This study investigates the V-51 + Tb-159 -> Ra-210* reaction through measurements of both the entrance-channel barrier distribution and detailed excitation functions for the xn, pxn, and axn channels over a wide energy range. This research extends systematic studies of reactions involving beams heavier than Ca-48 on deformed heavy targets, linking cross section measurements to the side-collision configuration effects observed in superheavy nuclei synthesis. Additionally, a significant enhancement of channels with charged-particle emission is observed compared to the neutron exit channels, with the alpha 3n channel yielding a peak cross section of 41.7 +/- 5.0 mu b at E-c. m. = 177.7 +/- 1.5 MeV, an order of magnitude higher than 4.7 +/- 1.5 mu b measured at the peak of the 3n exit channel at E-c. m. = 162.5 +/- 1.5 MeV. Comparisons with reactions using the same target but different projectiles, Ca-48 and Ti-50, which do not exhibit such enhancement, are discussed. The analysis, interpretation, and comparison with theoretical calculations are performed using the CCFULL code and a statistical model.

This study of isomeric states in 255No was performed with the GABRIELA detector array at the focal plane of the SHELS recoil separator. The 208Pb(48Ca, xn)256-xNo fusion-evaporation reaction was used to produce nobelium isotopes with a beam energy optimized for the one-neutron and two-neutron evaporation channels. These nobelium isotopes were studied by decay spectroscopy leading to the identification of isomeric states in 255No by means of the calorimetric method. In order to isolate the radioactive decays of 255No from the more numerous decays of 254No, the characteristic signal of the internal decay of the daughter 251Fm was used as a tag. Under these conditions, the decay of four isomeric states was observed. They are interpreted as high-K structures decaying in cascade. The first isomeric state is assigned to a v[725] 11 - neutron one quasiparticle (qp) configuration, in good agreement with the trend of this state in the neighboring isotones. The second and the third ones were attributed to three-qp 21/2+ and 27/2+ states and are interpreted as resulting from the coupling of the same v[725] 11 - one-qp configuration with the 2{[624] 9 + circle times [521] 1 -}5- and with the 2{[624] 9 + circle times [514] 7 -}8- two-qp configurations, respectively. According to its excitation energy E* 2.5 MeV, the fourth isomeric state should have a five-qp structure, which requires more statistics to be detailed.

Very heavy nuclei owe their stability against spontaneous fission to quantum shell effects, which depend on the local density of single-particle states. The height but also the width and the structure of the barrier in multi-dimensional deformation space determine the fission half-lives. Other effects come into play, such as the conservation of quantum numbers and superfluidity or stiffness of the system in the fission process. This is why odd nuclei have longer fission partial half-lives with respect to their even neighbours and also why multi-quasi-particle states, such as high-K states, are thought to be more stable against fission than the ground state. We will report here on two different fission studies carried out with the GABRIELA detector array at the focal plane of the recoil separator SHELS. The first study concerns the fission properties of 253Rf, the most neutron deficient Rf isotope known to date. The second study focusses on a new measurement of the fission hindrance of the known 8- isomer in 254No.

The measurement of the production cross sections of exotic neutron -rich heavy nuclei, in the uranium region, in the vicinity of the N = 152 deformed shell gap was carried out via multinucleon transfer reactions of 238U + 238U at 7.193 and 6.765 MeV/A using the VAMOS++ magnetic spectrometer coupled to the AGATA and ID-Fix photon detection arrays. This article reports on the status of the VAMOS++ data analysis and results on the population of the strongest (+/- 1n) transfer channels observed from the decay of long-lived products after irradiation.

The structure of the 102254No152 nucleus has been studied for more than 20 years: the last publications on its decay spectroscopy are from LBNL [1], GSI [2], JYFL [3] and ANL [4]. Four decay schemes featuring two isomers have been published and are interpreted differently in terms of excitation energy and decay scheme of the 2 nd isomer and configuration assignments of both K-isomers. These discrepancies have triggered new experiments including this one, performed with the GABRIELA [5, 6] array, at the focal plane of the SHELS [7] separator at the FLNR, Dubna. The first part of this proceeding will present the experimental setup and the analysis techniques used to reveal the electromagnetic decay of the known isomers in 254No. The second part will focus on the new results obtained with more than 1 million 254No nuclei implanted in the focal plane detector. In particular, the internal conversion electron spectrum observed in the decay of the 8− K-isomer has revealed the presence of a strong transition, most likely E0, suggesting low-lying shape coexistence in this nucleus as predicted in [8, 9]. The γ-ray spectrum obtained from the decay of the short-lived 170 μs isomer has revealed new γ-ray lines putting in doubt the previous interpretations about this isomer decay.

The new neutron-deficient isotope $$^{249}$$ No was synthesized for the first time in the fusion-evaporation reaction $$^{204}$$ Pb( $$^{48}$$ Ca,3n) $$^{249}$$ No. After separation, using the kinematic separator SHELS, the new isotope was identified with the GABRIELA detection system through genetic correlations with the known daughter and granddaughter nuclei $$^{245}$$ Fm and $$^{241}$$ Cf. The alpha-decay activity of $$^{249}$$ No has an energy of 9129(22) keV and half-life 38.3(2.8) ms. An upper limit of 0.2% was measured for the fission branch of $$^{249}$$ No. Based on the present data and recent information on the decay properties of $$^{253}$$ Rf and aided by Geant4 simulations, the ground state of $$^{249}$$ No is assigned the 5/2 $$^+$$ [622] neutron configuration and a partial decay scheme from $$^{253}$$ Rf to $$^{245}$$ Fm could be established. The production cross-section was found to be $$\sigma $$ (3n)=0.47(4) nb at a mid-target beam energy of 225.4 MeV, which corresponds to the maximum of the calculated excitation function. Correlations of the $$^{249}$$ No alpha activity with subsequent alpha decays of energy 7728(20) keV and half-life $$1.2_{-0.4}^{+1.0}$$ min provided a firm measurement of the electron-capture or $$\beta ^{+}$$ branch of $$^{245}$$ Fm to $$^{245}$$ Es. The excitation function for the 1n, 2n and 3n evaporation channels was measured. In the case of the 2n-evaporation channel $$^{250}$$ No, a strong variation of the ground state and isomeric state populations as a function of bombarding energy could be evidenced.

Background: An analysis of recent experimental data [J. Khuyagbaatar et al., Phys. Rev. C 104, L031303 (2021)] has established the existence of two fissioning states in 253Rf: The ground state anda low-lying isomeric state, most likely involving the same neutron single-particle configurations as in the lighter isotone 251No. The ratio of fission half-lives measured in 253Rf was used to predict the fission properties of the 1/2+ isomeric state in 251No and draw conclusions as to the stability against fission of even lighter Rf systems. Purpose: This paper focuses again on the fission properties of 253Rf and their impact on the stability of other neutron-deficient isotopes, using new and improved data collected from two experiments performed at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. Methods: 253Rf and 251No nuclei were produced in fusion-evaporation reactions between 50Ti and 48Ca ions and the atoms of isotopically enriched 204Pb targets. The nuclei of interest were separated from the background of other reaction products and implanted into a Si detector where their characteristic radioactive decays were observed through position and time correlations between detected signals. Results: Two fission activities with half-lives of 52.8(4.4) mu s and 9.9(1.2) ms were measured in the case of 253Rf, confirming the results of J. Kkuyagbaatar et al. A third state, at much higher excitation energy, was also observed through the detection of its electromagnetic decay to the 52.8-mu s state. This observation leads to the opposite quantum-configuration assignments for the fissioning states as compared to the ones established by Khuyagbaatar et al., namely, that the higher-spin state has the shortest fission half-life. This inversion of the ratio of fission hindrances between the low- and high-spin states is corroborated in the isotone 251No by the nonobservation of any substantial fission branch from the low-spin isomer. Conclusions: In going from 251No to 253Rf, the fission half-life of a specific quantum state is found to decrease by close to seven orders of magnitude. Large reductions of more than five and six orders of magnitude are also found between the fission half-lives of the ground states of 252No and 254Rf and between those of 254No and 256Rf, respectively, pointing to a similar rate of decrease inthe fission barrier as one removes neutrons from both systems. Following this trend to the N = 148 isotones, our results suggest that the fission half-life of the ground state of the next even-even Rf isotope 252Rf will be extremely short, possibly at the limit of existence of an atom.

An experiment on the study of the ^246Fm spontaneous fission was conducted using the SHELS separator. The isotope was synthesized in the complete fusion reaction of ^40Ar beam ions and ^208Pb target nuclei. The neutron yields of ^246Fm spontaneous fission (ν = 3.79±0.30, σ^2_ν = 2.1) were obtained using the SFiNx detector system. The multiplicity distribution of emitted prompt neutrons was restored using the Tikhonov method of statistical regularisation (ν_r = 3.79±0.20, σ^2_ν r = 2.8). The spontaneous fission branching ratio (b_SF = 0.061±0.005) and the half-life (T_1/2 = 1.50^+0.08_-0.07 s) of the isotope were determined. The experimental data were compared with scission point model predictions. Excellent convergence was observed in the average number of neutrons per spontaneous fission process. However, the forms of the experimental and model prompt neutron multiplicity distributions differ significantly.

An experiment on the study of the $$^{246}$$ Fm spontaneous fission was conducted using the SHELS separator. The isotope was synthesized in the complete fusion reaction of $$^{40}$$ Ar beam ions and $$^{208}$$ Pb target nuclei. The neutron yields of $$^{246}$$ Fm spontaneous fission ( $${\overline{\nu }} = 3.79\pm 0.30$$ , $$\sigma ^{2}_{\nu } = 2.1$$ ) were obtained using the SFiNx detector system. The multiplicity distribution of emitted prompt neutrons was restored using the Tikhonov method of statistical regularisation ( $${\overline{\nu }}_{r} = 3.79\pm 0.20$$ , $$\sigma ^{2}_{\nu r} = 2.8$$ ). The spontaneous fission branching ratio ( $$b_{SF} = 0.061\pm 0.005$$ ) and the half-life ( $$T_{1/2} = 1.50^{+0.08}_{-0.07}$$ s) of the isotope were determined. The experimental data were compared with scission point model predictions. An agreement was observed in the average number of neutrons per spontaneous fission process. However, the forms of the experimental and model prompt neutron multiplicity distributions differ significantly.

Isomeric states in $^{256}\mathrm{No}$ were investigated using internal conversion electron and $\ensuremath{\gamma}$-ray spectroscopy with the GABRIELA detection system at the focal plane of the SHELS recoil separator, at the Flerov Laboratory for Nuclear Research (FLNR, JINR, Dubna). The nuclei of interest were produced using the highly asymmetric fusion-evaporation reaction $^{238}\mathrm{U}(^{22}\mathrm{Ne},4n)^{256}\mathrm{No}$. The emission of internal conversion electrons and $\ensuremath{\gamma}$ rays occurring between a $^{256}\mathrm{No}$ implantation and a subsequent $\ensuremath{\alpha}$-decay event were studied, resulting in the observation of high-$K$ isomerism in this nobelium isotope. The nature of the isomeric states is discussed in terms of possible two- and four-quasiparticle structures.

Isomeric states in No-256 were investigated using internal conversion electron and gamma-ray spectroscopy with the GABRIELA detection system at the focal plane of the SHELS recoil separator, at the Flerov Laboratory for Nuclear Research (FLNR, JINR, Dubna). The nuclei of interest were produced using the highly asymmetric fusion-evaporation reaction U-238(Ne-22, 4n) No-256. The emission of internal conversion electrons and gamma rays occurring between a No-256 implantation and a subsequent alpha-decay event were studied, resulting in the observation of high-K isomerism in this nobelium isotope. The nature of the isomeric states is discussed in terms of possible two- and four-quasiparticle structures.