History of Physics Group meeting “From Newton to the free electron laser”

Lecture 5: A partial history of cosmic ray research in the UK

Professor Alan Watson



Prof. Watson’s work focuses on cosmic rays of the highest energy.



My notes from the lecture (if they don’t make sense then it is entirely my fault)

Julian Barnes stated “History is that certainty produced at the point where the imperfections of memory meet the inadequacies of documentation.”



Julian Patrick Barnes (born 19 January 1946) is an English writer.


The discoveries of X-rays, radioactivity and the electrons in the 1890s greatly improved the understanding of ionisation.


Cosmic rays are high-energy radiation, mainly originating outside the Solar System and even from distant galaxies.


After the discovery of radioactivity by Henri Becquerel in 1896, it was generally believed that atmospheric electricity, ionization of the air, was caused only by radiation from radioactive elements in the ground or the radioactive gases or isotopes of radon they produce.

In 1909, Theodor Wulf developed an electrometer, a device to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the Eiffel Tower than at its base. However, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911, Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 metres from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth.

In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5,300 metres in a free balloon flight (without oxygen). He found the ionization rate increased approximately fourfold over the rate at ground level. Hess ruled out the Sun as the radiation’s source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun’s visible radiation, Hess still measured rising radiation at rising altitudes. He concluded that “The results of the observations seem most likely to be explained by the assumption that radiation of very high penetrating power enters from above into our atmosphere.” In 1913–1914, Werner Kolhörster confirmed Victor Hess’s earlier results by measuring the increased ionization enthalpy rate at an altitude of 9 km.

Hess received the Nobel Prize in Physics in 1936 for his discovery.


Victor Franz Hess (24 June 1883 – 17 December 1964) was an Austrian-American physicist, and Nobel laureate in physics, who discovered cosmic rays.



Hess lands after his balloon flight in 1912.



Charles Thomson Rees Wilson, CH, FRS (14 February 1869 – 15 November 1959) was a Scottish physicist and meteorologist who won the Nobel Prize in Physics for his invention of the cloud chamber.

The invention of the cloud chamber was by far Wilson’s signature accomplishment, earning him the Nobel Prize for Physics in 1927. The Cavendish laboratory praised him for the creation of “a novel and striking method of investigating the properties of ionized gases”. The cloud chamber allowed huge experimental leaps forward in the study of subatomic particles and the field of particle physics, generally. Some have credited Wilson with making the study of particles possible at all.

The cloud chamber can detect cosmic rays.


The image below shows one of the first cloud chamber photographs showing the track of a cosmic ray.


It was taken by Dmitry Skobeltzyn in his laboratory in Leningrad in the former Soviet Union in 1927.


In the 1920s, the term cosmic rays was coined by Robert Millikan who made measurements of ionization due to cosmic rays from deep under water to high altitudes and around the globe.

There was limited interest in the UK, but Ernest Rutherford was interested.

Bruno Rossi wrote that:

In the late 1920s and early 1930s the technique of self-recording electroscopes carried by balloons into the highest layers of the atmosphere or sunk to great depths under water was brought to an unprecedented degree of perfection by the German physicist Erich Regener and his group. To these scientists we owe some of the most accurate measurements ever made of cosmic-ray ionization as a function of altitude and depth.



Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist honoured with the Nobel Prize for Physics in 1923 for the measurement of the elementary electric charge and for his work on the photoelectric effect.

Ernest Rutherford stated in 1931 that “thanks to the fine experiments of Professor Millikan and the even more far-reaching experiments of Professor Regener, we have now got for the first time, a curve of absorption of these radiations in water which we may safely rely upon”.

Discussion on ultra-penetrating rays https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1931.0104

The meeting of the Royal Society, held on May 14 1931, was devoted to a discussion on ultra-penetrating rays.

Geiger, H.; Rutherford, Lord; Regener, E.; Lindemann, F. A.; Wilson, C. T. R.; Chadwick, J.; Gray, L. H.; Tarrant, G. T. P.; et al. (1931). “Discussion on Ultra-Penetrating Rays”. Proceedings of the Royal Society of London A. 132 (819): 331. Bibcode:1931RSPSA.132..331G. doi:10.1098/rspa.1931.0104



Bruno Benedetto Rossi (13 April 1905 – 21 November 1993) was an Italian experimental physicist. He made major contributions to particle physics and the study of cosmic rays.



Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS HFRSE LLD (30 August 1871 – 19 October 1937), was a New Zealand-born British physicist who came to be known as the father of nuclear physics.



Patrick Maynard Stuart Blackett, Baron Blackett OM CH FRS (18 November 1897 – 13 July 1974) was a British experimental physicist known for his work on cloud chambers, cosmic rays, and paleomagnetism, winning the Nobel Prize for Physics in 1948.

Blackett spent some time in 1924–1925 at Göttingen, Germany working with James Franck on atomic spectra. In 1932 he devised a system of geiger counters which only took photographs when a cosmic ray particle traversed the chamber. He found 500 tracks of high energy cosmic ray particles in 700 automatic exposures. In 1933, Blackett discovered fourteen tracks which confirmed the existence of the positron and revealed the now instantly recognisable opposing spiral traces of positron/electron pair production. This work and that on annihilation radiation made him one of the first and leading experts on anti-matter.



Photograph from Occhialini and Blacket’s paper showing tracks of radiation (Image: Blackett, P.M.S., & Occhialini, G.P.S., Royal Society of London Proceedings Series A 139 (1933) 699)

In 1948 he was awarded the Nobel Prize in Physics, for his investigation of cosmic rays using his invention of the counter-controlled cloud chamber.


Cosmic rays at Earth Researcher’s Reference Manual and Data Book http://theor.jinr.ru/~vnaumov/Eng/JINR_Lectures/books/Grieder2001.pdf

“Cosmic Rays” by J.G. Wilson, The Wykeham Science Series, 1976, London.


The muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass.

Muons and positrons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936, while studying cosmic radiation.

https://en.wikipedia.org/wiki/Carl_David_Anderson (below left)


https://en.wikipedia.org/wiki/Seth_Neddermeyer (above right)


Pierre Auger, who had positioned particle detectors high in the Alps, noticed that two detectors located many metres apart signalled the arrival of particles at exactly the same time. A systematic investigation of the showers showed coincidences between counters separated horizontally by as far as 75 metres. While the counting rate dropped sharply in going from 10 centimetres to 10 metres, the rate decreased slowly at larger distances.

Auger had recorded “extensive air showers,” showers of secondary subatomic particles caused by the collision of primary high-energy particles with air molecules. On the basis of his measurements, Auger concluded that he had observed showers with energies of 1015 eV – 10 million times higher than any known before.



Pierre Victor Auger (14 May 1899 – 25 December 1993) was a French physicist, born in Paris. He worked in the fields of atomic physics, nuclear physics, and cosmic ray physics.

Bernard Lovell – Patrick Blackett and work with cloud chambers https://www.youtube.com/watch?v=pngyUYvqM2k

A detailed study in collaboration with J. G. Wilson and B Lovell was made of the scattering of penetrating cosmic rays particles in metal plates


Extensive shower. Two cloud chambers several metres apart record an extensive air shower. (Wilson and Lovell, 1939)

Lovell and Wilson were sent to Yorkshire in 1939 to work on radar

First evidence of muon decay was seen in cosmic rays



Cecil Frank Powell, FRS (5 December 1903 – 9 August 1969) was an English physicist, and Nobel Prize in Physics laureate for his development of the photographic method of studying nuclear processes and for the resulting discovery of the pion (pi-meson), a subatomic particle. He employed specialised photographic emulsions to facilitate the recording of the tracks of elementary particles, and in 1938 began applying this technique to the study of cosmic radiation, exposing photographic plates at high-altitude, at the tops of mountains and using specially designed balloons.

Elementary particle physics: The origins http://www.hep.princeton.edu/~mcdonald/examples/EP/fitch_rmp_71_S25_99.pdf

Carl Anderson and Patrick Blackett got together and decided that the new particles they had found should be called V particles.

The tau-theta puzzle

In 1946 cosmic rays were seen to produce forked tracks in a cloud chamber. It became clear that the decay of particles with a mass of the order of half the proton mass, about 1000 me were being observed (Rochester and Butler, 1947). These were the first of a new class of particles, the so-called strange particles. It was at this time that Anderson and Blackett got together and decided that these new types of particles should be called V particles. By 1952 it was established that the V particles were actually four types, two if which were neutral.

Robert Thompson at Indiana University (he had earlier been a student of Rossi’s at MIT) singlehandedly brought the cloud-chamber technique to its ultimate precision and clarified the puzzle of the neutral V particles and showed that there were two different particles, tau and theta.

In the next three years several hundred fully reconstructed tau-meson decays were observed worldwide, largely in emulsions. Almost immediately, a fundamental problem presented itself. One of the tau decay products was seen to have little energy in a few instances.

Theta and Tau (those names have since been retired or recycled), which had the same mass and spin. On those grounds, they should obviously have been the same particle. However, Theta decayed into two pions, and Tau decayed into three pions, which made it seem as though two particles just happened to have the same mass and spin. That seemed like too big a coincidence to be true.

There is now a solution to the Theta-Tau puzzle. The Thetas and Taus, now called kaons, are created as combinations of strange and light quarks. But those kaons are the superposition of two possibilities, which we call “CP-odd” or “CP-even,” and these specific states are appropriate to describe the decays of the kaon. The component that is CP-odd decays into three pions, whereas the CP-even component decays into two pions. The CP-even decays are fairly quick, in contrast to the CP-odd decays. It turns out that the masses of the CP-odd and CP-even cases are just a tiny bit different, too.



1.3 cm Pb plates; 10GeV proton; Shower initiated by proton in the lead plates of the cloud chamber. Fretter: Echo Lake, 1949

Penetrating showers produced in lead have been observed in a large cloud chamber at sea level and 3027 meters. Observations made on the showers include frequency of occurrence, multiplicity, angular distribution, and production of high energy electrons. An attempt was made to compare the numerical data obtained with predictions of various meson theories, assuming that the events are produced by high energy nucleons.



Prior to the Second World War Lovell was studying cosmic rays using a Wilson Cloud Chamber in the Physics Department of the University of Manchester. Whilst working on the development of radar systems during the war he became aware of sporadic echoes that were being detected by the early warning radar systems. He wondered if these might be caused by the passage of a cosmic ray particle through the atmosphere and so, when the war ended, he acquired some army radar equipment which he set up in the quadrangle outside the Schuster Laboratory in Manchester.

Interference from the trams along Oxford Road made him seek a site well away from the centre of Manchester. He found that the Botany Department had some land in Cheshire at a place called Jodrell Bank.

The first observations were made in the middle of December 1945, and many echoes were received. It soon became apparent that they were not due to cosmic ray particles entering the atmosphere but were instead echoes from “shooting stars”, the plasma trail of a meteor as it burns up in the atmosphere! Lovell and his students were able to show that many meteors are the dust particles released by a comet as it rounds the sun. These originally form the “dust tail” of the comet.

In 1948 Blackett pointed out that 1/10,000 of night-sky light should come from cosmic rays.

Previously Cherenkov light was only detected in solids and liquids.


Cherenkov radiation is an electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium.

In 1953 Galbraith and Jelley (A.E.R.E, Harwell) postulated that Cherenkov light might be detectable as light pulse from air cosmic shower.


A standard-issue dustbin containing a Second World War parabolic signalling mirror only 25 cm in diameter, with a 5 cm diameter photomultiplier tube (PMT) at its focus, along with an amplifier and an oscilloscope.


They captured the faint blue flash of Cherenkov light emitted from energetic particles travelling faster than the speed of light in air. The first time this was seen.


Above left is a cartoon drawn by Jelley of the atmospheric Cherenkov shower phenomenon. Above right is a diagram showing the essential elements of an atmospheric Cherenkov detector.

Cherenkov Radiation: Its Properties, Occurrence, and Uses John V. Jelley https://link.springer.com/chapter/10.1007/978-1-4684-4505-3_6


The discovery of Cherenkov radiation and its use in the detection of extensive air showers https://arxiv.org/ftp/arxiv/papers/1101/1101.4535.pdf

Neil Porter, at Harwell, was the first to design a water-Cherenkov detector for use in extensive air showers


He was born in Urmston, Manchester, on September 4th 1930 and died in Dublin on March 15th 2006. He made a number of original and fundamental contributions to his field, cosmic ray physics, during a long career dedicated to research, teaching and scholarship.

Observations on extensive air showers VII. The lateral distribution of energy in the electron-photon component N. A. Porter et al 1958 https://www.tandfonline.com/doi/abs/10.1080/14786435808237020



A Cherenkov telescope array: H.E.S.S. in the Khomas Highland of Namibia


Seeing the High-Energy Universe with the Cherenkov Telescope Array file:///F:/Users/Dell/Downloads/CTA_Special_Issue_own_all.pdf

The following image shows a scheme of a technique for the imaging of atmospheric Cherenkov radiation




Bruno Pontecorvo (22 August 1913 – 24 September 1993) was an Italian nuclear physicist, an early assistant of Enrico Fermi and the author of numerous studies in high energy physics, especially on neutrinos. A convinced communist, he defected to the Soviet Union in 1950, where he continued his research on the decay of the muon and on neutrinos. The prestigious Pontecorvo Prize was instituted in his memory in 1995.

He came up with the idea that neutrinos may convert into other types of neutrinos, a phenomenon known as neutrino oscillation. Somewhere between the Sun and the Earth, electron neutrinos might transform into muon neutrinos. An important point was that for this to happen, neutrinos could not have zero mass, and therefore could not travel at the speed of light. The existence of the oscillations was finally established by the Super-Kamiokande experiment in 1998 and later confirmed by other experiments.

Durham, Imperial, Leeds and Nottingham Universities took over the research when the Harwell array closed.


Photomultiplier tubes (photomultipliers or PMTs for short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. These detectors multiply the current produced by incident light by as much as 100 million times or 108 (i.e., 160 dB), in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is low.

Photomultipliers detected auroral light

By 1990 different techniques gave different results about cosmic rays


Astrophysical question: where do the cosmic rays come from?


Composition: mostly protons at ≲ 1015 eV (lots of detailed composition info) some indication of heavier nuclei at E ≳ 1018 eV

Galactic cosmic rays from supernova shocks

Gamma-ray emission from starbursts

High Density Star Forming Galaxies are a Significant Contributor to the Extragalactic Gamma-ray and Neutrino Backgrounds

The Sun generates cosmic rays, especially during solar flares




The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond 1018 eV. In Earth’s atmosphere such particles interact with air nuclei and produce various other particles. These effect particles (called an “air shower”) can be detected and measured. But since these high energy particles have an estimated arrival rate of just 1 per km2 per century, the Auger Observatory has created a detection area of 3,000 km2—the size of Rhode Island, or Luxembourg—in order to record a large number of these events. It is located in the western Mendoza Province, Argentina, near the Andes.

Design, construction, characterization, and operation of a hybrid cosmic rays detector based on an electron gas http://iopscience.iop.org/article/10.1088/1742-6596/792/1/012036/pdf

Abstract. There are several sources that produce very energetic cosmic rays that interact with the Earth’s atmosphere and create new particles. To detect them there are different methods such as the ionization of a material and Cerenkov radiation, among others. In this work a hybrid cosmic ray detector of 6 channels was designed, built, tested and operated. Being hybrid is possible to validate the signal with the two detection methods. Three Copper bars were used as detection material, each with an ionization and a Cerenkov radiation detection channel. To detect the Cerenkov radiation, Hamamatsu silicon photodiodes were used, and for the ionization channels an RC circuit was developed to measure the signal. The number of signals was counted using discriminator boards, which digitize the signal. With the counts the cosmic rays flux can be measured. The six channels were tested simultaneously. Data collections and analysis were performed. Details of the design, characterization, testing, operation, data analysis and preliminary results are presented.


The Pierre Auger Observatory is a huge array of detectors deployed over an area of some 3000 km2 in the Argentinian Pampa. Because of the sheer scale of the project, it can be difficult to meaningfully explore the layout of the array and display the various detector components in a way that illustrates the distances involved. To help facilitate this exploration, a model of the Pierre Auger Observatory layout was constructed, to be viewed interactively using Google Earth. This allows the user to display the various detector elements, zoom in on them, tilt and rotate the field of view, etc. Running a Google Earth session requires a computer with reasonably high bandwidth access to the internet.

The above picture shows the Los Leones fluorescence detector of the Auger Observatory, on a hill overlooking above the ground array of surface detectors (one of which appears in the foreground). The project utilizes two techniques to detect these extremely rare particles. When they reach the Earth’s atmosphere, they generate a cascade of billions of particles which can be detected when they strike the ground with an array of surface detectors. In addition, on dark nights the sky glow (known as nitrogen fluorescence) generated by the passage of these particles can be imaged with telescopes located on the boundary of the array. There are a total of four nitrogen fluorescence detectors with six telescopes each. This image shows the Los Leones detector, built on the summit of an extinct volcanic mound, or cerro.


Science 22/9/2017: Cosmic rays with energies above 8EeV come from outside our galaxy.

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