Delta Rays Research Articles

Primary Alpha Particles in the Cosmic Radiation Near the Geomagnetic Equator

An apparatus consisting of a G-M counter coincidence train in which is interposed a high-pressure ionization chamber has been utilized to obtain measurements of the flux of primary helium nuclei during a series of balloon-flights in India.The instrument records relativistic particles characterized by a specific ionization at least as great as that of an alpha particle. The experiments were conducted at Aligarh, Uttar Pradesh (geomagnetic latitude 18° N) and Bangalore, Mysore (geomagnetic latitude 3° N). At each station, the intensity N(I > 3.2Imin) of particles producing ionization chamber pulses exceeding the bias setting corresponding to 3.2Imin plotted on a logarithmic scale as a function of atmospheric depth, follows a straight line. The intensity Ntotal was also measured by removing the criterion I > 3.2Imin. Taking into account local nuclear interactions initiated by protons, knockon electrons accompanying protons, and slow protons (albedo) which actuate the apparatus, the alpha-particle flux is determined from the extrapolated values of Ntotal and N(I > 3.2Imin) at the “top of the atmosphere.” The results are: 49 ± 13 particles m−2 sec -1 sterad-1 at λ = 3° N, and 81 ± 22 particles M−2 sect sterad-1 at λ = 18° N. The qualitative effect of the presumably small systematic uncertainties is generally in the direction of making these values low. Both protons and helium nuclei can be represented by an integral energy distribution of the form: N(>E) = k(1 + E)−1.2, where E is kinetic energy per nucleon; k = 4000 and 1.5 < E < 15 Bev for protons; k = 450 and 0.3 < E < 7 Bev per nucleon for alpha particles. The composition of the primary cosmic radiation is not drastically different at λ = 3° and λ = 18°, although the total intensity is anomalously high at the latter station.

COSMIC RAY PHENOMENA AT MINIMUM IONIZATION IN A NEW NUCLEAR EMULSION HAVING A FINE GRAIN, MADE IN THE LABORATORY

The preparation of a silver bromide emulsion in the form of baseless sheets and their use in thick homogeneous stacks are described. In these sheets, a suitable development brings out minimum ionization tracks with a grain diameter 0.1 to 0.2 μ, and a linear grain density of 15 per 100 μ. The sequence of observations which led to the positive identification of minimum tracks is discussed. Short recoils and delta rays are visible, and excellent discrimination is available at all ionizing powers. The influence of grain size on fog is analyzed.Several cosmic ray phenomena containing minimum tracks are presented: single tracks, hard showers, πμe events, and an electron pair. Distortion is very small, and it is shown that the small grain size renders feasible better scattering measurements on higher energy particles. With this emulsion, nearly every possible measurement should become feasible with greater accuracy.

Energy Spectrum Resulting from Electron Slowing Down

The equation for the slowing down of electrons is cast in a form suitable for numerical calculations. Pilot calculations have been performed for source energies of $4m{c}^{2}$ and $80m{c}^{2}$ in Al and Pb. The spectrum of slowed-down electrons, which would be the reciprocal of the stopping power under the assumption of continuous slowing down, departs substantially from this elementary solution at the upper and lower energy ends of the spectrum. The departures are large throughout when bremsstrahlung is important. The accumulation of secondary knock-on electrons is also included in the calculations.

The Time Variation of Cosmic-Ray Heavy Nuclei

Two 4\ifmmode\times\else\texttimes\fi{}4 Ilford G-5 photographic emulsions in contact were exposed to the cosmic radiation in such a way that one plate was moved slowly and uniformly with respect to the other. By this technique it is possible to determine the time at which heavy nuclei pass through the plates. The plates were exposed above 90 000 feet on June 4, 1952, for 8 hours during the day. A reliable altitude record was available and was used to correct for the altitude changes during the 8 hours. 947 heavy nuclei with more than 10 delta rays per 100 microns, corresponding to $Z$ greater than about 10, were traced through and their time of passage measured. This was done by new techniques which are described in detail. The data have been divided into three time intervals. The intensity during the middle interval between noon and 2 p.m. is greater by 25\ifmmode\pm\else\textpm\fi{}8.5 percent than the average of the other two. It is concluded that this is due to a real fluctuation in the intensity of of cosmic-ray heavy nuclei at the top of the atmosphere. The possibility that this may be due to a dipole magnetic field of the sun is discussed.

On the possible existence of associated knock-on electrons

On the possible existence of associated knock-on electrons

LXXXIV. Cosmic rays at60 m.w.e.Underground: I. The knock-on electrons and nuclear interactions produced by relativisticμ-mesons

Abstract A length of 126·6 m of minimum ionization track has been examined in Ilford G5 plates, coated, exposed, and processed at 60 m.w.e. underground, and a detailed study of knock-on electrons of energy greater than 50 mev has been made. After making suitable corrections for scanning efficiency, it is found that the theoretical cross section, as derived by Bhabha, fits the data well for knock-on energies greater than 100 mev. The mean free path for the production of these knock-on electrons is (4·5±1) m of emulsion corresponding to a cross section of (20±4) ×10-28 cm2/electron. The theoretical cross section for the μ-meson spectrum at 60 m.w.e. is 18·4×10-28 cm2/electron. A typical μ-meson star has been found. It is shown that the number of small stars with less than three dark tracks produced by μ-mesons is not very different from the number of larger stars with three or more dark tracks. No evidence for or against the existence of pairs of associated penetrating particles has been obtained.

LXXXV. Cosmic rays at60 m.w.e.Underground II: The hard and soft components

Abstract The tracks of the relativistic charged particles, which have been found and examined by the methods described in I, are used to estimate the total vertical intensity and the electron component at 60 m.w.e. The total vertical intensity is found to be (6·8±1)10-4 particles/cm2/sec/steradian. About 0·5% of the relativistic charged particles with momenta greater than 100 mev/c are electrons. The possible sources of these electrons are examined and it is found that they consist almost entirely of knock-on electrons and. their cascade progeny. Both the absolute rate and the spectrum of the electron pairs which are found on the plates indicate an electron component whose magnitude is rather greater than can be accounted for by known sources. A detailed analysis is also made of 20 tridents and it is shown that they consist of 9 electron and 11 μ-meson tridents. The μ-meson tridents are classified further into the various cases covered by Bhabha's theory. I t is again found that, rather more electron trid...

ENERGY LOSS OF HIGHLY CHARGED PARTICLES PRODUCED BY FISSION AND BY COSMIC RAYS: III. THE LINEAR DENSITY OF DELTA RAYS. EXPERIMENTS

Delta rays having an energy as low as 2–5 kev. have been counted along the tracks of mesons, protons, and α rays of low velocity, allowing the identification of each. Three methods are presented and applied to determine the efficiency ƒ of counting delta rays of various energies; measured values of ƒ vary between 0.05% at 2 kev. and 100–180% near 50 kev. The number of grains, and the energy distribution among visible delta rays, are analyzed. A new method of determining velocity, based on the analysis of the number of grains in the delta rays, is presented. In the Appendix, the effect of relativistic corrections is computed and discussed. It is small except at large velocities where comparison with experiment is difficult.

The knock-on electrons produced by mesons in lead

An experiment to determine the relation between the relative number of knock-on electrons excited in Pb-layers by the penetrating component of cosmic radiation and the thickness of the Pb-layer, is described. To ensure that only those penetrating particles above a certain limit in the energy spectrum is explored, the total Pb-thickness for a whole series of readings was kept constant. An explanation of the curves that were obtained is also given.

High Energy Electron-Electron Scattering

Eradicated electron sensitive nuclear emulsions were exposed to 200-Mev electrons at the Berkeley synchrotron. In scanning the electron tracks 427 events were observed in which the scattered electron of lower energy, or knock-on electron, had an energy greater than 30 kev. The observed differential cross section was found to agree in absolute value with M\o{}ller's theoretical cross section, although an insufficient number of high energy knock-on electrons were observed to distinguish between the M\o{}ller, relativistic Mott, and relativistic Rutherford formulas. Two pairs initiated by primary electrons and two cases in which primary electrons vanished in the emulsion were also observed in 102.6 cm of track. No heavy particle events were seen.

XXXVI. A new method of determining the charge and energy of heavy nuclei in the cosmic radiation.

Summary The charge and energy of a heavy particle in cosmic radiation may be determined from the frequency of the accompanying delta rays and the multiple scattering in its path through an emulsion. The method is illustrated by the charge spectrum of 226 tracks in emulsions exposed at 95,000 feet.

The second shower maximum in Au, Hg and Pb

From earlier experiments with ionisation chambers we had already obtained the certainty that the second maximum for Pb exists and is found under a layer of about 16 cm Pb. It was now measured again with counters recording showers with at least 2 particles, the counters being disposed in a way enabling to distinguish between particles with tracks at different angles. The showers with 3 or more and 4 or more particles were registered as well. Measurements were also made with layers of gold and of mercury. For both materials the second maximum is found to exist with perfect certainty. It can be brought about by knock-on electrons produced by mesons.

The Energy Distribution in Cosmic-Ray Showers

The track length distribution $f(E)\mathrm{dE}$ in a shower is defined as the total distance traveled by all electrons while in the energy interval $\mathrm{dE}$. It is representative for the average energy distribution in a shower. The present paper obtains by numerical methods the complete functions for both electrons as well as for photons in showers of high primary energy. Calculations have been made for air and for lead, down to energies of about 4 Mev. Close approximations to the actual cross sections have been used for all energies and all physically significant processes have been included---radiation, pair production, energy loss through collision, Compton effect, and knock-on electrons. As a special result of importance we mention the high number of low-energy photons that accompany a shower, a quantity that has here been evaluated for the first time.

A cloud-chamber investigation of penetrating showers

An account is given of a cloud-chamber investigation of penetrating showers. It is concluded that the cloud-chamber data are consistent with Jánossy’s counter data and also with the view that penetrating showers consist of a small number of penetrating ionizing particles which are mainly mesons. There is no evidence to show that the showers are produced by processes other than those postulated in the theory of meson production proposed by Hamilton, Heitler &amp; Peng, together with the addition suggested by Jánossy, i. e. the emission of small groups of mesons every few centimetres of lead. There are given several photographs of showers of penetrating particles which may be examples of the successive production of penetrating particles by an incident nucleon and its recoil particles. The spectrum of the penetrating particles seems to be approximately of the same form as the meson spectrum at sea-level. Some 20% of penetrating showers are accompanied, in the cloud chamber, by what appear to be electron cascades. It is shown that these showers cannot be due to knock-on electrons, to high-energy electron cascades penetrating the whole thickness of the absorber, or to decay electrons unless a meson of lifetime less than 10 -10 sec. is postulated. It is suggested that these showers may be due to electrons or photons produced in processes which become important at very high energies, e. g. &gt; 10 11 eV.

Cloud-Chamber Photographs of Heavy Particles at High Altitudes

A series of 5000 cloud-chamber photographs was obtained at an altitude of 15,500 ft., by use of a chamber in a field of 1165 gauss supplied by a permanent magnet. The determination of mass from cloud-chamber photographs of heavily ionizing particles and knock-on electrons is discussed in general and the methods are applied to specific tracks of the present series. It is shown that the errors of mass determination from cloud-chamber data are large but that there is good evidence for a distribution of mesotron masses. The number of slow mesotrons at 15,500 ft. is about equal to the number of slow protons and amounts to 1 percent of the number of fast mesotrons at that altitude. The extremely rapid increase of slow mesotrons with altitude probably means that they are created as such at high altitudes. One photograph, which shows the pair production of low energy mesotrons, is an example of such a process.

A Cloud-Chamber Analysis of Cosmic Rays at 14,120 Ft.

Protons and mesotrons near the end of their ranges are distinguished from each other by a method involving the degree of ionization in the gas of the cloud chamber and the scattering in the lead plates in the chamber. Photographs are shown of the production of protons and mesotrons in the lead by non-ionizing and ionizing radiation. Evidence is presented for the presence of an extremely large number of neutrons. Both neutrons and protons are shown to be secondary particles with a maximum energy near 200 Mev. The conclusion is reached that this maximum energy arises from the large cross section of the atmosphere for the production of pairs of mesotrons. The value of this maximum energy can be used as a measure of the mass of the mesotron. Photographs are shown of cascade showers produced by knock-on electrons, stars produced in the lead and the gas of the chamber, and Auger showers filling the whole chamber.

Some new investigations on cosmic ray showers

Some experiments performed by my pupils and myself during the last two years have yielded results which seem difficult to reconcile with the pure cascade theory of cosmic-ray showers. Among these are: the presence of penetrating particles (mesons) in extensive atmospheric showers (A-showers), the variation with altitude of the frequency of these A -showers, and the special structure of some local showers. Using a meson selector in coincidence with distant counters, Dr Rogozinski could explain his results by : (1) knock-on electrons accompanying a meson; (2) mesons in A -showers; (3) multiple simultaneous mesons (meson show er). This last phenomenon being frequent only in high altitude.

I.On the δ-rays produced by α-particles in different gases

I.<i>On the δ-rays produced by α-particles in different gases</i>

VI. Delta rays from gases

VI. <i>Delta rays from gases</i>

LXXIX. Delta rays produced by beta rays

LXXIX. <i>Delta rays produced by beta rays</i>