Hans Mark

Ta181(p, n)W181 and Au197(p, n)Hg197 excitation functions between 4 and 13 MeV

Excitation functions for the Ta/sup 181/(p,n)W/sup 181/ and Au/sup 197/ (p,n)Hg/sup 197/ reactions were measured for incident proton energies from 4 to 13 Mev. The stacked foil method was used. The activity of the foils was measured by counting the gamma rays and X-rays emitted when the product nuclei decay by electron capture. Absolute values of the cross sections were measured at several energies for these reactions and were compared with the cross sections for compound nucleus formation given by Shapiro. Threshold energies for the (p,2n) reactions were obtained by comparing the present data with neutron yields obtained from long counter measurements. The (p,2n) thresholds are 7.5 Mev for Ta/sup 181/ and 8.3 Mev for Au/sup 197/. The absolute (p,2n) cross section values were also obtained. The total reaction cross sections above 7 Mev are compared with optical model calculations. Results confirm the assumption of a surface absorption potential. (auth)

Proportional Counters and Electronic Systems for Observing Cosmic X Rays

A low‐energy x‐ray detection system has been developed and used on two sounding rocket flights. Proportional counters, sensitive to x rays with quantum energies between 2 and 30 keV, are used in this system. The signals from these counters are modified so that they can be telemetered with an FM‐FM system in such a way that the pulse amplitude is preserved. Pulse‐height analysis is done at the ground station. With this simple system, it is possible to obtain spectra of cosmic x‐ray sources limited only by the resolution of the detectors.

THIN FIBER SCINTILLATION COUNTER FOR DETERMINING PARTICLE BEAM DISTRIBUTIONS IN ACCELERATORS

Thin fiber scintillation counters for studying particle beams in accelerators were developed using small plastic scintillation fibers made for use in high-energy physics. A fiber of 0.5-mm diameter or less and 1 to 10 cm long is mounted on a long thin (0.5-mm diameter and 20 ft long) two-layer glass pipe; the pipe serves as a light transmitter. The pipe passes through a vacuum seal and is joined to the face of a photomultiplier. Since the pipe is susceptible to radiation damage. it is placed inside a steel tube filled with Woods metal. Using this counter, electrons were shown to be trapped in the Astron E-layer tank for times longer than 1 sec, and estimates of the number of the initially trapped particles were made. (D.L.C.)

Measurement of High-Energy Gamma-Rays with a Photographic Bent Crystal Spectrograph

It has been shown by one of the authors and his coworkers nthat it is possible to determine accurately the nwavelengths of gamma rays with quantum energies up to n1.3 Mev by direct crystal diffraction methods using the nMark I 2-meter bent crystal spectrograph at the California nInstitute of Technology. They were able to record and to nmeasure with a precision of one part in 10^3 the two gamma nrays at 1.17 and 1.33 Mev which are emitted by a Co^(60) nsource.