Small-angle neutron scattering from Pb and 238U between 0.6 and 2.2 MeV

Differential cross sections for neutrons scattered from natural Pb and 99.9 % isotopically pure ²³⁸U have been measured at 0.5°, 1.0°, and 1.5°. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5° measurements an annular detector geometry with an angular resolution of ± 0.1° was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function $\text{A + B}\text{cot}{}^2\text{case1}\text{2}$θ at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15 % too low.     

A remeasurement of the 12C(α, γ0) excitation function in the vicinity of the 12.44 and 13.1 MeV levels of 16O

The excitation function of the ${}^{12}\text{C(α, γ}{}_0\text{)}$ reaction at θ = 90° has been remeasured for bombarding energies between 6.5 and 8.5 MeV. The measurement was made to resolve discrepancies apparent in earlier measurements relating to the absolute cross section, the location of the lower 1^? resonance near 7.05 MeV (¹⁶O excitation energy 12.44 MeV) and to the relative peak cross sections of this resonance and a second 1^? resonance at 7.88 MeV.     

Total reaction cross sections of deformed nuclei: A study of the 233, 238U + α systems

The cross sections for α-particle scattering and α-particle induced fission of ^{233, 238}U were measured at bombarding energies of 15 to 27 MeV. For these fissionable systems, the fission cross sections are very nearly equal to the total reaction cross sections. These experimental reaction cross sections are compared with various theories based on spherical and deformed potentials in order to investigate the effect of static target deformation on the reaction cross sections. From such comparisons no effect of target deformation is established. An interaction barrier (defined by the condition of 22.34 MeV is obtained from a spherical optical model fit to the experimental reaction cross-section data of uranium. This value agrees within 2.3 % with values deduced by a number of other methods.     

Measurement of elastic scattering in antiproton-proton collisions at 52.8 GeV centre-of-mass energy

We measured the differential cross section for p?p and pp elastic scattering in the momentum-transfer range 0.01 <|t| < 1.0 GeV² at the CERN Intersecting Storage Rings with center-of-mass energy $\text{s}\text{= 52.8}\text{GeV}$. Fitting the differential cross section with an exponential [Aexp (bt)], we found $\text{b}\text{p}\text{p = 13.92 ± 0.59}\text{GeV}{}^{\mathrm{?2}}$ for |t| < 0.05 GeV², whilst for |t| > 0.09 GeV², $\text{b}\text{p}\text{p = 10.68 ± 0.26}\text{GeV}{}^{\mathrm{?2}}$. Using the optical theorem, we obtained for the total cross section $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p)= 44.86 ± 0.78}\text{mb}$ and, by integrating the differential cross section, we obtained for the total elastic cross section $\text{σ}{}_{\mathrm{<mtext>el</mtext>}}\text{(}\text{p}\text{p) = 7.89 ± 0.28}\text{mb}$. Calculations of σ_tot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.     

Complete fusion studies of the 20Ne+235U system

The probability for complete fusion has been measured for the ²⁰Ne+²³⁵U system at bombarding energies of 175 and 252 MeV. The fission fragment angular correlation technique was used to obtain both the absolute cross section for complete fusion and relative cross sections for the ratio of complete fusion to incomplete fusion processes. Total reaction cross sections were also determined from elastic scattering measurements. Values of σ_R = 1900±40 and 2810 ± 140 mb were obtained at 175 and 252 MeV, respectively. These measurements yield if$\text{σ}{}_{\mathrm{<mtext>CF</mtext>}}\text{σ}{}_{\mathrm{<mtext>R</mtext>}}\text{= 0.74±0.05}\text{at}\text{175}\text{MeV and}\text{0.48 ±0.06}\text{at}\text{252}\text{MeV}$. The corresponding values of the critical angular momentum are compared with the predictions of several heavy-ion interaction models. It is observed that the l_c values obtained from these data agree well with the current models, although the energy dependence is not as strong as predicted. In addition, it is observed that these values of l_c exceed the limiting value for a charged rotating drop.     

Direct transfer and two-step processes in the 42Ca(α, 3He)43Ca reaction

The ⁴²Ca(α, ³He)⁴³Ca reaction has been studied at 36 MeV incident energy. Angular distributions have been measured from 4° to 42° using a split-pole spectrometer and position sensitive Si detectors, for about 40 levels located up to 6 MeV excitation energy. A local zero-range DWBA analysis has been carried out; l = 3 and 4 assignments are tentatively proposed for levels located above 4 MeV excitation energy, indicating a strong fragmentation of the $\text{1}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ strength between 4 and 6 MeV and the location of the main component of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ strength above 6 MeV. A number of weakly excited levels cannot be reproduced by DWBA analysis. Their angular distributions have been compared with the results of coupled-reaction-channel calculations assuming two-step excitation of weak coupling states with a [⁴²Ca¹ ? $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ structure. A reasonable agreement has been obtained, confirming that the two-step process cannot be neglected in the analysis of the (α, ³he) reaction.     

Analyzing power measurements for n-p scattering between 13.5 and 16.9 MeV

The analyzing power A_γ(θ) for neutron-proton scattering has been measured for θ = 90°(c.m.) from 13.5 to 16.9 MeV and from θ = 50° to 145°(c.m.) at 16.9 MeV. Extensive Monte Carlo calculations have been made to correct for multiple scattering effects. Overall uncertainties are about ± 0.002. All the A_γ(θ) data, but primarily those at 16.9 MeV, disagree with predictons based on the phase-shift sets which have been derived previously by way of global analyses of nucleon-nucleon scattering data. Data for the product σ(θ)A_γ(θ) have been fitted with an expansion of the form (sin θ)($\text{a}{}_0\text{+ a}{}_1\text{cos}\text{θ + a}{}_2\text{cos}{}^2\text{θ)}$. For the first time the need for a non-zero a₂ has been illustrated for energies below 20 MeV. This parameter is shown to be related to the nucleon-nucleon F-state spin-orbit phase parameter. In addition, the P, D, and F spin-orbit phase parameter values derived from the present data differ significantly from the ones based on the Yale-IV and Liver-more-X global analyses. The derived D and F spin-orbit phase parameters also differ from those obtained in the recent analysis of nucleon-nucleon scattering data by Arndt et al.     

Near 90° scattering in the channels K̄°p → π+Λ°, K̄°p → π+Σ° and KL°p → KS°p from 1.0 to 7.5 GeV/c

Differential cross sections for center of mass scattering angles near 90° are presented for the reactions $\text{K}\text{?}\text{°}\text{p}\text{→ π}{}^{\mathrm{+}}\text{Λ°}$, $\text{K}\text{?}\text{°}\text{p}\text{→ π}{}^{\mathrm{+}}\text{Σ°}$ and K_L°p → K_S°p in the momentum interval 1.0 to 7.5 GeV/c. The energy dependences of these cross sections are found to be equally well described by the parameterization: $\text{(}\text{d}\text{σ}\text{d}\text{Ω}\text{)}{}_{\mathrm{90°}}\text{∞ s}{}^{\mathrm{?2}}$ or $\text{(}\text{d}\text{σ}\text{d}\text{Ω}\text{)}{}_{\mathrm{90°}}\text{∞}\text{exp}\text{(? bp}{}_{\mathrm{\perp }}\text{)}$.     

Elastic scattering slope and total cross section relations

The empirical equality of $\text{B}{}^2\text{σ}{}_{\mathrm{<mtext>t</mtext>}}$ is noted, for the pomeron terms in NN, πN, KN, ?N, ωN, and φN scattering, where B is the elastic slope parameter and σ_t is the total cross section. This ratio increases slowly with energy, but remains the same in all channels. This is equivalent to a relation between the diffractive interaction radii and opacities; the opacity scales with the square of the radius. We conjecture that this systematics extends to ψN scattering. We contrast $\text{B}{}^2\text{σ}{}_{\mathrm{<mtext>t</mtext>}}$ universaility with the slope predictions of an f-coupled pomeron model. Some other predictions of the f-dominance hypothesis are tested against data.     

Noncoplanar correlation spectra from the 2H(p, 2p)n reaction at Einc = 44.9 MeV

The differential cross section $\text{d}{}^3\text{σ/}\text{d}\text{Ω}{}_3\text{d}\text{Ω}{}_4\text{d}\text{E}{}_3$ for the ²H(p, 2p)n reaction at E_inc = 44.9 MeV is measured in noncoplanar geometry. The Amado model in general gives a good fit to the absolute cross section. The dependence of the cross section on the momentum of the undetected particle Q₅, on the scattering angle θ₃₄, as well as on the angle of the undetected particle is investigated.     

Final state interactions in deuteron breakup by protons at 585 and 800 MeV

Neutron-proton final state interactions (FSI) were observed in the deuteron breakup reaction ²H(p, 2p)n-via a kinematically complete experiment at incident proton energies of 585 and 800 MeV. Kinematic conditions were chosen which allowed the final state proton and neutron to have small relative energies; data were taken at four proton c.m. scattering angles at 800 MeV, ranging from 71° to 119° and at 94° and 106° at 585 MeV. The data are analyzed in terms of the Goldberger-Watson formalism for final state interactions, and the individual contributions of the ¹S₀ and ³S₁ np states are determined. The ${}^3\text{S}{}_1{}^1\text{S}{}_0$ ratio is large, as expected from some reaction models. The ratio of ³S₁ (almost elastic) to pd elastic cross sections is in good agreement with FSI analysis.     

Evidence of a rise in the antiproton-proton total cross section at the CERN intersecting storage rings

We measured the total cross section for $\text{p}$p scattering at $\text{s}\text{= 52.8}\text{GeV}$ at the CERN ISR, using the direct, total-rate method. The result obtained, $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p}\text{) = 44.70 ± 0.53}\text{mb}$, shows that, in common with σ_tot(pp), this cross section also starts to rise in the ISR energy range. We remeasured the total cross section for pp scattering at the same energy, obtaining σ_tot(pp) = 43.26 ± 0.33 mb, and found for the difference, $\text{Δσ}{}_{\mathrm{<mtext>tot</mtext>}}\text{= σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p}\text{) ? σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{pp}\text{)}$, a value of 1.44±0.45 mb.     

Proton capture by 11B above the giant resonance

The cross sections for proton capture by ¹¹B to the ground and excited states of ¹²C have been measured in the proton energy interval between 18 and 43 MeV. The ground-state cross section shows good agreement with theoretical calculations including correlations. Capture photons have also been observed to all the residual 1p-1h states of ¹²C having a dominant $\text{1}\text{p}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ hole: the corresponding cross sections systematically show a giant resonance whose energy increases with the increasing excitation energy of the “background” level. The resonances at 27.4, 31, 33.2, 37 and 43 MeV, seem to show observable interference effects.     

Neutral current and the nuclear scattering of reactor antineutrinos

Expressions are derived for evaluating the integrated inelastic cross section, $\text{}\text{?}\text{gs}{}_{\mathrm{v}}$, for the nuclear scattering of reactor antineutrinos in terms of experimentally determined B(Ml) values and Gamow-Teller matrix elements. These expressions are used to compute $\text{}\text{?}\text{gs}{}_{\mathrm{v}}$ for many nuclear transitions.     

Proton-proton bremsstrahlung and the 2H(p, 2p)n reaction at 51.8 MeV

Proton-proton bremsstrahlung cross sections were measured at 33°-33° and 8.5°-8.5° with a coplanar symmetric geometry. A comparison between experimental cross sections and theoretical predictions was made. The ²H(p, 2p)n reaction was also investigated at 12.5°–12.5° and 8.5°–8.5°. The cross sections were compared with the values calculated by existing theories.     

On the two body mesonic nucleon-antinucleon annihilations

It has been shown that significant difference between cross section for the reaction $\text{p}\text{?}\text{p → K}{}^0{}_{\mathrm{S}}\text{K}{}^0{}_{\mathrm{S}}$ in hydrogen and in deuterium as well as the suppression of this reaction in hydrogen relative to the process $\text{p}\text{?}\text{p → K}{}^0{}_{\mathrm{S}}\text{K}{}^0{}_{\mathrm{L}}$ may be explained by interference of two quasi-nuclear mesons. Existence of these mesons results in large cross sections for the processes $\text{p}\text{?}\text{p → 2π°}$ and $\text{p}\text{?}\text{p → π°η°}$.     

Neutron-proton elastic scattering at 325 MeV

Accurate measurements of the P and D_T parameters in np elastic scattering at 325 MeV resolve a major ambiguity in the phase shift analysis. The mixing parameters $\text{ε}{}_1\text{= 8.4 ± 0.6°}$ and $\text{ε}{}_3\text{= 7.2 ± 0.4°}$ are particularly well determined, and in good agreement with theoretical expectations.     

The γ-decay of the 1g92 and 2p inner-hole states in 111Sn via the 112Sn(3He, αγ) reaction at 32 MeV

The γ-decay of the deeply-bound hole states in ¹¹¹Sn has been investigated at 32 MeV incident energy by means of the ¹¹²Sn(³He, αγ) reaction. The α-particles emitted near 0° were detected in a Si counter located at the image plan of the superconducting solenoidal spectrometer SOLENO. The γ-rays in coincidence with the α-particles were detected by two Ge(Li) detectors located at 90° and 142° with respect to the beam direction, respectively. Energies, spins and decay schemes have been established for the low-lying states up to 2.5 MeV excitation energy in ¹¹¹Sn. The γ-decay of the broad bump, located around 4.2 MeV and previously attributed to neutron pick-up from the inner $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{,}\text{and}\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ neutron. Subshells, reveals the importance of quasiparticle-phonon m the spreading mechanism of the inner-hole strengths. The $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and 2p strength functions have been deduced from the α-decay of the enhanced structures (3 ≦ E_x≦ 8 MeV). They are compared to the ones measured in previous inclusive neutron pick-up experiments and to those calculated in the framework of the quasiparticle-phonon nuclear model.     

Excitation function of giant resonances as doorway states in the 12C(p, p′)12C1 reaction between 19 and 23 MeV

Differential cross section and analyzing power angular distributions for the elastic scattering and inelastic scattering to the 2⁺ state at 4.44 MeV and the 1⁺ state at 12.7 MeV have been measured at incident proton energies varying from 19.15 to 23.34 MeV in 200 keV steps. Elastic scattering data are analyzed using an averaged optical model. Coupled-channel calculations reproduce roughly the 2⁺ data. The rapid variation of the data concerning the 1⁺ state is explained by virtual excitation of giant resonances. For each value of the incident energy, the coupling strength for each resonance is found by fitting the experimental angular distributions. The analysis assuming a weak coupling in the compound system gave a satisfactory fit to the cross section but a poor reproduction of the analyzing power. The assumption of a strong coupling in the ¹³N system allowed a good fit of all data. The angular distributions are dominated by the E1 resonance, whose $\text{1}\text{2}{}^{\mathrm{+}}$ component exhausting more than 37 % of the energy weighted sum rule, explains the isotropy of the cross section below 22 MeV. A $\text{7}\text{2}{}^{\mathrm{+}}$ resonance (15 % EWSR) is located at 19.9 MeV. The $\text{5}\text{2}{}^{\mathrm{?}}$ resonance with its maxima at 20.2 and 21.4 MeV, exhausts about 18 % of the sum rule, which is in good agreement with the results of previous works.