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An isomeric state in 52 Fe has been located at E x ~ 6.83 ±0.25 MeV with the reaction 40 Ca( 14 N,/w) 52 Fe. The state decays by positron emission to the (11 + ) 3.837-MeV state of 52 Mn with T 1 / 2 = 56 ±8 sec. The probable spin and parity of the isomer is 12 + .It is well known that residual interactions acting within the ground-state shell-model configuration can produce long-lived "spin-gap" isomers at high excitation with unusual decay properties. For example, theJ 7r =^" isomers at E x = 3.1 MeV in the mirror nuclei 53 Fe and 53 Co decay by £4, M5, and E6 y-ray transitions 1 (T 1/2 = 2.5 min) and by combined proton-/3 + emission 2 (T 1/2 = 242 msec), respectively. Up to now, however, the only reported example of this phenomenon in an even-even nucleus is the 45-sec a?-decaying state at 2.93 MeV in 212 Po. 3 ' 4 This Letter reports the observation of an isomeric state analogous to that in 212 Po at 6.83 ±0.25 MeV excitation in theiV=Z nucleus 52 Fe. The state decays by /3 + emission (T 1/2 = 56 ±8 sec) and evidently has J" = 12 + , the maximum spin attainable in the (/ 7 / 2 )" 4 configuration. The 52 Fe isomer, as well as the absence of isomerism 5 in the conjugate nucleus 44 Ti, can be accounted for by shell-model calculations based on the (f 7/2 T 2 spectra of 54 Co and 42 Sc, respectively.The 52m Fe activity was first observed in the course of delayed-)3-y coincidence experiments designed to study proton-rich nuclei in the/ 7/2 shell. A natural calcium target ~2 mg/cm 2 thick evaporated onto a gold backing was bombarded with 46-MeV 14 N ions from the Stony Brook FN Van de Graaff accelerator. A slotted rotating wheel periodically interrupted the incident beam and provided a signal to enable the electronics and initiate a linear ramp voltage. Electrons passing through a thin Mylar window were detected in a collimated NE102 scintillator, and y rays were observed with a 50-cm 3 Ge(Li) detector. For each beam-off event the )3-and y-energy signals, the p-y time-to-amplitude signal, and the magnitude of the ramp voltage were converted to digital words and stored sequentially on magnetic tape for later analysis. Figure 1 shows a typical delayed-y-ray coincidence spectrum. In addition to lines from known 6 P activities, y rays at 622, 870, 929, 1416, and 2038 keV are apparent. Recently, a y-ray cascade through high-spin states in 52 Mn has been observed in studies of the reactions 51 V( 3 He, 2n) 52 Mn and 24 Mg( 32 S, 3/>w) 52 Mn by Signorini and Stefanini. 7 The five transitions in their 52 Mn level scheme (Fig. 2) appear to be identical to those seen in Fig. 1, suggesting that the activity observed results from the /3 + decay of a high-spin isomeric level formed in the reaction 40 Ca( 14 N, pn) 52 Fe. The results of our experiments to date can be summarized as follows.The five y rays associated with the new activity have intensities in the delayed-y-ray singles spectra consistent with the 52 Mn cascade, 7 and they decay with a common half-life of 56 ±8 sec. The 42m Sc peaks provide an internal check on th...

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has observed that the application of a correction calculated by Chen for nuclear polarization restores the skin thickness to more normal values (c = 5.75±0.03 F, £ = 2.38±0.08 F). This application of polarization corrections to muonic x-ray data is consistent with the results of recent work by Anderson et al. 8 on Pb 206 where "an effect tentatively interpreted as due to the polarization of the nucleus by the muon" was reported.The close analogy between low-energy electron scattering and muonic x-ray measurements suggests that dispersion corrections should be applied to our data. Previous estimates 9 " 12 of the dispersion correction as it applied to electron scattering have indicated that the effect should be small at our incident energies. However, inherent in these calculations are drastic assumptions concerning the distribution of electromagnetic strengths; in view of our results, a need for further calculations in indicated.The authors wish to express their gratitude to C. S. Wu, E. R. Macagno, and Min-Yi Chen for their timely discussions; and to H. A. Bentz for a check run with the Buhring code.The success of the optical model 1 in explaining the scattering of nucleons of 10-MeV energy or higher from nuclei of all masses has prompted 2 the application of optical-model techniques in the analysis of alpha-particle scattering. Optical potentials providing a good fit to scattering data would give physical information about the form of the alpha-nucleus interaction and would be useful in distorted-wave and coupled-channel analyses of inelastic alpha-particle scattering. However, such optical-model analyses of the alpha-particle elastic-scattering data generally lead to a number of families of parameters which give fits of similar quality. These ambiguities are found 2 to be either continuous, where a small change in the value of one parameter is compensated by small changes in the values of the others, in which families of parameters correspond to different numbers of half-wave lengths of the alpha-particle wave function included within the nuclear potential well. The continuous ambiguities can arise from several causes: The optical model may not be able to account adequately for the nuclear interaction embodied in the data (as one would expect at lower energies), or measurements may not have been made over a sufficiently large angular range; finally, the model may be overparametrized. One can circumvent these difficulties by studying the scattering at progressively higher energies, where there should be no difficulty in justifying the application of the optical model, and by extending the measurements over a large angular range, especially those in the backward hemisphere. However, measure-Optical-model analysis of elastic-scattering data taken at 40 Me V produces the familiar potential ambiguities, but at 80 MeV a single set is obtained. The parameters V, W, r 0 , and a are found to be highly correlated and hence cannot be uniquely determined. The functions which are determined most uniquely are the rms radiu...

Excitation functions for inelastic scattering of "C+ ' 0 to the 2+ state in "C at 4.43 MeV, the (3, 0+) doublet at 6.1 MeV and the (2+, 1 ) states at 7.0 MeV in ' 0 have been measured over the energy range 33 & E» & 54 MeV in 200-keV steps, at c.m. angles ranging from 100' to 165 . Several new intermediate structure resonances are observed in the inelastic channels. A statistical analysis reveals strong correlations in angle and in exit channels. Complete elastic and inelastic angular distributions were measured at the energies of E, = 13.6, 19.7, 20.5, 22.0, and 22.6 MeV as well as as at-21.3 MeV. Optical model fits to the elastic angular distributions result in the spin assignments J = 9, 14+, and 15 (16+) for the resonances at E, = 13.6, 19.7, and 22.0 MeV, respectively. Partial widths are extracted from the data. The reduced widths of the inelastic channels are large, establishing their importance in the resonance mechanism. The results are compared to predictions of existing models, and it is found that a simple double-resonance model does not adequately describe the data. NUCLEAR REACTIONS C{ 0 0+) C+; E=33-54 MeV, Oc~= 100'-160' measured 0 (E, 8), deduced resonances, J, reduced widths.

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