U. Fasoli

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 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.

Scattering of neutrons by α-particles at 14.1 MeV

SummaryThe angular distribution of 14.1 MeV neutrons elastically scattered by α-particles has been measured by observing the α recoils in a helium-filled cloud chamber. The results are in satisfactory agreement with those previously obtained by other authors. Inspection of the smallangle region of the measured distribution shows that phase shifts of orbital angular momentum higher than L=1 are not negligible, although, according to the present experiment, quantitative information on D-waves turns out to be somewhat elusive. The azimuthal angular distribution agrees well with the value P = 0.02 of the neutron beam polarization, as measured by Perkins.Riassuntoè stata misurata la distribuzione angolare dei neutroni di 14.1 MeV diffusi elasticamente da particelle α osservando le α di rinculo in una camera a nebbia piena d‘elio. I risultati sono in soddisfacente accordo con quelli ottenuti da altri autori. La forma della distribuzione angolare nella regione dei piccoli angoli suggerisce che gli sfasamenti di momento angolare orbitale peggiore di L=1 non sono trascurabili. La presente misura non fornisce perÒ informazioni quantitative conclusive sulle ondeD. La distribuzione angolare azimutale è in buon accordo con il valore P = 0.02 della polarizzazione del fascio di neutroni, misurato da Perkins.

A monocrystal of 59Co as a nuclear orientation thermometer in neutron experiments with oriented targets

Abstract An apparatus for measuring temperatures in the millikelvin region is described based on the “deformation effect” on fast neutron transmission through an aligned 59 Co monocrystal, employing a 252 Cf pill as the neutron source. A statistical accuracy of a few percent in a few minutes is obtainable with a heat input of some tens of pW. The apparatus is suitable in neutron experiments with oriented targets when the gamma-ray background hinders the use of gamma-ray anisotropy thermometers. In these and similar cases, in which the temperature must be held constant for long periods, the large heat capacity of the cobalt sample is not a drawback.

ON THE CORRECTION OF THE INTENSITY OF COSMIC RAYS AT SEA LEVEL BY MEANS OF ATMOSPHERIC DATA

SummaryVarious correlations have been investigated between the total intensity of Cosmic Kays and the meteorological factors of the atmosphere. These measurements have been carried out at Padua using three different sets of apparatus. An analysis is made of the atmospheric data, and the effect of the seasonal variation on the correlation coefficients is discussed.RiassuntoSi sono eseguite diverse correlazioni sulle misure di intensità di raggi cosmioi, effettuate in Padova con tre diversi dispositivi. Si fa un’analisi dei dati atmosferici e si discute l’effetto stagionale presentato dai coefficienti di correlazione.