A sample of ${\mathrm{Ta}}_{2}$${\mathrm{O}}_{5}$ containing 151 mg of Ta enriched to 5.47% in $^{180}\mathrm{Ta}^{\mathrm{m}}$ was counted in a well-type high-purity Ge detector. This was enclosed in a large NaI(Tl) detector operated in anticoincidence to reduce the cosmic-ray continuum background. Several runs of \ensuremath{\sim}100 days each were made under different conditions to search for \ensuremath{\gamma}-ray singles or summing peaks that would follow the electron capture decay of $^{180}\mathrm{Ta}^{\mathrm{m}}$ to $^{180}\mathrm{Hf}$ or the ${\ensuremath{\beta}}^{\mathrm{\ensuremath{-}}}$ decay to $^{180}\mathrm{W}$. Lower limits derived were ${T}_{1/2}$>3.0\ifmmode\times\else\texttimes\fi{}${10}^{15}$ yr, log${f}_{0}$t>22.9 for electron capture decay and ${T}_{1/2}$>1.9\ifmmode\times\else\texttimes\fi{}${10}^{15}$ yr, log${f}_{0}$t>21.3 for ${\ensuremath{\beta}}^{\mathrm{\ensuremath{-}}}$ decay. The total half-life of $^{180}\mathrm{Ta}^{\mathrm{m}}$ is therefore ${T}_{1/2}$>1.2\ifmmode\times\else\texttimes\fi{}${10}^{15}$yr.
Particle production in proton-induced reactions at 14.6 GeV/c on Be, Al, Cu, and Au targets has been systematically studied using the E-802 spectrometer at the BNL-Alternating Gradient Synchrotron. Particles are measured in the angular range from 5\ifmmode^\circ\else\textdegree\fi{} to 58\ifmmode^\circ\else\textdegree\fi{} and identified up to momenta of 5, 3.5, and 8 GeV/c for pions, kaons, and protons, respectively. Mechanisms for particle production are discussed in comparison with heavy-ion-induced reactions at the same incident energy per nucleon.
In order to study the mechanism of a simple spallation reaction induced by GeV-energy protons, measurements were made of the momentum properties of ${\mathrm{Na}}^{24}$ nuclei produced from an aluminum target. Data were obtained on: (1) the fraction of ${\mathrm{Na}}^{24}$ nuclei recoiling out of targets thick with respect to the range of the recoils (the targets were oriented both perpendicular and parallel to the proton beam); (2) the distribution of ${\mathrm{Na}}^{24}$ ranges from a thin target measured with plastic catchers subtending an angle of $2\ensuremath{\pi}$; (3) the angular distribution of the ${\mathrm{Na}}^{24}$ recoils with respect to the beam. Results of Monte Carlo knock-on cascade and evaporation calculations for 0.36- and 1.8-GeV bombarding energies are compared with the data in the laboratory system. The calculations predict sharper sideways peaking in the angular distributions, and more momentum deposition at the higher bombarding energy, than are observed. The experimental data are also reduced to a set of velocity vectors which is then interpreted in terms of a simple, constant-deposition-energy mechanism in which the incident proton makes only one quasi-elastic collision with a single nucleon which does not escape from the nucleus. This treatment accounts for most of the data but also predicts a much larger sideways peaking in the angular distribution than is observed.
Relative yields of 35 products extending from $^{7}\mathbf{Be}\mathbf{to}$ $^{67}\mathrm{Ga}$ have been measured for the interaction of 25-GeV (2.1-GeV/amu) $^{12}\mathrm{C}$ ions with Cu. For purposes of comparison, cross sections of 48 nuclides produced by the irradiation of Cu with 28-GeV protons are also reported. The mass yield curve deduced for the 2.1-GeV/amu $^{12}\mathrm{C}$ ions is very similar to that reported for 0.28-GeV/amu $^{14}\mathrm{N}$, which implies that there is little energy dependence of target fragmentation cross sections in this energy range where meson production effects in nucleon-nucleon collisions become important. Charge dispersion curves for products with $37\ensuremath{\le}A\ensuremath{\le}64$ are the same within errors for $^{12}\mathrm{C}$ and protons. Compared with 28-GeV protons, the mass yield curve for $^{12}\mathrm{C}$ shows some favoring of products near the target (possibly due to increased secondary effects). Formation of light fragments such as $^{7}\mathrm{Be}$ and $^{24}\mathrm{Na}$ is significantly enhanced possibly due to highly damaging central collisions of the heavy ions. The results are discussed in terms of the concepts of limiting fragmentation and factorization.NUCLEAR REACTIONS Cu($^{12}\mathrm{C}$, spallation), $E=25$ GeV; measured relative $\ensuremath{\sigma}(A,Z)$, 35 products $^{7}\mathrm{B}\mathrm{e}\ensuremath{-}$ $^{67}\mathrm{Ga}$. Cu $p$, spallation), $E=28$ GeV; measured $\ensuremath{\sigma}(A,Z)$, 48 products $^{7}\mathrm{B}\mathrm{e}\ensuremath{-}$ $^{67}\mathrm{Ga}$. Natural targets, Ge(Li) detectors, radiochemistry.
The angular distribution of ${\mathrm{Na}}^{24}$ nuclei produced by bombardment of thin bismuth targets with 2.9-GeV protons has been measured. The forward-to-backward ratio in the laboratory system was found to be 1.52\ifmmode\pm\else\textpm\fi{}0.06. Differential range curves for the ${\mathrm{Na}}^{24}$ nuclei have been obtained at angles of 15, 90, and 165\ifmmode^\circ\else\textdegree\fi{}, with respect to the beam direction. The mean energy of emission at 90\ifmmode^\circ\else\textdegree\fi{} is 47 MeV with a full width at half-maximum of 40 MeV. The mean is only 60% of the energy expected from Coulomb repulsion. Velocity spectra at 15 and 165\ifmmode^\circ\else\textdegree\fi{} are nearly identical to the 90\ifmmode^\circ\else\textdegree\fi{} spectrum linearly shifted by \ensuremath{\approx} 10% to higher and lower velocities, respectively. From the analysis of the angular distribution and the range data, we conclude that there is no moving system in which both the angular distribution and velocity spectra of the ${\mathrm{Na}}^{24}$ nuclei are symmetric about the direction perpendicular to the beam. This indicates that this typical fragmentation product is produced by a direct (rapid) process and not by the usual fast nucleonic cascade followed by a slower de-excitation step.
Semi-inclusive spectra of ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{\ifmmode\pm\else\textpm\fi{}}$, and p have been measured near midrapidity for central collisions of 14.6A-GeV/c $^{28}\mathrm{Si}$ with $^{197}\mathrm{Au}$ nuclei. The invariant cross sections are all well fit by exponential distributions in transverse mass, within the measured ranges. The \ensuremath{\pi} and K cross sections can also be fit by Boltzmann distributions. From integrated yields, at midrapidity, the kaon/pion yield ratios are (19.2\ifmmode\pm\else\textpm\fi{}3)% for ${K}^{+}$/${\ensuremath{\pi}}^{+}$ and (3.6\ifmmode\pm\else\textpm\fi{}0.8)% for ${K}^{\mathrm{\ensuremath{-}}}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$; the ${\ensuremath{\pi}}^{+}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ ratio is 1.00\ifmmode\pm\else\textpm\fi{}0.04.
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