Pr Isotopes Research Articles

Study of decay properties of Ba to Nd nuclei (A~160) relevant to the formation of the r-process rare-earth peak

Half-lifes (T1/2) of exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured at the RIKEN Nishina Center. The experimental setup consisted of the BigRIPS in-flight separator for ion selection identification, the Advance Implantation Detector Array (AIDA) for ions and β detection, and the BRIKEN detector for neutron counting. Using this setup, 4 new T1/2 have been measured for the first time, and 38 T1/2 have been remeasured with improved precision in several cases. These new experimental data should help to constrain theoretical models for calculations of T1/2. The status of the experimental analysis and preliminary results are provided in this contribution.

Study of decay properties for Ba to Nd nuclei relevant for the formation of the r-process rare-earth peak (A∼160)

At the RIKEN Nishina Center, exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured. This work reports their half-lives (T1/2) and β-delayed neutron-emission probabilities (Pxn). The setup consisted of the BigRIPS in-flight separator for particle identification, the Advanced Implantation Detector Array (AIDA) for ions and β detection, and the BRIKEN neutron counter for neutron detection. Using this arrangement, 4 new T1/2 and 14 new P1n were measured. Furthermore, 38 T1/2 and 2 P1n values were remeasured, decreasing the uncertainties for some of them. In addition to improving predictions of nucleosynthesis models that describe the production of the rare-earth peak at A ∼ 160 via the r-process, these additional experimental data should help to constrain theoretical models for calculations of T1/2 and Pxn in this region.

Positive-parity states and electromagnetic transitions of odd-A Pr and Ce isotopes

Energy levels and electromagnetic transition probabilities of odd-mass [Formula: see text] and [Formula: see text] isotopes have been calculated using the interacting boson fermion model. The even–even [Formula: see text] isotopes have been used as the cores. In the model space, the bosons have angular momentum, [Formula: see text] ([Formula: see text]-boson) and [Formula: see text] ([Formula: see text]-boson) have been considered, while the nine protons for [Formula: see text] and 19–25 neutrons for [Formula: see text] are allowed to occupy the [Formula: see text] and [Formula: see text] single particle orbitals. The quasi-particle energies and occupation probabilities have been obtained by solving the BCS equation. According to the model space, the wave function for low-lying states has been investigated. The calculated results are in good agreement with the available experimental data.

High-spin states and collective oblate bands in the odd-oddPr138nucleus

High-spin states in the odd-odd {sup 138}Pr nucleus were reinvestigated with the reaction {sup 128}Te({sup 14}N,4n) at a beam energy of 64 MeV. Six collective bands were observed, and two of them were newly identified. For the {pi}h{sub 11/2}x{nu}h{sub 11/2} band, high-spin states are followed up to I{sup {pi}}=16{sup +}. The spin values for this band have been reassigned based on the systematical comparison with the neighboring nuclei. The observed band crossing is proposed to be due to the alignment of protons, and the signature inversion with the neutron number changing in La and Pr isotopes has been discussed. The other five collective bands are proposed to be based on oblate deformation with {gamma}{approx}-60 deg.

Observation of excited states in the near-drip-line nucleus125Pr

High-spin states have been observed in the near-drip-line nucleus ${}^{125}\mathrm{Pr}$ following the reaction ${}^{64}\mathrm{Zn}{(}^{64}\mathrm{Zn},p2n).$ The detection of charged particles and neutrons evaporated from the compound system, along with the $M/q$ of the recoiling nucleus, have allowed the identification of excited states in ${}^{125}\mathrm{Pr}$ and the unambiguous assignment of five rotational structures to this nucleus. This is the most neutron-deficient Pr isotope in which excited states have been observed. The strongest band is identified as the ${h}_{11/2}$ single-quasiproton configuration, and is observed to a maximum spin of $I=(67/2\ensuremath{\Elzxh}).$ Another structure is interpreted as the ${g}_{9/2}$ proton hole state, which is associated with bands of enhanced deformation observed in several nuclei in this mass region. These two bands are compared with analogous bands in the heavier odd-$A$ Pr isotopes and changes in deformation are discussed.

Ground-state and pairing properties of Pr isotopes in relativistic mean-field theory

The ground-state and pairing properties of Pr (Z=59) isotopes are investigated in the relativistic mean-field (RMF) theory. The pairing correlations are studied in the Bardeen-Cooper-Schrieffer (BCS) approximation, and the pairing forces are taken to be isospin dependent. The blocking method is adopted to deal with unpaired odd nucleons. The occupation numbers in the continuum for Pr isotopes are studied, which may indicate the domain of the validity of BCS theory. The positions of the neutron and proton drip lines are investigated. It is shown that the RMF-BCS theory provides a good description of the binding energy, isotope shifts, and deformation of nuclei over a large range of Pr isotopes, which are in good agreement with those obtained in the finite-range droplet model.

Quadrupole moments of highly deformed structures in the A approximately 135 region: probing the single-particle motion in a rotating potential.

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei ( >30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.

Spectroscopy near the proton drip-line in the A=130 mass region

The near proton drip-line nucleus 126Pr was studied via in-beam γ-ray spectroscopy using the 40Ca+82Mo reaction at 190 MeV. We observed for the first time excited states above the known isomer in this nucleus, up to spin 31h. The observed band is assigned to a πh11/2 ⋇ νh11/2 configuration. The experimental information suggest a spin 8+ for the lowest observed state. With such a spin assignment the excitation energy of the excited states in 126Pr and 128Pr get smaller than in the heavier Pr isotopes, suggesting a sudden change in deformation close to the proton drip line.

Possible octupole correlation in147Prandπh11/2bands in149,151Pr

Neutron-rich ${}^{147,149,151}\mathrm{Pr}$ nuclei, produced in the spontaneous fission of ${}^{252}\mathrm{Cf},$ were studied using the Gammasphere array. Possible parity doublets in ${}^{147}\mathrm{Pr}$ with $N=88$ and $\ensuremath{\pi}{h}_{11/2}$ bands in ${}^{149,151}\mathrm{Pr}$ are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich ${}_{59}^{147}{\mathrm{Pr}}_{88}$ nucleus such as those observed in ${}_{58}^{146}{\mathrm{Ce}}_{88},$ and also that the ${h}_{11/2}$ bands in the ${}^{149,151}\mathrm{Pr}$ track in energy the yrast bands in ${}^{148,150}\mathrm{Ce}.$ The backbending related to the breaking of the neutron ${i}_{13/2}$ pair is observed at $\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approx}0.27 (\mathrm{MeV})$ for the proton ${h}_{11/2}$ band of ${}^{149}\mathrm{Pr}.$

Ground-State Properties of Z = 59 Nuclei in the Relativistic Mean-Field Theory

Ground-state properties of Pr isotopes are studied in a framework of the relativistic mean-field (RMF) theory using the recently proposed parameter set TM1. Bardeen-Cooper-Schrieffer (BCS) approximation and blocking method is adopted to deal with pairing interaction and the odd nucleon, respectively. The pairing forces are taken to be isospin dependent. The domain of the validity of the BCS theory and the positions of neutron and proton drip lines are studied. It is shown that RMF theory has provided a good description of the binding energy, isotope shifts and deformation of nuclei over a large range of Pr isotopes, which are in good agreement with those obtained in the finite-range droplet model.

Enhanced deformation in light Pr nuclei

We observe for the first time rotational bands of enhanced deformation (ED) in 127 Pr and 128 Pr, and suggest that these bands are built upon πg 9/2 ( [404] 9 2 ) in 127 Pr and on the πg 9/2 νh 11/2 orbitals in 128 Pr. These are the lightest isotopes of Pr for which ED bands have been observed. A contrasting trend in the dynamical moments of inertia ( J (2) ) versus N is observed at low frequencies for the “normal-deformed” πh 11/2 and “enhanced-deformed” πg 9/2 bands of 127 –131 Pr both experimentally and in self-consistent Woods-Saxon calculations. The trends in J (2) and β 2 are correlated with a decreasing probability for pair scattering into the deformation-driving νh 9/2/ f 7/2 ( [541] 1 2 ) orbital.

Extruder proton-hole band in the near-drip-line nucleus127Pr

The near-drip-line nucleus ${}^{127}$Pr was populated with the reaction ${}^{92}$Mo${(}^{40}$Ca,$\ensuremath{\alpha}p)$ at a beam energy of 175 $\mathrm{Me}$V. Particle-$\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences were collected, and the total energy plane gating technique was used to enhance events associated with the $\ensuremath{\alpha}p$ exit channel. This enabled two new rotational bands to be assigned to ${}^{127}$Pr, including a strongly coupled structure. Its similarity with analogous bands in heavier Pr isotopes suggests this structure is most likely based on a hole in the extruder $[404]{9/2}^{+}$proton orbital. The occupancy of this orbital is associated with enhanced quadrupole deformation in this mass region.

Bands of enhanced deformation in light Pr nuclei

Rotational bands based on the π g9=2 structure have been assigned for the first time in127Pr and128Pr, through GAMMASPHERE measurements. This extends the region of these bands of enhanced deformation down toN = 68 and 69, the lightest Pr isotopes for which this structure has been observed.

High spin structure in odd-proton nuclei 129,131Pr.

High spin states in $^{129}\mathrm{Pr}$ and $^{131}\mathrm{Pr}$ have been investigated using in-beam \ensuremath{\gamma}-ray spectroscopy techniques. The yrast band of $^{129}\mathrm{Pr}$ based on the ${\mathit{h}}_{11/2}$ 3/${2}^{\mathrm{\ensuremath{-}}}$[541] proton configuration was observed from 11/${2}^{\mathrm{\ensuremath{-}}}$ up to 43/${2}^{\mathrm{\ensuremath{-}}}$. The band based on the same configuration and two positive-parity side bands based on the ${\mathit{g}}_{7/2}$ 5/${2}^{+}$[413] proton configuration, were observed in $^{131}\mathrm{Pr}$. The delayed yrast band crossing of $^{129}\mathrm{Pr}$ at \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$=0.37 MeV is interpreted as being due to the alignment of the second and third ${\mathit{h}}_{11/2}^{\mathrm{\ensuremath{-}}}$ protons. The band crossing at \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$=0.26 MeV, with a gain in alignment of about 8\ensuremath{\Elzxh}, based on the ${\mathit{g}}_{7/2}$ 5/${2}^{+}$[413] configuration in $^{131}\mathrm{Pr}$ was attributed to the alignment of two ${\mathit{h}}_{11/2}$ protons. The systematics of the proton alignments in a series of Pr isotopes is discussed.

M1-transitions and the mutual orientation of the unpaired nucleons in odd-odd nuclei

Experimental lifetimes and branching ratiosB(M1)/B(E2) are used to determine reduced M1-transition probabilities between collective-band levels withδI=1 in102, 104, 106Ag and in the odd-odd isotopes of La, Pr, Pm and Tl. The extractedB(M1) values are compared with calculations in the framework of the quasiclassical approximation and the model “axial rotor+two quasiparticles“. The reduced M1-transition probabilities along with the magnetic moments were found to depend on the mutual orientation of the angular momenta of the unpaired nucleons in the odd-odd nuclei.

Level structure of the odd mass Pr isotopes: Levels of 143Pr84 populated in the beta decay of 143Ce.

We have studied the levels of $^{143}\mathrm{Pr}$ populated in the beta decay of $^{143}\mathrm{Ce}$ using singles and Compton suppression gamma-ray spectroscopy techniques. We determined a value of 33.10\ifmmode\pm\else\textpm\fi{}0.05 h for the half-life of $^{143}\mathrm{Ce}$. In contrast to previous studies, we find no evidence for low-energy negative-parity levels in the decay of $^{143}\mathrm{Ce}$ to $^{143}\mathrm{Pr}$. In addition we have performed calculations in the framework of the interacting boson-fermion model, which compare well with the level structure of $^{143}\mathrm{Pr}$. These calculations have been extended to the heavier Pr isotopes.

Selective mass separation of light lanthanoids by means of ionization of their monoxides

To strengthen elemental selectivity in isotope separation on-line, ionization of the monoxides of light lanthanoids in a thermal ion source has been studied. Currents of the monoxide ion MO + and the metallic ion M + were measured in off-line experiments using oxide reagents of the elements from Ba to Sm at ion-source temperatures from 1900 to 2730 K. The observed MO + M + ratio was the highest for La and Ce, and decreased with increasing atomic number and temperature. In on-line experiments using heavy-ion fusion-evaporation reactions, La isotopes were mass-separated as La 16O +, being well separated from the Cs and Ba isobars, while Pr isotopes were obtained at a higher temperature as Pr + since the La and Ce isobars were still ionized favorably as MO +. Using this method, the isotope 121La was newly identified with a half-life of 5.3 ± 0.2 s.

Band structures in doubly odd 130Pr.

Two rotational band structures have been identified in doubly odd $^{130}\mathrm{Pr}$ following the $^{110}\mathrm{Cd}$${(}^{28}$Si,\ensuremath{\alpha}p3n${)}^{130}$Pr reaction. One band, having no signature splitting, is believed to be built on the near-prolate \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${g}_{7/2}$ configuration. A second band, with a small signature splitting, is built on the triaxial \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${h}_{11/2}$ configuration. Systematics of recent results for the doubly odd $^{130}$,132,134Pr isotopes are presented.

A new TRISTAN thermal ion source

A new thermal ion source with an integrated target which is heated by electron bombardment to a temperature of 2500°C has been developed for the TRISTAN on-line fission product mass separator at Brookhaven National Laboratory. Initial on-line tests demonstrated that this ion source can extend the range of accessible elements to the rare-earth region. Yields are presented for isotopes of Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, ho, Ga, Ge, As, Y, Zr, Nb, In, Sn and Sb.

Comparison between solid graphite and graphite cloth as a target backing material for an Isol system

A high temperature target-ion source system developed for the TRISTAN on-line isotope separator at Brookhaven National Laboratory is described. The system consists of a surface ionization chamber with a Re surface and 235U in a graphite target matrix. Both solid graphite and graphite cloth targets were tested. The overall separation efficiencies for isotopes of Rb, Cs, Sr, Ba, In, Ce,Pr, Nd and Pm which were extracted directly from the ion source were measured. Production rates were measured as a function of temperature up to 2000°C and the ion source performance was monitored over long periods of time. The performance of solid graphite targets was found to give superior stable operation with no deterioration in production rates for operation times of up to 2000 h. In contrast, graphite cloth targets exhibited deterioration in efficiency with time for most elements with differing rates. The production rates of Ce and Pr isotopes increases significantly during the first 400 h of operation, followed by a slow decrease.