approaches are reviewed.
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