From University of Tokyo [(東京大学](JP) : “Closing the gap on the missing lithium”

From University of Tokyo [(東京大学](JP)

July 1, 2021

Researchers account for some of the lithium missing from our universe.


There is a significant discrepancy between theoretical and observed amounts of lithium in our universe. This is known as the cosmological lithium problem, and it has plagued cosmologists for decades. Now, researchers have reduced this discrepancy by around 10%, thanks to a new experiment on the nuclear processes responsible for the creation of lithium. This research could point the way to a more complete understanding of the early universe.

There is a famous saying that, “In theory, theory and practice are the same. In practice, they are not.” This holds true in every academic domain, but it’s especially common in cosmology, the study of the entire universe, where what we think we should see and what we really see doesn’t always match up. This is largely because many cosmological phenomena are difficult to study due to inaccessibility. Cosmological phenomena are usually out of our reach because of the extreme distances involved, or often they have occurred before the human brain had even evolved to worry about them in the first place — such is the case with the big bang.

Project Assistant Professor Seiya Hayakawa and Lecturer Hidetoshi Yamaguchi from the Center for Nuclear Study at the University of Tokyo, and their international team are especially interested in one area of cosmology where theory and observation are very misaligned, and that is the issue of the missing lithium, the cosmological lithium problem (CLP). In a nutshell, theory predicts that in the minutes following the big bang that created all matter in the cosmos, there should be an abundance of lithium around three times greater than what we actually observe. But Hayakawa and his team accounted for some of this discrepancy and have thus paved the way for research that may one day resolve it entirely.

“13.7 billion years ago, as matter coalesced from the energy of the big bang, common light elements we all recognize — hydrogen, helium, lithium and beryllium — formed in a process we call Big Bang nucleosynthesis (BBN),” said Hayakawa. “However, BBN is not a straightforward chain of events where one thing becomes another in sequence; it is actually a complex web of processes where a jumble of protons and neutrons builds up atomic nuclei, and some of these decay into other nuclei. For example, the abundance of one form of lithium, or isotope — lithium-7 — mostly results from the production and decay of beryllium-7. But it has either been overestimated in theory, underobserved in reality, or a combination of the two. This needs to be resolved in order to really understand what took place way back then.”

Lithium-7 is the most common isotope of lithium, accounting for 92.5% of all observed. However, even though the accepted models of BBN predict the relative amounts of all elements involved in BBN with extreme accuracy, the expected amount of lithium-7 is around three times greater than what is actually observed. This means there is a gap in our knowledge about the formation of the early universe. There are several theoretical and observational approaches which aim to resolve this, but Hayakawa and his team simulated conditions during BBN using particle beams, detectors and an observational method known as the Trojan horse.

“We scrutinized more than ever before one of the BBN reactions, where beryllium-7 and a neutron decay into lithium-7 and a proton. The resulting levels of lithium-7 abundance were slightly lower than anticipated, about 10% lower,” said Hayakawa. “This is a very difficult reaction to observe since beryllium-7 and neutrons are unstable. So we used deuteron, a hydrogen nucleus with an extra neutron, as a vessel to smuggle a neutron into a beryllium-7 beam without disturbing it. This is a unique technique, developed by an Italian group we collaborate with, in which the deuteron is like the Trojan horse in Greek myth, and the neutron is the soldier who sneaks into the impregnable city of Troy without tipping off the guards (destabilizing the sample). Thanks to the new experimental result, we can offer future theoretical researchers a slightly less daunting task when trying to resolve the CLP.”

Experimental setup. As a beam of beryllium comes in from the left, the deuteron Trojan horse intercepts it at the target and delivers its neutron soldier. This allows the decay products of the beryllium and neutron reactions to be captured by a curved array of six detectors on the right. ©2021 Hayakawa et al.

Science paper:
Astrophysical Journal Letters

See the full article here .


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The University of Tokyo [(東京大学](JP) aims to be a world-class platform for research and education, contributing to human knowledge in partnership with other leading global universities. The University of Tokyo aims to nurture global leaders with a strong sense of public responsibility and a pioneering spirit, possessing both deep specialism and broad knowledge. The University of Tokyo aims to expand the boundaries of human knowledge in partnership with society. Details about how the University is carrying out this mission can be found in the University of Tokyo Charter and the Action Plans.

The university has ten faculties, 15 graduate schools and enrolls about 30,000 students, 2,100 of whom are international students. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is among the top echelon of the select Japanese universities assigned additional funding under the MEXT’s Top Global University Project to enhance Japan’s global educational competitiveness.

University of Tokyo (Todai) is considered to be the most selective and prestigious university in Japan and is counted as one of the best universities in the world. As of 2018, University of Tokyo’s alumni, faculty members and researchers include seventeen Prime Ministers, sixteen Nobel Prize laureates, three Pritzker Prize laureates, three astronauts, and a Fields Medalist.

The university was chartered by the Meiji government in 1877 under its current name by amalgamating older government schools for medicine, various traditional scholars and modern learning. It was renamed “the Imperial University [帝國大學; Teikoku daigaku]” in 1886, and then Tokyo Imperial University [東京帝國大學; Tōkyō teikoku daigaku] in 1897 when the Imperial University system was created. In September 1923, an earthquake and the following fires destroyed about 700,000 volumes of the Imperial University Library. The books lost included the Hoshino Library [星野文庫; Hoshino bunko], a collection of about 10,000 books. The books were the former possessions of Hoshino Hisashi before becoming part of the library of the university and were mainly about Chinese philosophy and history.

In 1947 after Japan’s defeat in World War II it re-assumed its original name. With the start of the new university system in 1949, Todai swallowed up the former First Higher School (today’s Komaba campus) and the former Tokyo Higher School, which thenceforth assumed the duty of teaching first- and second-year undergraduates, while the faculties on Hongo main campus took care of third- and fourth-year students.

Although the university was founded during the Meiji period, it has earlier roots in the Astronomy Agency (天文方; 1684), Shoheizaka Study Office (昌平坂学問所; 1797), and the Western Books Translation Agency (蕃書和解御用; 1811). These institutions were government offices established by the 徳川幕府 Tokugawa shogunate (1603–1867), and played an important role in the importation and translation of books from Europe.

In the fall of 2012 and for the first time, the University of Tokyo started two undergraduate programs entirely taught in English and geared toward international students—Programs in English at Komaba (PEAK)—the International Program on Japan in East Asia and the International Program on Environmental Sciences. In 2014, the School of Science at the University of Tokyo introduced an all-English undergraduate transfer program called Global Science Course (GSC).


The University of Tokyo is considered a top research institution of Japan. It receives the largest amount of national grants for research institutions, Grants-in-Aid for Scientific Research, receiving 40% more than the University with 2nd largest grants and 90% more than the University with 3rd largest grants. This massive financial investment from the Japanese government directly affects Todai’s research outcomes. According to Thomson Reuters, Todai is the best research university in Japan. Its research excellence is especially distinctive in Physics (1st in Japan, 2nd in the world); Biology & Biochemistry (1st in Japan, 3rd in the world); Pharmacology & Toxicology (1st in Japan, 5th in the world); Materials Science (3rd in Japan, 19th in the world); Chemistry (2nd in Japan, 5th in the world); and Immunology (2nd in Japan, 20th in the world).

In another ranking, Nikkei Shimbun on 16 February 2004 surveyed about the research standards in Engineering studies based on Thomson Reuters, Grants in Aid for Scientific Research and questionnaires to heads of 93 leading Japanese Research Centers. Todai was placed 4th (research planning ability 3rd/informative ability of research outcome; 10th/ability of business-academia collaboration 3rd) in this ranking. Weekly Diamond also reported that Todai has the 3rd highest research standard in Japan in terms of research fundings per researchers in COE Program. In the same article, it is also ranked 21st in terms of the quality of education by GP funds per student.

Todai also has been recognized for its research in the social sciences and humanities. In January 2011, Repec ranked Todai’s Economics department as Japan’s best economics research university. And it is the only Japanese university within world top 100. Todai has produced 9 presidents of the Japanese Economic Association, the largest number in the association. Asahi Shimbun summarized the number of academic papers in Japanese major legal journals by university, and Todai was ranked top during 2005–2009.

Research institutes

Institute of Medical Science
Earthquake Research Institute
Institute of Advanced Studies on Asia
Institute of Social Science
Institute of Industrial Science
Historiographical Institute
Institute of Molecular and Cellular Biosciences
Institute for Cosmic Ray Research
Institute for Solid State Physics
Atmosphere and Ocean Research Institute
Research Center for Advanced Science and Technology

The University’s School of Science and the Earthquake Research Institute are both represented on the national Coordinating Committee for Earthquake Prediction.