Study of the excitation function fluctuations of the dissipative28Si+48Ti binary collision in the incident energy interval from 206.9 MeV to 213.8 MeV

It is shown that the Partially Overlapping Molecular Level Model (POMLM) accounts for the experimental results of the dissipative²⁸Si +⁴⁸Ti collision around 210 MeV incident energy. The general trend of the properties of the fluctuations as well as the average angular distributions are reproduced by the same set of main parameters. A general consistency is also found between the present data and the data obtained in previous work on the same colliding system performed at lower incident energy (around 123 MeV).     

Rapid decrease of fragment emission time in the range of 3–5 MeV/u excitation energy

Multifragment emission processes from highly excited nuclei produced in ⁴⁰Ar + ¹⁹⁷Au reactions at incident energies of 30 and 60 MeV/u are compared. At the lowest bombarding energy and 3.3 MeV/u excitation energy, the composite system decay process supports the hypothesis of long-lived equilibrated nucleu decaying by successive binary splittings. For excited nuclei around 5 MeV/u, the depletion observed at small relative angles in the correlation functions is interpreted as the result of a strong reduction in the fragment emission time scale.     

Photoabsorption of indium in the 4d excitation energy range

We report on the absorption coefficient of indium deduced from transmission measurements on thin films in the 40–200 eV range. The strong 4d → ?? continuum is clearly seen and is in good agreement with partial 4d photoemission cross section and also with Kennedy and Manson's atomic cross-section calculation for xenon. Some structures are seen in the 40–80 eV range, which cannot be related to any known models.     

Theoretical models for deuteron photodisintegration in the energy range between 250 MeV and 800 MeV

Two theoretical models of γd → pn are developed to study the differential cross-section and'the proton polarization data in a coherent way. The first model is an extension of conventional diagrammatic summations of Born terms and isobar excitation terms. The second model is novel in that the isobar excitation terms are replaced by experimentally determined _γN → N_π helicity amplitudes. The second model allows us to extend to higher energies with the introduction of only one arbitrary parameter. The differential cross-section data are fairly well reproduced in the whole energy range, while the proton polarization data are very far removed from the calculations.     

Measurements of the neutron-proton analyzing power in the energy range from 17 to 50 MeV

Measurements of the analyzing power A_y for neutron-proton scattering in the energy range from 17 to 50 MeV are reported. These data improve considerably the precision of the np data base in this energy range. Preliminary phase-shift analyses indicate reduced uncertainties in the np ³P(T = 1) phases and in the ³D(T = 0) phase shifts.     

Elastic scattering of B on B in the energy range from 4 to 15 MeV

Angular distributions (at E_c.m. = 4, 6.5 and 10.5 MeV) and excitation functions (at 30°, 60° and 90°) are given for the elastic scattering of ¹⁰B on ¹⁰B. The results of an optical model (OM) analysis are presented and discussed. In the energy range covered the Sommerfeld parameter η varies from 4.4 to 2.3.     

On the spectroscopy of atomic electrons (positrons)in the energy range of 10 to 50 MeV from heavy-ion collisions at intermediate energies

The feasibility of the spectroscopy of dynamically ionized electrons (positrons) from heavy-ion collisions at intermediate energies, e.g. Pb+Pb at 60 AMeV has been studied. We propose a magnetic toroid spectrometer for lepton spectroscopy in an energy range between 5 and 50 MeV. Special emphasis was laid on large solid angles, on broad-band characteristics and on a good suppression of secondary events. The device is a versatile compact-size instrument for lepton detection in in-beam experiments at a moderate energy resolution of %. Received: 28 December 1999 / Accepted: 29 March 2000     

Resonance transfer of molecular excitation energy: Enhancement in channels

An analysis is made of the influence of the boundary of the region in which resonant transfer of excitation energy takes place from one molecule to another, and it is pointed out that under appropriate circumstances boundary effects can lead to enhancement of energy transfer.     

Fluctuations in inelastic proton scattering from58Ni in the energy range 17.1 to 20.6 MeV

Excitation functions of proton elastic and inelastic scattering on⁵⁸Ni have been measured for proton energies in the range 17.1 to 20.6 MeV, at laboratory angles of 90°, 120° and 155°. All show cross section fluctuations. Excitation functions are presented for the elastic and for five inelastic groups in the energy range 18.1 to 18.59 MeV. These were analyzed by the Fourier analysis method, and the average level width found to be about 13 keV. The observation of strong fluctuations in the higher inelastic yields has implications for several microscopic analyses reported in the literature of⁵⁸Ni(p, p′) data obtained at 17.7 MeV incident proton energy.     

Photoproduction of high-energy neutrons in thick targets by electrons in the energy range 150 to 270 MeV

Photoneutron spectra with energies greater than 12 MeV produced by electrons incident on a thick lead target have been measured for primary electron energies between 150 and 266 MeV and at a fixed angle of 90 ° to the beam axis. Measurements of the neutron yield have furthermore been performed at a primary energy of 234 MeV as a function of target depth for the same lead target and as a function of the mass number for C, Al, Cu, Cd and Pb targets. The results were obtained with three independent neutron detectors: two proton recoil counters and one time-of-flight set-up. The high-energy regions of the spectra are compared with the predictions of the phenomenological quasi-deuteron model and a satisfactory agreement in shape and scale of the spectra is found. Additional high-energy neutrons from pion reabsorption processes were observed at electron energies of 234 and 266 MeV.     

Quantum numbers of26Al levels above 6 MeV excitation energy

Measurements of resonance strengths and ofγ-ray angular distributions or anisotropies have been performed on selected resonances of the²⁵Mg(p, γ) reaction in the rangeE _p=2–4 MeV,E _x=8.2?10.1 MeV with an emphasis on high-spin andT=1 analog resonances. EightT=1 states are identified, among them high-spin states at 8747 keV (I=6), 9286 KeV (I=5), and 9986 keV (I ^π = 7⁺, 6⁺). Shell model calculations in thes-d basis space reproduce the branching ratios of these states and clarify the nature of final states. New high-spinT=0 states are observed at 9720 keV (I ^π = 7⁺), 8602 keV (I = 6), and 6695 keV (I ^π = 7⁺). TheI ^π assignments to severalE _x = 6–8 MeV states are revised and the role of two-particle excitations into thef-p shell is elucidated. A revised spectrum of 73 positive-parity,T = 0 states is compared to the predictions of shell-model calculations in thes-d basis space using the universals-d shell Hamiltonian.     

Bhabha to Møller cross section ratios in the energy range 2.15–2.45 MeV

The cross sections for Bhabha and Møller scattering have been investigated in the energy range 2.1–2.4 MeV using monoenergetic positrons and electrons to search for hypothetical resonances superimposed to the continuum predicted by quantum electro dynamics. Bhabba-to-Mott, Møller-to-Mott and Møller-to-Bhabha cross section ratios were measured. The Bhabha-to-Mott ratios could be determined with statistical errors of typically 1% and remaining systematic errors not exceeding the statistical ones. No resonances in Bhabha scattering were observed. Limits for the intrinsic widths of hypothetical resonances are given. For the first time upper limits are deduced from our data for hypothetical resonances in the Møller scattering cross section in the MeV range. Additionally, Møller-to-Bhabha cross section ratios could be determined with good precision. A good agreement between the experimental and theoretical Møller-to-Bhabha ratios can be stated calling in question the recently predicted existence of series of narrow, unresolvable resonances in the Bhabha scattering cross section.     

Nuclear level densities below 40 MeV excitation energy in the mass regionA ≃ 50

Consistent pre-equilibrium emission and statistical model calculations of fast neutron induced reaction cross sections are used to validate nuclear level densities for excitation energies up to 40 MeV in the mass regionA ?50. A “composed” level density approach has been employed by using the back-shifted Fermi gas model for excitation energies lower than 12 MeV and a realistic analytical formula for higher excitations. In the transition region from the BSFG model range to that of full applicability of the realistic formula, an interpolation between the predictions of the two models is adopted. The interpolation rule, suggested by microscopic level density calculations, has been validated through the comparison of the calculated and experimental cross sections.     

Electromagnetic transition properties and isospin excitation in the cross-conjugate nuclei 44Ti and 52Fe

The interacting boson model with isospin (IBM-3) is applied to study the band structure and electromagnetic transition properties of the low-lying states in the cross-conjugate nuclei 44Ti and S2Fe. The isospin excitation states with T=0, 1 and 2 are identified and compared with available data. The E2 and M1 matrix elements for the low-lying states have been investigated. According to this study, the 2+3 state is the lowest mixed symmetry state in the cross-conjugate nuclei 44Ti and 52Fe. The excitation energy of the second 0+2 and 2+2 states with T=0 in the nucleus 52Fe are identified. The agreement between the model calculations and data is reasonably good.     

Resonance strength measurements of the 27Al(p,γ)28Si reaction in the energy range Ep= 0.8–2.0 MeV

An excitation function of the ²⁷Al(p,%)²⁸Si reaction has been measured over the proton beam energy range E_p = 800-2000 keV using a 4? NaI segmented crystal. In the above energy range 47 narrow resonances were measured and their strengths have been deduced. The absolute efficiency of the detection system has been determined for each one of the resonances via Monte-Carlo simulation, taking into account the decay scheme of each resonance. The results of the present work are compared with literature.     

K-shell excitation of HCN by electron energy loss spectroscopy

Small angle inelastic scattering of fast electrons has been used to study carbon and nitrogen K-shell excitation and ionization of HCN. The K→π* transitions in HCN have been investigated with high resolution.     

High-precision measurement of proton momentum by microstrip detectors in energy range from 2 to 70 MeV

The STT particle detection system, comprised of dual-sided microstrip silicon detectors, provides data on detection time and particle track, type, and ionization losses. One technique for calibrating and analyzing the data from the energy channel of the system uses all this information and allows us to limit the error of reconstructing the initial kinetic energy to ～1% for such products of nuclear reactions as protons and deuterons. This technique, which is described in this work, involves an integral comparative analysis of the response of all readout channels. Laboratory measurement data (including the detection of α-emission), data from scientific experiments, and data from simulations are all used. The technique, combined with the track reconstruction method also described below, allows us to determine the vector value of the initial particle momentum that is needed in advanced research on the spin physics of nucleon-nucleon interaction.     

Low energy electron spectroscopy of CO in the 10.600–14.400 eV energy loss range

Excitation spectra of CO have been obtained at low electron impact energy in the 10.600–13.400 eV energy loss range for scattering angles from 10 to 120°, with a 35 meV experimental resolution. The angular behaviour of the observed peaks is used to discriminate singlet-singlet and singlet-triplet transitions. Previously calculated Rydberg states are observed, in particular the triplet analogue of the F¹Σ⁺ state. A new high energy valence triplet state is identified; the first observed vibrational level is at 11.595 eV and the vibrational spacing is 90 meV. Upper levels are strongly affected by predissociation.     

Interactions of neutrons with239Pu in the energy range between 1.5 and 5.5 MeV

Neutron scattering angular distributions of²³⁹Pu were measured at seven primary neutron energies between 1.5 and 5.5 MeV. Absolute differential scattering cross-section results are plotted and tabulated. Cross section calculations using a central optical model were made and the results were compared with the experimental values. Moreover, nuclear temperatures of the fission and the inelastic neutron evaporation processes were extracted from the measured spectra.