Victor F. Hess (Vienna), About Observations of the Penetration {through-going} Radiation During 7 Balloon Flights ============================================================== [Physikalische Zeitschrift XIII, 1912, pages 1084-1091] In the previous year I already had the opportunity to perform two balloon flights to examine the penetration {through-going} radiation; I already reported about the first flight during the science convention in Karlsruhe (1). At both balloon flights, radiation levels at altitutes up to 1100 meters showed no significant differences from the {typically} observed surface radiation. Gockel (2) couldn't find the expected decrease in altitude radiation during {his} two balloon flights either. It was therefore concluded that there must be another source of penetration {through-going} radiation besides the gamma ray radiation of radioactive substances on the earth surface. A subsidy of the Emperial Academy of Science in Vienna now allowed me recently to perform a series of another seven balloon flights, where a larger amount and in other respect extended number of observation material was gained. Two Wulf radiation instruments of 3 millimeter wall thickness served for the observation of the penetration radiation. They were completely airtight and capable to withstand the {typical} pressure fluctuations occuring at all balloon flights. Instrument 1 had an ionization chamber volume of 2039 cubic centimeters and a capacity of 1.597 centimeters. Instrument 2 had a volume of 2970 cubic centimeter and capacity of 1.097 centimeters. A charge loss of 1 Volts per hour was therefore proportional to a ionization intensity {force, strength} of q = 1.56 iones per cubic centimeters and second {iones/ccm/sec} in instrument 1, and q = 0.7355 iones per ccm and sec in instrument 2 {number missing in text; typo}. Both instruments were electrolytically galvanized to reduce the internal radiation {Eigenstrahlung} of their walls as much as possible. The suggestion for this {treatment} was made by Herr Privatdozent (private lecturer) Dr. Bergwitz. After this treatment, instrument 1 showed a normal ionization of approx. 16 iones, and instrument 2 showed approx. 11 iones per ccm and second. A further essential improvement was added by the company Guenter & Tegetmeyer in Braunschweig: so far, the focussing of the threads {wires?} was made just by shifting the eyepiece, which non-trivially changed the magnification and made reading differences of up to 0.5 possible after repeated adjustments. The mentioned company now installed an adjustable negative lense {?} in the eyepiece which enables the focussing at the various thread spreadings without noticeably changing the magnification. The accuracy of adjustability is thereby considerably improved. Since the wall thickness of the instruments 1 and 2 was three millimeters, only gamma rays could substantially take effect. To simultaneously study the effects of beta rays I also used a third instrument: this one was not airtightly built, but consisted of an ordinary Wulf two-threaded {-wired} electrometer enclosed in a cylindrical ionization container of 16.7 liters volume, made of the thinnest commercially available zink sheet (0.188 millimeters thickness). This way, even soft radiation by beta rays could in part still take effect. A zink pin of 20 cm height set onto the thread{wire}attachment{clamp} served as dispersion body. The capacity was 6.57 centimeters. The determination of the ionization loss was done with the thick-walled Wulf radiation instruments 1 and 2 in usual way with pushed-down {open} protection tube. The hourly charge loss was 0.2 Volts with instrument 1 and 0.7 Volts with instrument 2. The isolation was never disturbed, even during the soggiest weather. With the thin-walled instrument, the ionization chamber had to be detached to read the ionization loss {value}. Then, only the voltage loss of the electrometer was subtracted from the observed total dispersion, after converting to the capacity of the completely assembled instruments. Since all observations of penetration radiation made on towers always stated a decrease in radiation, whereas Gockel and I so far could not find such {a decrease} for sure, it was important to do measurements during longer flights at lower altitude to accumulate confident average values. Further attention was required about the fluctuations of the radiation. Pacini (1) undoubtedly found simultaneous fluctuations of discharge speeds at two Wulf radiation instruments after hourly readout intervals during parallel observations, both on land and also over water {ocean}; obviously, the reason {source} of the fluctuations lies outside the instruments, in the radiation itself. It was therefore very important to find out whether such simultaneous changes of radiation could be noticed during balloon flights, too. Since this could possibly be done most soundly on long duration flights at constant altitude, I achieved most part of my observations during night flights. The last and most important point of his examinations was the measurement of radiation at altitudes as high as possible. While the low carrying capacity of the gas used at the six flights started at Vienna didn't allow {to fly high altitudes}, along with metereological contingencies, I managed during an ascent conducted with {a} hydrogen {balloon} at Aussig at the Elbe to perform measurements at altitudes of up to 5350 meters. Before every flight, several hours of control observations were made with all three instruments. For this, the instruments were attached to the balloon basket via consoles, same as they were mounted during the flight. The observations prior to the flights carried out on the club field of the k.k. {?, old-fashioned emperial title acronym} Austrian Aeroklub, which was a flat lawn in the Vienna Prater. L. V. King (2) recently expressed the assumption, that observations at balloons could possibly be distorted by the near presence of radioactive ballast sand. I never found an increase of radiation in close vicinity of larger stocks of ballast sand. The air pressure inside the ionization chambers of instruments 1 and 2 is always the same, same as at {the gound at} the lawn of the ballon flight start (750 millimeters in average). Whereas the thin-walled instrument 3, the air pressure is always the same as the surrounding air. Therefore, it is required to apply a reduction of directly observerd {readout} values, especially from observations at higher altitudes. Under the condition that the ionization generated by the penetration radiation is proportional with the pressure, the currently observed radiation value was multiplied with the ratio of the normal pressure (750 mm) and the averaged pressure b observed during the measurement interval. One needs to remark that this type of reduction brings {hides} a certain uncertainty: because it is assumed without question that the remaining radiation of the container walls also changes proportionally with the pressure inside the container. This may not be true {by all means} if for example this remaining radiation only has a very weak penetration capability, such as alpha rays. Therefore, the non-reduced radouts of instrument 3 will be included in the discussion about the measurements. In the following tables, q1, q2, q3 stand for iones per cubic centimeter and second of the observed penetration radiation at instruments 1, 2, 3, respectively. For this, the elementary quantum is assumed to be e = 4.65 * 10^-10 E.S.E. The averaged altitude of the balloon during each of the observation intervals (one hour each, in average) was gathered by a geometric method from the barograph curve. Then the averaged relative altitude {from ground level} was determined using the {known} sea level altitude of each of the towns flown over. The daytime hours are displayed in the tables in 24-hour format. The detailed report about all observations made during the balloon flights was handed over to the Emperial Academy of Science in Vienna and it is released in their meeting minutes {reports}. First Flight. The first flight happened in occurence with the solar eclipse on April 17, 1912, which was stronly partial in Lower Austria. Between 11am and 1pm at 1900 - 2750 meters absolute altitude, observations were made over an almost completely covered Kumulusdecke {cumulus cover/blanket?, don't know the term, sounds like a scientific term for a type of cloud pattern}. No decrease of penetration radiation was noticeable during the eclipse. E.g. before the flight, instrument 1 showed an ionization of 10.7 iones, 11.1 iones at average relative altitude of 1700 meters, then 14.4 at 1700 - 2100 meters, during the first phases of the eclipse, and later 15.1 iones at approx. 50% blockage of the sun. Further measurements were not possible since the balloon was forced to descent due to cooling of the gases. Thus, an increase of radiation was found at approx. 2000 meters {altitude}. Since the eclipse didn't have a noticeable effect on the penetration radiation, we may conclude that, if a part of the radiation is of cosmical origin, it unlikely comes from the sun itself - at least if one assumes a direct straight path {spread} of gamma radiation. This point of view will be further confirmed since I never found a significant difference in radiation between daytime and nighttime. Second Flight (April 26-27, 1912). Balloon: "Excelsior" (1600 cubic meters illumination gas) Skipper: Hauptmann (Captain) W. Hoffory. Observer: V. F. Hess -------------------------------------------------------------------- # | | av.altitude | observed radiation | time |-------------|------------------------------------ | | abs. | rel. |instr.1|instr.2| instrument 3 | | m | m | q1 | q2 | q3 | q3 (reduced) -------------------------------------------------------------------- 1 | 16:40-17:40 | 156 | 0 | 15.6 | 11.5 | -- | -- * before the 2 | 17:40-18:40 | 156 | 0 | 18.7 | 11.8 | 21.0 | 21.0 * ascent at 3 | 18:40-21:00 | 156 | 0 | 17.8 | 11.6 | 19.5 | 19.5 * club lawn 4 | 21:30-22:30 | 156 | 0 | 17.8 | 11.3 | 20.0 | 20.0 * (Vienna) 5 | 23:26-00:26 | 300 | 140 | 14.4 | 9.6 | 19.4 | 19.8 6 | 00:26-01:26 | 350 | 190 | 16.2 | 9.9 | 17.4 | 17.9 7 | 01:26-02:26 | 300 | 140 | 14.4 | 10.1 | 17.7 | 18.1 8 | 02:26-03:32 | 330 | 160 | 15.0 | 9.6 | 18.2 | 18.7 9 | 03:32-04:32 | 320 | 150 | 14.4 | 9.8 | 18.5 | 19.0 10 | 04:32-05:35 | 300 | 70 | 17.2 | 13.2 | 20.6 | 21.0 11 | 05:35-06:35 | 540 | 240 | 17.8 | 11.8 | 19.6 | 20.8 12 | 06:35-07:35 | 1050 | 800 | 17.6 | 10.0 | 18.1 | 20.3 13 | 07:35-08:35 | 1400 | 1200 | 12.2 | 8.8 | 17.3 | 20.3 14 | 08:35-09:35 | 1800 | 1600 | 17.5 | 10.9 | 17.3 | 21.3 The above table shows an overview over all observations made at the second flight. The ascent occured at 11pm {night time}. By careful steering it was successful to keep the balloon at almost stable altitude (300-350 meters) for 6 hours, which was important for the determination of fluctuations in the radiation. The flight was leading over the Prater into southern direction, then wind was calm, and finally the balloon drifted back north back over Florisdorf, Stockerau, Guntersdorf to Maehren. At 10:30am, after reaching a maximal altitude of 2100 meters, we landed {docked} in Pausram, south of Bruenn. The sky was free of clouds during the entire 11.5 hour trip. From the table it shows, above all, that the radiation is indeed lower at low altitude than at ground level itself. If we compute the averages: instrument 1 instrument 2 instrument 3 before ascent: q1=17.5 q2=11.55 q3=q3(red)=20.2 140-190m above ground: q1=14.9 q2=9.8 q3=18.2 q3(red)=18.7 The ion differences therefore are 2.6, 1.8, 2.0, and 1.5, respectively. In average, the difference is approx. 2 iones. This decrease in radiation by 2 iones apparently comes from the absorption of gamma radiation by radioactive ground substances in the air. According to a calculation of King (1) is the gamma radiation already reduced to 24% at 160 meters altitude. The above mentioned difference by 2 iones is therefore equivalent to approx three quarters of the total ionization intensity generated by gamma radiation in the earth crust. ==> Thus, the total amount of gamma radiation in the earth crust probably generates approx. 3 iones per cubic centimeter and second. <== (At the low altitude of 160 meters, a decrease of induction amount {?} and an eventually possible increase of radiation coming from above can be ruled out.) Also, the fluctuations in radiation are strikingly appearant in the table. At first, we can already see from the ground level observations that the readouts of several neighboring instruments are not exactly parallel. This is probably mainly due to the readout errors.