14-Mev (n, α) Cross Section in Zirconium. III

Abstract

A collimated beam of 14.1-Mev neutrons from the H 3 (<i,^)He 4 reaction was incident upon a 4-mil normal zirconium target at the center of a nuclear-plate camera. 1 Ilford E-l plates were placed around the periphery of the camera floor, with their long axes coinciding with radii extending from the center of the base of the camera. Two runs were made, one with the target in position and the other a background run without the target.Equivalent areas on run and corresponding background plates were analyzed at eight camera positions such that the angles made by the reaction particles with the direction of the incident neutron beam extended from 17.5° to 128°. Measurements were made of all tracks longer than 10 microns entering the surface of the emulsion in directions consistent with targetdetector geometry. The tracks were further identified, from grain density, as proton or a-particle tracks. Thus data for the (n,p) cross section were obtained at the same time as those for the (n,a) cross section.The value obtained for the (n y a) cross section integrated from 17.5° to 128° is 10=1=10 mb for reaction a particles of energy greater than 3 Mev. Since in these calculations it is assumed that all the stable isotopes of normal zirconium contribute to the observed reaction particles, the value given is one-half the upper limit for Zr 90 .A preliminary value for the (n,p) cross section obtained from this experiment is 180±70 mb, which is in fair agreement with that given by Paul and Clarke. 2 The energies of essentially all the observed reaction protons are below 6 Mev.A DIRECT measurement of the yield of alpha particles produced by bombarding normal zirconium with 14.1-Mev neutrons has confirmed the smallness of the Zr 90 and Zr 94 (n,a) -reaction cross sections observed by the activation measurements of Brolley et at. reported in the first of the preceding letters.A one-mil foil of zirconium metal was bombarded with monoenergetic neutrons from the H 3 (i,w)He 4 reaction, and the alpha particles were detected by means of a counter telescope, consisting of two proportional counters and a Nal(Tl) scintillator, described in 20 40 60 80 IOO LAB ANGLE, 6L-DEGREES 120 FIG. 1. Differential cross section for the yield of alpha particles of energies greater than six Mev from normal zirconium bombarded by 14.1-Mev neutrons.detail elsewhere. 1 The counters were biased to a lower limit of ionization energy loss so that alpha particles of energies < 18 Mev were detected, while protons and deuterons of energies >0.8 and 1.6 Mev were excluded.At each telescope angle the scintillator pulse-height spectrum was observed between alpha-particle energies of 6 and 18 Mev. Background was measured by exposing a platinum blank to the telescope. The energy spectrum at zero and 15 degrees was peaked at its upper limit of 17 Mev and decreased to zero at about 10 Mev. Between 10 and six Mev, no alpha particles were observed. At larger angles, up to 115 degrees, yields were too low for significant spectrum determinations.The measured differential ...

Energy Levels ofO18andF21

“…The situation at higher energies is not so clear. A preliminary observation 8 of a level at 2.45 Mev, counterindicated by the present work and several previous experiments, [5][6][7]9 is probably spurious. Hough and Bach 7 observed a level at 3.555±0.013 Mev in agreement with our value of 3.504±0.034 Mev; however, Ahnlund 6 searched up to 4.5 Mev and found nothing other than the 2-Mev state.…”

“…It is interesting to compare the three-particle continua observed here with those obtained recently in several different reactions by workers 5,6 investigating states in INTRODUCTION I NTEREST has been growing in the nuclei whose protons and neutrons number one or two more or less than the closed p shell (O 16 ). A nucleus with just one odd proton or neutron can be described, in part, by shell theory.…”

“…The first excited state near 2 Mev has been seen by all observers [5][6][7][8][9] and is well established. The situation at higher energies is not so clear.…”

An Analysis of the Charged Particles Emitted Following Negative Muon Absorptions in Photographic Emulsions

“…As to the emission rate, the latter spectra is only about 20% larger than the former. In this paper it is assumed that level density is determined by (19), (20) and (21) for all assumed momentum distributions, and considering the emission processes it is assumed that the term, "Fermi gas at kT=9 Me V", means only the condition corresponding to the state that has the momentum distribution given by (15). Due to these two reasons, we calculate the energy spectra considering only Pd 107 and Se 79 • The comparison between the calculated and experimental energy spectra is given inT Figs.…”

“…In fact the statistical theory may not give good agreement with proton experiments when (19), (20) and (21) are used. In order to investigate this disagreement, the data from low energy Ag (r, p) Pd experiments have been compared with the theoretical values.…”