No abstract

Conformal representation theory is applied to a grid ionization chamber having plane parallel electrodes to give formulas useful in design. Expressions are obtained for the inefficiency of grid shielding of the electron collector, the spread of pulse size caused by the induced effect of positive ions, and the proportion of electrons collected by the grid. The theory was verified by experiment. The width of the polonium α-particle line at half-maximum was reduced to 50 kev. or about 1% of the energy by the use of a suitable grid and operating voltages. The corresponding standard deviation from all causes was 22 kev., made up of 2 kev. resulting from induced effect of positive ions, about 17 kev. from noise in the amplifier, and 14 kev. from straggling of ionization, thickness of source, and other effects. The spread caused by positive ions can therefore be almost completely eliminated by a grid.

No abstract

Reso»rice neutron interactions with the stable isotopes of magnesium were measured at the Oak Ridge electron linear accelerator time-of-flight facility. The transmission of a natural metal sample (78.7% Mg} was measured at 200 m and capture by natural metal and by enriched isotope samples was measured at 40 m. Twenty-six reso»races in Mg+ n up to 1.8 MeV were fitted with Breit-Wigner multilevel parameters. The data were sufficient to assign spin and parity to 19 of these. The capture data were analyzed for resonances up to 850 keV for Mg+n, 265 keV for 2 Mg+n (17+ resonances), and 440 keV for Mg+n (4 resonances). Average capture at stellar interior temperatures was calculated. The Mg+ n data serve to assess the isospin impurities in three isobaric analog states. Three other states exhibit reduced neutron widths each several percent of the Wigner limit which may be understood in terms of simple shell model configurations.

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The neutron transmission through 91 Zr was measured at both the 80 and 200 m stations of ORELA and, in combination with a capture measurement at .the 40 m. station, has resulted in resolved resonance parameters below. 20 keV bombarding , energy. The average s-wave resonance parameters obtained were as follows: the average level spacing

No abstract

Neutron induced fission and total cross sections of "-"U have been measured over the neutron energy range from a few eV to 8.9 MeV. Neutron and fission widths for 118 cross section resonances below 1500 eV have been determined and give a class I level spacing of ]0.6+0.5 eV and an s-wave strength function of (0.86+ 0.11) g 10 '. These fine structure resonances form two narrow intermediate structure resonances in the subthreshold fission cross section of '"U. Parameters for the Lorentzian energy dependence of the mean fission width are deduced by maximum likelihood analysis on the assumption that, relative to this mean, the observed fission widths have a Porter-Thomas distribution. Two large fission widths measured for resonances at 1092.5 and 1134 eV prompted a likelihood ratio test which indicates the presence of a narrow irtermediate structure resonances at 580 and at 1227 eV. The class II level spacing derived from the observation of seven intermediate structure resonances below 14 keV is 2. 1 + 0.3 keV. Broad structures in the fission cross section at 310, 550, and 770 keV are assumed to be due to P-vibrational levels in the second minimum of the Strutinsky potential. Fluctuations due to the presence of class II resonances are strongly evident for each of these vibrational levels. It is shown that the fluctuations near 310 keV are consistent with parameters deduced from the!ow energy data and this allows parameters for the double humped fission barrier potential to be obtained.