Eighty years of science at 5,200 metres

Millikan's expedition passes by

An expedition led by the American physicist Robert Millikan travels through South America measuring the variation of cosmic radiation with latitude. It involves no Bolivian scientists and leaves no continuity behind.

The Bolivian Andean Club builds the road and the hut

The sporting infrastructure of La Paz makes the country's scientific infrastructure possible without knowing it: without that road there is no weather station in 1942.

From the Argelès-sur-Mer camp to the ship “Cuba”

Ismael Escobar crossed into France at Le Perthus in January 1939 and was interned at Argelès-sur-Mer. His father managed to get him out; in December he sailed from Bordeaux for the Dominican Republic.

Ismael Escobar arrives in Bolivia

A meteorologist of the Spanish Republican Air Force, a refugee after the Civil War. He left Paris on one of the last trains and reached the Caribbean on a French ship.

The summit hut and the journal Nimbus

A weather hut is inaugurated at the summit, at 5,600 m, and the Meteorological Service's scientific journal begins publication. The complete run is held in the IIF library.

UMSA appoints Escobar as a professor

Official letter 54/953: Interim Professor of Cosmography and Meteorology. The University's link to the science of the mountain predates the Laboratory's formal creation by nine years.

Pic du Midi: two events

Occhialini exposes the new Ilford emulsions in the Pyrenees, at 2,900 m. Marietta Kurz, a microscopist at Bristol, identifies the first double meson. Two cases are a hint, not a proof: more altitude was needed.

Nature 159, 694

"Processes involving charged mesons", by Lattes, Muirhead, Occhialini and Powell. The Pic du Midi result.

César Lattes exposes the plates on Chacaltaya

He travels on his holidays and essentially at his own expense. Some forty days of exposure at 5,200 m. Developed in Bristol, the plates yield some thirty double-meson tracks.

The first artificial pions

Gardner and Lattes, in Science: the Berkeley synchrocyclotron had been producing pions from day one, only nobody knew how to recognise them. This is the moment particle physics begins to move from the mountain to the machine.

The CBPF is founded in Rio de Janeiro

The prestige of the finding underpins the creation of the Centro Brasileiro de Pesquisas Físicas, with Lattes as scientific director at the age of 24. The CNPq will follow in 1951.

Two Nobel Prizes in Physics

Hideki Yukawa (1949) for predicting the particle; Cecil Powell (1950) for the photographic method and his discoveries regarding mesons. Both citations describe, without naming it, a result obtained with plates exposed here.

Escobar submits the draft plan for the observatory

He submits it to the Rector of UMSA and publishes it in Nimbus. As the site lies within a National Park, the University obtains a special permit: article 5 of the 1942 decree requires one. The Minister of Agriculture will grant it in a note to the Rector on 11 January 1952. The Laboratory was not built in spite of the protection regime, but within it.

The University Council creates the Laboratory

Defined as a "centre for research, teaching and meteorological observation", operated partly by UMSA and partly by the Meteorological Service.

The Laboratory starts publishing

Six months after coming into existence, the first results appear. Under the title Resumen de Labores, one of the oldest scientific journals at UMSA, publication will continue without interruption and will receive, in 1962, the national "Faja Verde" Prize for the best scientific and technological work in Bolivia.

Expeditions from more than ten countries

The United States, Brazil, Great Britain, Japan, India, Italy, France, Argentina and the Soviet Union, among others. The Brazilian Air Force carries staff and equipment free of charge on its Rio–La Paz flights until the 1970s.

The power line, and eight names

226 pylons, more than two tonnes of copper wire and 160 km of line dismantled from a tin mine and carried up to the mountain. The interconnection was achieved by Juan Hersil and Alfonso Lazo with eight workers: José and Eusebio Monasterios, Arturo López, Tiburcio Quisucala, Vicente Cabaya, Marcos Calisaya, Honorio Paco and Ceferino Quilla. Without that line there is no BASJE and no sixty years of data.

First Inter-American Course in Modern Physics

In collaboration with UNESCO, with physicists from Argentina, Bolivia, Brazil, Chile, Ecuador and Paraguay. One of the instructors, the Argentine philosopher Mario Bunge, published his book La Edad del Universo in La Paz during the course.

The proposal that starts it all

Ismael Escobar puts before the UMSA rectorate the creation of a National Institute of Nuclear Research. Rector Gastón Aráoz accepts and suggests adding a Department of Mathematical Research, considering the development of that science urgent in Bolivia; Escobar proposes the mathematician Wilhelm Damköhler to head it. The country's nuclear energy commission comes out of this.

Physics Today devotes an article to the Laboratory

As a place unique in the world for the study of cosmic rays.

1st Inter-American Symposium on Cosmic Rays

With UNESCO's cooperation and some 50 papers. That same year Pierre Auger — Director of Natural Sciences at UNESCO — provides the means for the Physical Research Laboratory of Ahmedabad to install its meson telescope on Chacaltaya.

Supreme Decree 04715: the International Geophysical Year

The government of Hernán Siles Zuazo sets up the Comité Nacional del Año Geofísico (National Committee for the Geophysical Year), as the Gazette names it. The Laboratory's successes, together with those of the San Calixto Observatory and the Military Geographic Institute, were decisive factors. The Committee will become the Bolivian Geophysical Institute. It is the third of the four supreme decrees in the dossier.

BASJE pilot experiment at El Alto

Forerunner of the Bolivian Air Shower Joint Experiment.

Yukawa writes to Lattes

The physicist who predicted the pion proposes a collaboration to the physicist who established it. From that letter the Brazil–Japan Collaboration will be born. That same year Japanese physicists fund two fares to Moscow by selling a popular science book: Minoru Oda and Jun Nishimura travel.

The bomb in the Sahara

The atmospheric radioactivity equipment the US Naval Research Laboratory installed at Chacaltaya detects the first French nuclear explosion, carried out at Reggane in the Algerian Sahara. In 1962 John Bland will measure the seven-day delay with which that signal reaches Bolivia. It is dated proof that the atmosphere of the whole planet can be watched from this point.

The Bolivian Nuclear Energy Commission is born

Its activities begin, created under the Laboratory's umbrella and with Escobar as its first director. It is the first of a long list of Bolivian scientific institutions to come out of this mountain. In 1983 it will be replaced by IBTEN.

The Brazil–Japan Collaboration begins

Fujimoto and Yokoi arrive in Brazil with the first emulsions and set up the pilot experiment on Chacaltaya with Lattes. The instrument — a "sandwich" of lead, X-ray film and nuclear emulsion — is too heavy to fly on a balloon. Hence the mountain.

5th Inter-American Symposium on Cosmic Rays

Organised by the Laboratory and UNESCO: 42 speakers from 11 countries and 58 lectures. The proceedings were published under both institutions' names — a locatable document with UNESCO and the Laboratory on the same title page.

The U.S. Geological Survey photographs the Moon from Chacaltaya

Morris, Ring and Stephens, of the USGS, together with the Bolivian researcher José Antonio Zelaya — invited by Ismael Escobar as an associate researcher — attempt to photograph the Moon's dust clouds at the L4 and L5 libration points with a 6-inch Maksutov-Cassegrain telescope: 17 plates of L4 and 28 of L5. The result was inconclusive, but in 2018 and 2022 a Hungarian team showed that those clouds do exist. It is the one episode in which Chacaltaya looks not upwards but at the Moon.

Ozone observation begins

During the International Year of the Quiet Sun, Ramón Schulczewski and Fernando Sheriph begin the measurements. During the total eclipse of 12 November 1966 they will measure ozone profiles and upper-level winds.

Ozone begins, the original partner leaves

During the International Year of the Quiet Sun, Ramón H. Schulczewski and Fernando Sheriph begin observing atmospheric ozone. The same year the Bolivian Meteorological Service leaves Chacaltaya: twenty-three years of surface data at 5,200 metres come to an end, and the Laboratory loses, in Aguirre's words, "its original partner in the scientific adventure".

Two thousand radiosonde flights

From Ovejuyo and later from El Alto, over seven years, in a joint project of the World Meteorological Organization, the United States Air Force Office of Research and UMSA. The profiles of the upper atmosphere over Bolivia are published for the first time, and the daily data are sent to the Miami Hurricane Center. Some sondes fell in remote places and were taken for objects of extraterrestrial origin.

The "Superpila" neutron monitor

It joins the atmospheric radioactivity equipment of the US Naval Research Laboratory, with which the first French nuclear explosion in the Sahara was detected.

Ozone profiles during a total eclipse

Schulczewski and Sheriph measure ozone profiles and high-altitude winds during the total solar eclipse, with the support of the Armed Forces and the work of Max Schreier, Ángel García Ontiveros, Gastón Mejía Brown and Israel Saravia. The observations had international repercussions.

Yukawa speaks of Chacaltaya in Kyoto

Carlos Aguirre presents his work on the neutron-to-proton ratio at a seminar at Kyoto University. In the audience is Hideki Yukawa, who recalls fondly his part in the Brazil–Japan project and the discovery of the pi–mu decay at Chacaltaya, the one that earned him the Nobel Prize.

Ahead of the accelerators

BASJE measures the proton–air cross section between 3.4 and 8.8 TeV before artificial machines could verify it in that range. A Bolivian mountain measured, with detectors buried under lead, something the world's most expensive accelerators could not yet reach.

Ozone closes for good

The ozone project is transferred, at the instruction of the United States Air Force, to the Bolivian Air Force. There it lasts a short time and closes for good; the ionosphere project closes too. Aguirre does not gloss over it: "Continuity was lost in the study of a subject of enormous current importance in which Bolivia was acquiring great experience. The understanding between air forces prevailed over scientific rationality."

The 6th Inter-American Seminar, the last one

The sixth and last edition of the series begun in 1957. It was organised by Ramón H. Schulczewski, Gastón Mejía and Carlos Aguirre, and President Ovando Candia received the participants. That a head of state should host a cosmic-ray conference says something about the place the Laboratory held in the country.

The Laboratory is renamed Instituto de Investigaciones Físicas

The Institute's archive dates the change of name to 1972, during Gastón Mejía's directorship. Aguirre Bastos's book describes it as a University decision taken between 1970 and 1973, with the transformation carried through from September 1973 by Aguirre himself, who between 1973 and 1975 also heads the University's Research Planning and Coordination Centre, with seventeen institutes in his charge. None of the three dates has yet been checked against the University Council resolution.

Saitama and Turin come up the mountain

Two new groups arrive to study small air showers: one from Saitama University, led by Tsuneo Matano — the experiment known as SYS, for Saitama, Yamanashi and San Andrés: the acronym carries the Bolivian university's name inside it — and one from the University of Turin, led by Giani Navarra. The Italian group will still be publishing from Chacaltaya in the year 2000: twenty-seven years of continuous presence.

The Patacamaya Astronomical Observatory opens

Under the Bolivia–USSR scientific cooperation agreement, whose implementation the Institute took on in late 1973. Rector Jorge Siles Salinas; Soviet promoters Vitaly Cheleaguine and Yuri Spirin. Satellite geodesy was done there, with missions from Czechoslovakia as well. A year earlier the University Planetarium had opened.

The Institute absorbs the Bolivian Geophysical Institute

The arc closes: the institution that twenty years earlier had helped create a state body ends up absorbing it. Out of it come the Andean Charaña–San Borja geotransect — the origin of UNESCO's worldwide geotransect programme — and the first magnetic and gravimetric charts of Bolivia.

Aerosol agreement with the University of Antwerp

The results show pollution three times lower than that of Antwerp. In 1974 the Seguencoma Magnetic Observatory had been installed with the Carnegie Institution.

Chacaltaya–Pamir: three mountains, four countries

Out of the Collaboration come IUPAP's International Emulsion Chamber Committee and the Chacaltaya–Pamir Collaboration, linking three high-altitude stations: Chacaltaya (5,200 m), Pamir in the USSR (4,370 m) and Mount Fuji (3,750 m). At the height of the Cold War, with the Bolivian station the highest of the three. The collaboration's second seminar is held in 1982 in La Paz and Rio de Janeiro.

An excess from Scorpius X-1

The SYS experiment verifies a significant excess of hadron-poor showers from the direction of the X-ray binary Scorpius X-1, and an excess of diffuse gamma emission along the galactic plane. It is the closest Chacaltaya came to a source detection. In those same years the Turin group observes gamma-ray arrival directions from Supernova 1987A.

SYS: the mountain's two techniques in a single instrument

The SYS experiment combines nuclear emulsions and an air-shower detector into a hybrid instrument, and searches for diffuse high-energy gamma-ray emission from hadron-poor showers. It surveys eight X-ray sources and the galactic centre: every result is negative. For twenty years the emulsion chamber and the surface array had run in parallel without meeting; here they come together.

"Out of all proportion"

The physicist John Linsley writes in Physics Today that the research done at Chacaltaya between 1950 and 1980 improved the understanding of cosmic rays "out of all proportion" when compared with countries in similar conditions of development.

"Near a minimum" in 1970, recovered by 1982

The physicist Larry W. Jones, of the University of Michigan, writes after visiting Bolivia and Brazil that he was impressed once again by "the unique nature of Mount Chacaltaya", and compares that year's programmes with the ones he had seen in 1970, "when they were near a minimum". It is the third international endorsement in the dossier, alongside the IUPAP declaration of 1964 and Linsley's letter of that same 1982.

The OMEGA proposal

With the Cosmic Ray Research Laboratory of the University of Tokyo: a 900 m² emulsion chamber surrounded by eighty scintillators over 40,000 m². It was never built, but it set the ambition of what would follow.

A telescope for the Sun's neutrons

Nagoya University installs on top of the Rossi hall the third telescope of its international solar neutron network: four square metres of scintillator measuring from September, and still measuring today. With it, the Bolivian group signed the detection of neutrons from the flares of 24 November 2000 and 7 September 2005. In 1994 Carlos Aguirre backed the cooperation before the Ambassador of Japan.

Half a century in figures

600 original scientific contributions and 120 undergraduate and postgraduate theses between 1952 and 1994.

Ozone and UV Radiation Laboratory

The atmospheric line that began in 1942 with an actinometer continues with modern instrumentation. The LAGO collaboration will join later.

Science corrects itself

Kopenkin, Fujimoto — one of the founders of the Collaboration — and Sinzi publish "Solution to the Centauro puzzle": the correspondence between the two storeys of the chamber was incorrect, and without it no new physics is required. The following year Ohsawa, Shibuya and Tamada confirm the error but hold that the event remains peculiar. The site's most famous finding was revised by its own authors; the debate is not closed.

LAGO starts taking data at Chacaltaya

Three water Cherenkov detectors of the Latin American Giant Observatory, the Latin American network of high-altitude sites devoted to gamma-ray bursts. Bolivia is a founding country of the collaboration, begun in 2005 together with Argentina and Mexico. A collaboration paper describes Chacaltaya as the highest and oldest observatory in the world.

The Chacaltaya glacier disappears

The mountain that hosted the world's highest ski run loses its ice. The site that measures the climate becomes a witness to it as well.

Seven Cherenkov light detectors on the BASJE array

Yoshiki Tsunesada (Tokyo Institute of Technology) commissions with Pedro Miranda, Juan Salinas and Wilfredo Tavera a hybrid system: 49 scintillation counters over 500 × 650 m and seven non-imaging Cherenkov detectors, to measure the composition of cosmic rays above the knee of the spectrum. The seven boxes, with motorised lids, will measure on their own some 700 hours of moonless nights in 2013–2014.

BASJE’s surface array and Cherenkov project stop measuring

On the same site since 1961: the small array of 1987 and Yoshiki Tsunesada’s seven Cherenkov light detectors (2010) cease in 2015 ⚠. The muon detector of the Rossi hall was not part of that stage.

Takaaki Kajita travels to Bolivia

The 2015 Nobel laureate in Physics, then director of the ICRR at the University of Tokyo, arrives to drive forward OMEGA's heir. UMSA awards him an honorary doctorate. Fifty-seven years after the two air tickets to Moscow, the director of that same Japanese house returns to the same mountain to sign the next experiment.

ALPAQUITA starts observing

ALPACA's prototype — 18,450 m², 97 scintillators and a 900 m² muon detector, a quarter of the final array — takes its first observations, and has been operating stably since April 2023.

The Moon shadow

ALPAQUITA detects the deficit of cosmic rays the Moon casts by blocking them, with a significance of 8σ and an angular resolution of about 1.0°, matching the simulations. It is the calibration standard for instruments of this kind: proof that the detector sees what it is meant to see, with the precision expected.