Zenithal Distribution of Low Energy Mesons

Abstract

for by varying the amplifier gain. Lead shielding between the two counters minimized scattering between the crystals. Figure 1 shows the single-crystal pulse-height distribution obtained in channel I for In 111 . The two photoelectron peaks are associated with the 172-and 247-kev gamma-rays. Figure 2 shows the zero-delay coincidence spectrum obtained when channel II was adjusted to transmit only the 247-kev peak with a large slit width and channel I ranged over the entire spectrum. A coincidence peak is seen at the position of the 172-kev gamma-ray since the time resolution of the coincidence circuit is insufficient to prevent true coincidences at zero delay. The ratio of true to chance coincidences at the peak is about thirty to one. The introduction of a 0.1-Aisec delay in channel I alone increased the coincidence rate by a factor of two, whereas the same delay introduced only in channel II practically eliminated true coincidences. This shows that the 247-kev gamma-ray is delayed with respect to the lower energy one and establishes directly the correspondence between the Cd m 247-kev level and the 247-kev gamma-ray associated with the decay of In 111 . I T is well known that the zenithal distribution of the integral meson spectrum at sea level obeys the empirical law Ie-Iocos x d } where 1$ is the intensity of cosmic-rays making an angle 0 with the zenith. The value of X is approximately two. It has been shown, 1 however, that this law does not apply for the differential spectrum, in particular, in the momentum range 300-410 Mev/c.In the present experiments a limited band in the spectrum was obtained by an arrangement of counters and absorbers such that the particles which stop in a block of lead are detected. In Fig. 1 the counters ABC define a beam which has passed through ababsorbers Pi, P 2 , and P 3 . P 2 and P 3 are each 5 cm thick. By ob-serving the particles which are registered in ABC but not in D t a band of the spectrum is selected which is fixed in position by P\-\-P 2 -\-Pz and in width by the thickness of Q\. At the same time a second band of longer range and of width fixed by Q 2 can be studied by observing particles which register in coincidence in A BCD but not in E. A group of counters G was included to exclude showers.The whole apparatus was mounted in a steel frame that could be rotated about a horizontal axis. For the results described here Pi+P 2 -\-Pz=lS cm of lead and Qi and Q 2 were each 7.5 cm thick.The results were corrected for the background and for the scattering in the absorber. These corrections will be described when a detailed account of the experiment is published. Table I shows the counting rate AIBD for particles stopped in the absorber Q\ and AI$E for particles stopped in Q 2 . Table II shows the values of X calculated from logr/log cos0, where r=Ald/Alo. Since the values of X are far from constant, the cos 2 0 law is not applicable. A much better fit is obtained if a function of the form r=(l -asin b e)is assumed. If log(X-r) is plotted against log sin0, the points fall on...

Chambre à diffusion à sensibilité continue

“…La chambre à diffusion mise au point à l'Institut d'Astrophysique était destinée surtout à l'étude du rayonnement cosmique présent sous de grands angles au zénith, pour lesquels nous avions observé certaines anomalies [16], [17]. Une telle chambre, dont la couche sensible est horizontale et dans laquelle il est possible de disposer des écrans verticaux, se prête bien, en effet, au genre d'étude envisagé.…”