1127mately Gaussian with a mean square fluctuation given by r E * 4?reWZ ((X-X 0 )%= 7T7I^E> (A3) JEI {dE/dxf where e is the electronic charge, N is the number of atoms per cm 3 of absorber, Z is the number of electrons per atom that are effective in the ionization process, and -dE/dx is the rate of energy loss of the pion at the energy E. Using Eq. (A3) the rms spread in range due to this Gaussian straggling was calculated to be [<(i?-i?o) 2 >Av?=1.54 g/cm 2 of copper. F OLLOWING the Brookhaven cloud-chamber experiments 1 in which hyperons and a K particle were observed to be produced by 1.5-Bev pions, nuclear emulsions were exposed to high-energy negative pions from the Cosmotron. On account of the low intensity of pions (^1.5 per cm 2 per pulse) available at that time it was found necessary to irradiate the emulsions for a protracted period, and because of the high intensity of background radiation present it was found essential to have a clean pion beam and very good shielding of the emulsions. In the present experiment, stacks of 24 strips of 400ju G5 emulsions were irradiated in a 10-ton lead house at the end of a collimator 4 feet long. The total pion intensity in the emulsions was approximately 20 000 per cm 2 . A preliminary report 2 of some of the results of scanning these emulsions has been given. Approximately 9 cc of emulsion in all were areascanned by the three groups (B. N. L., M. I. T., and Rochester) analyzing these emulsions. Although a few and Whittemore, Phys. Rev. 93, 861 (1954). 2 Hill, Salant, Widgoff, Osborne, Pevsner, Ritson, Crussard, and Walker, Phys. Rev. 94, 797 (1954).Taking into account the multiple scattering and straggling effects discussed above and assuming that the distribution in true range of the incident beam was approximately Gaussian, the rms spread in range was estimated from the rms spread observed in the counter range curve> which was ±4.5 g/cm 2 of copper. The mean range was taken to be the mean measured range plus the mean shortening due to multiple scattering. The resulting range of the incident beam was 124.4±3.4 g/cm 2 of copper. There was also an estimated uncertainty of about 1.5 g/cm 2 of copper in the value of the mean range.K particles were observed, these experiments were not fruitful in producing observable i^-particle endings within the emulsions. The results of the experiments which will be given here include, in addition to the heavy mesons, information on pion-produced stars and several hyperfragments emitted from pion stars. PRONG DISTRIBUTIONS OF ^-PRODUCED STARSThe population of 7r-produced stars in the emulsions can be gauged from the following details of area scanning by one group of observers. In 2.9 cc of emulsion (54.8 cm 2 of 400^ strips), 716 7r-produced stars were observed, as compared with 740 neutron-produced stars.In a sample of 75 7r-produced stars, the numbers of stars as a function of the prong-number of the stars are given in Fig. 1. Also shown on the same plot and normalized to the same total number of stars, are distributions of pron...
FIG. 2. Stereoscopic photograph of V° decay "B." Its apex is just below the horizontal bar across the picture, which is a sweeping field electrode suspended above the sensitive layer of the cloud chamber. The apex of the V° particle is vertically separated from the sweeping field electrode by about 5 cm in depth. The dashed line at the top of the picture points toward the part of the shield struck by the neutron beam. Information concerning the V° is given in Table I. C ALCULATIONS have been made 1 of the differential cross section for proton-proton scattering at 18.3 and 32 Mev. The pseudoscalar meson theory was analyzed and comparison was made with the 18.3-Mev data 2 and the 32-Mev data. 3 " -4
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