Recent Articles

Off-shell effects in elastic pion-nucleus scattering

D. J. Ernst, C. M. Shakin, and R. M. Thaler

Phys. Rev. C 9, 1370 (1974) - Published 1 April, 1974

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For elastic scattering of pions from nuclei in the energy region of the (3, 3) resonance, the effects of the binding of the target nucleons are shown to be important in the calculation of the pion-nucleus optical potential. The size of these binding effects is estimated for the case in which the free pion-nucleon scattering amplitude is represented by a separable form.

Unitarity and off-shell effects in the impulse approximation

D. J. Ernst, C. M. Shakin, and R. M. Thaler

Phys. Rev. C 9, 1374 (1974) - Published 1 April, 1974

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For elastic scattering of a particle from a finite many-body target, the procedure of eliminating the two-body potential in favor of a two-body scattering matrix is examined. It is shown that the theory of Kerman, McManus, and Thaler leads to unitary relations which are not of a particularly convenient form. A simple procedure which identifies the appropriate off-shell scattering matrix to be used in the impulse approximation is presented. The projection operator technique is employed to define an optical potential and then, in a truncated Hilbert space, a relation similar to a two-body Low equation is used to identify the appropriate two-body $T$ matrix. With this latter procedure the unitarity relations are maintained in a form which allows them to be used as a guide to the validity of the impulse approximation.

Cross sections for the spallation production of ${}^{10}{Be}$ in targets of N, Mg, and Si and their astrophysical applications

G. M. Raisbeck and F. Yiou

Phys. Rev. C 9, 1385 (1974) - Published 1 April, 1974

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Using an isotope-separator technique, cross sections have been measured for the spallation production of ${}^{10}{Be}$ in targets of N, Si, and Mg by protons of 600 MeV and in N by protons of 150 MeV. For 600-MeV protons $σ ({}^{10}{Be}) = 1.3 \pm 0.6, 0.7 \pm 0.3, and 1.3 \pm 0.4$ mb in N, Si, and Mg respectively. For 150-MeV protons $σ ({}^{10}{Be}) = 0.6 \pm 0.2$ mb in N. The results are discussed in terms of the cosmogenic production of ${}^{10}{Be}$ in meteorites, lunar surface, cosmic dust, the earth's atmosphere, and the interstellar gas. It is shown that the Si and Mg components of chondritic material will be important sources of ${}^{10}{Be}$ , at least as far as the primary galactic flux is concerned. It is also pointed out that the quantitative evaluation of the ${}^{10}{Be}$ from lighter nuclei such as oxygen in meteorites and nitrogen in the earth's atmosphere depends strongly on the magnitude of the (unmeasured) secondary-neutron-induced reactions. ${}^{10}{Be}$ is shown to be a small fraction of the total Be formed in the spallation of cosmic rays over the whole range of important primary nuclei. Using standard radiochemical techniques cross sections have also been measured for ${}^{7}{Be}$ and ${}^{22}{Na}$ production in targets of Si and Mg irradiated by 600-MeV protons. The results differ significantly from previously published values.

[NUCLEAR REACTIONS ${}^{14}N (p, x) {}^{10}{Be}$ , $E = 150, 600$ MeV, ${}^{24}{Mg}$ , ${}^{28}{Si} (p, x) {}^{10}{Be}$ , ${}^{7}{Be}$ , ${}^{22}{Na}$ , $E = 600$ MeV, measured $σ$ 's. Discuss implications for cosmogenic production of ${}^{10}{Be}$ .]

Study of excited states of ${}^{75}{As}$ with the ${}^{74}{Ge} (p, γ) {}^{75}{As}$ reaction

C. W. Wang, Y. C. Liu, E. K. Lin, C. C. Hsu, and G. C. Kiang

Phys. Rev. C 9, 1396 (1974) - Published 1 April, 1974

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The $γ$ radiation following the proton capture reaction ${}^{74}{Ge} (p, γ) {}^{75}{As}$ has been studied with a Ge(Li) detector. From the analysis of the measured $γ$ -ray spectra, a detailed decay scheme of ${}^{75}{As}$ was constructed in which the energy levels of ${}^{75}{As}$ up to 2938 keV excitation were determined. Spin and parities for some levels are suggested. The deduced level schemes are in good agreement with results of Wilenzick et al. and Moreh and Shahal.

[NUCLEAR REACTION ${}^{74}{Ge} (p, γ)$ , $E = 2.531$ MeV; measured $E_{γ}$ , $Q$ . ${}^{75}{As}$ deduced levels, $J$ , $π$ . Enriched target.]

Absolute cross sections for the ${}^{58, 60}{Ni} ({}^{16}O, X)$ reactions

R. L. Robinson, H. J. Kim, and J. L. C. Ford, Jr.

Phys. Rev. C 9, 1402 (1974) - Published 1 April, 1974

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The absolute cross sections for a variety of reactions resulting from bombardment of ${}^{58, 60}{Ni}$ with 38-, 42-, and 46-MeV ${}^{16}O$ ions were determined from yields of $γ$ rays observed from the decay of resulting radioactivities and from yields of in-beam $γ$ rays. The strongest reactions are ( ${}^{16}O, p n$ ), ( ${}^{16}O, 2 p$ ), and ( ${}^{16}O, α p$ ). Other identified reactions are ( ${}^{16}O, p$ ), ( ${}^{16}O, 2 n$ ), ( ${}^{16}O, α$ ), ( ${}^{16}O, α n$ ), ( ${}^{16}O, 2 α$ ), ( ${}^{16}O, 2 pn$ ), ( ${}^{16}O, 3 p$ ), ( ${}^{16}O, {}^{12}C$ ), and ( ${}^{16}O, {}^{15}N$ ). At the higher projectile energies the total cross sections are in reasonable agreement with the reaction cross sections based on an optical-model calculation. The relative yields of the reaction products were compared to predictions for statistical decay of a compound-nuclear system by neutron, proton, and $α$ -particle emission. This model does account for the general features of the experimental data; in particular it correctly predicts that charged-particle emission strongly competes with neutron emission.

[NUCLEAR REACTIONS ${}^{58, 60}{Ni} ({}^{16}O, X)$ , $E_{{}^{16}O} = 38, 42, 46$ MeV; measured $E_{γ}$ , $I_{γ}$ ; deduced $σ (E)$ . RADIOACTIVITY ${}^{74}{Br}$ ; measured $E_{γ}$ , $I_{γ}$ , $T_{\frac{1}{2}}$ .]

Ionization loss for high-energy electrons in thin targets

James T. O'Brien, Hall Crannell, F. J. Kline, and S. Penner

Phys. Rev. C 9, 1418 (1974) - Published 1 April, 1974

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The most-probable ionization loss has been measured for relativistic electrons passing through thin absorbers of carbon, aluminum, and copper. Incident energies of 50 and 100 MeV were used. Target thicknesses ranged from 48 to 614 mg/ ${cm}^{2}$ and encompass the range of thicknesses most frequently used in electron scattering experiments at these energies. The measured values of the most-probable ionization losses are in good agreement with the theoretical predictions of Sternheimer. The techniques for using values of the ionization loss to determine the target thickness in electron scattering experiments are presented.

[NUCLEAR REACTIONS Nat. C, Al, $Cu (e, e^{'})$ , $E = 50, 100$ MeV; measured most-probable energy loss for electrons.]

Gamma-ray spectroscopy studies of ${}^{52}{Ti}$

J. G. Pronko, T. T. Bardin, J. A. Becker, T. R. Fisher, R. E. McDonald, and A. R. Poletti

Phys. Rev. C 9, 1430 (1974) - Published 1 April, 1974

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Nuclear properties of the excited states of ${}^{52}{Ti}$ were measured using the ${}^{50}{Ti} (t, p γ)$ reaction at a bombarding energy of $E_{t} = 2.9$ MeV. Angular correlations of $γ$ rays were obtained using an array of five NaI(Tl) counters in time coincidence with an annular particle detector positioned near 180°. Unique spin assignments for some of the excited states were obtained in addition to multipole-mixing-ratio and branching-ratio information. Nuclear lifetimes were measured using the Doppler-shift-attenuation method. Some of the measured excitation energies, spins, and mean lifetimes [ $E_{x}$ (keV), $J$ , and $τ$ (psec)], respectively, are as follows: ( $1047.1 \pm 0.3, 2, {4.8}_{- 2.1}^{+ 8.0}$ ); ( $2259.4 \pm 0.6, 2, {0.05}_{- 0.02}^{+ 0.03}$ ); (2427.9 ± 1.5, 2, ≤0.1); and (3582.5 ± 2.0, ≥1, ≤0.09).

[NUCLEAR REACTIONS ${}^{50}{Ti} (t, p)$ , $E = 2.9$ MeV; measured $θ_{p γ}$ , $E_{γ}$ , $T_{\frac{1}{2}}$ , $Γ$ , $δ$ for transitions in ${}^{52}{Ti}$ . Deduced $J$ , $π$ for levels.]

Lifetime measurements in ${}^{45}{Sc}$

R. L. Schulte, J. D. King, and H. W. Taylor

Phys. Rev. C 9, 1436 (1974) - Published 1 April, 1974

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The lifetimes of levels in ${}^{45}{Sc}$ have been determined by the Doppler-shift-attenuation method with the ${}^{44}{Ca} (p, γ) {}^{45}{Sc}$ reaction for 11 levels between 1.4 and 3.8 MeV. The energies (keV) of the levels and mean lives (psec) studied in this work are: 1408 (< 0.12); 1800 (0.095); 2092 (0.012); 2151 (0.087); 2303 (0.080); 2352 (0.060); 2531 (0.12); 2590 (0.050); 2778 (0.019); 2895 (0.010); 3714 (0.019). On the basis of $E 2$ transition strengths the spin assignment of $\frac{5}{2}$ has been determined for the 2092-keV state and further restrictions have been made to the range of possible spins for a number of states.

[NUCLEAR REACTIONS ${}^{44}{Ca} (p, γ)$ , $E = 0.86$ MeV; ${}^{45}{Sc}$ levels, $E_{x} = 1.4 - 3.8$ MeV, measured $T_{\frac{1}{2}}$ , deduced $J$ .]

Radiative proton capture study of the giant dipole resonance in ${}^{55, 57}{Co}$

J. V. Maher, L. Meyer-Schützmeister, E. L. Sprenkel-Segel, D. von Ehrenstein, R. J. Nemanich, G. C. Kiang, J. F. Tonn, and R. E. Segel

Phys. Rev. C 9, 1440 (1974) - Published 1 April, 1974

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Extensive yield-curve and angular-distribution measurements have been made for the ${}^{54}{Fe} (p, γ_{0})$ and the ${}^{56}{Fe} (p, γ_{0})$ reactions. Both yield curves clearly show the envelope of the giant dipole resonance. The giant resonance appears to be broader in ${}^{57}{Co}$ and this is attributed to a greater isospin splitting and to the fact that proton emission from the two isospin components is expected to be more nearly equal. In both cases the angular distributions appear to be somewhat different for the two $T$ components with the difference greater in ${}^{57}{Co}$ .

[NUCLEAR REACTIONS ${}^{54}{Fe} (p, γ_{0})$ , $E_{p} = 4.75 - 16.80$ MeV, ${}^{56}{Fe} (p, γ_{0})$ , $E_{p} = 4.65 - 17.40$ MeV; measured $σ (E_{p})$ , $σ (θ)$ at many $E_{p}$ values. Deduced for $(γ, p_{0}) σ (E_{γ}, θ)$ in giant dipole resonance of ${}^{55, 57}{Co}$ .]

Gamma-ray transitions in ${}^{50}V$

D. G. Rickel and J. D. McCullen

Phys. Rev. C 9, 1446 (1974) - Published 1 April, 1974

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$γ$ -ray transitions from states in ${}^{50}V$ up to 1680 keV excitation have been studied using the ( $p, n γ$ ) reaction. Branching ratios and some lifetime information was obtained. There is an indication of a doublet at 910 keV, the existence of which is previously unreported. Relative transition probabilities are compared to the $1 f_{\frac{7}{2}}$ model of ${}^{50}V$ .

[NUCLEAR REACTIONS ${}^{50}{Ti} (p, n γ)$ , $E = 3.5 - 5.0$ MeV measured $γ$ , $γ γ$ , Doppler shift, deduced decay scheme. Ge(Li) detector, 3.5 keV at 1.33 MeV.]

Some new features of the decay of ${}^{37}S$

John C. Hill

Phys. Rev. C 9, 1453 (1974) - Published 1 April, 1974

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The $γ$ decay of ${}^{37}S$ to levels in ${}^{37}{Cl}$ was investigated using Ge(Li) detectors and sources produced by the ${}^{36}S (n, γ) {}^{37}S$ reaction. In addition to $γ$ rays at 3103.3 and 3740.4 keV observed previously, new $γ$ rays at 906.3 and 4009.3 keV were seen depopulating a level whose energy from the weighted average of the two depopulating cascades is 4009.5 keV. The above results are compared with the findings of previous decay and reaction experiments.

[RADIOACTIVITY ${}^{37}S$ [from ${}^{36}S (n, γ)$ ]; measured $E_{γ}$ , $I_{γ}$ , $γ - γ$ coin.; deduced $log ft$ , ${}^{37}{Cl}$ deduced levels. Natural target, Ge(Li) detector.]

Levels in ${}^{72}{Se}$ populated by ${}^{72}{Br}$

W. E. Collins, J. H. Hamilton, R. L. Robinson, H. J. Kim, and J. L. C. Ford, Jr.

Phys. Rev. C 9, 1457 (1974) - Published 1 April, 1974

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The level structure of ${}^{72}{Se}$ was investigated via the decay of ${}^{72}{Br}$ produced in the ${}^{58}{Ni}$ ( ${}^{16}O, p n$ ) reaction. 32 transitions were assigned to ${}^{72}{Se}$ on the basis of half-life, energy, and/ or relative $γ$ -ray yields for different beam energies with 18 transitions confirmed by coincidence data. 32 transitions are placed into the decay scheme which consists of the following levels: 862.0, $2^{+}$ ; 936.8, $0^{+}$ ; 1316.7, $2^{+}$ ; 1636.8, $4^{+}$ ; 1876.0; 1998.4, 1, $2^{+}$ ; 2150.3 ( $2^{+}$ ); 2371.6 ( $2^{+}$ ); 2433.2; 2586.2; 2965.6; 3124.1; 3225.9; and 3239.5 keV. The half-life of ${}^{72}{Br}$ was measured to be 1.31 ± 0.04 min.

[RADIOACTIVITY ${}^{72}{Br}$ ; measured $T_{\frac{1}{2}}$ , $E_{γ}$ , $I_{γ}$ , $γ γ$ coin. ${}^{72}{Se}$ deduced levels, $J, π$ .]

Levels of ${}^{84}{Se}$ from the ${}^{82}{Se} (t, p) {}^{84}{Se}$ reaction

J. D. Knight, C. J. Orth, W. T. Leland, and A. B. Tucker

Phys. Rev. C 9, 1467 (1974) - Published 1 April, 1974

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The levels of ${}^{84}{Se}$ have been investigated by the ${}^{82}{Se} (t, p)$ reaction with 15-MeV tritons. Proton spectra were recorded with a semiconductor counter telescope at lab angles between 12.5 and 90°. Differential cross sections were measured for 19 levels up to 5.633 MeV and compared with distorted-wave Born-approximation angular distributions. The first excited state in ${}^{84}{Se}$ occurs at 1.455 MeV. Excited $0^{+}$ states were observed at 2.247 and 2.655 MeV, with cross sections equal to that for the ground state. The two-neutron separation energy of ${}^{84}{Se}$ was determined to be $S_{2 n} = 14.498 \pm 0.015$ MeV. Eight excited states of ${}^{82}{Se}$ were observed by the ${}^{80}{Se} (t, p)$ reaction.

[NUCLEAR REACTIONS ${}^{82}{Se} (t, p)$ , $E = 15$ MeV, enriched targets, $Δ E - E$ counter telescope; measured $Q$ , $σ (θ)$ , $θ = {12.5 - 90}^{\circ}$ , DWBA analysis; ${}^{84}{Se}$ levels $E_{x}$ , $J^{π}$ . ${}^{80}{Se} (t, p)$ , enriched targets; ${}^{82}{Se}$ levels $E_{x}$ .]

Three-body final states in ${}^{16}O$ + ${}^{12}C$ -induced reactions: The structure of ${}^{24}{Mg}$ at high excitation

R. Wieland, R. Stokstad, A. Gobbi, D. Shapira, L. Chua, M. W. Sachs, and D. A. Bromley

Phys. Rev. C 9, 1474 (1974) - Published 1 April, 1974

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A kinematically complete study has been made of the ${}^{12}C + {}^{16}O \to {}^{12}C + {}^{12}C + α$ and ${}^{12}C + {}^{16}O \to {}^{20}{Ne} + α + α$ reactions at $E_{16_{O}} = 58.3$ MeV (lab). $α$ particles were detected at a mean laboratory angle of 2°, while the remaining reaction products were observed in coincidence by two large-area position-sensitive detectors placed symmetrically about the beam axis and subtending angles in the range $15^{\circ} \leq θ_{lab} \leq 75^{\circ}$ . Particle identification was based on the reaction kinematics. Intense yields to the lowest four states of ${}^{20}{Ne}$ were observed, with a significant fraction thereof proceeding through well defined intermediate states in ${}^{24}{Mg}$ . The predominant interaction in the ${}^{12}C + {}^{12}C + α$ final state appears to involve ${}^{12}C + α$ corresponding to an excited state at ${}^{16}O$ near 10 MeV excitation. No evidence was found for a ${}^{12}C$ + ${}^{12}C$ final state interaction, i.e., for quasimolecular states in ${}^{24}{Mg}$ in the region of excitation $21 \leq E^{*} \leq 29$ MeV. The predictions of a Hauser-Feshbach statistical model agree rather well with the observed ${}^{20}{Ne} + α + α$ yields. A selected portion of the ${}^{12}C + {}^{12}C + α$ yield, not necessarily proceeding through an excited state in ${}^{16}O$ , is accounted for by a statistical model assuming formation and decay of compound states in ${}^{24}{Mg}$ .

[NUCLEAR REACTIONS ${}^{12}C ({}^{16}O, α_{0} α_{1}) {}^{20}{Ne}$ , ${}^{12}C ({}^{16}O, α_{0} {}^{12}C_{1}) {}^{12}C_{2}$ , $E = 58.3$ MeV; measured $σ (E α_{0, 1}, E_{20_{Ne}}; θ_{α_{1}}, θ_{20_{Ne}})$ , $σ (E α_{0}, E_{12 C_{1, 2}}; θ_{12 C_{1, 2}})$ , $θ α_{0} = 2^{\circ}$ . Deduced intermediate $α - {}^{12}C$ interaction; Hauser-Feshbach analysis. Position-sensitive detectors.]

Multipole mixing ratios in ${}^{77}{Se}$ from $γ γ$ directional correlations following 56-h ${}^{77}{Br}$ decay

Robert A. Braga and Demetrios G. Sarantites

Phys. Rev. C 9, 1493 (1974) - Published 1 April, 1974

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The decay properties of the levels in ${}^{77}{Se}$ were investigated following the decay of 56-h ${}^{77}{Br}$ . Singles $γ$ -ray energy and intensity measurements were obtained with a 42- ${cm}^{3}$ high-resolution Ge(Li) $γ$ -ray detector in an anti-Compton arrangement employing a large NaI(T1) annular detector. Extensive $γ γ$ -coincidence and directional-correlation measurements were obtained with two large Ge(Li) detectors. An improved decay scheme was constructed. From $γ γ$ correlation measurements, deduced $log ft$ values, and internal-conversion coefficients, the $J^{π}$ values in parentheses for the following levels in keV were confirmed: g.s. ( $½^{-}$ ), $161.83 ({\frac{7}{2}}^{+})$ , $238.98 ({\frac{3}{2}}^{-})$ , $249.65 ({\frac{5}{2}}^{-})$ , $439.42 ({\frac{5}{2}}^{-})$ , $520.59 ({\frac{3}{2}}^{-})$ , 817.78 ( $½^{-}$ ), and $1005.08 ({\frac{3}{2}}^{-})$ ; and further $J^{π}$ assignments in parentheses for the following levels are proposed: $300.78 ({\frac{5}{2}}^{+})$ , $580.90 ({\frac{5}{2}}^{+})$ , $679.7 ({\frac{5}{2}}^{+})$ , $824.35 ({\frac{3}{2}}^{-}, {\frac{5}{2}}^{-})$ , $911.40 ({\frac{3}{2}}^{+})$ , $1186.55 ({\frac{3}{2}}^{-})$ , and 1230.62 ( ${\frac{3}{2}}^{+}, {\frac{5}{2}}^{-}$ ). With the 249.77- and 439.47-keV transitions assumed to be pure $E 2$ , the mixing ratio $δ (\frac{M 2}{E 1}) = - 0.09 \pm 0.05$ was obtained for the 87.59-keV transition, while the $δ (\frac{E 2}{M 1})$ mixing ratios obtained were: 200.40 keV, 0.00 ± 0.09; 238.98 keV, 0.13 ± 0.04; 270.83 keV, ${0.30}_{- 0.06}^{+ 0.05}$ ; 281.65 keV, ${- 0.12}_{- 0.04}^{+ 0.03}$ ; 297.23 keV, 0.17 ± 0.03 or -2.7 ± 0.2; 303.76 keV, ${- 0.44}_{- 0.16}^{+ 0.05}$ or ${0.09}_{- 0.04}^{+ 0.05}$ ; 384.99 keV, ${- 0.23}_{- 0.05}^{+ {0.07}^{'}}$ ; 484.57 keV, ${- 0.27}_{- 0.03}^{+ 0.04}$ ; 520.69 keV, ${0.17}_{- 0.07}^{+ 0.06}$ ; 574.64 keV, 0.23 ± 0.06 for ${\frac{3}{2}}^{-} \to {\frac{5}{2}}^{-}$ or ${- 0.31}_{- 0.08}^{+ 0.07}$ for ${\frac{5}{2}}^{-} \to {\frac{5}{2}}^{-}$ ; 578.91 keV, ${0.16}_{- 0.04}^{+ 0.03}$ or ${- 2.6}_{- 0.3}^{+ 0.2}$ ; and 755.35 keV, ${0.31}_{- 0.08}^{+ 0.09}$ . From these multipole mixing ratios, present branching ratios and previously measured lifetimes improved and new values of reduced transition probabilities were calculated for the transitions at 87.59, 200.40, 238.98, 249.77, 270.83, 277.47, 281.65, 439.47, and 520.69 keV. The results of this study are compared with previous work and the structure of the lower levels in ${}^{77}{Se}$ is discussed in terms of recent theoretical models for nuclear structure.

[RADIOACTIVITY ${}^{77}{Br}$ , ${}^{75}{As} (α, 2 n)$ at 22 MeV, measured $E_{γ}$ , $I_{γ}$ , $γ γ$ , $γ γ (θ)$ ; deduced ${}^{77}{Se}$ levels, $log ft$ , $J$ , $π$ , $δ (\frac{E 2}{M 1})$ , $B (E 2)$ , $B (E 1)$ , and $B (M 1)$ values.]

Search for low-yield products in the neutron-induced highly asymmetric fission of uranium

V. K. Rao, V. K. Bhargava, S. G. Marathe, S. M. Sahakundu, and R. H. Iyer

Phys. Rev. C 9, 1506 (1974) - Published 1 April, 1974

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The results of investigations aimed at defining the nature of mass distribution in the reactor neutron-induced highly asymmetric binary fission of natural, depleted, and enriched uranium are presented. Fission yields of mass chains 66, 67, 72, 77, 161, 172, 175, 177 were determined relative to ${}^{99}{Mo}$ using radiochemical methods. Upper limits for the yields of ${}^{183}{Ta}$ and ${}^{199}{Au}$ were also set to see the trend of mass distribution beyond $A = 177$ . As expected the yields of highly asymmetric products in the region $A < 70$ and $A > 161$ are sensitive to the excitation energy of the fissioning nucleus, a trend observed in symmetric fission. Computer extrapolation of the yields up to $A = 180$ on the heavier side and $A = 60$ on the lighter side indicates that both wings of the mass-yield curve cannot be represented by a single Gaussian, thereby disturbing the complementarity of the mass-yield curve in the highly asymmetric region. The relatively higher yields for mass regions around $A = 67 and 177$ , together with the upper limits for $A = 183 and 199$ in the reactor neutron fission of ${}^{238}U$ , tend to suggest the possibility of shoulders in the low-yield wings of the mass-yield curve.

Electromagnetic properties of the excited states in ${}^{239}{Pu}$

S. B. Patel, A. P. Agnihotry, P. N. Tandon, and K. P. Gopinathan

Phys. Rev. C 9, 1515 (1974) - Published 1 April, 1974

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The electromagnetic properties of the 285.5- and 391.6-keV levels in ${}^{239}{Pu}$ populated in the $β^{-}$ decay of ${}^{239}{Np}$ have been investigated. The half-lives of these levels have been measured using the delayed-coincidence technique to be $T_{\frac{1}{2}} (285.5) = 1.12 \pm 0.05$ nsec and $T_{\frac{1}{2}} (391.6) = 192 \pm 6$ nsec. The multipole mixing ratios of the 106.1-, 209.8-, 228.2-, and 277.6-keV transitions have been determined from $γ - γ$ angular-correlation measurements to be $δ {(\frac{M 2}{E 1})}_{106.1} = - 0.05 \pm 0.02$ , $δ {(\frac{E 2}{M 1})}_{209.8} = - 0.12 \pm 0.03$ , $δ {(\frac{E 2}{M 1})}_{228.2} = - 0.10 \pm 0.03$ , and $δ {(\frac{E 2}{M 1})}_{277.6} = + 0.17 \pm 0.02$ . The mean precession angle $ω τ$ for the 285.5-keV level, in an external magnetic field of 20 kG, is measured to be $ω τ = 0.166 \pm 0.037$ . From this the value of $g β$ is obtained to be, $g β = - 1.06 \pm 0.25$ . The paramagnetic correction factor $β$ for the ${Pu}^{4 +}$ state is estimated to be 2.16 in the limit of $L - S$ coupling. Using this the $g$ factor of the 285.5-keV level has been deduced to be -0.49±0.11. The magnetic moment and the reduced transition probabilities have been compared with the theoretical estimates based on Coriolis-coupling calculations.

[RADIOACTIVITY ${}^{239}{Np}$ ; measured $β - γ$ and $γ - γ$ delay, $γ γ (θ)$ , $γ γ (θ, H)$ . ${}^{239}{Pu}$ levels, deduced $T_{\frac{1}{2}}$ , $δ$ , $B (M 1)$ , $B (E 2)$ , $g$ .]

${}^{208}{Pb} (α, α) {}^{208}{Pb}$ scattering near the Coulomb barrier

G. M. Hudson and R. H. Davis

Phys. Rev. C 9, 1521 (1974) - Published 1 April, 1974

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Differential cross sections for the elastic scattering of $α$ particles by ${}^{208}{Pb}$ have been measured over the laboratory energy range 16.0 to 25.5 MeV in 0.5-MeV steps and over the laboratory angle range of 30 to 170° in 5° steps. A unique real potential of 35±3 MeV is found in an optical-model analysis with $γ_{0} = 1.22$ fm in $R = γ_{0} ({A_{1}}^{\frac{1}{3}} + {A_{2}}^{\frac{1}{3}})$ and $a = 0.57 fm$ . Uniqueness is expected for scattering in the vicinity of the Coulomb barrier once size parameters are fixed. No discrete ambiguities are found over the energy range investigated consistent with a square-well $R$ -matrix model, but they may exist at higher energies.

[NUCLEAR REACTIONS ${}^{208}{Pb} (α, α)$ , $E = 16 to 25.5$ MeV, $Δ E = 0.5$ MeV; measured $σ (θ)$ , $θ = 30 to 170^{\circ}$ ; extracted optical model $U$ and $W$ .]

Resonant scattering of bremsstrahlung by ${}^{90}{Zr}$

F. R. Metzger

Phys. Rev. C 9, 1525 (1974) - Published 1 April, 1974

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Resonant scattering of bremsstrahlung photons has been observed for the 3.308- ( $2^{+}$ ), 3.842- ( $2^{+}$ ), 4.580-, and 5.504-MeV ( $1^{(-)}$ ) levels in ${}^{90}{Zr}$ in addition to the previously excited 2.186-MeV $2_{1}^{+}$ level. The angular distribution of the 4.580-MeV radiation characterizes the spin of this level as 1. From the yield data and reported branching ratios, radiative widths of 4.6 ± 0.8, 28 ± 4, 48 ± 13, and 80 ± 32 meV were obtained for the ground-state transitions. The $E 2$ transition strengths measured for the three $2^{+}$ states in this model-independent way are compared with the strengths deduced from the cross sections of ( $α, α^{'}$ ) and other inelastic scattering reactions.

[NUCLEAR REACTIONS ${}^{90}{Zr} (γ, γ)$ , $E < 5.6$ MeV; measured $σ (E; E_{γ}, θ)$ . ${}^{90}{Zr}$ deduced levels, $J$ , $π$ , $Γ$ . Natural and enriched targets.]

$K$ -shell autoionization in the beta decay of ${}^{203}{Hg}$

A. Bond, O. P. Gupta, and A. Zide

Phys. Rev. C 9, 1529 (1974) - Published 1 April, 1974

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$K$ -shell autoionization has been observed in the $β$ decay of ${}^{203}{Hg}$ . The intensity of $Tl K x$ rays was measured in coincidence with 279-keV $γ$ rays from ${}^{203}{Tl}$ . The coincidence technique allowed a separation of autoionization x rays from internal-conversion x rays and simplified the normalization of the $K$ -shell autoionization probability $P_{K}$ . The experimental value of $P_{K}$ obtained was (1.1 ± 0.35) × $10^{- 5}$ , in good agreement with the theoretical prediction of Law and Campbell.

[RADIOACTIVITY ${}^{203}{Hg}$ ; measured $γ$ -x-ray coinc; deduced autoionization probability $P_{K}$ .]

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Off-shell effects in elastic pion-nucleus scattering

Unitarity and off-shell effects in the impulse approximation

Cross sections for the spallation production of ${}^{10}{Be}$ in targets of N, Mg, and Si and their astrophysical applications

Study of excited states of ${}^{75}{As}$ with the ${}^{74}{Ge} (p, γ) {}^{75}{As}$ reaction

Absolute cross sections for the ${}^{58, 60}{Ni} ({}^{16}O, X)$ reactions

Ionization loss for high-energy electrons in thin targets

Gamma-ray spectroscopy studies of ${}^{52}{Ti}$

Lifetime measurements in ${}^{45}{Sc}$

Radiative proton capture study of the giant dipole resonance in ${}^{55, 57}{Co}$

Gamma-ray transitions in ${}^{50}V$

Some new features of the decay of ${}^{37}S$

Levels in ${}^{72}{Se}$ populated by ${}^{72}{Br}$

Levels of ${}^{84}{Se}$ from the ${}^{82}{Se} (t, p) {}^{84}{Se}$ reaction

Three-body final states in ${}^{16}O$ + ${}^{12}C$ -induced reactions: The structure of ${}^{24}{Mg}$ at high excitation

Multipole mixing ratios in ${}^{77}{Se}$ from $γ γ$ directional correlations following 56-h ${}^{77}{Br}$ decay

Search for low-yield products in the neutron-induced highly asymmetric fission of uranium

Electromagnetic properties of the excited states in ${}^{239}{Pu}$

${}^{208}{Pb} (α, α) {}^{208}{Pb}$ scattering near the Coulomb barrier

Resonant scattering of bremsstrahlung by ${}^{90}{Zr}$

$K$ -shell autoionization in the beta decay of ${}^{203}{Hg}$

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