Conceptual design and performance study for the first implementation of AGATA at the in-flight RIB facility of GSI

Domingo‐Pardo, C.; Bazzacco, D.; Doornenbal, P.; Farnea, E.; Gadea, A.; Gerl, J.; Wollersheim, H. J.

doi:10.1016/j.nima.2012.08.039

Cited by 19 publications

(17 citation statements)

References 38 publications

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“…For longer lifetimes, the primary sensitivity is to the tails of the peak shape, while shorter lifetimes affect the positions of the peak maximum. We note that similar sensitivity studies for other beam and target combinations simulated for the AGATA array can be found in [27]. The deduced effective lifetimes (95% confidence interval for the fit) are τ eff (2 + 1 ) = 120 +15 −11 ps and τ eff (4 + 1 ) = 2.3 ± 1.5 ps, respectively.…”

Section: Partial Cross Section (Mb)supporting

confidence: 70%

Structure of Fe70 : Single-particle and collective degrees of freedom

et al. 2019

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Excited states in the neutron-rich 70 Fe nucleus were populated in a one-proton removal reaction from 71 Co projectiles at 87 MeV/nucleon. A new transition was observed with the γ-ray tracking array GRETINA and shown to feed the previously assigned 4 + 1 state. In comparison to reaction theory calculations with shell-model spectroscopic factors, it is argued that the new γ ray possibly originates from the 6 + 1 state. It is further shown that the Doppler-reconstructed γ-ray spectra are sensitive to the very different lifetimes of the 2 + and 4 + states, enabling their approximate measurement. The emerging structure of 70 Fe is discussed in comparison to LNPS-new large-scale shell-model calculations.A goal of nuclear science is to achieve an understanding of nuclei and their properties rooted in the fundamental nucleon-nucleon interactions, while demonstrating predictive power for the shortest-lived species located at the fringes of the nuclear chart. In the quest to extrapolate knowledge to the most neutron-rich systems, including those that may remain beyond experimental reach, much can be learned from nuclei with large neutron excess that clearly display the effects of structural evolution away from the valley of stability. Observables measured for such nuclei provide important extrapolation points toward unknown regions and their successful modeling offers critical benchmarks for theory. Specifically, the complex interplay between single-particle and collective degrees of freedom in the nuclear many-body system provides unique and interesting experimental and theoretical challenges.Neutron-rich 70 Fe is such a nucleus where singleparticle structure is impacted by shell evolution, driven by the spin-isospin parts of the nucleon-nucleon force, and where significant quadrupole collectivity develops. In fact, 70 Fe is said to be part of the N = 40 island of inversion [1,2] where the neutron-rich Fe and Cr nuclei around N = 40 become the most deformed in the region. This is thought to be caused by the strong quadrupolequadrupole interaction producing a shape transition in which highly correlated, many-particle-many-hole configurations become more bound than the normal-order (spherical) ones [1]. Such islands of inversion are characterized by rapid structural changes and shape coexistence [2,3], providing insight into nuclear structure physics far from stability [4]. 70 Fe has 12 neutrons more than the heaviest stable iron isotope, while the heaviest one discovered to date is 76 Fe [5], a nucleus predicted to display collectivity and shape coexistence [2] just two protons below 78 Ni. Indeed, within the iron isotopic chain, 70 Fe is located on the path between the N = 40 and N = 50 islands of inversion [2], with the latter remaining a challenge for next-generation rare-isotope facilities presently under construction. 70 Fe has also been used as a seed nucleus in r-process calculations and associated sensitivity studies [6,7]. Spectroscopic information on 70 Fe, limited to the identification of two states, the first...

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Section: Partial Cross Section (Mb)supporting

confidence: 70%

Structure of Fe70 : Single-particle and collective degrees of freedom

et al. 2019

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“…1 of Ref. [27] I. The number of events that were recorded in the experiment presented in this paper.…”

Section: Fragment Identificationmentioning

confidence: 99%

“…The relation between the mean lifetime and the energy shift was determined using Monte Carlo (MC) simulations following a similar methodology as the one described in Refs. [27,42]. Because the reaction cross sections at the secondary target are independent of the beam energy [43], we assumed an excitation at the center of the target.…”

Section: Lifetime Determinationmentioning

confidence: 99%

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Ralet¹,

Piétri²,

Rodríguez³

et al. 2017

Phys. Rev. C

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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-shiftattenuation 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 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 108 Mo which may be related to its well-pronounced triaxial shape indicated by the calculations.

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“…Lifetime effects: Lifetime effects on the energy spectrum [13,14] may complicate the peak separation and reduce the peak-tobackground ratio because they can lead to a significant broadening of the observed peaks at angles not in the proximity to θ det ¼ arccosðβÞ. These lifetime effects are included in the simulated spectra shown in Figs.…”

Section: Methodsmentioning

confidence: 99%

“…applied to the very same data-set: one assuming the velocity of the ions leaving the first target as ion velocity at the time of deexcitation and the position of the first target as ion position at the time of de-excitation, and one Doppler-correction assuming the respective quantities for the second target. In the first case, deexcitation γ-rays from ions excited in the first target will be properly Doppler-corrected to the laboratory frame and result in a sharp peak at unshifted γ-ray energy E γ (or, depending on the lifetime of the excited state, in a characteristic Doppler-broadened lineshape like in DSAM experiments [14], see previous subsection) while γ-rays from ions excited in the second target would be transformed to a different energy due to improper Dopplercorrection. In the second case, γ-rays emitted from ions excited in the second target appear as a sharp peak at the unshifted γ-ray energy E γ while γ-rays from ions excited in the first target are transformed to a different energy.…”

Section: Methodsmentioning

confidence: 99%