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A systematic study was made of methods of increasing the light collection efficiency of scintillation counters. Various reflectors, surface treatment of the scintillator, relative geometries of scintillator and photodiode, and light pipes were tried, using plastic scintillator cubes, 3 and 6 in. on a side, and right circular cylinders, 3 in. in diameter by 3 in. in length and 6 in. in diameter by 6 in. in length. The maximum factors by which light output could be increased, relative to a polished scintillator, were about 2.8 for 6‐in. scintillators and 3.3 for 3‐in. scintillators without the use of light pipes, and 5.0 for a 3‐in. scintillator with light pipe. The fraction of light trapped in a right circular cylinder by total internal reflection is derived as a function of index of refraction, as are the percentages of light coming out the ends and sides of a cylinder.

A systematic study has been made of the reactions $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}$ and $\mathrm{pp}\ensuremath{\rightarrow}p{N}^{*}$ in the angular range from ${\ensuremath{\theta}}_{\mathrm{lab}}={10}^{\ensuremath{\circ}}$ to ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}={90}^{\ensuremath{\circ}}$ at 3, 4, 5, 6, and 7 $\frac{\mathrm{GeV}}{c}$. An orthogonal dispersion magnetic spectrometer detected protons from interactions in hydrogen with momentum transfer ($\ensuremath{-}t$) in excess of 0.5 ${(\mathrm{GeV})}^{2}$. Well-defined peaks in the missing-mass spectra occurred at average ${N}^{*}$ masses of 1240\ifmmode\pm\else\textpm\fi{}6, 1508\ifmmode\pm\else\textpm\fi{}2, and 1683\ifmmode\pm\else\textpm\fi{}3 MeV with average full widths of 102\ifmmode\pm\else\textpm\fi{}4, 92\ifmmode\pm\else\textpm\fi{}3, and 110\ifmmode\pm\else\textpm\fi{}4 MeV, respectively. Below 2400 MeV no other significant enhancements were found. The ${N}^{*}$ production cross sections $\frac{d\ensuremath{\sigma}}{\mathrm{dt}}$ near ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}={90}^{\ensuremath{\circ}}$ are in qualitative agreement with the predictions of the statistical model. For each isobar the differential cross section at fixed energy varies as $\mathrm{exp}(\ensuremath{-}\frac{v}{{v}_{0}})$, where $v\ensuremath{\equiv}[\ensuremath{-}\frac{\mathrm{tu}}{(t+u)}]$; ${v}_{0}$ varies systematically with energy and tends toward the same value ($\ensuremath{\approx}0.4$ Ge${\mathrm{V}}^{2}$) for each isobar at the upper limit of our energy range.

For interactions of the type M1 + M2 ? M3 + M4 the kinematics of both initial particles and one secondary particle determine the reaction completely. Given a fixed initial state and any missing mass M4, the momentum-angle correlation for particle M3 is determined uniquely. In the spectrometer described, this correlation is preserved as a line image in the focal plane of a double focusing magnetic lens. Dispersions both in the plane of production and at right angles to it separate the images corresponding to different values of M4, for which the spectrum is obtained directly by means of a 28-counter hodoscope in the focal plane. Each hodoscope counter is gated with a scintillation and Cerenkov counter telescope to identify particle M3. During each beam pulse the outputs from the hodoscope counters are recorded on 10 Mc/sec scalers. Between accelerator pulses the contents of these scalers are read onto magnetic tape and into a PDP-5 computer, which accumulates, corrects, and displays the data continuously to provide an on-line monitor.

We have measured the missing mass spectrum of nucleon isobars produced in the reaction p+p→ +p by 7.1 GeV/c protons incident on a liquid-hydrogen target. Scintillation counters detected the recoil protons after momentum analysis. Cross-sections were obtained for production of isobars of mass 1238, 1512 and 1688 MeV at momentum transfers of 0.09, 0.15, 0.24, 0.33, and about 5 (GeV)2. At low momentum transfers, the spectrum has additional structure at a mass of about 1430 MeV. TheT=1/2 isobar production cross-sections at |t|=5 (GeV)2 are comparable with the elastic scattering cross-section.