Fusion-evaporation Reaction Research Articles

High-spin states and possible chirality in odd-odd Ag110

High-spin states of $^{110}\mathrm{Ag}$ have been studied by in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques using the fusion-evaporation reaction $^{110}\mathrm{Pd}$($^{7}\mathrm{Li}, \ensuremath{\alpha}3\mathrm{n}$)$^{110}\mathrm{Ag}$ at a beam energy of 46 MeV. The previously known level scheme of $^{110}\mathrm{Ag}$ is significantly extended and modified with the addition of 50 new $\ensuremath{\gamma}$ transitions and 21 new levels. In total, four new rotational bands are observed, among which two negative-parity coupled bands are assigned to the four-quasiparticle $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}{({g}_{7/2}/{d}_{5/2})}^{2}$ configuration based on the quasiparticle alignment analysis and cranked shell model calculations. The properties of both bands show general agreement with the fingerprints of chiral rotation, and thus such two negative-parity bands are suggested to be candidates for near degenerate chiral doublet bands. A new decoupled $\mathrm{\ensuremath{\Delta}}I=2$ band decaying directly to the yrast band is established, and probably results from one-particle-one-hole (1p-1h) proton excitation from the ${g}_{9/2}$ orbital to the ${g}_{7/2}$ orbital across the large $Z=50$ shell gap, i.e., the 2p2h $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration. In addition to, a weak positive-parity sequence consisting of magnetic dipole $(M1)$ and no $E2$ crossover transitions is also identified in the present work.

Spectroscopy along Flerovium Decay Chains: Discovery of ^{280}Ds and an Excited State in ^{282}Cn.

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1) MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518 μs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

Proton therapy range verification method via delayed γ-ray spectroscopy of a molybdenum tumour marker

In this work, a new method of range verification for proton therapy (PT) is experimentally demonstrated for the first time. If a metal marker is implanted near the tumour site, its response to proton activation will result in the emission of characteristic γ rays. The relative intensity of γ rays originating from competing fusion-evaporation reaction channels provides a unique signature of the average proton energy at the marker, and by extension the beam’s range, in vivo and in real time. The clinical feasibility of this method was investigated at the PT facility at TRIUMF with a proof-of-principle experiment which irradiated a naturally-abundant molybdenum foil at various proton beam energies. Delayed characteristic γ rays were measured with two Compton-shielded LaBr3 scintillators. The technique was successfully demonstrated by relating the relative intensity of two γ-ray peaks to the energy of the beam at the Mo target, opening the door to future clinical applications where the range of the beam can be verified in real time.

Fine structure of α decay in 222Pa * *Supported by the National Natural Science Foundation of China (11805289, 11775316), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34010000) and the National Key R&D Program of China (2018YFA0404402)

With the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system, the fine structure of the decay for Pa was studied. The nuclides were produced through the 1p3n evaporation channel via the heavy-ion induced fusion evaporation reaction Ar + W. Based on the ER- - - and - correlation measurement, three new decays were observed in addition to the three branches known previously. The one with the largest decay energy was regarded as the ground state to ground state transition. The newly measured decay properties of Pa were examined in a framework of reduced width.

Calculation of the shape of energy-ordered spectra for investigations of the nuclear continuum

The nuclear continuum may potentially be investigated by means of fusion-evaporation reactions in combination with the $Hk$ technique. The $\ensuremath{\gamma}$ radiation in such experiments can be analyzed using energy ordering which produces complex spectra. A method for computing the shape of the energy-ordered spectra is presented and benchmarked by reproducing simulated data. The spectrum shape computation is applied to experimentally relevant cases and is used for extracting the level density parameter from simulations. Furthermore, the calculation shows to be useful for the characterization of nuclear phase transitions.

GEANT4 simulation of a range verification method using delayed γ spectroscopy of a 92Mo marker

In this work, we propose a novel technique for in-vivo proton therapy range verification. This technique makes use of a molybdenum hadron tumour marker, implanted at a short distance from the clinical treatment volume. Signals emitted from the marker during treatment can provide a direct measurement of the proton beam energy at the marker’s position. Fusion-evaporation reactions between the proton beam and marker nucleus result in the emission of delayed characteristic γ rays, which are detected off-beam for an improved signal-to-noise ratio. In order to determine the viability of this technique and to establish an experimental setup for future work, the Monte Carlo package GEANT4 was used in combination with ROOT to simulate a treatment scenario with the new method outlined in this work. These simulations show that the intensity of delayed γ rays produced from competing reactions yields a precise measurement of the range of the proton beam relative to the marker, with sub-millimetre uncertainty.

Evolution of collectivity and shape transition in Zn66

Excited states in $^{66}\mathrm{Zn}$ were investigated through the in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques using the $^{52}\mathrm{Cr}(^{18}\mathrm{O}, 2p2n$) fusion-evaporation reaction at a beam energy of 72.5 MeV. The $\ensuremath{\gamma}$-rays emitted by the de-exciting nuclei were recorded in coincidence mode using the 14 Compton suppressed Ge clover detectors of the Indian National Gamma Array. With 14 new transitions being identified, the level scheme of $^{66}\mathrm{Zn}$ has been extended up to the excitation energy $\ensuremath{\approx}12.3\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and spin $\ensuremath{\approx}17\phantom{\rule{0.28em}{0ex}}\ensuremath{\hbar}$. A rotational band, associated with the two quasineutrons from the $1{g}_{9/2}$ orbital, has been found to exhibit a band crossing with the ground-state band at a spin of $6\ensuremath{\hbar}$. The evolution of the collectivity and shape transition in this nucleus have been discussed in the framework of the total Routhian surface calculations and in comparison with the neighboring $^{68,70}\mathrm{Ge}$ nuclei.

Search for elements 119 and 120

A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab = 281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability. (Less)

The Super Separator Spectrometer (S3) for the SPIRAL2 facility

The Super Separator Spectrometer S3 is, with the NFS (Neutrons For Science) facility, a major experimental system developed for SPIRAL2. It is designed for very low cross section experiments at low (<15MeV/u) energy. It will receive the very high intensity (more than 1pμA) stable ion beams accelerated by the superconducting LINAG accelerator of SPIRAL2. S3 will be notably used for the study of rare nuclei produced by fusion evaporation reactions, such as superheavy elements and neutron-deficient isotopes. Such experiments require a high transmission of the products of interest but also a separation of these nuclei from unwanted species. Hence S3 must have a large acceptance but also a high selection power including physical mass resolution. These properties are reached with the use of seven large aperture superconducting quadrupole triplets which include sextupolar and octupolar corrections in a two - stage separator (momentum achromat followed by a mass spectrometer) that can be coupled to the SIRIUS implantation-decay spectroscopy station or to the REGLIS3 gas cell with laser ionization to provide very pure beams for low energy experiments. S3 is now in the construction phase. We will present the scientific objectives of S3 as well as the current status of the facility and its different elements.

Lifetimes of core-excited states in semi-magic ^{95}mathrm {Rh}

Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus ^{95}mathrm {Rh}. The fusion-evaporation reaction ^{58}Ni(^{40}Ca, 3p) was used to populate high-spin states in ^{95}mathrm {Rh} at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6;mathrm {mg/cm}^2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.

Lifetime measurements in 104Pd

High spin states in 104Pd were populated via 94Zr(13C, 3nγ) fusion-evaporation reaction at a beam energy of 55 MeV. The Indian National Gamma Array was utilized to detect the de-exciting γ-rays. Lifetimes of states in the negative parity bands have been determined using the Doppler shift attenuation method. The present lifetime results suggest a moderate quadrupole deformation (β 2 ≈ 0.2) for the negative parity bands. The Woods–Saxon total Routhian surface calculations have also been carried out which predicted a similar deformation for these bands. In addition, lifetimes of states in the positive parity band have also been determined. Present results found in agreement with the earlier reported values of lifetimes and hence agreed with the antimagnetic rotational character of the band as interpreted earlier.

Lifetime measurements of Er162 : Evolution of collectivity in the rare-earth region

Lifetimes of low-lying yrast states in $^{162}\mathrm{Er}$ are measured using the electronic $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ fast-timing technique. Excited states were populated in a $^{154}\mathrm{Sm}(^{12}\mathrm{C},4n)^{162}\mathrm{Er}$ fusion-evaporation reaction and $\ensuremath{\gamma}$ rays were detected in a combined setup of high purity germanium and ${\mathrm{LaBr}}_{3}$(Ce) scintillation detectors. The lifetimes of the ${4}_{1}^{+}$ and ${6}_{1}^{+}$ states are determined for the first time and the lifetimes of the ${2}_{1}^{+}$ and ${7}^{\ensuremath{-}}$ states are remeasured with higher precision. Reduced transition probabilities are extracted and well reproduced by theoretical calculations in the framework of the confined $\ensuremath{\beta}$ soft model and the interacting boson model.

Spectroscopy of P30 and the abundance of Si29 in presolar grains

The astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction is expected to play a key role in determining the final $^{29}\mathrm{Si}$ yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion $^{28}\mathrm{Si}(^{3}\mathrm{He},p$) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus $^{30}\mathrm{P}$ that govern the rate of the astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction. In particular, $\ensuremath{\gamma}$ decays were observed from resonances up to ${E}_{r}=500\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, and key resonances at 217 and 315 keV have now been identified as ${2}^{+}$ and ${2}^{\ensuremath{-}}$ levels, respectively. The present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of $^{29}\mathrm{Si}$ ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.

Spectroscopic investigation of complex nuclear excitations in Ga66

In-beam spectroscopic technique using the fusion evaporation reaction $^{52}\mathrm{Cr}(^{18}\mathrm{O},1p3n)$, at a beam energy of 72.5 MeV, was employed to explore the structural phenomena in $^{66}\mathrm{Ga}$, mainly at intermediate and high spins. The experimental setup involved an array of 14 Compton suppressed Ge clover detectors, placed around the target position to detect emitted $\ensuremath{\gamma}$ rays from excited states. A new level scheme has been proposed, which is enriched with more than 20 new transitions and is extended up to an excitation energy $\ensuremath{\approx}12$ MeV. A few observed intermediate spin states of $^{66}\mathrm{Ga}$ are discussed in the framework of coupling of single-particle configurations with the vibrational core of $^{64}\mathrm{Zn}$. Shell model calculations have also been performed with two different interactions, viz., jj44bpn and jun45pn, for the interpretation of the observed level structure in $^{66}\mathrm{Ga}$.

Indication of γ-vibration in 123,125,127I

High spin states in 127I were populated via 124Sn(7Li, 4nγ) fusion-evaporation reaction at Ebeam = 33 MeV. Level scheme of 127I has been updated by placing new γ-rays and also by confirming the spin/parity of several energy levels. Two new levels at Ex = 2628 and 3199 keV have been identified which are found to decay into the negative parity πh11/2 band. These two states and two earlier reported states at 3502 and 3989 keV have been interpreted as the γ-vibrational states on the basis of their decay pattern. Two positive parity three-quasiparticle bands above Iπ = 23/2+ states at 2901 and 3060 keV have been identified to be a possible candidate of chiral band. A comparison in the isotopic and isotonic chains reveals the possible existence of γ-vibration and chiral rotation in 123–127I.

High-spin states of 218Th

High-spin states in the N = 128 nucleus 218Th have been investigated following fusion–evaporation reactions, using the recoil-decay tagging technique. Due to the short-lived nature of the ground state of 218Th prompt γ rays have been correlated with the α decay of the daughter nucleus 214Ra. The level scheme representing the decay of excited states has been extended to (16+) with the observation of six previously unreported transitions. The observations are compared with the results of shell model calculations and within the context of the systematics of neighbouring nuclei.

Production mechanism of proton-rich actinide isotopes in fusion reactions and via multinucleon transfer processes

Within the dinuclear system model, unknown neutron-deficient isotopes Np, Pu, Am, Cm, Bk, Cf, Es, Fm are investigated in $^{40}$Ca, $^{36,40}$Ar, $^{32}$S, $^{28}$Si,$^{24}$Mg induced fusion-evaporation reactions and multinucleon transfer reactions with radioactive beams $^{59}$Cu,$^{69}$As,$^{90}$Nb,$^{91}$Tc, $^{94}$Rh, $^{105,110}$Sn, $^{118}$Xe induced with $^{238}$U near Coulomb barrier energies. The production cross sections of compound nuclei in the fusion-evaporation reactions and fragments yields in the multinucleon transfer reactions are calculated within the model. A statistical approach is used to evaluate the survival probability of excited nuclei via the both reaction mechanisms. A dynamical deformation is implemented into the model in the dissipation process. It is found that charge particle channels (alpha and proton) dominate in the decay process of proton-rich nuclides and the fusion-evaporation reactions are favorable to produce the new neutron-deficient actinide isotopes. The total kinetic energies and angular spectra of primary fragments are strongly dependent on colliding orientations.

Lifetime measurements using a plunger device and the EUCLIDES Si array at the GALILEO [formula omitted]-ray spectrometer

The GALILEO γ-ray spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), benefits from intense stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and from radioactive beams to be delivered in the near future by the SPES facility. The spectrometer is complemented with a variety of ancillary devices to allow for nuclear structure and reaction studies. The 4π Si-ball array EUCLIDES coupled to the GALILEO γ-ray spectrometer represents one of the commonly used setup for experiments aiming at spectroscopic studies. High-efficiency detection of light-charged particles in a fusion–evaporation reaction guarantees good discrimination of different reaction channels and provides essential information for the kinematic reconstruction. In this paper we discuss a configuration of the EUCLIDES array developed for the lifetime measurements of nuclear excited states populated in a fusion–evaporation reaction. In such a configuration a part of the EUCLIDES detectors is disassembled allowing for the installation of a plunger device in the reaction chamber. The reduced configuration of EUCLIDES provides high detection efficiency necessary for reliable light charged-particle discrimination. We report on the commissioning experiment focused on the 58Ni(58Ni,3p)113I reaction. The lifetimes of 11/2− and 15/2− states were measured by applying the Recoil Distance Doppler Shift method to be equal to 206(20) ps and 7.9(12) ps correspondingly and were in good agreement with the values cited in the literature. Thus, the combination of the GALILEO and EUCLIDES arrays, and the plunger device has resulted in a powerful experimental setup to determine lifetimes of excited states in neutron-deficient nuclei in the picosecond range.

Shape coexistence in neutron-deficient Hg188 investigated via lifetime measurements

Shape coexistence in the $Z \approx 82$ region has been established in mercury, lead and polonium isotopes. Even-even mercury isotopes with $100 \leq N \leq 106$ present multiple fingerprints of this phenomenon, which seems to be no longer present for $N \geq 110$. According to a number of theoretical calculations, shape coexistence is predicted in the $^{188}$Hg isotope. The $^{188}$Hg nucleus was populated using two different fusion-evaporation reactions with two targets, $^{158}$Gd and $^{160}$Gd, and a beam of $^{34}$S, provided by the Tandem-ALPI accelerators complex at the Laboratori Nazionali di Legnaro. The channels of interest were selected using the information from the Neutron Wall array, while the $\gamma$ rays were detected using the GALILEO $\gamma$-ray array. The lifetimes of the excited states were determined using the Recoil Distance Doppler-Shift method, employing the dedicated GALILEO plunger device. Using the two-bands mixing and rotational models, the deformation of the pure configurations was obtained from the experimental results. The extracted transition strengths were compared with those calculated with the state-of-the-art symmetry-conserving configuration-mixing (SCCM) and five-dimentional collective Hamiltonian (5DCH) approaches in order to shed light on the nature of the observed structures in the $^{188}$Hg nucleus. An oblate, a normal- and a super-deformed prolate bands were predicted and their underlying shell structure was also discussed.

Single-particle and collective excitations in the N=28 isotones Fe54 and Mn53

Author(s): Rudolph, D; Ragnarsson, I; Andreoiu, C; Bentley, MA; Carpenter, MP; Charity, RJ; Clark, RM; Ekman, J; Fahlander, C; Fallon, P; Reviol, W; Sarantites, DG; Seweryniak, D | Abstract: The fusion-evaporation reaction S32+Si28 at 125 MeV beam energy was used to populate high-spin states in the semimagic N=28 nuclei Mn53 and Fe54. With a combination of the Gammasphere spectrometer and ancillary devices including the Microball CsI(Tl) array, extensive high-spin level schemes are derived. They exhibit rotational-like collective structures and competing single-particle excitations. The experimental results are compared with predictions from shell-model calculations, for which the inclusion of isopin-symmetry-breaking terms is found to improve the description. An interpretation of the high-spin states is put forward using cranked Nilsson-Strutinsky calculations, indicative of contributions from collective excitations beyond some 8-MeV excitation energy and highlighting the importance of the g9/2 intruder orbital in this energy range.