(Received May 26, 1950)
Since long ago, it has been obscure whether the second maximum of Rossi curve really exists or not. If the maximum exists, it is very important to explain what kind of showers gives rise to such a maximum. Bothe and others ascertained this phenomenon by their experiment and attempted to explain it as due to hard or knock-on showers. However, Janossy maintained it from his experiment as a spurious effect, while, on the other hand, there exists some experiments which contradict with his results. Although the experiments and the interpretation of the above authors are partly convincing, they seem to be not free from such ambiguity and inconsistency that we are forced to take up this problem on the ground of the later development of cosmic ray physics.
Recent experiment carried out by Kameda and Miura seems to establish the evidence of the existance of the second maximum, and they inferred that this maximum is caused by the nucleonic component on the absorption law of agent rays and of the initial increase of the shower frequencies in lead and paraffin. The similar result was also obtained by Clay, but the attributed it to knock-on showers. His interpretation may, however, not be accepted because of the following reasons:
1) Primary rays show the characteristic feature of nucleons as already seen.
2) According to the theoretical and experimental reasons, the saturation of knock-on showers should take place in the much smaller thickness of the absorber of the second maximum.
3) The frequency of the second maximum can not be explained consistently by knock-on hypothesis for both narrow and wide zenith angle of the agent rays, as discussed in later section (§4).
4) The absorption coefficient of meson is so small that the knock-on shower can not produce such a sharp maximum.
In this paper, first we describe briefly the experiment of Kameda and Miura (§2), and present the further argument for their nucleonic hypothesis (§3). Then we show that this assumption gives right order of the frequency of the shower and inquire some conditions to give rise to the appreciable maximum (§4). We also discuss some feature of the secondary rays referring to the shape of the transition curve and study whether or not this feature favours other experimental results (§5). But our interpretation contain some ambiguity and may not be conclusive (§6).
URL : http://ptp.ipap.jp/link?PTP/5/948/
DOI : 10.1143/PTP.5.948