Half-lives of the neutron-rich isotopes100Sr,100Y,148Ba and148La

We have deduced the linear momentum transferred from the projectile to the fissioning nucleus in the reaction²⁰Ne+¹⁹⁷Au at 30 MeV/A by measuring the folding angle between the two fission fragments. We found that the most probable linear momentum transfer represents 76% of the initial value.     

Masses of Rb,Cs and Fr isotopes

The results of the direct mass measurements of the unstable isotopes of Rb, Cs and Fr are rewritten in a form-linear combination of masses-which allows a direct analysis with other experimental data. An up-to-date least-square adjustment which takes into account new reference masses is subsequently performed. A systematic study of isomers is carried out for evaluating isomeric corrections to apply to the measured masses in order to obtain the ground-state masses.     

Half-lives and delayed neutron emission probabilities of short-lived Rb and Cs precursors

Half-lives and delayed-neutron emission probabilities (P _n ) of short-lived Rb and Cs precursors in the mass chains 94–98 and 143–147 were measured. Sources of isotope separated nuclides were obtained from the on-line mass-separator OSTIS installed at the Grenoble high-flux reactor. A newP _n -value of (25.4±3.2)% is given for the (214±30) ms¹⁴⁷Cs; theP _n -values of nine alkali precursor nuclides were redetermined: (2,730±20) ms⁹⁴Rb with (9.7±0.5)%, (377 ±6)ms⁹⁵Rb with (8.6±0.5)%, (197±5)ms⁹⁶Rb with (12.5±0.9)%, (171±4) ms⁹⁷Rb with (25.2±1.8)%, (114±13)ms⁹⁸Rb with (18.4±2.9)%, (1,765±30)ms¹⁴³Cs with (1.74 ±0.12)%, (1,000±10)ms¹⁴⁴Cs with (2.95±0.25)%, (616±20) ms¹⁴⁵Cs with (12.2±0.9)%, (325±10)ms¹⁴⁶Cs with (13.2±0.8)%. The results are compared with the existing data, and theP _n -values are discussed within some simple model predictions.     

Mass-spectrometric measurements of exotic Rb,Cs and Fr isotopes

Direct mass measurements of exotic nuclei have been performed with a double-focussing mass spectrometer on line with an isotope separator. We report here on mass measurements with improved accuracy of exotic isotopes of Rb and Cs and on the first measurement of the masses of ¹¹⁶Cs and ¹⁴⁸Cs.     

On-line production of Rb and Cs isotopes from uranium carbide targets

A series of on-line mass separation experiments have been performed at the IRIS facility to measure the yield and release of Rb and Cs neutron-rich isotopes produced by fission reaction of ²³⁸U. A 1 GeV proton beam was used to bombard uranium carbide targets with the densities of 11 g/cm³ and 1.5 g/cm³ held at temperatures in the range (2000-2230) ^°C. The release curves of Rb and Cs long-lived isotopes were measured from both kinds of targets. The overall production efficiency was determined making use of experimentally measured cross-sections of that isotope production. Comparison of the experimental yields of Rb and Cs isotopes with the calculated ones after corrections for losses due to finite release times suggests that the diffusion is the dominating process reducing the efficiency for short-lived isotopes. When normalized to the same thickness, an enhancement for the high-density rod target of the measured isotope yields is observed when going far from stability. This is possibly explained by the reactions induced by secondary neutrons. A significant odd-even effect with higher yields of Cs even neutron isotopes has been observed, confirming a similar effect obtained in earlier experiments.     

Beta-decay energies and nuclear masses of very neutron-rich Rb and Cs isotopes

Theβ-endpoint energies of very neutron-rich Rb and Cs isotopes with mass numbers 94≦A≦98 and 142≦A≦146, respectively, have been measured with a plastic scintillatorβ-telescope at the on-line mass separator OSTIS. From these,Q _β-values and mass excesses are calculated and compared with the results obtained in direct mass determinations.     

Lifetime measurements in99Sr and100Zr

The lifetime of the first excited state in⁹⁹Sr has been determined by the delayed γ-γ coincidence method. The value of t_/2=0.58(9) ns corresponds to a deformation parameter ß=0.38(4). The deduced z> value confirms the previously proposed ν[411]3/2 Nilsson assignment for the⁹⁹Sr ground state. In addition, lifetime values for the 2⁺ (t_1/2=0.40(8) ns) and 0⁺ (t_1/2=5.36(23) ns) states in¹⁰⁰Zr are obtained, which deviate from older measurements and indicate a larger deformation of ß=0.39(4).     

Half-lives of levels in99Nb and99Mo

The half-lives of the 469-keV level in⁹⁹Nb and the 236-keV state in⁹⁹Mo have been determined to (0.21±0.06) ns and (0.87±0.15) ns, respectively, fromβ,γ-delayed coincidences. Values ofB(E2)=(89±28)e ² fm⁴ andB(M1)=(0.017±0.003) μ _n ² are deduced for the 469-keV transition in⁹⁹Nb and the 138-keV transition in99Mo. The result for theE2-transition probability seems to be in accordance with the particle-core coupling interpretation of the low-lying levels in⁹⁸Nb if⁹⁸Zr is used as the core. TheM1 probability for⁹⁹Mo agrees with the systematics for “l-forbidden” 1g_7/2→2d _5/2 neutron transitions.     

Half-lives,neutron emission probabilities and fission yields of neutron-rich rubidium isotopes in the mass regionA=96 toA=100

Neutron-rich rubidium isotopes were produced by thermal-neutron induced fission of²³⁵U and were isolated by surface ionization and mass separation. The new isotope (51 ±17) ms¹⁰⁰Rb was identified. The half-lives of the rubidium isotopes with mass numberA=96 toA=100 were measured using neutron multiscaling or gamma multispectrum analysis. Measurements of the delayed-neutron emission probabilityP _n of⁹⁹Rb and of the fission yields of⁹⁷Rb,⁹⁸Rb, and⁹⁹Rb were performed.     

Gamma-ray energies of short-lived Rb,Sr, and Y isotopes indicating delayed neutron emission to excited states

Gamma energies in the level schemes of ^95,96,97Sr, ^95,96,97Y, and ^95,97Zr are reported. Some of their excited levels are populated by delayed neutron emission. These nuclei were produced as daughters of Rb fission fragments originating from the reaction ²³⁵U(n, f). By thermal ionization they were separated from fission products having other nuclear charge states and by an on-line mass separator according to their respective masses.     

Polarization spectroscopy of Rb and Cs

Theoretical calculation of ⁸⁵Rb and ¹³³Cs D₁ signals in polarization spectroscopy is presented by using the method of velocity-selective optical pumping in a four-level system. Since good agreement between theory and experiment has been found in Na D₁ polarized signals, the theoretical calculation can be also applied to Rb and Cs D₁ lines. Rb and Cs atoms have higher total angular momentum F in the hyperfine structures than Na atom and then the calculation is more complicated. The relative signal intensities in polarization spectroscopy are compared with those in saturation spectroscopy.     

Determination of the isotopic shift of the first resonance line in Cs(I) spectrum for the isotopes 131Cs, 132Cs,and 136Cs

The isotope shifts of the resonance line $\text{λ = 8521}\text{A}\text{?}$ of ¹³¹Cs, ¹³²Cs, and ¹³⁶Cs with respect to ¹³³Cs were determined by a new scanning technique to be $\text{v}\text{?}\text{(}{}^{133}\text{Cs}\text{)-}\text{v}\text{?}\text{(}{}^{131}\text{Cs}\text{) = +1.70(40)}\text{mK}$, $\text{v}\text{?}\text{(}{}^{133}\text{Cs}\text{)-}\text{v}\text{?}\text{(}{}^{132}\text{Cs}\text{) = ?0.95(80)}\text{mK}$, $\text{v}\text{?}\text{(}{}^{136}\text{Cs}\text{)-}\text{v}\text{?}\text{(}{}^{133}\text{Cs}\text{) = ?4.0(3.0)}\text{mK}$. In accordance with results from other Cs isotopes and neighbouring elements they show the change 〈δr²〉 in the second radial moment of the nuclear charge distribution to be a factor of 5 to 10 smaller than expected from the model of uniform charge distribution. Integral isotope shifts over the isotopic chains of Xe, Cs, and Ba were analyzed in terms of collective models. Assuming an isotopic shift discrepancy of 0.5 for the nuclear volume shift it was possible to derive deformation parameters $\text{〈β}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in quantitative agreement with those from B(E2) measurements.     

The half-life of87Rb measured as difference between the isotopes87Rb and85Rb

The half-lifeT of⁸⁷Rb was determined by means of a 4π proportional counter using thin sources of RbCl on thin conducting backings. The total thicknessD investigated (RbCl+support) ranged from 11 to 525 μg/cm². Comparative measurements with (inactive) layers of⁸⁵RbCl showed that, in the energy range below 185 eV, RbCl layers give rise to spurious pulses. Linear extrapolation of the specific activity belowD=45 μg/cm² toD=0 yieldsT=(4.88 _?0.10 ^+0.06 )·10¹⁰ y. Previously published half-lives are discussed.     

Decay energies of the low-spin states of147Tb and148Tb

Using¹¹²Cd(⁴⁰Ar,pxn) reactions andγ-ray spectroscopy, the EC/β ⁺ and EC(K)/β ⁺ probability ratios were determined for individualβ-transitions in the¹⁴⁷Tb(1.6 h)→¹⁴⁷Gd and¹⁴⁸Tb(60 min)→¹⁴⁸Gd decays. Under assumption of applicability of theoretical ratios for allowedβ-decays on the first-forbidden nonunique transitions studied here, the experimental ratios were converted into information on decay energies. Combining the results with the known masses of^147,148Gd andQ _α values of neutron-deficient holmium-to-lutetium isotopes, mass excesses could be determined for¹⁴⁷Tb,¹⁴⁸Tb, low-spin¹⁵¹Ho, low-spin¹⁵²Ho,¹⁵⁵Tm,¹⁵⁶Tm and¹⁵⁹Lu.     

Influence of Rb,Cs, and Ba on the superconductivity of magnesium diboride

Magnesium diboride has been thermally treated in the presence of Rb, Cs, and Ba. The magnetic susceptibility shows the possible onsets of superconductivity in the resulting samples at 52 K (Rb), 58 K (Cs), and 45 K (Ba). Room-temperature ¹¹B NMR indicates the cubic symmetry of the electric field gradient at the boron site for the samples reacted with Rb and Cs, in contrast to the axial symmetry in the initial MgB₂ and in the sample treated with Ba. The text was submitted by the authors in English.     

Ionic conductivity in the new series MSbTeO6 (M = K,Rb, Cs,Tl, Ag)

The series of pyrochlores MSbTeO₆ (M = K, Rb, Cs, Tl, Ag) were prepared and characterized by means of powder X-ray diffraction methods. ac measurements by the complex impedance method were performed at different temperatures. The conductivity of AgSbO₃ was also measured to be compared with the conductivity of AgSbTeO₆.     

Delayed neutron emission probabilities and half-lives of Rb,Sr, Y,In, Cs,Ba and La precursors with A = 93–98, A = 127–131 and A = 142–148

Delayed neutron emission probabilities (P_n) for ^93–98Rb,^{97, 98}Sr,^{97, 98}Y,^127–131 In,^142–146Cs, ^{147, 148g}Ba and ¹⁴⁷La were measured at the SOLIS on-line isotope separator. The P_nvalues for ^{97, 98}Sr,^{97, 98}Y, ^{147, 148}Ba and ¹⁴⁷La were measured for the first time. Delayed neutron emission is energetically unfavourable for ¹⁴⁷Ba and ¹⁴⁸Ba precursors, according to predictions of at least four of the most common mass formulas, however, respective P_n values of (5.21 ±0.52) % and (23.9 ± 2.1 )% were determined. The P_n values were determined by counting β and neutron activities simultaneously. The energy dependence of the counting system was ～ 3 % for the relevant delayed neutron spectra range, i.e., 0–1.5 MeV. Half-lives for all precursors were measured from both β and neutron decay curves.     

High pressure calculation of the melting curve: Na,K, Rb and Cs

The melting of four alkali metals is investigated in the present paper, in the theoretical framework defined in a preliminary study on sodium. The calculations enable us to predict the existence of a very flat maximum on all four phase lines. The obtained results are in good agreement with experiment in the case of Na, K and Rb, and emphasize the importance of “d” effects and the dramatic influence of the electronic transition on the high pressure fusion curve of Cs.