Study of the level structure of239U using the thermal neutron capture reaction

For the investigation of vibrational states in odd A nuclei we have studied the level structure of²³⁹U by the²³⁸U (n _thermal,γ) reaction. Various complementary measurement techniques as curved-crystal-, anti-Compton-,γ-γ coincidence- and conversion electron spectroscopy have been applied. The resulting data have been used to establish the deexcitation scheme of²³⁹U up to ～1.3 MeV and to make spin assignments. Most of the levels are interpreted in terms of the Nilsson model. The data also indicate the presence of the Nilsson states ¦501?¦ and ¦750¦. Three members of theΒ-vibrational band built on the ¦631?¦ state and one member of theΒ-vibration built on the ¦622↑¦ ground state have been identified through transitions with strongE0 admixtures. The octupole vibrational state built on the ¦631?¦ band is proposed at 815 keV.     

In beam gamma spectroscopy of62Zn

The decay scheme of⁶²Zn has been investigated by studying the yield functions, angular distributions and coincidence relation-ships of theγ-rays emitted in the⁶³Cu(p, 2nγ) and⁶⁰Ni(α, 2nγ) reactions. Spins up to7? were assigned to the observed states. Nuclear Reactions ⁶⁰Ni(α, 2nγ)⁶²Zn,E _α=28–35 MeV and⁶³Cu(p, 2nγ)⁶²Zn,E _p = 22–31 MeV; measuredE _γ,I _γ(θ),I _γ(E _p , andI _γ,E _α-γ coincidences,⁶²Zn deduced decay scheme. Enriched target, Ge(Li) detectors.     

Ionization cross sections and rate coefficients for the ground state of AsI-like ions

Detailed level-by-level calculations of cross sections and rate coefficients for electron impact direct ionization and excitation-autoionization of AsI-like ions in the 3d ¹⁰4s ²4p ³ (⁴S_3/2) ground state have been performed. The cross sections are presented in the energy range near the threshold for the five ions Mo⁹⁺, Xe²¹⁺, Pr²⁶⁺, Dy³³⁺ and W⁴¹⁺. The rate coefficients are given for all the ions from Sr⁵⁺ to U⁵⁹⁺ in the AsI sequence at the seven electron temperatures (k T _e = 0.1E _I ,0.3E _I ,0.5E _I ,0.7E _I ,E _I ,2E _I and 10E _I , where E _I is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated using the Lotz formula approximation and the contributions of excitation-autoionization (EA) computed in the framework of the Distorted Wave (DW) approximation for the 4s ? nl, 3d ? nl and 3p ? nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is presented as a function of Z along the AsI isoelectronic sequence. The present results show the great importance of the EA processes; an ionization enhancement factor of up to 6.5 is predicted for instance for Dy³³⁺ (Z = 66) at electron temperature of coronal equilibrium maximum abundance.     

Negative-parity bands in the 88-neutron nuclei153Tb and155Ho

Bands of negative-parity levels have been observed in in-beam studies of¹⁵³Tb and¹⁵⁵Ho. The data are qualitatively accounted for in the rotation-alignment model as decoupled bands based on the h_11/2 proton orbital. Nuclear Reactions:¹⁵³Eu(α, 4nγ)¹⁵³Tb,E=45–55 MeV;¹⁵⁰Sm(¹⁰B, 5nγ)¹⁵⁵Ho,E=60–70 MeV; measuredE _γ,I _γ (0), γ ? γ coinc.,E _e, I _e ^K ,¹⁵³Tb and¹⁵⁵Ho deduced levels,J, π. Ge(Li) and Si(Li) detectors. Enriched targets.     

Approximately linear relations between two-nucleon and three-nucleon parameters

The correlation between the triton binding energyE _t and then-d scattering length² a and the zero energy singlet and triplet wound integral I_os and I_ot is investigated, with phaseequivalent separableNN interactions obeying all the important off-shell constraints. It is found that the correlation betweenE _t and² a is stronger than betweenE _t (² a) andI _os ,I _ot separately. A strong correlation is also found between the percentageD-state in the deuteronP _d andI _ot . Fixing all the other off-shell parameters but allowing variations ofI _os andI _ot leads to surprisingly accurate linear relations betweenE _t(² a) andI _os ,I _ot (P _d). These relations depend strongly on the other off-shell parameters.     

Directional correlations in the decay of 1200y 166Ho

γγ-directional correlations have been measured between the ground state band transitions 6→4, 4→2 and 2→0 and the γ-rays depopulating the levels of the gamma vibrational band and the negative parity states of¹⁶⁶Er. Thereby angular momenta could be assigned to the latter states andM2/E1 multipole mixtures determined for the depopulating γ-transitions. TheE2/M1 mixing ratios were obtained for a series ofI _γ→I _g transitions up toI _γ=8⁺. These are used to investigate the angular momentum dependence of theE2/M1 admixtures.     

Konversion der 238,6 keV-γ-Linie des ThB und Vergleich mit den Tabellen von Sliv und von Rose

The conversion ratiosK/L _I andK/L _II of the 238.6 keVγ transition of ThB have been measured with the new Heidelbergπ/2 √13Β-ray spectrometer. For this transition there are great discrepancies between the values as given bySliv andBand, and byRose. The experimental resultsK/L _I=5.96±0.26 andK/L _II=60.3±7.1 are in excellent agreement with the values ofSliv andBand.     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

The long-time behaviour of the electric-field autocorrelation function in a finite photon gas

We investigate an autocorrelation function of a soluble three-dimensional system, namely the temporal coherence functionC _E(t)∝<E(0)E(t)> of the thermal radiation field in a cube-shaped cavity for the stochastic electrical fieldE. In the thermodynamic limit,C _E(t) relaxes exponentially at intermediate times, but a “long-tail” behaviourC ₀(t)=At^?4 withA<0 is predominant for long times. In the case of a finite, but not too small, cavity lengthL obeyingΛ=hc/k _BT?L and at timest withct?L, C _E(t) is described by an asymptotic expansion in powers ofL ^?1 using generalized Riemann zeta functions. Surface-and shape-effects enhance the long-tail. In the case of very small cavities withL«Λ, we calculate an expansion ofC _E(t) in terms of exp(?L ^?1) and cosines. An oscillatory, but not strictly periodic, long-time behaviour is observed in this case.     

Coulomb energies and nuclear radii in the energy density formalism

The relation between Coulomb displacement energies,ΔE _c , andΔr=r _n -r _p , the difference between the rms radii of neutrons and protons in nuclei, is investigated within the energy density formalism (EDF). The variational equation, obtained by minimizing the Coulomb plus symmetry energies, is solved assuming the symmetry interaction is a simple functional of the local nuclear matter density. Varying parameters of the model, rather unique relation betweenΔE _c andΔr is obtained (within ±50 keV).ΔE _c isindependent ofr _ex, the rms radius of the excess neutrons distribution. Using the experimental values ofr _p and adjusting the model to reproduce the recent data onΔr (Δr∽~0.05 fm for⁴⁸Ca and²⁰⁸Pb), which are significantly smaller than those obtained from current Hartree-Fock calculations, the calculatedΔE _c agree with the experimental results. Using the value ofΔr～0.05 fm and the experimental values ofr _ex, a small compression (<0.02 fm) of the proton core in the analogue state relative to its parent state emerges, thus contributing an additional electrostatic term to the Coulomb displacement energy. The size of this relative core-compression effect depends on the values assumed forΔr andr _ex, it increases with the decreasing ofΔr and the increasing ofr _ex. IfΔr～0.05 fm the effect is large enough to remove the long standing Coulomb energy anomaly. The main result of the present work is the correlation betweenΔE _c andΔr, suggesting that the difficulties of current Hartree-Fock calculations in reproducing isotope shifts ofr _p , the small value ofr _n ?r _p and the values ofΔE _c may all be different manifestations of some missing residualp n effective interaction.     

Fixed-J level densities beyond spin cut-off approximation

It is well known that the expression for fixed-J level densityI _?(E, J)=?I(E) $\frac{\partial }{{\partial M}}$ I(M|E)| _M=J+1/2 reduces to familiar Bethe’s formula provided the conditionalM-distributionI(M|E) is approximated by a Gaussian form, so called spin cut-off approximation (M is thez-component of total angular momentumJ andE is the excitation energy). After a detailed analysis, we find that the Bethe’s formula which overestimatesI?(E, J) at highJ values, in particular near the yrast line, can be significantly improved by including a few higher-order moment terms in a suitable expansion forI(M|E) with the lowest-order term to be a Gaussian, e.g., Edgeworth expansions. We also find that, except at very low excitation energies, reasonable values (close to exact) of the moments ofI(M|E) can easily be obtained when multiple Laplace-back transform of the partition function for grand canonical ensemble is evaluated within the saddle point approximation. Furthermore, we study the effects of shell structure as well as residual interaction on the excitation energy dependence of these moments.     

Decay of90m,g Rb

The decay of mass separated⁹⁰Rb has been studied usingβ,γ and conversion electron spectrometers in single and coincidence modes. The half-lives of the ground state and the isomeric level have been confirmed to be 162± 3 and 258±4 s, respectively. Theγ-rays from the decays of ground state and metastable state have been identified by measuring the decay of individual photopeaks using Ge(Li) detectors. The multipolarity of the 106.6 keV isomeric transition has been determined to beM3. Separate decay schemes of the ground and metastable states are presented. The levels of⁹⁰Sr are discussed in terms of the available experimental and theoretical information. Radioactivity.^90m,gRb [from²³⁸U(p, f)]; measuredT _1/2,E _γ,I _γ,γ—γ coin,I _ce,cc,E _β deduced logft,⁹⁰Sr levels, mass separated⁹⁰Rb.     

The electronic conductivity of lead fluoride and the D.C. Polarization theory

The electronic conduction characteristics of solid lead fluoride were investigated using the Wagner d.c. polarization technique. It was found that when the (?) Pb/PhF₂/graphite ( + ) cell was polarized at potentials much below a critical value, E_c, the steady state current, I, as a function of the polarization potential, E, behaves in accordance with the Wagner equation. The log I vs E plots gave straight lines with slopes having the theoretical value of F/2.303 RT. On the other hand, when the polarization potential was equal or higher than E_c, an anomalous behavior was observed. Slopes with values less than the theoretical were obtained from the log I vs E plots. This anomalous behavior was attributed to the high concentration of electron holes at the PbF₂/graphite interface resulting from the high polarization potential. The critical potential was defined as the applied potential where the electron hole concentration at the PbF₂/graphite interface becomes so high that the electronic conductivity is equal to the ionic conductivity which contradicts the assumptions for the Wagner equation. Consequently, the Wagner equation is not applicable under these conditions.     

Optical pumping of short lived Β-radioactive isotopes and the magnetic moment of37K

²¹Na (T _1/2=23 sec) and³⁷K(T _1/2=1.25 sec) have been produced in gas targets by (d, n) reactions and polarized by means of optical pumping or spin exchange scattering with optically pumped⁸⁷Rb. An asymmetry up to 3% in theΒ-decay of the polarized nuclei was found, which served to detect rf transitions between hfs levels of the atomic ground states of²¹Na and³⁷K.δF=0 andδF=1 resonances have been recorded, yielding spin, hfs separation and magnetic moment, especiallyI(³⁷K)=3/2,δW(³⁷K)=240.266 (3) Mc/sec andΜ _I(³⁷K)=0.02033(6) nm (diamagnetically corrected). For²¹Na earlier rf-spectroscopic data have been confirmed.     

Radioactive decay of 1.7-h149Nd to levels of transitional149Pm

Sources of¹⁴⁹Nd were produced by thermal-neutron irradiation of enriched¹⁴⁸Nd. High resolution Ge(Li) spectrometers were used to collect gamma-ray singles and coincidence spectra in the study of the decay of 1.7-h¹⁴⁹Nd. A total of 214 gamma rays have been assigned to the decay of¹⁴⁹Nd, and 201 of these transitions have been placed in a level scheme of¹⁴⁹Pm involving 42 excited states. Absolute values for the beta-group intensities were determined for transitions to the¹⁴⁹Pm levels, and spin and parity assignments were made for many of the observed states. The experimentally determined level structure of¹⁴⁹Pm was compared with corresponding levels in other odd-mass Pm and Eu nuclides. Interpretations were made in terms of the core-coupling model. Radioactive decay¹⁴⁸Nd(n, γ)¹⁴⁹Nd; measuredE _γ,I _γ,γ-γ coinc.¹⁴⁹Pm deduced levels,J,π. Compton-suppression. Ge(Li) detector. Enriched targets.     

Nuclear levels in152Eu

The transitional nucleus¹⁵²Eu has been studied using the (n, e), (n, γ), (n _res,γ), (n, γγ), (d, p), (d, t) and (p, d) reactions. The experiments have been performed at nine different laboratories. A model independent level scheme was established including 95 levels below 510 keV and nearly 900 transitions by combination of low energy transitions and reaction data. More than 20 additional levels result from gamma rays and/or charged particle reactions. The level scheme is interpreted in terms of the Nilsson model indicating that¹⁵²Eu is a deformed nucleus. Seven rotational bands and Nilsson configurations are established. An additional 27 rotational bands are tentatively or speculatively assugned. Gallagher-Moszkowski splittings are discussed. The neutron binding energy was determined as 6305.2±0.5 keV. The energy of the 9.3 h 0^? isomer is 45.599 keV. The lifetimes of four levels were measured. Nuclear Reactions¹⁵¹Eu(n,γ),E _n =thermal and resonance; measuredE _γ ,I _γ ,E _c.e.,I _c.e.,γγ Coinc.,γγΔt coinc.;¹⁵¹Eu(d, p),E=12MeV and 14MeV;¹⁵³Eu(d, t),E=12MeV;¹⁵³Eu(p, d),E =18MeV; deduced level scheme of¹⁵²Eu,J, π, T _1/2,cc, Nilsson configurations. Magnetic electron spectrometer, curved crystal spectrometer, Ge(Li) and Si(Li) detectors, magnetic spectrographs. Enriched targets.     

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in²⁵Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the²⁴Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the²²Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2O d _5/2 — 1s _1/2-O d _3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of²⁵Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of²⁵Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of²⁵Mg in great detail. The prospectiveI ^π=9/2^?, 13/2^?, and 15/2^? members of the established negative-parity,K=1/2 band are found in levels atE _x=7801, 9410, and 8896 keV.     

Quantum numbers of26Al levels above 6 MeV excitation energy

Measurements of resonance strengths and ofγ-ray angular distributions or anisotropies have been performed on selected resonances of the²⁵Mg(p, γ) reaction in the rangeE _p=2–4 MeV,E _x=8.2?10.1 MeV with an emphasis on high-spin andT=1 analog resonances. EightT=1 states are identified, among them high-spin states at 8747 keV (I=6), 9286 KeV (I=5), and 9986 keV (I ^π = 7⁺, 6⁺). Shell model calculations in thes-d basis space reproduce the branching ratios of these states and clarify the nature of final states. New high-spinT=0 states are observed at 9720 keV (I ^π = 7⁺), 8602 keV (I = 6), and 6695 keV (I ^π = 7⁺). TheI ^π assignments to severalE _x = 6–8 MeV states are revised and the role of two-particle excitations into thef-p shell is elucidated. A revised spectrum of 73 positive-parity,T = 0 states is compared to the predictions of shell-model calculations in thes-d basis space using the universals-d shell Hamiltonian.     

The Decay of130La to levels in130Ba

Theγ-radiation associated with the β⁺ decay of¹³⁰La to levels in¹³⁰Ba is studied. The level scheme is established on the basis of theγ-γ coincidence measurements emploing two Ge(Li) detectors. The available experimental data are compared to collective model calculations withγ-soft P.E.S. andγ-dependent inertial functions. To reproduce levels energyB _ββ value twice as large as other mass parameters is needed.Radioactivity: ¹³⁰La [from¹³⁰Ba(p, n),E _p=10MeV]; measuredE _γ,I _γ,γγ-coin.¹³⁰Ba deduced levels,J, π, logft. Enriched target, Ge(Li) detectors.     

Relative internal conversion electron intensities of the 113 keV transition in177Hf

The intensities of the internal conversion lines of the 113 keVM1 +E2 transition in¹⁷⁷Hf have been measured. From comparison with theoretical conversion coefficients the transition has been found to be (95.2 ± 0.5)%E2 corresponding to ¦δ¦=4.5 ± 0.3. The theoreticalL _I andM _I conversion coefficients used in the comparison have been increased by 5% according to the result that for pureE2 transitions in the deformed region theL _I/L _II,L _I/L _III,M _I/M _II, andM _I/M _III theoretical ratios are too low (～5%). Moreover, the present result indicates that theL _II/L _III andM _II/M _III ratios obtained from the tabulations by Hager and Seltzer and from the computer program by Pauli are too high (1–2%).