Recent Articles

Study of the Reaction ${}^{20}{Ne} (h, h_{0, 1, 2}) {}^{20}{Ne}$ at 17.83 MeV

K. W. Kemper, D. S. Haynes, and N. R. Fletcher

Phys. Rev. C 4, 108 (1971) - Published 1 July, 1971

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Angular distributions for the scattering of helions to the $0^{+}$ , $2^{+}$ , and $4^{+}$ members of the ground-state rotational band of ${}^{20}{Ne}$ were measured at 17.83 MeV. An optical-model analysis of the elastic scattering was performed as well as a coupled-channels analysis of the inelastic data. Good agreement between the coupled-channels calculations and the experimental data was found for the $2^{+}$ data, with $β_{2}$ in the range 0.42 to 0.48. These calculations gave a poor description of the $4^{+}$ data, but from the shape of the angular distributions an upper limit of 0.05 for $β_{4}$ was assigned.

Level Structure of ${}^{42}{Ca}$ by ${}^{41}K ({}^{3}{He}, d) {}^{42}{Ca}$ and ${}^{39}K (α, p) {}^{42}{Ca}$ Reactions at 10 MeV

F. Pellegrini, F. Gentilin, and I. Filosofo

Phys. Rev. C 4, 112 (1971) - Published 1 July, 1971

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The level structure of ${}^{42}{Ca}$ , below 6 MeV in excitation, has been studied by ${}^{41}K ({}^{3}{He}, d) {}^{42}{Ca}$ and ${}^{39}K (α, p) {}^{42}{Ca}$ reactions at 10-MeV bombarding energy. Particles detection was achieved with a surface-barrier detector telescope. Comparison of 12 measured ( ${}^{3}{He}, d$ ) angular distributions with zero-range distorted-wave Born-approximation calculations indicated a predominance of $l = 3$ and $l = 1$ transfers, and gave information about states arising from the ( $1 f_{\frac{7}{2}} 1 d_{\frac{3}{2}}^{- 1}$ ) and ( $2 p_{\frac{3}{2}} 1 d_{\frac{3}{2}}^{- 1}$ ) configurations. Shell-model calculations have been performed to investigate the level scheme in ${}^{42}{Ca}$ arising from the ${(1 f_{\frac{7}{2}}^{3} 1 d_{\frac{3}{2}}^{- 1})}_{JT}$ configuration using four different sets of effective interaction parameters between the $1 f_{\frac{7}{2}}$ particle and $1 d_{\frac{3}{2}}$ hole. The resulting wave functions were used to calculate spectroscopic factors, which have been compared with the experimental ones. The measured ( $α, p$ ) angular distributions analyzed with Hauser-Feshbach calculations indicated a predominance of compound-nucleus mechanism for this reaction. Good agreement has been found between the integrated experimental and theoretical cross section.

Stopping of 1- to 1.8-keV ${}^{73}{Ge}$ Atoms in Germanium

K. W. Jones and H. W. Kraner

Phys. Rev. C 4, 125 (1971) - Published 1 July, 1971

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Measurements of the amount of energy lost to ionization in the stopping of low-energy ${}^{73}{Ge}$ atoms, produced by inelastic neutron scattering in a germanium $γ$ -ray detector, have been extended down to energies of about 1 keV. The results are about 35% higher than theoretical values of the Lindhard theory found from an extrapolation to this energy region. The energy of the ${}^{73}{Ge}$ third excited state was measured for this experiment and found to be 68.752 ± 0.007 keV.

Strong $L = 0 (t, p)$ Transitions in the Even Isotopes of Ti, Cr, and Fe

R. F. Casten, E. R. Flynn, Ole Hansen, and T. J. Mulligan

Phys. Rev. C 4, 130 (1971) - Published 1 July, 1971

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Absolute differential cross sections for strong $L = 0 (t, p)$ transitions on targets of ${}^{46, 48, 50}{Ti}$ , ${}^{50, 52, 54}{Cr}$ , and ${}^{54, 56, 58}{Fe}$ have been measured. The bombarding energy was 13 MeV and reaction angles of 12.5 and 20° were used. The data are compared with model predictions, with special emphasis on the pairing-vibrational model with isospin. The latter model correctly predicts the dependence on neutron number of the ( $t, p$ ) cross sections but fails, as do all other models, to predict the steady cross-section decrease with increasing $Z$ . It is suggested that the latter effect is caused by a slow change in the ground-state correlations.

Differential Recoil Study of the ${}^{25}{Mg} (p, 2 p) {}^{24}{Na}$ Reaction

F. Michael Kiely and Albert A. Caretto, Jr.

Phys. Rev. C 4, 137 (1971) - Published 1 July, 1971

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Differential recoil spectra for the ${}^{25}{Mg} (p, 2 p) {}^{24}{Na}$ reaction have been measured radiochemically at recoil angles of 90 and 60° for an incident energy of 300 MeV and at a recoil angle of 90° for 100-MeV bombarding energy. All the spectra display two peaks. The position of the lower-energy peak seems to remain unchanged with a shift in incident energy, while the higher-energy peak shifts to higher kinetic energies with an increase in bombarding energy. The results are compared with the spectra calculated from a plane-wave impulse-approximation calculation which assumes that only the $1 d_{\frac{5}{2}}$ protons in ${}^{25}{Mg}$ are available for interaction. Limited agreement is obtained.

Lifetime of the 78-keV Level of ${}^{32}P$

D. M. Gordon and R. W. Kavanagh

Phys. Rev. C 4, 145 (1971) - Published 1 July, 1971

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A mechanical-recoil method has been used to measure the lifetime of the 78-keV first excited state of ${}^{32}P$ . This state was populated near threshold by the ${}^{29}{Si} ({}^{4}{He}, p) {}^{32}P$ reaction, using an enriched ${}^{29}{Si}$ $O_{2}$ target on the down-beam side of a thin copper backing, so that the ${}^{32}P$ nuclei recoiled into vacuum. The 78-keV $γ$ rays were detected, after passing the edge of a movable absorber, by a narrow rectangular Ge(Li) detector (2×2×20 mm). From the exponential curve of count rate vs absorber displacement, a value of $τ = 402 \pm 13$ psec is found for this level. A similar measurement, using the ${}^{19}F ({}^{4}{He}, n) {}^{22}{Na}$ reaction, gave an upper limit of $τ \leq 26 \pm 6$ psec for the 74-keV $M 1$ transition from the 657-keV excited state of ${}^{22}{Na}$ .

Photoneutron Cross Sections for ${}^{24}{Mg}$ , ${}^{26}{Mg}$ , and Natural Magnesium

S. C. Fultz, R. A. Alvarez, B. L. Berman, M. A. Kelly, D. R. Lasher, T. W. Phillips, and J. McElhinney

Phys. Rev. C 4, 149 (1971) - Published 1 July, 1971

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Photoneutron cross sections for ${}^{24}{Mg}$ , ${}^{26}{Mg}$ , and natural magnesium have been measured with the use of monochromatic photons obtained from the annihilation in flight of fast positrons. The resolution was less than 200 keV at 10-MeV photon energy, and 300 keV at 30 MeV. About 14 resonant structures in ${}^{24}{Mg}$ and 32 in ${}^{26}{Mg}$ were distinguished and parametrized. A Porter-Thomas treatment of the distributions of transition widths throughout the giant resonances of ${}^{24}{Mg}$ and ${}^{26}{Mg}$ indicates that the resonances belong to single-spin states, or have one degree of freedom in each case. The ${}^{26}{Mg} (γ, 2 n)$ cross section contains considerable structure, most of it coinciding with the structure in the total photoneutron cross section. It is confirmed that the giant resonance of ${}^{26}{Mg}$ is split into two isospin components. Integrated total cross sections up to 28 MeV are 50 MeV mb for ${}^{24}{Mg}$ , 226 MeV mb for ${}^{26}{Mg}$ , and 76 MeV mb for natural magnesium.

Nuclear Structure of ${}^{22}{Na}$ : The ${}^{21}{Ne} ({}^{3}{He}, d)$ Reaction

J. D. Garrett, R. Middleton, and H. T. Fortune

Phys. Rev. C 4, 165 (1971) - Published 1 July, 1971

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The bound states of ${}^{22}{Na}$ have been studied using the ${}^{21}{Ne} ({}^{3}{He}, d) {}^{22}{Na}$ reaction at a bombarding energy of 18 MeV. Angular distributions of the deuterons have been compared with distorted-wave Born-approximation predictions. The resulting spectroscopic factors are compared with those calculated using the rotational and shell models. ( ${}^{3}{He}, d$ ) spectroscopic factors for $T = 1$ final states in ${}^{22}{Na}$ are compared with ( $d, p$ ) spectroscopic factors from a ${}^{21}{Ne} (d, p) {}^{22}{Ne}$ study. The levels of ${}^{22}{Na}$ are discussed in terms of Nilsson configurations and associated rotational bands.

$p - {}^{3}{He}$ Elastic Scattering from 13 to 20 MeV

R. L. Hutson, Nelson Jarmie, J. L. Detch, Jr., and J. H. Jett

Phys. Rev. C 4, 17 (1971) - Published 1 July, 1971

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Accurate differential cross sections for protons elastically scattered by ${}^{3}{He}$ are presented for bombarding energies of 13.600, 16.232, and 19.480 MeV. The data have relative errors on the order of 0.7% and a scale error of 0.4%. The results are compared with the work of others and phase-shift analyses are briefly discussed.

On-Line Spectroscopy of ${}^{134 m, g}I$

E. Achterberg, E. Y. de Aisenberg, F. C. Iglesias, A. E. Jech, J. A. Moragues, D. Otero, M. L. Pérez, A. N. Proto, J. J. Rossi, W. Scheuer, and J. F. Suárez

Phys. Rev. C 4, 188 (1971) - Published 1 July, 1971

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Sources of mass-134 iodine have been produced in ${}^{235}U$ fission and studied on line in the Buenos Aires Isotope Separator On Line project using Ge(Li) and Si(Li) detectors. A transition of 272.2 ± 0.3 keV, with $T_{\frac{1}{2}} = 3.56 \pm 0.08$ min, $α_{K} = 0.20 \pm 0.03$ , and $\frac{K}{L} + \dots = 2.6 \pm 0.3$ , thus $E 3 (+ \leq 1 % M 4)$ in character, was determined to be the transition depopulating the isomeric state in ${}^{134}I (E_{L} - E_{K} = 28.4 \pm 0.2 keV and K binding energy = 32.9 \pm 0.6 keV)$ . The $β$ branching from this isomeric state to levels of ${}^{134}{Xe}$ amounts to (8 ± 6)%. $γ$ -ray intensities following the ground-state decay of ${}^{134}I (T_{\frac{1}{2}} = 53.2 \pm 0.2 min)$ are given. Internal-conversion coefficients for 11 transitions have been measured ( $10^{4} α_{K}$ ): 135 keV, 2600±500; 188 keV, 1300±500; 236 keV, 700±100; 406 keV, 110±20; 433 keV, 150±30; 541 keV, 60±8; 596 keV, 70±8; 622 keV, 52±8; 628 keV, 25±19; 847 keV, 18±3; and 884 keV, 19±4. Parities and angular momenta for levels of ${}^{134}{Xe}$ are proposed.

Study of the Zirconium Isotopes with the ( $p, t$ ) Reaction

J. B. Ball, R. L. Auble, and P. G. Roos

Phys. Rev. C 4, 196 (1971) - Published 1 July, 1971

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The ( $p, t$ ) reaction has been studied on all stable isotopes of zirconium at a proton energy of 38 MeV. Triton spectra were analyzed with a magnetic spectrograph yielding over-all resolution on the order of 25 keV. Comparison of experimental angular distributions with two-nucleon transfer distorted-wave Born-approximation calculations is made to extract spin-parity assignments and transition enhancement factors for many of the observed levels. The observed $L = 0$ transitions are discussed in terms of the shell model and the pairing-vibration model. The levels observed in ${}^{88, 89, 90, 92, 94}{Zr}$ are compared with results of other experiments to derive a number of new level assignments. Measurements are also obtained of the one- and two-neutron binding energies from $Q$ values deduced for the ( $p, t$ ) and ( $p, d$ ) ground-state transfer reactions.

Radioactive Decay of 23-min ${}^{131}{Sb}$ to Levels of ${}^{131}{Te}$

J. Blachot, H. N. Erten, C. D. Coryell, E. S. Macias, and W. B. Walters

Phys. Rev. C 4, 214 (1971) - Published 1 July, 1971

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The levels of ${}^{131}{Te}$ have been investigated by studying the $γ$ rays following the $β$ decay of 23-min ${}^{131}{Sb}$ using Ge(Li) detectors. The ${}^{131}{Sb}$ sources were produced by rapid separation of Sb from ${}^{235}U$ thermal-neutron-fission products. 60 $γ$ rays attributed to ${}^{131}{Sb}$ decay have been observed and $γ - γ$ coincidence relationships have been obtained for the prominent lines. A level scheme has been constructed which incorporates 40 of these $γ$ transitions between 23 levels in ${}^{131}{Te}$ . This level scheme is compared with the level structure of other odd- $A$ Te isotopes and is discussed within the framework of the pairing-plus-quadrupole model.

Measurements of Six Light Masses

Lincoln G. Smith

Phys. Rev. C 4, 22 (1971) - Published 1 July, 1971

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The mass differences of 16 doublets involving the six atoms H, D, ${}^{14}N$ , ${}^{16}O$ , ${}^{35}{Cl}$ , and ${}^{37}{Cl}$ have been measured with a new rf mass spectrometer with considerably greater precision than was attainable with the mass synchrometer. By least-squares adjustment, best values of the mass excesses of these six atoms have been determined for which the estimated errors are materially less than for previously published values.

Subthreshold Neutron-Induced Fission in ${}^{238}U$

M. G. Silbert and D. W. Bergen

Phys. Rev. C 4, 220 (1971) - Published 1 July, 1971

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In an attempt to observe subthreshold fission in ${}^{238}U$ , a sample with very low ${}^{235}U$ content was exposed to the intense neutron beam of the Physics-8 nuclear explosion. A high-sensitivity oscilloscope setting allowed individual fission-fragment pulses from a semiconductor detector to be counted. In the region from 37 to 327 eV, the average fission width for eight resonances was determined to be (0.03 ± 0.05) × $10^{- 6}$ eV. In the keV region, the average fission cross section was measured to be 61 ± 24 μb from $10^{4}$ to 3 × $10^{4}$ eV and 36 ± 14 μb from 3 × $10^{4}$ to $10^{5}$ eV.

Energy and Angular Distribution of Alpha Particles Emitted in Thermal-Neutron Fission of ${}^{235}U$

Y. Gazit, A. Katase, G. Ben-David, and R. Moreh

Phys. Rev. C 4, 223 (1971) - Published 1 July, 1971

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The energy and angular distributions of $α$ particles emitted in thermal-neutron fission of ${}^{235}U$ have been studied in a three-parameter correlation experiment for $α$ angles between 50 and 130°. These distributions are compared with the results of trajectory calculations to get a "best fit" set of initial scission conditions. The derived initial fragment separation of 24 fm and initial average kinetic energy of 31 MeV are in good agreement with liquid-drop calculations, while the initial most probable $α$ energy was found to be 3.4 MeV. The results indicate a shift in the scission point of 1-2 fm towards the light fragment, for a variation in mass ratio between 1.1 and 2. The effect of $α$ recoil on the experimental distributions is discussed in detail.

Form Factors for Proton Transfer Reactions to Unbound Isobaric Analog States

S. A. A. Zaidi and W. R. Coker

Phys. Rev. C 4, 236 (1971) - Published 1 July, 1971

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Proton form factors for isobaric analog resonances populated directly as residual states in ( $d, n$ ) and ( ${}^{3}{He}, d$ ) reactions are discussed and computed explicitly using a Lane-model Hamiltonian and the formalism of Feshbach's unified reaction theory. The resonance form factors thus obtained are compared in specific cases with equivalent parent bound-state form factors and with single-particle resonance wave functions. Numerical results and tests using data are presented for ${}^{92}{Mo} (d, n) {}^{93}{Tc}^{A}$ , and it is shown that resonance form factors lead to a dramatic enhancement of the magnitude of the calculated cross section for some transitions, compared with calculations using conventional form factors. Such enhancements are consistent with the available data.

New $K^{π} = 8^{-}$ Isomer in ${}^{182}{Hf}$

T. E. Ward and P. E. Haustein

Phys. Rev. C 4, 244 (1971) - Published 1 July, 1971

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A new $β$ active $K^{π} = 8^{-}$ isomer of 9 × $10^{6}$ -yr ${}^{182}{Hf}$ has been produced via the reaction ${}^{186}W (p, p α) {}^{182 m}{Hf}$ . $14 γ$ rays have been observed to follow a half-life of 65 ± 5 min. Six of the transitions result from the deexcitation of a $K^{π} = 8^{-}$ isomeric level in ${}^{182}{Hf}$ at 1173.5 keV to members of the $K^{π} = 0^{+}$ ground-state rotational band. The decay of this new $K$ isomer is discussed in relation to the well-known decay of 5.5-h ${}^{180 m}{Hf}$ to which it is remarkably similar.

( $d, p$ ) and ( $d, t$ ) Studies of the Actinide Elements. II. ${}^{243}{Cm}$ , ${}^{245}{Cm}$ , ${}^{247}{Cm}$ , and ${}^{249}{Cm}$

T. H. Braid, R. R. Chasman, J. R. Erskine, and A. M. Friedman

Phys. Rev. C 4, 247 (1971) - Published 1 July, 1971

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Properties of states in ${}^{243}{Cm}$ , ${}^{245}{Cm}$ , ${}^{247}{Cm}$ , and ${}^{249}{Cm}$ were determined by ( $d, p$ ) and ( $d, t$ ) reactions on targets of ${}^{244}{Cm}$ , ${}^{246}{Cm}$ , and ${}^{248}{Cm}$ . Assignments of one-quasiparticle states are made. Single-particle level schemes are extracted from the data by use of a pairing calculation. The extracted single-particle level schemes are compared with single-particle calculations, which include $β_{4}$ and $β_{6}$ deformations. Equilibrium values of $β_{2}$ , $β_{4}$ , and $β_{6}$ are estimated for the odd-mass Cm isotopes.

Antiproton- and Pion-Induced Fission at 2.5 GeV/c

L. Husain and S. Katcoff

Phys. Rev. C 4, 263 (1971) - Published 1 July, 1971

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Mica track detectors were used to measure the fission cross sections of U, Bi, and Au irradiated with 2.5-GeV/c antiprotons and negative pions. The binary-fission results in mb are: U, 2170 ± 330 for $\bar{p}$ and 1090 ± 160 for $π^{-}$ ; Bi, 293 ± 60 for $\bar{p}$ and 191 ± 40 for $π^{-}$ ; Au, 210 ± 40 for $\bar{p}$ and 107 ± 20 for $π^{-}$ . The $π^{-}$ cross sections are about the same as for protons but the $\bar{p}$ cross sections are higher by about a factor of 2. Approximate ternary-fission results in mb are: U, 8 for $\bar{p}$ and 4 for $π^{-}$ ; Bi, 6 for $\bar{p}$ and 1.5 for $π^{-}$ ; Au, 6 for $\bar{p}$ and 2 for $π^{-}$ . Ternary fission induced by antiprotons appears to be about an order of magnitude more probable than that induced by protons of the same momentum. The results are discussed relative to the large annihilation cross section of antiprotons.

Effect of ${Pu}^{240}$ Compound-Nucleus State on the Fission-Fragment Mass and Kinetic Energy Distributions

Jayashree Toraskar and E. Melkonian

Phys. Rev. C 4, 267 (1971) - Published 1 July, 1971

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Fission-fragment mass and kinetic energy distributions have been obtained for fission of ${Pu}^{239}$ induced by neutrons filtered through beryllium and by neutrons filtered through samarium. The beryllium filter enhances the contribution of the negative-energy resonance level to the fission cross section, and the samarium filter enhances the contribution of the 0.297-eV level. Surface-barrier detectors were used for the simultaneous measurement of both the fragment energies. Absolute fragment energies were calculated by using mass-dependent pulse-height energy relations.

The average total kinetic energy of the fragments produced in the fission induced by samarium-filtered neutrons was observed to be 0.75 ± 0.05 MeV greater than in the case of fission induced by beryllium-filtered neutrons. This result, when combined with the results of other experiments, implies $J = 0^{+}$ for the negative-energy level and $J = 1^{+}$ for the 0.297-eV level of ${Pu}^{239}$ . The two mass distributions are similar except for a difference in the symmetric fission yield. This difference again implies the same spin assignments as above. The absolute average total kinetic energies were determined with somewhat less accuracy and are found to be 173.0 ± 1.5 and 173.7 ± 1.5 MeV for fissions induced by beryllium- and samarium-filtered neutrons, respectively, as directly measured, and 175.8 ± 1.5 and 176.5 ± 1.5 MeV, respectively, after correction for neutron emission.

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Recent Issues

Study of the Reaction ${}^{20}{Ne} (h, h_{0, 1, 2}) {}^{20}{Ne}$ at 17.83 MeV

Level Structure of ${}^{42}{Ca}$ by ${}^{41}K ({}^{3}{He}, d) {}^{42}{Ca}$ and ${}^{39}K (α, p) {}^{42}{Ca}$ Reactions at 10 MeV

Stopping of 1- to 1.8-keV ${}^{73}{Ge}$ Atoms in Germanium

Strong $L = 0 (t, p)$ Transitions in the Even Isotopes of Ti, Cr, and Fe

Differential Recoil Study of the ${}^{25}{Mg} (p, 2 p) {}^{24}{Na}$ Reaction

Lifetime of the 78-keV Level of ${}^{32}P$

Photoneutron Cross Sections for ${}^{24}{Mg}$ , ${}^{26}{Mg}$ , and Natural Magnesium

Nuclear Structure of ${}^{22}{Na}$ : The ${}^{21}{Ne} ({}^{3}{He}, d)$ Reaction

$p - {}^{3}{He}$ Elastic Scattering from 13 to 20 MeV

On-Line Spectroscopy of ${}^{134 m, g}I$

Study of the Zirconium Isotopes with the ( $p, t$ ) Reaction

Radioactive Decay of 23-min ${}^{131}{Sb}$ to Levels of ${}^{131}{Te}$

Measurements of Six Light Masses

Subthreshold Neutron-Induced Fission in ${}^{238}U$

Energy and Angular Distribution of Alpha Particles Emitted in Thermal-Neutron Fission of ${}^{235}U$

Form Factors for Proton Transfer Reactions to Unbound Isobaric Analog States

New $K^{π} = 8^{-}$ Isomer in ${}^{182}{Hf}$

( $d, p$ ) and ( $d, t$ ) Studies of the Actinide Elements. II. ${}^{243}{Cm}$ , ${}^{245}{Cm}$ , ${}^{247}{Cm}$ , and ${}^{249}{Cm}$

Antiproton- and Pion-Induced Fission at 2.5 GeV/c

Effect of ${Pu}^{240}$ Compound-Nucleus State on the Fission-Fragment Mass and Kinetic Energy Distributions

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