Yb Reaction Research Articles

Study of transfer-like fragments for 136Xe+209Bi/176Yb: Prospect for multinucleon transfer reactions at IGISOL

Multinucleon transfer (MNT) reactions have been demonstrated as a promising pathway to produce and study very neutron-rich heavy nuclei, which can enhance our understanding of the nuclear structural features relevant to the r-process. Translead fragments were produced from the MNT reaction approach using 136Xe+209Bi at IGISOL utilizing an MNT gas cell. The 211Bi, 211mPo, 211Po, and 212mPo nuclei have been observed prominently in the α-decay spectrum. The Geant4 simulation, which played a crucial role in optimizing the experimental parameters, reveals broader angular-energy distributions of MNT fragments released from a thick target compared to those observed from the GRAZING and Langevin models for a mono-energetic beam. Comparative yield analyses of MNT fragments for 136Xe+209Bi and 136Xe+176Yb reactions estimated using Geant4 Simulation as well as analytical formula support the production of many neutron-rich unknown mass nuclei in the rare-earth region.

Measurement of the flux-weighted cross-sections for the natYb(γ,xn)175,169,167Yb reactions in the Bremsstrahlung end-point energies of 12–16 MeV and 60–70 MeV

Measurement of the flux-weighted cross-sections for the natYb(γ,xn)175,169,167Yb reactions in the Bremsstrahlung end-point energies of 12–16 MeV and 60–70 MeV

Spectroscopy of a tetrahedral doubly magic candidate nucleus <sup>160</sup><sub>70</sub>Yb<sub>90</sub>

The decay scheme of $^{160}$Yb nucleus populated in the $^{148}$Sm($^{16}$O, 4n)$^{160}$Yb reaction at 90 MeV has been studied. The gamma-coincidence data have been collected by using Indian National Gamma Array (INGA) composed of twenty Compton-suppressed Clover-Germanium detectors. Compared to the prior publications, the level scheme has been significantly modified owing to the observation of triple $\gamma$-coincidences and the measurements of $\gamma$ intensities, R$_{\theta}$ (asymmetry ratio), DCO (Directional Correlation of Oriented States) and IPDCO (Integrated Polarisation Directional Correlation of Oriented States) ratios.
 
 Theoretical results relevant for the exotic shape-coexistence related to the present context are presented and discussed. They illustrate the consequences of the fact that $^{160}$Yb is expected to be a doubly-magic (Z=70 and N=90) tetrahedral-symmetry nucleus as predicted by other authors. The historical criteria of identification of such a symmetry in nuclei are critically revisited in the context of the actual measurement and interpretation of its results and the precise new criteria are formulated employing recent results of the Fukuoka-Strasbourg collaboration.
 
 The experimental results are interpreted and discussed in detail. Limiting values of branching ratios for transitions observed by other authors but unseen in the present work are estimated. The population criteria of the $\beta$ and $\gamma$ vibration bands are revisited and discussed.
 
 Although no indication of the presence of the stable tetrahedral configuration has been obtained, arguments are given towards the possible presence of the $Y_{32}$ (`tetrahedral component') vibrations around the ground-state equilibrium. With the improvement of the spectroscopic information provided by the new data the way is opened for designed experiment(s) based on the unambiguous identification criteria of tetrahedral symmetry presented in this article.

Activation cross-sections of proton induced reactions on natHf in the 38–65 MeV energy range: Production of 172Lu and of 169Yb

In the frame of a systematical study of light ion induced nuclear reactions on hafnium, activation cross sections for proton induced reactions were investigated. Excitation functions were measured in the 38 to 65 MeV energy range for the $^{nat}$Hf(p,xn)$^{180g,177,176,175,173}$Ta, $^{nat}$Hf(p,x)$^{180m,179m,175,173,172,171}$Hf, $^{177g,173,172,171,170,169}$Lu and $^{nat}$Hf(p,x)$^{169}$Yb reactions by using the activation method, combining stacked foil irradiation and off line gamma ray spectroscopy. The experimental results are compared with earlier results in the overlapping energy range, and with the theoretical predictions of the ALICE IPPE and EMPIRE theoretical codes and of the TALYS code reported in the TENDL2015 and TENDL2017 libraries. The production routes of $^{172}$Lu (and its parent $^{172}$Hf) and of $^{169Y}$b are reviewed.

Half-life measurement of the medical radioisotope 177Lu produced from the 176Yb(n,γ) reaction

177 Lu is a medium energy beta-emitter commonly used in Nuclear Medicine for radiotherapeutic applications. In this work, the half-life of 177 Lu has been measured using a re-entrant ionisation chamber over a period of 82 days (approximately 12 half-lives). Unlike the majority of previous studies, the material used in this work was produced via the 176 Yb(n,γ)177 Yb reaction followed by the β-decay to 177 Lu, producing insignificant quantities of 177m Lu. This has resulted in the most precise half-life measurement of 177 Lu to date. A half-life of 6.6430 (11) days has been determined. This value is in statistical agreement with the currently recommended half-life of 6.6463 (15) days (z-score = 1.8).

Non-compound nucleus fission in actinide and pre-actinide regions

In this article, some of our recent results on fission fragment /product angular distributions are discussed in the context of non-compound nucleus fission. Measurement of fission fragment angular distribution in 28Si +176Yb reaction did not show a large contribution from the non-compound nucleus fission. Data on the evaporation residue cross-sections, in addition to those on mass and angular distributions, are necessary for better understanding of the contribution from non-compound nucleus fission in the pre-actinide region. Measurement of mass-resolved angular distribution of fission products in 20Ne +232Th reaction showed an increase in angular anisotropy with decreasing asymmetry of mass division. This observation can be explained based on the contribution from pre-equilibrium fission. Results of these studies showed that the mass dependence of anisotropy may possibly be used to distinguish pre-equilibrium fission and quasifission.

Measurement of (α,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions

The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser–Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the Er(α,n)Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined 162Er(α,n) and 162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.

Ultracold chemistry with alkali-metal–rare-earth molecules

A first principles study of the dynamics of $^6$Li($^{2}$S) + $^6$Li$^{174}$Yb($^2\Sigma^+$)$ \to ^6$Li$_2(^1\Sigma^+$) + $^{174}$Yb($^1$S) reaction is presented at cold and ultracold temperatures. The computations involve determination and analytic fitting of a three-dimensional potential energy surface for the Li$_2$Yb system and quantum dynamics calculations of varying complexities, ranging from exact quantum dynamics within the close-coupling scheme, to statistical quantum treatment, and universal models. It is demonstrated that the two simplified methods yield zero-temperature limiting reaction rate coefficients in reasonable agreement with the full close-coupling calculations. The effect of the three-body term in the interaction potential is explored by comparing quantum dynamics results from a pairwise potential that neglects the three-body term to that derived from the full interaction potential. Inclusion of the three-body term in the close-coupling calculations was found to reduce the limiting rate coefficients by a factor of two. The reaction exoergicity populates vibrational levels as high as $v=19$ of the $^6$Li$_2$ molecule in the limit of zero collision energy. Product vibrational distributions from the close-coupling calculations reveal sensitivity to inclusion of three-body forces in the interaction potential. Overall, the results indicate that a simplified model based on the long-range potential is able to yield reliable values of the total reaction rate coefficient in the ultracold limit but a more rigorous approach based on statistical quantum or quantum close-coupling methods is desirable when product rovibrational distribution is required.

Investigation of (d,x) nuclear reactions on natural ytterbium up to 24 MeV

Production cross-sections of the natYb(d,x)169,170,171,172,173,174m,174,176m,177gLu and 169,175,177Yb reactions have been measured from a 24-MeV deuteron energy down to their respective thresholds by using a stacked-foil activation technique combined with high resolution γ-ray spectrometry. Our new experimental data extended the experimental database toward the lower energy region for 169Yb, 171Lu, 172Lu, and 176mLu, and the higher region for 174Lu, 176mLu, and 177Yb. An overall good agreement is found with some of the earlier measurements, whereas a partial agreement is obtained with the theoretical data extracted from the TENDL-2013 library. The (d,p) channel contribution underestimated by the TENDL-2013 library is successfully reproduced in the global renormalization by Ignatyuk for the FENDL-3.0 library. The production cross-sections of 175Yb available in the literature were revised based on the latest γ-ray intensity adopted in 2004. Physical thick target yields for the investigated reaction products were also deduced and compared with the directly measured ones in the literature. The derived thick target yields for 173Lu and 174gLu are higher than the directly measured ones by Dmitriev et al. at 22MeV. The deduced yield curves indicate that a low energy (<11MeV) cyclotron and a highly enriched 176Yb target could be used to obtain 177gLu with negligible impurity from 177mLu.

Fission fragment mass distribution in the13C+182W and176Yb reactions

Shell effects can play a prominent role in fission fragment mass distributions. For lighter systems in the region of A~180-200, mass distributions were generally expected to be symmetric. However, a recent experiment showed that fission of 180 Hg following electron capture of 180 Tl leads to an asymmetric mass split. Recent calculations by various groups indicate that the mechanism of asymmetric fission could be very different in this mass region compared to the actinide region. To investigate the role of shell effects in this mass region, we have measured the fission fragment mass distribution for the 13 C+182 W,176 Yb reactions forming the compound nuclei 195 Hg and 189 Os respectively, at lab bombarding energies of 60, 63 and 66 MeV using the CUBE detector setup located at the ANU Heavy Ion Accelerator Facility. The experimental data were fitted with single and double Gaussian distributions. The results indicate an asymmetric mass split for 195 Hg, whereas for 189 Os, the mass distribution is well fitted with a single Gaussian distribution.

Neutron-induced fission cross sections of short-lived actinides with the surrogate reaction method

Determination of neutron-capture cross sections of short-lived nuclei is opening the way to understand and clarify the properties of many nuclei of interest for nuclear structure physics, nuclear astrophysics and particularly for transmutation of nuclear wastes. The surrogate approach is well-recognized as a potentially very useful method to extract neutron cross sections for low-energy compound-nuclear reactions and to overcome the difficulties related to the target radioactivity. In this work we will assess where we stand on these neutron-capture cross section measurements and how we can achieve the short-lived Minor Actinides nuclei involved in the nuclear fuel cycle. The CENBG collaboration applied the surrogate method to determine the neutron-capture cross section of 233 Pa (T 1/2 = 27 d). The 233 Pa (n,γ ) cross section is then deduced from the measured gamma decay probability of 234 Pa compound nucleus formed via the surrogate 232 Th (3 He ,p) reaction channel. The obtained cross section data, covering the neutron energy range 0.1 to 1 MeV, have been compared with the predictions of the Hauser-Feshbach statistical model. The importance of establishing benchmarks is stressed for the minor actinides region. However, the lack of desired targets led us to propose recently the 174 Yb (3 He ,pγ ) reaction as a surrogate reaction for the (n,γ ) predetermined benchmark cross section of 175 Lu. An overview of the experimental setup combining gamma ray detectors such as Ge and C6D6 in coincidence with light charged particles Δ E-E Telescopes will be presented and preliminary results will be discussed.

Prolate and Oblate Shape Coexistence in 188Pt

A standard in-beam γ-spectroscopy experiment for 188Pt is performed via the 176 Yb(18O, 6n) reaction at beam energies of 88 and 95MeV, and the level scheme for 188Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in 188Pt by applying the projected shell model. The rotation alignment of i13/2 neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10h, indicating likely a new type of shape phase transition along the yrast line in 188Pt.

Observation of a superdeformed band in 190Pb

A new superdeformed band, identified in data from the24Mg+173Yb reaction, is assigned to192Pb on the basis of excitation function and coincidence results. Properties of this band are discussed briefly, and compared to the superdeformed bands known in other Pb nuclei.

Population of superdeformed excitations inPo198

Superdeformed excitations in {sup 198}Po were studied using the {sup 174}Yb({sup 29}Si,5n) reaction and {gamma}-ray spectroscopy with Gammasphere. Energy-spin entry distributions for populating normal (ND) and superdeformed (SD) excitations were extracted by gating on discrete ND and SD transitions, respectively. Information on the SD excitation energy, SD well depth, and fission barrier in {sup 198}Po was deduced.

Level densities andγ-ray strength functions inYb170,171,172

Level densities and radiative strength functions in $^{171}$Yb and $^{170}$Yb nuclei have been measured using the $^{171}$Yb($^3$He,$^3$He$^\prime\gamma$)$^{171}$Yb and $^{171}$Yb($^3$He,$\alpha\gamma$)$^{170}$Yb reactions. New data on $^{171}$Yb are compared to a previous measurement for $^{171}$Yb from the $^{172}$Yb($^3$He,$\alpha\gamma$)$^{171}$Yb reaction. Systematics of level densities and radiative strength functions in $^{170,171,172}$Yb are established. The entropy excess in $^{171}$Yb relative to the even-even nuclei $^{170,172}$Yb due to the unpaired neutron quasiparticle is found to be approximately 2$k_B$. Results for the radiative strength function from the two reactions lead to consistent parameters characterizing the ``pygmy'' resonances. Pygmy resonances in the $^{170,172}$Yb populated by the ($^3$He,$\alpha$) reaction appear to be split into two components for both of which a complete set of resonance parameters are obtained.

STRUCTURE OF POLONIUM ISOTOPES AT HIGH SPIN WITH RFD + EUROBALL IV

An experiment has been performed to investigate the structure at high spin of the neutron-deficient polonium isotopes using the Recoil Filter Detector coupled to the EUROBALL IV gamma array. High spin states of 200,201 Po have been populated by the 30 Si +176 Yb reaction at a beam energy of 160 MeV. We report here the performances of the RFD + EUROBALL IV coupling.

Multi-quasiparticle isomers and rotational bands in [formula omitted] Re

High-spin states in 181 Re have been populated using the 176 Yb( 11 B, 6n) reaction and their decays studied using the CAESAR γ -ray spectrometer. Thirteen bands of rotational states have been observed based on 1-, 3- and 5-quasiparticle structures, including two new 5-quasiparticle isomers, with half-lives of 1.2 μ s and 22 ns. Angular correlation and distribution coefficients were obtained and γ -ray intensity ratios were used to extract |g K−g R|/Q 0 ratios. Three K -forbidden decays were observed and their reduced hindrance factors were obtained and found to be consistent with known systematic behaviour. Band crossings were observed between 1- and 3-quasiparticle bands. These rotation-aligned 3-quasiparticle bands appear to have high K , and are identified as t -bands. Band mixing calculations support the assigned K -values. A unique degeneracy was observed for two I π=23/2 − states at 1883 keV.

Rotational and multi-quasiparticle excitations in [formula omitted]Re

The high-spin structure of the nucleus 183 Re has been studied following the 176 Yb( 11 B,4n) reaction. High- K, multi-quasiparticle excitations compete with collective rotation in the formation of the yrast and near-yrast structures. Broken-pair (i 13/2) 2 excitations ( t-bands) play a dominant role, generating considerable angular momentum both along and perpendicular to the prolate symmetry axis. The stability of axially symmetric, prolate shapes is explored through comparisons with potential-energy-surface calculations. The possible onset of oblate rotation at high angular momentum is discussed.

Extraction of level density and γ strength function from primary γ spectra

We present a new iterative procedure to extract the level density and the γ strength function from primary γ spectra for energies close up to the neutron binding energy. The procedure is tested on simulated spectra and on data from the 173 Yb ( 3 He,α) 172 Yb reaction.

Decay and properties of the yrast superdeformed band in192Pb

The {sup 173}Yb({sup 24}Mg,5n) reaction at E({sup 24}Mg) = 134.5 MeV with a gold-backed target was used to populate high-angular momentum states in {sup 192}Pb. Resulting {gamma} rays were detected with Gammasphere located at the 88-Inch Cyclotron. A discrete transition of energy E{sub {gamma}} = 2057.7(6) keV has been identified in the depopulation the yrast superdeformed (SD) band in {sup 192}Pb. This transition has been tentatively placed in the level scheme based on coincidence relationships. Thus, the excitation energy of the SD level populated by the 262-keV in-band transition is tentatively assigned E{sub x} = 4.572(1) MeV. Confidence limits are discussed. Other transitions in coincidence with the SD band and general features of the band and its decay are also presented. In particular, we confirm that the J{sup (2)} of the SD band decreases by {approx}13{percent} at the lowest frequency. Also, by comparing the masses of the SD ground states in {sup 192,194}Pb to liquid drop model expectations and to each other we have been able to confirm enhanced stability for N=112 at superdeformation. {copyright} {ital 1997} {ital The American Physical Society}