Electromagnetic transitions in 51Mn

The nuclear structure of ⁵¹₂₅Mn was studied by γ-ray spectroscopy in the ⁵⁴Fe(p, α)⁵¹ Mn reaction (E_p = 9.0–13.2 MeV) and the ¹⁴N+³⁹K, ¹⁶O+⁴⁰Ca and ¹⁴N+⁴⁰Ca fusion-evaporation reactions (E_beam = 36 MeV). In the ⁵⁴Fe(p, αγ)⁵¹Mn reaction γ-rays were detected in coincidence with α-particles emitted near 180°; mean lifetimes and γ-ray mixing and branching ratios were deduced from Doppler shift attenuation and α-γ angular correlation measurements, respectively. Definite spin assignments are: 237 and 2416 keV, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{?}}$; 1140 keV, $\text{9}\text{2}$^?; 1488 keV, $\text{11}\text{2}$^?; 1825 and 2140 keV, $\text{3}\text{2}$^?. The results for other states below 3 MeV are consistent with the existence of rotational bands (/kh²/2/OI/t~ 95 keV) built on the ($\text{3}\text{2}$⁺) 1817 keV and $\text{1}\text{2}$⁺ 2276 keV hole states. The various measurements together with an earlier value for the lifetime of the first-excited state determine unambiguously the B(M1) and B(E2) values for all of the decay branches of the $\text{7}\text{2}$^?, $\text{9}\text{2}$^? and $\text{11}\text{2}$^? lowest three excited states. From the γ-singles and γ-γ coincidence observations with fusion-evaporation reactions, the yrast cascade proceeds through these three states and higher states at 2957, 3250,3680 and 4139 keV which are suggested to have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{13}\text{2}{}^{\mathrm{?}}$, $\text{15}\text{2}$^?,$\text{15}\text{2}$^? and $\text{19}\text{2}$^?, respectively. The various experimental results for the $\text{5}\text{2}$^? → ($\text{19}\text{2}$^?) yrast states are in good overall agreement with shell-model calculations in the (f_{$\text{7}\text{2}$}¹ space.     

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.     

Spins and lifetimes of levels in 55Mn

The study of excited ⁵⁵Mn levels with the ⁵²Cr(α, pγ) reaction was extended to levels up to 3161 keV. With a Ge(Li) detector, DSA measurements in gold-backed targets were made, as well as angular correlations; both of these experiments were done in coincidence with protons detected near 180°. A multiple-detector NaI(Tl) array was also used in the same reaction geometry for better γ-ray detection efficiency. Mean lifetimes of 12 levels from 2727 to 3161 keV are reported. Spins and sometimes parities of the following levels were deduced from the angular-correlation analyses and lifetime results: 1885 keV, $\text{7}\text{2}$^?; 2199 keV, $\text{7}\text{2}$(^?); 2311 keV, ($\text{13}\text{2}$); 2366keV, $\text{5}\text{2}$^?; 2727 keV, $\text{7}\text{2}$; 2823 keV, $\text{9}\text{2}$. Multipole mixing ratios and M1 and E2 transition rates of the radiations from these and from the 1292 keV level are presented. The similarity of the low-lying level structure and of interlevel transitions in ⁵⁵Mn to those in certain other f_{$\text{7}\text{2}$}³ nuclei is examined.     

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.     

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.     

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.     

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.     

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.     

Spectroscopic study of 55Co via the 54Fe(τ, d)55Co and 54Fe(τ, dp̃)54Fe reactions

The ⁵⁴Fe(τ, d)⁵⁵Co reaction has been studied at 25 MeV incident energy with a split-pole spectrometer. About one hundred levels have been observed in ⁵⁵Co up to 10 MeV excitation energy. Angular distributions have been measured and analyzed with DWBA and Gamow functions as form factors for unbound levels. The ⁵⁴Fe(τ,dp?)⁵⁴ reaction has been investigated at 24 MeV incident energy. The angular distributions of the emitted protons were measured in coincidence using method 2 of Litherland and Ferguson, with 0 detection of deuteron groups. Spins, population parameters, branching ratios and proton partial widths for the transitions to the ground and excited states of ⁵⁴Fe were determined from the analysis of the angular correlation data. The results of these two experiments provide a large number ofspectroscopic properties of unbound proton states and in particular of analog states of ⁵⁵Fe low-lying levels. The IAS of the $\text{3}\text{2}{}^{\mathrm{?}}$ ground state of ⁵⁵Fe is observed to be split between two individual levels. The amplitude of neutron coupling to the first 2⁺ excited state of ⁵⁴Fe is obtained for the $\text{lg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and $\text{2}\text{d}\text{5}\text{2}$ low-lying parent statfes in ⁵⁵Fe. summed spectroscopic factors and the centroid energies of the proton states in ⁵⁵Co are obtained. A comparison is made with previous (τ, d), (d, p) and (p, p) results.     

Nuclear γ-rays induced by pions stopping in 55Mn

Stopping pions have been shown to excite the 126 keV level in a target of ⁵⁵Mn. A nonlinear variation of yield of the γ-ray versus target thickness suggests that the principal mechanism responsible for the excitation is a two-stage process. The production mechanism for the same γ-ray seen elsewhere in kaonic atoms experiments is discussed.     

Energy levels,decay scheme, γ-ray branching ratios and lifetimes in 55Fe from the 55Mn(p,nγ)55Fe reaction

The reaction ⁵⁵Mn(p, nγ)⁵⁵Fe has been studied at E_p = 4.0 and 6.0 MeV using a pulsed beam. From the experiments at 6.0 MeV, the energy levels of ⁵⁵Fe up to an excitation of 3810 keV, their decay scheme and the γ-ray branching ratios have been determined. Levels have been identified for the first time in the (p, nγ) reaction. The results have been compared with those available from the literature. From the 4.0 MeV experiment, the mean lifetime of the 1408 keV level has been determined to be 142.7 ± 6.6 ps by direct timing techniques.     

55Mn(n,n'γ) cross-section studies for En = 1.0–3.6 MeV

Absolute ⁵⁵Mn(n, n′γ) γ-ray production cross sections have been measured for 19 transitions from levels up to and including the 2429 keV state in ⁵⁵Mn over the energy range E_n = 1.0–3.6 MeV. Angular distributions were also measured for 6 of the transitions. Branching ratios were extracted and total inelastic neutron cross sections were inferred for these ⁵⁵Mn excited states. The measured and inferred cross sections are compared with calculated cross sections using the statistical compound nucleus theory.     

54Cr, 54, 58Fe, 58Ni(d,p)55Cr, 55, 59Fe, 59Ni Vector analyzing power measurements

(d, p) cross sections and vector analyzing powers have been measured at 10 MeV bombarding energy for targets ⁵⁴Cr, ⁵⁴Fe, ⁵⁸Fe and ⁵⁸Ni. The systematic behaviour of the analyzing powers with Q for states of a given J^π has been observed. Spins of a number of states in ⁵⁵Cr and ⁵⁹Fe have been deduced.     

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.     

Coulomb excitation of levels in 143Nd and 145Nd

The low-lying states of ¹⁴³Nd and ¹⁵⁴Nd have been studied by means of Coulomb excitation with ¹⁶O and α-particles. Angular distribution measurements were carried out for some transitions in ¹⁴⁵Nd with 11.2 MeV α-particles. Level energy decay schemes and B(E2)↑ values were measured for two states in ¹⁴³Nd and for six states in ¹⁴⁵Nd. Some spin assignments have been established for the ¹⁴⁵Nd nucleus. ¹⁴³Nd and ¹⁴⁵Nd have been theoretically described by coupling one and three particles, respectively, to quadrupole vibrations, and rather good agreement with experiment was achieved.     

The reaction 55Mn(d, t)54Mn

Neutron pick-up cross sections and vector analyzing powers have been measured for the reaction ⁵⁵Mn($\text{d}$, t)⁵⁴Mn at 17 MeV. The mixture of $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ transfer to the low-lying l_n = 1 states has been found. Evidence of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ hole nature of several strong l_n = 3 states above 1 MeV has been obtained.     

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.     

Recoil-distance lifetime measurements of levels in 36Ar and 36Cl

Lifetimes of levels in ³⁶Ar and ³⁶Cl populated in the ²H(³⁵Cl, n) and ²H(³⁵Cl, p) reactions, respectively, were measured with the recoil distance method. Gamma rays were detected in coincidence with a neutron detector to study the ³⁶Ar levels and in singles to study the ³⁶Cl levels. Mean lifetimes τ_m = 125 ± 20, 19.6 ± 3.1 and 4.1 ± 0.9 ps were obtained from decay curves for the ³⁶Ar levels at 5171, 4974 and 4178 keV, respectively and τ_m = 23 ± 2, 10.4 ± 0.5, 2.95 ± 0.14 and 4.9 ± 1.0 ps for ³⁶Cl levels at 788, 1165, 1951 and 2810 keV, respectively. Shell-model calculations, with a model space comprising selected 5h-1p configurations and with an effective charge of 0.5e, are compared to the transition rates for the low-lying negative parity states in ³⁶Ar.     

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.