Cross sections were measured at five angles for alpha-particle groups from the reaction $^{12}\mathrm{C}(^{16}\mathrm{O}, \ensuremath{\alpha})^{24}\mathrm{Mg}$. The measurements were made with 40-50-keV resolution over energy intervals as long as 9.9 MeV (c.m.). The data provided large samples for fluctuation analyses over compound-nucleus excitation energies from about 25 to 35 MeV. The average coherence width, which is dominated by compound states with $J\ensuremath{\sim}10$, was found to be about 118 keV. It does not vary significantly with exit channel, angle, or excitation energy in the compound nucleus. Most of the data are well represented by the simple Ericson-Brink-Stephen statistical model and show no significant direct-interaction component. A pronounced peak appearing in several of the excitation functions near 31.8-MeV bombarding energy is not consistent with this model.
Angular distributions for a number of $\ensuremath{\alpha}$-particle groups from $^{12}\mathrm{C}(^{16}\mathrm{O}, \ensuremath{\alpha})^{24}\mathrm{Mg}$ were measured with 45-keV resolution at closely spaced energies centered on bombarding energies of 19, 31, 42, and 49 MeV. Fluctuations of the type described by Ericson were observed. The data near 31 MeV were extensive enough to permit a statistical analysis. Compound levels with spins of about 10 are predominant at this energy. The average coherence width is about 125 keV and is independent of angle. No finer structure was found when the energy resolution was reduced to 15 keV. The strength of the fluctuations is generally in agreement with the expectation for a pure compound-nucleus process, though some anomalies were discovered. The coherence angle is about 6\ifmmode^\circ\else\textdegree\fi{}, in agreement with expectation based on the size of the nucleus and the wave number. The angle-integrated average cross sections near 31 MeV are proportional to the statistical weights of the final levels.
Angular distributions for a number of $\ensuremath{\alpha}$-particle groups from $^{12}\mathrm{C}(^{16}\mathrm{O}, \ensuremath{\alpha})^{24}\mathrm{Mg}$ were measured with 45-keV resolution at closely spaced energies centered on bombarding energies of 19, 31, 42, and 49 MeV. Fluctuations of the type described by Ericson were observed. The data near 31 MeV were extensive enough to permit a statistical analysis. Compound levels with spins of about 10 are predominant at this energy. The average coherence width is about 125 keV and is independent of angle. No finer structure was found when the energy resolution was reduced to 15 keV. The strength of the fluctuations is generally in agreement with the expectation for a pure compound-nucleus process, though some anomalies were discovered. The coherence angle is about 6\ifmmode^\circ\else\textdegree\fi{}, in agreement with expectation based on the size of the nucleus and the wave number. The angle-integrated average cross sections near 31 MeV are proportional to the statistical weights of the final levels.
The internal conversion electron and gamma-ray spectra due to proton-induced reactions with separated zinc isotopes 67, 68 and 70 have been measured at various incident beam energies between 1.5 and 5.0 MeV. Many lines seen in the spectra are attributed to transitions in the gallium isotopes produced by the Zn(p, n)Ga reaction. The transition energies together with other available data have been used to assign energy levels in 67Ga at 0.166, 0.356, 0.820, 0.910, 1.25, and 1.55 MeV; in 68Ga at 0.174, 0.316, 0.373, 0.510, 0.573, 0.828, 0.879 and 1.10 MeV; and in 70Ga at 0.188, 0.448, 1.03 and 1.66 MeV. Threshold measurements confirmed the existence of levels at 0.174, 0.316, 0.373, and 0.510 MeV in 68Ga.
The angular distribution of particles emitted in the statistical decay of a compound nucleus will show forward-backward peaking if the angular momentum available in the final system is limited. Furthermore, the decay will not be independent of the mode of formation. These effects were demonstrated by measurements of the energy and angular distributions of alpha particles emitted from reactions of $^{14}\mathrm{N}$ with $^{16}\mathrm{O}$, $^{23}\mathrm{Na}$, and $^{27}\mathrm{Al}$ at about 27 MeV. The angular distributions were analyzed by the semiclassical theory of Ericson and Strutinski to determine the spin cutoff parameter $\ensuremath{\sigma}$, or equivalently the moment of inertia $\mathcal{I}$. The values of $\ensuremath{\sigma}$ ranged from 2.6 for the residual nucleus $^{26}\mathrm{Al}$ to 3.5 for $^{37}\mathrm{Ar}$. The moment of inertia was approximately 0.9 ${\mathcal{I}}_{\mathrm{rigid}}$. The energy dependence of the level density was determined from the energy spectra. With the simple form $\mathrm{exp}[2{({a}_{1}E)}^{\frac{1}{2}}]$, good fits were obtained with ${a}_{1}\ensuremath{\approx}\frac{A}{10}$ for the two heavier residual nuclei. The data did not distinguish between this expression and the form ${E}^{\ensuremath{-}2}\mathrm{exp}[2{({a}_{2}E)}^{\frac{1}{2}}]$; equally good fits were obtained with ${a}_{2}\ensuremath{\approx}\frac{1}{6}A$.
Rapid fluctuations were observed in the excitation functions at two angles for C12(O16, α)Mg24 reactions involving the low-lying states of Mg24. The energy resolution in the entrance channel was 45 keV. The fluctuations were found at compound-nucleus excitation energies of about 25 and 30 MeV. At 30 MeV they were as strong as at 25 MeV. The statistical theory of Ericson was applied and autocorrelation functions were used to determine the width of the fluctuations. The average width, ≈ 116 keV, corresponds to a compound-nucleus lifetime of 0.57 × 10−20 sec. Cross correlations between different transitions are usually small, as predicted by the theory. Upper limits on the non-compound cross section are given for the ground-state transition. A comparison is made with Al27(p, α)Mg24 results at the same angles and energies in the light of the statistical theory. Other possible interpretations of the experimental data are discussed.
Rapid fluctuations were observed in the excitation functions at two angles for C/sup 12/(O/sup 16/, alpha )Mg/sup 24/ reactions involving the low- lying states of Mg/sup 24/. The energy resolution in the entrance channel was 45 kev. The fluctuations were found at compound-nucleus excitation energies of about 2 plus or minus and 30 Mev. At 30 Mev they were as strong as at 2 plus or minus Mev. The statistical theory of Ericson was applied and autocorrelation functions were used to determine the width of the fluctuations. The average width, approximately 116 kev, corresponds to a compound-nucleus lifetime of 0. plus or minus 7 x 10/sup -20/ sec. Cross correlations between different transitions are usually small, as predicted by the theory. Upper limits on the noncompound cross section are given for the ground state transition. A comparison is made with Al/sup 27/(p, alpha )Mg/sup 24/ results at the same angles and energies in the light of the statistical theory. Other possible interpretations of the experimental data are discussed. (auth)
The spectra of internal conversion electrons due to Coulomb excited transitions in Au197, the five abundant isotopes of osmium, Th230, 232, and U234, 236, 238 have been obtained with a beta-ray spectrometer of the single-segment “orange” type. Some of experimental problems connected with these measurements are discussed. Reduced transition probabilities have been measured for the first 2+ excited states of all the even nuclei none of which have been investigated heretofore by means of the conversion electrons. For the even isotopes of osmium, some evidence suggesting enhanced internal conversion is found. The quadrupole moments and deformation parameters derived from the reduced transition probabilities agree well with the values obtained in recent theoretical calculations. Evidence for a weak cascade transition between the well-known states at 548 and 279 keV in Au197 has been found, and a level in Os189 at 69.7 keV is confirmed which is identified as the 52− first excited rotational state. Two weak conversion lines in the osmium spectrum believed to be contributed by Os189 are assigned the probable transition energies of 194 and 245 keV.
The internal conversion spectra from Th/sup 232/ and U/sup 238/ bombarded with 6-Mev protons were examined for EOenhanced transitions between 2/ sup +/' beta -vibrational and 2/sup +/ first-excited rotational states. For U/ sup 238/ the 991-kev transition is assigned at the EO-enhanced 2/sup +/ yields 2/sup +/ cascade from the 1036-kev beta -vibrational state, and for Th/sup 232/ both the strong monopole-enhanced 725-kev and wesk 738-kev transitions are assigned as 2/sup +/' yields 2/sup +/ from 775kev beta - and 788-kev gamma - vibrational states, respectively. The various transition probabilities are calculated for testing theories of monopole enhancement. (D.L.C.)
