Study of even-mass Ba nuclei by the (p,t) reaction

The (p, t) reaction on the nuclei ^{134, 136, 138}Ba has been studied at a bombarding energy of 52 MeV. Angular distributions of emitted tritons were obtained between 6° and 60°. The following six negative-parity states were strongly excited by the (p, t) reaction: 5^?(2.121 MeV) and 7^?(2.482 MeV) in ¹³²Ba, 5^?(1.998 MeV) and 7^?(2.274 MeV) in ¹³⁴Ba, and 5^?(2.139 MeV) and 7^?(2.031 MeV) in ¹³⁶Ba. DWBA calculations using the code DWUCK successfully reproduce these angular distributions. The 0⁺ assignment to the 1.761 MeV level in ¹³⁴Ba is confirmed. Intensities of the (p, t) reaction for low-lying states are discussed.     

A measurement of B(E3;0+ → 31−) and some E2 transition probabilities in 132, 134, 136, 138Ba using Coulomb excitation

Reduced transition probabilities, B(E2) and B(E3), have been measured for low-lying 2⁺ and 3^? states in ^{132, 134, 136, 138}Ba using Coulomb excitation by 40 MeV ¹²C ions. The B(E2) values are in general consistent with previous measurements and the B(E3;0⁺ → 3₁^?) values are 0.176 ± 0.022, 0.148 ± 0.018, 0.155 ± 0.018 and 0.133 ± 0.013 e² · b³ for ^{132, 134, 136, 138}Ba respectively. These B(E3) values correspond to about 24 to 17 W.u. and such enhancements suggest that these 3^? states have an essentially collective character which may be attributed to octupole vibrations.     

On the inelastic excitation of 2− state of 16O by α particles

The excitation of the unnatural parity state (2^?, 8.87 MeV) of ¹⁶O by inelastic scattering of 40 MeV α particle is investigated microscopically. The two step excitation mechanism via the 3^? state at 6.13 MeV is found to reproduce the magnitude of the measured cross section of the 2^- excitation. The α-nucleon interaction used for the 2^- excitation also reproduces the 3^- excitation.     

High-spin states of145Sm

High-spin states of¹⁴⁵Sm were studied by using the²⁰Ne(¹³⁶Xe, α7n),¹³⁹La (¹⁰B, 4n) and¹³⁸Ba(¹³C,6n) reactions. The decay scheme of a high-spin isomer of¹⁴⁵Sm was established. The excitation energy and the spin-parity of the isomer were determined to be 8.8 MeV and (49/2⁺), respectively. The level scheme was extended up to the (65/2) state at 14.6 MeV. The experimental results were discussed comparing with the deformed independent particle model (DIPM) calculation.     

A study of the 138Ba(d,p)139Ba reaction at 19 MeV

The ¹³⁸Ba(d,p) reaction has been studied at an incident deuteron energy of 19 MeV, using the injector-tandem accelerator and the multichannel magnetic spectrograph of the University of Oxford. Deuteron and proton optical model parameters have been obtained from the analysis of elastic scattering experiments on a ¹³⁸Ba target. The parameters have been used to calculate theoretical (d, p) angular distributions on the basis of the DWBA. From the comparison of experimental and theoretical distributions, orbital angular momentum transfers have been deduced and spectroscopic factors determined for all the levels observed up to an excitation energy of 2.5 MeV in ¹³⁹Ba. The spectroscopic information thus obtained is more complete than that from previous studies, and is in satisfactory agreement with expected sum rule limits. A notable item of new information is the assignment of an l_n = 6 transition to the level at 1.54 MeV in ¹³⁹Ba.     

Neutron scattering lengths and cross sections of the barium isotopes

Coherent neutron scattering lengths and total cross sections have been measured for barium compounds and on isotopically enriched samples for neutron energies from 0.5 meV up to 132 eV using different techniques. From the experimental data the following quantities were obtained:

the coherent scattering lengths (in fm) of Ba (5.07±0.03) and of the isotopes with mass numbers 130 (?3.6±0.6); 132 (7.8±0.3); 134 (5.7±0.1); 135 (4.66±0.10); 136 (4.90 ±0.08); 137 (6.82±0.10); and 138 (4.83±0.08).

the absorption cross sections σ_γ (at 0.025 eV in barn): of Ba (1.1±0.1) and of the isotopes: 130 (30±5); 136 (0.68±0.17); 137 (3.6±0.2); and 138 (0.27±0.14).

zero-energy scattering cross sections for Ba and the isotopes 136, 137 and 138. On the basis of these data, the isotopic- and spin-incoherent cross sections and the (s)-resonance contributions to the coherent scattering lengths have been determined and discussed.

     

Spectroscopy of 41Sc by resonant scattering of protons: Observation of an intermediate structure

Excitation functions of elastic and inelastic scattering of protons on ⁴⁰Ca have been measured for incident proton energies between 4.8 and 8.2 MeV. Spin and parity assignments and partial width determinations of ⁴¹Sc states between 5.8 and 8.7 MeV excitation energy have been made on the basis of quantitative analyses of the data for the different inelastic channels. Intermediate structure has been identified in the excitation function for the inelastic scattering to the 3^? (3.73 MeV) state in ⁴⁰Ca. This has been interpreted as being due to the presence of a state in ⁴¹Sc which consists primarily of the core nucleus ⁴⁰Ca in its 3^? state with a 2p particle weakly coupled to it.     

132，134，136，137Ba（n，p）、132，134Ba（n，2n）反应截面测量

本文叙述１４．２±０．１ＭｅＶ中子能量的１３７Ｂａ（ｎ,ｐ）１３７Ｃｓ、１３６Ｂａ（ｎ,ｐ）１３６Ｃｓ、１３４Ｂａ（ｎ,ｐ）１３４Ｃｓ、１３２Ｂａ（ｎ,ｐ）１３２Ｃｓ、134Ｂａ（ｎ,２ｎ）１３３Ｂａ和１３２Ｂａ（ｎ,２ｎ）１３１Ｂａ等反应截面的测量,测量方法采用以５４Ｆｅ（ｎ,ｐ）５４Ｍｎ和５４Ｆｅ（ｎ,ａ）５１Ｃｒ反应为标准截面的相对活化法,并用现有的数据对本结果进行了比较． The cross sections of the 137Ba (n, p) 137Cs, 136Ba (n, p)136Cs, 134Ba (n, p ) 134Cs, 132Ba (n, p) 132Cs, 134Ba(n, 2n) 133Ba and 132Ba(n, 2n ) 131Ba reactions have been measured by using the activation method relative the cross sections of 54Fe(n, p ) 54Mn and 54Fe(n,a)51Cr reactions at the neutron energy of 14. 2 ±0. 1MeV. The results obtained are compared with the data on hand.     

Properties of N=84, even-even nuclei populated in the spontaneous fission of 248Cm

Excited states in the neutron-rich, N=84 nuclei ¹³⁴Sn, ¹³⁶Te and ¹³⁸Xe, populated in the spontaneous fission of ²⁴⁸Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h_9/2 excitation in the ¹³²Sn region. A discrepancy between the observed and calculated excitation energy of the I^π= 12⁺ level in ¹³⁶Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in ¹³⁸Xe. Received: 10 November 1999 / Revised version: 22 December 1999     

Effect of nuclear shell structure on fusion reaction

The dependence of the fusion reaction on the nuclear shell structure was investigated for the two reaction systems ⁸²Se + ¹³⁸Ba and ⁸²Se + ¹³⁴Ba, where the nucleus ¹³⁸Ba has a closed neutron shell N=82, while the nucleus ¹³⁴Ba has a neutron number 78. Evaporation residues for these fusion reactions were measured near the Coulomb barrier region. The measured evaporation residue cross sections for the reaction system ⁸²Se + ¹³⁸Ba were two orders of magnitude larger than those for the reaction system ⁸²Se + ¹³⁴Ba in the excitation energy region of 20–30 MeV. The evaporation residue cross sections were compared with those of the other reaction systems that produce the same compound nucleus as the present systems. It was found that the fusion reaction ⁸²Se + ¹³⁸Ba occurs without hindrance, while that of ⁸²Se + ¹³⁴Ba is considerably hindered, as commonly observed in the massive reaction system with the charge product Z _p Z _t >1800 of projectile and target. This suggests the importance of the shell closure N=82 in the heavy-ion fusion reaction.     

Elastic and inelastic scattering of 185 MeV protons from 12C

The polarization of 185 MeV protons in elastic scattering and in the excitation of the 2⁺ state at 4.44 MeV and the 0⁺ state at 7.65 MeV in ¹²C has been measured in the angular region 2°–60°. Optical model calculations are performed for the elastic scattering. Angular distributions for the inelastic scattering from the 2⁺ state at 4.44 MeV and the 3^? state at 9.64 MeV are calculated in the distorted-wave impulse approximation (DWIA) as well as in the distorted-wave Born approximation (DWBA).     

Inelastic proton scattering from Ba and Sm at 30 MeV

Measurements of the inelastic scattering of 30 MeV protons from ¹³⁸Ba and ¹⁴⁴Sm have been carried out with 7–10 keV energy resolution. Differential cross sections were measured for levels up through 3.4 MeV excitation energy. For most of these states J^π assignments are suggested on the basis of angular distributions distinctly characteristic of angular momentum transfer L = 2, 3, 4,or 6.     

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1⁺, T = 1) level and for the M2 transition to the 16.58 MeV (2^?, T = 1) level in ¹²C have been measured in the momentum transfer region q = 0.4–3.0 fm^?1, with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ_γ0 = 38.5 ± 0.8 eV.     

Inelastic electron scattering from 6Li near the α-d threshold

The form factor for the alpha-deuteron continuum in ⁶Li has been measured in the excitation region within 2 MeV of threshold, for momentum transfers q < 1.2 fm^?1. The results are interpreted in terms of an α-d cluster model. The monopole breakup appears to be predominant near threshold, but the influence of the J = 2⁺ (4.31 MeV) quadrupole resonance becomes important a few MeV above threshold. The form factor for the C2 transition to the 3⁺ (2.185 MeV) state is also presented.     

The 14C(α, α')14C and 13C(d,p)14C reactions

The isoscalar transition rates and neutron-stripping probabilities to states of ¹⁴C have been measured using the 35 MeV ¹⁴C(α, α')¹⁴C and 17.7 MeV ¹³C(d, p)¹⁴C reactions. States showing great charge asymmetries in pion scattering at 8.32 MeV (2⁺) and 11.7 MeV (4^?) were examined in detail. Isoscalar transition rates B(02) were determined to be 168, 96 and 74 fm⁴ for the 7.01, 8.32 and 10.45 MeV 2⁺ states, with identical single-neutron spectroscopic factors of 0.065, from the (d, p) data, for the lowest two states.     

Unelastische Elektronenstreuung am 1,78 MeV- und 11,4 MeV-Niveau des Si28

TheE2 transition at 1.78 MeV and the strongM1 transition at (11.42±0.02) MeV (measured excitation energy) in Si²⁸ have been studied by inelastic electron scattering at the Darmstadt linear accelerator. Primary energies between 30 and 56 MeV, and scattering angles from 104° to 165° were used. In Born approximation, the following radiation widths to the ground state have been deduced: (1.21±0.17) · 10^?3eV (1.78 MeV,E2), and (32.4±4.5)eV (11.4 MeV,M1). Transition radii have been determined from the dependence of transition probability on momentum transfer.     

Elastische und inelastische Streuung von 104 MeV Alpha-Teilchen an58,60,62,64Ni

Differential cross sections are measured for the elastic and inelastic scattering of 104 MeV α-particles from^{58, 60, 62, 64}Ni. The experimental results are analyzed in terms of coupled channels on the basis of an anharmonic vibrational model and prove to be quite sensitive to the values of the deformation parameters. For forward angles the 4⁺ angular distributions of^58,60Ni are dominated by aL=4 single excitation mechanism. This is in keeping with theE4-transitions observed in (e, e′) scattering. From the 2 ₁ ⁺ - and 3 ₁ ⁺ -results transition rates are derived which can be compared to results of electromagnetic methods and of inelastic proton scattering studies. The comparison indicates that the transition rates differ and are generally higher for the proton scattering. Especially in the case of the 3^? states of^58,60Ni the differences are obvious. The elastic cross sections are analyzed both on the basis of the usual phenomeno-logical model and in terms of a semimicroscopic folding model resulting in values of rms-radii for the nuclear matter distribution.