In this paper, we present a novel position sensitive signal pickup scheme for a cavity BPM. The scheme utilizes the H-plane of the waveguide to couple magnetically to the side of the cavity, which results in a selective coupling to the dipole mode and a total rejection of the monopole mode. This scheme greatly simplifies the BPM geometry and relaxes machining tolerances. We will present detailed numerical studies on such a cavity BPM, analyze its resolution limit and tolerance requirements for a nanometer resolution. Finally present the measurement results of a X-band prototype.

The Beam-Position Monitor (BPM) system for the SLAC PEP-II B-Factory has been in operation for over two years. Although the BPM system has met all of its specifications, several problems with the system have been identified and solved. The problems include errors and limitations in both the hardware and software. Solutions of such problems have led to improved performance and reliability. In this paper we will report on this experience. The process of identifying problems is not at an end and we expect continued improvement of the BPM system.

Photoneutron spectra from $^{17}\mathrm{O}$ have been obtained at bremsstrahlung end-point energies of 13.7, 16, 22, 28, and 34 MeV using the neutron time-of-flight technique. The angle between the incident photon beam and the 49.2-m flight path was 98\ifmmode^\circ\else\textdegree\fi{}. From the measured spectra the differential cross section for the $^{17}\mathrm{O}$($\ensuremath{\gamma}$,${n}_{0}$)$^{16}\mathrm{O}$ reaction between 5 and 33 MeV was obtained. The considerable structure in the cross section is compared with the known spectrum of levels for this nucleus compiled from previous studies using various reactions. In the region below 19 MeV, 18 resonances correspond to levels previously identified. In addition at least 12 other resonances which have not been seen previously have been observed. In the giant dipole resonance region (above 19 MeV) the present results delineate the $T=\frac{1}{2}$ strength. The measurement is compared to the $^{16}\mathrm{O}$($p$,${\ensuremath{\gamma}}_{0}+{\ensuremath{\gamma}}_{1}$)$^{17}\mathrm{F}$ reaction with the expected similarities observed. The measurement also is compared to 1p,2p-1h shell-model calculations.NUCLEAR REACTIONS $^{17}\mathrm{O}$($\ensuremath{\gamma}$,${n}_{0}$) $^{16}\mathrm{O}$, ${E}_{x}=5.0\ensuremath{-}33.0$ MeV; measured photoneutron time-of-flight spectra; deduced ($\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$) (${E}_{x}$, 98\ifmmode^\circ\else\textdegree\fi{}), resonant structure; $T=\frac{1}{2}$ strength of the GDR.

The structure in the photoneutron cross sections of 16O and 208Pb has been studied by the measurement of high resolution photoneutron energy spectra using the neutron time-of-flight technique and bremsstrahlung irradiations. For 16O, the ground state differential cross section at 98° has been deduced between 17.3 and 28.5 MeV and is in good agreement with most previous studies. Fine structure is seen throughout the cross section. Eight neutron energy spectra for 208Pb from bremsstrahlung endpoint energies in the range 11.0 to 15.5 MeV were obtained. Strong peaks are seen at center of mass neutron energies of 1.67, 1.85, 2.06, 2.19, 2.68, 3.15, 3.27, 3.50, 3.77, and 4.03 MeV with weaker peaks elsewhere. The energies of these peaks are in good agreement with previous measurements in this laboratory. The energies of peaks in the spectra are compared with recent cross section measurements.

The photonucleon reaction has been studied by using a straightforward extension of bound-state shell-model theory. Continuum wave functions are replaced by their value at the centre of small energy intervals. When this process is truncated at some maximum excitation energy, a finite set of wave functions describing the continuum is produced. Calculations are performed using a finite square well and a zero-range residual interaction in the 1p-1h space. Application of the method is illustrated by calculating the photoneutron and photoproton cross sections and angular distributions for 4He. Good agreement between the calculated cross sections and most experimental data is obtained.

Results of research toward measuring the neutron cross sections for N and O in the neutron energy range from 4 to 12 Mev are presented. New techniques for the use of lowyield and multiple-group neutron source reactions, which were developed to perform these measurements, are shown, along with additional data obtained for the neutron source reactions Be/sup 9/( alpha ,n)C/sup 1//sup 2/ and N/sup 1//sup 5/(d,n)O/sup 1//sup 6/. In addition to the N/sup 1//sup 4/ (n,d/sub 0/)C/sup 1//sup 3/ reaction measurements, the C/sup 1//sup 3/(d,n)N/sup 1//sup 4/ rea ction was investigated to provide additional deuteron stripping data for evaluating the spins and parities of the low-lying states of N/sup 1//sup 4/, and to provide additional information on the reaction mechanism for deuteron induced reactions. Measurements and results are given for the differential elastic, total, and nonelastic neutron cross sections for nitrogen and oxygen at several neutron energies. (auth)