Structure ofO16

Abstract

sion neutrons has little effect on the shape of the distribution. Fine details in the behavior of V(A) may be obscured by the dispersion in mass. The result of v(A) for Pu 239 + wt n 9 is shown for comparison with the U 238 results. The fissioning nuclei are similar and the difference in the two curves is presumably mainly due to the difference in excitation energy. The difference in v(A) seems to be much larger for the heavy fragments than for the light fragments. Figure 3 shows V(A) plotted for groups of "reduced" total kinetic energies Eg defined by £% = EK(239/2) 2 /(239-A)A. V(A) is shown for groups of "reduced" total kinetic energy £% rather than the uncorrected kinetic energy Ej^ in order to eliminate to a first approximation the effect of the charge division (as correlated with the mass division) on the variation of the total kinetic energy. Britt, Wegner, and Gursky 10 have found that in medium-excitation fission the average Ej( (they use a parameter called "scission distance" which is inversely proportional to E^) is lower for events in the symmetric mass region than for events in the asymmetric region and have suggested that the symmetric fission events appearing in medium-excitation fission are due to a second "fission mode" not influenced by shell structure of the fragments and occurring with increasing yield as the excitation energy increases.The graph for high values of EK [ Fig. 3(a)] shows very strong variations in number of neu-We wish to present a model which gives a good description of the energy spectra of O 16 and neighboring nuclei. An outstanding property of O 16 is the coexistence of low-lying states with so widely divergent characteristics that they have hitherto been described by unrelated models, e.g., developments of the spherical shell model using the particle-hole picture for negative parities 1 and trons as a function of mass and very asymmetric mass distribution, whereas the sawtooth behavior becomes less pronounced as Ej£ decreases and the symmetric mass yield increases [Figs. 3(b) and 3(c)]. For very low Ej£ there is no minimum of V{A) at A = 130; this function increases smoothly in the symmetric mass region between A = 115 and A -140 as also observed by Schmitt and Konecny 3 in the symmetric mass region of Ra 226 .

Isospin Mixing in Light Nuclei

“…These give similar and probably fairly accurate descriptions of the relevant T = 1 states. More elaborate calculations involving IPl/2' Id s/2 and 2s 1/2 orbits (Zuker et al 1968;Reehal and Wildenthal 1973) give coefficients of O· 8-0' 9 for the Ip-Ih components of these states, and a similar value for the Ip-2h component of the 15N ground state. Likewise Ip-lh coefficients of about 0·8 are given for the lowest 0-, 1 -, 2-and 3 -, T = 0 states (and these include the 10·95 MeV 0-state); however, the coefficients for the second lowest 1 -, 2 -and 3 -, T = 0 states, which we identify with the states of interest here, are '" 0·4.…”

Asymptotic normalization coefficients and continuum coupling in mirror nuclei

“…For sd-shell nuclei, we took the ZBM effective interaction [43] between valence nucleons outside the 12 C core. The continuum-coupling term (37) was approximated by means of the Wigner-Bartlett contact interaction:…”

Evidence for Two-step Processes in Photonuclcar Reactions

“…However, using Zuker's wave functions (Zuker et al 1968;Zuker 1969) we note the interesting fact that the overlap of the 19F ground state wave function with that of 15N* (5·27 MeV) plus an a particle is large; the Zuker wave functions give a lower limit of 0·2. This nonzero overlap suggests a two-step model of the reaction mechanism in which the incident photon is absorbed by a nucleon which then is reabsorbed and scatters from an (X-particle cluster, the latter being emitted.…”

“…The first requires the presence in the 15N ground state wave function of configurations of the type (IP3(2)8 (lP1(2)1 (ld)2 or (1 P3(2)8 (lP1/2/ (2S1(2)2. According to Zuker et al (1968) and Zuker (1969), the intensity of the former configuration in the 15N ground state wave function is approximately 20%.…”

“…The dipole states of 19F must then have wave functions which are admixtures of the 19F ground state wave function modified by: (i) the excitation of one s-d nucleon to the 2p-If shell, or (ii) the excitation of one Ip nucleon to the 2s-ld shell. The wave functions of the dipole states so formed, and of an a particle plus the 15N (5·27 MeV) state, with its wave function as given by Zuker et al (1968) and Zuker (1969), are orthogonal. Since the 15N (5·27 MeV) state wave function consists of components with two and four holes in the 1 p shell, and we demand that the nucleons constituting the emitted a particle be in a relative s state before emission, the overlap integral described must be zero.…”