Nuclear spectroscopy of neutron-richA=143 nuclei

A study of the beta decay of¹⁴³Cs and¹⁴³Ba fission products was undertaken by the use of two on-line mass-separators OSTIS and OSIRIS. Level schemes for¹⁴³Ba and¹⁴³La are deduced from gamma and conversion electron spectra,γ-γ andβ-γ coincidences.Q _β values and ground state beta feedings were also measured. The nuclei¹⁴³La and¹⁴³Ba are tentatively inserted in a systematic of odd-even nuclei aroundA=143 and even-odd nuclei with 87 neutrons respectively.     

Structure of high-spin states in 143Pm

High-spin states of ¹⁴³Pm have been studied in the reactions ¹⁴¹Pr(α, 2n)¹⁴³Pm and ¹⁴³Nd(d, 2n)¹⁴³Pm by means of in-beam spectroscopy. The level scheme, spin and parity assignments are based on results obtained from singles γ-ray spectra, conversion electron spectra, prompt and delayed γ-γ coincidences, γ-ray angular distribution and linear polarization measurements. Positive- and negative-parity states with energies up to 4580 keV and spins up to $\text{25}\text{2}$ have been established including 22 new levels. For two nanosecond isomeric states the nuclear spin precession in an external magnetic field was observed providing the following g-factors:

$\text{g(}\text{11?}\text{2}\text{, 959.7 keV)=1.14(9), g(}\text{15+}\text{2}\text{, 1898.3 keV)=1.00(7).}$

The experimental results are well understood by calculations which have been performed in the framework of the shell model (for positive-parity states of 11 valence protons above a Z = 50, N = 82 core) and of the cluster-vibration model (for 3 holes in a Z = 64, N = 82 core). In the case of positive-parity states no evidence for particle-core coupling could be found, while the negative-parity states could qualitatively be understood within the particle-core coupling picture.     

Shape of the 935 keV beta transition of143Pr

The beta spectrum shape of the 7/2⁺ → 7/2^? beta transition in the decay of¹⁴³Pr is measured employing a thoroughly tested intermediate image beta ray spectrometer of the Siegbahn-Slatis type and using the source produced by irradiation of highly enriched stable¹⁴²Ce sample. The spectrum exhibits a definite energy dependence and is well fitted with shape factorC(W) = 1 ? (0·057 ± 0·006)W whereW is in m₀c² units for an end point energy of 935 ± 2 keV agreeing well with the results of Hamiltonet al and Spejweskiet al and disagreeing with the results of Persson and Reynolds. The single particle configurations for the low lying levels of¹⁴³Pr could not give quantitative results.     

Proton states in143Pm and145Pm populated in the (3He,d) reaction

The (³He,d) reaction on targets of¹⁴²Nd,¹⁴⁴Nd and on a target of natural Nd have been studied, using a beam of 24 MeV³He from the McMaster University Tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge type magnetic spectrograph and recorded on photographic emulsions. Information on thel-values was obtained from the (³He,d) angular distribution. In the¹⁴³Pm nucleus no fragmentation of the shell model strength was found while in the¹⁴⁵Pm nucleus the fragmentation of thed _3/2 ands _1/2 states was significant, giving a total of 11l=2 and 51=0 transitions. The results are analyzed in terms of the spherical shell model and the agreement with pairing theory is excellent in both cases. A survey of the stripping strength to promethium isotopes with mass numbers ranging fromA=143 toA=151 is presented, using normalizations based on the results from the experiments on the target of natural neodymium.     

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.     

Decay of the 4.2-min152Pm into levels of152Sm

After bombardments of enriched¹⁵²Sm with 14-MeV neutrons, three isomers of¹²⁵Pm reaction, have been observed with half-lives of 4.2±0.2 min, 7.5±0.2 min and 15.0±1.0 min. Sources of pure 4.2-min¹⁵²Pm were obtained by separating the promethium from its parent 11-min¹⁵²Nd produced by thermal-neutron induced fission of²³⁵U. The beta and gamma radiations of the 4.2-min¹⁵²Pm have been investigated using semiconductor and scintillation spectrometers. Most of theγ-ray transitions could be placed in a level scheme for 152Sm. Especially interesting is a level at 1083 keV for which the assignmentI ^π=0⁺ is proposed. In a 4πβγ experiment, the ground state feeding of¹⁵²Sm in theβ ^?-decay of the 4.2-min¹⁵²Pm has been measured to be 61% of allβ-ray transitions. AQ _β-value of 3.4±0.2 MeV has been obtained.     

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.     

Beta-Gamma-Winkelkorrelation bei146Pm

A measurement of theβ-γ directional correlationω(W, Θ) of the 3^?(β)2⁺(γ)0⁺ decay of¹⁴⁶Pm is described. Spin and parity of the ground state of¹⁴⁶Pm are found to be 3^?. A set of matrix elementsY=0.94;x=0.20;u=0.20;z=1, which is chosen to fit the experimental results for ω(W, Θ) and which is in agreement with the CVC theory, indicates aK-selection rule effect for the 0,795 MeV beta transition of¹⁴⁶Pm.     

High spin level structure of 63 143 Eu80

The level scheme of ¹⁴³ Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the ¹¹⁰ Pd(³⁷ Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.     

Structure of140Pm from beta decay of140Sm

The structure of¹⁴⁰Pm is investigated through the beta decay of¹⁴⁰Sm, whose half-life is measured to be (14.7 ± 0.2) m. A level structure comprising 41 transitions among 17 excited states is constructed. Using the deduced ft values and measured internal conversion coefficients, spin-parity assignments to several states in¹⁴⁰Pm were made. From beta end-point measurement, the total decay energy is deduced to beQ _EC =3.4±0.3 MeV, which is compared with the predictions of several mass formulae. The systematics of the odd-Z, N=79 isotones are discussed.     

Radioactive decay of 1.7-h149Nd to levels of transitional149Pm

Sources of¹⁴⁹Nd were produced by thermal-neutron irradiation of enriched¹⁴⁸Nd. High resolution Ge(Li) spectrometers were used to collect gamma-ray singles and coincidence spectra in the study of the decay of 1.7-h¹⁴⁹Nd. A total of 214 gamma rays have been assigned to the decay of¹⁴⁹Nd, and 201 of these transitions have been placed in a level scheme of¹⁴⁹Pm involving 42 excited states. Absolute values for the beta-group intensities were determined for transitions to the¹⁴⁹Pm levels, and spin and parity assignments were made for many of the observed states. The experimentally determined level structure of¹⁴⁹Pm was compared with corresponding levels in other odd-mass Pm and Eu nuclides. Interpretations were made in terms of the core-coupling model. Radioactive decay¹⁴⁸Nd(n, γ)¹⁴⁹Nd; measuredE _γ,I _γ,γ-γ coinc.¹⁴⁹Pm deduced levels,J,π. Compton-suppression. Ge(Li) detector. Enriched targets.     

Comparison of cluster and shell model wave functions of deformed32S states

The 786 keV beta-286keV gamma angular correlation in the ground state decay of¹⁴⁹Pm is measured for the first time, using the conventional slow-fast scintillation assembly. Integral correlation results characterize the involved beta transition to be of first-forbidden non-unique type. The present results combined with the other experimental parameters, strongly support a 9/2^? spin-parity character to the 286 keV level in¹⁴⁹Sm. The energy independence of the reduced correlation coefficient as found in this work shows the validity ofξ-approximation for the 786 keV beta transition in¹⁴⁹Pm and is also consistent with the logft value and spectrum shape reported by earlier authors.     

Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

¹³⁶Pm and¹³⁶Nd were studied using theβ decay of¹³⁶Sm and¹³⁶Pm. The radioactive nuclei were produced by the⁹²Mo (⁴⁸Ti,xpyn) and¹¹²Sn (²⁸Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of¹³⁶Pm was constructed and the half-life of¹³⁶Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of¹³⁶Nd.     

New states and γ-transitions in 209Bi observed in the (3He, d*γγ)-subcoulomb-reaction

High-spin states in ¹⁴³Pm have been investigated via the ¹²⁸Te(¹⁹F,4nγ)¹⁴³Pm reaction using techniques of in-beam γ-spectroscopy. γ-ray singles, γ-γ coincidences, γ-ray anisotropies and DCO ratios have been measured. Based on these measurements, the level scheme of ¹⁴³Pm has been extended up to an excitation energy of 10535.4 keV, including 48 new γ-rays deexciting 28 new levels. The yrast levels in ¹⁴³Pm can be understood qualitatively in the framework of a weak-coupling model. Received: 10 July 2000 / Accepted: 12 October 2000     

Discrete γ-rays in the reactions of 143 MeV32S with58Ni

The reactions induced by 143 MeV³²S on⁵⁸Ni have been studied detecting discrete γ-rays in coincidence with projectile-like fragments (PLF). Information on PLF excitation probability and sequential decay of target-like fragments (TLF) has been obtained. For the²⁸Si+⁶²Zn outgoing channel at small energy loss (¦Q¦<20 MeV), both PLF and TLF data indicate that thermal equilibrium is not attained. The hypothesis of an equal excitation energy partition between the two reaction fragments does not describe properly experimental TLF data. A dependence of PLF excitation probability on the outgoing channel is found for the two final channels³²S+⁵⁸Ni and²⁸Si+⁶²Zn. The values of the spin alignment parameterP _zz, derived for PLF and TLF from measurements ofγ-rays anisotropy, are in disagreement with the expectations of the transport theory for dissipative collisions.     

Lifetimes of a dipole cascade in 192Hg

The β-spectrum of the 3^?-2⁺ transition in the decay of¹⁴⁶Pm has been investigated with a 4π-Si(Li)-semiconductor spectrometer in a β-γ-coincidence experiment for the first time. The shape factor has been determined: C(W)=1?0.394W}-0.275/W+0.044 W². The spin and parity of the ground state of¹⁴⁶Pm can be determined to be 3^?. The shape of this non-allowed spectrum indicates the existence of the “cancellation” or “selection rule” effect.     

Gamma decay of the giant dipole resonance and feeding of superdeformed states in 143Eu

The γ decay of the giant dipole resonance (GDR) built on excited nuclear states has been measured in coincidence with the low-energy γ discrete transitions for the nucleus ¹⁴³Eu. The reaction used was ¹¹⁰Pd(³⁷Cl, 4n)¹⁴³Eu at a beam energy of 165 MeV. The EUROBALL spectrometer (for the measurement of discrete γ transitions) coupled with the HECTOR array (for high-energy γ-ray detection) has been used. The high-energy γ-ray spectrum in coincidence with superdeformed (SD) discrete transitions of ¹⁴³Eu shows an “excess” between 9–12 MeV if compared with the one associated to cascades which do not pass through the SD configurations. Such an “excess” is in the energy region where one expects the low-energy component of the GDR strength function built on a SD state. The measured intensity can be reproduced by the statistical model assuming that the superdeformation survives only few MeV above the yrast line. A similar and consistent scenario has also been obtained by comparing the high-energy γ-ray spectra of ¹⁴³Eu in coincidence with its spherical (which is fed by the SD configuration) and its triaxial configuration (which is bypassed by the decay of the SD states).     

壳模型对143Pm核跃迁几率的计算

原子核跃迁几率理论计算和实验对比是分析描述原子核内部结构的主要手段之一。目前采用重离子核反应观测到^143Pm核（Z=61，N=82）高自旋能级结构:激发态最大能级达x=8397．6keV，对应自旋J=47／2（h=1）。利用核壳模型在计算^143Pm核能级结构及对应的自旋宇称基础上，系统地对其γ级联跃迁链以及纯E2跃迁进行了计算，并与实验数据进行对比。采用OXBASH程序的单粒子跃迁公式计算了^143Pm的跃迁几率。At present, the high spin state of ^143 Pm（Z = 61, N = 82） have been investigated. The level scheme of ^143Pm has been extended up to an excitation energy Ex = 8 397.6 keV and spin J =47/2（ h = 1 ）. Based on the nuclear shell model （NSM）, we have calculated the sequences of γ-ray transition rates and the pure E2 reduced transition probabilities of ^143Pm, and compared with experimental data. The formula of single-particle transition probability in the OXBASH code was applied in this paper.     

Tentative level diagram of146Pm below 1.1 MeV

The level scheme of the doubly odd nucleus¹⁴⁶Pm was investigated by means of in-beam spectroscopy. The¹⁴⁶Nd(p, n) reaction in the 3.5–8 MeV proton energy interval on enriched targets has been used to populate the exited states of¹⁴⁶Pm. High resolutionγ-ray spectra using Ge(Li) and hyperpure Ge detectors and conversion electrons with a mini-orange spectrometer were measured. Withγ-exitation functions andnγ-coincidences usingnγ-discriminated NE231 neutron detectors transitions in¹⁴⁶Pm were identified,γγ-coincidences gave information aboutγ-cascades. With these data a level scheme of 38 levels below 1.1 MeV exitation energy has been deduced including 73 transitions. For 12 transitions experimental conversion coefficients have been evaluated, which agree with the expected values forM1/E2-transitions.     

Coulomb excitation of levels in 143Nd and 145Nd

The low-lying states of ¹⁴³Nd and ¹⁵⁴Nd have been studied by means of Coulomb excitation with ¹⁶O and α-particles. Angular distribution measurements were carried out for some transitions in ¹⁴⁵Nd with 11.2 MeV α-particles. Level energy decay schemes and B(E2)↑ values were measured for two states in ¹⁴³Nd and for six states in ¹⁴⁵Nd. Some spin assignments have been established for the ¹⁴⁵Nd nucleus. ¹⁴³Nd and ¹⁴⁵Nd have been theoretically described by coupling one and three particles, respectively, to quadrupole vibrations, and rather good agreement with experiment was achieved.