Differential cross sections for radiative capture of energetic protons by 110Cd and 115In

Spectra of high-energy photons following the radiative capture of 8–22 MeV protons in ¹¹⁰Cd and ¹¹¹In are measured. The (p, γ) differential cross sections at 90° with respect to the beam axis is deduced from the integration of measured spectra. The photon angular distribution is measured for the ${}^{110}\text{Cd}\text{(}\text{p}\text{, γ}{}_0\text{)}$ reaction, too, at 13 MeV incident energy. Satisfactory agreement between theory and experiment is obtained by using the direct-semidirect model for dipole and quadrupole fast nucleon radiative capture.     

γ-Ray multiplicity in 239Pu fission induced by resonance neutrons: experimental evidence for the (n, γf) reaction

The fission γ-ray multiplicity measurement in the ²³⁹Pu resonances has been carried out, using the Saclay 60 MeV electron linac as a neutron source. Large fluctuations are observed from resonance to resonance, in correlation with the number $\text{}\text{?}$Gn of prompt neutrons, the total energy of these γ-rays and the fission width Γ_f. The results are interpreted in terms of a competition between the fission and the radiative capture during the de-excitation of the compound nucleus. They are the first experimental evidence of the (n, γf) reaction. Some parameters like the width $\text{Г}{}_{\mathrm{\gamma f}}$ are deduced.     

Decay of 48K, 49K and 50K

The ⁴⁸K, ⁴⁹K and ⁵⁰K nuclides have been produced in high energy fragmentation and analyzed by mass spectroscopy techniques. Their half-lives have been measured as 6 ± 1 s, 1.1 ± 0.3 s and and 0.7 ± 0.3 s, respectively. The γ-rays from their radioactive decay have been observed and the corresponding γ-intensities measured. The nuclide ⁵⁰K is shown to be a delayed neutron emitter. The antianalog states in the daughter Ca nuclei with a $\text{(1d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?}}$ neutron configuration, preferentially populated in the β-decay, have been located. The corresponding $\text{1d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ neutron single-particle energy is found to remain approximately constant for these neutron-rich Ca isotopes.     

The β− decay of 102Mo

The ¹⁰²Mo activity was obtained by photofission of natural U and thermal-neutron induced fission of ²³⁵U, with subsequent chemical separation of the molybdenum fraction. In addition, nuclei with mass 102 were separated from fission products of ²³⁵U(n_th, f) using the mass separator LOHENGRIN. A decay scheme and absolute γ-intensities are deduced from measured γ-ray, X-ray and γ-coincidence spectra. Logftvalues are calculated. Shell-model calculations for a $\text{(πlg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^3$$\text{(νlg}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^3$ multiplet have been carried out using effective nucleon-nucleon interactions. The γ-decay between low-lying, low-spin members of this multiplet was studied in detail and compared with the experimental data.     

The excited states of 85Sr

High resolution γ-ray studies have shown the decay patterns of isomers of ⁸⁵Y to be very complex. A level scheme of ⁸⁵Sr is proposed from the results of γ-γ coincidence measurements. Spin and parity assignments to the levels of ⁸⁵Sr were made on the basis of log ft values, nuclear reaction data and γ-ray branchings. The level scheme is discussed within the theoretical framework of $\text{n(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?3}}$ cluster properties.     

Proton capture by 11B above the giant resonance

The cross sections for proton capture by ¹¹B to the ground and excited states of ¹²C have been measured in the proton energy interval between 18 and 43 MeV. The ground-state cross section shows good agreement with theoretical calculations including correlations. Capture photons have also been observed to all the residual 1p-1h states of ¹²C having a dominant $\text{1}\text{p}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ hole: the corresponding cross sections systematically show a giant resonance whose energy increases with the increasing excitation energy of the “background” level. The resonances at 27.4, 31, 33.2, 37 and 43 MeV, seem to show observable interference effects.     

In-beam study of 144Gd

A level scheme of ¹⁴⁴Gd has been established using the ¹⁴⁴Sm(α, 4nγ) reaction and in-beam spectroscopy methods. Excitation functions, γ-ray angular distributions, γ-γ coincidence spectra, γ-spectra time related to the cyclotron beam bursts and conversion coefficients for the delayed transitions have been measured.The level scheme comprises 11 levels with spins up to I = 12. Two isomers, a 13 ± 2 ns, 7^? state at 2471.4 keV and a 145 ± 30 ns, 10⁺ state at 3433.0 keV have been observed. The former has similar excitation energy as the 7^? isomers in ¹⁴²Sm, ¹⁴⁰Nd and ¹³⁸Ce and it may arise from the $\text{{ν}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{× ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{}}$ configuration although its lifetime seems to indicate some degree of collectivity. The 10⁺ state has a similar excitation energy as the 10⁺ isomer found in ¹³⁸Ce and it may arise from the dominant $\text{ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?2}}$ configuration. Below the 10⁺ isomer in ¹⁴⁴Gd only two excited states have positive parity; the hitherto known first 2⁺ and 4⁺ states. The 11⁺ and 12⁺ states must include four-particle configurations or they have to be of collective nature. The latter possibility is supported by the considerable E2/M1 mixture (≈ 20 %) observed for the 11⁺ to 10⁺ transition. An analysis of the systematics of ground band levels in the N = 80 isotones shows the same gradual behavior between the two VMI solutions previously found for the Te isotopes.     

A remeasurement of the 12C(α, γ0) excitation function in the vicinity of the 12.44 and 13.1 MeV levels of 16O

The excitation function of the ${}^{12}\text{C(α, γ}{}_0\text{)}$ reaction at θ = 90° has been remeasured for bombarding energies between 6.5 and 8.5 MeV. The measurement was made to resolve discrepancies apparent in earlier measurements relating to the absolute cross section, the location of the lower 1^? resonance near 7.05 MeV (¹⁶O excitation energy 12.44 MeV) and to the relative peak cross sections of this resonance and a second 1^? resonance at 7.88 MeV.     

A neutron decoupled from a rotating odd core in 114Sb and 116Sb

The ^{113, 115}In(α, 3nγ)^{114, 116}Sb reactions have been studied using γ-ray spectroscopic techniques. The experiments included γ-ray excitation function, γ-γ coincidence, lifetime, γ-ray angular distribution and conversion electron measurements. A ΔJ = 1 rotational band has been observed in either of the ^{114, 116}Sb final nuclei. Energy spacings and electromagnetic properties of the band show strong resemblances with those of rotational bands in the adjacent odd-mass Sb nuclei. In addition two-quasiparticle and two-quasiparticle core coupled states have been observed in these nuclei. One isomer was identified in ¹¹⁶Sb, i.e. a J^π = 11⁺ state at 1889 keV ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext><mtext>\; =\; 4.0\pm 0.1\; </mtext><mtext>ns</mtext>}}$). A simple model is proposed which explains the ΔJ = 1 band in terms of rotational alignment of the $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ neutron with the deformed rotating odd-A core.     

Level structure of 100Tc

Gamma and electron spectra following thermal neutron capture on ⁹⁹Tc have been studied with a bent-crystal spectrometer, Ge(Li) and Si(Li) detectors and a magnetic spectrometer. Prompt and delayed γ-γ coincidences with Ge(Li) detectors have been performed. A level scheme is proposed for ¹⁰⁰Tc comprising 21 excited states up to 640 keV. The binding energy of the last neutron in ¹⁰⁰Tc was deduced. For most levels, spin and parity values were assigned. Two isometric transitions of respective half-lives 10.2 and 4.6 μs have been identified using the ¹⁰⁰Mo(d, 2n)¹⁰⁰Tc reaction with a pulsed beam of deuterons. From the comparison of the present (n, γ) study and the collaborative study of the ⁹⁹Tc(d, p) reaction, several members of the multiplets $\text{π}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{ν}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$, $\text{π}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{ν}\text{g}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$, $\text{π}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{ν}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{π}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{ν}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ have been identified.     

VAMPIR calculations for 128Ba and 130Ce: Two mechanisms of backbending

Hartree-Fock-Bogoliubov calculations with spin and number projection before the variation (VAMPIR) are performed for the nuclei ¹²⁸Ba and ¹³⁰Ce using a slightly renormalized Brueckner G-matrix as effective interaction in a rather large single-particle basis. The results are compared to those of Hartree-Fock-Bogoliubov calculations with projection after the variation, those of multiconfiguration calculations (MONSTER) and to experiment. In both nuclei the VAMPIR and the MONSTER approaches turn out to be of about the same quality and agree rather well with the experimental data. Analysis of the VAMPIR mean fields reveals that two somewhat different mechanisms are responsible for the backbending observed in the yrast bands of the two nuclei. While in ¹³⁰Ce the well-known alignment of two high-j quasiparticles (proton $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$) is found, in ¹²⁸Ba first a neutron pair is scattered from the $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ to the $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ orbit, and then the larger alignment energy of the less occupied neutron $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ states produces the backbend. This latter effect is in agreement with the predictions of a simple model presented by us some years ago.     

High-resolution measurements of analogue states in 55Co

Differential cross sections were measured at four angles for proton elastic and inelastic scattering on ⁵⁴Fe at energies from 3.25 to 4.0 MeV by means of a high-resolution beam. An overall resolution of 400 eV was realized using thin solid targets. Spins, parities and partial widths were extracted for all resonances observed: two p-wave, one f-wave and one g-wave analogue state, all of them being fragmented and identified in the elastic and inelastic data. Spectroscopic factors and Coulomb displacement energies were obtained for these analogue states. The γ-ray angular distributions and resonance strenghts were measured on the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ resonances to determine rates of the IAR-AIAS M1 transition and the El transitions to the low-lying states including the g.s.     

Low-lying levels of 140Pr

The doubly odd nucleus ¹⁴⁰Pr has been investigated by means of the ¹⁴¹Pr(d, t)¹⁴⁰Pr and ¹⁴⁰Ce(p, nγ)¹⁴⁰Pr reactions. Twenty-eight levels, up to 1300 keV excitation, were observed in the pickup study. DWBA analysis was used to determine l-values and spectroscopic factors for all but a few which are very weakly populated. Gamma-ray angular distributions, measured at E_p = 4.78 MeV for the five strongest γ-rays, show appreciable nuclear alignment and demonstrate the feasibility of such experiments in this mass region. Taken together, the two studies have permitted the identification of the 12 levels expected from the low-lying ($\text{π2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{ν2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$), ($\text{π2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{ν3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$), ($\text{π1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{ν2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$) and (π1g_{$\text{7}\text{2}$}ν3s_{$\text{1}\text{2}$}^?1) configurations. Tenta assignments for the strong odd-parity states are suggested on the basis of their spectroscopic factors.     

Neutron resonance parameters and radiative capture cross sections of 147Sm and 149Sm

Neutron capture and transmission measurements have been carried out on the separated isotopes of ¹⁴⁷Sm (98.34 %) and ¹⁴⁹Sm (97.72 %) at the 55 m time-of-flight station of the Japan Atomic Energy Research Institute electron linear accelerator. Resonance energies and neutron widths for a large number of resolved resonances were determined up to 2 keV for ¹⁴⁷Sm and 520 eV for ¹⁴⁹Sm. Radiation widths for 5 resonances in ¹⁴⁷Sm + n and 7 resonances in ¹⁴⁹Sm + n were derived. The s-wave strength functions, average level spacings and average radiation widths were obtained to be: $\text{10}{}^4\text{S}{}_0\text{= 4.8 ± 0.5,}\text{D}\text{= 5.7 ± 0.5}\text{eV}$ and $\text{Γ}{}_{\mathrm{\gamma }}\text{= 69 ± 2}\text{meV for}{}^{147}\text{Sm}$; a $\text{10}{}^4\text{S}{}_0\text{= 4.6 ± 0.6,}\text{D}\text{= 2.2 ± 0.2}\text{eV}$ and $\text{Γ}{}_{\mathrm{\gamma }}\text{= 62 ± 2}\text{meV for}{}^{149}\text{Sm}$. The average capture cr sections were deduced from 3.3 to 300 keV with an estimated accuracy of 5 to 15 %. The measured capture cross sections for ¹⁴⁹Sm are largely different from the evaluated data, which are obtained based on the statistical model calculation. Possible reasons for this disagreement are discussed.     

Measurement of neutron energy spectra and neutron-gamma angular correlations for the muon capture process 16O(μ−, νμxn)14, 15N

Neutron-gamma coincidence spectra have been measured for muon capture in ¹⁶O. The γ-spectrum is dominated by the ground state transitions from the $\text{3}\text{2}{}^{\mathrm{?}}\text{(6.32}\text{MeV}\text{)}\text{and}\text{1}\text{2}{}^{\mathrm{+}}\text{+}\text{5}\text{2}{}^{\mathrm{+}}\text{(5.3}\text{MeV}\text{)}$ states of ¹⁵N that are populated after the emission of one neutron. The neutron energy spectra and the neutron energy dependence of the ny angular correlation coefficient A₂ for these final states are presented. The observed transitions in ¹⁴N and the associated neutron spectra give direct evidence for the emission of two correlated neutrons. The data are discussed in terms of direct neutron emission plus emission via giant resonance intermediate states of ¹⁶N. The large yield for the emission of one and two fast neutrons is explained by a capture mechanism involving short-range nucleon-nucleon correlations.     

Interference effects in 12C(p, γ)13N and direct capture to unbound states

Excitation functions of the capture reaction ¹²C(p, γ₀)¹³N have been obtained at θ_γ = 0° and 90° and E_p = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in ¹³N is included in the analysis in addition to the two well-known resonances in this beam energy range $\text{[E}{}_{\mathrm{p}}\text{= 457(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}$ and 1699 $\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{) keV]}$. The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C²S(l = 1) = 0.49 ± 0.15 has been deduced for the $\text{1}\text{2}{}^{\mathrm{?}}$ ground state in ¹³N. Excitation functions for the reaction ${}^{12}\text{C(p,γ}{}_1\text{p}{}^1\text{)}{}^{12}\text{C}$ have been obtained at θ_γ = 0° and 90° and E_p = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. Above E_p = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below E_p = 1 MeV, i.e., E_p → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at $\text{E}{}_{\mathrm{p}}\text{? 1 MeV}$, a spectroscopic factor of C²S(l = 0) = 1.02 ± 0.15 has been found for the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. A search for direct capture transitions to the $\text{3512 (}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$and $\text{3547 (}\text{5}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound states resulted in upper limits of C²S(l = 1) ≦ 0.5 and C²S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the ¹²C(p, γ₀)¹³N reaction also is discussed.     

β-delayed charged particles from 9Li and 11Li

β-delayed emission of α-particles from ⁹Li and of both α and ⁶He particles from ¹¹Li is observed. Singles energy spectra and two-dimensional energy spectra of coincident particles are measured. A time-of-flight versus energy measurement is used to identify the mass of the particle. New β-branches are observed which populate high-energy levels in the daughter nuclei. The branching ratios are measured and the β-delayed neutron emission probabilities $\text{P}{}_{\mathrm{<mtext>n</mtext>}}\text{for}{}^9\text{Li and}\text{P}{}_{\mathrm{3n}}\text{for}{}^{11}\text{Li}$ are deduced.     

Excitation of the deeply bound g92 neutron hole state in 117Sn by a neutron pickup reaction with 81.7 MeV 3He particles

Neutron hole states have been investigated by neutron pickup reactions on ⁹²Mo, ¹¹⁸Sn, ¹⁴⁰Ce and ²⁰⁸Pb with 81.7 MeV ³He particles. A strong effect of angular momentum mismatch has been observed to reduce the cross section for low-spin orbits. It causes the deeply bound $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbit to appear in the spectrum of the α-particles from the ${}^{118}\text{Sn(τ, α)}{}^{117}$Sn reaction as a strong broad peak. It may provide a nice tool for investigating the coupling mechanism between the deeply bound holes and the core.     

Nuclear reactions of 118Sn, 121Sb,and 127I with argon ions

Excitation functions have been measured for a number of (⁴⁰Ar, xn), (⁴⁰Ar, pxn), (⁴⁰Ar, 2pxn), and (⁴⁰Ar, 3pxn) reactions induced in ¹¹⁸Sn, ¹²¹Sb and ¹²⁷I over the lab. energy interval 150–280 MeV. Values of the total fusion cross section are obtained and J_crit is deduced. The value of J_crit increases with energy and becomes as large as 110–140?, in reasonable agreement with the yrast limit deduced from the ellipsoidal liquid drop model. The competition between proton and neutron emission from the compound nucleus is examined and $\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}$ is found to increase rapidly with the number of emitted nucleons, thereby imposing severe limits on the production of very neutron deficient miclides via compound nuclear reactions. The effect of very high angular momentum on the excitation functions is examined.     

Neutron and proton alignment at high spin in 168W

Excited states in the neutron-deficient nucleus ¹⁶⁸W, populated in the ¹⁴⁸Sm(²⁴Mg, 4n)¹⁶⁸W reaction, have been studied using γ-ray spectroscopy. The yrast band, which is identified up to about spin 28, shows a very strong backbend at low frequency, $\text{h}\text{?}\text{ω}{}_{\mathrm{c}}\text{= 0.235}\text{MeV}$, attributed to the $\text{(i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{)}{}^2$ neutron alignment. Evidence for a second backbend is also observed. A strongly populated odd-spin (probably negative-parity) sideband is also identified to the spin, and shows several band-crossing anomalies. The characterisation of the anomalies is made by comparison with CSM calculations. Proton and neutron alignments are probably present in the sideband, and the second backbend in the yrast sequence may be due to alignment of $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ protons.