G. Zago

Elastic and inelastic scattering of protons by7Li in the energy interval (3.0÷5.5) MeV

SummaryThe cross-section and angular distribution of the reactions7Li(p, p)7Li and7Li(p, p’)7Li* have been measured in the energy interval between 3.0 and 5.5 MeV. The elastic scattering cross-section presents a resonance at about 4.2 MeV attributed to a new7Be state at the excitation energy of 20.9 MeV.RiassuntoSono state misurate la sezione d’urto e la distribuzione angolare delle reazioni7Li(p, p)7Li e7Li(p, p’)7Li* nell’intervallo di energia fra 3.0 e 5.5 MeV. La sezione d’urto di diffusione elastica presenta una risonanza a circa 4.2 MeV dovuta ad un nuovo stato dell’8Be con energia di eccitazione di 20.9 MeV.

Fast-neutron transmission through a polarized holmium target

The observation of the nuclear deformation effect, that is the dependence of the neutron total cross-section of deformed nuclei on the degree of nuclear orientation, is particularly convenient on 165Ho because this nuclide is isotopically pure, strongly deformed, and relat ively easy to orient by means of the hypcrfine ferromagnetic interaction at low temperature. Among the works on this subject (1-6), we mention that one of MARSHAK et al. (6), who measured the effect in the neutron energy range from 2 to 135 McV and explained its oscillatory nature with a semi-empirical model based on the consideration of the socalled (~ nuclear Ramsauer effect ~) and also in terms of the optical model by an adiabatic coupled-channel calculation. A theoretical calculation of the effect has been presented also in the work of FASOLI et al. (7), by using the optical-model parameters obtained from a measurement of fast-neutron total and differential elastic-scattering crosssection. A fairly good agreement has been found with the experimental results. The nuclear deformation is expected to play an important role also in other types of interaction of neutrons with oriented targets. With the aim of extending this field of investigation we constructed a polarizcd holmium target (s), and as preliminary work, described here, we performed a new measurement of the deformation effect of the neutron total cross-section in the energy interval from 0.6 to 4.0 MeV. The longitudinal orientation required to observe the effect has been achieved by cooling a polycristalline homium sample 11 cm long with a diameter of 1.8 cm, to (0.31 -40.10) ~ in a magnetic field of 40 T obtained by means of a superconducting solenoid. The nuclear-orientation degree has been evaluated to be intermediate between

Interaction of fast neutrons with 165Ho

Abstract Differential elastic, inelastic and total neutron cross sections for 165 Ho have been measured at 3.0, 4.3, 6.0 and 7.5 MeV. The elastic scattering is analysed in terms of the optical model using a coupled-channel calculation. The inelastic neutron energy spectra are analysed in the framework of the statistical model.

Scattering of 1 and 2 MeV neutrons from oriented 165Ho

Abstract The “deformation effect” in the neutron- 165 Ho differential scattering cross section, defined as the relative variation of the cross section induced by the orientation of the target, has been measured at 1 and 2 MeV incident neutron energy, in the scattering angular interval from 30° to 130°. A polycrystalline holmium target has been employed, oriented normally to the scattering plane, with a nuclear alignment parameter B 2 B 2 max = 0.24 . The observed effect has an oscillating character as a function of the scattering angle with a maximum value of 0.12 ± 0.02 at 2 ( emMeV ). The effect has been theoretically calculated by an adiabatic coupled-channel calculation performed by using the optical model and deformation parameters deduced from the analysis of previous experiments. The agreement between the experimental and the theoretical results is good, particularly at 2 MeV energy where the compound nucleus contribution in the scattering is negligible.

Neutron-carbon interaction: Total and elastic scattering differential cross sections and phase shift analysis, 2.1 to 4.7 MeV

Abstract A measurement of the neutron total and differential elastic scattering cross sections is described, performed by means of the time-of-flight technique in the neutron energy interval 2.1 to 4.7 MeV. The experimental data have been analyzed by the phase shift formalism, and the 12C neutron analyzing power has been calculated and compared with the results obtained by various authors. More precise values of some level parameters of 13C have been obtained in the excitation energy interval from 7 to 9 MeV. The calculated map of the polarization induced in neutron-12C scattering indicates the energy and angle regions where carbon may be usefully employed as a polarization analyzer.

The scattering of positive 120 MeV pions on protons

SummaryAn investigation of the elastic scattering of 120 MeV positive pions by protons is described. The experiment was done by exposing a liquid propane chamber to the CERN 600 MeV synchro-cyclotron. The results refer to 5405 selected events in which the contamination from scattering on carbon nuclei is shown to be negligible. The values obtained for the phase-shifts are: α31= − 2.600±0.690, α3 = − 11.050±1.320, α33 = 31.670± 1.010. The value of α3 differs significantly from that expected if the linear dependence of α3 on the momentum, which has been proposed by some authors, is assumed. The present result is discussed, particularly in connection with some recent theoretical developments.RiassuntoSi descrive una ricerca sull’urto elastico di pioni positivi di 120 MeV su protoni. L’esperimento è stato fatto esponendo una camera a bolle a propano al sincrociclotrone da 600 MeV del CERN. I risultati si riferiscono a 5 405 eventi opportunamente scelti, per i quali si dimostra che la contaminazione da urti su nuclei di carbonio è trascurabile. I valori ottenuti per le fasi sono α31 = − 2.600±0.690, α3 = − 11.050± 1.320, α3 = 31.670± 1.010. Il valore della fase α3 differisce notevolmente da quello che ci si attenderebbe assumendo che essa dipenda linearmente dal momento, come è stato proposto da alcuni autori: questo risultato viene discusso, particolarmente in relazione ad alcuni recenti sviluppi teorici.

The spin-spin effect in the total neutron cross section of polarized neutrons on polarized 165Ho

Abstract The spin-spin effect in the total neutron cross section of polarized neutrons on polarized 165 Ho has been measured in the energy interval 0.4 to 2.5 MeV, in perpendicular geometry. The results are consistent with zero effect. The spin-spin cross section σ ss has been theoretically evaluated by a non-adiabatic coupled-channel calculation. From the comparison between the experimental and theoretical results a value V ss = 9 ± 77 keV for the strength of the spin-spin potential has been obtained. Compound-nucleus effects do not seem to be relevant.

An anomalous V 0 event

SummaryAn even has been observed in a multiplate cloud chamber and has the typical aspect of an anomalous V0 decay: it is compatible with the decay scheme τ0 → π+ + π-+ π0+ 80 MeV.RiassuntoÈ stato osservato in una camera a setti un evento che ha le caratteristiche di un decadimento V0 anomalo. Esso può essere interpretato con lo schema τ0 → π+ + + π- + π0 80. MeV.

Sulla distribuzione zenitale delle particelle degli sciami estesi

Riassuntoé stata dedotta direttamente da misure angolari in camera di Wilson la distribuzione zenitale delle particelle degli sciami estesi per due diverse densità medie: i risultati sono in buon accordo con quelli ottenuti da altri con contatori. Si sono anche derivati valori approssimati per eccesso dei cammini di assorbimento in aria per gli sciami delle due densità considerate.SummaryZenithal distributions for two average densities of particles of extensive air showers have been deduced directly from angular measurements in a cloud chamber: these results are in good agreement with those obtained by other workers using counters. Upper limits for the attenuation length values have also been derived.

Forward scattering of 2 MeV neutrons from oriented165Ho

In a previous article published in this review, in which we presented the results of a measurement of fast-neutron transmission through a polarized holmium target (1), we gave the general outline of a programme of investigation into nuclear shape by means of the interaction of neutrons with deformed oriented nuclei. In this article we shall present the first experimental evidence regarding the influence of the polarization of the target on the differential scattering cross-section of fast neutrons. This effect was brought to light through a measurement of the difference between the scattering cross-section of 2 MeV neutrons by a 165I-Io target polarized normally to the scattering plane and that of another identical but unpolarized target. The results have been compared to those obtained from an adiabatic coupled-channel calculation using the optical-model parameters obtained in one of our previous experiments on the scattering of neutrons by unpolarized holmium (2). The experiment was carried out in a very similar manner to the one described in ref. (1). By using the 5.5 MeV pulsed Van de Graaff accelerator at Legnaro, neutrons of 2 MeV energy and of about 100 kcV of energy spread were produced by (p, t) reaction in a gaseous t r i t ium target which was located in the centre of a cubic block of paraffin having a side of 0.5 m. A collimated neutron beam was obtained through a rectangular channel in the paraffin block. A counter aligned with the incident neutron beam was used as a monitor while the scattered neutrons in the horizontal plane were detected by a second counter. The proton beam pulsing tecniquc and the time-of-flight electronics were the same as those used in a previous experiment on scattering by unpolarized holmium (2). The time-of-flight base was 1.80 m. The target was a cylinder of polyerystalline hohnium, 3 cm in diameter, 2.5 cm high and 45 cm from the neutron source. The polarization of the target was obtained by cooling it down to a temperature of 0.36 ~ in a magnetic field of about 30 kG. The cryostat used for this purpose has already been described and is the same as the one used in measuring the deformation effect on the neutron-l~Ho total cross-section (1). The only change we made was to substi tute the magnet with a split-pair solenoid with