The -decay fine structure of ^179 Hg and ^177 Au was studied by means of decay spectroscopy. Two experiments were performed at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland, utilizing the recoil separator RITU and a digital data acquisition system. The heavy-ion induced fusion-evaporation reactions ^82_36 Kr + ^100_44 Ru and ^88_38 Kr + ^92_42 Mo were used to produce the ^179 Hg and ^177 Au nuclei, respectively. Studying the evaporation residues (ER, recoils)- α _1 - α _2 correlations and - γ coincidences, a new decay with E _α = 6156(10) keV was observed from ^179 Hg. This decay populates the (9/2 ^- ) excited state at an excitation energy of 131.3(5) keV in ^175 Pt. The internal conversion coefficient for the 131.3(5) keV transition de-exciting this state was measured for the first time. Regarding the ^177 Au nucleus, a new decay with E _α = 5998(9) keV was observed to populate the 156.1(6) keV excited state in ^173 Ir. Two de-excitation paths were observed from this excited state. Moreover, a new 215.7(13) keV transition was observed to depopulate the 424.4(13) keV excited state in ^173 Ir. Properties of the ^179 Hg and ^177 Au decays were examined in a framework of reduced widths and hindrance factors. For clarity and simplicity, the spin and parity assignments (e.g. J^π ) are presented without brackets throughout the text.

Atomic nuclei serve as prime laboratories for investigations of complex quantum phenomena, where minor nucleon rearrangements cause significant structural changes. 190Pb is the heaviest known neutron-deficient Pb isotope that can exhibit three distinct shapes: prolate, oblate, and spherical, with nearly degenerate excitation energies. Here we report on the combined results from three state-of-the-art measurements to directly observe these deformations in 190Pb. Contrary to earlier interpretations, we associate the collective yrast band as predominantly oblate, while the non-yrast band with higher collectivity follows characteristics of more deformed, predominantly prolate bands. Direct measurement of the E0(0_2^+→0_1^+) transition and γ-e− coincidence relations allowed us to locate and firmly assign the 0_2^+ state in the level scheme and to discover a spherical 2_3^+ state at 1281(1) keV with B(E2;2_3^+→0_1^+)=1.2(3) W.u. These assignments are based purely on observed transition probabilities and monopole strength values, and do not rely on model calculations for their interpretation. Direct measurements reveal that the neutron-deficient isotope 190Pb can adopt three different deformations near the ground state. The present work identifies the collective yrast band as predominantly oblate, the non-yrast band as predominantly prolate, and discovers a candidate spherical 2_3^+ state at 1281 keV.

At a fundamental level, the interactions between protons and protons, protons and neutrons, and neutrons and neutrons are not identical. Such isospin nonconserving interactions emerge when comparing the excitation energy of analog states in T = 1 triplet nuclei. Here, we extend such an analysis to the A = 78, T = 1 triplet system-the heaviest system for which such complete data exists-and find strong disagreement with contemporary theory. This was achieved by pioneering the technique of recoil-/3-/3 tagging to identify excited states in 78Zr. We also established a 78Zr half-life of 25+17 -8 ms and extended the T = 1 band in 78Y to Jn = (10+).

Polonium isotopes having two protons above the shell closure at Z=82 show a wide variety of low-lying, high-spin isomeric states across the whole chain. The structure of neutron-deficient isotopes up to ^{210}Po  (N=126) is well established as they are easily produced through various methods. However, there is not much information available for the neutron-rich counterparts for which only selective techniques can be used for their production. We report on the first fast-timing measurements of yrast states up to the 8^{+} level in ^{214,216,218}Po isotopes produced in the β^{-} decay of ^{214,216,218}Bi at ISOLDE, CERN. In particular, our new half-life value of 607(14) ps for the 8_{1}^{+} state in ^{214}Po is nearly 20 times shorter than the value available in the literature and comparable with the newly measured half-lives of 409(16) and 628(25) ps for the corresponding 8_{1}^{+} states in ^{216,218}Po, respectively. The measured B(E2;8_{1}^{+}→6_{1}^{+}) transition probability values follow an increasing trend relative to isotope mass, reaching a maximum for ^{216}Po. The increase contradicts the previous claims of isomerism for the 8^{+} yrast states in neutron-rich ^{214}Po and beyond. Together with the other measured yrast transitions, the B(E2) values provide a crucial test of the different theoretical approaches describing the underlying configurations of the yrast band. The new experimental results are compared to shell-model calculations using the KHPE and H208 effective interactions and their pairing-modified versions, showing an increase in configuration mixing when moving toward the heavier isotopes.

The complex low-spin structure of the proton-rich 114 53I61 nucleus has been investigated with the JUROGAM 3 germanium array coupled with the MARA mass separator using the 58 Ni( 64 Zn , alpha 3pn) fusion-evaporation reaction. The depopulation of the previously known high-spin bands to low-spin states is firmly established, fixing the excitation energies, spins and parities of the states. The present results combined with fragmentary communications and results published from the decay of separated mass-114 beams measured long time ago at ORNL and GSI, led to the conclusion that the previously known 6 s, 266 keV, I = (7) isomer has to be repositioned at 134 keV and its spin-parity changed to 4+. Three new isomers are identified from intensity imbalance of the populating and depopulating transitions, one at 204 keV with I = 6+ and a half-life longer than several nanoseconds, and two at 635 and 966 keV with I = 5- and I = 7-, respectively, with half-lives of a few nanoseconds. The spins of one high-spin band are changed from odd to even and a new interpretation of the two resulting bands with even spins is proposed based on cranked Nilsson-Strutinsky calculations. From the comparison of the observed low-spin states with shell-model calculations it is suggested that the states of the ground-state cascade are oblate, while the other positive-parity states and the high-spin negative-parity bands are prolate.

High-spin states of the odd-odd Pr-136 nucleus have been investigated using the Mo-100(Ar-40, 1p3n) reaction with the JUROGAM II gamma-ray spectrometer. Many new transitions and levels were identified in addition to the confirmation of most previously known transitions and levels. The high statistics of the present data set allowed the multipolarity assignments for many transitions to be established, which were previously assigned tentatively. Possible configuration assignments for the bands above the I-pi = 6(+) isomer are analyzed within the tilted axis cranking covariant density functional theory framework, and the experimental energy spectra and ratios of reduced transition probabilities are reproduced fairly well. A complete picture of the band structure of this nucleus is established. In particular, the effect of the neutron h(9/2) and f(7/2) intruder orbitals involved in the configurations of the decoupled bands is discussed in detail.

A detailed level scheme of 213Fr126 following the EC/beta+ decay of the 1/2- 213 Ra parent ground state was built in an experiment performed at the ISOLDE Decay Station, CERN. The fragmented total beta decay strength favours the direct population of several low-spin (J 7/2) excited states. The analysis of the gamma-singles spectrum and gamma-gamma coincidences allowed us to identify many new gamma-ray transitions and excited states in 213 Fr up to about 3.6 MeV excitation energy. The spins and parities of the newly established levels, on top of the (7/2-1 ) state, were mainly assigned based on the systematics of the N = 126 isotones and further compared with shell-model calculations. The level scheme displays a structural pattern, with several groups of states with negative parity, emerging from the well-defined, simple, pi ( h 59 / 2 ), pi ( h 4 9 / 2 f 17 / 2 ) configurations or from their configuration mixing. The strength of the E 2 transitions within the multiplets is compared with shell-model theoretical calculations performed with the KHPE and H 208 effective interactions. A new (3/2-) isomer with a half-life of 26(3) ns has been identified. An upper limit of 35 ps was determined for the half-life of the first excited state, 7/2-. The possibility of a mixed M 1 + E 2 character is discussed for the 7/2-1 -> 9/2-gs decay in 213 Fr, which leads to an l-forbidden nature of the pi f 7 / 2 -> pi h 9 / 2 transition.

The excited structure of the single-hole nucleus 131 Sn populated by the beta - decay of 131 In was investigated in detail at the ISOLDE facility at CERN. This new experiment took advantage of isomeric purification capabilities provided by resonant ionization, making it possible to independently study the decay of each isomer for the first time. The position of the first-excited nu h 11 / 2 neutron-hole state was confirmed via an independent mass spectroscopy experiment performed at the Ion Guide Isotope Separator On-Line facility at the University of Jyv & auml;skyl & auml;. The level scheme of 131 Sn was notably expanded with the addition of 31 new gamma-ray transitions and 22 new excited levels. The gamma-emitting excited levels above the neutron separation energy in 131 Sn were investigated, revealing a large number of states, which in some cases decay by transitions to other neutron-unbound states. Our analysis showed the dependence between the population of these states in 131 Sn and the beta-decaying 131 In state feeding them. Profiting from the isomer selectivity, it was possible to estimate the direct beta feeding to the 3/2+ / 2 + ground and 11/2- / 2 - isomeric states, disentangling the contributions from the three indium parent states. This made possible to resolve the discrepancies in log ft for first-forbidden transitions observed in previous studies, and to determine the beta-delayed neutron decay probability (Pn) P n ) values of each indium isomers independently. The first measurement of subnanosecond lifetimes in 131 Sn was performed in this work. A short T 1 / 2 = 18(4)-ps value was measured for the 1/2+ / 2 + neutron single-hole 332-keV state, which indicates an enhanced l-forbidden M 1 behavior for the nu 3 s - 1 1/2 / 2 -> nu 3 d - 13 / 2 transition. The measured half-lives of high-energy states populated in the beta decay of the (21/2+) / 2 + ) second isomeric state ( 131 m 2 In) provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states analogous to those observed in the doubly-magic 132 Sn.

The very neutron-deficient strongly deformed 117Cs nucleus has been studied using the 58Ni(64Zn, 1 alpha 1p) reaction and JUROGAM 3 gamma -ray detector array coupled to the MARA recoil-mass separator. Three previously known and three newly identified rotational bands were observed up to very high spin and excitation energy. All bands are firmly assigned to 117Cs based on measured mass spectra and interconnecting transitions. The ground-state spin and parity are suggested based on the systematics of low-lying states in odd-even cesium nuclei. The systematics of bandheads in cesium nuclei reveal maximum collectivity and deformation is reached for neutron numbers 64-66, corresponding to the middle of the N = 50-82 magic shell. The rotational frequencies of the first and second crossings in the different bands are similar to those observed in the corresponding bands in the neighboring 119Cs nucleus, suggesting similar deformations of the two nuclei, but enhanced softness in 117Cs. Particle number conserving cranked shell model calculations describe the observed band structures well.

Excited states in the neutron-deficient nuclide Hf155 have been investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The Hf155 nuclei were produced in fusion-evaporation reactions induced by beams of 295 and 315 MeV Ni58 ions bombarding an isotopically enriched Pd102 target and separated using the recoil mass separator MARA. An isomeric state having a half-life of 510(30) ns was discovered and is interpreted as a seniority υ=3, (πh11/22⊗νf7/2)27/2− configuration. The γ-ray transitions emitted in the deexcitation of the isomeric state to the ground state were identified and a level scheme was constructed, from which the excitation energy of the isomer was determined to be 2581.5(10) keV. A B(E2) value of 0.45(3) W.u. was deduced for the 105.4 keV transition depopulating the isomeric state. The deduced level scheme and B(E2) value are compared with systematics and shell-model calculations. Published by the American Physical Society 2024

Excited states in the 70 Kr and 70 Br nuclei were populated via the 40 Ca( 32 S , 2n) n ) 70 Kr and 40 Ca( 32 S , pn ) 70 Br fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyv & auml;skyl & auml;. The 2+--> + --> 0+ + and 4+ + --> 2+ + transitions in 70 Kr have been found to be 881(1) keV and (tentatively) 1037(2) keV, respectively. Several new gamma-ray transitions were also identified in 70 Br, and the T = 1 band has been tentatively extended up to J pi pi = 10+. + . The newly observed transitions in 70 Kr and 70 Br resolve discrepancies in the previously reported results for these nuclei. The experimental Coulomb, triplet, and mirror energy differences are compared with the results of two independent shell-model calculations. The comparisons aim to investigate the shape evolution and the role of the isospin breaking interactions in this mass region.

Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.

The first in-beam gamma-ray spectroscopic study of the neutron-deficient actinium isotopes 211,213Ac has been carried out at the Accelerator Laboratory of the University of Jyv & auml;skyl & auml; using a highly selective recoil-decay tagging method with the JUROGAM 3 germanium-detector array and MARA separator. The nuclei of interest were produced using the 175 Lu( 40 Ar , 4n) 211 Ac and 180 Hf( 37 Cl , 4n) 213 Ac fusion-evaporation reactions. Excited states in 211 Ac were observed for the first time. In 211 Ac and 213 Ac low-lying core-excited states whose excitation energies follow the systematic trends of their respective core states in even-even isotones 210 Ra and 212 Ra were identified. Additionally, we were able to extend the level scheme of 211 Ra, which was also produced in the 40 Ar + 175 Lu reaction. We also remeasured the half-lives of the ground states of these nuclei and also that of the ( 13 / 2 + ) isomeric state of 211 Ra.

A detailed β-decay study of the low- and high-spin states in Bi216 has been performed at the ISOLDE Decay Station at the CERN-ISOLDE facility. In total, 48 new levels and 83 new transitions in the β-decay daughter Po216 were identified. Shell-model calculations for excited states in Bi216 and Po216 were performed using the H208 and the modified Kuo-Herling particle effective interactions. Based on the experimental observations and the shell-model calculations, the most likely spin and parity assignments for the β-decaying states in Bi216 are (3−) and (8−), respectively. Published by the American Physical Society 2024

Excited states above the 9^+ isomer in the odd-odd N = Z nucleus ^66 As were studied by employing the ^40 Ca( ^28 Si, pn) fusion-evaporation reaction at the Accelerator Laboratory of the University of Jyväskylä, Finland. A key method in this study was the use of conversion electrons emitted in the de-excitation of the isomeric state in ^66 As as a tag for prompt γ rays. Several new states have been added to the ^66 As level scheme, which was extended up to a tentative spin of 23 ħ . The previously reported even-spin yrast band has been reassigned to have odd spin values. The odd-spin states above the 9^+ isomer are compared with shell-model calculations using the jj44b and JUN45 interactions. Additionally, the recoil- β tagging efficiency of the recently developed scintillator detector named Tuike has been determined experimentally for the first time.

A segmented High-Purity Germanium (HPGe) detector with a thin front segment together with various active and passive shield configurations was simulated with the aim of reducing the level of background events in lung counting applications. Eight different detector models were tested in a Geant4 simulation environment in a scenario where inhaled 241Am activity was deposited in the lungs of an ICRP adult reference computational phantom. In lung counting measurements, the Compton continuum in the spectrum is generated by the natural and man-made radionuclides inside the human body and the natural background radiation from the environment. The reduction in Minimum Detectable Activity (MDA) using the segmented HPGe detector combined with an active shield compared to a model with a single germanium crystal was investigated. A reduction in MDA up to 30% and 66% was obtained for internal and external sources, respectively. The results show that the detection limit and/or the measurement time in lung counting can be reduced using such a detector configuration. Furthermore, combining the segmented HPGe detector with an active shield would be particularly useful in field measurements.

Competing configurations, assigned with three different shapes, are mixed at low angular momentum in the neutron-deficient 188Pb nucleus. Here, we present a simultaneous conversion electron and γ-ray in-beam spectroscopic precision measurement employing the sage spectrometer. The level energy of the first excited state, 02+, has been determined at 591(1)keV through direct measurement of conversion electrons. By using the intensity of the observed 02+→01+ transition to the ground state, the feeding of the 02+ state has been determined for the first time, which suggests the 02+ state is the head of the predominantly prolate band. The compositions of the 42+→41+ and 22+→21+ inter-band transitions have been determined, indicating configuration mixing between the bands.