Scientist Toshiko Yuasa The Forerunner of Japan’s Brain Drain after World War II

Summary

Toshiko Yuasa (1909–1980) was at the forefront of the first brain drain from Japan after World War II. After going to France in 1940, during the war, and studying under Frédéric Joliot-Curie (1900–1958) of Collège de France, Yuasa was forced to return to Japan just before the end of the war in 1945. Thus, during the early postwar period, she lived in her native country, but she moved back to France in 1949. This article discusses documents donated by the family of Joliot-Curie to Bibliothèque Nationale de France in 2007, which are now available for inspection at the Curie Archive in Paris. The article also follows Yuasa’s journey, from her return to Japan and move back to France, through records from 1946 to 1949, centering on letters between Yuasa and Joliot-Curie, analyzed from a gender perspective.
Keywords: Toshiko Yuasa, Frédéric Joliot-Curie, Marie Curie, Irène Joliot-Curie, Gender, Radium Institute ^[2]

Introduction

Toshiko Yuasa was Japan’s first female physicist and the first Japanese woman to work internationally as a scientist. Yuasa first went to France in 1940, during World War II, where she studied radioactivity under Frédéric Joliot-Curie (1900–1958, hereafter referred to as Joliot, or Frédéric). Joliot was a French scientist who jointly discovered artificial radioactivity with his wife, Irène Joliot-Curie (1897–1956, hereafter referred as Irène, or Irène Curie), the eldest daughter of the Curies (Marie Curie, 1867–1934; Pierre Curie, 1859–1906), whose discovery won the couple the Nobel Prize for chemistry in 1935. Due to the worsened war situation, Yuasa returned home in 1945. However, in 1949, she traveled back to France, where she worked as a researcher at Centre National de Recherches Scientifiques (CNRS). She continued working as a scientist until her death in Paris in 1980. Yuasa's career could be forerunner of the brain drain from postwar Japan. ^[3] This paper follows Yuasa’s trajectory during the period between her return Japan and her relocation to France, based on correspondence, letters that she exchanged primarily with Joliot from 1946 to 1949. In particular, this paper will clarify why Yuasa, who had been expected to work in Japan, left the country. The discussion will also shed light, from a gender perspective, on the situation of Japanese intellectuals, especially female intellectuals, during the period right after the end of the war.

Letters of Toshiko Yuasa

The main documents consulted in this research were found in Correspondence between Yuasa and Joliot: 1946–49 (hereafter referred as to CYJ; see Annex). To the best of my knowledge, I am the first researcher in the world to have read these letters. The letters were donated to Bibliothèque Nationale de France (BNF) in 2007 by Hélène Langevin-Joliot (1927–) and Pierre Joliot (1932–), children of the Joliot-Curies. While these historical sources belong to BNF, they can now be browsed in the Curie Archive of the Curie Museum in Paris. But where are Yuasa’s other documents? After her death in Paris in 1980, Yuasa’s belongings were first sent to Ochanomizu University, her alma mater. After being sorted and classified there, public documents, such as scientific papers, were retained by the university, while letters were returned to their senders, to the extent possible, and other private items, such as diaries, were returned to the bereaved family. As for the Yuasa archive at the library of Ochanomizu University, the details are presented on the homepage and catalog of the library. Most of the Japanese diaries and letters that Yuasa had in her possession until the end of her life cannot be viewed at present. Besides these documents, many of the historical sources, related to Yuasa are stored in the reference room of CNRS in Orsay, a suburb of Paris, where the Institute de Physique Nucléaire (IPN), Yuasa’s last workplace, is located. While these materials are precious historical documents offering insight into the cooperative system between the Japanese and French scientific communities, there is no sorting/arrangement plan and, of course, the documents are not available for browsing. ^[4]

Therefore, the letters and diaries of Yuasa in Japanese, which are cited in this paper, besides CYJ, are those published by Yuasa herself or by Miwae Yamazaki, a junior of Yuasa at the university, who was involved in the aforementioned classification and arrangement of Yuasa’s belongings, with the permission of Yuasa’s surviving relatives. ^[5] In addition, regarding CYJ, I would like to explain that some contents are not cited in this paper because I cannot confirm their authenticity, as it is impossible to view the unpublished letters and diaries. ^[6]

Japan’s first female student with a science background to win a French government scholarship

Yuasa has been widely discussed in English articles in this publication and the website of Ochanomizu University (when Yuasa was enrolled, the school was Tokyo Women’s Higher Normal School), and so on. ^[7] Let us first consider the first half of her life according to the latter source: Yuasa was born in 1909 in Tokyo. She attended the Division of Science, Tokyo Women’s Higher Normal School, and moved on to the Department of Physics, Tokyo Bunrika University. In 1934 she graduated from the university and began physics research. Gender discrimination was still strong, however, and it was difficult to find a position where she could conduct the research she wanted. It was around this time that the Joliot-Curies discovered artificial radioactivity, and Yuasa, deeply moved by their paper, decided to travel to France .^[8]

During the prewar period, Yuasa was unable to fully demonstrate her ability in the patriarchal Japanese society. Stifled, she, an assistant professor at her alma mater at the time, went to France in 1940, in the midst of World War II, under the sponsorship of the government. She was the first female student of science in Japan to receive this honor. ^[9]It was decided that she would prepare a doctoral thesis under the guidance of Frédéric Joliot of the Collège de France. Joliot had been an assistant of Marie Curie at the Radium Institute, making Yuasa a disciple of Marie Curie’s disciple. Joliot who studied under Curie was a person who, like Curie, honored scientific rationalism as well as equal treatment of men and women. Furthermore, he also was compassionate to foreign researchers, as was Curie, who herself had been a foreign student from Poland. ^[10] Joliot’s left-wing political thought is also relevant, as his laboratory was characterized by a free and equal atmosphere. ^[11] Furthermore, Joliot did not discriminate against Yuasa for being from Japan, which was allied with Germany, although Germany was at war with France. It was an unbelievably fortunate experience for Yuasa—a Japanese woman born in the Meiji era. ^[12] Yuasa’s efforts in Paris bore fruit when she earned a doctorate (doctorat d’État) in science in 1943. ^[13] What Yuasa found in Joliot was a rare teacher, not only with respect to science but also to his view of gender, and he provided her with a guidepost for her later life. However, World War II had a strong impact on her life, in other words, her life was continued to be tossed about by the war. In July 1944, the Japanese government issued a final order to its citizens living in France to return home. After staying in Berlin for several months ^[14], Yuasa went to Manchuria via the Siberian Railway and returned to mainland Japan at the end of June 1945. The mother with whom she was finally reunited was dying and passed away just before the end of the war. Furthermore, the atomic bombs dropped in Hiroshima and Nagasaki were an intense shock to Yuasa, who was a researcher of radioactivity.^[15] A few days later, Japan finally declared its unconditional surrender, and this is when the postwar period of Yuasa’s life began.

Background of CYJ

For the Japanese scientific community, shortly after the end of the war, the existence of Yuasa, who was conducting state-of-the-art research on radioactivity in France and Germany, was valuable. Yuasa became an indispensable figure to the Tokyo Women’s Higher Normal School, where she returned to work; the scientific community; and the academic world. At that time, the Japanese government was preparing to implement a major reform of the school system, and educators who wished for girls’ education to be equal to that of boys were struggling to achieve this goal. Thus, Yuasa’s life was hectic.^[16] CYJ is the historical source from that period. From the outside, Yuasa appears to have been a star of the Japanese intellectual world right after the end of the war. However, as will be described in detail below, Yuasa found the situation in Japan, where she found neither decent laboratories nor respect for female scientists, intolerable. Yuasa did not show her distress to the Japanese. According to Miwae Yamazaki, “[Yuasa’s sorrow] was kept entirely in the diary, as she did not want aunyoneelse to be aware of her sorrow.”^[17] However, at present, the diary cannot be viewed. Even Kenji Ito, who wrote an interesting paper on Yuasa during this period, did not refer to the actual diary. He just read what had been printed.^[18] Therefore, there is consensus that Yuasa did not tell others about her distress. She did, however, write about her suffering in France. CYJ conveys Yuasa’s suffering as a female scientist at this time and the circumstances that led her to becoming a participant in the brain drain.

Yuasa and Japan just after the end of the war (1)—behind her success

The first letter of CYJ was written by Sarah Pressly Watson (1885–1959) to Joliot in March 1945. Watson, an American, was the director of the Foyer Internationale des Etudiantes in Paris, where Yuasa was living while studying in France (letter 1, CYJ; see Annex). In the letter, Watson stresses that Yuasa is safe, and Joliot replies that he is relieved to receive this news (letter 2).

In fact, when Yuasa left Paris on August 15, 1944, Frédéric Joliot-Curie had already gone underground as a member of the resistance since June 1944. Thus, when Yuasa was forced to leave Paris, she could not say goodbye to her teacher. For that reason, she wanted to somehow inform him that she was safe. Therefore, she wrote a letter to Watson from Germany, and Watson forwarded the information to Joliot.

The letter of October 8, 1946 is probably the first one in which Yuasa informs Joliot herself about her safety (letter 3). At the time, Yuasa had officially returned to the Tokyo Women’s Higher Normal School as an Associate Professor (fig. 1). With permission from Yoshio Nishina (1890–1951), who was the director of RIKEN (Institute of Physical and Chemical Research), she became a part-time researcher at the institute and planned to commence research on RIKEN’s cyclotron at the end of August 1945. However, on September 22 of that year, GHQ (US General Headquarters) prohibited research on nuclear energy in Japan, and on November 24, the Japanese cyclotron was destroyed. Yuasa was at a complete loss. Therefore, she focused on writing a paper on β collapse for the time being.^[19] Her letter describes these difficulties:

I am very happy to be able to write to you, my professor. I have not seen you for two years. I have been wondering how you are doing. Sometimes, I see your name in Japanese magazines, and I feel very happy. Indeed, my life was meaningful only when I was in your laboratory, under your guidance. My life now is completely colorless. [Description of her mother’s death and Great Tokyo Air Raid] I have no other hope except studies. And yet, the only hope of mine, studies, cannot be fulfilled adequately due to lack of materials. In particular, it was a great upset that I lost the cyclotron in Professor Nishina’s laboratory, where I was working […] I fully understand that such things are all due to the war. But still, I regret that we Japanese people could not avoid the war. (letter 3)

Next, Yuasa states that she is now translating Pierre Curie, which she received from Irène.^[20] Then, at the end the letter, she informs Joliot of her present address—the address of her dormitory at Tokyo Women’s Higher Normal School.

Joliot seems to have replied to this letter by telegraph, as often indicated by Yuasa: “I am glad to hear from you. Let’s resume the work. I hope that you will come back to the laboratory and study again.”^[21] Yuasa expresses joy at receiving a letter from Joliot in her New Year’s greeting card in 1947 (letter 5). She states, “It gave me unlimited pleasure to receive a reply from you, my professor. It gives me the courage to survive in this completely ruined Japan, where I have neither a home nor parents, and more than anything else, any laboratory.” She then mourns the radical transformation of RIKEN after the destruction of the cyclotron,^[22] and states that because she cannot conduct research in Japan, “I wish that I could go back to your laboratory and study for a few more years.” This suggests that Yuasa initially had not considered residing permanently in France; she had considered completing her research in France, which was interrupted by the war, and then returning to Japan to live.

For example, in the next letter (letter 11), she states that she is waiting for a letter from Paris because she has to teach classes for 17 hours per week and she cannot conduct basic research at RIKEN, and that the purpose of her education is to improve the situation of Japanese women.^[23] During that period, Yuasa was struggling to create educational and research environments where female scientists could be active. However, she faced an extremely thick wall of discrimination against women in Japan. Yuasa, at that time, wrote the following in an essay:

Sometimes I thought about what prevents Japanese women from advancing in scientific fields. […] After my return to Japan, what I strongly feel is that life in Japan is so male-oriented. And how much men interfere, under the microscope, with women’s lives. There is no other place, no matter which country I go, where men even interfere with the women’s way of dressing or their hair styling. Thus, women forget to think by themselves. How can science come from people who do not have the power to think? ^[24]

She may have believed that going back to France and becoming familiar with the postwar education and research circumstances there would be useful for her to foster female scientists in Japan. In reality, however, she did not relocate to Japan; as previously mentioned, Yuasa would remain in France for the rest of her life.

Later on, in 1955, Yuasa submitted a letter of resignation to Ochanomizu University, as she had decided to stay in Paris.^[25] She was not publicly clear about the reason for her decision. However, in a private letter to Kono Yasui (1880–1971), who was an honorary professor at Ochanomizu University, she confesses that her decision was prompted by Joliot’s advice:

Professor Joliot also says that even if I return Japan now, it would not be possible for me to change the Japanese men’s way of thinking completely. It also seems like the conditions for research there may not be favorable. So, it would be better for me, and for Japan, to study hard here and return to Japan within 10 years.^[26]

What we can see here is that when she returned to France after the war, the main reasons why she wanted to leave Japan were the inadequate research environment there and discrimination against female researchers. The latter especially, as stated at the beginning of this paper, had been a continuous problem since before the war. From this letter we can infer that Yuasa felt that even in 1955, these two problems had not improved in Japan. Ito, in the above-mentioned thesis, insists that Yuasa’s return to France should not be tied simply to discrimination against women in Japan. According to Ito, at that time, RIKEN was a rare laboratory in Japan with little gender bias, and thus the conflict between Nishina and Yuasa in their research styles would have been a more important factor behind Yuasa’s return to France. ^[27] Certainly, the difference in their research styles was significant, and Ito’s argument about RIKEN’s situation regarding gender is simply that it is “true.”

However, the point on which we should focus is that one cannot understand Yuasa’s feelings by using such “objective” judgment. To what did Yuasa compare Japanese laboratories? She was not comparing them to average French laboratories but to Joliot’s laboratory and the Radium Institute, which was led by Irène Curie. The two research institutes, led by disciples of Marie Curie, were among the best in the world at that time, in terms of gender equality.^[28] With this, even RIKEN, which was “relatively good in Japan,” could not compete.

What is worth noting here is Yuasa’s expression of her dissatisfaction “as an opinion of Joliot (a male scientist)” in her letter to Yasui. In other words, even Yuasa, who was said to be a very assertive person, found it difficult for women to defend their interests in Japan, even in 1955.^[29]

Yuasa and Japan just after the end of the war (2)—Struggle to go back to France

Eager to return to France, Yuasa was in contact with GHQ to get permission to go abroad and related institutions in France. For example, she wrote a letter as a former scholarship student to André Honorat (1868–1950), a prominent political leader in France and someone who had helped her publish her doctoral thesis in France. What is stored in CYJ is Yuasa’s letter, which Honorat typed and sent to Joliot.^[30]
I returned to Japan in July of 1945, just before the end of the war. My mother died from an illness. All four houses we used to have burned down due to air raids. I am, thus, left alone. I have no house and no way to work on scientific research […]
Yet I do not know how to give up my scientific research. I would be extremely happy if I could return to France to continue my research.I would greatly appreciate if you would kindly inform the Ministry of Foreign Affairs of my wish. […] The U.S. authorities would not have any objection (against my study in France). But without the award of a scholarship, it would not be possible. (letter 7)

Honorat sent a copy of this letter to Joliot on March 12, 1947, and asked him to write a letter to Marx in the Ministry of Foreign Affairs, because Honorat wanted to invite Yuasa to France (letter 9). Joliot immediately wrote this letter to Marx (letter 10). However, the letter also states that it would be better to wait a year to prepare the research environment.
It is unlikely that Yuasa heard about this one-year wait. In August of that year, she once again wrote to Joliot expressing her distress and emphasizing her desire for an invitation letter to go to France (letter 14). In the letter, she argues that she cannot conduct research in Japan, owing to the country’s insufficient supplies of electricity, gas, and water: “If you give me a formal invitation letter to France, I want to fly to France right away.” She wrote, even though the cost of living in France was higher than in Japan, “If I can conduct research works under you, I do not mind any hardships, so please give me the pleasure of doing research with you again.” Joliot’s reply to this letter (dated November 5) is located in both the Curie Archive and the library of Ochanomizu University.^[31]
Your letters have given me great pleasure and I am very touched by the friendship and loyalty you gave to me.I would be very happy to see you again working with us at the College Laboratory. […] [For you to come to France again to study] need to apply to the National Center for Scientific Research to try to obtain a research fellowship for 1948/1949.
Madame Joliot is very impressed that you translated Pierre Curie, written by Mme Curie […]
Once again, I would be very happy if you could come back to Paris to work in my laboratory. (letter 15)

However, Yuasa had difficulty getting back to France to study. She was irritated and, while the reason was not mentioned, she, for some reason, left a letter with a person named Mme Raptis to give to Joliot. Yuasa’s letter is dated July 26, 1948 (letter 18), and Raptis forwarded it to Joliot on September 21 (letter 19). Yuasa was very worried about whether CNRS would grant her a scholarship and she would be able go to France by the end of that year. She declared that if she could not get a scholarship, she would like to go to France even if it meant bearing the expense herself.
What is so surprising here is that although Raptis sent the letter to Joliot on the 21st, he wrote his own letter about this to Georges Teissier (1900–1972), general director of CNRS, on that same day, requesting a scholarship for Yuasa. In his letter, Joliot explains that Yuasa is an international student who completed her doctoral dissertation under his supervision during the period of the German occupation. He then highly praises her ability and personality:
I am extremely satisfied with the work of this excellent scientist. She presents very high moral quality, as evidenced especially during a difficult time of the occupation. All the workers in my laboratory as well as Mme Joliot-Curie agree in this regard. With deep understanding and love of France and full of enterprising sprit, she will be able to accomplish notable service to our country. […] If you give Mlle Yuasa the opportunity to study here, she will make a big contribution to French scientific research with superb work which is appropriate for this first-ranked scientist. On the other hand, because of her passion and deep understanding of our country, it is possible for her to make a great contribution to our country. (letter 20)

Yuasa also wrote several letters to Joliot in a row that fall and was concerned about the CNRS’s response. What is interesting here, which I will discuss later, is that while she wanted to study in France, Yuasa also was considering going to the United States to study at that time. In the letter to Joliot dated September 21 (letter 22), she states that she has received an invitation from the Institute for Nuclear Studies of the University of Chicago, but that she really wants to go to France.
hen Joliot received this letter, the scholarship matter had already been settled. Teissier assured Joliot that the organization would give the research scholarship to Yuasa (letter 22). Yuasa went into raptures about CNRS’s reply of acceptance:
No words can describe how happy I was [by the acceptance notice from CNRS].
It is all thanks to you, my professor. I’m too happy, and this joy is driving me crazy! I even lost my appetite since the day I received this news.
I can study all day long under you. Can it be real for me to feel such happiness?
Soon, I can go to your place. Oh, how excited I am! (letter 23)

However, this meant that she had only obtained a scholarship, which would only cover living expenses. The problem of paying travel expenses remained. Thus, Joliot then struggled to find sponsorship for her travel. He negotiated with CNRS many times, but could not get a good response (letters 26, 27, 28).
There is no letter in CYJ from the French side stating that Yuasa’s travel expenses would be paid. However, it seems that the problem was solved in the end. In a letter to Joliot the following year, in January 1949 (letter 29), she notes that if all goes well, she will leave Japan at the end of that month and will arrive in Paris in March.^[32] Thus, the preparations to go to France were underway at this time.

Evaluation of Toshiko Yuasa, a scientist

This section will consider CYJ from another perspective. In these letters, Yuasa requests support from the French side not only for herself but also for other Japanese to go to France. Yuasa was renowned for her service-minded personality, and we can see evidence of this in these letters. This was an especially difficult period for the Japanese as a whole, and everyone was hungry for culture. Although Yuasa herself was starving for culture, as a person “having returned from France” and having experienced the state-of-the-art laboratory experience there, she was an important person through whom many Japanese researchers could satisfy their intellectual hunger. Yamazaki wrote repeatedly that the Yuasa Laboratory of Tokyo Women’s Higher Normal School had become a kind of intellectual salon during this postwar period.^[33] Thus, in CYJ, various Japanese researchers, not only scientists, are given recommendations by Yuasa. In addition to physicist Eizo Tajima (1913–1998), Yuasa mentioned Rikutaro Fukuda (1916–2006), who later became an expert scholar in comparative literature.^[34] Surprisingly, in Yuasa’s resume she named Fukuda, along with Nishina and Joliot, as guarantors, besides family members (letters 12, 13).
The interesting thing here is that Joliot warned Yuasa about her do-gooder attitude. Indeed, he chided Yuasa: “I will talk about your friends to the authorities, but to get your own satisfaction is the first priority” (letter 14).
Actually, even if we consider the virtue of modesty of the Japanese who were born during the Meiji era, Yuasa generally had a self-deprecating tendency with respect to her scientific talent, her ability as a teacher, and her appearance^[35]. However, Yuasa was far from incompetent. For example, Tajima praises Yuasa as follows:
The story goes back to the end of 1943, before the end of the war [Tajima’s faulty memory: Actually, it was in the summer of 1945]. Ms. Toshiko Yuasa came back from France, where she had been staying to study, for the first time in four years. She is my senior by three years at the Tokyo University of Arts and Sciences [...] has been conducting nuclear research.
[In the Siberian Railway to return home] Only one backpack was permitted as a portable item, and in the backpack, there was one experimental device. […] Under such hard circumstances, she brought experimental apparatus all the way back to Japan, as the most important thing above anything else, and I was so impressed and took off my hat to her for her heart. […]
August 15th, the day of the end of the war, came. The towns suddenly became bright, and the topics among the two of us focused on future trends of Japanese science. But for the time being, all we could do was support ourselves to live; thus, there would be no leeway to study. And for the Nishina laboratory, the removal of the Cyclotron was a mortal blow. So, she strongly encouraged me to go to a university in the U.S. and continue my research there. As the method for the plan, she taught me to write a letter expressing my desire to study abroad with a list of my grades in courses and mail the letter to a big university in the U.S. […] I made letters as I was told and mailed them to ten universities in the U.S. Ms. Yuasa herself also made similar documents and sent them to universities in the U.S. We said that, if possible, let’s study together at the same university, and so on. […]
At the end of 1948, I received a letter from Professor L. H. Anderson of Chicago that I was invited as a researcher to the Institute for Nuclear Studies of the University of Chicago (now the Enrico Fermi Institute), so come to the U.S. immediately, which made me feel so surprised.^[36]

Yuasa was seen by Tajima as a positive person, who was full of vitality—far from being defeated by the loss of the war. Tajima’s resume was attached to a letter she sent to Joliot (letter 6). This means that the reason why the resume was in English is that it was for submission in the United States. As for Yuasa’s resume (letters 12, 13), the reason why there are copies in both English and in French is most likely because she did not know which of the two countries she would ultimately study in. In short, Yuasa wanted to escape Japan by any means.
What did Joliot think about Yuasa’s personality? In Joliot’s letters in CYJ, Yuasa is referred to prominently as a “hard worker.” This term is emphasized (letters 2, 10, 24), and Joliot pleads in all directions for support for Yuasa. As for her personality, he praises her using the expression “very high moral quality” (letters 2, 24). Moreover, his letters contain expressions such as “excellent scientist” and “first-ranked” research (letter 24); thus, Joliot’s overall rating of Yuasa is high.
In the first place, Yuasa was probably the first Japanese scientist to secure a regular job in France. This is not something that one could achieve only through a personal connection of Joliot. It was the result of Yuasa’s efforts and her talent. Moreover, Joliot was a person who prioritized sustained effort and accurate experimental results. He often said things such as “I do not think there is genius as to be said in the world, but how far people can make their best effort”; “I would rather trust people who make constant efforts than people who temporarily work very hard and then play afterwards”; “To be a good experimentalist, one must be a good craftsman first.”^[37] Among what appear to be his favorite phrases, thus, the term “hard worker” would be Joliot’s best tribute.
But how was Yuasa as a teacher? This is the point on which her self-deprecation was the farthest from the truth. Especially in her later years until her death, when we see how much money and time Yuasa’s juniors in school and her students devoted to her, organizing symposiums and editing anthologies of her essays, and the unfeigned praise they directed at Yuasa in those anthologies, we can well understand that she was loved as a teacher.^[38] Yuasa probably felt inadequate because she compared herself to Joliot, who was also a first-class teacher, but, in truth, the two of them were equal in this regard. If differences manifested, it would be due to their cultural and gender differences. For example, Joliot’s affability was probably based on what the French culture requires of men, and Yuasa, a Japanese woman, could not imitate this. In addition, because Yuasa was a woman, she would have been subjected to gender discrimination in Japan in particular, but also in France, no matter what she might have said.^[39] This is because, apart from the laboratories of Joliot and Irène Curie, in general, before the May Revolution (1968), there had been significant discrimination against women in the majority of laboratories even in France. Under such circumstances, it would not have been easy for female scientists to become “pleasant” people. Irène offers a typical example.
Irène, who had famous parents and was a precocious female scientist, was always an object of envy of the world. Moreover, due to the education of her mother Marie, who did not teach “common sense,” Irène’s attitude was very straightforward, and she was not socially adept at all. Thus, in France, regarding the Joliot-Curies, there was always a comparison between a friendly and caring “well-balanced” husband and a very smart but unfriendly wife. Indeed, even Yuasa was shaken up by the “coldness” of Irène when she met her for the first time.^[40]
In short, it was impossible for Yuasa to become a likeable science teacher on the model of Joliot in either Japan or France, as there was severe discrimination against women. Thus, it can be said that this predicament for Yuasa as equivalent to mourning, “I can no more become God.” Yuasa was a sufficiently good educator. One certainty is that there was no place in Japan at that time to utilize the talent of this rare female scientist, and it was Joliot and the French culture behind him that put her talent to use.^[41]

Return to France!

Upon obtaining permission from CNRS, Yuasa finally left Japan from the port of Yokohama on February 21, 1949.^[42] She wrote letters to Joliot while on board the ship. Since the first letter is dated February 22 (letter 29), it can be said that Yuasa wrote a letter to her teacher immediately after boarding. This letter is very emotional, expressing that Joliot as a teacher is “equal to God” and that he is essentially the only one on whom she could rely. Although this was supposed to be a long-awaited departure, owing to the intertwining of thoughts of various things that she had left in Japan, Yuasa was emotionally perturbed.
In addition, an incident occurred in Singapore. She was supposed to change ships to travel onward to France from there, but due to a strike by a shipping company from Marseille, the ship did not arrive. Yuasa was delayed in Singapore for a long time. As there was a limit on the amount of foreign currency a Japanese citizen could take overseas, she was forced to pay her expenses, and her money was running out. Yuasa bore the shame of asking her teacher for financial assistance and appealed that she wanted to somehow reach Paris (letter 32).
Joliot, who was aware of the incident in Singapore, immediately contacted Teissier of CNRS (letters 32, 33, 34) and even arranged an air ticket, arguing that Yuasa should not have to wait for a ship.^[43] Joliot’s scrupulous attention, considering how busy Yuasa observed him to be after her arrival to Paris, was remarkable. Therefore, it is natural that Yuasa continued to feel deep gratitude toward her teacher.^[44] Ultimately, a ship to France would come before an airplane, and Yuasa’s relief is evident in her last letter:
I would like to offer a big apology for the [deranged] previous letter I wrote you from Singapore. I really did not know what to do at that moment. At the last moment, it was proposed to me to board this French ship leaving on April 2.
[Explanation that it was more convenient for her to take this ship than the airplane that Joliot had arranged]
I will be in Paris in late April, and I cannot remain calm because of the joy of being able to work with you again. (letter 35)
Thus, after many twists and turns, Yuasa arrived at the port of Le Havre on May 5, 1949. The next day, she arrived in Paris and finally found herself back in Joliot’s laboratory.^[45] This is how, CYJ, which depicts Japan just after the end of the war, ends.

Conclusion

With the aid of CYJ, we have followed the steps of Yuasa from her return to Japan and her eventual voyage back to France. What have we learned from this?
First, during this period, Yuasa did not withhold her suffering from others, as has been considered conventionally. She clearly confided in Joliot and Honorat in France about her plight and was making steady efforts to go abroad to study again. Second, although France was her first choice for a destination in which to study, escaping Japan was her first priority at this time, and thus she also considered the United States as an option. Third, Yuasa’s strong desire to escape Japan was not only due to the poor research environment just after the end of the war, but also the prejudice against female scientists in Japanese society, as part of the overall discrimination against women in Japan. Those two problems became factors that led to Yuasa’s permanent residence in France, although she had gone abroad to study with the intention of returning home at some point. It was not in her home country that Toshiko Yuasa could dedicate herself to scientific research.
However, she could not study in France exactly as she desired. While Paris was the place in which she had been continuously hoping to study, she made very slow progress in her research. It was not easy to fill in the gap of five years. Furthermore, Yuasa was not the only one. The figure of a former colleague, who was an excellent researcher, but had exhausted all his energy due to the resistance movement and could no longer write a doctoral thesis, made Yuasa feel depressed. She lamented, “how many destinies of talents that should have flourished were destroyed by the war of this time.”^[46]
In an essay, Yuasa notes the impression of seeing burnt-out Tokyo in July 1945 as follows: “really, it seemed like a nightmare, or rather, it seemed that I came to hell. I remember hoping ‘not to bring any war to our country’ from the bottom of my heart.”^[47] She also recorded Joliot’s remarks that “To be able to study calmly, it cannot be done with grief both inside and outside. It can only be realized in the country without fighting, no worrying about family life and with a deep understanding of the family.”^[48] In this way, Yuasa hated the war, and processed such thoughts on occasion. That spirit reappears throughout CYJ. We should not forget the strong wishes of Yuasa and Joliot for peace—thoughts they have entrusted to later generations. In that sense, CYJ can be regarded as correspondence aimed at international cooperation in science by people wishing for peace.
Finally, regarding the historical materials that researchers are not permitted to read, despite the clear fact of their existence in Japan and France, I sincerely wish that someday, the documents will be available to us, so we can develop the truest possible image of this rare Japanese female scientist.

Annex: Correspondence between Yuasa and Joliot (CYJ), Bibliothèque Nationale de France / Musée Curie, NAF 28161. Archives Joliot-Curie, N.68^[49]