Spin assignments from the 142Nd(7Li, 6He)143Pm and 144Sm(7Li, 6He)145Eu reactions at 52 MeV

Angular distributions have been measured for transitions to low-lying states in ¹⁴³Pm and ¹⁴⁵Eu populated by the ¹⁴²Nd(⁷Li, ⁶He)¹⁴³ and the ¹⁴⁴Sm(⁷Li, ⁶He)¹⁴⁵Eu reactions at $\text{E(}{}^7\text{Li}\text{) = 52}$ MeV. Elastic scattering of ⁷Li at 52 MeV on ¹⁴²Nd and ¹⁴⁴Sm, and ⁶Li at 46 MeV on ¹⁴²Nd and at 45 MeV on ¹⁴⁴Sm, were measured. Optical-model parameters extracted from fits to the scattering data were used in a finite-range DWBA analysis of the angular distributions for levels below 1.40 MeV excitation energy in ¹⁴³Pm and 1.84 MeV in ¹⁴⁵Eu. The reaction cross sections forward of 6° c.m. allow unambiguous distinction to be made between 2d_{$\text{5}\text{2}$} and 2d_{$\text{3}\text{2}$} final states. Final-state spins have been assigned to d-states in ¹⁴³Pm at 1.40 MeV($\text{3}\text{2}$⁺)and in ¹⁴⁵Eu at 1.042 MeV ($\text{3}\text{2}$⁺). Existing assignments to other levels in both residual nuclei have been confirmed.     

Energy levels in 142Nd

The excited states of ¹⁴²Nd were studied by means of the decay of 40 sec ¹⁴²Pm and the ¹⁴²Nd(p, p') reaction via isobaric analog resonances. Approximately sixty levels of ¹⁴²Nd were observed below 5.3 MeV excitation, including several neutron particle-hole states excited strongly in (p, p') at f_{$\text{7}\text{2}$}, p_{$\text{3}\text{2}$}, p_{$\text{1}\text{2}$} and f_{$\text{5}\text{2}$} analog resonances. We have collected together all known energy levels in ¹⁴²Nd and have proposed J^π assignments for 22 excited states. We have also compared the experimental level spectrum (positive-parity states only) with a calculated one based on the shell model.     

High-spin states in the single-closed-shell nucleus 142Nd

The excited states of ¹⁴²₆₀Nd₈₂ have been studied using the ¹⁴⁰Ce(α, 2nγ)¹⁴²Nd and ¹⁴²Ce(α, 4γ)¹⁴²Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in ¹⁴²Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.     

Angular correlation studies in 144Nd

The decays of ¹⁴⁴Pr and ¹⁴⁴Pm populate ten excited states in ¹⁴⁴Nd. We have carried out detailed γγ angular correlation measurements in order to establish spin assignments for these levels. The measurements were performed with Ge(Li)-Ge(Li) and NaI(Tl)-Ge(Li) systems. Eleven sets of A₂₂ and A₄₄ values were obtained. The J^π assignments for levels in ¹⁴⁴Nd (level energies in keV) are as follows: g.s.,0⁺; 696, 2⁺; 1314, 4⁺ ; 1511, 3^?; 1561, 2⁺ ; 1791, 6⁺; 2084, 2⁺ ; 2093, 5^?; 2186, 1^?; 2204, 4; 2644, 1. Mixing ratios were determined for six γ-transitions.     

Energy levels of 56Co studied by the 58Ni(d, α)56Co reaction near 0°

Tensor analyzing powers, T₂₀, of outgoing α-particles in the ⁵⁸Ni($\text{d}$, α)⁵⁶Co reaction at detection angles near 0° have been measured for excited states in ⁵⁶Co for beam energies of 6.75, 7.0, 7.5, 9.0 and 9.5 MeV. Thirty-seven spin-parity combinations for ⁵⁶Co excited states have been deduced. Previous J^π ambiguities for 11 of these states have been eliminated, and results in conflict with existing assignments for the levels at 3.235 and 3.378 MeV have been obtained. A search for 0⁺ states was carried out from angular distribution measurements at forward angles of the unpolarized (d, α) reaction. The combined results from this and previous experiments were found to be in reasonable agreement with calculated level schemes.     

Reactions of 40Ar with 159Tb, 142Nd and 144Sm; New α-activities from 189Bi, 173Pt and 177Au

Reactions of ⁴⁰Ar ions with targets of ¹⁵⁹Tb, ¹⁴²Nd, and ¹⁴⁴Sm have been studied at energies below 300 MeV with a helium gas-jet system. Excitation functions for (Ar, xn) reactions, where x = 5–10, were obtained for the radioactive products that decay by α-emission. Based on the characteristics of these excitation functions and on the systematics of α-decay, evidence is presented for the existence of the nuclides ¹⁸⁹Bi with α-particle energy E_α = 6.67±0.01 MeV and half-life < 1.5 sec, and ¹⁷³Pt with E_α = 6.19±0.01 MeV; and for the emission from ¹⁷⁷Au of an α-particle with E_α = 6.15±0.01 MeV.     

The (t, α) reaction on 121Sb and 123Sb

Angular distributions of α-particles from the (t, α) reaction on ¹²¹Sb and ¹²³Sb have been measured for incident tritons of 12 MeV. Levels up to excitation energies of 5.2 and 4.9 MeV in ¹²⁰Sn and ¹²²Sn, respectively, have been identified and analysed by the DWBA. Values of orbital angular momenta of the transferred protons have been assigned and spectroscopic factors deduced for all strongly excited levels. The extracted ground-state wave functions of the target nuclei have been compared with the calculated ones. A mixture of collective degrees of freedom is present in the low-lying states, weakly excited by the above very selective proton pick-up reaction. These states are populated by the pick-up of external protons (outer shells). At higher excitation energy (between 4 and 5 MeV) there are many strongly excited states populated by the proton pick-up from the Z = 50 proton core (inner shells); a predominantly 1p-1h character has been assigned to these states.     

12C1 and 8Be production in 12C + 208Pb collisions

The mechanisms involved in the production of fast α-particles in ¹²C-induced reactions have been studied for the ¹²C + ²⁰⁸Pb system at the bombarding energies of E_12c = 132, 187 and 230 MeV. Absolute cross sections for the reactions ²⁰⁸Pb(¹²C. ¹²C¹→α + ⁸Be), ²⁰⁸Pb(¹²C, ⁸Be(g.s.)) and ²⁰⁸Pb(¹²C, ⁸Be(2.94 MeV)) have been determined by coincidence measurement of two or three correlated α-particles. Inclusive α-particle production cross sections were also measured at E_12c = 187 MeV. It is found that the inelastic process (¹²C, ¹²C¹→α + ⁸Be) does not contribute significantly to fast α-particle production but that the production of ⁸Be by projectile fragmentation is an important source of α-particles. At the highest bombarding energy (230 MeV) it appears that the ¹²C → 3α fragmentation reaction becomes more prominent at the expense of the ¹²C→α + ⁸Be fragmentation channel.     

In-beam study of 136Ce and 138Nd isotones with N = 78

Excited states in ¹³⁶Ce and ¹³⁸Nd have been investigated by means of in-beam spectroscopy with the (p, 4nγ) reaction. Excitation functions and angular distributions of γ-rays were measured with a Ge(Li) detector, and conversion electron spectra were taken with a magnetic spectrometer. Time-dependent spectra of γ-rays revealed delayed components with half-lives of 2.2μsec and 0.41μsec in ¹³⁶Ce and ¹³⁸Nd, respectively. Most of the excited states are classified as belonging to the quasi-ground-state rotational band and the quasi-gamma band. Negative parity 5^? and 7^? states were also observed.     

Level structure of 147Nd2 (iii). The 146Nd(n,e?) reaction

The conversion electrons following thermal neutron capture in ¹⁴⁶Nd have been studied in the energy range 30 < E_e < 125 keV, with a conversion electron spectrometer installed at the Grenoble high-flux reactor. Precise values of the multipole mixing ratio M1/E2 have been obtained for transitions up to 100 keV. Furthermore, the spin and parity for the 215 keV level is verified. The states of ¹⁴⁷Nd are compared with the two other N = 87 isotones; the properties of these nuclei can be understood in the framework of the spherical shell model.     

Nuclear and Coulomb deformation parameters of 142Nd

Nuclear and Coulomb deformation parameters have been deduced from DWBA analyses of angular distributions of 67.5 MeV ¹³C ions inelastically scattered from ¹⁴²Nd. Optical model parameters from fits of measured elastic scattering data were used with previously measured B(EL) values to determine initial deformation parameters. Comparison With the experimental data indicates that DWBA calculations can be used to understand the inelastic scattering from the nearly spherical nucleus ¹⁴²Nd.     

Correlations between emerging alpha-particles and heavy ions in 32S+197 Au collisions

In-plane angular correlations between α-particles and projectile residue nuclei (Z=5?22) emerging from ³²S+¹⁹⁷Au collisions have been measured at 373 MeV incident energy. In the combined Coulomb field of the projectile residue and the target nucleus coincident α-particles are strongly focused into a narrow cone. Model calculations indicate that α-emission originates from the region of the projectile which is facing the target nucleus during the collision.     

Investigation of backward α-particle scattering in 24Mg and 28Si through α-γ angular correlations

Alpha-gamma angular correlations have been measured for the reaction ²⁴Mg(α, α'γ) in the energy range 15.50 to 17.00 MeV in steps of 300 keV and for ²⁸Si(α, α'γ) from 15.00 to 16.20 MeV in steps of 200 keV to provide energy averaged results. The scattered α-particles were detected for lab angles θ_α = 115°–178° in a multidetector arrangement. The coincident γ-rays were observed with a Ge(Li) detector placed at 90° in the reaction plane. Data were obtained for the 1st, 2nd and 3rd excited states of ²⁴Mg and for the 1st, 2nd, 3rd and 4th excited states of ²⁸Si. The absolute doubledifferential cross sections were analysed with Hauser-Feshbach calculations. The analyses show that compound nuclear processes are responsible for the rise of backward α-scattering in ²⁴Mg(α, α'γ)²⁴Mg and ²⁸Si(α, α'γ)²⁸Si at the energy studied.     

Inelastic electron scattering from the giant isoscalar E2-resonance in 142Nd and 150Nd

Inelastic electron scattering has been used to study the isoscalar E2 giant resonances in ¹⁴²Nd and ¹⁵⁰Nd, which were found at excitation energies of 12.0 and 11.2 MeV with total widths of 2.8 and 5.0 MeV, respectively. The energy shift and the larger width in ¹⁵⁰Nd indicate a splitting due to the deformation of ¹⁵⁰Nd.     

An investigation of the 144Sm(α, 3He)145Sm reaction

The ¹⁴⁴Sm(α, ³He)¹⁴⁵Sm stripping reaction has been studied up to 3 MeV excitation energy with a 40 MeV α-beam. Angular distributions have been recorded, and spectroscopic factors are deduced using a standard DWBA procedure. The reaction favours high-l transfers, and is found to be very useful for the investigation of large-j states. From a comparison with the spectroscopic factors known from the ¹⁴⁴Sm(d, p)¹⁴⁵Sm reaction the normalization factor for the (α, ³He) reaction is found to depend strongly on the optical model parameters and on the transferred angular momentum l.     

Particle-core coupling in141Nd

High-spin states in¹⁴¹Nd have been studied using in-beam γ-ray spectroscopic techniques via the¹³⁰Te(¹⁶O, 5nγ)¹⁴¹Nd reaction. The level scheme of¹⁴¹Nd has been extended up to an excitation energy of 7614.5 keV including 12 new γ rays deexciting 15 new levels. According to particle-vibrator coupling and semi-empirical shell model calculations, the level structure of¹⁴¹Nd can be well interpreted by coupling an h_11/2 neutron-hole to the respective excited states in¹⁴²Nd core.     

Spin-parity assignments of excited states in 12C

The reaction ¹²C(α, α')¹²C¹(3α) is observed by using 90 MeV a-particles in ionographic matter. The energies of the three α-particles from the break-up of ¹²C¹ are plotted in Dalitz diagrams. The density distributions for the three α-particles in the diagrams are calculated by assuming the spins and parities for the states in ¹²C¹(3α). The spin-parities for the states are assigned by comparing the observed density distributions with those calculated.     

Spin and parity assignments for 35Cl levels from the 31P(α, p)34S reaction

³⁵Cl states at excitation energies between 9.9 and 11.8 MeV have been identified through sharp resonances in the ³¹P(α, p_o)³⁴S excitation functions at 25°, 105° and 155° for E_α = 3.25–5.50 MeV. Forty-eight on-resonance angular distributions, normalized to an absolute cross section scale, have been subjected to single-level and two-level analyses resulting in spin and parity assignments for each resonance. Approximately half the resonances were of the pure single-state type, having unique angular distribution shapes. Data from 12 resonances of an earlier experiment ¹) were analyzed with the same theory, extending the diagnostics down to a ³⁵Cl excitation energy of 9.1 MeV. A set of optical potentials consistent in all four reactions that this experimental program encompasses has been incorporated in the present analysis. Validity of the optical potential is demonstrated for α-particles elastically scattered by ³¹P.     

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.     

Multiparameter study of 1H, 3H and 4He in fast neutron induced fission of 235U

The emission probabilities per fission of α-particles, tritons and protons have been measured in fast neutron induced fission of ²³⁵U. The measurements were carried out at neutron energies of 120, 180, 230 and 550 keV. AΔE-E semiconductor detector telescope was used to identify different light charged particles and the fission fragments were detected with an ionization chamber. The three-parameter data corresponding to the pulse heights from the ΔE-E detectors and the ion-chamber were recorded event by event on magnetic tape and were analyzed off-line by computer. No significant variation in the most probable energy ($\text{E}$) and the standard deviation (σ_E) of the energy spectra of different light charged particles with incident neutron energy was observed, although $\text{E}{}_{\mathrm{\alpha }}$ was seen to have a slightly higher value beyond E_n = 230 keV. The yield of α-particles in fission induced by neutrons of E_n ～ 200 keV was found to be higher by about 20 % than that in thermal neutron induced fission. The yields of tritons and protons were found to increase significantly with neutron energy.