The contribution by Domenico
Pacini to the cosmic ray physics
CRIS2010 - Catania
N. Giglietto
Dipartimento di Fisica
Università di Bari
Abstract
Between 1909 and 1911, several researches started to
investigate the unknown radiation that later identified as
cosmic rays. Several experimentalists tried to identify the
origin of this radiation in particular Victor Franz Hess,
Theodor Wulf and Domenico Pacini.
Among them the important work by Domenico Pacini,
almost forgotten now but perfectly known at that time,
had a crucial role to address the answer to the origin of
the radiation in the right way.
The most surprising and interesting thing moreover is that
these important pioneers practically defined at that time
the experimental ways to study comic rays: from space
and air, on ground and underground using only
electroscopies!
Domenico Pacini in particular may be considered as the
pioneer of underground cosmic ray experiments, and
Hess proved with his systematic balloon studies the
extra-terrestrial origin of CRs originating the air-space
studies on CRs
Acknowledgments
• This talk is based on the work started (and
going to be published) by F. Guerra(Rome)
and N.Robotti (GE) that have studied the
original documentation and the work by A.
De Angelis (Udine University), S.
Stramaglia, A. Garuccio (Bari University)
and myself to translate original papers and
discover documents inside the Bari
University
Timeline-1
• 1896 Bequerel discovered the radioactivity
• 1901 – two groups J.Elster and H. Geitel (Germany) and
C.T.R. Wilson(England) concluded that some unknown
source of ionizing radiation exists and Ernst Rutherford
and other Canadian groups confirmed
• 1903 Ernst, Mc Lennan, Burton, Rutherford Cooke:
confirmed the radiation was penetrating using a lead
absorber (In those years the radiation was thinked to be
originated by the soil)
• 1907 T.Wulf realized a new electroscope
• 1907-1910- Pacini measure the ionization rate on ground
and on sea
• 1910-1911: radiation intensity doesn’t decrease with the
height as calculated taking into account the air absorprtion
(and still considering the soil as the origin)
• 1910 Theodor Wulf developed an electrometer and used it
on top of Eiffel tower and in a cave in Valkenburg(Holland),
the rate in the cave is less then that on surface, the rate on
top of Eiffel tower doesn’t decrease and his paper on
Physikalische Zeitschrift was not widely accepted
Timeline-2
• Gockel (balloon), 4500 m (1910)
• 1910 Pacini performed measurements on ground and
sea and underwater 1911
• 1912 Hess performed the balloon flights (5530m) and
during a solar eclipse
• 1913- Hess and Kolhorster ballon flights up to 9Km
• 1922-23 measurements up to 16km doesn’t evidentiate
changes with the height (terrestrial origin?)
• 1925-new measurements (less precise than Hess) by
Millikan proved the extraterrestral origin (thinking to
gamma-rays) and conied the term "cosmic rays“ , and
excluding any effect due to the atmospheric electricity as
Hess had thought. Starting the debate about neutral
(gamma-rays) or charged nature of the radiation
• During the decade from 1927 to 1937, a wide variety of
experimental investigations demonstrated that the
primary cosmic rays are mostly positively charged
particles
Introduction
At the beginning of the XX century the italian Domenico
Pacini and the austrian Victor Hess reasearchers involved
in studies to understand the reason of the spontaneous
ioniziation properties of the air, and developed at the
same time two experimental reasearch lines that led later
to the discovery of Cosmic Rays.
•D. Pacini, “La radiazione penetrante alla superficie ed in seno
alle acque”, Il Nuovo Cimento 3 (1912) 93 now translated
http://xxx.lanl.gov/PS_cache/arxiv/pdf/1002/1002.1810v1.pdf
•V. F. Hess, ¨Uber Beobachtungen der durchdringenden
Strahlung bei sieben Freiballonfahrten“, Physik. Zeitschr. XIII,
1084-1091 (1912)
There is no doubt about the relevant role of these studies
in the community at that time
Pacini’s short curriculum
• Born in Marino (Rome) on february, 20th 1878
• Physics degree on 1902, at Rome University
• 1903-1905 assistant at the Physics Institute in
Rome
• 1905-1927 assistant at the Main Royal Bureau of
Meteorology and Geodynamics (Regio Ufficio
Centrale di Meteorologia e Geodinamica), in this
role was born his interest on the electrical
properties of the atmosphere
• Agosto 1927: he become main geophysics role
• 1928 he becomes full professor in physics at the
Bari University – Medicine Faculty
• 1934 died for a pulmunite
Review by Wigand, Phys. Z. XXV, 445
(1924), “About the radiation coming from
above the Earth”
“...Pacini was the first to try to measure
the amount of external penetrating
radiation,
indipendently
from
the
radioactive elements inside the soil and
the air, kwnown to emit radiation.”
This sentence confirm the well known Pacini contribute to the
scientific community around 1910
But more recently only few reviews mention Pacini:
(1)AW Wolfendale, Rep. Prog. Phys. ,(1984)
(2)Castagnoli e Morra, Giornale di Fisica, (1994).
In this talk I'll shortly explain the experimental work done by
Pacini
1900-1910 studies on the air discharge and
construction of new kind of electroscopes
Origin and nature of
penetrating radiation, studies
around 1910
Study of discharge
rates at different
weather conditions
and during the day
(electrical
properties and
atmosphere
studies)
(hyphothesis of an
electrical property
of the atmosphere)
Underground and
space (balloon)
measurements
- Conclusive tests
Study of discharge rates at of extraterrestral
sea level, study of variation nature of CRs -
with distance from the coast
Testing the hyphothesis of
soil radioactivity
Need a developement of new instruments for the different
experimental conditions
The detector evolution 19001920 (all contributions)
The main initial effort was the realization of
instruments to detect the radiation:
• Modification of the original electroscope to
be protected by some shielding
• Studies of the shielding effects on the
detected radiation
• Defining the way to protect the instrument
for the different exp. conditions (balloon,
sea,underwater)
Pacini (1907-1912) considered the
experimental problem
For each cm3 of air. Near the soil, about
13 ions every second are generated.[1]
Are the known sources of this ionization
sufficient to explain the production of this
ion rate? An appropriate measurement is
necessary to understand this point.
[1] well known average value see:
C.T.R. Wilson Proc.Roy.Soc. 68 (1901) and
Elster and Geiter Ann. d. Physics, 2 (1900) 425
Using the Ebert instrument (later the Wulf instrument for
underwater measurements), Pacini measured the discarge
rate of the electroscopy and therefore the radiation
intensity, in 3 experimental situations:
1)Electroscopy at ground level (on
soil and on sea) 1907-1910
2)Electroscopy on the sea surface
(Livorno and Genova gulf) few
miles from the coast 1907 and
later
3)Undersea 1911, june-july (3m
depth on Livorno gulf and
Bracciano lake in Italy)
The Beginning of
UNDERGROUND Physics !!!
The Italian Navy Cacciatorpediniere “Fulmine” used
by Pacini in 1910-1911
Pacini measurements
• On “La radiazione penetrante alla superficie ed in seno alle
acque”, Il Nuovo Cimento 3 (1912) 93 now translated “The
penetrating
radiation
on
surface
and
undersea”http://xxx.lanl.gov/PS_cache/arxiv/pdf/1002/1002.
1810v1.pdf D. Pacini reported that “the measurements on
sea in 1910 let me to conclude that a not negligible fraction
of the penetrating radiation is not dependent by the
radioactive elements in the soil” since on the sea surface
the level of radiation was practically the same as over the
soil (about 2/3 respect ground).
• So the missing prove to conclude for an extraterrestrial origin
is to verify the ionization rate vs the depth. In the same
paper he explain how proceeded: “using the same
electroscope and inserting it in a copper box” he performed
new measurements from 24 to 31 june 1911, 300m far from the
coast and 3m depth in the sea in the (Livorno) Leghorn sea and
later underwater in the Bracciano lake (Rome-Italy)
Pacini measurements-2
• For both set of measurements the rate resulted
attenuated according to an exponential law I/I0=exp(ld)
• The same paper report “The measurements by Hess
and Goeckel have repeated and obtained the same
conclusion previously reported by me i.e. that
exists in the atmosphere a ionization source,
producing
penetrating
radiation,
and
not
depending from the radioactive elements in the
soil”
• So both Pacini and Hess reached the conclusion
that something in the atmosphere produce the air
ionization
• Some fragments of some letter in 1920 between
Pacini and Hess seem to confirm that Hess was
well informed about Pacini results. [there is room for more
detailed historical searches]
Surface measurements:
13,2−12,2−12,1−12,6−12,5−13,5−12,1−12,7
Average: 11 ions per cm3 per second
Undersea measurements:
10,2−10,3−10,3−10,1−10,0−10,6−10,6
Average: 8.9 ions per cm3 per second
Pacini concluded that the measurements on sea,
undersea and under lake let to exclude the soil as the
only responsable of the radiation therefore he
was the first to think to exclude a terrestrial contribution
to the penetrating radiations
In the same years Hess, was performing his
balloon experiments fully supported by
austrian imperial Academy of Sciences
The flight 7 was the good
one (5200 m), on August,
7 1912, few weeks after
the undersea
measurements by Pacini
The beginning of the
space research of CRs
He reached the same conclusion of Pacini:
The penetrating radiations has a non-terrestrial origin
And his measurements were definitively excluding a
relevant contribution from soil radiactive elements
Kolhoerster balloon
Measurements[**]
• After Hess measurements and Gockel
confirms, however the physics community
was reluctant to exclude the terrestrial
origin[*] of CRs and the studies on the
radiation take different paths (and the Ist
world war in the middle): people mainly
interested to the atmosphere electricity
studies and people studying the
composition of the radiation, that later let to
discover new particles. The dibate about the
origin restarted only about 10 years later
Pacini and Hess measurements
[*] see for example the interpretation as radiactive elements in the air by
G. Hoffmann, Zeit. f. Phys. 7 (1921) 254; Phys. Zeit. 24 (1923) 475; Phys. Zeit. 25
(1924) 177; Phys. Zeit. 26 (1925) 40 and 669 F. Behounek, Phys. Zeit. 27 (1926) 8
[**] G. Homann, Zeit. f. Phys. 7 (1921) 254; Phys. Zeit. 24 (1923) 475; Phys. Zeit. 25
(1924) 177; Phys. Zeit. 26 (1925) 40 and 669
Millikan in the studies around 1925 considered
the hypothesis of neutral radiation from outside
and conied the term “Cosmic Rays” starting the
debate about the nature of the radiation.
The measurements in 1927-28 showing
geomagnetic effects on the intensity let to
conclude in favour of charged particles against
gamma-rays and new detectors confirm the
corpuscolar nature of radiation[*]
[*] A. Compton, Phys. Rev. 41 (1932) 681;
Phys. Rev. 43 (1933) 387
M. Schein et al., Phys. Rev. 59 (1941) 615
The Nobel prize
In 1936 Hess got the Nobel prize for the
discovery of cosmic rays (together Anderson for
the positron discovery)
Pacini, died before (1934) but in the report on the cosmic rays,
commissioned by the Nobel Committee, prepared by E. Hulthén,
one of the members of the Committee sorbers, Hulthén points out
that considering the experiments by Eve, Pacini, Mache and
others it became clear that only a small fraction of the ionisation
could be attributed to radioactive substances. Moreover Hulthén
notes that the Gockel measurements, in agreement with
measurements of Pacini, “show that a not insignificant part of the
radiation is independent of direct action of substances in the crust
Earth“ but the careful works by Hess confirm the results of Eve
but he was the first to prove a clear increase of the radiation with
the height
Conclusion about Pacini work
• Pacini studies were well known, appreciated
and inserted in an international framework, and
the CR discoveries in every case are due to the
joint efforts of many people
• In Pacini notes and papers is well evident the
logical path followed, based on the idea, reported
in his first paper, that the radioactivity in the soil
and in the air was not sufficient to explain the
observed measurements of the air ionization
• However Pacini studies were scarsely supported
in Italy by the scientific academy (i.e. balloon
flights were performed in Italy for other studies)
and after the war the Pacini role was forgotten
Conclusions-1
• Hess, Pacini and Wulf and other researchers
defined around 1910 the basic experimental lines to
study CRs and contributed to the instrument
developements to detect this penetrating
radiation.
• Pacini was probably among the first to think to
exclude a terrestrial origin of CRs, and was the first to
study CRs underground and on the sea (I’m particular
proud to say this here near the site of one undersea
experiment)
• Hess systematic measurements however revelead
to be more complete, systematic and conclusive
about the origin, were better known and probably
better supported by his national agency
• Pacini and Wulf were practically forgotten for several
reasons but mainly due to the different support of
science agencies and academy
Conclusions-2
• CR discovery was the result of a world effort with
many contributions despite the slow and hard
communication problems at that time (Pacini and
Hess published in their native language and the
others in english) and the war problems, but finally
the CR nature problem was understood about 20
years after the first measurements
• Let us start the celebration of the centenary of CRs
discoveries (2012) starting to remember Pacini
underground measurements(1911) and ending with
Hess air measurements(1912) and extablishing the
link with the actual underground and space
researches on CRs
Electroscopies
Citations to Pacini studies
• Nature note at page 107 del vol. LXX
(1904)
• G.A.Cline phys. Rev. 30 (1910) 35
• Wigand, Phys. Z. XXV, 445 (1924)
Pacini bibliography
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D. Pacini, Intorno ad un fenomeno di polarità di scarica, Il Nuovo Cimento, 13 (1907),
182-188
D. Pacini, Misure di ionizzazione dell'aria su terraferma ed in mare, Il Nuovo Cimento,
15 (1908), 5-23
D. Pacini, Sulla radioattività indotta dell'atmosfera nel golfo ligure, Il Nuovo Cimento,
15 (1908), 24-28
D. Pacini, Intorno ad un fenomeno di polarità di scarica, Il Nuovo Cimento, 13 (1907),
182-188
D. Pacini, Misure di ionizzazione dell'aria su terraferma ed in mare, Il Nuovo Cimento,
15 (1908), 5-23
D. Pacini, Sulla radioattività indotta dell'atmosfera nel golfo ligure, Il Nuovo Cimento,
15 (1908), 24-28
D. Pacini, Questioni di elettricità atmosferica, Il Nuovo Cimento, 19 (1910), 449-466
D. Pacini, Sui prodotti del radio e del torio nell'atmosfera, Il Nuovo Cimento, 19
(1910), 345-357
D. Pacini, La radiazione penetrante alla superficie ed in seno alle acque, Il Nuovo
Cimento, 3 (1912), 93-100
D. Pacini, Sulle emissioni di cariche elettriche per parte di sali non radiattivi alla
temperatura ordinaria, Il Nuovo Cimento, 7 (1914), 267-290
Nuovo Cimento 15,5 1908
In this paper systematic measurements of ionization at ground
level and on the sea at different daily times
Nuovo Cimento 15,24 1908
Nuovo Cimento 15,24 1908
aaRAD
Nuovo Cimento 1912,3,93-100