Curves Of Reactions Research Articles

Isomerism ofIn110andIn112

The decay of ${\mathrm{In}}^{110}$ and ${\mathrm{In}}^{112}$ has been investigated with the aid of beta-ray spectrometer and coincidence measurements. From the half-life 20.7\ifmmode\pm\else\textpm\fi{}0.3 min and the $\frac{K}{(L+M)}$ ratio 3.7\ifmmode\pm\else\textpm\fi{}0.4, the 155\ifmmode\pm\else\textpm\fi{}1-kev isomeric transition in ${\mathrm{In}}^{112}$ is identified as $M3$. The 14.5\ifmmode\pm\else\textpm\fi{}1-min ground state emits an allowed negatron spectrum of 656\ifmmode\pm\else\textpm\fi{}6 kev and an allowed positron spectrum of 1.52\ifmmode\pm\else\textpm\fi{}0.05 Mev. Even parity and spins of 4 and 1 are assigned to the two states. The 66-min ground state of ${\mathrm{In}}^{110}$ decays by emission of an allowed positron spectrum of 2.25\ifmmode\pm\else\textpm\fi{}0.02 Mev to the 657-kev level of ${\mathrm{Cd}}^{110}$. The electron capture from the $4.9\ifmmode\pm\else\textpm\fi{}0.2\ensuremath{-}h$ isomeric state is followed by the known 884, 937, and 657-kev gamma-rays in ${\mathrm{Cd}}^{110}$. Even parity is assigned to both levels. Conversion lines, with $\frac{K}{(L+M)}=4.5\ifmmode\pm\else\textpm\fi{}1$ indicate an additional gamma-ray of 121 kev which may be the isomeric transition having a branching ratio of about 0.6 percent. It would have to be an $M3$ transition with an abnormally long (factor ${10}^{3}$) half-life. The existence of the ${\mathrm{In}}^{110}$ isomer is shown to remove several difficulties in the interpretation of the excitation curves of the alpha-particle reactions with silver.

Gamma-Neutron Reactions in Fluorine

The cross-sectional curves for the reactions ${\mathrm{F}}^{19}(\ensuremath{\gamma},n){\mathrm{F}}^{18}$ and ${\mathrm{F}}^{19}(\ensuremath{\gamma},2n){\mathrm{F}}^{17}$ have been determined by measurement of the induced positron activities. The ($\ensuremath{\gamma},n$) cross-sectional curve rises almost vertically from the threshold to a value of about 2 mb, remains constant for about 3 Mev, and then increases again to a maximum value of 3.48 mb at 20 Mev. The ($\ensuremath{\gamma},2n$) cross-sectional curve has a peak value of 0.66 mb at about 26 Mev. The integrated cross sections for the ($\ensuremath{\gamma},n$) and ($\ensuremath{\gamma},2n$) reactions are 0.039 and 0.0024 Mev-barns, respectively. However, the ($\ensuremath{\gamma},2n$) reaction is evaluated only up to its peak position at 26 Mev. A new value of 60\ifmmode\pm\else\textpm\fi{}1 seconds is reported for the ${\mathrm{F}}^{17}$ activity.

The Theory of Excitation Functions on the Basis of the Many-Body Model

The theory of transmutation functions for charged particles is examined in the light of recent developments in nuclear theory. It is found that ignoring all factors besides the penetrability of the incident particle is justifiable only for processes without effective competition. For these, the usual applications of the Gamow-Condon-Gurney theory must be modified to include the influence of incident particles with nonvanishing orbital momentum which causes a continued rise of the yield for energies greater than the Coulomb barrier. For processes subject to effective competition, the comparative density of residual states available to each alternative process is important in determining relative yields. The densities of the states are calculated on the basis of the liquid drop model for the nucleus and a table is obtained giving the relative probabilities of neutron and charged particle emissions. The overwhelming factor in favor of neutron emission by heavy nuclei seems to be confirmed by experiment. The shape of an excitation curve expected for the less probable of two processes is shown. Finally the effect of selection rules in the yield curves of reactions involving very light nuclei is considered. Special cases are discussed.

LI. A method of obtaining general reaction-velocity curves for complete homogeneous gas reactions at constant pressure

LI. <i>A method of obtaining general reaction-velocity curves for complete homogeneous gas reactions at constant pressure</i>