The141Eu nuclide and its decay properties

The nuclide¹⁴¹Eu is identified to have two beta decaying isomers,^141g Eu and^141m Eu, whose decay half-lives are measured to be 40.0±0.7 s and 3.3±0.3s, respectively. Their decay properties are studied by means of beta and gamma spectroscopy techniques. The states withJ ^π assignments in¹⁴¹Sm thus deduced are compared with those of the other odd-A, N=79 isotones. The total decay energy of^141g Eu is measured to be 6.03±0.10 MeV, which is compared with the predictions of several mass formulae and with the decay energy systematics of theN=78 isotones. The^141g Eu and^141m Eu are deduced to haveJ ^π =5/2⁺ and 11/2^?, respectively. A 96.4 keV isomeric transition between them is found to be anE3 transition with aB(E3)=1.6±0.4e ²fm⁶. The structure of¹⁴¹Eu is compared with that of the otherN = 78 isotones.     

Annealing of PrF3 nanoparticles by microwave irradiation

The influence of microwave irradiation on the recovery of nanocrystalline PrF₃ powders has been experimentally analyzed by nuclear magnetic resonance (NMR) at T = 1.5 K. It is established that the relaxation times of ¹⁴¹Pr and ¹⁹F nuclei rise significantly with an increase in the hydrothermal-treatment time, whereas the ¹⁴¹Pr NMR spectra narrow, which indicates a decrease in the number of defects in the lattices of nanosamples.     

Nuclear structure effect on internal conversion ofl-forbidden transitions in139La,141Pr and203Tl

Accurate experimental internal conversion data have been used to study the effect of nuclear penetration in the case of thel-forbidden transitions in¹³⁹La (165.8 keV),¹⁴¹Pr (145.4 keV) and²⁰³Tl (279.2 keV). The nuclear penetration parameterλ and theE2/M 1 mixing ratioδ ² have been deduced by graphical analysis. Following results were obtained:λ=2.8±1.3,δ ² =(8.4 _?8.4 ^+14.0 )·10^?4 for¹³⁹La,λ=1.2±0.6,δ ²=(4.8±0.5)·10^?3 for¹⁴¹Pr, andλ=6.4±1.1,δ ²=1.36±0.12 for²⁰³Tl.     

High-spin,discrete line spectroscopy of 162Yb and 164Hf and the systematics of N = 92 isotones

The high spin states of ¹⁶²Yb and ¹⁶⁴Hf have been studied using ¹²²Sn(⁴⁴Ca, 4n) and ¹²⁰Sn(⁴⁸Sn(⁴⁸Ti, 4n) reactions respectively. The resulting new level schemes for ¹⁶²Yb and ¹⁶⁴Hf are presented and compared with existing data for ¹⁶⁰Er. The systematic behaviour of these three N = 92 isotones at large angular momentum yields information both on modifications of the single-neutron spectrum of states resulting from the polarisation of the nuclear field and on the single-proton spectrum of states.     

Excitation of isomeric 1h 11/2 states in nuclear reactions induced by γ rays and neutrons and in beta decay

Isomeric ratios were measured for N=81 isotones (¹³⁵Xe, ¹³⁷Ba, ¹³⁹Ce, ¹⁴¹Nd, ¹⁴³Sm). In the experiment reported here, μ _ν ≤3±10^? J ^π=11/2^? isomers were excited in (n, γ) and (γ, n) reactions and in the β ⁺ decay of ¹³⁹Pr and ¹⁴¹Pm. In order to determine the reaction yields, use was made of the activation method involving measurement of the gamma-ray spectra of reaction products. It is found that, in the same reactions, isomeric ratios are different for isotones characterized by different atomic numbers Z. Isomeric ratios were calculated with the spectra of low-lying levels and radiative-transition probabilities established on the basis of the quasiparticle-phonon model. Good agreement between the experimental and calculated values of isomeric ratios is obtained for all isotopes invesigated here. The dependence of isomeric ratios on the atomic number Z of a nucleus is explained by the difference of reaction energies, which leads to different probabilities of excitation of activation levels through which the isomers being considered are populated.     

Neutron diffraction study on the hyperfine-induced nuclear spin order in the antiferromagnet PrSn3

At several $\text{(h+}\text{1}\text{2}\text{0 0)}$ reciprocal lattice positions of PrSn₃, we observed Bragg scattering of neutrons which is purely due to the nuclear spin polarization of ¹⁴¹Pr, and could measure the temperature dependence of the polarization between 10 mK and 4.2 K. From the perfectly polarized state of the nuclear spins, the difference between the spin-dependent nuclear scattering lengths b⁺ and b^- has been determined to be b⁺ - b^- = -0.110 ± 0.006 × 10^-12 cm, which is significantly larger in magnitude than the previously reported value. An additional electronic polarization which is linearly proportional to the nuclear spin polarization has also been observed.     

Nuclear magnetic order in PrF3

PrF₃ is an enhanced nuclear paramagnet for which the resonance parameters have been determined both by acoustic resonance (Al’tshuleret al., 1979 [1]) and by conventional nuclear magnetic resonance (Nielsen, 1983 [2]). In this paper, the temperature at which the nuclei of the single stable isotope¹⁴¹Pr,I=5/2, enter an ordered state is estimated to beca. 0.1 mK, smaller than the overall nuclear electric quadrupole splitting 6P/h=1.2 mK. Possible arrangements of the nuclear moments in the ordered state are discussed, together with the requirements for a neutron diffraction measurement.     

Nuclear pseudoquadrupole resonance of <Superscript>141</Superscript>Pr in Van Vleck paramagnet PrF<Subscript>3</Subscript>

Nuclear pseudoquadrupole resonance of ¹⁴¹Pr in Van Vleck paramagnet PrF₃ has been observed in singlecrystal and micro- and nanopowder samples at a temperature of 4.2 K. The spectra of nuclear pseudoquadrupole resonance of ¹⁴¹Pr, as well as the spin-spin and spin-lattice relaxation parameters, have been obtained. The parameters of the nuclear spin Hamiltonian have been determined. It has been found that the parameters of the crystal electric field in nanocrystals differ strongly from those in microcrystals.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.     

Energies and electromagnetic moments of deformed nuclei in the rare-earth region

Strutinsky-type cranking calculations with inclusion of pairing correlations have been performed for the rare-earth nuclei ^{156, 158, 164}Dy and ¹⁶⁴Er. The pairing effects contribute significantly and with their inclusion the calculated yrast spectra agree very well with experiments. Using Hartree-Fock-Bogouliubov cranking wave functions we have calculated the magnetic moments and quadrupole moments for states up to spin $\text{I = 20}\text{h}\text{?}$. The quadrupole moments are found to be constant over the whole spin range. The gyromagnetic factors g(I) show a strong I-dependence for ^{156, l58}Dy, a weaker one for ¹⁶⁴Er and none for ¹⁶⁴Dy. The sensitivity of this spin dependence on the single-particle occupation and the pairing degrees of freedom is studied. It is found that the spin variation of the gyrofactors is a rotational alignment effect.     

Single-Proton states of159Ho studied with the (p,α) reaction spectroscopic evidence for the unusual coriolis strengths in159, 161, 163Ho nuclei

The proton-hole character of states in¹⁵⁹Ho has been studied using the^{162, 164}Er(p, α)^{159, 161}Ho reactions with 17 MeV protons. The shapes of angular distributions measured for both nuclei were compared, with good agreement in most cases, to tritoncluster-transfer DWBA calculations. The deviations obtained and the experimental normalization factors deduced for the¹⁶⁴Er(p, α)¹⁶¹Ho reaction by comparisons to (t, α) cross sections indicate a need for a revised treatment of the mechanism of the (p, α) reaction on deformed nuclei. By comparisons to the well-known states in¹⁶¹Ho, nuclear structure factors were obtained for many levels in¹⁵⁹Ho. The Nilsson assignments for the 3/2⁺[411], 5/2^?[532] and 5/2⁺[413] bands were confirmed and the lowest rotational members of these bands were established. The anomalous strengths of the strongly mixed positive parity states in^{159, 161, 163}Ho are discussed in the frame-work of the Nilsson model with the pairing and effective Coriolis strengths included. The Coriolis strengths giving best fits to excitation energies also improve the agreement of theory with the experimental nuclear structure factors. Rotational spacings of the 5/2⁺[413] and especially those of the 5/2^?[532] bands in^{159, 161, 163}Ho show mixmg effects unexplainable by the present calculations.     

Frequency of lamb-dip-stabilized 1.52 μm He-Ne lasers

A ³He-²⁰Ne and a ³He-²²Ne 1.52 m laser were frequency stabilized to the Lamb-dip of their respective gain curve and provided a resettability of 2 MHz. Using these lasers, absolute frequencies for the ²⁰Ne and ²²Ne laser transitions were measured by interferometric frequency comparison with an I₂-stabilized He-Ne laser at 0.633 m. A least-square analysis which accounts for the linear frequency dependence of the laser gas pressure yielded two parameters which can reproduce the measured frequencies within an accuracy of ±1.0·10^–8 at 1.52 m.     

Decay of high-spin isomers in Os nuclei by barrier penetration

A decay scheme for the 130±20 ns high-spin isomer in ¹⁸²Os has been established. The excitation energy of the isomer is 7049±1 keV and it has I^π = 25⁽⁺⁾. A 2.4% decay directly to the yrast 24⁺ level at 5988 keV is observed. In ¹⁸⁴Os a 20±5 ns isomer is observed at 2366±1 keV excitation energy with I^π = 10⁺. Again, direct transitions into the yrast 8⁺ and 10⁺ levels are observed. Contrary to previous speculations, there is no compelling evidence for stable triaxial shapes in the structure of the levels through which the isomers decay. The abnormally short half-lives observed, as well as the unusual decay patterns, are best understood in terms of a γ-soft nuclear potential. Motion in the γ-direction allows the isomer to decay via barrier penetration from an axially symmetric prolate shape with the angular momentum along the nuclear symmetry axis (deformation aligned state) via oblate shapes to another prolate shape with the angular momentum perpendicular to the nuclear symmetry axis (rotation-aligned state).     

Unambiguous identification and properties of high spin isomers in nuclei close to N = 82

The search for and study of high spin isomers produced by ¹²C, ¹⁴N and ¹⁶O induced reactions on targets close to N = 82 has been performed. The observed isomers were identified unambiguously by a detailed study of the excitation functions, delayed gamma-ray multiplicity and multiparametric gamma-gamma coincidences. The isomers with the highest spin above the ground state were observed in ¹⁵²Er and ¹⁵¹Ho nuclei.     

The 12C(18O, α)26Mg and 12C(18O, 8Be)22Ne reaction

Excitation functions for α-emission leading to the ground and first excited states of ²⁶Mg and ⁸Be emission leading to the ground and first and second excited states of ²²Ne have been measured at several forward angles for E_c.m. = 15 to 22.4 MeV. There is little evidence for correlated structure. The angular distribution at 16.5 MeV for the α + ²⁶Mg(g.s.) channel is rather structureless while that for the ⁸Be+²²Ne(g.s.) channel appears to be dominated by a J = 13 contribution. Statistical model calculations indicate that much of the yield for both the α and ⁸Be exit channel is compound nuclear in origin, with some indication of a larger direct contribution for the ⁸Be channel at the lower end of the bombarding energy range.     

The decay of 3.0 min143Eu and the levels of theN=81143Sm and141Nd nuclei

The decay of 3.0 min¹⁴³Eu has been investigated by means of a Ge(Li) detector. TheΒ ⁺ spectrum obtained with a Si(Li) spectrometer leads to aQ-value of 5100±50 keV. For the first time a decay scheme including levels situated at 107.5, 755.0, 1107.9, 1537.5 and 1912.8 keV has been established. The data are compared to those obtained for the neighbouringN=81¹⁴¹Nd nucleus. Besides, new experimental measurements indicate that the 1345.4 keV level in¹⁴¹Nd has not the odd-parity and would be 5/2⁺, 7/2⁺. Hence, the 7/2^? state is situated at 1967.4 keV. Those data are in reasonable agreement with intermediate coupling calculations.     

Production of high multiplicity yrast isomers in147Gd and146Gd in a-particle induced reactions

High spin isomers in ¹⁴⁷ Gd and ¹⁴⁶ Gd have been produced in (α, xn)reactions, and their half-lives, excitation energies and maximum spins have been determined. It is proposed that these isomers are identical with those recently observed in bombardments with ⁵⁰ Ti and ⁴⁰ Ar projectiles.     

Etude par diffraction neutronique de l'ilmenite ferrimagnetique NiMnO3

The magnetic structure of ferrimagnetic ilmenite Ni²⁺Mn⁴⁺O₃ has been investigated by neutron diffraction. Below the Curie temperature (164°C), the spins are oriented into two kinds of ferromagnetic planes perpendicular to the [111] rhomboedral axis, one containing Mn⁴⁺ and the other Ni²⁺ cation. Two successive planes are coupled antiferromagnetically. The experimental magnetic moments are respectively found equal to 1.8 and 2.2 μ_B for Ni²⁺ and Mn⁴⁺ at room temperature. The positional atomic parameters have been redetermined from nuclear diffraction data taken above the Curie temperature.     

Isomeric yield ratio of fission product148Pr in235U(n th,f)

The independent isomeric yield ratio of¹⁴⁸Pr in thermal neutron induced fission of²³⁵U has been determined experimentally. The fission product¹⁴⁸Pr isomers, extracted directly by on-line mass separation technique, have high-spin (J=4) to low-spin (J=1) isomer ratio of 0.14±0.04 using growth and decay analysis. Statistical model calculation of isomeric yeild ratio using constant initial r.m.s. angular momentumJ _rms can not reproduce either present results or other recent measurements of isomer ratios. TheJ _rms derived from isomer ratio data in all thermal fissioning systems indicate a wide spread ranging from 2? to 13?. No clear correlation betweenJ _rms and isomeric spins or number of neutrons of isomers is found, thus, more model refinements and experimental works should be done in order to evaluate independent isomeric yields correctly.     

Surface-enhanced nuclear spin conversion in CH3F

The nuclear spin conversion of a molecule is the modification of the total nuclear spin I of its equivalent atoms. This phenomenon is observed by measuring the relaxation rate of a gas sample initially prepared with a population of spin isomers far from the equilibrium given by nuclear spin statistics. New experimental data obtained at low pressure show a surface-induced enhancement of the nuclear spin conversion in ¹³CH₃F. Contrary to binary collisions in the gas phase, hitting the surface induces direct conversion. Several mechanisms are proposed.