arXiv subjects

A. Esmaylzadeh

Publications and source records attributed to A. Esmaylzadeh.

9 recordsLinked to original sources

arXiv2026

Lifetime measurements in neutron-rich odd-A yttrium isotopes ($^{93-99}$Y): Investigation of shape coexistence and the intertwined quantum phase transition

Lifetimes of 16 excited states in the neutron-rich odd-$A$ nuclei $^{93-99}$Y were measured using fast-timing $γ$-$γ$ coincidence spectroscopy with fast scintillation detectors at the LOHENGRIN recoil separator. Particular attention is given to the region around $N \approx 59$, where rapid changes in nuclear deformation and shape coexistence occur. The lifetimes, determined using the generalized centroid difference method, are compared with interacting boson-fermion model calculations with configuration mixing, in which the odd-$A$ yttrium isotopes are described as a proton coupled to a bosonic core containing normal and intruder configurations. The results provide new constraints on theoretical descriptions of shape coexistence and structural evolution in neutron-rich nuclei near $A \approx 100$, particularly for odd-$A$ systems where experimental information remains limited.

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arXiv2026

Multiple shape coexistence near Sn118: First 03+ lifetime measurement

The intruder bands in Sn isotopes, built on the 2p-2h excitation across the $Z = 50$ proton shell gap, are well-known examples of shape coexistence near the neutron mid-shell region. Spectroscopic signatures for shape coexistence include enhanced $E0$ transitions between the $0^+$ band heads. However, the underlying shape coexistence and mixing has been unclear because lifetime information for the excited $0^+$ states was incomplete in $^{118}$Sn. We thus present here the first measurement of the $0^+_3$ lifetime in $^{118}$Sn using the fast-timing technique following thermal-neutron capture. The observed enhancement in $ρ^2(E0; 0^+_3 \rightarrow 0^+_2)$ of 150(30) milliunits provides compelling indications for multiple shape coexistence in $^{118}$Sn. Additionally, three distinct shapes in $^{116,118,120}$Sn naturally emerged in theoretical calculations based on the quantum-number-projected generator coordinate method employing a relativistic energy density functional.

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arXiv2026

Lifetime of the $4^+_1$ state of $^{132}$Te

The evolution of the collectivity of tellurium isotopes from mid-shell towards $N=82$ is currently based mainly on properties of the first excited $2^+$ states. To extend structural information in this isotopic chain, in particular with respect to the balance of microscopic, seniority-type and collective excitations, electric quadrupole transition strengths from $4^+$ states need to be considered. An experiment was performed to determine the $4_1^+$ lifetime of $^{132}$Te via the recoil-distance Doppler-shift method at the University of Cologne tandem accelerator. The isotope of interest was populated in the two neutron-transfer reaction $^{130}$Te($^{18}$O,$^{16}$O)$^{132}$Te$^*$. The $E2$ decay transition strength has been determined to be $B(E2; 4^+_1\rightarrow 2^+_1) = 9.3(10)\, \text{W.u.}$ and compares favourably to shell model calculations.

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arXiv2025

Modeling of Light Production in Inorganic Scintillators

In recent experiments, inorganic scintillators have been used to study the decays of exotic nuclei, providing an alternative to silicon detectors and enabling measurements that were previously impossible. However, proper use of these materials requires us to understand and quantify the scintillation process. In this work, we propose a framework based on that of Birks [Proc. Phys. Soc. A 64, 874] and Meyer and Murray [Phys. Rev. 128, 98] to model the light output of inorganic scintillators in response to beams of energetic heavy ions over a broad range of energies. Our model suggests that, for sufficiently heavy ions at high energies, the majority of the light output is associated with the creation of delta electrons, which are induced by the passage of the beam through the material. These delta electrons dramatically impact the response of detection systems when subject to ions with velocities typical of beams in modern fragmentation facilities. We test the accuracy of our model with data from Lutetium Yttrium Orthosilicate (LYSO:Ce), a common inorganic scintillator. We compare calculated light production and quenching factors with experimental data for heavy ions of varying mass and energy as well as make a quantitative estimate of the effects of delta rays on overall light output. The model presented herein will serve as a basic framework for further studies of scintillator response to heavy ions. Our results are crucial in planning future experiments where relativistic exotic nuclei are interacting with scintillator detectors.

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arXiv2025

Evidence for shape coexistence in $^{120}$Sn from the first $0^+_3$ lifetime measurement

The lifetime of the $0^+_3$ state in $^{120}$Sn was measured for the first time applying the fast-timing technique following thermal neutron capture. The mean lifetime of $τ= 50(7)$~ps leads to a $E0$ transition strength of $10^3\times ρ^2(E0;0^+_3\rightarrow0^+_2) = 120(50)$, suggesting shape coexistence and a high degree of mixing between the $0^+_2$ and $0^+_3$ states. With the newly measured lifetime, the $B(E2;0^+_3\rightarrow 2^+_1)$ value is 0.50(7)~W.u., which reveals that the $ρ^2(E0;0^+_3\rightarrow0^+_1)$ increases by a factor of $\approx 3.4$ from $^{116}$Sn to $^{120}$Sn.

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arXiv2025

Revised $B(E2; 2^{+}_{1} \rightarrow 0^{+}_{1})$ value in the semi-magic nucleus $^{210}$Pb

The lifetime of the $2^+_1$ state of $^{210}$Pb was measured in the $^{208}$Pb($^{18}$O, $^{16}$O)$^{210}$Pb two-neutron transfer reaction by $γ$-ray spectroscopy employing the recoil-distance Doppler-shift method. The extracted absolute $B(E2)$$\downarrow$ value of ${119\;^{+\;9}_{-\;8}\;\hspace{-0pt}\,\text{e}^2\text{fm}^4}$ is consistent with previously reported measurements, but with significantly improved precision. The available experimental data for the $2^+_1$-$4^+_1$-$6^+_1$-$8^+_1$ multiplet are compared with shell-model calculations based on the well-established Kuo-Herling interaction. The new $B(E2)$$\downarrow$ value agrees well with the shell-model prediction, providing evidence that the properties of the $2^+_1$ and $8^+_1$ states of $^{210}$Pb can be consistently described together within the nuclear shell-model framework.

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arXiv2024

Shape evolution in even-mass $^{98-104}$Zr isotopes via lifetime measurements using the $γγ$-coincidence technique

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first $2^+$ state and the increase in the transition strength B(E2; $2_1^\rightarrow 0_1^+$ going from $^{98}$Zr to $^{100}$Zr has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the $γγ$-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in $^{98-104}$Zr carried out to extract reduced transition probabilities. The new lifetime values in $γγ$-coincidence and $γ$-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock-Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

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arXiv2023

Investigating timing properties of modern digitizers utilizing interpolating CFD algorithms and the application to digital fast-timing lifetime measurement

The performance of two implementations of digital real-time interpolating constant fraction discriminator algorithms with respect to fast-timing lifetime measurements are investigated. The implementations integrated in two different digitizers were evaluated in terms of the effects of tuning parameters of the digital CFDs and the influence of different input amplitudes on the time resolution and time walk characteristics. Reference is made to the existing analog standard of fast-timing techniques. The study shows, that the timing performance of both modules is comparable to established fast-timing setups using analog constant fraction discriminators, but with the added benefit of digital processing. Both digitizer modules were found to be highly effective and user-friendly instruments for modern fast-timing requirements.

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arXiv2021

Tests of collectivity in $^{98}$Zr by absolute transition rates

Lifetimes of low-spin excited states in $^{98}$Zr were measured using the recoil-distance Doppler-shift technique and the Doppler-shift attenuation method. The nucleus of interest was populated in a $^{96}$Zr($^{18}$O,$^{16}$O)$^{98}$Zr two-neutron transfer reaction at the Cologne FN Tandem accelerator. Lifetimes of six low-spin excited states, of which four are unknown, were measured. The deduced $B(E2)$ values were compared with Monte Carlo shell model and interacting boson model with configuration mixing calculations. Both approaches reproduce well most of the data but leave challenging questions regarding the structure of some low lying states.

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