Search

We report experimental measurements in ${}^{241}\mathrm{Pu}$ of the following: primary and secondary $\ensuremath{\gamma}$ rays and conversion electrons from thermal neutron capture in ${}^{240}\mathrm{Pu};\ensuremath{\gamma}$ rays from ${}^{245}\mathrm{Cm}$ \ensuremath{\alpha} decay; proton and triton spectra, respectively, from $(d,p)$ and $(d,t)$ reactions on ${}^{240}\mathrm{Pu}$ and ${}^{242}\mathrm{Pu}$ targets. From these data and those of other investigations, we have identified 53 excited levels in ${}^{241}\mathrm{Pu}$ below 1400 keV. Of these, 44 are placed in 10 rotational bands (with connecting transitions) that have been assigned Nilsson configurations. For the bands below 1 MeV in ${}^{241}\mathrm{Pu}$ that are largely of single-particle character, there is good correspondence with similar bands in ${}^{239}\mathrm{U}$ and with the theoretical model of Gareev et al. For those bands in ${}^{241}\mathrm{Pu}$ where there is mixing between single-particle and vibrational modes, we find some significant deviations from theoretical predictions. For example, the $\frac{5}{2}[622]\ensuremath{\bigotimes}{0}^{\ensuremath{-}}$ state at 519 keV appears to mix less with other states than predicted, while a trio of ${K}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}}$ bands show unexpected mixing patterns.

Excited states in ${}^{208}$Pb have been studied by measuring $\ensuremath{\gamma}$ rays in time coincidence with reaction charged particles. ${}^{208}$Pb states were produced with both the ${}^{207}$Pb${(d,p)}^{208}$Pb and ${}^{209}$Bi$(t,\ensuremath{\alpha})$${}^{208}$Pb reactions. The energy resolution of the particle spectra of 100 keV allowed a rough determination of level excitation, which then was determined with high resolution from the coincident $\ensuremath{\gamma}$ decay measured in Ge detectors. Many new $\ensuremath{\gamma}$ transitions have been found and previously unresolved multiplets of states resolved. The data give spectroscopic factors for neutron transfer and proton pickup. Spins and parities of levels could be deduced from their $\ensuremath{\gamma}$ decays. A least squares fit of all $\ensuremath{\gamma}$ energies gave very precise (0.1 keV) level energies. All states predicted by the shell model below 4.6 MeV are now found and their spins determined unambiguously.

We have made experimental measurements in {sup 170}Tm of the following: secondary {gamma} rays, conversion electrons, and {gamma}-{gamma} coincidences from thermal neutron capture in {sup 169}Tm, primary {gamma} rays from average resonance capture with 2-keV and 24-keV neutron beams, and proton spectra from the ({ital d},{ital p}) reaction on {sup 169}Tm. From these data and those of previous investigations, we have identified more than 130 excited levels in {sup 170}Tm below 1550 keV. Of these, 62 (with connecting transitions) are placed in 18 rotational bands with assigned Nilsson configurations. These results are in good agreement with a semiempirical modeling of {sup 170}Tm level structure. Values for seven Gallagher-Moszkowski splittings and four Newby shifts have been obtained. These matrix elements show remarkably good agreement with calculation. Among the observed {ital K}{sup {pi}}=1{sup {minus}} and 2{sup {minus}} rotational bands, configuration mixing appears to play a significant role. {copyright} {ital 1996 The American Physical Society.}

Three experiments using the (174) Yb(Mg-25,5n)Pb-194 reaction have been undertaken at the Early Implementation of Gammasphere to study the decay of known superdeformed states in Pb-194. A single di ...

An iron-free beta spectrometer with pre- and post-acceleration of electrons was used to study \ensuremath{\beta} branches and conversion electrons at very low energies in the \ensuremath{\beta} decay of $^{228}\mathrm{Ra}$. Results of conversion-electron and \ensuremath{\gamma}-ray spectroscopy are analyzed using \ensuremath{\beta} selection rules and two-quasiparticle-rotor model considerations. A tentative $^{228}\mathrm{Ac}$ level scheme, including model-dependent spin-parity and configuration assignments consistent with the available data, is presented.

Six superdeformed bands have been observed in [sup 193]Pb following the [sup 174]Yb([sup 24]Mg,5[ital n]) reaction at a beam energy of 131 MeV. The in-beam [gamma] rays were detected with GAMMASPHERE early implementation. Two of the bands have dynamic moments of inertia which have an anomalously low increase with rotational frequency, and are interpreted as the favored and unfavored signature components of the [ital N]=7 neutron orbital. The other four bands have increasing dynamic moments of inertia typical of superdeformed bands in the [ital A]=190 region, and are interpreted as two pairs of signature partner bands based on high-[ital K] quasineutron excitations. The effects of the intruder [ital N]=7 neutron orbital on the superdeformed rotational characteristics are discussed.

A new superdeformed band with an intensity [similar to]5% relative to the yrast superdeformed band has been observed in [sup 194]Pb. Evidence for a second new band corresponding to the signature partner is also presented. These bands were observed with GAMMASPHERE early implementation via the [sup 174]Yb([sup 25]Mg, 5[ital n]) reaction at a beam energy of 130 MeV. The rotational characteristics of the new bands suggest an interpretation involving particle-hole excitations in the doubly-magic [sup 194]Pb superdeformed core. The results are compared to neighboring nuclei and recent theoretical calculations, and possible configurations are suggested.

The double neutron capture reaction 169Tm(n,γ)170Tm(n,γ)171Tm and the proton transfer reaction 170Er(3He,d)171Tm were used to study nuclear levels in 171Tm. The level scheme up to 1 MeV was confirmed and very precise level energies were determined. The results are compared with the quasiparticle-phonon model. Evidence was found, that the 1/2−[541] orbit has larger deformation than the other states.

Nuclear level lifetimes have been measured in two superdeformed bands in $^{194}\mathrm{Hg}$ using the Doppler-shift attenuation method. Average transition quadrupole moments derived from the lifetimes of an excited and yrast superdeformed bands are ${\mathit{Q}}_{\mathit{t}}$=17.6(30) and 17.2(20)eb, respectively. The Doppler shifts of the excited band relative to the yrast band indicate a slight difference in quadrupole moments [+4(5)%], assuming similar side feeding..ul2 These results imply that the second well is stable and rigid with respect to the particle excitation responsible for this excited band.

Lifetimes of states in the regular \ensuremath{\Delta}I=1 band in $^{197}\mathrm{Pb}$ have been measured with the Doppler-shift attenuation method. Excited states in $^{197}\mathrm{Pb}$ were populated using the $^{154}\mathrm{Sm}$${(}^{48}$Ca, 5n) reaction at ${\mathit{E}}_{\mathit{b}}$=210 MeV. The target consisted of 1 mg/${\mathrm{cm}}^{2}$ $^{154}\mathrm{Sm}$ evaporated onto a 10 mg/${\mathrm{cm}}^{2}$ Au backing. Discernible lineshapes for \ensuremath{\gamma} rays in the energy range 300${\mathit{E}}_{\ensuremath{\gamma}}$500 keV in the regular band were observed in a spectroscopic study with the 20 Ge-detector array, HERA. Level lifetimes were obtained from a lineshape analysis. Averaged reduced transition strengths, B(M1)\ensuremath{\sim}1.7 W.u. and B(E2)\ensuremath{\sim}18 W.u., are deduced and these are compared with theoretical predictions for the suggested configuration of this band.

We investigated the nuclear properties of several mendelevium isotopes produced in the reactions of heavy ions with 245Esg. We measured the alpha particles, spontaneous fissions (SF), and photons emitted by counting samples resulting from chemical and/or mass separations. The 256Md half-life is (78.1 ± 1.8) min; it decays primarily by electron capture (EC), but also by alpha emission (11 ± 3)% of the time. The 256Md ground state has J ⩽ 2 (probably Jπ = 1−), and a mass excess of (87.611 ± 0.053) MeV. The 257Md half-life is (5.523 ± 0.050) h; it decays primarily by EC, but also by alpha emission (15.2 ± 2.6)% of the time and by SF less than 1% of the time. The 256Md mass excess is (88.989 ± 0.003) MeV. The 258Mdg (Jπ = 8−) half-life is (51.50 ± 0.29) d. It decays by alpha emission; the sum of SF, EC, and β− decay branches is less than 3 × 10−3 %. The alpha decay of 258Mdg populates 254Esm (0.60 ± 0.08)% of the time. The 256Mdg mass excess is (91.691 ± 0.007) MeV. The half-life of J π = 1 − 258 Md m is (57.0 ± 0.9) min. It decays by EC; the branch for decay by alpha emission is less than 1.2%. The sum of SF and β− decay branches is less than 30%. The half-life of 259Md is (1.60 ± 0.06) h; it decays primarily by SF. The alpha decay branch of 259Md is less than 1.3%. From the 259Md half-life we calculated a SF hindrance factor associated with the 7 2 − [514] proton configuration of 3.6 × 106. From our data we proposed partial level schemes for 252Es, 253Es, and 254Es.

Since the first discovery in 1986 of a rotational band at high angular momentum with deformation parameters near β =0.6, a great deal of research has been devoted to the study of these superdeformed (SD) bands in nuclei leading to the identification of similar bands in numerous nuclei in the mass 130, 150, and 190 regions. While superdeformed shape isomers have been observed at low spin in the actinides via spontaneous fission and in a few cases via γ decay, below mass 200 the low-spin members of the SD bands have not been observed. Theoretical calculations are able to account for the relative stability of the superdeformed bands in the nuclei where they have been observed. These calculations suggest that in the HgPb region the SD shape should be stable at a rotational frequency of 0. Several experiments have been performed to search for the population and decay of the lower spin members of the SD bands in the mass 190 region and some are still in progress. To this date, none has provided conclusive observation of the 0 + bandhead of a superdeformed band. The experimental techniques utilized in several of these are described.

The $^{179}\mathrm{Hf}$(t,\ensuremath{\alpha}${)}^{178}$Lu reaction has been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph, and the resolution achieved for the alpha spectra was \ensuremath{\sim}20 keV (FWHM). Two-quasiparticle states in $^{178}\mathrm{Lu}$ involving the 9/${2}^{+}$[624] target neutron coupled with the 7/${2}^{+}$[404], 9/${2}^{\mathrm{\ensuremath{-}}}$[514], and 1/${2}^{+}$[411] proton orbitals were identified. The difference in ground-state (t,\ensuremath{\alpha}) Q values for $^{178}\mathrm{Hf}$ and $^{179}\mathrm{Hf}$ components of the target, combined with the known masses of $^{177}\mathrm{Lu}$, $^{178}\mathrm{Hf}$, and $^{179}\mathrm{Hf}$, yields an improved value of -50 351\ifmmode\pm\else\textpm\fi{}5 keV for the mass excess of $^{178}\mathrm{Lu}$. This result, combined with the two-quasiparticle assignments from the present work, has resolved the long-standing puzzle concerning the character and excitation energy of the well-known 23 min high-spin beta-decaying isomer in $^{178}\mathrm{Lu}$.

A search for the population of superdeformed (SD) states in [sup 194]Pb following the [beta][sup +] decay of [sup 194]Bi was performed with the UNISOR on-line isotope separator at the Oak Ridge National Laboratory. The [beta] decay of [sup 194]Bi, with its large [ital Q][sub [beta]] value and high spins of the decaying isomeric states, provides a favorable opportunity to search for population of known SD states in the daughter nucleus, [sup 194]Pb. Both [gamma] rays and conversion electrons were measured in singles and coincidence; however, no evidence for the population of SD states was observed. Upper limits for the population of certain SD states are presented. A possible explanation for the lack of SD band population following this [beta] decay is discussed.

A data set of 29 experimentally determined Newby shifts in rare-earth nuclei is examined for the reliability of each values. Using this data set, Newby shifts are obtained which are free from the Coriolis and the particle-particle coupling effects. These new empirical values help resolve the failure of a recently proposed rule for the sign of the Newby shift in the {5/2[413]p − 5/2[642]n} configuration of160Tb and the {5/2[402]p − 5/2[512]n} configuration of174Lu. Also the Newby shifts are significantly modified in two other cases namely the {1/2[411]p − 1/2[521]n} configuration in168Tm and the {1/2[541]p − 1/2[521]n} configuration in172Lu. Only marginal changes are seen in the rest of the cases in the rare-earth nuclei.

The spin-parity assignments of 223 Ac are discussed based on a critical reexamination of the experimental data and the theoretical calculations.

The experimental measurements made in this investigation include secondary $\ensuremath{\gamma}$ rays and conversion electrons from thermal neutron capture in $^{237}\mathrm{Np}$, primary $\ensuremath{\gamma}$ rays from average resonance capture with a 2-keV neutron beam and from resonance capture with thermal neutrons, and $\ensuremath{\alpha}$ particles and $\ensuremath{\gamma}$ rays, singles and coincidences, from $^{242}\mathrm{Am}^{m}$ $\ensuremath{\alpha}$ decay. From these data and those of previous investigations, 69 excited levels in $^{238}\mathrm{Np}$ with energies 700 keV were identified and, of these, 46 were placed in 13 rotational bands with assigned Nilsson configurations. The results are found to be in good agreement with a semiempirical model calculation. A special feature is the observation of four different $K=0$ rotational bands in the low-energy structure of $^{238}\mathrm{Np}$. Experimentally determined Gallagher-Moszkowski and Newby matrix elements show reasonable agreement with calculated values.

The level structure of $^{249}\mathrm{Bk}$ has been investigated by measuring the \ensuremath{\gamma}-ray spectra of an extremely pure $^{253}\mathrm{Es}$ sample obtained by milking this nuclide from $^{253}\mathrm{Cf}$ source material produced in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Additional information on the $^{249}\mathrm{Bk}$ levels was obtained from the ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay study of $^{249}\mathrm{Cm}$, produced by neutron irradiation of $^{248}\mathrm{Cm}$. Using the results of the present study together with the data from previous $^{248}\mathrm{Cm}$($\ensuremath{\alpha},t$) and $^{248}\mathrm{Cm}$($^{3}\mathrm{He},d$) reactions, the following single-particle states have been identified in $^{249}\mathrm{Bk}$: 7/2${}^{+}$[633], 0.0 keV; 3/2${}^{\ensuremath{-}}$[521], 8.78 keV; 1/2${}^{+}$[400], 377.55 keV; 5/2${}^{+}$[642], 389.17 keV; 1/2${}^{\ensuremath{-}}$[530], 569.20 keV; 1/2${}^{\ensuremath{-}}$[521], 643.0 keV; 5/2${}^{\ensuremath{-}}$[523], 672.9 keV; and 9/2${}^{+}$[624], 1075.1 keV. Four vibrational bands were identified at 767.9, 932.2, 1150.7, and 1223.0 keV with tentative assignments of {7/2${}^{+}$ [633] $\ensuremath{\bigotimes}{1}^{\ensuremath{-}}$}9/2${}^{\ensuremath{-}}$, {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {0}^{\ensuremath{-}}$}7/2${}^{\ensuremath{-}}$, {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {1}^{\ensuremath{-}}$}5/2${}^{\ensuremath{-}}$, and {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {0}^{+}$}7/2${}^{+}$, respectively. A band at 899.9 keV was observed in $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements and given a tentative spin assignment of 3/2. It is possibly associated with a 2${}^{\ensuremath{-}}$ phonon coupled to the ground state, with configuration {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {2}^{\ensuremath{-}}$}3/2${}^{\ensuremath{-}}$. Three levels at 624.3, 703.5, and 769.1 keV were assigned spins of 5/2, 7/2, and 9/2, respectively. These could be the members of the 3/2${}^{+}$ [651] band, expected in this energy region.

The level structure of 249Bk has been investigated by measuring the γ‐ray spectra following the α decay of a chemically and isotopically pure 253Es sample. Alpha‐gamma coincidence measurement was performed using a Si detector for α particles and a 25% Ge detector for γ rays. A gamma‐gamma coincidence measurement was performed with the Gammasphere spectrometer. The Es sample was obtained by extracting the 253Es which grew in a 253Cf source material produced in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Additional information on the 249Bk levels was obtained from the study of γ rays produced in the β− decay of 249Cm. The 249Cm sample was produced by neutron irradiation of 248Cm. Using the results of the present study and the results of previous 248Cm(α,t) and 248Cm(3He,d) reaction spectra, the following single‐particle states have been identified in 249Bk: 7/2+[633], 0.0 keV; 3/2−[521], 8.78 keV; 1/2+[400], 377.55 keV: 5/2+[642], 389.17 keV; 1/2−[530], 569.19 keV; 1/2−[521], 643....

The nucleus ${}^{166}\mathrm{Ho}$ was studied with thermal and average resonance neutron capture and with $(d,p)$ and ${(d,}^{3}\mathrm{He})$ reactions. We have devoted a large effort to the measurements of $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence spectra in the broad energy interval 50\char21{}6243 keV. From these data and those of previous studies, the level scheme has been developed containing levels grouped into 23 rotational bands below 1 MeV. Of these, six bands are new and several others, known previously, have been modified and expanded based upon our experimental data. In all, 32 new levels have been identified. Of particular note has been the identification of two rotational bands whose underlying structure consists of $\ensuremath{\gamma}$-vibrational states built upon the two lowest energy quasiparticle states in ${}^{166}\mathrm{Ho}.$ Two new Gallagher-Moszkowski matrix elements were determined: ${E}_{\mathrm{GM}}{(p7/2}^{\ensuremath{-}}[523]\ifmmode\pm\else\textpm\fi{}{n5/2}^{\ensuremath{-}}[523])=\ensuremath{-}108.5$ keV and ${E}_{\mathrm{GM}}{{(p7/2}^{\ensuremath{-}}[523]\ifmmode\pm\else\textpm\fi{}{n7/2}^{+}[633])\ensuremath{\mp}{Q}_{22}}=+138.2$ keV. The resultant level scheme is in good agreement with semiempirical and quasiparticle phonon models where residual interactions have been taken into account. Suggestions are given for further experimentation on ${}^{166}\mathrm{Ho}$ level structure using existing technology.

The structure of the odd‐odd 192Ir nucleus presents an interesting and challenging problem for both experimentalists and theorists. As a result of the common efforts of nine laboratories, it is possible, for the first time, to propose an extended scheme with 34 levels. The experiments included observation of γ‐ray transitions and of conversion electrons emitted after thermal and resonance neutron capture, of direct (d,p) and (d,t) neutron transfer reactions and of the angular distribution of γ‐rays from aligned 192Ir nuclei. The results are interpreted in the framework of the rotor‐plus‐particle and IBFFM models. The nuclear states appear to be strongly mixed. The complex and interesting ground‐state configuration is discussed.

The application of a simple semi-empirical model is discussed in terms of interpreting experimental nuclear structure data for twelve of the best characterized odd-odd deformed nuclei. An essential part of this modeling is to calculate values of the Gallagher-Moszkowski splittings and Newby shifts, the observables that arise from the n-p residual interaction in odd-odd nuclei. Assumptions regarding the form for this n-p force are traced historically. The predictive power of a favored form of the n-p force, one that includes a central force with short-and long-range components, a tensor force, and some effects of core polarization, is examined in light of experimental data obtained since its formulation. A data set of forty-two experimentally-determined Newby shifts has been reviewed as to the reliability of each entry. Exceptions to a recently proposed rule for the a priori determination of the sign of a Newby shift are discussed. Evidence is presented for the existence of an odd-even staggering or signature effect in the rotational spacings of many K - bands (with K > 0). By use of corioliscoupling calculations, it has been possible to reproduce the staggering observed in some of the K - rotational bands of 156Tb, 168Tm, 176Lu, 182Ta, and 182Re.

A technique for modeling level structures of odd-odd nuclei has been used to construct sets of discrete states with energies in the range 0 – 1.5 MeV for several nuclei in the rare-earth and actinide regions. The accuracy of the modeling technique was determined by comparison with experimental data. Examination was made of what effect the use of these new, more complete sets of discrete states has on the calculation of level densities, total reaction cross sections, and isomer ratios.

The neutron-induced fission cross sections of Cm-244, Cm-246, and Cm-248 which were measured with the RINS lead spectrometer system at RPI have been analyzed for intermediate structure. Gross structure is observed in Cm-244 near 200, 400, 800, and 2000 eV and in Cm-246 near 350, 800, and 3300 eV. For Cm-248 a very broad type of structure is observed near 10 keV. Assuming double-barrier fission, the Cm-244 and Cm-246 structure is consistent with the outer potential well lying 2 to 3 MeV above the inner potential well. The broad structure observed in Cm-248 fission implies significantly different barrier parameters than for Cm-244 or Cm-246.

Configuration assignments are derived for the observed energy levels in the odd-odd deformed nucleus170Lu99 based on the calculations of the two-particle band head energies for a zero range residual interaction, the beta-feeding characteristics, and the observed features for similar bands in the neighbouring nuclei. In particular, specific assignments are given for theJπ=1+ levels at 198.4 keV, 349.0 keV and 785.5 keV. The ambiguities with respect to the assignments for theKπ=3− bands are discussed. A new isomer withJπ=7+ and half-life of several seconds is predicted around (225±25) keV and experiments are suggested to identify it.

Secondary gamma rays and conversion electrons following the /sup 243/Am(n,..gamma..)/sup 244/Am reaction have been studied with crystal spectrometers and an electron spectrometer, respectively. Primary gamma rays following thermal neutron capture in /sup 243/Am have also been measured. A level scheme of /sup 244/Am has been constructed containing 67 excited levels. The levels are interpreted in terms of coupled proton and neutron Nilsson configurations. The results are found to be in good agreement with a semiempirical model with which excitation energies in odd-odd nuclei are calculated from those in adjacent nuclei.

The nuclide 251Cm ( t 1 2 = 16.8 ± 0.2 min ) was produced by neutron capture from 250Cm with an approximate cross section of 80 barns. In the decay of 251Cm, we measured the energies and intensities of 12 γ-rays from which we constructed a level scheme for 251Bk and assigned configurations for six single-particle states in 251Bk and for the ground state of 251Cm ( 1 2 ) + . The levels of 251Bk fed by 251Cm β-decay are compared with those of 249Bk fed by 249Cm β-decay. We also compare our measured Qβ− value of 1.42 MeV for 251Cm with previous closed-cycle estimates.

The experimentally known isomers of $^{158}\mathrm{Ho}$ have been characterized by estimating the energies of two-quasiparticle excitations. Included in this modeling is the effect of a residual n-p interaction. A 21-min isomer is assigned the configuration ${K}^{\ensuremath{\pi}}$${=9}^{+}${${(7/2)}^{\mathrm{\ensuremath{-}}}$[523\ensuremath{\uparrow}] $_{\mathrm{p}{+(11/2)}^{\mathrm{\ensuremath{-}}}[505\mathrm{\ensuremath{\uparrow}}{]}_{\mathrm{n}\mathit{}}}}$ and is predicted to lie 180 keV above the ${5}^{+}$ ground state. The antiparallel ${K}^{\ensuremath{\pi}}$${=2}^{+}$ state of this configuration is assigned to an observed level at 316 keV. The 21-min isomer decays by an allowed unhindered transition to a 2528-keV level in $^{158}\mathrm{Dy}$ for which we confirm the two-quasineutron configuration ${K}^{\ensuremath{\pi}}$${=8}^{+}${${(5/2)}^{\mathrm{\ensuremath{-}}}$[523\ensuremath{\downarrow}] $_{\mathrm{n}}$ ${+(11/2)}^{\mathrm{\ensuremath{-}}}$[505\ensuremath{\uparrow}${]}_{\mathrm{n}\mathit{}}}$. A 27-min ${2}^{\mathrm{\ensuremath{-}}}$ isomer at 67.3 keV and a 29-ns ${5}^{\mathrm{\ensuremath{-}}}$ isomer at 156.9 keV are assigned the configuration {${(7/2)}^{+}$[404\ensuremath{\downarrow}${]}_{\mathrm{p}}$ \ensuremath{\mp}${(3/2)}^{\mathrm{\ensuremath{-}}}$[521\ensuremath{\uparrow}${]}_{\mathrm{n}\mathit{}}}$. A 1.85-ns ${1}^{\mathrm{\ensuremath{-}}}$ isomer at 139.2 keV is assigned the configuration {${(5/2)}^{+}$[402\ensuremath{\uparrow}${]}_{\mathrm{p}}$ ${+(3/2)}^{\mathrm{\ensuremath{-}}}$[521\ensuremath{\uparrow}${]}_{\mathrm{n}\mathit{}}}$ and the ${K}^{\ensuremath{\pi}}$${=4}^{\mathrm{\ensuremath{-}}}$ member of this Gallagher-Moszkowski pair is predicted to occur at 70 keV. Specific experiments are suggested to verify these predictions.

A radioactive /sup 226/Ra (t/sub 1/2/ = 1600 yr) target was used to study the /sup 226/Ra(..cap alpha..,t)/sup 227/Ac and /sup 226/Ra(/sup 3/He,d)/sup 227/Ac reactions at an incident energy of 30 MeV for both the ..cap alpha.. and /sup 3/He particles. These measurements have confirmed most levels observed in earlier decay-scheme studies, and give evidence for 11 additional levels. Several of the new levels were used in the tentative assignment of two K/sup ..pi../ = (5/2/sup +- / bands. The experimental data are compared with results from the Nilsson model and a nonadiabatic, rigid, reflection-asymmetric rotor (octupole) model. Although the order and spacing of levels in this mass region can be explained better by models that include an octupole deformation, the spectroscopic strengths in /sup 227/Ac are in better agreement with those calculated for the reflection-symmetric potential.

The excited levels of /sup 249/Cm have been determined by use of neutron-capture gamma-ray spectroscopy. Gamma-ray measurements were made with curved-crystal spectrometers of focal lengths 5.8 and 24 m and a pair spectrometer. These experimental data represent the first measurement of gamma transitions depopulating the levels of /sup 249/Cm. We present evidence for the population of 23 levels in /sup 249/Cm up to 1300-keV excitation. The following new configuration assignments were made (listed with the corresponding bandhead energies): (5/2)/sup +/(622), 529.58 keV; (3/2)/sup -/(752), 772.74 keV; (1/2)/sup -/(501), 917.49 keV. Comparison of the experimentally determined level structure with theoretical calculations shows best agreement with calculations by Soloviev's group where a Woods-Saxon potential form was used and quasiparticle-phonon coupling was included. The neutron binding energy was determined to be 4713.7 +- 0.3 keV.

The half-life of long-lived 236Np, due to α, β and electron-capture decay, was found to be 1.55 × 105 yr. Of all decays, 88% populate excited states in 236U and 12% populate levels in 236Pu. Lifetimes measured by growth of the ground states of 236U and 236Pu agree with values from corresponding γ de-excitations in these daughter nuclei. Therefore, nearly all the electron-capture decays populate the 6+ level of the ground-state band in 236U. Similarily, essentially all the β− decay populates an analogous 6+ level in 236Pu, which de-excites through a previously unreported transition of 158.3 keV. If a very weak γ-ray at 894 keV can be ascribed to a level in 232U populated by β decay of 232Pa, its existence establishes a 0.2% α-branching decay in 236Np.

The existence of the $\ensuremath{\gamma}$ branch in the decay of the $^{238}\mathrm{U}$ shape isomer is confirmed by the observation of an $E0$ transition between the isomer and the ground state. The data are consistent with the excitation energy of 2558 keV, spin of ${0}^{+}$, and half-life of \ensuremath{\approx} 200 ns of the isomer.

The interacting boson model is able to reproduce the elusive two-particle-transfer data in the actinides (uranium and thorium). The same calculation also reproduces well the energy systematics and the B(E2) data.

The ORNL Electromagnetic Isotopic Enrichment Facility (EMIEF) has the foremost capability in the world for large-scale enrichment of stable isotopes. Despite the importance of these isotopes in research and medical applications, the funding levels for EMIEF operation since 1982 have decreased significantly, forcing operation at rates far below replacement of isotopes sold or loaned. The availability of enriched stable isotopes is presented, along with a summary of EMIEF User Group concerns and activities.

The ..gamma..-ray decay of the J/sup ..pi../ = 0/sup +/ shape isomer at 2557.6 keV of excitation in /sup 238/U has been reinvestigated using the /sup 238/U(d,pn)/sup 238/U/sup m/ reaction with a new two-detector technique. A line at 2512.7 +- 0.5 and another possible one at 1877.6 keV are attributed to decay of the isomer. The cross section for production of the 2512.7-keV ..gamma.. ray by 18-MeV deuteron bombardment of /sup 238/U is 42 +- 12 ..mu..b, consistent with our earlier conversion-electron work on /sup 238/U/sup m/. The isomer decay is about 5% by fission and 95% by ..gamma.. rays and conversion electrons.

The fission cross sections of 244Cm, 246Cm, and 248Cm have been measured from 0.1 eV to 80 keV using the Rensselaer Intense Neutron Spectrometer. The cross sections were normalized to the 235U ENDF...

The level structure of the doubly-odd /sup 242/Am nucleus was investigated by means of thermal-neutron-capture gamma-ray and conversion electron spectroscopy. Pair, curved-crystal, and ..beta.. spectrometers were used. The data from these measurements, combined with previous direct reaction results, permit us to establish a detailed level scheme including six new well-developed bands. Our experimental results are interpreted in the framework of the Nilsson model. Precise Gallagher-Moszkowski splittings and Newby odd-even shifts extracted from the data are compared with theoretical calculations.

The branching ratio, β − / EC = 5·1 ± 0·1, for 242 m Am decay has been measured by determining the relative amounts of the decay products, 242 Cm and 242 Pu formed. The 16 hour 242 m Am was produced by neutron irradiation of 241 Am in the Materials Testing Reactor. A pile neutron cross-section of 620 ± 65 barns for the reaction 241 Am(n, γ) 242m Am was measured.

We have prepared targets of many of the actinide elements, e.g., U, Pu, Am, Cm, Bk, Cf, Es, and Fm, for use in a comprehensive series of fission cross-section measurements. Other experiments requiring actinide targets have involved accelerator bombardments, e.g., irradiation of 253 Es and 257 Fm at the HILAC, and symmetry studies of neutron-induced fission, e.g., recent studies of 257 Fm and 258 Fm fission. The experimental techniques require the targets be uniformly deposited in a thin layer on various backing materials such as Al, Ni, Pt, Be, Cu, and stainless steel. The backing materials ranged in thickness from 0.007 cm to 150 cm with target diameters ranging from 2 to 250 mm. In most cases the rarity of the nuclide required a deposition method that produces high yields, ≥90%. The various methods developed to produce acceptable targets may be summarized as follows: Electrodeposition technique (1) Dilute nitric acid electrolyte: Useful for actinides on a tracer level where high yields and small target area are desirable (e.g., einsteinium, fermium targets on a beryllium backing plate). (2) Isopropyl alcohol-dilute nitric acid electrolyte: Useful for actinides from tracer to microgram levels where uniformity of deposit is critical (e.g., berkelium, curium, einsteinium targets for Physics VIII cross-section experiment). (3) Ammonium chloride electrolyte: Useful for deposition of massive amounts ( 2 ) of actinides over large areas (180 cm 2 ). Also useful for deposition of actinides that are subject to hydrolysis in dilute acid (e.g., preparation of 232 U, 238 Pu, 242m Am targets on nickel foils for fission cross-section measurement). Chemical replacement technique . (1) The method is useful for plating uranium on aluminium. The preparation of 1-mg/cm 2 deposits on 1-mil aluminum is typical. Following deposition, it is usually necessary to determine the absolute amount of the actinide in the targets. This quantity is most often determined by absolute alpha counting. In the case of targets with high activity levels (10 6 –10 11 α dis/min) and large backing plates (8-in. diam.), a new low-geometry counter has been designed, built, and calibrated for this purpose. Uniformity of sample deposition has been monitored through alpha counter scanning techniques.

The neutron-induced fission cross section of ${\mathrm{Am}}^{242m}$ has been measured from 0.02 eV to 6 MeV by the time-of-flight method at the Livermore 30-MeV linear electron accelerator. The data are normalized at 0.0253 eV to a value of 6600 b measured in a reactor thermal-neutron flux. The cross section at 0.2 eV is 4700 b; at 1 eV it is 540 b; and at 4 MeV it is 2.1 b. The data are analyzed to obtain values for the neutron strength function $〈\frac{{\ensuremath{\Gamma}}_{{n}^{0}}}{D}〉$ of 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, the level spacing $D=1.2$ eV, and the quantity $2\ensuremath{\pi}〈\frac{{\ensuremath{\Gamma}}_{f}}{D}〉=2.5$. All three quantities are quoted per spin state. The high cross section at low energies can be attributed to the unusually high value for $2\ensuremath{\pi}〈\frac{{\ensuremath{\Gamma}}_{f}}{D}〉$, and to the existence of a very large resonance at 0.173 eV. The fission cross section of ${\mathrm{Am}}^{241}$ also was measured in the MeV region and found to be 1.96\ifmmode\pm\else\textpm\fi{}0.2 b at 2.5 MeV.

The spontaneous-fission half-life for the odd-odd nucleus ${\mathrm{Am}}^{242m}$ has been measured by a prompt-neutron fission-fragment coincidence method to be (9.5\ifmmode\pm\else\textpm\fi{}3.5)\ifmmode\times\else\texttimes\fi{}${10}^{11}$ years. A correlation of experimental spontaneous-fission half-life data for nuclei of all classes was found to be ${log}_{10}\ensuremath{\tau}\ensuremath{-}(\ensuremath{\beta}\ensuremath{-}\frac{{Z}^{2}}{A})\ensuremath{\delta}M=\ensuremath{-}9.268(\frac{{Z}^{2}}{A})+374.0$, where $\ensuremath{\beta}$ takes the values 42.22, 40.67, and 40.40 for even-even, odd-$A$, and odd-odd nuclides, respectively, $\ensuremath{\tau}$ is the spontaneous-fission half-life in years, and $\ensuremath{\delta}M$ is the mass difference in milli-mass-units (mmu) between the values obtained from Green's smoothly varying mass formula and the experimentally measured values.

The following thermal-neutron fission cross sections have been measured in the thermal column of the Materials Testing Reactor at Idaho Falls, Idaho: ${\mathrm{Pu}}^{238}$, 18.4\ifmmode\pm\else\textpm\fi{}0.9 barns; ${\mathrm{Am}}^{241}$, 3.13\ifmmode\pm\else\textpm\fi{}0.15 barns; ${\mathrm{Am}}^{242}$, 6390\ifmmode\pm\else\textpm\fi{}500 barns; ${\mathrm{Am}}^{243}$, 0.072 barn; ${\mathrm{Cm}}^{243}$, 690\ifmmode\pm\else\textpm\fi{}50 barns; ${\mathrm{Cm}}^{245}$, 1880\ifmmode\pm\else\textpm\fi{}150 barns. In addition, a pile neutron capture cross section of 520\ifmmode\pm\else\textpm\fi{}40 barns has been measured for ${\mathrm{Pu}}^{238}$.

The electron capture and alpha decay of ${\mathrm{Np}}^{235}$ have been investigated. An $\frac{L}{K}$ capture ratio of 30\ifmmode\pm\else\textpm\fi{}2 is found from absolute $L$ and $K$ x-ray measurements. No gamma rays are observed in the electron capture decay of ${\mathrm{Np}}^{235}$. An alpha branching ratio of (3.5\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ was measured for this nuclide. The alpha particles have coincident 26- and 85-kev gamma rays with an intensity of 0.054\ifmmode\pm\else\textpm\fi{}0.005 gamma per alpha disintegration for the 85-kev gamma ray. The intensity of the 26-kev gamma ray is comparable, although somewhat more uncertain.

A summary is presented of the results obtained in a radiochemical investigation of the debris in fused rock from the Anacostia underground explosion on Nov. 27, 1962. The relative yields of the actinides of mass numbers 239 to 254 (Np to Cf) are tabulated, and the mass-yield curve is compared with that of the Mike event. (D.L.C.)

Energies, natural widths and intensities of K X-ray lines have been measured for several actinides between Z=88 and Z=98 : Ra, Ac, Th, Pa, U, Pu, Cm, Bk and Cf. An overall agreement is observed with recent theoretical values.