DECAY OF MESOTRONS 225 circuit, the following events were simultaneously number of anticoincidence, which is not neces- recorded:(1) Fivefold coincidences between sarily the same with and without the absorber. counters A, B, C, D and one of counters F or E Since, however, only slow mesotron are ap- (coincidences [ABCD(E+F)];(2)coincidences preciably scattered as well as absorbed, the between counters A, B, C and d not accompanied difference in the number of anticoincidence due by a pulse either of counters F or of counters e to scattering is a small and constant fraction of anticoincidence [ABCD-(E+F)D. The co- the difference in the number of anticoincidence incidences [ABCD(E+F)] were mainly caused due to absorption. Thus, the difference between by mesotron going through counters A, B, C, d the number of anticoincidence recorded with and F, After entering the apparatus; i.e after and without lead in 2 is proportional, if not crossing the surface indicated by a in Fig. 1, accurately equal, to the number of mesotron these mesotron had to traverse 196g/cm?? of lead which traverse 10 g/cm of lead and are absorbed when there was no absorber in 2, or 311 g/cm of by 125 g/cm? of lead between D and F. These lead when 115 g/cm2 of lead were placed in 2. mesotrons are those which enter the apparatus Chance coincidences were negligible and coinci- with a residual range between Ra=196 and dences due to air showers were certainly rare on Ra=311 g/ cm of lead account of the heavy lead shield at the side of the punters. Coincidences caused by ionization THE MEASUREMENTS showers generated by me esotrons Measurements were taken alternately at absorbers could not introduce any error because they were a small and constant fraction of the Denver, Colorado, and at Echo Lake, approxi- mately 30 miles west of Denver. The geomagnetic coincidences caused directly by mesotron trav- latitude is practically the same(49 N) for both ersals 8 Thus, one is justified in taking the counting rate [ABCD(E+F)] as a measure of locations. The difference in altitude is 1624 m the number n of mesotron entering the appa The difference in atmospheric pressure, as meas ratus with a residual range larger than the total ured during the experiments, was 108 mm Hg quivalent to 147 g/ cm amount of matter present above or between the The measurements at Echo Lake were per- counters. Anticoincidences [ABCD-(E+F)] could be formed partly with an iron absorber of 200 g/cm2 counted for by one of the following events in S and partly without this absorber. No iron (a)A mesotron has traversed A, B, C and D and absorber was used at Denver. Three complete has been stopped between D and F.(b)A meso- sets of measurements were carried out at Denver counter battery F has failed to detect it for lack single readings from the averages were within the pulses of counters A, B, C and D has occurred. summarized in Table l. The errors given are the (d)A mesotron has traversed counters A,B, c standard statistical deviations and D, but has been scattered through a wide table SBcde + f ]e md tabcd-(e+hJare the angle so as to miss the counter battery F. The stopping of mesotron between D and F a is the diference between the nsem anticoincidence recorded with lead in 2, which The errors are the standard statistical deviation. lead in zs (case (a)) is certainly the main origin of the are, as we shall see, several times more equent than those recorded without lead. The events LOcATION S(Fe)2(Pb) scattering(case(d)) ttribute a small This was not always the case for the experimental f-7deskoo 1 13686492420.06 0.183#0.021 120.8 cussion on p. 464, reference 1(b)