Absolute cross sections were measured for elastic scattering of 9Be on 9Be at lab energies of 5, 9, 12 and 16 MeV. These differential cross sections were fit with a computer code to ascertain optical model parameters. Absolute differential cross sections were measured at lab energies of 5 and 12 MeV for the reactions 9Be[9Be, (p, t, α)]17N, 15N, 14C.
Thick adenine (C6H6N6) targets have been used to investigate the reaction of 6Li ions with 14N. Relative angular distributions at bombarding energies of 5.3, 5.64 and 6.0 MeV have been determined for protons, deuterons and alphas leading to the lower states in 19F, 18F and 16O, respectively. A yield curve was obtained between 4.1 and 6.3 MeV to compare the cross sections at the various energies.
Angular distributions of neutrons from the ${\mathrm{Li}}^{6}({\mathrm{Li}}^{6}, n){\mathrm{C}}^{11}$ reaction have been measured at 4.1-MeV bombarding energy for all bound levels in ${\mathrm{C}}^{11}$ except the ground state. The 6.39-6.41-MeV doublet was not resolved. The angular distributions, generally, agree in relative magnitude and shape with those from analog states in the mirror reaction ${\mathrm{Li}}^{6}({\mathrm{Li}}^{6}, p){\mathrm{B}}^{11}$. This result is most easily understood by assuming that both reactions proceed predominately by compound-nucleus formation. The 8.43-MeV level in ${\mathrm{C}}^{11}$ is observed to decay by $\ensuremath{\gamma}$ emission even though it is unbound to $\ensuremath{\alpha}$-particle emission by 890 keV. This retardation of the $\ensuremath{\alpha}$ decay cannot be understood as being due to the Coulomb barrier alone.
The angular distribution of the ground state alpha particles from the 10B(3He,α)9B reaction has been measured at a bombarding energy of 5.50 MeV. A strong backward peak is observed, suggesting significant contributions from a direct exchange mode. The implications of this result on the possible formation of a low lying positive parity state in 9B are discussed.
uncertainties. The dependence of the experimental values on the energy of the radiated gamma ray and the mass of the radiating nucleus is consistent with both the semiclassical prediction A/sup 2/3/ E/sub gamma //sup 3/ and the recent prediction of the giant-dipole-resonance approximation, A/sup 2/3/ E/sub gamma //sup 5/. Further, if either of these mass-energy factors is removed, the resulting reduced widths are observed to be closely proportional to the spacing of neutron resonances, as predicted by both theories. It thus becomes significant to define an El gamma-ray strength function as the resonance- average value of the partial width divided by the average spacing between neutron resonances and the appropriate energy factor and to study its dependence on the atomic mass of the radiating nucleus. The E1 gammaray strength functions have been constructed according to both proposed energy dependences and are found to follow the predicted mass dependence, although there are suggestions of peaks near the closed neutron shells. The absolute value of the strength function constructed according to the giant-dipole-resonance approximation is in reasonable agreement with the theoretical prediction, but there is violent disagreement in the other case. The implications of this and other aspects of the results are discussed. Since the techniques used to analyze the data are for the most part new, they are dealt with in considerable detail. The pertinent theory and the techniques used to obtain the data are also discussed. (auth)
The Argonne fast chopper has been used to study the neutron resonances of mercury. The neutron transmissions of five samples of normal mercury and six isotopically enriched samples were measured in the energy interval from 10 to 30 000 eV. Twenty-eight resonances were isotopically identified and parameters, including the spin, were determined for most of them. Average values of level spacings, radiations widths, and neutron strength functions were derived from the individual parameters. The spacings and radiation widths exhibit the expected rapid increase as the doubly closed shell is approached. Unexpectedly, the total radiation widths of different resonances of Hg201 are found to fluctuate by a larger factor than has been previously observed in any other nuclear species. The gamma-ray spectra and the multiplicity of gamma rays from capture in these resonances were measured and both quantities were found to differ from resonance to resonance in a way that is consistent with the fluctuations in the widths. Seven high-energy gamma rays were resolved in the capture gamma-ray spectra of three resonances in Hg201. The absolute intensities of the transitions were determined by a least-squares fit of the data to an experimentally determined line shape. It was found that these high-energy transitions are on the average enhanced, relative to those of lower energy, by about a factor of 15 beyond the usual Eγ3 law. The remainders obtained by subtracting the partial widths of the seven high-energy transitions from the total radiation widths are constant, within errors, for the three resonances investigated. This indicates that the fluctuations in the total radiation width are the result of fluctuations in the intensities of the transitions of highest energy. The observed magnitude of the fluctuations is shown to be consistent with that expected from random fluctuations of the partial radiation widths.
The response of a 134″ × 2″ NaI(T1) cylinder to neutrons in the pulse height region between 2.5 and 7 MeV gamma energy equivalent was studied as a function of incident neutron energy for a range of neutron energies between room scattered neutrons and 1.162 MeV. The Li7(p, n) Be7 reaction was used as a source of neutrons since it is relatively free from high energy gamma ray background. Monoergic neutron response curves were obtained for neutron energies of 166 keV, 341 keV, and 469 keV. All other distributions were for proton energies giving rise to two neutron groups. The pulse height distributions were measured for a fixed number of counts of a shielded long counter at each neutron energy. The long counter was calibrated against Ilford C2 emulsions for the case of 1.162 and 0.698 MeV neutrons in order to obtain the neutron flux from the long counter counts. The pulse height distributions are nearly linear between 4 and 6.6 MeV. The extrapolations of these distributions intersect the gamma equivalent axis at approximately the binding energy of the last neutron in I128.
The Argonne fast chopper was used to select the energy of the incident neutrons on the basis of their time of flight. The gamma-ray spectra resulting from capture of these timed neutrons by Mn/sup 55/ were measured with two 4-in. NaI(Tl) scintillators using a fast-slow coincidence technique. The gamma-ray coincidence spectra associated with capture in the resonances at investigation of the low-lying excited state of Mn/sup 56/ was made by means of coincidence measurements on the gamma rays following capture of thermal neutrons. (W.D.M.)
The Argonne fast chopper was used to select the energy of the incident neutrons on the basis of their time of flight. The gamma-ray spectra resulting from capture of these timed neutrons by Mn/sup 55/ were measured with two 4-in. NaI(Tl) scintillators using a fast-slow coincidence technique. The gamma-ray coincidence spectra associated with capture in the resonances at investigation of the low-lying excited state of Mn/sup 56/ was made by means of coincidence measurements on the gamma rays following capture of thermal neutrons. (W.D.M.)
