Ground State Of Pr Research Articles

Magnetic and some thermal properties of chalcogenides of Pr and Tm and a few other rare earths

The magnetic properties of all known sulfides, selenides, and tellurides of Pr and Tm (as representative of the light and heavy rare earths, respectively) have been studied. In most cases, Pr and Tm compounds exhibit Van Vleck paramgnetism at low temperatures owing to crystal-field singlet ground states. Splittings have been derived in several cases by specific-heat measurements. In the case of ${\mathrm{Pr}}_{3}{X}_{4}$ ($X=\mathrm{S},\phantom{\rule{0ex}{0ex}}\mathrm{S}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{T}\mathrm{e}$) compounds, specific-heat and susceptibility measurements reveal exchange-induced ferromagnetism. This is further supported by the study of the magnetic phase diagrams of ${\mathrm{Pr}}_{3}$${\mathrm{Se}}_{4}$-${\mathrm{Pr}}_{2}$${\mathrm{Se}}_{3}$, ${\mathrm{La}}_{3}$${\mathrm{Se}}_{4}$-${\mathrm{Pr}}_{3}$${\mathrm{Se}}_{4}$, and of superconductivity in the ${({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x})}_{3}({\mathrm{S}}_{4}, {\mathrm{Se}}_{4}, {\mathrm{Te}}_{4})$ series. Superconductivity persists to very high Pr concentrations, as in the ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}\mathrm{Se}$ system, indicating a nonmagnetic ground state of Pr. The higher chalcogenides appear to exhibit in general semimetallic or semiconducting behavior, while most of the metallic La compounds are usually superconductors.

The 0 + excited state of Ce 140 studied by the decay of Pr 140

The 1.902 MeV 0 + state in Ce 140 was studied by the decay of Pr 140. First, the 0.306 MeV gamma ray, which was assigned to be the transition from the1.902 MeV 0 + (denoted by 0 +′) to the 1.596 MeV 2 + states, was found in the coincidence spectrum gated by the 1.596 MeV gamma ray. The gamma-gamma angular correlation for the 0.306—1.596 MeV cascade was found to be consistent with the (0-2-0) spin sequence. The 0.306, 1.596 and 1.902 MeV internal conversion electrons were observed using a sector-type double focussing spectrometer. The branching ratio of the (0 +′ → 0 +) to the (0 +′ → 2 +) transition was obtained to be 1.13±0.12. The strength parameter ϱ is discussed assuming the partial life of the (0 +′ → 2 +) transition. The log ft values from Pr 140 to the ground, the first 2 + and the second 0 + excited states of Ce 140 were determined to be 4.4, 6.0 and 5.9, respectively. From the log ft values the spin and parity of the ground state of Pr 140 is assigned to be 1 +.

Pairing model for Pr-isotopes

The interaction between neutrons and protons filling different major shells is treated as a perturbation within the framework of the pairing force model. The lowest order effect is to keep the pairing model equations unchanged; only the single nucleon energies to be used therein are modified by an amount dependent on the number of the opposite kind of nucleons and the zero-rank component of the n-p potential. This effect produces the observed ground-state spins of Pr 141, 143, 145. The quasi-neutron-quasi-proton interaction, which contains the effect from the higher multipole components of the n-p potential, must be diagonalised to attempt a detailed fit to the spectra. This is particularly true for the odd nuclei Pr 142, 143. There are two competing configurations for the ground state of Pr 144, a diagnolisation between which is now in progress.

The Hyperfine Structure and Nuclear Moments ofPr141

The hyperfine structure of the ground state of ${\mathrm{Pr}}^{141}$ has been studied by the atomic beam magnetic resonance method. It has been established that the electronic ground state of Pr is $4{f}^{3}6{s}^{2}$, $^{4}I_{\frac{9}{2}}$. Of the five hyperfine intervals arising from this electronic state and a nuclear spin of $\frac{5}{2}$, the lowest two have been observed. They are $W(F=4)\ensuremath{-}W(F=3)=3708.05$ Mc/sec and $W(F=3)\ensuremath{-}W(F=2)=2782.25$ Mc/sec. If the hfs is assumed to be entirely due to an interaction between the $^{4}I_{\frac{9}{2}}$ state and the nucleus, the observed intervals may be expressed in terms of a magnetic dipole interaction constant $A$ and a nuclear electric quadrupole interaction constant $B$. It is found that $A=926.03\ifmmode\pm\else\textpm\fi{}0.1$ Mc/sec and $B=\ensuremath{-}13.9\ifmmode\pm\else\textpm\fi{}1.0$ Mc/sec. From these constants, the nuclear moments have been evaluated by means of approximate methods. The values obtained are $\ensuremath{\mu}=+3.8 \mathrm{nm}, Q=\ensuremath{-}0.054\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24} {\mathrm{cm}}^{2}.$