Considering the surprising results, which these radiation observations brought out, it is very desirable that such investigations would be repeated at the most diverse places under the most diverse conditions. However if these results should have their full value and be comparable together, then they must be employed with the same apparatus. By the Campbell's work (2) it is particularly proven that the instrument walls themselves send an ionizing radiation, which is different with different metals.
I tried therefore first to make the apparatus more perfect and its handling more simple. Then I arrived at the following results.
As the threads themselves were used as scatter bodies, the capacity of the whole loaded system amounted to only 1.2 cm (3).
The volume of the housing could not be too large considering the need for easy transportability. For the shape of the housing it was considered to have possibly perfect isolation from air and the possibility of partial radiation absorption by adding thick{er} disks. A situated drum of 17 cm diameters and 13 cm depth was chosen, with a volume of 2700 ccm after subtraction of the inserted microscope piece. The two even boundary surfaces are completely free and can be strengthened by slid-over lead disks. The disks themselves are produced from thin zinc sheet, but can be exchanged easily by others. In the cylinder barrel are let in openings for the light and a microscope, the load device and two Na dry containers.
The threads are fastened to an amber plug {Bernsteinpfropf?} completely in the inside of the housing. It is carried by a brass stick, which protrudes above from the housing and ends in a rimmed disk A. With this disk, the level of the two threads can be turned and be placed always perpendicularly to the axis of the microscope.
Also, it seemed necessary that one could convince oneself at any time of the isolation ability of the instruments. Since it was however shown that the scattering depends much on whether air in the inside can renew itself or not, it seemed valuable to be able to make this check without the need to open the housing {container}.
C.T.R. Wilson (4) makes himself free from isolation errors by charging the carrier of the isolating sulfur piece to the middle potential of the aluminum lamella and then assumes that the errors cancel out each other just evenly. However, the procedure requires a constant battery and is therefore somewhat complicated for use outside of the laboratory. But especially at places where one encounters abnormal radiation values, e.g. in caves, the proof of isolation becomes particularily necessary.
The following method requires no {additional} helping instruments and can
be performed with completely closed housing. In a certain time, about 1
second, the observed charge loss Q is generally put together
from the isolation loss A and the loss by the ions in the enclosed
air. If V is the air volume and B the produced ion
charge of a sign per ccm and second, then, with saturation current:
If one strongly reduces the volume V, then the proportion of the
radiation decreases accordingly, while the isolation losses remain the
same with the same potential, so that one can determine the two parts
separately. Thus, now is
Therefore B = (Q - Q1 / (V - V1) and A = (V Q1 - V 1 Q) / (V - V1) , and if V1 is small against V, then A = Q1 - Q V1 / V .
The volume reduction is simply obtained if one shifts a small cylinder over the threads of the instrument. The figure shows the mechanism in the inside. The cylinder has a diameter of 2 cm.
It normally sits in a slit pipe over the instrument. If one wants to check the isolation, one reads off only the position of the threads and then shifts the cylinder down guided by two screws S S reaching into the slits. After an appropriate time, about 1 hour, one pushes it {the cylinder} back again and immediately reads off the loss. For example, while the loss in my apparatus without cylinders came on 25 volts/h, it decreased down to 0.4 volts/h with cylinder slid over. The volume of the whole housing was 2700 ccm and that of the cylinder was 30 ccm.
From this observation now follows:
1. In no case is the isolation loss larger than Q1, thus here 0.4 volts or 1.6 per cent of the total effect. For many cases that will already be sufficient.
2. From this value however, one should subtract the amount of the penetrating radiation falling onto volume V1 and all of the radiation by the same excited secondary radiation {???}. Unfortunately it has not been successful so far to separate this effect cleanly from the influence of the walls. However, as it will be shown in the following, at least 42 percent of the whole effect must be set with this instrument to come from penetrating rays from the outside. That is 10.5 Volts out of 25 Volts. 0.1 Volts from these 10.5 Volts are allotted to the volume of the narrow pipe. The isolation loss is therefore surely smaller than 0.3 Volts or 1.2 percent of the whole effect.
Strictly taken, one would still have to note that the gamma-rays are partially absorbed by the wall of the cylinder. However one can easily make sure that the absorption does not achieve a noticeable amount by such a thin wall.
3. A fraction of these 0.3 Volts are attributed to ionization by alpha rays, which come from the walls of the narrow pipe itself. The amount of this influence is not exactly well-known. Meanwhile Campbell (5) showed that with sufficiently small containers the effect of the radiation from the walls is also proportional with the volume. So, if one builds the small tube with a material with the same isolation capabilty than the whole housing, then the reult will be that the effect of the radiation coming from the walls will reduce proportionally with the volume. In that measure, when this condition is fulfilled, the above formula applies exactly, and results e.g. from my observations for the isolation loss to
or 1/2 percent of the total effect.
The capacity of the instrument changes by approximation of the cylinder and it would make a separate calibration necessary. Therefore, the reading is to be made only with a removed cylinder, then everything can be referred to the same calibration. And thus to make a mistake completely impossible, there are no light openings in the cylinder. Then at the same time the construction becomes simpler and the separation of the small {cylinder} space of the large space {of the whole unit} more perfect.
To avoid penetration of fresh air through the slot of the adjustable tube {pipe} into the inside of the apparatus, another cylinder is intended, which is closed on top amd which closes the whole out-standing pipe and seals it with a layer of a greased leather ring. In similar way, the other openings are locked, too.
Originally, when the lower thread ends were locked via a quartz thread, a bad state resulted in that the quartz thread electrified itself and thereby tightened the threads. Now the threads are made free-hanging, only kept by a small spinning thread {?}. The same is selected in such a way that it hangs completely loosely during measurements and holds only the lower ends when turned {?}. The mechanism proved sufficently durable even with violent impacts during transport.
The readings of the apparatus are independent of the temperature. Meanwhile it showed up that internal air flows formed inside the wide housing if the apparatus is heavily illuminated on one side by the sun or another source. Although, this does not cause an error in the reading since both threads always move a little back and forth at the same time. Nevertheless we have tried to avoid this effect by mirrorfinish polishing of the housing. And it is recommended to protect the apparatus against direct sunbeams. It proved very excellently to surround the housing with a cotton wool layer.
At first, the influence of the polarization showed up very strongly when loading {charging}, and it must have been the more noticeably, the smaller the capacity and the more largely the sensitivity of the apparatus was. However, after the housing was closed for several days and drained with sodium, this circumstance disappeared completely. One can immediately take the first reading after charging {loading}.
The execution of the experiments is therefore extremely simple. One adjusts the apparatus in such a way with the help of the foot screws that the threads appear sharp, loads at the best by connecting to a zamboni pillar {battery?} and then only needs to read out every half hour or full hour. To make sure of the saturation current, one should never let the charge drop below 100 Volts.
The apparatus is produced by the company Guenther & Tegetmeyer to Braunschweig and, if desired, supplied with a light wooden housing for transportation.
The continuously beautiful weather during last October and November was extraordinarily favorable for these observations. The month of October was particularly characteristic thereby because in course of this month the summer type of the potential gradient changed to the winter type with vanishing midday depressions. The gamma radiation also showed a deviating winter type without the midday depression.
After some preparing observations at the beginning of October rainy weather set in on the 10th and 11th. With the clearing-up on the 12th the observations started. On the 12th to 15th the weather was continuously beautiful with completely summerly character. On every four days the same process of the radiation were measured, two maxima at 8am-9am in the morning and 8pm-9pm in the evening, and two minima after noon and after Midnight. The following table contains the hourly average values in Volts per hour:
| Time | 12-1 | 1-2 | 2-3 | 3-4 | 4-5 | 5-6 |
|---|---|---|---|---|---|---|
| In the morning | 17.2 | 16.6 | 16.6 | 16.6 | 16.7 | 16.7 |
| In the afternoon | 18.4 | 18.3 | 17.7 | 17.3 | 17.3 | 18.6 |
| Time | 6-7 | 7-8 | 8-9 | 9-10 | 10-11 | 11-12 |
| In the morning | 17.9 | 18.9 | 19.7 | 19.4 | 18.6 | 18.8 |
| In the afternoon | 18.4 | 18.5 | 19.2 | 18.6 | 18.3 | 18.3 |
Under consideration of the capacity and the volume, the result is that an hourly loss of 1 Volts corresponds approximately to 1.6 produced ions per ccm and second. The corresponding values in this table thus range between 25,6 and 31,5 ions. The smallest ion number, observed without any other shield than the housing walls, amounted to 20 ions per second.
The amplitude of the morning fluctuation is the larger one. It amounts to 16 percent of the max. value, compared to 10 percent for the afternoon fluctuation. It is not impossible that this small difference would turn around with a larger set of days. Otherwise we would have a deviation from the summer type of the potential gradient here, where mostly the afternoon maximum is the larger one {of the two}.
Rain weather occured on October 16th and 17th. Although the observations showed generally the same process, they were nevertheless not used for calculating the average values.
Then came the large fair weather period from October 18th until November 10th, which was only once, on October 24th, interrupted by clouds and small precipitation. The weather had however an already winterly character and during the night times the thermometer dropped repeatedly below zero {Centigrade} {= below freezing level}.
Now it is to be seen very characteristic, how the midday depression also disappeared in the penetration radiation during the progress of the season.
In the second half of October, each hour was read off and the observations were usually continued at the night, however only every 2 - 3 hours of readings. For some of these readings I am very obligated to thank some of my friends.
The amplitude of the afternoon course amounted to only about 4.5 percent of the maximum value.
In November the midday depression almost disappeared completely. At the same time, the morning maximum seemed to shift to 10am - 11am. The amplitude amounted to 21 percent of the highest value, was thus around 5 percent higher than in October. Both are in full agreement with the potential gradient, which indicates a stronger daily fluctuation in the winter with somewhat delayed morning maximum (6).
As then in December bad weather set in with frequent precipitation, clouds and fogs, there was no more noticeable period to be seen with the penetration radiation.
As far as these observations probably are enough, they result with a complete parallelism between air potential and penetrating radiation of the atmosphere in all details.
2. Likewise, the influence of the location on the radiation is of greatest importance. It is however difficult to obtain safe results over this point because of the temporal fluctuations, which always occur in parallel. In particular one can call such small fluctuations, which remain in the area of the daily period, only real with the largest caution. Only if one operates with two apparatuses, which are compared together beforehand at a longer time, one will be able to state something more determining about it {the effect}. Then particularly observations in ballons and with kite flights could give very valuable information whether the starting point of this radiation is the earth, or the atmosphere, or the stars. Elster and Geitel (7) already have seriously pointed out the importance of observations in caves.
At the beginning, only one apparatus was used. With that apparatus, the following influences could be proven with sufficient certainty. In the room, even close to an open window, the amplitude of the daily period was on the average 9 percent of the highest value, averaged from values collected during eight consecutive and undisturbed days, those of November 1st to 8th.
On November 9th to 16th, the apparatus was outdoors just in front of a window of a room at southeastern direction. There, the fluctuations amounted to 21 percent. From the relatively small fluctuations in closed spaces it explains itself probably sufficiently that some researchers found the radiation as strong at day as at night.
In contrast, the absolute values of the scatter were noticeably stronger in the room than outdoors. The following specification contains the losses in volts/hour:
| time | outdoors | inside the room |
|||
|---|---|---|---|---|---|
| 28 December | 12 | to | 3 p.m. | 20.7 | |
| 3 | 7 " | 25.0 | |||
| 7 | 8 " | 19.7 | |||
| 8 | 9 " | 27.0 | |||
| 29 December | 6 | 7 a.m. | 25.4 | ||
| 7 a. | 6 p.m. | 20.0 | |||
| 6 | 8 " | 22.3 | |||
| 8 | 9 " | 19.0 | |||
| 30 December | 6 | 6:30 a.m. | 25.2 | ||
| 6:30 | 12 " | 20.0 | |||
| 12 | 1 p.m. | 22.4 | |||
| 1 | 9 " | 19.5 | |||
| average | 19.8 | 24.5 | |||
The room was surrounded by brick walls of approximately 1 m thickness. Thus, those observations acknowledge the specification of Rutherford (8) that according to Cooke's measurements noticeable penetrating radiation comes from clay bricks. Anyhow, since the thick walls also absorb a fraction of the outside available radiation, then its self-radiation is still larger than the corresponding difference of these numbers.
Additionally, I had the opportunity to perform observations in the expanded chalk caves, which are in the proximity of our college. The rock, known in geology {science} as Maastrichter chalk, is very soft. For centuries it served as building material for simple buildings, whereby in the course of time the caves stretched several kilometers long. The stones are not dynamited, but instead cut with the saw. Therefore, air pollution by smoke of explosives is not present. At some distance from the entrance, the temperature {inside the caves} is almost 11o C during the whole year. The humidity is 100 percent.
The observations were repeated on different days and different places of the caves. Above all, those days were selected where the outside temperature also amounted to almost 11o C.
Always, observations were performed outside beforehand and afterwards. These values differ no longer from each other than otherwise observations in the appropriate time interval probably did {?}. The stay in the caves themselves was expanded from 1 hour to 5.5 hours.
The apparatus was loaded {charged} beforehand and already 1 - 2 hours {later} the voltage drop {loss} was observed. Then the apparatus was carried into the caves in loaded status and observations were simply continued there without opening anything on the apparatus.
Then it showed without exception, but even more strongly pronounced, the same appearance which Elster and Geitel observed in a rock salt cave, i.e. an important reduction of scatter inside the caves. The following compilation shows in the losses in volts per hour. The latter gives the reduction of the scatter in percent of the average value from the observations, which were made outside beforehand and afterwards.
| Day | Duration Hours |
Loss in Volts | Reduction in Percent |
||
|---|---|---|---|---|---|
| beforehand | in caves | afterwards | |||
| Oct. 31 | 1 1/3 | 17.3 | 9.9 | 18.6 | 42 |
| Nov. 6 | 1 | 15.4 | 9.0 | 14.2 | 40 |
| Nov. 14 | 5 1/2 | 13.5 | 8.3 | 15.3 | 43 |
While the scatter in the salt mines reduced by 28 percent, the same reduced in the chalk caves of Valkenburg by 42 percent. The reduction immediately started after entering the cave and stopped when leaving the same. The thickness of the rock layer above amounted to about 15 meters at the used {observation} places. In the proximity of an exit a reduction occured likewise, but to a accordingly smaller amount {?}.
Since observation errors appear impossible, both after the whole process of the investigation and because errors in the sense of the changes are improbably to begin with, then it follows with certainty from these observations with the used apparatus that at least 42 percent of the losses are based on penetrating radiation from the outside. This result is still to that extent remarkable, since Cooke (9) did not succeed to dim more than 30 percent of the radiation with help of lead shields, even after he set the apparatus into a 5 ton {5000 kg = 5.5 US tons} heavy lead block. Since however the lead is radioactive, then this difference cannot appear strange.
If one compares this result with what Elster and Geitel found in the rock salt mines, and Gockel and Wulf (10) found in the Simplon Tunnel, then the influence of the surrounding rock mass results to be a double one. Once, and it probably agrees therein for all rocks, they protect from the outside available radiation and, on the other hand, themselves send out penetrationable radiation. Depending on whether the second {latter} effect outweighs against the first one, the total radiation inside the earth is either more largely (Simplon) or smaller (salt mines, Valkenburger chalk) than in the free {outside} air.
One has therefore a very simple medium with the described apparatus to examine the radioactivity of rocks in caves, tunnels and mines. Just recently J. Joly (11) pointed out that such observations would be of greatest importance for geology science. It would contain direct proof for the question whether the temperature increase the inside the earth can be attributed to radioactive substances or not. Thus, the temperature gradient should rise or fall the same time than the penetrating radiation {gradient}. Especially, places with abnormally large or small temperature gradient would be significant. Our observations in the Simplon Tunnel, where the temperature gradient is well known to be far above normal, speak for the radioactive origin of the warmth. The Valkenburger observations are not to be used for this purpose because the caves are not situated deeply enough to determine the temperature gradient with some certainty.