Recent Articles

Spin and Magnetic Moment of the 1.094-MeV State in ${}^{168}{Er}$

B. T. Kim, W. K. Chu, and J. C. Glass

Phys. Rev. C 8, 1920 (1973) - Published 1 November, 1973

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The time-differential directional-correlation function of the 448 - 198-keV $γ - γ$ cascade has been measured and the half-life of the 1.094-MeV state in ${}^{168}{Er}$ is found to be 107.3±2.2 nsec. The time-differential behavior of $A_{22} (t)$ shows a possible time-dependent interaction with a decay constant $λ_{2} = (1.0 \pm 0.5) \times 10^{7}$ ${nsec}^{- 1}$ . Extrapolation of $A_{22} (t)$ to zero time-delay gives $A_{22} (0) = 0.007 \pm 0.004$ , which is compatible with spin 4 for the 1.094-MeV state and multipolarity $M 1 + < 8 % E 2$ for the 448-keV transition. The $g$ -factor of the 1.094-MeV state has been measured, by use of the constant-angle-differential-delay method, and is found to be $g = + 0.45 \pm 0.02$ . The time-dependent perturbation is interpreted in terms of rapidly fluctuating $4 f$ electron magnetic hyperfine fields with a time-averaged value of 0.9 MG in ${Er}^{3 +}$ at room temperature.

[NUCLEAR MOMENTS ${}^{168}{Er}$ level; measured $γ γ$ coin., deduced $J$ , $T_{\frac{1}{2}}$ , $γ$ mixing. Measured $γ γ (θ, H)$ , D. D. C. A. method, deduced $g$ , ${Er}^{3 +}$ hyperfine field.]

Potential-Energy Surface for the Fission of the Superheavy Nucleus ${}_{114}^{298}X_{184}$

M. G. Mustafa and H. W. Schmitt

Phys. Rev. C 8, 1924 (1973) - Published 1 November, 1973

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The asymmetric two-center model has been used to calculate the potential-energy surface of the superheavy nucleus ${}_{114}^{298}X_{184}$ . Four shape variables, including two for asymmetric degrees of freedom, were used to describe the nuclear shape. The minimum-potential-energy path for fission follows reflection-symmetric shapes from the ground state to beyond the second barrier; in this region the surface becomes soft and a variety of paths becomes available. For lesser elongations, asymmetric shapes are briefly preferred; for greater elongations, symmetric shapes are preferred. The paths converge in the main, steeply descending scission valley, for which the liquid-drop term dominates and reflection-symmetric shapes are slightly preferred.

Gamma-Ray Transitions in ${}^{159}{Tb}$ Following the ( $n, n^{'}$ ) Reaction

J. Felsteiner and H. Lindeman

Phys. Rev. C 8, 1929 (1973) - Published 1 November, 1973

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Energy levels of ${}^{159}{Tb}$ have been studied from the $γ$ -ray spectrum produced by the ${}^{159}{Tb} (n, n^{'} γ)$ reaction using a Ge(Li) detector. The spectrum shows peaks at 317, 331, 395, 440, and 520 keV which do not fit into the existing level scheme of ${}^{159}{Tb}$ . The possibility that the $γ$ -ray transitions found at 912, 947, and 976keV might belong to a ${1 / 2}^{+}$ [411] rotational band is discussed. A $γ$ ray at 248 keV is interpreted as a transition originating in the recently found 386-keV level. The weak transition from the 429-keV level to the ground state has been detected. Some doublets in the $γ$ spectrum are discussed.

Interference Between Direct Nuclear Reactions and Coulomb Excitation with Alpha Particles on ${}^{154}{Sm}$ , ${}^{166}{Er}$ , and ${}^{182}W$

C. E. Bemis, Jr., P. H. Stelson, F. K. McGowan, W. T. Milner, J. L. C. Ford, Jr., R. L. Robinson, and W. Tuttle

Phys. Rev. C 8, 1934 (1973) - Published 1 November, 1973

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Striking destructive interference effects have been observed in the ${}^{4}{He}$ excitation of the $2^{+}$ and $4^{+}$ ground-state band rotational states in deformed even- $A$ ${}^{154}{Sm}$ , ${}^{166}{Er}$ , and ${}^{182}W$ . The $E 2$ and $E 4$ transition moments and charge deformation parameters, $β_{20}^{c}$ and $β_{40}^{c}$ , are given.

[NUCLEAR REACTIONS ${}^{154}{Sm} (α, α^{'})$ , $E = 11 - 19$ MeV; ${}^{166}{Er} (α, α^{'})$ , $E = 12.5 - 19.5$ MeV, ${}^{182}W (α, α^{'})$ , $E = 13 - 21$ MeV; measured $σ (E_{α}; θ = 150^{\circ})$ ; deduced $B (E 2)$ , $B (E 4)$ . Enriched targets. Extracted model-dependent deformations, $β_{20}$ and $β_{40}$ .]

( $n, 2 n$ ) Cross Sections for ${}^{238}U$ and ${}^{237}{Np}$ in the Region of 14 MeV

Jerry H. Landrum, Richard J. Nagle, and Manfred Lindner

Phys. Rev. C 8, 1938 (1973) - Published 1 November, 1973

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The cross sections for formation of ${}^{237}U$ from ${}^{238}U$ and for the eventual formation of ${}^{236}{Pu}$ from ${}^{237}{Np}$ by the ( $n, 2 n$ ) reaction were measured relative to the ${}^{27}{Al} (n, α) {}^{24}{Na}$ cross section. Neutrons were produced by the irradiation of titanium tritide targets with 400-keV deuterons on the Livermore insulated core transformer (ICT) neutron generator. The determinations covered the neutron energy range from 13.7 to 14.9 MeV. From the partial cross section for ${}^{236}{Pu}$ formation, the cross section was calculated for the ${}^{237}{Np}$ total ( $n, 2 n$ ) reaction, including the branch leading to ${}^{236}{Np}^{m}$ .

Decay of Mass-Separated ${}^{93}Y$

W. L. Talbert, Jr. and R. J. Hanson

Phys. Rev. C 8, 1945 (1973) - Published 1 November, 1973

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The levels of ${}^{93}{Zr}$ populated in the $β$ decay of ${}^{93}Y$ have been deduced from Ge(Li)-Ge(Li) coincidence and Ge(Li) singles $γ$ -ray spectra. 22 of the 23 observed $γ$ -ray transitions have been placed in a level scheme for ${}^{93}{Zr}$ with 11 excited states. These results are compared with those of previous investigations. A number of corrections, clarifications, and expansions of decay schemes previously reported resulted from the use of high-resolution detectors and a mass-separated source strong enough to permit coincidence studies of the weak as well as the intense transitions. Spin-parity assignments of the ${}^{93}{Zr}$ levels have been deduced using relative $γ$ -ray transition rates, $β$ -decay $log ft$ values, and results of nuclear-reaction studies. Possible interpretations of some of the levels are presented, based on shell-model descriptions.

[RADIOACTIVITY ${}^{93}Y$ (from ${}^{93}{Kr}$ decay); measured $E_{γ}$ , $I_{γ}$ , $γ - γ$ coin, calculated $log ft$ . ${}^{93}{Zr}$ deduced levels, $J$ , $π$ . Mass-separated ${}^{93}{Kr}$ activity.]

$β - γ$ Directional Correlation of ${}^{203}{Hg}$

J. M. Wyrick and A. H. Weber

Phys. Rev. C 8, 1955 (1973) - Published 1 November, 1973

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The $β - γ$ directional correlation of the first-forbidden $β$ transition of ${}^{203}{Hg}$ has been investigated. The energy dependence of the $β - γ$ directional-correlation coefficient $A_{22}$ in the directional-correlation function $W (θ) = 1 + A_{22} P_{2} (cos θ)$ was measured as a function of $β$ energy $\bar{W}$ . Experimental values obtained for the $β - γ$ directional-correlation coefficient were $A_{22} (\bar{W}) = - 0.0069 \pm 0.0010 (\bar{W} = 1.157)$ ; -0.0083 ± 0.0010 ( $\bar{W} = 1.196$ ); -0.0100 ± 0.0010 ( $\bar{W} = 1.254$ ); -0.0118 ± 0.0010 ( $\bar{W} = 1.313$ ).

Exchange Effects in Radiative $n - p$ Capture

J. Thakur and L. L. Foldy

Phys. Rev. C 8, 1957 (1973) - Published 1 November, 1973

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The contribution of the one-pion-exchange interaction current to the transition amplitude for radiative $n - p$ capture at thermal energies is evaluated using the Chew-Low static model for the amplitude for photoproduction of pions off nucleons. A correct treatment of the pion-rescattering term in that amplitude gives essential agreement with the static-quark-model calculation of Riska and Brown which considers only nucleon excitation to the $Δ (1236)$ state.

Magnetic Reorientation

J. J. O'Brien and J. X. Saladin

Phys. Rev. C 8, 1959 (1973) - Published 1 November, 1973

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Mass of ${}^{31}S$

A. Moalem and B. H. Wildenthal

Phys. Rev. C 8, 1961 (1973) - Published 1 November, 1973

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A high-resolution study of the ${}^{32}S (p, d) {}^{31}S$ reaction shows a discrepancy with the current table of mass values. The ${}^{32}S (p, d) {}^{31}S$ reaction $Q$ value is found to be - 12 817.8 ± 1.5 keV, 45.6 keV more positive than the published value, which carried an 11-keV uncertainty. Similar studies of the ( $p, d$ ) reaction on ${}^{23}{Na}$ , ${}^{27}{Al}$ , ${}^{33}S$ , ${}^{34}S$ , ${}^{35}{Cl}$ , and ${}^{37}{Cl}$ indicate no discrepancies with the $Q$ values (of 1- to 2-keV accuracy) tabulated for these nuclei. Possible sources for the sulfur discrepancy are discussed.

[NUCLEAR REACTIONS ${}^{23}{Na}$ , ${}^{27}{Al}$ , ${}^{32, 33, 34}S$ , ${}^{35, 37}{Cl} (p, d)$ , $E = 35$ MeV, measured Q, deduced new value for the mass of ${}^{31}S$ .]

Projected Hartree-Fock Wave Functions

Raj Muthu Krishnan

Phys. Rev. C 8, 1963 (1973) - Published 1 November, 1973

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Isospin Dependence of the Nuclear Level Width

M. Kildir and J. R. Huizenga

Phys. Rev. C 8, 1965 (1973) - Published 1 November, 1973

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Statistical fluctuation analyses of ${}^{31}P (p, α)$ and ${}^{31}P (p, p^{'})$ excitation functions are used to deduce level widths for the $T_{<}$ and $T_{>}$ isospin states in ${}^{32}S$ at 17.8 MeV of 38.7±2.7 and 26.2±3.5 keV, respectively. These two widths in ${}^{55}{Mn}$ at 17.6 MeV are reported also. Relative level densities of the two isospins are calculated for each nucleus.

[NUCLEAR REACTIONS ${}^{31}P (p, α)$ , ( $p, p^{'}$ ), $E = 8.5 - 10.0$ MeV, measured $σ (E; θ)$ ; deduced level widths and level densities for $T_{<}$ and $T_{>}$ isospin states in ${}^{32}S$ at 17.8 MeV.]

Erratum: Isobaric Mass Quartets in the Mass-21 and Mass-37 Nuclei

W. Benenson, E. Kashy, and I. D. Proctor

Phys. Rev. C 8, 1968 (1973) - Published 1 November, 1973

Erratum: Parameters of the Subthreshold Fission Structure in ${}^{242}{Pu}$

George F. Auchampaugh and C. D. Bowman

Phys. Rev. C 8, 1968 (1973) - Published 1 November, 1973

Interaction of 24.0- and 27.2-MeV Neutrons with Deuterons

Thomas W. Burrows

Phys. Rev. C 8, 1173 (1973) - Published 1 October, 1973

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The angular distributions of 24.0- and 27.2-MeV neutrons scattered elastically by deuterons through angles between 90 and 166 ° (c.m.) were measured. Proton-emission energy spectra were studied at 11 and 22 ° (lab) and angular distributions were measured between 11 and 46° (lab). The spectra and angular distributions were normalized to the $n - p$ differential cross section at 158° (c.m.). The minimum cross sections of neutrons elastically scattered by deuterons were found to be less than the minimum cross sections of elastically scattered protons.

[NUCLEAR REACTIONS ${}^{2}H (n, d)$ , ( $n, p$ ), $E = 24.0, 27.2$ MeV; measured $σ (θ_{n})$ , $θ_{n} = 90 - 166^{\circ}$ (c.m.), $Δ θ_{n} = 5.6 - {10.0}^{\circ}$ ; measured $σ (Θ_{p})$ , $Θ_{p} = 11 - 45^{\circ}$ (lab), $E_{p} \geq 10$ MeV, $Δ Θ_{p} = 5 - 6^{\circ}$ (lab); measured $σ (E_{p}, Θ)$ , $Θ = 11, 22^{\circ}$ (lab), $E_{p} \geq 10$ MeV, $Δ Θ = 5^{\circ}$ .

Search for Doubly Radiative $np$ Capture

R. G. Arnold, B. T. Chertok, I. G. Schröder, and J. L. Alberi

Phys. Rev. C 8, 1179 (1973) - Published 1 October, 1973

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We have made a search for doubly radiative $np$ capture $n + p \to γ_{1} + γ_{2} + {}^{2}H$ . It has been suggested that this process might contribute to the total $np$ -capture cross section and thus explain the long-standing discrepancy in $np$ capture ( $σ_{expt} = 334.2 \pm 0.5$ mb and $σ_{th} = 302.5 \pm 4.0$ mb). Previous $np$ -capture experiments have been insensitive to the energy distribution of the capture $γ$ rays. In this experiment we searched for two-photon events by looking for $γ$ rays in coincidence from a $H_{2}$ O target exposed to a beam of thermal neutrons using two 5×5-cm NaI detectors. Analysis of the coincidence spectra indicates two-photon $np$ -capture events have not been observed. An upper limit at the 3 standard deviation confidence level of $σ_{2 γ} \leq 1.0$ mb can be placed on the doubly radiative $np$ -capture cross section. Therefore the two-photon cross section does not explain the discrepancy between the theoretical and experimental $np$ -capture cross sections.

Mechanism of the ${}^{12}C ({}^{6}{Li}, d) {}^{16}O$ Reaction at $E_{{}^{6}{Li}} = 19 - 24$ MeV

D. P. Balamuth

Phys. Rev. C 8, 1185 (1973) - Published 1 October, 1973

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The mechanism of the ${}^{12}C ({}^{6}{Li}, d) {}^{16}O$ reaction has been studied in the energy range $E_{{}^{6}{Li}} = 19 - 24$ MeV. For the states at $E_{x} = 6.92 and 7.12$ MeV we have (a) measured excitation functions in 200-keV steps where the deuterons were detected at 0°, and (b) measured $d - γ$ angular correlations at three bombarding energies where the deuterons were also detected at 0°. The excitation curves are found to be relatively smooth functions of bombarding energy. The angular correlations are similar at all three bombarding energies. The results of the angular-correlation measurements are compared with the predictions of both an $α$ -transfer mechanism (using the distorted-wave Born approximation) and a compound-nucleus mechanism (using the Hauser-Feshbach theory). The observed correlations are not completely consistent with the predictions of either theory. Angular correlations measured at lower energies were found to show strong changes with bombarding energy.

Primary Singularities, Asymptotic Wave Functions and Unitarity in the Three-Body Problem

T. A. Osborn and D. Bollé

Phys. Rev. C 8, 1198 (1973) - Published 1 October, 1973

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This paper studies the singular pole structure present in the momentum space three-body-scattering wave functions. We prove that this structure alone is entirely responsible for the asymptotic behavior in coordinate space. We are also able to prove, without further assumptions, that the residues of each of the singularities in the wave function must be physical scattering amplitudes. We extend our study of these primary poles in three-body physics by using the singularity structure to obtain a derivation of the on-shell unitarity relations.

98° Differential Cross Section for the Reaction ${}^{4}{He} (γ, n) {}^{3}{He}$

J. D. Irish, R. G. Johnson, B. L. Berman, B. J. Thomas, K. G. McNeill, and J. W. Jury

Phys. Rev. C 8, 1211 (1973) - Published 1 October, 1973

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The 98 ° differential photoneutron cross section for ${}^{4}{He}$ has been measured for excitation energies between 22 and 33 MeV with a liquid ${}^{4}{He}$ target at its normal boiling point and for excitation energies between 23 and 37 MeV with a ${}^{4}{He}$ gas target at a pressure of 51.6 bars. The cross-section values obtained with the gas target were approximately a factor of 1.9 greater than those obtained with the liquid target. This apparent dependence of the cross section upon the physical state of the ${}^{4}{He}$ target may explain the large values for the ratio $\frac{σ (γ, p)}{σ (γ, n)}$ obtained by comparing photoneutron and photoproton cross sections obtained with targets in different physical states.

Compound-Nucleus and Deuteron $D$ -State Effects Observed in the $T_{20}$ Analyzing Power of ( $d, p$ ) Reactions

H. O. Meyer and J. A. Thomson

Phys. Rev. C 8, 1215 (1973) - Published 1 October, 1973

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The tensor-analyzing power $T_{20}$ of ( $d, p$ ) reactions on ${}^{12}C$ , ${}^{28}{Si}$ , and ${}^{40}{Ca}$ are measured at small angles as a function of bombarding energy. Measurements are carried out for $θ_{lab}$ from 0-15° and $E_{d}$ from 5-12 MeV. Strong fluctuations of $T_{20}$ with energy are observed. The measurements are not explained by distorted-wave calculations which neglect the deuteron $D$ state. Inclusion of the $D$ state leads to better agreement with the data. The remaining discrepancy between the $D$ -state calculation and the measured $T_{20}$ can be explained by a compound-nucleus contribution to the reaction mechanism.

[NUCLEAR REACTIONS ${}^{12}C (\vec{d}, p_{0})$ , ${}^{28}{Si} (\vec{d}, p_{0})$ , ${}^{28}{Si} (\vec{d}, p_{1})$ , ${}^{40}{Ca} (\vec{d}, p_{0})$ ; $θ_{lab} = 0 - 15^{\circ}$ , $E_{d} = 5 - 12$ MeV; measured $T_{20} (θ_{p}, E_{d})$ . Natural targets.]

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Spin and Magnetic Moment of the 1.094-MeV State in ${}^{168}{Er}$

Potential-Energy Surface for the Fission of the Superheavy Nucleus ${}_{114}^{298}X_{184}$

Gamma-Ray Transitions in ${}^{159}{Tb}$ Following the ( $n, n^{'}$ ) Reaction

Interference Between Direct Nuclear Reactions and Coulomb Excitation with Alpha Particles on ${}^{154}{Sm}$ , ${}^{166}{Er}$ , and ${}^{182}W$

( $n, 2 n$ ) Cross Sections for ${}^{238}U$ and ${}^{237}{Np}$ in the Region of 14 MeV

Decay of Mass-Separated ${}^{93}Y$

$β - γ$ Directional Correlation of ${}^{203}{Hg}$

Exchange Effects in Radiative $n - p$ Capture

Magnetic Reorientation

Mass of ${}^{31}S$

Projected Hartree-Fock Wave Functions

Isospin Dependence of the Nuclear Level Width

Erratum: Isobaric Mass Quartets in the Mass-21 and Mass-37 Nuclei

Erratum: Parameters of the Subthreshold Fission Structure in ${}^{242}{Pu}$

Interaction of 24.0- and 27.2-MeV Neutrons with Deuterons

Search for Doubly Radiative $np$ Capture

Mechanism of the ${}^{12}C ({}^{6}{Li}, d) {}^{16}O$ Reaction at $E_{{}^{6}{Li}} = 19 - 24$ MeV

Primary Singularities, Asymptotic Wave Functions and Unitarity in the Three-Body Problem

98° Differential Cross Section for the Reaction ${}^{4}{He} (γ, n) {}^{3}{He}$

Compound-Nucleus and Deuteron $D$ -State Effects Observed in the $T_{20}$ Analyzing Power of ( $d, p$ ) Reactions

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