Laser spectroscopy enables the determination of fundamental atomic and nuclear properties with high precision. In view of the low production rates of the heaviest elements, a high total efficiency is ...a crucial requirement for any experimental setup to be used in on-line experiments. The setup requires the use of gas stopping techniques to slow down the radionuclides of interest. In previous studies laser spectroscopy was performed inside a gas-filled stopping cell with a limited spectral resolution of a few GHz. Collisional broadening inside stopping cells ultimately limits the precision of laser spectroscopic studies and hampers in particular hyperfine spectroscopy. The spectral linewidth is reduced by an order of magnitude when the laser spectroscopy is performed in a well-collimated gas jet formed by the exit nozzle of a gas stopping cell. In addition, the exposure of the jet to high-repetition rate laser light which saturates the optical transitions allows maintaining a high total efficiency. Here, we present a new setup dedicated to laser spectroscopy of the heaviest elements with an improved resolution, which is presently under construction. This setup combines the efficient filament neutralization demonstrated for nobelium with the improved resolution of in-gas-jet spectroscopy.
The first direct determination of the ground-state-to-ground-state
β
-
-decay
Q
-value of
77
As to
77
Se was performed by measuring their atomic mass difference utilizing the double Penning trap mass ...spectrometer, JYFLTRAP. The resulting
Q
-value is 684.463(70) keV, representing a remarkable 24-fold improvement in precision compared to the value reported in the most recent Atomic Mass Evaluation (AME2020). With the significant reduction of the uncertainty of the ground-state-to-ground-state
Q
-value and knowledge of the excitation energies in
77
Se from
γ
-ray spectroscopy, the ground-state-to-excited-state
Q
-value of the transition
77
As (3/2
-
, ground state)
→
77
Se
∗
(5/2
+
, 680.1035(17) keV) was refined to be 4.360(70) keV. We confirm that this potential low
Q
-value
β
-
-decay transition for neutrino mass determination is energetically allowed at a confidence level of about 60
σ
. Nuclear shell-model calculations with two well-established effective Hamiltonians were used to estimate the partial half-life for the low
Q
-value transition. The half-life was found to be of the order of 10
9
years for this first-forbidden non-unique transition. Since the half-life of
77
As is only
≈
2 days, usage of it as source for rare-event experiments searching for the electron antineutrino mass would be challenging.
Abstract
Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans ...functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus
100
Sn, where the near-equal number of protons (
Z
) and neutrons (
N
) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the
N
= 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of
96
Ag (
N
= 49). The results provide a challenge for nuclear theory: calculations are unable to reproduce the pronounced discontinuity in the charge radii as one moves below
N
= 50. The technical advancements in this work open the
N
=
Z
region below
100
Sn for further optical studies, which will lead to more comprehensive input for nuclear theory development.
The multinucleon transfer (MNT) reaction approach was successfully employed for the first time to measure the isomeric ratios (IRs) of 211Po isomer (25/2+) and its ground state (9/2+) at the IGISOL ...facility using a 945 MeV 136Xe beam impinged on 209Bi and natPb targets. The dominant production of isomers compared to the corresponding ground states was consistently revealed in the α-decay spectra. Deduced IR of 211Po populated through the 136Xe+natPb reaction was found to have an enhancement of ≈1.8-times than that observed for the 136Xe+209Bi. State-of-the-art Langevin-type model calculations have been utilized to estimate the spin distribution of an MNT residue. The computations qualitatively corroborate with the considerable increase in the IRs of 211Po produced from 136Xe+natPb compared to 136Xe+209Bi. Theoretical investigations indicate a weak dependence of target spin on the IRs. The enhancement of the 211Po isomer in the 136Xe+natPb over 136Xe+209Bi can be attributed to the different proton (p)-transfer production routes. Estimations demonstrate an increment in the angular momentum transfer, favorable for isomer production, with increasing projectile energy. Comparative analysis reveals the two entrance channel parameters, projectile mass and p-transfer channels, strongly influencing the population of the high-spin isomer of 211Po (25/2+). This letter reports the first experimental and theoretical study on the IRs of nuclei formed from two different p-transfer channels via two independent MNT reactions.
Abstract
The production of very neutron-rich nuclides heavier than fission fragments is an ongoing experimental challenge. Multi-nucleon transfer reactions (MNT) have been suggested as a method to ...produce these nuclides. By thermalizing the reaction products in gas-filled stopping cells, we can deliver them as cooled high-quality beams to decay, laser and mass spectrometry experiments. High precision mass spectrometry will allow for the first time to universally and unambiguously identify the atomic and proton numbers of the ions produced in MNT reactions. In this way their ground and isomeric state properties can be studied in high-precision measurements. In experiments at IGISOL, Finland and at FRS Ion Catcher, Germany, we have done and will perform broadband measurements of the reaction products, with the aim to improve the understanding of the reaction mechanism and to determine the properties of the ground and isomeric states of the produced nuclides. First results and preparations for upcoming experiments are presented.
To study exotic nuclides at the borders of stability with laser ionization and spectroscopy techniques, highest efficiencies in combination with a high spectral resolution are required. These usually ...opposing requirements are reconciled by applying the in-gas-laser ionization and spectroscopy (IGLIS) technique in the supersonic gas jet produced by a de Laval nozzle installed at the exit of the stopping gas cell. Carrying out laser ionization in the low-temperature and low density supersonic gas jet eliminates pressure broadening, which will significantly improve the spectral resolution. This article presents the required modifications at the Leuven Isotope Separator On-Line (LISOL) facility that are needed for the first on-line studies of in-gas-jet laser spectroscopy. Different geometries for the gas outlet and extraction ion guides have been tested for their performance regarding the acceptance of laser ionized species as well as for their differential pumping capacities. The specifications and performance of the temporarily installed high repetition rate laser system, including a narrow bandwidth injection-locked Ti:sapphire laser, are discussed and first preliminary results on neutron-deficient actinium isotopes are presented indicating the high capability of this novel technique.
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