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.     

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.     

Intrinsic and rotational states in 173Ta

High spin rotational levels in ¹⁷³Ta are populated in the ¹⁶⁵Ho(¹²C, 4n)¹⁷³Ta and ¹⁷⁵Lu(α, 6n)¹⁷³Ta reactions. The de-excitation γ-ray cascades are studied with Ge(Li) detectors. The rotational bands, which are built on the $\text{7}\text{2}$⁺(404), $\text{5}\text{2}$⁺(402), $\text{9}\text{2}$^?(514) and $\text{1}\text{2}$^?(541) intrinsic states, are identified up to high spin values. A state, interpreted as a three quasi-particle state with a probable spin of $\text{21}\text{2}$ is located at 1713 keV. Its half-life is about 100 ns. The behaviour of the moment of inertia of each rotational band versus the rotational frequency is compared with that of the doubly even core.     

Transition probabilities in the doubly odd nuclei 176Lu and 182Ta

The depopulation of isomeric states in ¹⁷⁶Lu and ¹⁸²Ta was studied in the (n, γ) reaction by means of delayed γ-γ coincidence measurements with NaI(Tl) and Ge(Li) detectors. The following half-lives, unknown so far, have been obtained for ¹⁷⁶Lu: $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(198.0}\text{keV}\text{) = 35.0 ± 1.0}\text{ns}$, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(638.8}\text{keV}\text{) = 8.0±1.0}\text{ns}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(662.1}\text{keV}\text{) = 6.3±0.5}\text{ns}$; and for ¹⁸²Ta: $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(270.4}\text{keV}\text{) = 1.2 ± 0.2}\text{ns}$, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(402.6}\text{keV}\text{) = 1.00 ± 0.05}\text{ns}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(443.6}\text{keV}\text{) = 2.2 ± 0.2}\text{ns}$. The existence of the isomeric level at 443.6 keV in ¹⁸²Ta was confirmed. Weisskopf hindrance factors have been deduced for the K- and Ω-forbidden transitions. The K-allowed transitions are considered in terms of the Nilsson model taking into account pairing correlations. The experimental results for the transitions de-exciting the 270.4 keV level in ¹⁸²Ta agree with earlier model predictions including band mixing effects. The influence of the pairing effect on K-allowed E1 transitions in doubly odd nuclei is demonstrated.     

The 181Ta(γ, π+)181Hf reaction

Yields for the reaction ¹⁸¹Ta(γ, π⁺)¹⁸¹Hf have been measured by an activation method using bremsstrahlung radiation with end-point energies in the range 150–360 MeV. The data have been unfolded to give cross section results corresponding to bombarding with monoenergetic photons. A comparison is made with respect to previous results and a semiclassical cascade-model calculation.     

Some M1 transition strengths in odd-A nuclei away from closed shells

By the in-beam application of the generalized centroid shift method, nanosecond half-lives have been determined for the first time: in ${}^{101}\text{Pd}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1337.4}\text{keV}\text{) = 1.2}{}^{\mathrm{+0.6}}{}_{\mathrm{?0.3}}\text{ns and}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(261.0}\text{keV}\text{) = 0.7 ± 0.2}\text{ns}$ using the reaction $\text{(}{}^{12}\text{C}\text{,x}\text{n}\text{)}$, in ${}^{71}\text{As}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(147.5}\text{keV}\text{) = 0.85 ± 0.25}\text{ns}$ using the reaction (¹⁶ O, αp), in ${}^{91}\text{Nb}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(5455.3}\text{keV}\text{) = 1.2 ± 0.3}\text{ns}$ using the reaction (¹⁶O,2np), in ${}^{103}\text{Pd}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(244.0}\text{keV}\text{) < 0.2}\text{ns}$ and in ${}^{91}\text{Nb}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(3110.2}\text{keV}\text{) < 0.2}\text{ns}$ using the reaction P(α, xn). Some known nanosecond isomers in different nuclei produced as by-products have also been detected. In the nuclei investigated far away from closed shells with complex wave functions, M1 transitions are considered which would be l-forbidden in the pure shell model. A retarded $\text{Ml}\text{(+}\text{E}\text{2)}\text{25}\text{2}{}^{\mathrm{+}}\text{→}\text{23}\text{2}{}^{\mathrm{+}}$ transition in ⁹¹ Nb is considered as proceeding between possible multiparticle-hole configurations.     

Retardation of E1 transitions and the neutron effective charge in 29Si

The effect of the giant dipole resonance on E1 transition rates is investigated, and an expression is derived which allows E1 effective charges to be calculated using the γ-absorption cross section of the neighbouring even-mass core. It is shown how this expression can be approximated using a sum rule in cases where the absorption cross section is not adequately known. Application is made to ²⁹Si; using wave functions from a particle-core model, calculated E1 transition rates are in excellent agreement with experiment.     

High-spin states in 107Sn and 107In isotopes

The isotopes ¹⁰⁷Sn and ¹⁰⁷In were produced through the ¹⁰⁶Cd(³He, 2n)¹⁰⁷Sn and ¹⁰⁶Cd(³He, pn)¹⁰⁷In reactions. They were studied by means of γ-spectroscopy, excitation functions, γγ coincidences and angular distributions of γ-rays. A level scheme is proposed for the newly discovered ¹⁰⁷Sn, and new states belonging to ¹⁰⁷In are given. Microscopic calculations have been performed in a three-quasiparticle approximation for a large number of tin isotopes in order to get a wide view of the systematic evolution of the various states.     

E0/E2 and E2/M1 multipole mixing amplitudes of γ-transitions in 192Pt

Angular correlation measurements of conversion electrons and γ-rays in ¹⁹²Pt following the decay of ¹⁹²Ir (74 d) have been made. In particular, the 296 keV e^?-316 keV γ correlation was measured in order that the electric monopole admixture in the 296 keV transition could be determined. The results of the angular correlation coefficients measured here and the ratio of K-shell to L_III shell conversion electrons measured by others are: ?0.09 < q < +0.26 as +62 < λ < +92 or ?0.29 < q < ?0.06 as ?5 < λ < +45. A possible explanation of the disagreement between two earlier measurements is suggested. The angular correlation coefficients for the measured e^?-γ and γ-γ cascades and the derived multipole mixing ratios are tabulated and compared with other recent measurements and with the predictions of the Kumar-Baranger nuclear model.     

Elastic and Raman scattering of 8.5–11.4 MeV photons from 175Lu and 181Ta

Differential cross sections for elastic and inelastic Raman scattering from ¹⁷⁵Lu and ¹⁸¹Ta were measured. Five photon energies between 8.5 and 11.4 MeV were used and were obtained from the (n, γ) reaction on Ni and Cr using thermal neutrons. The results are compared with calculations using a modified simple rotator model (SRM) of the giant dipole resonance (GDR) in which the effect of Delbrück scattering was incorporated. In general, fair agreement between theory and experiment is obtained. A new set of GDR parameters is extracted, based on photon scattering data and, as expected, yield better agreement between experimental and predicted cross sections.     

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.     

Reactions of 40Ar with 159Tb, 142Nd and 144Sm; New α-activities from 189Bi, 173Pt and 177Au

Reactions of ⁴⁰Ar ions with targets of ¹⁵⁹Tb, ¹⁴²Nd, and ¹⁴⁴Sm have been studied at energies below 300 MeV with a helium gas-jet system. Excitation functions for (Ar, xn) reactions, where x = 5–10, were obtained for the radioactive products that decay by α-emission. Based on the characteristics of these excitation functions and on the systematics of α-decay, evidence is presented for the existence of the nuclides ¹⁸⁹Bi with α-particle energy E_α = 6.67±0.01 MeV and half-life < 1.5 sec, and ¹⁷³Pt with E_α = 6.19±0.01 MeV; and for the emission from ¹⁷⁷Au of an α-particle with E_α = 6.15±0.01 MeV.     

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.     

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.     

Intrinsic states,high-spin rotational bands and rotation alignment in 177Os and 179Os

Low-lying intrinsic states and their associated rotational bands have been identified in ¹⁷⁷Os and ¹⁷⁹Os. They are the mixed i_{$\text{13}\text{2}$} neutron states and the $\text{1}\text{2}$^?[521] states in ¹⁷⁷Os and ¹⁷⁹Os, as well as the $\text{5}\text{2}$^?[512] state in ¹⁷⁷Os and the $\text{7}\text{2}$^?[514] state in ¹⁷⁹Os. The $\text{1}\text{2}$^? sta is assumed to be the ground state, the other intrinsic states giving rise to isomers. The in-band decay properties of the $\text{7}\text{2}$^?[514] band, and the i_{$\text{13}\text{2}$} bands show the effect of mixing. In the rotational bands in ¹⁷⁷Os a low frequency backbending anomaly is observed but no anomaly is observed in the i_{$\text{13}\text{2}$}. band. In ¹⁷⁹Os the i_{$\text{13}\text{2}$} band does backbend but at a higher frequency than in the yrast bands of the even neighbours. The systematics of the backbending frequencies, and the effects of blocking, are discussed. The rotation aligned angular momentum is deduced, and a comparison made between the i_{$\text{13}\text{2}$} bands and the s-bands in the even neighbours. The results broadly support the identification of the s-bands with the aligned (i_{$\text{13}\text{2}$})² configuration.     

Excitation of 3−1, 5−1 and 7−1 states in Te isotopes A = 120, 122; 124, 126, 128 WITH (p,t) reactions

The reactions ^ATe(p, t)^A?2Te have been studied with even-A targets using 51.9 MeV protons. Three or more strongly excited triton peaks were observed in the spectra of the ^A-2Te nuclei at energies of ≈ 2–3 MeV excitation. Angular distributions are analyzed using DWBA theory. The lowest octupole (3^?₁) states of five Te isotopes are strongly excited. The lowest 3^? state in ¹²⁰Te is established at 2.09 ±0.02 MeV. The systematics of excitation energies and cross sections for the lowest 5^? and 7^? states are interpreted by a quasiparticle model.     

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.     

Three-quasiparticle states in 177Ta

The feeding of the $\text{21}\text{2}{}^{\mathrm{?}}$, 1355 keV isomeric state in ¹⁷⁷Ta in the ¹⁷⁵Lu (α, 2n)¹⁷⁷Ta reaction has been studied by means of the delayed coincidence technique. Three other three-quasiparticle states have been observed and their configuration is proposed.     

Negative-parity states in Pb isotopes: g-factor of the 480 ns,if Jπ = 9− isomer in 200Pb

The g-factor of the 480 ns, 9^? isomer at 2.237 MeV in ²⁰⁰Pb was measured by the time-differential perturbed angular distribution method. The result, g = ?0.0285±0.0011 confirms the rather pure $\text{(}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{)}$ quasiparticle structure of this state. Half-lives of 480±20 ns, 43±3 ns and 42±4 ns have been measured for the 2237 keV 9^?, 2154 keV 7^? states in ²⁰⁰Pb and the 2208 keV state in ²⁰²Pb, respectively; E2 transitions and g-factors of negative-parity states in even, neutron-deficient Pb isotopes are discussed.     

α1 clusters in 12C

The results of a microscopic calculation for ¹²C states using bound state boundary conditions show that even for the lowest state, wave function components which describe two α-clusters plus one α¹ cluster in relative motion are important. Furthermore, there is evidence for excited states which contain one α¹ cluster.