Elastic and Inelastic Scattering of 18-Mev Alpha Particles from Neon, Argon, and Xenon

Abstract

NEEDof protons, and perhaps the parameters in the leveldensity formula need to be specially adjusted for this situation. It would seem that much more experimental evidence needs to be obtained to discover systematics which may exist. CONCLUSIONThe results of the present experiment suggest that the statistical theory of nuclear reactions describes adequately, at least, the shapes of the energy spectra of light particles from nitrogen-induced reactions at zero degrees. Angular distributions and experiments onThe scattering of 18-Mev alpha particles from neon, argon, and xenon was studied with a multiplate reaction chamber. The scattered particles were denned within an rms angular width of 0.45° by a system of slit pairs, spaced every 2^° from 10° to 170°. The elastic scattering from neon and argon show the pronounced maxima and minima characteristic of diffraction scattering but are equidistant in <j> } not sin(<£/2). The ratio to Rutherford scattering varies as much as 25-fold between successive maxima and minima in the case of neon, the well-defined structure indicating a small mean free path for absorption of alpha particles in the nucleus. Nuclear interaction radii calculated by the formula 2&i?A[sin(0/2)] = 7r were found to be 6.36X10 -13 cm for neon and 6.95 XlO -13 cm for argon. Xenon, investigated chiefly for control purposes, showed no definite deviation from Rutherford INTRODUCTIONT HERE has been renewed interest in the scattering of alpha particles from nuclei following the establishment by Farwell and Wegner 1 of a pronounced variation with energy of the scattering cross section for heavy nuclei. They found that the ratio of the observed differential scattering cross section to the Rutherford cross section, <r(E)/<r R (E), was unity only for energies below certain values and decreased exponentially with higher energies. Further experiments on alpha-particle scattering from heavy nuclei were per-heavier targets have yet to be explored. Heavy-ion reactions might provide a useful means of measuring statistical aspects of nuclear structure. ACKNOWLEDGMENTSThe authors gratefully acknowledge their indebtedness to John G. Harris for constructing the proportional counters and mechanical apparatus, to Gertrude Foster for carrying out the cross-section calculations and for constructing graphs used in the analysis of the data, to A. Zucker for help and encouragement, and to R. S. Livingston for interest in and support of the experiment. scattering up to 50°. Groups corresponding to the excitation of the 1. 63-, 4.25-, 4.97-, 5.81(5.63)-, and 7.2-Mev levels of Ne 20 and the 1.46-Mev level of A 40 were observed. No excited states were observed in xenon. Notably absent was excitation of the 6.74-Mev (0 + ) level in Ne 20 . As predicted by direct-interaction theories, the cross sections for inelastic scattering leading to the first excited (2 + ) states of neon and argon could be approximated by the squares of spherical Bessel functions of the second order with interaction radii of 6.71 X10~1 3 cm for neon and 6.60X10...

Cross sections of α-induced reactions for targets with masses A ≈ 20–50 at low energies

“…It turns out that the limited angular range of the angular distributions by Bucurescu et al [95] is not sufficient to derive the total reaction cross section σ reac from these data. The angular distribution of Seidlitz et al [96] covers the full angular range; however, at forward angles the measured cross section is almost twice the Rutherford cross section of pointlike charges. Therefore, Gaul et al [75] have suggested to scale the angular distribution by Seidlitz et al by a factor of 0.55; a similar scaling factor of 0.57 is suggested from the best fit obtained in this work.…”

“…Therefore the following study is restricted to the data by Seidlitz et al [96] and the data at the lowest energies by Bucurescu et al [95]. It turns out that the limited angular range of the angular distributions by Bucurescu et al [95] is not sufficient to derive the total reaction cross section σ reac from these data.…”

“…Because of the noticeable behavior of σ red of 40 Ar at low energies, σ red of 40 Ar was additionally studied at higher energies using 40 Ar(α,α) 40 Ar elastic scattering. Data at relatively low energies are available in [95,96], and data above 20 MeV have also been measured in [75,90]. Only the 18 MeV data by Seidlitz et al [96] are available numerically from Table I of [96]; the other data had to be redigitized from small figures with logarithmic scale in [95, …”

Elasticα+Ne20scattering in theα+OYang1, Tan2, Li3 2010Phys. Rev. C161230View full textAdd to dashboardCite

“…The α scattering on some light and medium-heavy nuclei exhibit strong enhancement of cross section at backward angles [i.e., the so-called anomalous large angle scattering (ALAS)]. This phenomenon brought considerable interest and was explained by various approaches (e.g., modified WoodsSaxon potential, L-dependent potential, folding potential, α exchange, Regge poles, and so on [1][2][3][4][5][6][7][8][9][10][11][12]). …”

“…For the elastic α+ 20 Ne scattering, there have been the measured differential cross sections over complete angular range: in the lower incident energy region, the angular distributions at E α = 16.8 MeV [3], 18.0 MeV [4], 20.2-23.0 MeV [5], and 25.8-31.1 MeV [6]; in higher incident energy region, the very detailed measured angular distribution at E α = 54.1 MeV [7]. All these experimental angular distributions exhibit remarkable ALAS features.…”