Level structure in 117Sb investigated in the decay of the isomeric three-quasiparticle state

The level structure of ¹¹⁷Sb was investigated in the reactions ¹¹⁵In(α, 2nγ)^117mSb, ¹¹⁷Sn(d, 2nγ)^117mSb and ¹¹⁷Sn(p, nγ)^117mSb. In order to confirm level sequences and to assign spins and parities to levels populated in the decay of the isomeric three-particle state $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ = 340 μs), prompt and delayed γ-ray spectra, lifetimes, γ-γ coincidences, γ-ray angular distributions, conversion electrons and excitation functions were measured. The spin $\text{25}\text{2}$⁺ of the isomeric state can be explained by the three-particle configuration [$\text{π(}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{); v(}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{)}{}^2\text{10}{}^{\mathrm{+}}\text{]}\text{25}\text{2}{}^{\mathrm{+}}$. This is supported by the experimentally determined g-factor of g = O.115 ± 0.006. Other levels in ¹¹⁷Sb can be interpreted as particle states coupled to anharmonic vibrations of the core. The existence of an excited $\text{9}\text{2}{}^{\mathrm{+}}\text{[404]}$ quasirotational band is experimentally proved and is supported by calculations of the equilibrium deformation.     

Collective excitations in the 123, 125I nuclei

The odd-proton nuclei ¹²³I and ¹²⁵I have been studied in the reactions ¹²¹Sb(α, 2n)¹²³I and ¹²³Sb(α, 2n)¹²⁵I, respectively. The level schemes, spin and parity assignments are based on results obtained from singles γ-ray spectra (E_α = 27 MeV) and excitation functions, from measurements of delayed γ-rays, γ-γ coincidences, internal conversion electrons and γ-ray angular distributions. High-spin positive- and negative-parity bands with energies up to 2948 keV and spins up to $\text{23}\text{2}$ in ¹²³I and with energies up to 3775 keV and spins up to $\text{27}\text{2}\text{in}{}^{125}\text{I}$ have been established. In the decay schemes of both nuclei two separated structures of levels have been observed. One group of levels shows a strong ΔJ = 2 quasirotational pattern predicted by the particle-vibration coupling model. The ΔJ = 1 sequence on a $\text{9}\text{2}$⁺ state is assigned as a rotational structure built on the axially symmetric deformed state $\text{9}\text{2}{}^{\mathrm{+}}\text{[404]}$. In ¹²³I a 28 ns isomer at 2660.0 keV has been found.     

Spin-parity,lifetime and magnetic moment of a short-lived isomeric state in 118Sb

A 3⁺ isomeric state has been identified in ¹¹⁸Sb by pulsed-beam time-differential γ-ray measurements following 4the ¹¹⁸Sn(p, n) and ¹¹⁵In(α, n) reactions. The results of these measurements are: $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 20.6 ± 0.6μ, E}{}_{\mathrm{\gamma }}\text{= 54.4 ± 0.5 keV, α}{}_{\mathrm{<mtext>K</mtext>}}\text{= 8.3 ± 1.0}$ and μ = +2.61 ± 0.05 n.m.     

The level structure of 156Gd studied by means of the (α, 2nγ) reaction

A complete set of conventional γ-ray spectroscopic techniques has been applied to investigate the level structure of ¹⁵⁶Gd. A total of twenty-five new levels has been established; unambiguous spin assignments could be given for twelve of them on the basis of angular distributions and conversion electron measurements. The proposed level scheme contains 49 levels, which can be ordered in seven rotational bands. The ground-state band was excited up to J^π = 14⁺, the β-band up to 10⁺, the γ-band up to (11⁺), the second K^π = 0⁺ band tentatively up to (10⁺), the K^π = 4⁺ band up to (8⁺). Two negative-parity bands, one with even spins and one with odd spins, were excited to J^π = (12^?) and (13^?). An isomeric state was established with $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1.3 μs, J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, E}{}_{\mathrm{<mtext>x</mtext>}}\text{= 2137.7}\text{keV}$. The properties of the K^π = 4⁺ band and the isomeric state can be well explained by two-quasiparticle configurations. The negative-parity bands are interpreted as aligned octupole bands. Positive and negative-parity bands have been calculated in terms of the IBA model. Good agreement with the experimental results is obtained.     

The β− decay of 102Mo

The ¹⁰²Mo activity was obtained by photofission of natural U and thermal-neutron induced fission of ²³⁵U, with subsequent chemical separation of the molybdenum fraction. In addition, nuclei with mass 102 were separated from fission products of ²³⁵U(n_th, f) using the mass separator LOHENGRIN. A decay scheme and absolute γ-intensities are deduced from measured γ-ray, X-ray and γ-coincidence spectra. Logftvalues are calculated. Shell-model calculations for a $\text{(πlg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^3$$\text{(νlg}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^3$ multiplet have been carried out using effective nucleon-nucleon interactions. The γ-decay between low-lying, low-spin members of this multiplet was studied in detail and compared with the experimental data.     

Photoneutron cross sections of 121Sb, 123Sb and natSb

The cross sections for the reactions ${}^{121}\text{Sb}\text{(γ,n)}$, ¹²³Sb(γ, χn) and ^natSb(γ, χn) have been measured. The ¹²¹Sb and ¹²³Sb photoneutron reaction cross sections are consistent with collective model predictions for negatively deformed nuclei.     

Nuclear reactions of 118Sn, 121Sb,and 127I with argon ions

Excitation functions have been measured for a number of (⁴⁰Ar, xn), (⁴⁰Ar, pxn), (⁴⁰Ar, 2pxn), and (⁴⁰Ar, 3pxn) reactions induced in ¹¹⁸Sn, ¹²¹Sb and ¹²⁷I over the lab. energy interval 150–280 MeV. Values of the total fusion cross section are obtained and J_crit is deduced. The value of J_crit increases with energy and becomes as large as 110–140?, in reasonable agreement with the yrast limit deduced from the ellipsoidal liquid drop model. The competition between proton and neutron emission from the compound nucleus is examined and $\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{Γ}{}_{\mathrm{<mtext>n</mtext>}}$ is found to increase rapidly with the number of emitted nucleons, thereby imposing severe limits on the production of very neutron deficient miclides via compound nuclear reactions. The effect of very high angular momentum on the excitation functions is examined.     

The 153Sm nucleus: An experimental and theoretical study

The level structure of ¹⁵³Sm has been studied by means of the ¹⁵⁰Nd(α, n)¹⁵³Sm reaction. The experiment included measurements of the γ-γ coincidences and γ-ray yield as a function of projectile energy. The rotational band built on the $\text{11}\text{2}{}^{\mathrm{?}}$[505] Nilsson orbital was observed up to spin $\text{19}\text{2}$, and two ΔI = 2 bands of positive parity were identified with spins up to $\text{19}\text{2}\text{and}\text{21}\text{2}$, respectively. These bands are associated with the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ single-particle structure.The data obtained in the present work together with data available in the literature are compared to the result of a particle-rotor coupling calculation. The ¹⁵³Sm nucleus is found to be a wellbehaved rotor. An appropriate single-particle level scheme for ¹⁵³Sm is established.     

High-spin rotational states in 24Mg

The states of T = 0, J = 8, 9, 10, 11 and 12 in ²⁴Mg, calculated using the Preedom-Wildenthal interaction, have been studied with a view to assigning some of them to rotational bands. With the possible exception of a J = 9 member of the K = 2 excited band, there is no evidence that band structure persists beyond J = 8. The lowest J = 8 state has a very peculiar structure corresponding to a condensation of particles into the $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ shell.     

The 114In level scheme studied by the (n, γ) reaction

The level scheme of the nucleus ¹¹⁴In has been studied using capture of thermal neutrons. The experimental information is taken from γ singles spectra and γ-γ coincidence spectra and from delayed coincidence measurements. Levels up to 1.4 MeV excitation energy are proposed. Several short lifetimes of excited states in ¹¹⁴In and ¹¹⁶In could be measured. The binding energy of the last neutron in ¹¹⁴In, B_n = 7273.9 ± 1.2 keV, determined in this work is in strong disagreement with previously accepted values. Additional experimental information on the ¹¹⁶In level scheme is given. Six states of the ($\text{π(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?1}}\text{, ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$) multiplet (3^? to 8^?) in ¹¹⁴In. The expected close similarity between many low-lying states in ¹¹⁴In and ¹¹⁶In could be confirmed. In particular, it was found that the anomalous high isomeric cross-section ratio of the second isomeric state results from very selective reorientation transitions within the negative-parity multiplet. The coupling constant of the quadrupole part of the residual neutron-proton interaction obtained from a theoretical calculation of the ¹¹⁴In level scheme is similar in size to that of ¹¹⁶In, thus giving credit to the explanation given in our previous ¹¹⁶In work. The splitting of multiplets in doubly odd In nuclei gives additional information for an interpretation of the so-called $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^{\mathrm{?}}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ anomaly in stripping studies near A = 110. Transition probability ratios B(M1)/B(E2) and E1 hindrance factors are discussed for both ¹¹⁴In and ¹¹⁶In. No sign of states exhibiting stable deformation similar to those in odd-A In nuclei has been found up to now in the doubly odd In nuclei studied. There is some evidence that these doubly odd In nuclei behave more like Cd than like single closed shell Sn nuclei.     

Gamma-ray spectroscopy of 64Zn and 65Zn and the role of the g92 orbital

Measurements of γ-ray excitation functions, γ-γ coincidence spectra and γ-ray angular distributions have been made. following the reactions ⁶¹Ni(α, n)⁶⁴Zn, ⁶²Ni(α, n)⁶⁵Zn, ⁵⁶Fe(¹⁴N, αnp)⁶⁴Zn, ⁵⁶Fe(¹²C, 2pn)⁶⁵Zn, and ⁵⁴Fe(¹²C, 2p)⁶⁴Zn. Among the new levels observed in ⁶⁴Zn are those at 5624 keV, 6765 keV, 6940 keV, and 6124 keV, the last one with a suggested assignment of (9^?). In ⁶⁵Zn. ten new levels probably in the positive-parity chain, with spin up to ($\text{21}\text{2}$), and a few others, have been found. Comparison of the ⁶⁵Zn positive-parity levels with the ⁶⁴Zn ground-state band supports the concept of a single neutron in the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbital weakly coupled to a core essentially identical to ⁶⁴Zn. Many high-spin states in ⁶⁴Zn itself can be aggregated into bands whose band heads are suggestive of two-quasiparticle states involving one $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ excitation.     

The quadrupole moments of the 5− states in 116Sn, 118Sn and 120Sn

The quadrupole interaction frequencies $\text{ω}{}_0\text{=}\text{3eQ}{}_1\text{V}{}_{\mathrm{zz}}\text{41(21-1)}\text{h}\text{?}$ in the 5^? state of ¹¹⁸Sn have been measured by time differential perturbed angular correlation technique in Sn, Sb and (95% Sn+5% Sb) environments. The ω₀ for ¹¹⁶Sn was determined in Sn environment only. With the help of the known electric field gradient ¹) of Sn in a Sn lattice the quadrupole moments have been deduced as $\text{Q(5}{}^{\mathrm{?}}\text{,}{}^{118}\text{Sn}\text{) = ±0.10(4) b}\text{and}\text{Q(5}{}^{\mathrm{?}}\text{,}{}^{116}\text{Sn}\text{) = ±0.165(60)}\text{b}$. These values together with the known²) quadrupole moment of the analogous 5^? state in ¹²⁰Sn are interpreted in terms of the pure single-particle model. The data exhibit the expected strong systematic variation of Q_I with the number of particles in the h_{$\text{11}\text{2}$}. subshell which is being filled with 1, 3 and 5 neutrons in ¹¹⁶Sn, ¹¹⁸Sn, and ¹²⁰Sn, respectively.     

Rotational bands in the odd-odd 152Eu nucleus

The ¹⁵⁰Nd(⁷Li, 5n) reaction has been used to study the high-spin states in the odd-odd nucleus ¹⁵²Eu. Two rotational bands of different behaviour have been identified: a rather regular band based on the I^π = 8^? isomeric state of configuration $\text{[413}\text{5}\text{2}\text{]}{}_{\mathrm{<mtext>p</mtext>}}\text{[505}\text{11}\text{2}\text{]n}$ and a strongly decoupled system belonging to the configuration $\text{[}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{]}{}_{\mathrm{<mtext>p</mtext>}}\text{[i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{]}{}_{\mathrm{<mtext>n</mtext>}}$.It is shown in this work that the aligned angular momentum carried by each two-quasiparticle configuration in ¹⁵²Eu is the sum of the alignment of the odd neutron and odd proton, which indicates a negligible influence of the neutron-proton residual interaction. Particular attention has been focused on the strong deviations of the moment of inertia of the core when different quasiparticle configurations are involved.     

The excited states of 85Sr

High resolution γ-ray studies have shown the decay patterns of isomers of ⁸⁵Y to be very complex. A level scheme of ⁸⁵Sr is proposed from the results of γ-γ coincidence measurements. Spin and parity assignments to the levels of ⁸⁵Sr were made on the basis of log ft values, nuclear reaction data and γ-ray branchings. The level scheme is discussed within the theoretical framework of $\text{n(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?3}}$ cluster properties.     

Band structures in 98Ru and 99Ru

The level schemes of ^{98, 99}Ru were studied with the reactions ⁹⁸Mo(α, 3nγ) and ⁹⁸Mo(α, 4nγ) at E_α = 35 to 55 MeV, using a large variety of in-beam γ-ray detection techniques and conversion-electron measurements. A search for the 3^? state was carried out with the reaction ⁹⁸Ru(p, p′). The ground-state band of ⁹⁸Ru was excited up to J^π = (12)⁺ and a negative-parity band up to (15)^?. New levels in ⁹⁸Ru were found at E_x = 2285 (J^π = 4⁺), 2435 (J^π = (3^?, 4⁺)), 2671, 3540, 4224, 4847, 4915 (J^π = (12)⁺), 4989 (J^π = (12⁺)), 5521 (J^π = (13)^?), 5889, 6591 (J^π = (15)^?), and 7621 keV. New unambiguous spin and parity assignments were made for the levels at E_x = 2014 and 3852 keV, as J^π = 3⁺ and 9^?, respectively. New levels in ⁹⁹Ru were found at E_x = 1976, 2021 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{15}\text{2}{}^{\mathrm{+}}\text{)}$), 2393, 2401 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{17}\text{2}{}^{\mathrm{+}}\text{)}$), 2875 (π = (+)), 3037, 3201 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{23}\text{2}\text{)}{}^{\mathrm{?}}$), 3460 ($\text{J = (}\text{17}\text{2}\text{)}$), 3484 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{21}\text{2}{}^{\mathrm{+}}\text{)}$), 3985, 4224 ($\text{J}{}^{\mathrm{\pi }}\text{= (}\text{27}\text{2}{}^{\mathrm{?}}\text{)}$), and 5359 keV. The 1070 keV, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}$ level in ⁹⁹Ru has a half-life of 2.8 ns. A strongly excited negative-parity band is built on this level. A positive-parity band based on the ground state was excited up to $\text{J}{}^{\mathrm{\pi }}\text{= (}\text{21}\text{2}{}^{\mathrm{+}}\text{)}$. The level schemes are well reproduced by the interacting boson model in the vibrational limit.     

The ratio of K-capture to positon emission in the decay of 120Sb: Experiment and theory disagree

Recent review papers have indicated that experimental K.-capture to positon emission ratios in allowed decays disagree with theory especially for high-Z nuclei. The experimental error has never been sufficiently small to verify this with certainty. The K-capture to positon emission ratio, , in ¹²⁰Sb has been measured with an uncertainty of about 3% and found to lie about 16% lower than the most recent theoretical predictions.     

Collectivity and the role of two-proton and two-neutron excitations in 82Kr

Excited states in ⁸²Kr have been studied in the reaction ⁸⁰Se(α, 2n) by using in-beam γ-ray spectroscopy. Measurements of γγ coincidences, excitation functions, angular distributions and the linear polarization of the γ-rays have been carried out. All together, 38 levels have been identified up to $\text{I = 12}\text{h}\text{?}$ and excitation energies up to 6 MeV. For 23 of these levels the mean lifetime could be determined by Doppler shift and the pulsed-beam γ-timing methods. Most of the levels could be grouped into collective bands according to measured B(E2) values. Two sequences, I^π = 8⁺, 10⁺, 12⁺, are interpreted as rotation-aligned 2q.p. bands built up on $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ protons and neutrons, respectively. Interaction matrix elements between these bands were deduced as V ? 10 keV. Additional states, I^π = (6⁺), 7⁺, 8⁺, indicate coexistence of rotation-aligned and deformation-aligned 2q.p. excitations. An odd-parity ΔI = 1 band is ascribed to proton excitations of the type $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{?}\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$. Several fast M1 transitions with B(M1) = 0.1–1 W.u. have been observe states of equal spin. They are interpreted as being due to configuration mixing.     

Radiative capture of fast neutrons by 89Y and 140Ce

The γ-ray spectra from the reactions ⁸⁹Y(n, γ)⁹⁰Y and ¹⁴⁰Ce(n, γ)¹⁴¹Ce have been measured in the neutron energy range of 6.2–15.6 MeV. The pulse-height spectra were recorded with NaI(Tl) spectrometers and time-of-flight techniques were used to improve signal-to-background ratio. Capture cross sections were determined for γ-ray transitions to the two $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels at 0 and 203 keV of ⁹⁰Y and to the $\text{2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ ground state of ¹⁴¹Ce as well as integrated cross sections to bound states in these nuclei. The observed γ-ray spectra and partial radiative capture cross sections were compared with predictions of the direct-semidirect capture theory. The resonance behaviour with neutron energy of both the ground-state and integrated partial capture cross sections shows the validity of the semidirect model for ⁸⁹Y and ¹⁴⁰Ce in the region of neutron energy encompassing the giant-dipole resonance. The observed symmetry of the cross sections about the peak of the resonance argues strongly for the complex form of the particle-vibration coupling interaction. A detailed comparison of the predictions of the DSD model using the complex coupling interaction shows that the capture cross sections are relatively insensitive to the real part of the interaction.     

High-spin states in 155Ho

High-spin states in ¹⁵⁵Ho have been populated in the ¹⁴⁵Nd(¹⁴N, 4n)¹⁵⁵Ho reaction. Excitation functions, lifetimes, angular distributions and γ-γ coincidences were measured. An $\text{11}\text{2}{}^{\mathrm{?}}$ isomeric state with $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.88}\text{ms}$ has been found at very low energy. The rotational band built on this state is developed up to spin $\text{35}\text{2}$. The behaviour of its moment of inertia is compared with that of the doubly even neighbouring nuclei.