Excited levels and isobaric analogue states in55Co investigated with the54Fe(p, γ)55Co reaction

The yield curve for the⁵⁴Fe(p, γ)⁵⁵Co reaction in the energy regionE _p=1.5–2.9 MeV has been recorded and the decay of ten resonances has been investigated. For six of the resonances the strengths have been determined. The angular distributions of the gamma rays have been recorded for four resonances to obtain spins or spin limitations for excited levels. In addition the lifetimes of 10 bound levels were determined with the Doppler Shift Attenuation Method. The isobaric analogues of the ground state and five excited states in⁵⁵Fe are discussed.     

Study of the187W states excited in the (n, γ) reaction

A singles-ray spectrum and a spectrum of summed amplitudes of coinciding pulses (SACP) were measured in the¹⁸⁶W(n, )¹⁸⁷W reaction experiment on the thermal neutron beam. It was for the first time that the data on¹⁸⁷W-transitions were obtained in the excitation energy region from 1500–2500 keV. The neutron binding energy was determined to beB _n=5467.25 (4) keV (statistical error only). In result the level scheme of¹⁸⁷W was developed in the excitation energy interval 1E _f < 3.4=" mev,=" which=" contained=" 105=" levels=" with=" about=" 70=" of=" them=" being=" identified=" for=" the=" first=" time.=" the=" experimental=" values=" for=" summed=" intensities=" of=" two-step=" cascades=" were=" established=" to=" exceed=" those=" predicted=" by=" the=" modern=" statistical=" theory=" (by=" 36±6%).=" this=" is=" explained=" by=" a=" considerable=" contribution=" of=" few-quasiparticle=" components=" to=" wave=" functions=" of=" compound=" and=" intermediate=">     

On the mechanism of formation of excited states of the 8Be nucleus in the reaction 12C(γ, 3α)

The reaction ¹²C(γ, 3α) was studied with the aid of a diffusion chamber placed in a magnetic field, filled with a methane-helium mixture, and irradiated with bremsstrahlung photons of endpoint energy 150 MeV. The total reaction cross section was measured in the energy range E _γ < 40 MeV. The ground state; the first, second, and unseparated third and fourth excited states; and highly excited states (in the range 19.9 < E _x < 25.2 MeV) of the ⁸Be nucleus manifested themselves in the distribution of events with respect to the energy of the relative motion of two alpha particles. A resonance that is characterized by the energy of E₀ = 0.72 MeV and the width of Γ = 0.80 MeV and which was identified as a ghost anomaly was found between the ground state and the first excited state. Partial cross sections were measured for various channels. Excited states are formed in narrow photon-energy intervals, and their partial cross sections are of a resonance shape. It is found that the energy corresponding to the maximum of the partial cross section for the ith level, E _m ⁱ , and the excitation energy of the next level, E ₀ ⁱ⁺¹ , are correlated: E _m ⁱ = E ₀ ⁱ⁺¹ + ?, where ? is the reaction threshold. The results are qualitatively explained on the basis of a model that assumes photon absorption by an alpha-particle pair.     

Inelastic production of neutral pions in the4He(γ, πℴp)3H reaction

The yield of the⁴He(, p)³H reaction has been studied in a bremsstrahlung beam of photons with a maximum energy of 450 MeV. The measurements were made on an experimental setup consisting of a total absorption Cerenkov gamma spectrometer and a helium streamer chamber. A kinematic analysis is made of the angular distributions of the disintegration products of the⁴He nucleus to study the mechanism of inelastic photoproduction of neutral pions. The relatively high event density in the region of small proton-triton separation angles is attributable to the quasielastic mechanism of the reaction in which pion photoproduction is accompanied by excitation of the⁴He nucleus.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 51–56, September, 1989.     

Properties of some resonances of the 55Mn(p,γ)56Fe reaction in the E p = (1.3−1.8) MeV region

Radiative decay of 21 resonances in the ⁵⁵Mn(p, )⁵⁶Fe reaction was studied in the proton beam energy region E _p = (1.3–1.8) MeV. Branching of decay to many low lying bound states up to excitation energy E _x 8 MeV was measured. Exact energy of all resonances has been established, what pointed out that five of the resonances are very close doublets. For all studied resonances their spin-parity characteristics were determined. Assignment of some resonances as isobaric analogues of the states in the ⁵⁶Mn nucleus was discussed and short note about energy systematics of isobaric analogue resonances was given.     

Study of the Δ isobar excitation in nuclei with the (3He,t) reaction

Data for the Δ excitation by the (³He,t) reaction at 2.0 GeV on various nuclei are presented together with results on ¹²C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(³He,t) Δ⁺⁺ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.     

Investigation of 238U in the (n,n′γ) reaction

An irradiation of ²³⁸U with a beam of reactor fast neutrons permits revealing about 550 gamma transitions associated with the respective (n, n′γ) reaction and with fission fragments. The use of all known data on gamma radiation from fission fragments makes it possible to identify gamma transitions belonging to ²³⁸U with a high probability. The scheme of levels and gamma transitions is composed for ²³⁸U. New levels (including those of spin-parity J ^π = 0⁺) at excitation energies below 2 MeV are proposed. The low-lying levels in the rotational band for two-phonon octupole excitations are determined. It is found that a hybrid state is formed upon the crossing of this band and the band based on two-quasiparticle excitations. This hybrid state must involve excitations of both types. A small value of the rotational-band parameter in the isomer of energy 2559.0(4) keV is explained by the contribution to this state from two-quasiparticle configurations belonging to the 1k _17/2 subshell. The same circumstance may also be responsible for an enhanced yield of ternary fission for this isomer.     

Discovery of deeply bound π− states in the208Pb(d,3He) reaction

Narrow lines were observed around 133 MeV excitation energy in the²⁰⁸Pb(d,³He) reaction atT _d=300 MeV/u using the Fragment Separator System at GSI. They are assigned to the deeply boundπ ^??²⁰⁷Pb states with configurations of $\left( {2p} \right)_{\pi ^ - } $ (3p_1/2, 3p_3/2) _n ^?1 .     

Investigation of 166Er in the respective (n,n′γ) reaction

Physics of Atomic Nuclei - The spectrum, angular distribution, and linear polarization of gamma rays from the (n, n′γ) reaction on 166Er were measured in a beam of reactor fast neutrons....     

Study of the reaction 12C(γ, n 3He)2α

The possibility of separating, with the aid of photoemulsion, channels of the reaction ¹²C(γ, n ³He)2α that involve the formation of ⁷Be and ⁸Be intermediate nuclei in excited states is studied. The experimental energy distributions of these nuclei are obtained. The relative yields from these reaction channels are estimated.     

Spectroscopy of50V with (p,nγ) reaction

Information on the low-lying levels up to ～1.9 MeV excitation of the doubly odd nucleus⁵⁰V has been obtained through the Ge (Li)-Ge (Li) coincidence study with the⁵⁰Ti(p, nγ)⁵⁰V reaction. Branching ratios have been measured and tentative spin-parity assignments have been made. A detailed comparison with other measurements reported recently has also been made. Using the lowest seniority wave functions with (f_7/2) _p ³ (f _7/2) _n ^?1 configuration, energy levels and electromagnetic properties have been calculated. These have been compared with the present and earlier experimental data.     

Properties of Some Bound States of the 56Fe Nucleus Excited by the 55Mn(p,γ)56Fe Reaction

Radiative decay of 21 resonances in the ⁵⁵Mn(p,)⁵⁶Fe reaction was studied in the proton beam energy region E _p = (1.3-1.8) MeV. Properties of bound states in the final ⁵⁶Fe nucleus have been deduced from accurately measured very complex -ray spectra. About 150 levels have been firmly established for excitation energy up to 8 MeV and 93 of them have been observed for the first time or their established energy is substantially more accurate than in former publications or some other information is new. For each of the 57 levels, there has been established its decay and firmly observed at least one decay branch. Spin and parity have been newly determined or appreciated for 35 levels and for 35 levels the mean lifetime has been newly established by the DSAM method. Crude comparison of the observed level density with the statistical Fermi model prediction has been also performed.     

Nuclear interaction dynamics in the 56Fe (α, xn) reaction

Neutron spectra and angular distributions in the ⁵⁶Fe (α, xn) reaction are measured at α-particle energies of 12.5, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements are performed using time-of-flight fast neutron spectrometers on pulsed accelerators. The measured data are analyzed in the context of equilibrium, preequilibrium, and direct nuclear reaction mechanisms. The contributions from equilibrium, preequilibrium, and direct mechanisms of neutron emission are studied over a wide range of α-particle energies.     

Investigation of the40Ca(γ,N) reaction at 60 MeV

The values of the angle-integrated cross section for the decay to various low-lying states in³⁹K following the⁴⁰Ca(,) reaction at a mean photon energy of 60 MeV are reported on, together with the values of the reduced Legendre coefficientsa _i . The⁴⁰Ca(,gp) and⁴⁰Ca(,n) reactions yield the same angular cross-section values and these agree with the corresponding RPA-calculations.Senior Research Associate NFWO     

Photodisintegration cross section of the reaction (4)He(γ,p)(3)H between 22 and 30 MeV

The two-body photodisintegration cross section of (4)He into a proton and triton was measured with monoenergetic photon beams in 0.5 MeV energy steps between 22 and 30 MeV. High-pressure (4)He-Xe gas scintillators of various (4)He/Xe ratios served as targets and detectors. Pure Xe gas scintillators were used for background studies. A NaI detector together with a plastic scintillator paddle was employed for determining the incident photon flux. Our comprehensive data set follows the trend of the theoretical calculations of the Trento group very well, although our data are consistently lower in magnitude by about 5%. However, they differ significantly from the majority of the previous data, especially from the recent data of Shima et al. The latter data had put into question the validity of theoretical approaches used to calculate core-collapse supernova explosions and big-bang nucleosynthesis abundances of certain light nuclei.     

Level structure of 110in from the 110cd(p,nγ)110in reaction

γ-ray and γγ-coincidence spectra of the ¹¹⁰Cd(p, nγ)¹¹⁰In reaction were measured with Ge(Li), Ge(LEPS), and Ge(HP) spectrometers at 6 MeV bombarding proton energy. Energies (E_γ) and relative intensities (I_γ) of 95 ¹¹⁰In transitions (including 70 new ones) have been determined. The electron spectrum of the reaction was measured with a combined magnetic plus Si(Li) spectrometer at E_p = 6 MeV. Internal conversion coefficients of 41 transitions in ¹¹⁰In have been determined for the first time. The angular distribution of γ-rays was measured at 5.2, 5.6, and 6 MeV bombarding proton energies. A new, more complete level scheme of ¹¹⁰In has been deduced. On the basis of the internal conversion coefficients of transitions, Hauser-Feshbach analysis of (p, n) reaction cross sections, γ-ray angular distribution (and other) results unambiguous spin and parity assignments were made to 11 excited ¹¹⁰In levels. The energies of several ¹¹⁰In proton-neutron multiplets were calculated on the basis of the parabolic rule derived from the cluster-vibration model. The comparison of experimental and theoretical results provided identification of about 20 p-n multiplet states in ¹¹⁰In.     

Angular distributions of γ-rays from four resonances of the55Mn(p, γ)56Fe reaction

Four resonances in the⁵⁵Mn(p, )⁵⁶ Fe reaction at the centre-of-mass proton beam energy E _P ^CM =1320, 1504, 1508 and 1649 keV were studied. Angular distributions for some strong -rays following the radiative decay of the resonances were measured and analysed in terms of the channel-spin formalism. Spin-parity assignmentI _r =3⁺, 4⁺ and 3⁺ was acquired for the 1320, 1504 and 1649 keV resonances, respectively. No definite assignment was established for the 1508 keV resonance and the resonance is assumed to be a very tight multiplet. Analysis of primary transitions to bound states of the Fe final nucleus permited us to assign these states. The 2⁺, 2⁺, 2⁺, 6⁺ and 4⁺ assignments were ascribed to the states at excitation energyE _x =5705, 5303, 4738, 4692 and 4658 keV, respectively, while for the 5132 keV state ambiguous assignment 3⁺ or 4⁺ was found. Multipole mixing ratio was established for some primaries. The coupling of angular momenta of proton and target nucleus in the formation of the 3⁺ resonances was also roughly discussed.Participated partly in the course of his work on diploma thesis.The authors wish to thank the staff of the Van de Graaff accelerator at Charles University in Prague for the efficient operation of the machine. One of us (M. X. T.) acknowledges the staff of the Dept. of Nuclear Physics of Charles University, Prague, for the excellent working conditions.     

The quasi-free 3He(e,e′p) reaction

The proton spectral function has experimentally been determined with the ³He(e, e′p) reaction for missing energies, 0<E_m<70MeV, and recoil momenta, 0<P_B<310 MeV/c. Experimental results are obtained for both the two-body, ³He(e, e′p)²H, and three-body breakup processes. Proton momentum density distributions, obtained in a PWIA analysis, are compared with theoretical calculations: Faddeev solutions with the RSC and Paris potentials, and variational calculations with various potentials, including those with a three-nucleon interaction term. Energy-weighted sum rule results are presented and compared with theoretical predictions. The coincidence cross sections are also compared with calculations which include the effects of final state interactions and meson exchange currents. Consistency of the results with PWIA is investigated in the framework of the Chew-Low extrapolation procedure.