Study of Variations in Cosmic Radiation

S. N. Vernov, Yu. I. Logachev, A. E. Chudakov, Yu. G. Shafer

This article proposes to consider the question of using an artificial Earth satellite to study variations in cosmic radiation. With the aid of relatively simple apparatus, consisting of a counter and an ionization chamber, the following phenomena can be studied:

a) variations of primary cosmic radiation,
b) variations of the multiply charged component of primary cosmic radiation, consisting of the nuclei of helium atoms and heavier elements,
c) the geomagnetic field at large distances from the Earth,
d) the Earth’s albedo for cosmic radiation,
e) the structure of fluxes emitted by the Sun.

It is known that in recent years the study of variations in cosmic radiation has acquired great scientific significance. For the study of variations, installations with continuous recording of the intensity of cosmic radiation have been constructed; with their help it has been possible to detect numerous variations, both periodic and nonperiodic. The amplitude of these variations is measured at sea level in tenths and fractions of a percent, except in cases of large flares of intensity, in which the increase of ionization at sea level reached as much as 200–500%, as occurred during the flare of February 23, 1956.

Some of these variations are caused by changes in the state of the atmosphere, others are connected with solar activity, and still others with magnetic disturbances. A more detailed classification of variations is given in work ¹. The close connection of geo- and heliophysical phenomena with variations in the intensity of cosmic radiation has also determined the interest in variations that has appeared in recent years among scientists of many countries.

I. Possibilities for Studying Variations Provided by Artificial Earth Satellites

All continuous measurements of the intensity of cosmic radiation are now carried out either at sea level or at mountain altitudes. In both cases, above the recording instruments there is a great thickness of atmosphere, which leads to two kinds of difficulties.

First, it is desirable to study variations in the intensity of primary cosmic radiation, but after passing through the atmosphere the primary radiation is absorbed, and secondary radiation reaches the recording instruments; the variations of this secondary radiation differ greatly from the variations of the primary radiation. The variations recorded by instruments near sea level are usually much smaller than the variations of primary radiation. This occurs because the radiation reaching the surface of the Earth,

S. N. VERNOV, Yu. I. LOGACHEV, A. E. CHUDAKOV, Yu. G. SHAFER

is mainly due to primary particles possessing high energy. Meanwhile, the part of cosmic radiation that is most subject to changes is that which consists of primary particles of the lowest energies.

Secondly, the atmosphere itself is a source of variations. These variations of atmospheric origin often obscure the true effect, and in order to exclude them it is necessary to know the state of the atmosphere up to heights of 25–30 km. In connection with the absence of sufficiently accurate data on the temperature of the atmosphere at great heights, these so-called meteorological variations can be allowed for only very inaccurately.

Investigations in the upper layers of the atmosphere and beyond its limits are free of these shortcomings: the influence of the atmosphere is excluded, and variations of the primary radiation are measured. In addition, with the aid of apparatus located in the upper layers of the atmosphere or beyond its limits, one can observe variations of the multiply charged component of primary cosmic radiation, which is impossible either at sea level or at mountain altitudes.

Measurements carried out with apparatus lifted on rockets have low accuracy because of the short time during which the rocket remains at high altitude.

Experiments carried out with apparatus lifted into the upper layers of the atmosphere on balloon sondes provide considerably greater statistical material; however, even in this case continuous recording of the intensity of the primary radiation is impossible.

An artificial Earth satellite offers very great possibilities for the investigation of variations of cosmic radiation. A satellite, generally speaking, can exist for several years and will make it possible throughout this entire time to carry out continuous measurements of the intensity of primary cosmic radiation.

Simultaneous performance of measurements by means of counters and ionization chambers may provide the possibility of comparing variations in the intensity of primary protons with variations in the intensity of heavier nuclei that form part of the primary cosmic radiation.

To analyze the nature of those phenomena that cause variations of the primary radiation, it is necessary to know the variations in different regions of the energy spectrum of cosmic rays. For this purpose the results of measurements carried out at different geomagnetic latitudes are compared. However, the accuracy of such comparisons is very low, since one has to compare the results of measurements obtained with the aid of different instruments, distributed, moreover, extremely unevenly over the terrestrial globe. Therefore even a very large number of ground stations for recording cosmic rays does not give a complete picture of the distribution of cosmic radiation over different latitudes and longitudes. This problem can be solved only with the aid of instruments installed on satellites whose orbits are chosen in a suitable manner.

For the study of variations in the intensity of cosmic radiation, the most favorable orbit is one passing through the poles. Since a satellite will make one revolution around the Earth at heights of the order of 1000 km in approximately 90 minutes, in an orbit through the poles the satellite will pass through the polar regions 32 times in the course of a day (16 northern and 16 southern). Measurements of intensity in the polar regions are of substantial interest for three reasons:

a) particles of low energies can enter the polar region;

b) in the latitude region 60–70° the intensity of cosmic radiation ceases to increase with increasing latitude. Systematic measurements of the latitudinal ...

...of the geomagnetic effect in the indicated region may reveal the reasons for the absence in cosmic radiation of particles of low energies.

c) In the polar zones a strong increase in the intensity of cosmic radiation was found at altitudes of the order of \(80\)—\(100\ \text{km}^2\). This increase in intensity may possibly be explained by the appearance, at certain moments of time, at these altitudes and latitudes, of low-energy particles which execute cyclic motions along the lines of force of the Earth’s magnetic field and therefore have the possibility of crossing the registering instrument many times.

II. VARIOUS PHENOMENA THAT CAN BE STUDIED WITH THE AID OF APPARATUS INSTALLED ON A SATELLITE

Let us consider the case when the orbit passes through the poles, the satellite is in the Earth’s shadow half the time, and information is transmitted throughout the entire lifetime of the satellite.

In this case, in only one day the intensity of cosmic radiation and the ionization produced by it will be known at more than 1000 points distributed over the entire surface of the terrestrial sphere, provided that measurements are made approximately every minute. Each measurement with apparatus of acceptable dimensions can be performed with a statistical accuracy of not worse than 3% for measuring the number of cosmic particles in the equatorial region and about 1% at middle and high latitudes, and not worse than 5% for measuring ionization at all latitudes.

The material obtained in only one day of the satellite’s flight will greatly exceed the entire stock of experimental data on the intensity and ionizing capacity of cosmic radiation beyond the atmosphere that has existed up to now. During the following day, data will be obtained at another 1000 points, etc. By comparing data for different orbits, for different days, it will be possible to judge variations in the intensity of cosmic radiation. If necessary, data for different days can be averaged, which will make it possible to increase the statistical accuracy of the observations.

Having at one’s disposal data on the intensity and ionizing capacity of cosmic radiation over the entire surface of the terrestrial sphere, one can draw interesting conclusions about the following phenomena:

1. Temporal variations in the intensity of primary cosmic radiation

a) The effect of large bursts in the intensity of cosmic radiation in connection with chromospheric eruptions on the Sun

The five very large increases in the intensity of cosmic radiation observed over the last 20 years occurred simultaneously with solar chromospheric eruptions. During these flares, acceleration of particles (protons or heavier nuclei) takes place on the Sun, followed by their emission. If such an eruption occurs during the flight of one of the satellites, it will be possible to carry out a sufficiently complete analysis of this phenomenon, since the increases in intensity over a large portion of the surface above the atmosphere will be known for a short period of time. Such large increases in intensity are extremely rare; therefore the probability of their occurrence during

the flight of one of the satellites is small. However, variations of the primary radiation during flares exceed by tens of times the variations observed at sea level. For this reason, increases in the intensity of the primary radiation by tens of percent are certainly not recorded by ground stations.

There is reason to suppose that these small increases in intensity occur comparatively often. Such a conclusion is suggested by experiments on the study of cosmic radiation in the upper layers of the atmosphere,^3 during which a number of authors^4 observed increases in intensity. Thus, the probability of recording an intensity flare beyond the limits of the atmosphere may turn out to be considerable.

At the present time calculations have been carried out of the motion of charged particles of different energies in the Earth’s magnetic field. Applying these calculations to particles emitted by the Sun, one can calculate the place where they will strike the Earth. Similar calculations have been performed, and the so-called “entry zones” of particles^5 have been obtained. In these zones, increases in intensity during a cosmic-ray flare should be maximal in comparison with other regions of the Earth. Experimental verification of the correctness of these calculations and of the assumptions underlying them requires an accurate delineation of these “entry zones” of particles emitted by the Sun. Since ground stations are located far from one another, an accurate delineation of the “entry zones” proves practically impossible. With the aid of apparatus on a satellite, these entry zones can be recorded with sufficient accuracy. At the same time, determination of the dependence of the magnitude of the increase in the intensity of cosmic rays on latitude will make it possible to obtain the energy spectrum of the additional flux of particles arriving at the Earth during a flare in the energy interval from 2 to 15 Bev.

b) Decreases in intensity during magnetic storms

It is known that during some magnetic storms the intensity of cosmic radiation decreases. This decrease, for strong storms, sometimes reaches several percent. In all probability, this decrease is caused by the scattering of low-energy particles in the magnetic field of the flux emitted by the Sun and producing a magnetic storm on the Earth.

Recording, during the flight of a satellite, the decrease in intensity associated with a magnetic storm will make it possible to determine with good accuracy the spectrum of the cut-off radiation, which will permit an estimate of the strength of the magnetic field carried by the flux and the width of the flux.

At the present time the structure of the fluxes emitted by the Sun is completely unknown. The width of these fluxes can be determined very roughly from the duration of the magnetic storm, although it is not clear how long the magnetic storm may continue after the Earth leaves the flux (how long the resulting ring current may exist). Repeated measurements of the intensity of cosmic radiation by means of apparatus installed on a satellite may, from the changes in the intensity of cosmic radiation, make it possible to judge not only the dimensions of these fluxes, but also their structure, and the locations of the magnetic fields carried by these fluxes. It should be noted that the probability of observing, during the flight of a satellite, a decrease in the intensity of cosmic radiation associated with magnetic storms is considerably greater than the probability of recording an increase in intensity associated with a solar eruption.

c) Periodic variation associated with the rotation of the satellite around the Earth (1.5-hour variation)

This variation is an analogue of the diurnal variation recorded by an instrument rigidly connected with the Earth. At sea level the amplitude of this variation is \(0.3\%\). Beyond the atmosphere the amplitude of the diurnal effect still remains unknown.

An instrument located on the Earth’s surface will periodically, every 24 hours, return to its former position (apart from the motion of the Earth around the Sun). The motion of the satellite will take place 16 times faster and, consequently, in one day the intensity will pass 16 times through a minimum and a maximum. Hence the accuracy with which the diurnal effect will be recorded will be considerably higher than the accuracy obtained with terrestrial instruments, since all possible secondary fluctuations of the intensity in the case of the satellite will be averaged, whereas in the case of a terrestrial instrument they may obscure the true effect. In the case of the satellite we have a multiple repetition of the same measurements, whereas in the case of a terrestrial instrument it is impossible to carry out such repeated measurement.

It is known that the diurnal effect increases during a magnetic storm. This is explained by an additional acceleration of particles passing through the corpuscular stream in one direction, and by a deceleration of particles moving in the opposite direction. In this case the phase of the additional effect is shifted somewhat. If the Earth enters a corpuscular stream emitted by the Sun during the flight of the satellite, this additional diurnal effect can be investigated in detail.

The amplitude of the additional diurnal variations should depend on the velocity of displacement of the magnetic field carried by the corpuscular stream, i.e., on the velocity of the stream. Therefore, by investigating the additional diurnal variation, it will be possible to determine the velocity of corpuscular streams emitted by the Sun near the Earth.\(^1\)

d) Variations in the intensity of heavy nuclei of primary cosmic radiation

As is known, several papers\(^6\) have been published indicating the existence of significant variations (by a factor of 2–3) in the intensity of primary heavy nuclei as a function of the time of day. In the same period several other papers\(^7\) were published denying the existence of noticeable diurnal variations in the flux of heavy nuclei of primary radiation. The authors of these latter articles consider the conclusions obtained by the above-mentioned authors to be erroneous or caused by causes as yet unknown. This question remains open up to the present time.

A more general question may be posed: to what extent do the variations of the multiply charged component of primary radiation coincide with the variations of the flux of primary protons.

Simultaneous recording of the intensity of cosmic radiation and of the ionization produced by it makes it possible to record variations of the multiply charged component. This is entirely possible, since about \(50\%\) of all ionization beyond the atmosphere is due to multiply charged particles. Direct measurement of the variations of the various components of primary radiation during different fluctuations of primary radiation can provide valuable material for testing hypotheses on the origin of cosmic rays.

d) Long-periodic variations

Very interesting studies of the dependence of the low-energy portion of the spectrum of primary cosmic radiation on the phase of the solar-activity cycle (11-year variation) were carried out by Neher.⁸

It was shown that during the period of maximum solar activity (1937–1938) the intensity of the primary flux becomes minimal, but its fluctuations are considerable; and, conversely, in years when the Sun is less active (1951), the intensity of cosmic rays increases, but their variations in this period are significantly reduced. In 1954 the ionization produced by primary radiation near the poles increased, in comparison with 1937, by a factor of 1.5 (Fig. 1).

Fig. 1.

The inverse dependence between solar activity and the intensity of the flux of particles arriving at the Earth indicates that the Sun is not a source of cosmic rays, but rather a factor affecting particles moving toward the Earth from interstellar space. Proceeding only from this assumption, one can explain the fact of the increased influx of low-energy particles during the period of minimum solar activity, when they are able to pass more or less unhindered to the Earth. In years of enhanced solar activity this possibility disappears.

These cases of scattering of particles of primary radiation can be attributed to the modulating effect of the streams emitted by the Sun⁹ and genetically connected with various formations on the Sun. During a period of maximum activity the Sun emits these corpuscular streams, carrying “frozen-in” magnetic fields, more irregularly and more intensely; therefore the variations of cosmic rays, especially of the flux of low-energy particles observed at high latitudes, will be more significant.

Assuming that in the future satellites will be launched periodically, one may hope that a beginning will be made in more thorough studies of annual, 11-year, and, perhaps, other as yet unknown long-period variations of the intensity of cosmic radiation.

e) Experimental verification of the theory of the connection of primary variations with secondary ones

Simultaneous observations of intensity variations on a satellite and in a large network of ground stations, organized in many countries, make it possible to compare the variations of primary cosmic radiation with the variations of the various secondary components registered on ...

at sea level, underground, and at mountain altitudes, and to test experimentally the theory of the connection between primary and secondary variations in different parts of the energy spectrum[^1].

2. Terrestrial and Interplanetary Magnetic Fields

In the case of the Earth’s dipole magnetic field, north–south symmetry of the latitude effect of cosmic radiation should be observed. Knowing the intensity over the entire surface of the planet, this can easily be verified. From the minimum of the intensity one can determine the effective geomagnetic equator and study its changes during magnetic storms.

It should be noted that, unlike direct methods of measuring the magnetic field, with the aid of cosmic radiation the magnetic field is probed at large distances from the location of the recording instrument, and therefore the general character of this field can be determined more accurately, since local anomalies in this case have practically no effect.

Such determinations of the geomagnetic field are very important, since all theories of the motion of cosmic particles proceed from the dipole magnetic field of the Earth, whereas already now there are assumptions, based on recent data[^10], that the latitude effect of cosmic radiation cannot be explained solely by the Earth’s dipole magnetic field. Analysis of the dependence of the intensity of cosmic rays on latitude and longitude may make it possible to detect an interplanetary magnetic field.

3. Measuring the Earth’s Albedo for Cosmic Radiation

In work using rockets it was found that the intensity of cosmic radiation does not depend on altitude up to \(200\) km. With a further increase in altitude, the appearance of some altitude dependence should be expected. There are three reasons for this:

a) the minimum energy of particles admitted by the Earth’s magnetic field to a given latitude decreases with increasing altitude, which should lead to an increase in intensity;

b) the geometrical shielding by the Earth decreases with increasing altitude, which will also lead to an increase in intensity;

c) the Earth’s albedo for cosmic radiation decreases with increasing altitude, which should lead to a decrease in intensity. Knowing the magnetic field that determines the behavior of cosmic-ray particles near the Earth (with the reservations made in Section 2 of this chapter), one can calculate the first two effects. The remaining altitude dependence will be due only to the Earth’s albedo for cosmic radiation. Thus it may be possible to obtain this important characteristic and to expand our knowledge of the primary spectrum of cosmic radiation.

4. Search for Electrons and Photons in Primary Cosmic Radiation

The search for the locations of sources of cosmic radiation in space by studying the anisotropy of the primary flux of charged particles presents great difficulties because of the influence of interstellar magnetic fields, which mix cosmic rays.

It may be expected that even particles with energies of the order of \(10^{15}\div 10^{17}\) eV become entangled in these fields and reach the observer not from the direction toward the source, but most often from other, possibly even opposite, directions. For this reason, up to now no anisotropy has been found for particles possessing energies of \(10^{15}-10^{17}\) eV, although for several years extensive air showers caused by charged particles of such energies have been recorded.

It may be expected that more valuable results in the search for the locations of sources of cosmic radiation can be obtained by studying the direction of the flux of the photon component of the primary cosmic radiation with the aid of a directional detector installed on a satellite oriented in space. Such a photon detector may be a stack of photographic plates, in which it is possible reliably to identify electron–positron pairs produced by photons, and the direction of their motion. With the aid of two detectors with collimators directed—one toward the presumed source of cosmic radiation (or toward the center of the Galaxy), and the other in a perpendicular direction—it may be possible to discover an anisotropy of the photon flux and determine the direction toward their source.

These investigations can be performed only with the aid of apparatus located on an artificial Earth satellite, since measurements of photons in the upper layers of the atmosphere are impossible because of the masking influence of secondary photons produced in the atmosphere.

With the aid of apparatus installed on a satellite, it apparently will be possible to detect the presence of electrons in the primary flux of cosmic radiation. In this case a stack of photographic plates can also serve as the detector, since in photographic plates the track of an electron can be reliably distinguished among the tracks of other particles.

III. APPARATUS FOR STUDYING VARIATIONS OF COSMIC RADIATION BEYOND THE ATMOSPHERE

The study of variations of primary cosmic radiation can be carried out by two methods: by measuring variations of the ionization produced by cosmic radiation, and by measuring variations in the number of particles passing through a counter of charged particles.

Measurements of the latitude effect above the atmosphere\({}^{11}\) have shown that the intensity of primary cosmic radiation changes by a factor of 10 from its minimum value at the equator to its maximum at high latitudes. As was noted in the first part, both increases in intensity and decreases in it are possible. Thus, the minimum dynamic range of the apparatus for measuring intensity variations must be taken to be a 100-fold range.

A very important question is the accuracy of measurement of variations that can be achieved with the aid of apparatus installed on an artificial satellite. There are two causes leading to variations in the measured intensity of ionization when the primary cosmic radiation is constant. One of the causes is associated with the change in the altitude of the satellite’s flight. As already noted, in this case one should expect an increase in intensity with altitude because of the decrease in shielding by the Earth and the decrease in the minimum energy admitted to the given latitude by the Earth’s magnetic field.

On the other hand, the intensity must decrease because of a decrease in albedo. The first two effects may be theoretically calculated—

considered; the third can be estimated after the experiment has been carried out and the results obtained.

The second reason is connected with the satellite’s own rotation. Indeed, if the material of the satellite is arranged asymmetrically with respect to the recording instruments, then the rotation of the satellite will lead to the fact that this material will shield the instrument sometimes from the side of the Earth, sometimes from the side of open space. A rough estimate of this effect shows, under certain assumptions concerning the relative arrangement of the recording instruments and the material of the satellite, that the resulting variation will be of the order of 5%.

If the instrument is not spherically symmetric, as is the case for a counter, then still another variation arises, associated with the rotation of the satellite. Indeed, it is easy to see that even under the assumption of isotropy of the primary cosmic radiation, the number of charged particles recorded by the counter will depend on the orientation of the counter in space.

Let us consider this question in more detail.

The number of particles arriving from the upper hemisphere and crossing the surface of the counter does not depend on the orientation of the counter relative to the boundary of the hemisphere, for an isotropic distribution of particles in this hemisphere. If the instrument is at altitudes of the order of several hundred kilometers above the Earth’s surface, then the counters record not only radiation from the upper hemisphere, but also partly from the lower hemisphere

Fig. 2.

(Fig. 2). The number of these additional particles from the lower hemisphere will depend on the orientation of the counter relative to the surface of the Earth, namely: a vertically arranged counter will count more than a counter arranged horizontally.

Calculations show that the ratio of the number of particles counted by a vertically arranged counter to the number of particles counted by a horizontally arranged counter is about 5% for a counter with ratio \(l/d = 3\), and 8% for a counter with ratio \(l/d = 6\), where \(l\) is the length of the counter and \(d\) its diameter. In reality, cosmic radiation is not isotropic because of the presence of the Earth’s magnetic field, which will increase this effect somewhat further.

Thus, there are a number of reasons leading to 5–8% variations in the number of recorded particles and in ionization at unchanged intensity of the primary cosmic radiation. Since it is very difficult to calculate these variations theoretically (it is necessary to know the orientation of the satellite, the altitudes of the satellite, geomagnetic coordinates, and the actual arran-

limiting the substances around the counters and the chamber), then it makes sense to place two counters arranged perpendicular to one another, with one of the counters placed as far as possible from the main body of the satellite.

With such an arrangement of the counters, the rotation of the satellite will affect the operation of one counter much less than that of the other; and since in all other respects the counters are identical, the systematic difference between the numbers of particles registered by the counters may make it possible to estimate the effect of shielding of the counter by the material of the satellite. This discrepancy will at least give an experimental estimate of the lower limit of the accuracy of the measurements.

From this point of view, the ideal case would be a satellite oriented in space so that the satellite axis coincided with the direction drawn from the center of the Earth to the satellite. In this case the shielding by the Earth and the influence of the material would remain constant (assuming a circular orbit of the satellite).

The installation of two counters with independent transmission of the number of discharges of each counter is also a good check on the correct operation of the apparatus in flight.

For transmitting the results of the experiments by radio, the problem arises of reducing the number of pulses transmitted from the counter, which leads to the need to use a scaling radio circuit. The requirement of economy imposes a restriction on the choice of the radio circuit. As uneconomical, all radio circuits made with electron tubes are excluded. Circuits using semiconductor triodes and thyratrons with a cold cathode prove acceptable.

If a scaling circuit with a scaling factor of \(1024:1\) is used, every 1024th pulse will be sent to telemetry (at the average cosmic-ray intensity) at high latitudes after 20 sec, and in the equatorial region after 200 sec.

Let us consider the individual elements of the apparatus.

a) Charged-particle counters

It is expedient to use counters having a low operating voltage and a long service life.

The counter supply can be provided by means of a low direct voltage to high direct voltage converter built with semiconductors. To reduce fluctuations of the output voltage of these converters, it should be stabilized by means of a gas voltage regulator. The high voltage after the gas regulator depends very little on the load current and the input voltage of the converter. The change in voltage when the temperature changes from \(-20^\circ\) to \(+50^\circ\mathrm{C}\) does not exceed 5 volts, which leads to a change in the number of counts by no more than \(0.25\%\).

b) Counting circuit using semiconductor triodes

Pulses from the counter go to a shaping cell (Fig. 3) assembled with semiconductor triodes. A pulse from the shaping cell triggers the first cell of the counting circuit; a pulse from the output of the first cell triggers the second cell of the counting circuit, and so on. The circuit of one cell is shown in Fig. 4. The output stage is an emitter follower, in whose emitter circuit relay windings are connected. The scaling circuit, at a collector voltage of 15 V, consumes a current

about 20 mA, i.e., the power consumed is about 300 mW. The circuit is capable of operating over a wide range of collector voltages: from 6 V to 20 V.

A divide-by-2 counting cell, assembled according to the circuit given above, is capable of counting pulses arriving at its input with a frequency up to 50 kHz over a wide temperature range: from \(-20^\circ\)C to \(+50^\circ\)C. The dead time of the

Fig. 3.

counter is \(10^{-4}\) sec. Consequently, pulses from the counter are separated by a time interval greater than \(10^{-4}\) sec, and with such a resolving power of the counting circuit (50 kHz) all of them will be counted by the counting circuit.

The loss of counts due to the dead time of the counter does not exceed 0.5% in the high-latitude region and 0.05% in the equatorial region.

Let us describe the apparatus developed for measuring ionization by means of an ionization chamber.

The dimensions of the chamber determine the statistical accuracy of the results obtained. In calculating the statistical errors it is necessary to take into account

Fig. 4.

the ionization produced by multiply charged particles. The greater part of the primary flux consists of protons. They apparently make up about 80% of the total number of particles. Helium nuclei are observed in a considerably smaller quantity (20%). A very small fraction of the total flux consists of nuclei of C, N, O (1.0%) and of other elements with \(Z > 10\) (0.2%).

A calculation of the possible magnitude of the fluctuations of the ionization current in a chamber 270 mm in diameter shows that, with the aid of such a chamber, measurements of the global intensity above the equator can be carried out with a statistical accuracy no worse than 4% per minute of observation. This error is due to multiply charged particles, because the ionization contribution of each particle is very large.

S. N. VERNOV, Yu. I. LOGACHEV, A. E. CHUDAKOV, Yu. G. SHAFER

The most suitable method for measuring ionization is the method developed by one of the authors (A. E. Chudakov). This method consists of the following (Fig. 5): the charge accumulated, owing to the ionization current, on the central electrode of the ionization chamber is periodically removed by closing contacts, and in this process a pulse is produced whose amplitude is proportional to the ionization. The closures are made at definite time intervals by means of a relay. The question arises as to at what time intervals it is most expedient to close the relay. These time intervals cannot be longer than several minutes, since otherwise errors will arise as a result of leakage of the charge during the time of its accumulation.

Fig. 5.

To obtain detailed information on the dependence of the intensity of cosmic radiation on latitude, it is desirable to shorten the time interval between relay closures. However, excessive shortening of this interval reduces the accuracy of the measurements. It should be specially noted that the output pulse furnished by the radio circuit cannot exceed a certain magnitude. Therefore, if the pulse from the chamber is too large, its measurement becomes impossible. Meanwhile, the ionization of cosmic rays to be measured changes by a factor of 10 merely due to the latitude effect. Variations in the intensity of cosmic radiation further increase the range of ionization within which measurements must be carried out with good accuracy at any value of the ionization.

In this connection it is impossible to choose a single interval between relay closures for measuring ionization on the satellite. The following is the most universal method of measurement.

The flight time of the satellite is divided into equal intervals \(T\), approximately two minutes long. Each such interval consists of several working time intervals following one another in an increasing sequence.

Application of this method makes it possible to realize a two-hundredfold dynamic range of the measuring device with its limited scale; the accuracy of such measurements will be sufficiently high at all latitudes, with a considerable increase of intensity during solar flares and with its decrease during magnetic storms. The moments of the onset and decline of these phenomena can also be determined with high accuracy by using the described time divider.

In Fig. 5 a diagram of the chamber with an electronic unit is presented. The spherical chamber, filled with spectrally pure argon to 5–10 atmospheres, may be made of thin steel. A vibration-resistant electrode in the form of a hollow thin-walled sphere is fastened to a stem passing through an insulator with a grounded guard ring. The material of this insulator must have sufficient mechanical strength and high volume and surface resistivities. A stabilized voltage is applied to the chamber, ensuring operation in the saturation regime. The radio-engineering channel is linear for signals at its input from 0.5 volt to 10 volts. The circuit described has been used in many experiments and has proved satisfactory.^12

CONCLUSION

The instrument designs described above make it possible, in the very near future, to carry out on a satellite measurements of the number of primary cosmic particles and of the ionization produced by them. There is no doubt that, with time, measurements on satellites will become the principal method for studying variations of cosmic radiation. When the number of satellites simultaneously in flight becomes sufficiently large, it will be possible to record variations of cosmic rays by means of instruments installed on satellites better than with the aid of the entire network of ground stations. During the International Geophysical Year the number of stations over the whole globe will be brought up to 130. These stations will be equipped with complex apparatus recording the meson and neutron components of cosmic rays. Nevertheless, the nonuniform distribution of these stations over the globe makes impossible a complete analysis of the phenomena leading to changes in the intensity of cosmic radiation. Measurements on a satellite cover the entire globe. Therefore, even at the initial stage of the investigations, instruments installed on a satellite, in addition to direct measurements of variations, will make it possible to calibrate the entire ground-based network of stations for continuous registration of cosmic rays.

Simultaneous measurements of the total ionization and of the flux of all charged particles will make it comparatively simple to determine the intensity of strongly ionizing particles and thereby, for the first time, to study variations of the multiply charged component of cosmic rays, consisting of helium and heavier elements.

In further investigations, those carried out on a satellite will make it possible to measure directly the number of primary particles up to very high energies (of the order of \(10^{15}\) ev).

Special attention should be paid to searches, in the composition of primary cosmic radiation, for high-energy photons, since these photons, traveling in a straight line through the interstellar medium, will be able better than any other radiation to indicate where cosmic rays are produced. If searches for high-energy photons prove successful, then it is possible that subsequently, in addition to radio astronomy, a special branch—gamma astronomy—will arise.

At the same time, with the formulation of experiments to detect high-energy photons, the question of the presence of electrons in the composition of primary cosmic radiation can also be resolved.

CITED LITERATURE

1. L. I. Dorman, E. L. Feinberg, UFN 59, 489 (1956).
2. L. H. Meredith, M. B. Gottlieb, J. A. Van Allen, Phys. Rev. 97, 201 (1955).
3. H. V. Neher, V. Z. Peterson, E. A. Stern, Phys. Rev. 90, 655 (1952).

1. A. T. Biehl, R. A. Montromery, H. V. Neher, W. H. Pickering, W. C. Roesch, Rev. Mod. Phys. 20, 360 (1948); M. A. Pomerantz, Phys. Rev. 81, 731 (1951); J. J. Lord, A. W. Elston, M. Schein, Phys. Rev. 79, 540 (1950).

2. J. Firor, Phys. Rev. 94, 1017 (1954).

3. J. J. Lord, M. Schein, Phys. Rev. 80, 304 (1950); J. J. Lord, M. Schein, Phys. Rev. 78, 484 (1950); E. P. Ney, D. M. Thon, Phys. Rev. 81, 1068 (1951); V. H. Yngve, Phys. Rev. 92, 428 (1953).

4. P. S. Freier, G. W. Anderson, J. E. Naugle, E. P. Ney, Phys. Rev. 84, 322 (1951); G. W. McClure, M. A. Pomerantz, Phys. Rev. 84, 1252 (1951); G. W. Anderson, P. S. Freier, J. E. Naugle, Bull. Am. Phys. Soc. 28, No. 3, 7 (1953).

5. H. V. Neher, Phys. Rev. 103, 228 (1956).

6. H. Alfvén, Cosmic Electrodynamics, Foreign Literature Publishing House, Moscow, 1952.

7. J. A. Simpson, K. B. Fenton, Phys. Rev. 102, 1648 (1956).

8. L. H. Meredith, J. A. Van Allen, M. B. Gottlieb, Phys. Rev. 99, 498 (1955).

9. S. N. Vernov, N. L. Grigorov, G. T. Zatsepin, A. E. Chudakov, Izv. Acad. Sci. USSR, Phys. Ser. 19, 493 (1955).