Results are tabulated of the radioactivities produced by 4 Mev protons in targets of 7N, gO, 2oCa, 24O, 27C0, 3oZn, 34Se, 42M0, 46Pd, 48Cd, 49ln. In most cases the reactions are of the p-n type, and lead to isotopes which emit either + or -electrons. A detailed study was made of O, Zn and Se. The reaction 0 18 (p,n)F 18 (107 min.) shows a threshold at 2.56 Mev and a positron energy of 0.74 Mev in good agreement with the energy relations. The cross section for the reaction at 4 Mev is about 2X10 -25 cm 2 and there is a resonance maximum at 3.55 Mev. The cross section for the reaction 0 16 (p,y)F 17 is 4000 times smaller. The isomeric Br 80 periods (17.4 min. and 4.45 hr.) are observed in the reaction Se 80 (p,n)Br 80 . At 4 Mev the ratio of the short to long period activities for infinite bombardment is about 15 but the thresholds are at about 3.0 and 3.2 Mev, respectively. The cross section for the reaction is about 0.6 X 10~2 6 cm 2 at 4 Mev.
Proton Induced Radioactivity in OxygenAs previously reported 1,2 a large number of elements are found to become radioactive under bombardment by protons of energies up to 3.8 Mev. Two periods have been definitely established for oxygen, using targets of quartz and other solid oxides as well as a platinum foil in oxygen. The short period of 1.28±0.10 min. is at once identified with the well-known F 17 formed by the capture of a proton by O 16 . The activity becomes detectable at a proton energy of 1.4 Mev rising rapidly to about 3 Mev and then more slowly (thick target).The second period of 107±4 min. is shown by chemical separation to be due also to an isotope of fluorine and is close to the 112 min. period found by Snell 3 for F 18 . This period must be attributed to the reaction Fi8-^o i8 -f-e + .
P REVIOUSLY, it was shown 1 that C -N reactions can also explain the energy generation of the two well-known giant stars, Capella A and t Aurigae K, if they are built on the Gamow shell-source model, 2 and that in their envelopes the hydrogen content must be ^35 percent by weight if helium is neglected. Based on this chemical composition and the C -N reactions, possible structures of stars, which have given masses, 8 MQ and MQ, but dehydrogenized isothermal cores of various masses have been investigated.Under widely different assumptions as to luminosity, L, and radius, R, the usual four equations of stellar equilibrium 3 for p (pressure), T (temperature), M(r) (mass inside the radius r), and L{r) (energy flow across the surface of radius r) are numerically integrated inward. The following assumptions are made: In the envelopes the hydrogen content is 35 percent and the remainder is a Russell mixture which contains 1 percent of carbon and nitrogen, while in the cores hydrogen is replaced by helium; for the mean molecular weight, n, and the opacity, values tabulated by Strongren 4 and Morse 6 are used; in the convective regions, temperature gradients are given by the formula of an adiabatic change of matter and radiation. 3 Values of p, T } and M(r) at the points where L{r) vanishes are compared with those of the Emden solutions of the isothermal cores. Here, it is convenient to use the functions U, F, and \j/ (measure of electron degeneracy), which determine the core's solutions apart from the homologous transformations, defined bywhere p, p g , and /u e are density, gas pressure, and mean molecular weight of the electron, respectively. In our case, suitable conditions for the outer and inner solutions are given by the continuity of U/p, V/fi, and ^-f-logeC/WV). Appropriate solutions thus obtained by interpolation determine L, R, and internal conditions of stars in a series of one parameter ^c > the value of ^ at the center. The results are similar for the two masses as shown in Figs. 1 and 2. Calculated ranges of tp e are from -5.4 to +23.3 for 8 MQ and from -2.3 to +11.5 for MQ. They correspond to slight increases of the core's temperatures, from 3.5 X10 7 to 5.2X10 7°K for 8MQ and from 2.1 X10 7 to 2.4X10 7°K for Mo, and large increases of the central densities, from 10 to 5.1 X10 5 g/cm 3 for 8 M 0 and from 1.5X10 2 to 5.5X10 4 g/cm 3 for M Q. For minimum values of \p e > the core's masses M* are nearly zero and the stars lie within the main sequence. L and R increase with \j/ e when ^c<0 (perfect gas state), and then •-o 0 / / / / Mo -__ -__8M^^ --^^ __ FIG. 1. Luminosity-radius relations for stars of masses, 8 M Q and M Q.change abruptly when ^c-0 (incipient degeneracy). Further increases of \j/ c (strong degeneracy) give rapid increases of R, while increases of M* are relatively small and consequently the Eddington's relation L^R~* is approximately satisfied. Together with the earlier results, 1 these will give the general features of giants of any mass. Further, from their observed distribution and the ...
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