The γ-decay of the 1g92 and 2p inner-hole states in 111Sn via the 112Sn(3He, αγ) reaction at 32 MeV

The γ-decay of the deeply-bound hole states in ¹¹¹Sn has been investigated at 32 MeV incident energy by means of the ¹¹²Sn(³He, αγ) reaction. The α-particles emitted near 0° were detected in a Si counter located at the image plan of the superconducting solenoidal spectrometer SOLENO. The γ-rays in coincidence with the α-particles were detected by two Ge(Li) detectors located at 90° and 142° with respect to the beam direction, respectively. Energies, spins and decay schemes have been established for the low-lying states up to 2.5 MeV excitation energy in ¹¹¹Sn. The γ-decay of the broad bump, located around 4.2 MeV and previously attributed to neutron pick-up from the inner $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{,}\text{and}\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ neutron. Subshells, reveals the importance of quasiparticle-phonon m the spreading mechanism of the inner-hole strengths. The $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and 2p strength functions have been deduced from the α-decay of the enhanced structures (3 ≦ E_x≦ 8 MeV). They are compared to the ones measured in previous inclusive neutron pick-up experiments and to those calculated in the framework of the quasiparticle-phonon nuclear model.     

On the question of fine structure in νp and EK for 233U and 235U

The question of fine structure in the variation of the average number of prompt neutrons, $\text{ν}{}_{\mathrm{<mtext>p</mtext>}}$, emitted per fission with energy in the neutron fission of ²³³U and ²³⁵U has been examined. Consistent structure has been found in measurements of both $\text{ν}{}_{\mathrm{<mtext>p</mtext>}}\text{and}\text{E}{}_{\mathrm{<mtext>K</mtext>}}$ (the average total fission fragment kinetic energy) for ²³³U. Channel analysis of the neutron fission cross section of ²³³U allows the structure to be calculated quantitatively provided the collective energy at the second hump in the fission barrier is weakly coupled to the nuclear degrees of freedom at scission. A similar calculation for neutron fission of ²³⁵U supports the case for the absence of fine structure in $\text{ν}{}_{\mathrm{<mtext>p</mtext>}}\text{and}\text{E}{}_{\mathrm{<mtext>K</mtext>}}$ for this nucleus.     

β-delayed charged particles from 9Li and 11Li

β-delayed emission of α-particles from ⁹Li and of both α and ⁶He particles from ¹¹Li is observed. Singles energy spectra and two-dimensional energy spectra of coincident particles are measured. A time-of-flight versus energy measurement is used to identify the mass of the particle. New β-branches are observed which populate high-energy levels in the daughter nuclei. The branching ratios are measured and the β-delayed neutron emission probabilities $\text{P}{}_{\mathrm{<mtext>n</mtext>}}\text{for}{}^9\text{Li and}\text{P}{}_{\mathrm{3n}}\text{for}{}^{11}\text{Li}$ are deduced.     

Experimental study of some important characteristics of the thermal neutron induced fission of 237Np

Fission fragment mass and kinetic energy distributions and their correlations have been studied for the thermal neutron induced fission of ²³⁷Np. The global mass distribution is rather smooth, apart from a weak shoulder at μ_H = 140–141. When low excitation events are selected, fine structures associated with the charge of the fragments are observed. Furthermore, there is a sudden increase in E_k for μ_H > 155, which is probably due to a spherical shell N = 50 in the light fragment and the corresponding deformed (but stable) heavy fragments with masses in the rare earth region. For the average (pre-neutron emission) total fragment kinetic energy, a value of 176.4 ± 0.6 MeV has been obtained, in agreement with the systematics.Also the prompt neutron emission curve $\text{v(m}{}^1\text{)}$ has been calculated, which shows the well-known saw-tooth shape. Finally, the energy distribution and the emission probability of the ternary α-particles have been determined.     

Linear momentum transfer in the reaction 232Th(14N,light particles) AT 208 MeV

The longitudinal momentum transferred to a target nucleus (ΔP) has been studied for light-particle emission in the ¹⁴N-induced reaction on ²³²Th at 208 MeV. The transferred momentum was deduced by measuring folding angles between two fission fragments resulting from the sequential decay of the target-like nucleus. It was found that the fraction $\text{?}{}_2\text{=}\text{(〈ΔP〉 + P}{}_{\mathrm{<mtext>out</mtext>}}{}^{\mathrm{\parallel }}\text{)}\text{P}{}_{\mathrm{<mtext>beam</mtext>}}$ averaged over light-particle energy was about 0.68, almost independent of light-particle species and detection angle, where P_beam is the initial momentum of the beam particle and P_out^∥, the momentum component parallel to the beam carried away by the observed light particle. A possible mechanism for describing the phenomena is discussed.     

Fission-fragment angular distributions for 230Th(n,f) in the vicinity of the 715 keV resonance

Fission-fragment angular distributions have been measured for the neutron-induced fission of ²³⁰Th in the vicinity of the 715 keV resonance with a 2.5 keV (FWHM) neutron energy resolution. An analysis was performed to find a set of fission barrier characteristics that reproduce simultaneously the present angular distribution data and the fission cross-section data of Blons et al. The analysis results show that the data for the 715 keV resonance could be fitted only if allowance is made for the existence of two rotational bands with opposite parities but with the same K quantum number. The moment of inertia parameter $\text{kh}{}^2\text{2}\text{I}$ extracted from the analysis has a value of 1.9 keV, which is compatible with the existence of a third minimum in the fission barrier at a quadrupole deformation of ε₂ = 0.85.     

Spectroscopic information on 35S and 37S from the (d,p) reaction

The reactions ³⁴S(d,p)³⁵S and ³⁶S(d,p)³⁷S were studied at the incident deuteron energy of 12.3 MeV. Proton groups were analysed using a multi-angle magnetic spectrograph with the resolving power $\text{E}\text{ΔE}\text{≈ 1400}$. Precise Q-values corresponding to 13 states of ³⁵S up to the excitation energy of 7483 keV and 22 states of ³⁷S up to the excitation energy of 6406 keV are presented. The ground-state transition Q-value for the reaction ³⁶S(d,p)³⁷S was found to be 2079.12 ± 0.13 keV. Angular distributions of proton groups corresponding to 6 states in ³⁵S and to 11 states in ³⁷S were analysed using DWBA calculations. Transferred orbital angular momenta and spectroscopic factors were deduced. Summed spectroscopic strengths show that substantial parts of single-particle strengths for $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ in both reactions are exhausted b observed transitions.     

Time-of-flight measurement of the evaporation residues from fusion of 5.9 mev/u 84kr and 27al

Mass and Z-distributions of the evaporation residues from compound-nucleus formation in the reaction 5.9 MeV/u ⁸⁴Kr on ²⁷Al were measured using a time-of-flight ΔE ? E telescope, which is described in detail. The high recoil velocity attained by choosing the heavy reaction partner as projectile made it possible to resolve the reaction products by mass and atomic number. Data were taken in the angular range from 1.5 to 6°. The residue distributions are compared to evaporation calculations assuming the statistical decay by fission and particle evaporation of the compound nucleus ¹¹¹Mn formed at an excitation energy of 108 MeV with angular momenta up to $\text{L}{}_{\mathrm{<mtext>CN</mtext>}}\text{≈ 69}\text{h}\text{?}$. The data are consistent with the assumption of statistical equilibrium. Details of the de-excitation process, in particular the fission competition and the influence of nuclear deformations at high angular momenta, are discussed.     

γ-decay of the deeply-bound hole states in 101Pd, 105Pd, 107Pd, 111Sn, 117Sn observed in the (3He, αγ) reaction at 70 MeV

The γ-decay of deep-hole states in ^{101, 105, 107}Pd was studied via the (³He, αγ) reaction at E_³he = 70 MeV and supplemented by data from ^{112, 118}Sn targets to investigate the deep-hole spreading mechanism. The γ-decay pattern for the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ deep-hole state shows a strong dependence on the spreading width: if the deep-hole state is observed as a sharp peak, it mainly decays to the low-lying $\text{7}\text{2}{}^{\mathrm{+}}$ state by a spin-flip M1 transition with a large M1-E2 mixing ratio; if the deep-hole state is observed as a broad bump, it decays statistically indicating the complete spreading of the hole strength over the underlying states; if the deep-hole state is observed with a structure intermediate between a sharp peak and broad bump, its γ-decay shows both decay patterns.A sharp peak at E_x = 2.396 MeV in ¹⁰¹Pd which carries a large fraction of the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ hole strength (C²S = 2.0) was found to be a single state having a width of less than 2.5 keV.For the spin-flip M1 transition the destructive interference between the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ component and the coupled components of the deep-hole state was found in heavily spread states.A quasiparticle-plus-rotor (QPR) model was applied to calculate the fragmentation in the doorway stage for the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ neutron deep-hole state in the Pd isotopes. A reasonable agreement between the calculation and the experimental results was obtained for the strength fragmentation, for the nucleus ¹⁰¹Pd. However, the large M1-E2 mixing ratio experimentally observed was not reproduced.     

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.     

Proton threshold states in 26Al

The energy levels of ²⁶Al between E_x = 6.3 and 6.5 MeV, corresponding to proton threshold energies in the ²⁵Mg + p reaction from $\text{E}{}_{\mathrm{<mtext>p</mtext>}}\text{= 0}\text{to}\text{200}\text{keV}\text{, have been investigated using the reactions}{}^{27}\text{Al(su3}$He, α)²⁶Al and ²⁴Mg(³He, p)²⁶Al. Despite early work reporting a doublet at E_x = 6346 keV and E_x = 6362 keV, most subsequent work reported a single state with conflicting spin and parity assignments. Our work clearly establishes the presence of the doublet and resolves the conflicts. We find that there are six states in this excitation energy region, including a new state at E_x = 6410 ± 5 keV. The l-values leading to possible spin and parity assignments for all these states have been made using DWBA. We conclude however that only three of these six states may contribute to the production of ²⁶Al by the ²⁵Mg(p, γ) reaction in the MgAl cycle and the new structure of ²⁶Al reported here can substantially increase the production rate of ²⁶Al in stellar reactions.     

Interference effects in 12C(p, γ)13N and direct capture to unbound states

Excitation functions of the capture reaction ¹²C(p, γ₀)¹³N have been obtained at θ_γ = 0° and 90° and E_p = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in ¹³N is included in the analysis in addition to the two well-known resonances in this beam energy range $\text{[E}{}_{\mathrm{p}}\text{= 457(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}$ and 1699 $\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{) keV]}$. The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C²S(l = 1) = 0.49 ± 0.15 has been deduced for the $\text{1}\text{2}{}^{\mathrm{?}}$ ground state in ¹³N. Excitation functions for the reaction ${}^{12}\text{C(p,γ}{}_1\text{p}{}^1\text{)}{}^{12}\text{C}$ have been obtained at θ_γ = 0° and 90° and E_p = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. Above E_p = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below E_p = 1 MeV, i.e., E_p → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at $\text{E}{}_{\mathrm{p}}\text{? 1 MeV}$, a spectroscopic factor of C²S(l = 0) = 1.02 ± 0.15 has been found for the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. A search for direct capture transitions to the $\text{3512 (}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$and $\text{3547 (}\text{5}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound states resulted in upper limits of C²S(l = 1) ≦ 0.5 and C²S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the ¹²C(p, γ₀)¹³N reaction also is discussed.     

Particle-hole multiplets in 40Ca observed in the 41Ca(τ, α) reaction

Energy levels in ⁴⁰Ca up to 10.2 MeV have been studied in the neutron pickup reaction ⁴¹Ca(τ, α)⁴⁰Ca with 20 MeV bombarding energy. Thirty excited states have been identified and angular distributions have been measured in the interval from 5° to 40° by means of a split-pole magnetic spectrometer. The angular distributions together with DW calculations have been used to extract l_n values and spectroscopic factors. The l_n = 2 strength distribution for the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ particle-hole levels is compared to the l_p = 3 strength distribution from pr stripping data.     

Nuclear reaction studies of 168Tm

The intrinsic structure of ¹⁶⁸Tm has been studied using the (³He, d) and (α, t) proton stripping reactions as well as the (d, t) and (³He, α) neutron pick-up reactions. The beams of 24 MeV ³He particles, 25 MeV α-particles and 12 MeV deuterons were obtained from the McMaster tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge-type magnetic spectrograph and detected with photographic emulsions. The spectra have been interpreted in terms of the coupling of an odd proton and an odd neutron, each moving independently in a spheroidal potential, which gives rise to intrinsic two-quasiparticle states with $\text{K = ¦Ω}{}_1\text{±Ω}{}_2\text{¦}$. The identification of the intrinsic states was made by comparing the experimental cross-section patterns with those predicted with the aid of Coriolis coupling and distorted-wave Born approximation (DWBA) calculations. Rotational bands superimposed on the K^π = 3⁺ and $\text{K}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{+}}\text{, {}\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}{}_{\mathrm{n}}\text{±}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{p}}\text{}}$ configurations, the first of which is the ground state, ha been observed in the spectra of all four reactions. New assignments have been made for configurations resulting from coupling the $\text{1}\text{2}$^? [541], $\text{7}\text{2}$⁺ [404], $\text{5}\text{4}$⁺ [402] and $\text{1}\text{2}$^? [530] p to the $\text{7}\text{2}$⁺ [633] neutron state. The neutron pick-up measurements confirmed the earlier assignments based on (d, t) reaction studies and suggested tentative assignments for the {$\text{1}\text{2}$⁺ [400]_n±$\text{1}\text{2}$⁺ [411]_p} and {$\text{3}\text{2}$⁺ [402]_n±$\text{1}\text{2}$⁺ [411]_p}     

Properties of the lighest known caesium isotopes 114–118Cs

Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.7}\text{sec}$) in ¹¹⁶Cs has been observed and the new delayed-particle precursors ¹¹⁶Cs (protons and α-particles), ¹¹⁵Cs (protons), and ¹¹⁴Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for ¹¹⁸Cs (pγ and αγ) and ¹¹⁶Cs (pγ). A search for the possible proton-radioactive isotope ¹¹³Cs has been performed and an upper limit for its production yield is given.     

Study of isovector charge-exchange excitations and their decay via the 16O(3He,tp) reaction

The nucleus ¹⁶F was studied via the ¹⁶O(³He, t) reaction at 81 MeV. Differential cross sections for many states were obtained and interpreted with DWBA calculations, using microscopic wave functions and an effective projectile-nucleon interaction. Proton decay to several states in ¹⁵O was observed and angular correlations for protons in coincidence with tritons detected at θ = 0° were measured. Several spin-parity assignments have been made. The distribution of isovector ΔL = 1 strength could be deduced. The analog of the giant dipole resonance ($\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{? 9.5}\text{MeV}\text{)}$ is strongly excited. The magnetic quadrupole strength has two strong components, one low, at E_x = 0.424 MeV, and one high, at $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{? 7.5}\text{MeV}$. Evidence is given for a proportionality between cross section and M2 strength for transitions to J^π = 2^? states, which possibly make the (³He, t) reaction a suitable tool for determining quantitatively isovector M2 (or B_ij) strengths.     

Spectroscopy of 42Ca from 41Ca(d,p)

Energy levels in ⁴²Ca up to 7.8 MeV have been studied in the neutron capture reaction ⁴¹Ca(d, p)⁴²Ca with 12 MeV bombarding energy. Ninety-four excited states have been identified and angular distributions have been measured in the interval from 5° to 110° by means of a broad-range magnetic spectrograph. The angular distributions together with DW calculations have been used to determine I_n values and spectroscopic factors. The $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ strength sum agrees with shell-model expectations if the f_{$\text{7}\text{2}$} spectroscopic factors are renormalized by $\text{1}\text{0.75}$, in line with other $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$. transfer experiments on ⁴⁰Ca and ⁴¹Ca. A similar renormalization of the l_n = 1 spectroscopic factors brings this strength sum in accordance with the shell-model calculations. The effective ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^2$) matrix elements for ⁴²Ca are compared with the corresponding matrix elements of ⁴²Sc and ⁴⁸Sc. The differences between the three sets of matrix elements are of the order of a few hundred keV or less. The monopole centroid energy of the ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$ multiplet is shifted downwards in the mass-42 nuclei compared to ⁴⁸Sc, possibly indicating the importance of the monopole pairing force near ⁴⁰Ca.     

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.     

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.     

A cellular model for the Mössbauer isomer shift of 99Ru, 193Ir, 195Pt and 197Au in transition metal alloys

It is demonstrated that the isomer shift of Mössbauer nuclei in transition metal alloys can be quantitatively described in terms of an atomic cell model. The isomer shift ΔE, relative to the pure metal as a reference, is derived from a change in boundary conditions for the atomic cell; $\text{ΔE = PΔφ}{}^1\text{+ QΔn}{}_{\mathrm{ws}}$, where ø¹ is the electronegativity parameter, n_ws the cell boundary electron density and P and Q are constants for a given Mössbauer nucleus. For solid solutions there is in addition a relatively small size mismatch term.