| 1. |
- Clement, E., et al.
(författare)
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Conceptual design of the AGATA 1 π array at GANIL
- 2017
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 855, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This setup exploits the stable and radioactive heavy-ions beams delivered by the cyclotron accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam γ-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy γ rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA l π array are presented.
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| 2. |
- Lalovic, Natasa
(författare)
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Nuclear Structure Studies near 208Pb and γ-ray Imaging Techniques
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on a high-resolution γ-ray spectroscopy experiment where the fragmenta- tion of a 208 Pb primary beam was used to populate even-mass nuclei around 208 Pb. It was conducted in 2012 using the Advanced GAmma-ray Tracking Array (AGATA) while it was placed at GSI Darmstadt, Germany. Projectile-like fragments were selected and identified with the GSI Fragment Separator. The final aim is to study the aforementioned nuclei via Cou- lomb excitation. Yet, preceding measurements with stopped beams are necessary for reasons detailed here. Another part of this thesis is devoted to Research & Development (R&D) of position-sensitive scintillation detectors. These two different aspects are linked by studies of position sensitivity in devices utilized for detection of γ rays. Advances in γ-ray tracking algorithms are essential for both applied and basic nuclear physics. Here, the scintillation detector R&D is foreseen to contribute to applications in the realm of medical imaging as well as environmental and safety surveillance, whereas the basic research efforts yield improved nuclear structure information on heavy ions produced in relativistic fragmentation reactions. Paper I summarizes efforts regarding the image reconstruction algorithm when applied on a simulated data-set. In Paper II the performance of the AGATA sub-array is discussed, outlining the important aspects of the offline data processing and analysis. Paper III presents further treatment of the data partially scrutinized in Paper II using AGATA-tailored algorithms, assessing absolute efficiency and peak-to-total, and the performance of tracking algorithms with respect to different parameter-sets. Paper IV highlights an outstanding physics case from a stopped-beam AGATA measurement. In Paper V all aspects of the data analysis established in this thesis are described. The relevance of isomeric state measurements for both the experimental and theoretical aspect of relativistic fragmentation is emphasized.
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| 3. |
- Nesterenko, D. A., et al.
(författare)
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High-precision mass measurements for the isobaric multiplet mass equation at A = 52
- 2017
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 44:6
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Tidskriftsartikel (refereegranskat)abstract
- Masses of 52Co, 52Com, 52Fe, 52Fem, and 52Mn have been measured with the JYFLTRAP double Penning trap mass spectrometer. The isobaric multiplet mass equation for the T = 2 quintet at A = 52 has been studied employing the new mass values. No significant breakdown (beyond the level) of the quadratic form of the IMME was observed (). The cubic coefficient was 6.0(32) keV (). The excitation energies for the isomer and the T = 2 isobaric analog state in 52Co have been determined to be 374(13) keV and 2922(13) keV, respectively. The measured mass values for 52Co and 52Com are 29(10) keV and 16(15) keV higher, respectively, than obtained in a recent storage-ring experiment, and significantly lower than predicted by extrapolations. Consequently, this has an impact on the proton separation energies for 52Co and 53Ni relevant for the astrophysical rapid proton capture process. The Q value for the proton decay from the isomer in 53Co has been determined with an unprecedented precision, keV.
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| 4. |
- Podolyák, Zs., et al.
(författare)
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Role Of The Delta Resonance In The Population Of Excited States In High-Energy Reactions
- 2017
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Ingår i: The 26th International Nuclear Physics Conference. - 1824-8039. ; (INPC2016)
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Konferensbidrag (refereegranskat)abstract
- The 54Fe nucleus was populated from a 56Fe beam with an energy of E=A=500 MeV. The internal decay of the 10+ metastable state via g-ray emission was observed. The structure of this isomeric state has to involve at least four unpaired nucleons, therefore it cannot be populated in a simple two-neutron removal reaction from the ground state of 56Fe, and we suggest that it was populated via the decay of the D0 resonance into a proton. This process allows the population of four-nucleon states, such as the observed isomer. Therefore, the population of the four-particle 10+ isomer in 54Fe is a consequence of the quark structure of the nucleons. The possible use of this reaction mechanism for producing exotic nuclei is discussed.
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| 5. |
- Ralet, D., et al.
(författare)
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Lifetime measurement of neutron-rich even-even molybdenum isotopes
- 2017
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Ingår i: Physical Review C: covering nuclear physics. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 95:3
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Tidskriftsartikel (refereegranskat)abstract
- Background: In the neutron-rich A≈100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A=100 up to mass A=108, and the results that were obtained. Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the γ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a γ-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A=100 to A=108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: τ=29.7-9.1+11.3 ps for the 4+ state of Mo108 and τ=3.2-0.7+0.7 ps for the 6+ state of Mo102. Conclusions: The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A=100 to A=108 with a maximum reached at N=64. The transition probabilities decrease for Mo108 which may be related to its well-pronounced triaxial shape indicated by the calculations.
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