In-beam study and structure of the N = 82 nucleus 141Pr

High-spin states in ¹⁴¹Pr have been studied in the reactions ¹³⁹La(α, 2n)¹⁴¹Pr and ¹⁴⁰Ce(d, n)¹⁴¹Pr. Using in-beam spectroscopic methods energies, intensities, excitation functions, γγ coincidences, time and angular distributions and the linear polarization of γ-rays as well as conversion electron spectra were measured. Positive- and negative-parity states of ¹⁴¹Pr have been established for spin values up to $\text{J =}\text{27}\text{2}$ and E_x < 4750 keV including 19 news lvels. For three levels ns-lifetimes were determined. The experimental data on positive-parity states are in remarkable agreement with shell-model predictions. In the case of positive-parity states no evidence for particle-core coupling is found. The shell-model investigation suggests, however, that the negative-parity states in ¹⁴¹Pr as well as in ¹⁴³Pm can be explained by particle-core coupling.     

Temperature and volume dependence of some magnetic properties of Pr-pnictides

Several experiments relating to the volume dependence of crystal field interactions in rare earth pnictides have been carried out. These experiments include measurements of 1) the temperature dependence of the susceptibility of PrN, 2) the room temperature compressibilities of PrN and PrAs, 3) the NMR frequency shifts for ¹⁴¹Pr in PrN and PrSb, and 4) the low-temperature pressure dependence of the ¹⁴¹Pr frequency shift in PrN and PrSb. Although electrostatic screening effects on crystal field interactions in PrN are smaller than in the heavier Pr- pnictides, the anomalous volume dependence of the ¹⁴¹Pr NMR shift is essentially the same in all these compounds.     

141Pr Mössbauer spectroscopy using the current integrating technique

¹⁴¹Pr Mössbauer spectroscopy has been realized with use of the current integrating technique. As an example, we show the¹⁴¹Pr Mössbauer spectrum of PrCu₂Si₂ at 4.2 K.     

Observation of magnetic coupling between the nuclei of liquid <Superscript>3</Superscript>He and the <Superscript>141</Superscript>Pr nuclei of PrF<Subscript>3</Subscript> crystalline powder

The resonance magnetic coupling between the nuclei of liquid ³He and the ¹⁴¹Pr nuclei of a fine-dispersed powder of PrF₃ Van Vleck paramagnet with the grain size below 45 μm has been discovered at a temperature of 1.5 K with the use of a pulsed NMR technique. The magnetic specific heat of the corresponding spin systems is estimated theoretically.     

Kernspektroskopische Untersuchungen zu den Termschemata einiger Nuklide im Bereich der abgeschlossenen NeutronenschaleN=82:141Pr,143Pm,139Pr und141Pm

The level schemes of the nuclei¹⁴¹Pr,¹⁴³Pm,¹³⁹Pr, and¹⁴¹Pm were investigated by measuring theγ-spectra following theΒ-(decay of the corresponding (Z+1)-isobars. The existing level schemes for these nuclides were thereby enlarged or revised. The results are discussed using the weak-coupling picture.     

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.     

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.     

Half-life measurements in59Co,141Pr and227Ac

The half-lives of the 1291.6 keV level in⁵⁹Co, 145.43 keV level in¹⁴¹Pr and 27.35 keV level in²²⁷Ac have been measured using leading edge and zero-crossover timing techniques. The decay curves analysed by moments, Laplace transform and slope methods gave the following half-life values: $$\begin{gathered} T_{\tfrac{1}{2}} (1291.6 keV level in {}^{59}Co) = (0.538 \pm 0.004) ns \hfill \\ T_{\tfrac{1}{2}} (145.43 keV level in {}^{141}\Pr ) = (1.82 \pm 0.04) ns \hfill \\ T_{\tfrac{1}{2}} (27.35 keV level in {}^{227}Ac) = (41.0 \pm 1.1) ns. \hfill \\ \end{gathered} $$ From the measured half-lives, the reduced transition probabilitiesB(M1)↓,B(E2)↓ for gamma transitions de-exciting the above mentioned levels in⁵⁹Co and¹⁴¹Pr are determined and compared with single particle, intermediate coupling and Sorensen estimates. In²²⁷Ac, absolute transition probability for the 27.35 keV transition is determined and compared with single particle and Nilsson estimates.     

High spin levels in151Ho

We report here on the first study of the level structure of¹⁵¹Ho. High spin levels in¹⁵¹Ho have been populated in the¹⁴¹Pr+¹⁶O and¹⁴⁴Sm+¹²C reactions. The level structure has been established up to 6.6 MeV energy and the spins and parities determined up to 49/2^?. Most of the proposed level configurations can be explained by the coupling ofh _11/2 protons tof _7/2 and/orh _9/2 neutrons. An isomer with 14±3 ns half-life and a delayed gamma multiplicity equal to 17±2 has been found. Its spin is larger than 57/2? units.     

The probability of the reaction (π−, p) and the problem of Δ+ isobars in the atomic nucleus

The process of slow π^? absorption in ₂₁⁴⁵Sc, ₂₇⁵⁹Co, ₃₉⁸⁹Y, ₅₅¹³³Cs, ₅₉¹⁴¹Pr and ₇₉¹⁹⁷Au atomic nuclei, followed by the emission of one proton, has been investigated. Upper limits for the probabilities of single-proton emission have been determined from the yields of the isotopes produced. The following values are obtained, per stopped pion: W ? 6.1 × 10^?4 for the reaction ₂₁⁴⁵Sc(π^?, p)₁₉⁴⁴K, W ? 0.87 × 10^?4 for ₂₇⁵⁹Co(π^?, p)₂₅⁵⁸Mn, W ? 6.9 × 10^?4 for ₃₉⁸⁹Y(π^?, p)₃₇⁸⁸Rb, W ? 1.3 × 10^?4 for ₅₅¹³³Cs(π^?, p)₅₃¹³²I, W ? 3.0 × 10^?4 for ₅₉¹⁴¹Pr(π^?, p)₅₇¹⁴⁰La, and W ? 3.3 × 10^?5 for ₇₉¹⁹⁷Au(π^?, p)₇₇^196mIr.     

Investigation of spin dependence of neutron cross sections and of strength functions for rare earth nuclei in experiments with polarized neutrons and nuclei

Experiments on the spin dependence of the interaction of resonance neutrons (up to 100 keV) with the rare earth nuclei ¹⁴¹Pr, ¹⁵⁹Tb, ¹⁶⁵Ho, ¹⁶⁷Er and ¹⁶⁹Tm are reported. The measurements were performed with polarized neutrons and nuclei. The spin dependence of S-wave strength functions was investigated, and the imaginary part of the spin-spin potential (W_ss = 0.10 ± 0.06 MeV) was estimated in optical-model calculations with a potential in the form of a rectangular well. The energy dependence of the difference of strength functions for two J-states shows possible intermediate states in the formation of the compound nucleus. The J-values of about 230 resonances were determined.     

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.     

Excitation of single proton states in (p, α) reactions

A high resolution experiment, using the BIG KARL spectrometer has been made to identify the levels of ¹⁴¹ Pr excited in the ¹⁴⁴ Nd(p,α) reaction at 25 MeV. It has been found that only levels with a dominant single proton component are populated with appreciable intensity.     

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.     

Cross sections of the photoneutron reaction for <Superscript>141</Superscript>Pr and <Superscript>186</Superscript>W nuclei,estimated from physical criteria of data reliability

Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for ¹⁴¹Pr and ¹⁸⁶W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σ^exp(γ, xn) = σ^exp(γ, 1n) + 2 σ^exp(γ, 2ⁿ) + 3 σexp(γ, 3n) + … and ratios F _i ^theor= σ^theor(γ, in)/σ^theor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σ^eval(γ, in) = F _i ^theor σ^exp(γ, xn). It is found that for ¹⁴¹Pr and ¹⁸⁶W, ratios F ^exp _i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F _i ^theor and F ^exp _i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.     

Luminescence of Pr-doped LiCaAlF6 and LiSrAlF6 crystals

The spectral and kinetic parameters of LiCaAlF₆:Pr and LiSrAlF₆:Pr single crystals are studied at LHeT and room temperature (RT). Photon cascade emission (PCE), i.e., ¹S₀→¹I₆ and ³P₀→³H_j, ³F_j transitions after Pr³⁺ excitation via 4f²→4f 5d absorption results in the conversion of the vacuum ultraviolet photon to two visible photons. The excitation and photoemission spectra as well as decay times have been measured and compared with those for CaF₂:Pr and SrF₂:Pr crystals. X-ray luminescence was measured to study the emission origin from both ¹S₀ and ³P₀ states of Pr³⁺. An intense phosphorescence of LiSrAlF₆:Pr was observed in the visible range after X-irradiation at RT, contrary to LiCaAlF₆:Pr.     

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.     

Spectral and kinetic characteristics of trivalent praseodymium in LaF3-LiF and SrAl12O19

Recent data on cascade transitions in the 4f shell of the Pr³⁺ ion in various matrices are analyzed. Spectral and kinetic characteristics of LaF₃-LiF:Pr and SrAl₁₂O₁₉:Pr phosphors, which show photon cascade emission, were investigated. The emission intensities in the first (¹ S→¹ I ₆ transitions) and the second (transitions from the ³ P ₀ level to the ³ H and ³ F multiplets) cascade stages were measured and the temperature dependences of the intensities of the main emission lines and their kinetic characteristics were determined. The following parameters of SrAl₁₂O₁₉:Pr were found: the band gap width (7.5 eV), the energy gap between the ¹ S ₀, 4f and 5d levels (0.24 eV), and the characteristics of the 4f→5d band (6.0–7.5 eV) of the Pr³⁺ luminescence excitation. It is shown that the LaF₃-LiF:Pr compound has a number of specific features in comparison with other Pr³⁺-doped phosphors.     

Nuclear resonance scattering studies on238U using a dense series of γ-ray photons

Using the¹⁸¹Ta(n, γ) and¹⁴¹Pr(n, γ) reactions to provide a dense series of intenseγ-rays, photoexcitation of the²³⁸U nucleus has been studied in the 4–7 MeV range. It is shown that most of the effective cross sections are in line with an average strength function as given by the GDR Lorentzian line superimposed by Porter-Thomas fluctuations. Resonances of nonstatistical strength are found close to 5.2 MeV.     

PrBa2Cu3O7−y investigated by141Pr Mössbauer spectroscopy

The¹⁴¹Pr Mössbauer isomer shift and hyperfine field spectrum of PrBa₂Cu₃O_7–y were measured at 25 and 4.2 K, respectively. The isomer shift corresponds to an intermediate valency of 3.4(1) and the hyperfine field spectrum at 4.2 K seems to indicate a hyperfine field of 29(3) T.