Mean Free Path In Air Research Articles

HighZ nuclei in cosmic radiation

Adding the results obtained by measuring the charges of 117 heavy nuclei (Z ⩾ 10) to those obtained in a previous paper, we determined the values of the ratioN(Z ⩾ 15)/N(Z ⩾ 10) at flight altitude and at the top of the atmosphere, and of the ratioN(Z = 26)/N(Z ⩾ 10) at flight altitude, at the top of the atmosphere and at the C.R. source. It results that the chemical composition of the C.R. source differs from the average composition of the universe, being much richer in heavy nuclei (Z ⩾ 15) and in particular in Iron. The absorption mean free path in air was also determined studying the zenith angle dependence of C.R. flux.

Primary Cosmic-Ray Alpha Particles and Protons atλ=55°N

The intensities of the primary cosmic-ray alpha particles and protons at geomagnetic latitude 55\ifmmode^\circ\else\textdegree\fi{}N are determined from measurements of the ionization and range of the charged cosmic-ray particles observed at atmospheric depths of 8 g/${\mathrm{cm}}^{2}$ and deeper. The measurements were made with a balloon-borne Geigerproportional counter telescope which contained absorbers of mercury or lead. Showers of particles in the telescope were detected by out of line counters and eliminated. The particles having residual ranges between 1.5 g/${\mathrm{cm}}^{2}$ and 43 g/${\mathrm{cm}}^{2}$ are shown to be secondary electrons and secondary protons. The penetrating particles having range greater than 43 g/${\mathrm{cm}}^{2}$ divide into singly and doubly charged particles. Extension of the penetrating particle intensity curves to zero depth yields values for the primary intensities of 0.19 ${({\mathrm{cm}}^{2}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{e}\mathrm{c}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{d})}^{\ensuremath{-}1}$ for protons and 0.032 ${({\mathrm{cm}}^{2}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{e}\mathrm{c}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{d})}^{\ensuremath{-}1}$ for alpha particles. The alpha particles are absorbed exponentially in the atmosphere and the slope of the absorption curve yields the value 35\ifmmode\pm\else\textpm\fi{}7 g/${\mathrm{cm}}^{2}$ for their mean free path in air. Data obtained by removing the absorbers in flight indicate that the net results are free of shower effects. Other systematic uncertainties in the values of the primary intensities are estimated to be \ifmmode\pm\else\textpm\fi{}10%, which is larger than the statistical uncertainties.

Cosmic-Ray Nuclear Interactions in Gases

The natural rates of occurrence, in the gases He, N, Ne, and A, of nuclear interactions of the cosmic ray $N$ component in which more than 8 Mev are given to charged secondary particles, have been measured. The rates per gram atom of the four gases are in about the same ratio as their geometric nuclear cross sections. An integrated flux of $N$ rays of 6.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ would produce the observed rates of occurrence of nuclear interactions if the cross section were geometric. The rates in argon, measured at sea level and 10 600-ft elevation, correspond to an absorption mean free path in air of 132\ifmmode\pm\else\textpm\fi{}4 g ${\mathrm{cm}}^{\ensuremath{-}2}$ for the total flux of $N$ rays. The interactions, 2783 in total, were observed in the gas of a cloud chamber filled to 5 atmos pressure. Inside the cloud chamber was placed a system of wires forming an ionization chamber. An expansion was initiated whenever a pulse from the ionization chamber corresponding to an energy release of more than 8 Mev (1.5 Po alpha) occurred. Fast reduction of the high voltage after electron collection was over permitted track formation on the positive ions. Of the nuclear interactions produced in argon about 20 percent are produced by charged particles at the higher elevation, and about 15 percent at sea level.

On the Nucleonic Components producing Large Cosmic-Ray Bursts under Thick Shield

By analysing the size-frequenq, distributions of large cosmic ray bursts obtained at three stations by SRI ion chambers, it is concluded that: a) about 40% of the total bursts at sea level are those induced by N-rays, and the portion of them decreases with increasing size, b) apsorption mean free path of burst-producing N-rays is 120 g/cm2 in air, and decreases with increasing size, approaching to collision mean free path of air. Moreover, from the comparison of our results with others, it is shown that the absorption mean free path of burst-producing N -rays near sea level is not same as that at high altitude, but it elongates near sea level. Some discussions on burst production are presented in connection with our results.

On the Mechanism of Production of the Neutron Component of the Cosmic Radiation

Experiments have been performed on the neutron component of the cosmic radiation, with a system of B${\mathrm{F}}_{3}$ proportional counters embedded in paraffin, capable of recording neutrons in the energy range between \ensuremath{\sim}2 and \ensuremath{\sim}15 Mev. The neutron rate recorded with such a detector is due to both neutrons locally produced inside the detector and neutrons produced outside the detector, i.e., in the surroundings and in the atmosphere.The local neutron production is due to a radiation which in the great majority does not consist either of photons or $\ensuremath{\mu}$-mesons.The intensity of such a radiation increases with altitude with a mean free path in air of 120-130 g/${\mathrm{cm}}^{2}$, which is confirmed by the fact that it shows a barometric coefficient \ensuremath{\cong} -11 percent per cm Hg. At mountain elevation (4000 m) the intensity of this radiation is close to that of the total ionizing cosmic radiation. This suggests that it consists principally of fast neutrons.The locally produced neutrons are mostly produced in multiples, with multipliticy depending upon the material. In lead the average multiplicity observed was close to 8, in carbon smaller than 2.The rates of neutron production in different materials are satisfactorily described by a cross section proportional to the ⅔ power of the mass number of the material.The results indicate that the main source of all the neutrons present in the cosmic radiation are "stars," though high energy processes like penetrating and extensive showers do contribute to neutron production.