Electromagnetic properties of levels in 55Mn

Excited levels of ⁵⁵Mn were produced by the reaction ⁵²Cr(α, p) at 10.5 and 11.1 MeV beam energy. A series of γ-ray measurements was made, all in coincidence with protons detected near 180°. A Ge(Li) γ-ray detector was used at 4 angles, and extensive angular-correlation measurements were made with an array of NaI(Tl) detectors. Excitation energies of 25 levels up to 3161 keV were determined, including a new level at 2215 keV. Only the level at 2285 keV and the $\text{1}\text{2}{}^{\mathrm{?}}$ state near 1290 keV were not observed in this range. From Doppler-shift attenuations, the mean lifetimes of 14 levels up to 2565 keV were deduced. Branching ratios and multipole mixing ratios were obtained for most of these levels. The following spin assignments were determined: 1530 keV, $\text{J =}\text{3}\text{2}$; 1885 keV, $\text{J =}\text{7}\text{2}$ or $\text{5}\text{2}$; 2565 keV, $\text{J =}\text{3}\text{2}$. Reduced transition probabilities, B (M1) and B (E2), of many transitions were calculated from these experimental results and are compared with the available theoretical values.     

Photonuclear reactions in medium weight nuclei 51V, 55Mn and Cu

New results on the photospallation of the medium weight nuclei ⁵¹V, ⁵⁵Mn and Cu at maximum bremsstrahlung energy between 2 and 5 GeV are presented. The yields of residual nuclei were measured by the activation method using a Ge(Li) detector. The results are analyzed with the empirical Rudstam formula and compared with data obtained in lower energy photon and proton induced reactions.     

Recoil-distance lifetime measurements in 51Cr, 53Cr, 53Mn and 53Fe

Levels in ⁵¹Cr, ⁵³Cr, ⁵³Mn and ⁵³Fe were excited via (α, n) or (α, p) reactions. Using the recoil-distance method, mean-lives (in ps) have been obtained for excited states (keV) in the residual nuclei: ${}^{51}\text{Cr}\text{(2256) = 66±2,}{}^{53}\text{Cr}\text{(1536) = 21.5±3.5,}{}^{53}\text{Cr}\text{(2173) = 6.7±3.1,}{}^{53}\text{Mn}\text{(2564) = 20}{}^{\mathrm{+8}}{}_{\mathrm{?6}}\text{and}{}^{53}\text{Fe}\text{(1424) = 4.0±1.0}$. Reduced transition probabilities calculated from these values are compared with the available theoretical values.     

Electromagnetic transitions in 42Ti

Levels in ⁴²Ti up to 4 MeV have been investigated using the ⁴⁰Ca(³He, n)⁴²Ti reaction and a neutron time-of-flight method. Using the DSA method, lifetimes of 750±300, > 200, 350±250, > 2000 and < 250 fs have been measured for levels at E_x = 1.56, 1.85, 2.40, 2.68 and 3.74 MeV respectively. The level at E_x = 3043.0±1.5 keV is tentatively identified as the 6⁺ member of the $\text{(f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$ configuration, and its mean life has been measured as 26±5 ns by a direct timing method. Using isospin formalism, transition strengths are compared with theoretical and experimental values for ⁴²Ca and ⁴²Sc.     

Magnetic rotation of levels of 53Mn and 54Mn following the 53, 54Cr(p,n) and 51V(α, n) reactions

The low-lying levels of ⁵³Mn and ⁵⁴Mn have been studied using the ^{53, 54}Cr(p, nγ) and ⁵¹V(α, nγ) reactions. Angular distributions of γ-rays have been measured and their integral rotations in iron alloy targets studied. The g-factor of the 377 keV, $\text{5}\text{2}{}^{\mathrm{?}}$ level of ⁵³Mn is g = + 1.15±0.17. Products gτ have been found for the 55, 156, 368, 408 and 1072 keV levels of ⁵⁴Mn to be 124±42, 360±60, 75±25, > 10 and 150±80 ps respectively. Using shell model estimates for the g-factors, the lifetimes of the levels have been deduced. An interpretation of the results in terms of shell model wave functions is given.     

Investigation of isobaric analog resonances in 53Mn

The isobaric analog resonances in ⁵³Mn with different spins and parities are investigated by means of the ⁵²Cr(p, p), (p, p′), (p, p′γ), and (p, γ) reactions. Spectroscopic factors are derived and the experimental (p, γ) strengths are compared with theoretical single-particle estimations.     

High-resolution measurements of analogue states in 53Mn

Using a high-resolution proton beam, differential cross sections were measured for the ⁵²Cr(p, p) and ⁵²Cr(p, p') reactions at incident energies between 3.20 and 4.76 MeV. Spins, parities and partial widths were determined for all resonances observed. Two p-wave and two d-wave analogue states were identified in this energy region. Spectroscopic factors and Coulomb displacement energies were extracted for the analogue states. The width distributions were analyzed for $\text{1}\text{2}{}^{\mathrm{+}}\text{,}\text{1}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{and}\text{5}\text{2}{}^{\mathrm{+}}$ resonances. Proton strength functions were also deduced for each J^π value, and their proton energy dependence was discussed.     

Low-energy transitions in the 197Pb and 198Pb isotopes

The ¹⁹⁸Pb and ¹⁹⁷Pb isotopes are produced through the ¹⁸⁶W(¹⁶O, 4n, 5n) reactions. Conversion-electron, γ- and X-ray spectra are measured using the compound-nucleus recoil method. Conversion coefficients and multipolarities are deduced for a large number of transitions. Together with angular distribution measurements and the results of γγt multidimensional coincidences they lead to decay schemes for the two isotopes. Microscopic calculations, performed in the two- or three-quasiparticle approximation with a surface delta interaction, fail to reproduce completely the observed properties, showing similar defects for the odd and even isotope.     

Excitation functions and isobaric analogue states in the 55Mn(p, γ)56Fe reaction

Four excitation functions with proton energy range 1.3 to 1.85 MeV and γ-ray energy thresholds from 1.5 to 8.0 MeV were determined for the reaction ⁵⁵Mn(p, γ)⁵⁶Fe. Gamma-ray spectra were taken for two close-lying resonances at proton energies 1531 and 1537 keV. An analysis of the spectra suggests the spin-parity assignments for those two states to be 4⁺ and 2⁺, respectively, consistent with their being isobaric analogues to the close-lying third and fourth excited states in ⁵⁶Mn.     

Isomeric γ-ray transitions in 98Tc

Delayed γ-rays from ⁹⁸Tc have been observed following pulsed proton beam bombardment of an enriched ⁹⁸Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.     

A study of the 51V(6Li,d)55Mn reaction

Alpha particle spectroscopic strengths extracted for transitions to low-lying levels in ⁵⁵Mn observed in a study of the ⁵¹V(⁶Li, d) reaction at 32 MeV are compared with the results of shell-model calculations. These reproduce well the relative strengths of the levels.     

States in 53Mn from the 52Cr(p, γ)53Mn reaction

Eight resonances have been observed in the ⁵²Cr(p, γ)⁵³Mn reaction between E_p = 0.90 and 1.03 MeV. Gamma-ray spectra have been accumulated at four of the resonances. Spin assignments have been made to the resonant states on the basis of the measured angular distributions of primary γ-rays. Excitation energies and γ-ray branching ratios have been determined for 36 levels between 2.0 and 5.6 MeV. Mean lives for nine of the states have been extracted by the Doppler shift attenuation method.     

A study of the (α, t) reaction on 19F, 27Al, 51V and 59Co

The angular distributions of tritons from the (α, t) reaction on ¹⁹F, ²⁷Al, ⁵¹V and ⁵⁹Co nuclei corresponding to the (0⁺) ground states and (2⁺) excited states in the final nuclei have been measured in the angular range between 15° and 170° at α-particle energies of 25 MeV. For reactions on ²⁷Al and ⁵¹V nuclei, the differential excitation functions have also been obtained at different angles of outgoing tritons at E_α from 20 to 25 MeV. The experimental angular distributions are analysed by the DWBA approximation on the assumption of a nucleon stripping mechanism. The analyses of the present results and the data obtained earlier for the (α, t) reaction on the 1 p shell nuclei, A ? 30, reveal that the distinguishing feature of the reaction under study is the presence of backward angle peaks in the reaction cross section, which appear to be associated with exchange processes. For the (α, t) reaction on the heavier nuclei (A > 30), the dominant mechanism is nucleon stripping.     

Gamma transitions between low-lying levels in 119Sn

We have carried out measurements on the decay of ¹¹⁹In isomers and the ¹¹⁸Sn(n, γ) reaction to supplement Coulomb excitation measurements on ¹¹⁹Sn. In addition to the 311.39 keV isomeric transition in ¹¹⁹In, we observed 13 γ-rays in ¹¹⁹Sn from the decay of the 2 min and 18 min ¹¹⁹In isomers. These γ-rays have been incorporated into a level scheme of ¹¹⁹Sn with levels at 0, 23.867, 89.54, 787.01, 920.5, 921.4, 1089.5, 1187.76, 1249.67, 1304.44 and 1354 keV. Conclusive evidence for the existence of a 920.5–921.4 keV, $\text{3}\text{2}{}^{\mathrm{+}}\text{-}\text{5}\text{2}{}^{\mathrm{+}}$ level doublet was obtained from capture γ-ray measurements of resonance energy neutrons.     

The spin(6) scheme and electromagnetic transitions in 191Ir and 193Ir

The Coulomb excitation of natural Ir and Pt targets has been measured with protons and α-particles of energies between 5.0 and 6.0 MeV. Accurate γ-ray angular distributions were taken to determine the relative yields of observed γ-rays. Using ¹⁹⁴Pt as standard the reduced electric quadrupole transition probabilities to the ground states from Coulomb excited levels in the Ir and Pt isotopes were determined. Other B(E2) and B(M1) values were determined from the decay schemes obtained and from mixing ratios deduced from γ-ray angular distributions or from previously measured internal conversion coefficients. The detailed sets are compared with calcula- tions based on the Spin(6) scheme, which predicts several symmetries in ¹⁹¹Ir and ¹⁹³Ir. The possible existence of wider supersymmetry multiplets in this region of nuclei is examined on the basis of comparison of electromagnetic properties of Ir nuclei with those of Pt and Os isotopes.     

Gamma-ray transitions from the lowest f = 2 states of 24Na and 28Al

Using a DWBA code which exactly includes finite-range and recoil effects, calculations are shown for ¹²C(¹⁶O, ¹²O)¹⁶O, ⁴⁰Ca(¹⁶O, ¹²C)⁴⁴Ti and ⁴⁰Ca(⁶Li, d)⁴⁴Ti which seem to be in quantitative agreement with the assumption that these reactions proceed via the simple one-step transfer of an α-particle.     

The 26Mg(14N, 10B)30Si and 26Mg(14N, 11B)29Si reactions

Reactions induced by ¹⁴N on ²⁶Mg at bombarding energies of 60–95 MeV have been studied. Angular distributions for states populated in ²⁹Si by the (¹⁴N, ¹¹B) reaction and in ³⁰Si by the (¹⁴N, ¹⁰B) reaction have been compared with Hauser-Feshbach and DWBA calculations to determine the reaction mechanism and to deduce spectroscopic information. The cross sections for the states populated in ²⁹Si and ³⁰Si are in poor agreement with statistical model calculations, indicating a non-compound nucleus mechanism.     

Electromagnetic decay of a fragmented analogue state in 63Cu

The ⁶²Ni(p, p), (p, p'γ) and (p, γ) reactions were studied in the vicinity of the $\text{3}\text{2}{}^{\mathrm{-}}$ fragmented analogue of the first excited state of ⁶³Ni. The overall proton energy resolution was about 300 eV. The γ-rays were detected with both Nal(T1) and Ge(Li) detectors. Elastic and inelastic proton widths and partial and total γ-ray widths were measured for each of the fourteen fine structure states of the analogue. Statistically significant correlations were observed between the elastic proton widths, the inelastic proton widths and the total γ-ray widths.     

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.     

The 12C(18O, α)26Mg and 12C(18O, 8Be)22Ne reaction

Excitation functions for α-emission leading to the ground and first excited states of ²⁶Mg and ⁸Be emission leading to the ground and first and second excited states of ²²Ne have been measured at several forward angles for E_c.m. = 15 to 22.4 MeV. There is little evidence for correlated structure. The angular distribution at 16.5 MeV for the α + ²⁶Mg(g.s.) channel is rather structureless while that for the ⁸Be+²²Ne(g.s.) channel appears to be dominated by a J = 13 contribution. Statistical model calculations indicate that much of the yield for both the α and ⁸Be exit channel is compound nuclear in origin, with some indication of a larger direct contribution for the ⁸Be channel at the lower end of the bombarding energy range.