Oral histories in meteorites and planetary science: XI. Masatake Honda

Item Type Article; text

Authors Marvin, U. B.

Citation Marvin, U. B. (2003). Oral histories in meteoritics and planetary science: XI. Masatake Honda. Meteoritics & Planetary Science, 38(S7), A177-A187.

DOI 10.1111/j.1945-5100.2003.tb00327.x

Publisher The Meteoritical Society

Journal Meteoritics & Planetary Science

Rights Copyright © The Meteoritical Society

Download date 27/09/2021 07:16:35

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Link to Item http://hdl.handle.net/10150/655728 Meteoritics & Planetary Science 38, Nr 7, Supplement, A177–A187 (2003) Abstract available online at http://meteoritics.org

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Oral histories in meteoritics and planetary science: XI. Masatake Honda

Ursula B. MARVIN

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA E-mail: [email protected] (Received 27 May 2003)

Abstract–Masatake Honda majored in inorganic chemistry at the University of Tokyo and then pursued graduate studies in geochemistry. In 1943, he completed his first research project, which yielded new data on the behavior of strontium in carbonates. He then spent the next two years as a technical officer in the Japanese Imperial Navy. While on duty, he gained expertise in the important new field of ion exchange methods, which he ultimately chose as the topic for his Ph.D. thesis and then expanded into a book. In 1955, Honda traveled to Switzerland and spent a year in research laboratories at Bern and Zürich. He then joined Professor James R. Arnold at Princeton University and soon began focusing his research on cosmic-ray produced nuclides in meteorites. Two years later, he accompanied Dr. Arnold to the University of California at La Jolla where they joined the research group of Professor Harold C. Urey. Honda developed techniques for measuring terrestrial ages of meteorites and showed that most of them have survived weathering for vastly longer periods than had been anticipated. After spending nearly eight years abroad, he returned to Japan in 1962 as a full professor at the University of Tokyo. During the Apollo missions, he performed research on cosmogenic nuclides in lunar rocks, surface soils, and deep drill cores. In the same period, he studied terrestrial histories of numerous Antarctic meteorites. In 1992, he retired from his professorship but he continues to carry on his research and to publish papers. In 1987, the Meteoritical Society presented its Leonard Medal to Masatake Honda for his pioneering work in establishing the abundances and production rates of stable, long-lived, and short-lived nuclides by cosmic irradiation of meteorites and lunar samples.

UBM: Masa, today we call you a cosmochemist, but that UBM: Did Prof. Minami introduce you to the study of is a Space Age term. As a young student in Japan, did you meteorites? start out by majoring in inorganic chemistry? MH: No, but he made me aware of them. Professor MH: Yes, but in 1942, when I was a senior in the Tokyo Minami always used to wear a thick hat in the geochemistry Imperial University, I decided to study geochemistry in laboratory. When anybody asked him his reason he would say graduate school. The course I took toward graduation was that someday the hat might protect him from a meteorite taught by Professor Yuji Shibata, who had introduced the field falling on his head. Of course, we all took this to be a joke. of geochemistry into Japan. Professor Shibata had studied But, we knew that in his school days in 1923, he had worked chemical coordination compounds at Zürich under Professor on the Kushiike chondrite that had fallen in 1920, the year Alfred Werner and had learned to measure rare elements by when I was born in Tokyo. Meteorite falls were rare in Japan, spectroscopic analyses from Professor Georges Urbain at Paris. and it was an especially rare opportunity for him to be able to UBM: Did you do your graduate work with Professor do reliable analytical work on a fresh fall, under the Shibata? instruction of Professor Shibata. MH: No. In graduate school, I worked under Professor UBM: So, meteorites were one of Professor Minami’s Eiiti Minami, who was an assistant professor of inorganic special interests? chemistry. Professor Shibata retired in 1962 on his 61st MH: Yes, they were. He had written a monograph on birthday. meteorites in 1930 when he was 30 years old. He also was

A177 © Meteoritical Society, 2003. Printed in USA. A178 U. B. Marvin

examined. I now feel that Professor Minamu was right in rejecting the subject I had proposed as a young student who had no experience at all of research in geochemistry. UBM: So, you began working on strontium? MH: Yes. I started studying the chemistry of strontium and realized very soon that Sr always occurs with Ca, and Ca is an important bioelement that forms corals and other calcareous organisms in the oceans. UBM: It seems that you had a biogeochemical problem, after all. MH: Yes, I had. I quickly learned that calcium carbonate (CaCO3) crystallizes either as hexagonal calcite or as orthorhomic aragonite, but Sr carbonate enters only the aragonite structure. Corals consist of aragonite because, for some mysterious reason, the CaCO3 from seawater always forms the aragonite structure in the presence of Mg. Therefore, Sr and Ca occur together in marine deposits such as coral. But, they do not occur together in continental carbonate rocks because Sr is ejected from the structure during their recrystallization to calcite. The Sr returns to the ocean, Fig. 1. Masatake Honda with two prints of the Brenham pallasite at eventually. This is the reason why Sr/Ca is 1 atom percent Arizona State University in 2002. higher in sea water than the terrestrial mean value of <0.1 atom percent in continental limestone. In the most extreme cases, interested in the rare earth elements and their abundances in stalactites and stalagmites contain the very least amount of Sr rocks and meteorites. In 1933, he went to Göttingen, relative to Ca to be found in any carbonates. Germany, to study rare earth patterns in the laboratory of Prof. Minami supplied me with a glass prism Professor Victor M. Goldschmidt. He stayed there until 1935 spectrometer and a spark source generator. The presence of Sr and then left for Japan, just two months before Professor in association with Ca could be observed by the naked eye Goldschmidt, himself, had to resign his job, due to the rise of because the strongest blue Sr line, at 4607 angstroms, stands antisemitism, and leave Göttingen for his home country, out easily from among the weak Ca lines nearby. The Norway. principle was the same as the one used to determine the I would like to add that Dr. Minami was a very magnitude of visible stars. This was my first scientific project. independent person with unusual interests inside and outside I worked on it for about nine months and found it to be of science. He had been an instructor in the department of unforgettable. Professor Minami and I published a paper on mineralogy at the Imperial University of Tokyo before the strontium contents in natural calcium carbonates, but not coming back to the chemistry department at the same until 1950. I did not have a chance to go on and study the university. Such a move was quite rare, but he did it to pursue geochemistry of boron. his own interests. This did not make him popular among UBM: What happened to prevent you from studying chemists in Japan, but he gained an international reputation boron? for his interdisciplinary scholarship. Incidentally, Minami MH: In principle, nothing prevented me from it, except was a Roman Catholic and a devotee of Esperanto, but he did that during the war the arrangements to perform that work not succeed in interesting any of his students in Esperanto. were not available to us. UBM: Given his own interest in meteorites, if Professor UBM: From the dates you mentioned earlier, I gather that Minami, as your teacher—or “mentor” as we might now call the war began the year before you entered graduate school. him—did not encourage you to study them, what research MH: That’s right. topic did he assign to you? UBM: Did the bombing of Pearl Harbor come as the MH: He recommended that I start with the geochemistry complete surprise to you in Japan that it did to us? of strontium. At that time, I had become interested in the MH: Yes, it certainly did. No civilians knew of plans for papers on biogeochemistry by Professor V. I. Vernadsky in any such a thing. Russia and was strongly influenced by them, so I asked for a UBM: And it was such a stunning success—it nearly more biologically oriented theme. Professor Minami did not wiped out the U.S. Pacific fleet! I would think there must have entirely reject my idea, but he suggested that I should first try been great celebrations in Japan. studying strontium and then continue on with the MH: That’s true. We did celebrate when we heard the geochemistry of boron, which V. M. Goldschmidt had news. Oral histories in meteoritics and planetary science: XI. Masatake Honda A179

UBM: What did you do next, after you finished your same laboratory. Marriage between people in the same room work on strontium? in a laboratory has become quite popular since then. Besides MH: I began serving as a technical officer in the Japanese being a good chemist, my wife, Nobuko, is a highly talented Imperial Navy. During my tour of duty, I had my first chance painter. to study about ion exchange resins. Back then, ion exchange UBM: I have seen some of her water-color paintings of was a new topic in chemistry and I tried to apply the technique flowers. They are exquisite. for separating various elements. My idea was sound and it led MH: I quite agree. directly to what later would become the subject for my Ph.D. UBM: What were you working on at Mitsui? thesis. MH: I was doing mostly spectrographic analyses, as a UBM: Was the topic of ion exchange assigned to you by job. the Navy or did you discover it for yourself? UBM: When the war ended in 1945, did you feel relieved MH: I was stimulated to look into it when I found a book or disappointed? of industrial patents on plastics that had been compiled in the MH: To be honest, I felt relieved. During the war, I had 1930s. One chapter concerned ion exchange in plastic become disheartened by the activities of political groups in materials. In 1935, two English technical chemists invented Japan. But, even so, our defeat made me feel very depressed cation- and anion-exchange resins that are useful for water for quite a while. It left us with no clear objectives. We purification. That was a very important discovery, but the chemists could survive by selling saccharin in the unburned book had been left as the only remaining item on an otherwise corner of the city of Tokyo, but it took a long time for me to empty shelf in a local book shop. find a satisfactory job. UBM: So, you bought the book and it prompted a new UBM: Did you stay on with the Mitsui Chemical opening in your career. This is one more example of the role Company while looking for other jobs? of accident in science. MH: I stayed with Mitsui for about five years. MH: Yes, and it was an accident of practical importance. Meanwhile, in 1947, I learned from reading the Journal of the At that time, I was working in the the harbor city of Maizuru American Chemical Society that ion exchange techniques had at a boiler test laboratory. Pure water is very important for the been a useful tool in the USA for determining the chemistry of steam boiler in a destroyer, and although the boilers in our fission products, including rare earth elements. I also read that ships were 19th century machines they powered fast-running Dr. Goldschmidt had died in March of that year, so I reported vessels that reached top speeds faster than 30 knots per hour. this to Professor Minami and I still remember how very sad it UBM: Was your new knowledge of ion exchange resins made him feel. put to use by the Navy during the war? Later, in 1949, while I still was a member of the chemical MH: No. By the time I learned about it, the war was company, I got an offer of a teaching and research position at nearing its end. But the Navy started to concern itself about St. Paul’s University in Tokyo. It would pay a lower salary, the propulsion force of highly concentrated hydrogen but I chose to accept it because after losing the war, the peroxide, an important rocket fuel, using a technique academic activity in Japan was at such a low ebb that I could imported from Germany. For the preparation of this, pure contribute something of value. water was indispensable. UBM: Did you find teaching there to be rewarding? UBM: So, the Navy did have an application for ion MH: Yes I did. In fact, the year 1949 marked the real exchange? starting point of my later career. MH: It would have had, but, again, it was too late. UBM: Did you work on your thesis while you were UBM: Did you wait until after the war to write your there? thesis on this topic? MH: Yes, and in March of the following year, 1950, I MH: I had to. I served as a naval officer until 1944, and finished my thesis: “Inorganic analyses using the ion then I asked to return to being an ordinary citizen. exchange method,” and got my Ph.D. degree from Tokyo UBM: Could you do that, leave the Imperial Navy just by University. I was beginning to think that I would like to asking? No officer in the American Navy could have done continue my research at some university or institute outside of such a thing. Japan, but I found no opportunities at that time. MH: Yes, I could, I had a rare chance; the Navy changed UBM: How long did you remain at St. Paul’s? its policy that had led to drafting too many engineers from the MH: I stayed until 1953 and then Tokyo University civilian population. Boiler engineering does not need a great invited me to come there as an assistant professor of many chemists, so I was a good candidate for a release. After chemistry. On March 1, 1954, soon after I moved there, the regaining the status of a common citizen, I greatly enjoyed my debris from the hydrogen bomb test at Bikini Atoll fell on a freedom from the heavy chain of naval command. I went to Japanese fishing boat named, “The No. 5 Happy Dragon.” live in Tokyo where I became a member of a laboratory of the Suddenly, at the request of the Hospital of Tokyo University, Mitsui Chemical Industry. In 1947, I married a woman in the we Japanese scientists were busy day and night analyzing the A180 U. B. Marvin debris components to aid in finding the proper medical between the physics and chemistry departments were not treatment for the crew members and also for basic quite smooth—a similar situation has been quite common information. In our search, we detected uranium-237 in elsewhere in Europe. Houtermans knew about the Japanese addition to ordinary fission products. Uranium-237 in the work on the debris of the hydrogen bomb and expected to get debris was isolated by cation exchange and its activity help on this from me. For example, he gave me a large bottle confirmed by following the decay curve of the soft beta rays. of local rain water in which to detect 90Sr as the fallout of This, it turned out, was a component of a secret new bomb tests. I remember that the nature of the water was American nuclear weapon. Uranium-237 is an induced by- questionable, because the precipitation of gypsum in the product of 238U with a half-life of 7 days. It had been water interfered with the sampling process by cation exchage. discovered in 1940, just before the war by Dr. Yoshio Nishina He was disappointed by my results which seemed fruitless to and his colleagues of the Japanese cyclotron group at the him. On the whole, I had too short a time to contribute much Research Institute for Physics and Chemistry in Tokyo. In of value there. addition to more than 20 other nuclides, we detected α-tracks UBM: Did you also spend some time at Zürich? of plutonium-239 by the autoradiographic method. MH: Yes, we spent 4 months at the ETH, and what a UBM: With that project finished and your thesis done, difference there was between the atmospheres at Bern and what was your next big effort? Zürich! MH: During that busy time, I wrote my first book, Ion UBM: What did you work on with Professor Exchange, which was published in 1954. The contents were Schwarzenbach in Zürich? not very adequate from my current point of view. Even so, I MH: I studied the chemistry of organic complexes. We got a recommendation on the cover of the book from ex- worked on chelate formation of cis- and trans- 1, 2-diamino Professor Shibata. That pleased me very much, but I must cyclohexane bis-acetylacetone compounds and compared confess my shortcomings; I was too shy to meet with him to those formed of platinum and palladium with those of nickel, express my thanks for that courtesy. cobalt, and copper. We found that, due to steric hindrances, Pd UBM: At that time were you still hoping to do research and Pt compounds are stable, but Ni and Cu form only with abroad? the cis-derivatives, and Co does not form with any of them. I MH: Yes, and that year, I got a letter from Switzerland produced some positive results and was happy that I could do describing a possibility that I might receive a grant from the that during my very short stay in Zürich. Rockefeller Foundation to cover my living expenses for one UBM: Did you hope to stay on in Europe after your first year to do research in the department of chemistry at Bern. I year there? followed this up and when the offer became firm I accepted it. MH: I had no idea of remaining abroad indefinitely, but I By then, I had two small children. It was most unusual for a did hope to go to the USA sometime after leaving Switzerland Japanese scientist to be bringing a family of four to live in to learn more about nuclear science. Switzerland, but it gave me a welcome chance to leave for a UBM: I know that you eventually joined Professor Jim while the too busy living conditions in Japan. Arnold at Princeton. When did he first get in touch with you? UBM: I would like to hear about your trip. When did you MH: Before I left Japan, Jim had sent me a letter asking leave Japan for Switzerland? Did you fly or go by boat and if I would come and work with him at Princeton on techniques train? of making elemental separations. His letter came soon after I MH: I left Japan at the end of June, 1955, on a boat that had made my decision to go to Switzerland. Then, he invited took more than 30 days to reach Genoa, Italy. It sailed around me again while I was in Switzerland. Southeast Asia and through the Suez Canal into the UBM: Did you accept his offer immediately? Mediterranean. From Genoa, I went to Bern by train. My MH: No, I took some time to make up my mind to go. I family left Japan two months after my departure. still was sad that Japan had lost the war, and I felt that the UBM: So you arrived at Bern early in August of 1955? United States had a colonial atmosphere. I questioned how we MH: Yes, and soon after that, I went to Geneva to attend Japanese could live happily in the society of the USA. the First International Conference on the Peaceful Use of Perhaps an even more important question for me was what I Atomic Energy as a member of the Japanese delegation. I had could eventually bring back to Japan, or whether I should plan a chance to meet Dr. Willard F. Libby at the reception for to stay in the United States as long as I could. American delegates. Libby recommended that I should go to UBM: But, you finally did decide to go to Princeton. Zürich and work in Professor Gerold Schwarzenbach’s MH: Yes. In 1956, I sailed across the Atlantic Ocean with laboratory at the Eidgenössische Technische Hochhschule. my family and joined Jim Arnold at Princeton, New Jersey. I UBM: What research projects did you work on at Bern? spent most of my first year working on chemical separations. MH: I am not quite happy to recall my work at Bern. Jim was anxious to improve chemical techniques for Professor Friederich Houtermans had arrived earlier that year separating beryllium from pelagic sediments. In Tokyo, I had to become the head of the Physikalishes Institut, and relations developed a separation technique by cation exchange which Oral histories in meteoritics and planetary science: XI. Masatake Honda A181 was based on the valence differences among Li+, Be++, and other in Japanese. This sometimes makes people feel Al+++. According to ion exchange equilibria, the valency uncomfortable because we seem to be cutting them out by effects in dilute solutions can be enhanced extensively for ion using almost a secret code. Jim’s attitude is different. He says exchange adsorption affinities. it seems to him to be similar to the private communications It took a while for me to switch my interest from the between the musicians in an orchestra. There always must be chemistry I had learned in Japan and Europe to the study of some special contacts between experts in order for them to natural radionuclides produced by high energy nuclear achieve their best performance. Jim’s viewpoint must be reactions. I think it is quite natural to require some time to unique; at least, I never have heard anyone else express change one’s focus. similar opinions. UBM: What prompted your change? UBM: Neither have I, but I am not surprised to hear that MH: I read a book written in 1955 by Dr. Yasuo Miyake, Jim would have such an insight. When and how did you make of Tokyo, who described the discovery of cosmogenic your move to California? helium-3 by Dr. Friedrich A. Paneth in England. At first, it did MH: In 1958, I drove our family across the continent to not seem to impact me directly because it involved stable southern California and borrowed a house there. My new noble gases and meteorites, both of which still were specialty was to be the cosmogenic nuclides in meteorites. I unfamiliar objects to me. Soon afterward, however, I read a enjoyed a sense of complete freedom because I had resigned report, written in 1957 by Truman P. Kohman, who was at the my Japanese faculty post and was joining Dr. Harold C. Max Planck Institut für Chemie that year, and William D. Urey’s research group. Ehmann, a new Ph.D. recipient from Carnegie Institute of UBM: At that time, Harold Urey, himself, had only very Technology, on their preliminary work on beryllium-10 and recently moved to La Jolla from the University of Chicago. aluminium-26. Jim Arnold and I realized that we could apply Did you have any difficulties with settling into the resort with some of our knowledge to expand on their data. So we started that funny name? to work on iron meteorites, including Canyon Diablo, Odessa, MH: No, none at all. It was a great place for me and my Grant, and Williamstown, and the pallasites Admire and family to live, and I knew I would be opening an exciting new Brenham. field in which it would be easy to make new discoveries. UBM: So, at last, in 1957, we have you working on UBM: Did you build a whole new laboratory at La Jolla? meteorites! MS: Yes, we built a new lab but it needed no special MH: Yes, but in the following year, 1958, I had to choose design except for having to house Jim’s heavy shielding one of two possibilities. One was to return to Japan and accept “canon” for sensitive gas-flow counting. a full professorship in geochemistry at the University of UBM: What were the first kinds of problems you Tokyo. This is a normal career path for our young scientists, undertook there? and it is regarded as an honorable one. The alternative was to MH: Mostly, the identification and characterization of stay longer in the USA and look for other openings, perhaps cosmic ray-produced isotopes in meteorites, but also in in California. It was a hard decision and a risky one for me, sediments, in the atmosphere, and in targets we bombarded by because to stay I would have to resign my faculty post at the high energy particles. University of Tokyo. UBM: In looking through your bibliography, I noticed UBM: I’m sure I know the answer, but what choice did that you published your first paper on meteorites in 1959. It you make in 1958? was on cosmogenic potassium-40 in iron meteorites. MH: I decided to stay longer in the United States. MH: That’s right. But, I really began to focus on UBM: Did you inform Jim Arnold of this immediately? meteorites in 1961. Julian Shedlovsky, a student of Jim MH: Yes, and that proved to be my most exciting day in Arnold’s at Princeton, had come out west with us to search for Princeton. I confessed my decision to Jim at lunch time, and 53Mn in iron meteorites for his Ph.D. thesis. He brought along then he told me of a surprising decision he had just made: he a slice of the Williamstown iron he had obtained from Brian was going to leave Princeton and move to a resort in Mason, who was then the curator of meteorites at the California with the funny name: “La Jolla.” American Museum of Natural History in New York. UBM: And he wanted you to come with him? UBM: Jim told me in an earlier interview that 53Mn in MH: Yes, and I was so excited about it that I could not nature had never before been isolated and measured. continue eating my lunch. MH: That is true. It was expected to occur in iron UBM: What a fortunate outcome, after all your doubts! meteorites and its activity had been estimated, but no direct, MH: Yes, it was. And, I was especially happy with the experimental measurements had been made. We dissolved prospect of working longer with Jim Arnold. Jim is very Julian’s specimen in aqua regia (HNO3 + HCl). Julian found broad minded and he readily accepts differences of opinion. his 53Mn and measured it by X-ray counting. Then, he wrote He understands quickly and correctly whatever I want to tell it up for his Ph.D. thesis, which he submitted to Princeton in him. In the USA, we Japanese often communicate with each 1960. A182 U. B. Marvin

UBM: Was it after the successful search for 53Mn that MH: Yes, and now terrestrial ages of about two million you decided to measure other isotopes in irons? years have been measured on some stony meteorites from MH: Yes. We saved the acid solutions for further Antarctica. This has been a really astonishing result. It is counting. Devendra Lal, from India, had joined us and he surprising to me to look back into Dr. Vagn Buchwald’s built a special counter for each isotope we could isolate. voluminous set of books on iron meteorites, published in Besides 53Mn, we counted 40K, 36Cl, 26Al, and 10Be. Then, we 1975, and find that he still was expressing doubts about measured these isotopes in three other irons, Grant, Odessa, isotopic evidence for very long terrestrial ages of irons. This and Canyon Diablo, and in 1961, we published a paper by was because some of them still had well-preserved fusion Honda, Shedlovsky, and Arnold about cosmogenic isotopes crusts and thin near-surface zones of heat-effected metal, as in four iron meteorites. though they scarcely had been eroded at all. UBM: That paper was strictly on the effects of cosmic- UBM: That’s right. I remember that Vagn listed the ray bombardment of the meteorites in orbit, that is, their Carbo iron as having an isotopic terrestrial age of ~100,000 cosmogenic isotopes and cosmic ray exposure ages. At that years, but its thin heat-altered zone was still visible, so he said time, had you ever thought about their residence times on the that would mean that it could not have corroded more than ~1 Earth? mm while it lay on the ground in northern Mexico all during MH: No. We had not been interested in measuring those 100,000 years. That did present a problem. terrestrial ages. Everybody knew that meteorites, even large MH: But, I would trust the isotopic age. irons, would rust away in a few hundred years. UBM: Naturally. You mentioned earlier that you looked UBM: In his interview, Jim described to me a special forward to entering an exciting new field and solving lots of problem that arose with respect to the 36Cl in Williamstown. new problems, and, in fact, you and your colleagues soon MH: When we dissolved Williamstown to isolate 53Mn, were publishing at a prolific rate. we had no expectation of measuring 36Cl. If we had planned MH: Yes, my hopes came true. During my first four years to look for that, we would not have put the iron into aqua at La Jolla, from 1958 to 1962, I coauthored 18 papers mostly regia, which, of course, swamped it with chlorine. Later on, on cosmogenic isotopes, with five of them in the October without thinking of this problem, we measured the 36Cl in 1961 issue of volume 66 of the Journal of Geophysical Williamstown and found more than three times more of it Research. than had been reported in 1959 by Esther Sprenkel, a student UBM: You arrived at La Jolla in 1958, the year after Fred working with Oliver Schaeffer at the Brookhaven National Begemann, Johannes Geiss, and David Hess published the Laboratory. She had measured 36Cl for her Ph.D. thesis. We first cosmic-ray exposure age of a meteorite, the Norton knew of Sprenkel’s result, but we supposed she had made a County achondrite, based on their measurements of 3H and mistake and said so in our manuscript. When Oliver Schaeffer 3He. Soon after that, groups in several institutions were read our draft, he asked Jim if he would run Williamstown studying cosmic-ray nuclides and exposure ages. again if he sent him a fresh piece. We ran it again, using no Cl- MH: Yes, they were, or soon would be, at Chicago, bearing acid bath, and this time we duplicated Sprenkel’s Berkeley, La Jolla, Mainz, Heidelberg, Bern, Zürich, the results! I have been told that Jim expressed his deepest Smithsonian Astrophysical Observatory, and other places. apologies to Oliver for his unfounded criticism. UBM: Then, in 1959, you opened up the question of UBM: Then, in a final note added in proof, Honda, terrestrial ages, and in 1964, Bob Walker, Paul Pellas, and Shedlovsky, and Arnold said this new result was difficult to Michel Maurette published the first paper reporting heavy interpret, unless Williamstown has a long terrestrial age. cosmic-ray tracks in meteoritic minerals. MH: That was because the disintegrations per minute per MH: Yes, their work added a whole new dimension to kg of 36Cl in Williamstown seemed to be such an studies of cosmic ray effects. unreasonably low value, about 1/3 relative to other longer- UBM: What are some of the major changes in your lived cosmogenic radionuclides. We couldn’t think of any laboratory procedures that have taken place since the early way to get such a low value unless the iron had lain on the 1960s? ground for a time span approaching 500,000 years. Back then, MH: In the earlier days of 1960 to 1968, the techniques this seemed completely unrealistic, because metallurgists had for detecting stable and radionuclides were not very sensitive, told Jim that any meteorite would decompose on the ground and we could make our determinations only by using large within 1000 years—at most. Archaeological iron products samples. According to our records, we used up 3 kg samples have rusted within prehistoric time. It was our low 36Cl values of large irons, such as Odessa, and 300 g samples of stony- that forced us to consider the possibility that meteorites can iron meteorites, in order to detect minor contents of nuclides. have very long terrestrial residence times. For the large chondrite, Bruderheim, we dissolved a 1 kg UBM: So, the concluding sentence to your note added in sample. Even so, some nuclides, including 7Be and 32Si, proof opened the door to the whole new field of meteorite among others, could not be detected reliably. In general, the terrestrial ages? chemical compositions of stony meteorites were not well Oral histories in meteoritics and planetary science: XI. Masatake Honda A183 analyzed, and much of the data obtained were not interpreted UBM: To study cosmogenic nuclides, you had to satisfactorily. distinguish between the effects of stable isotopes and of short- However, in 1967, in collaboration with Dr. Masako and long-lived radioisotopes. Weren’t some of these studies Shima, we established the techniques of making fractional new to science? dissolutions that are especially useful for stony meteorites MH: Studies of cosmogenic nuclides grew out of noble because these are composed of so many different chemical and gas determinations, which had been developed earlier. As one mineral species. As a chemist, I find this approach to be very result, the stable and radioisotopes have been studied by attractive. It incorporates some of the wet chemical methods different scientists in different disciplines. By historical that were in use early in the 20th century. If we wish to purify tradition, physicists study noble gases using mass- the metal phase of a chondrite, we can remove traces of silicates spectroscopy, and nuclear scientists study radioisotopes using by putting it in Na(OH); or we can dissolve the metal in a neutral counting techniques. This still is presenting problems in our solution of persulfate. The purified metal will contain less than science. We need data from both sources for the estimation of 0.01% of silicates. Oldhamite (CaS) in the enstatite chondrites cosmic-ray irradiation histories. We all understand the need can easily be decomposed and dissolved in an acetate buffer. for collaborations between the two disciplines, but these are Then troilite (FeS) can be dissolved in an oxidant like Br2, or not easy to arrange because the two groups have such hydrogen peroxide. The phosphates can be attacked with different attitudes and view-points. For example, the chelating agents like EDTA so as to recover rare earth elements physicists make relatively cautious estimations of errors in in the solutions. In principle, this method can be applied to their mass-spectroscopic results and tend to limit the concentrating mineral species for use in determining internal applications of their data. On the other hand, the nuclear isochrons that will yield the formation ages of meteorites. scientists usually rely on the counting statistics (which must Some geologists and mineralogists are not happy with amount to only a part of the uncertainty of their results), and these techniques. They suspect that leaching errors may occur they like to extend their data to wider applications. These during the fractionations. Also, many of them don’t like these differences in philosophies lead to broad differences in laboratory procedures because the reagents decompose the opinions among the scientists. important mineral and petrographic structures. Everybody understands that radiation effects can be UBM: But, surely, they can obtain thin sections of the obtained from the equally reliable data sets of both stable and same meteorites and examine the minerals and textures, and radiogenic nuclides. But, since most data on stable nuclides do electron and ion microprobe analyses to supplement your are taken from measurements of noble gases, there always are findings. And you must be using much smaller samples now. possibilities of losses by the escape of gases from meteorites. MH: Yes, we are using much smaller samples, but some Losses of 3H from metals on the Earth and in space are well people still see our methods as being too destructive. known. To avoid such difficulties, techniques have been UBM: In comparison with irons, you must have special developed to measure solid stable isotopes such as 50V, 53Cr, difficulties in trying to measure cosmogenic nuclides in stony 45Sc, and other Ca and K isotopes. In addition, new methods meteorites. of mass-spectroscopy have been applied for measuring 53Mn, MH: The main difficulties are that stony and most stony- 59Ni, and 40K, and recently, by the Accelerator Mass- iron meteorites contain as many minor elements as they do Spectrometer method, for 10Be, 26Al, 36Cl, and 41Ca. intrinsic ones. For measuring cosmogenic nuclides, we would Nevertheless, even now, for estimation of exposure ages, the like to have our target elements in a single phase of a pure most useful combination is 36Ar versus 36Cl in metal, composition. But this is impossible. Magnesium, silicon, and measured by different techniques, at different laboratories, oxygen cannot be separated into pure phases, and the and by different scientists. activities of 3He, 21Ne, 10Be, and 26Al cannot be wholly UBM: We haven’t yet discussed the problems caused by attributed to discrete target elements. However, a meteorite shielding effects and the breakup of meteorites into showers. such as the Brenham pallasite presents an exceptional MH: The depth effect on cosmogenic nuclide production example in which the stony phase is strictly pale yellow rates has been a main subject of our studies. The easiest olivine. After purification in an HCl solution, the olivine is answers are obtained in large iron meteorites which we can essentially pure Mg, Si, Fe, and O, with very low contents of slice open, or from which we can take cores, so as to measure lithophile elements such as K, Ca, Sr, Rb, light REE, U, and samples from the surface to the deepest interior. In 1979, Drs. Th. In fact, in 1998, Dr. Mitsuru Ebihara found an H. Voshage and H. Feldmann at Mainz, using a highly exceptionally low value in it of about 3 ppb of K and a similar reproducible technique, determined values of cosmogenic trend for light REE. The 4He in this olivine seems to be light noble gases in the range of 4He/21Ne = 192–449 for produced solely by cosmic-ray bombardment, with none from about 80 different irons. They demonstrated that the ratios of uranium and thorium, although I badly need reliable figures noble gases are functions of 4He/21Ne. The 3He/38Ar values for original U and Th. In any case, purely cosmogenic 4He are quite uniquely observed as being practically constant at was first determined in a sample of the Brenham olivine. 17, with only small deviations after making corrections for A184 U. B. Marvin some loss by the escape of helium. In 1985, I found that these MH: The most common answer is that the irons are more data could be systematized simply using two parameters: one resistant than stones to being broken up in orbit, so they representing the cosmic-ray intensity and the other preserve longer records of their cosmic-ray bombardments. representing the spectral shape of flux in meteorites. That last The majority of irons have cosmic ray exposure ages between parameter is applied as a power coefficient to the mass loss, 500 and 1200 million years, but all stones have exposure ages that is, the target mass minus the product mass. of less than 60 million years. Multi-stage exposure models are The most popular indicator of the shielding effects has currently accepted to explain the gap. That doesn’t mean become 4He/21Ne, which varies with depth. Radionulide these models are necessarily right, but an old idea that ratios such as 53Mn/36Cl or 53Mn/(26Al or 10Be) can be used meteorites will give us evidence of changes in the intensity of for the same purpose. For chondrites, 22Ne/21Ne has widely cosmic radiation in time and space has been pretty much been used as the shielding indicator, but the applications have abandoned for lack of evidence. I sometimes have felt guilty to be limited. The use of 3He/21Ne is less useful because of the when our data have denied people the confirmation they tendency for the escape of gases from the meteorites. The best hoped for of their favorite imaginary models about technique for measuring shielding effects on production rates meteorites. in chondrites is to analyze separated fractions of their metal I believe it is very important for us always to keep open phase. minds toward every possibility. One of our oldest and most UBM: Because metals, even in small grains, are more difficult problems is to account for the origin of the elements. reliable indicators than silicates? Our knowledge of past cosmic-ray irradiation is still obscure. MH: Yes, but to get the best results, it is very important to We cannot explain the extinct radioactivities at the end of work on the deepest fragments from the largest meteorites, nuclear syntheses. We should continue to make reasonable because the depth effects can go up to factors of several tens hypotheses on all such questions. I tried to look at the of thousands. However, except with very large meteorites, we contents of 40K to learn about the formation of iron have no way of judging their depths or orientations within meteorites. This turned out to be one of my own imaginary their parent bodies. This is especially true of the meteorites stories. In short, even with iron meteorites, we can decipher we find in museum collections, or fragments collected on the the history of their break-ups but not their record of Antarctic ice sheet, or in hot deserts. We have to make formation. So, I insist that we always should go back and re- estimates based on models or on artificial high-energy examine our initial assumptions. bombardment experiments. UBM: And we keep getting surprises when we do. When UBM: Do you have any better luck with fragments from did you leave La Jolla and return permanently to Japan? fresh falls? MH: Late in 1962. I had spent seven-and-a-half years MH: No, because most of the samples are collected abroad, during which I never had visited my home country. In randomly. However, we recently spent about three years Japan, the new Institute for Solid State Physics had been measuring depth profiles of 10Be and other nuclides in established at the University of Tokyo, and my older friends randomly collected samples of the Gibeon iron. urged me to return and join the Institute. I felt that I had UBM: I assume you chose Gibeon because it has by far something I could bring back to Japan and that I might be able the largest known meteorite strewn field and there are plenty to extend my research in a new post there. of specimens of it available. I suppose you were looking for UBM: Did you find it easy to settle-in back home in fragments showing the greatest contrast in values of Japan? cosmogenic nuclides. MH: Our problems with the move fell into two different MH: That’s right. After determinations on about 40 categories. One was my own problem of how I could samples, we had obtained a maximum factor of 50,000 collaborate with other Japanese scientists in our group. between those with the highest and lowest effects. In the Because of my long absence from Japan, I actually was seen future, we should have a non-destructive method to judge as a foreigner. I was able to resolve this problem, in time. these factors. With current sensitivities for 10Be, we could Another one was our children’s problem. The three determine a much higher ratio of up to one million. But, so far, children, one boy in junior high school, and two girls, one in we have found no fragment of Gibeon with a nuclide content elementary school and the last one a baby, were faced with below our detection limits, so we still have not sampled what learning a language and living in a culture new to them. Each we think would have been the deepest part of the iron. We of us had a hard time with that. Some of them blamed me and must remember, however, that if, for example, the interior thought that their difficulties must all be my responsibility. In portions of large meteorites are evaporated completely at the my view, I felt I had, perhaps, made some wrong choices— time of fall, none of our current assumptions apply. but not by 100%. We also had some successes. In time, I got UBM: How do you explain the striking difference the idea of bringing up bilingual children. Now, I have only between average cosmic-ray exposure ages of irons and one possibility of doing that: our last granddaughter is a child stones? of two Japanese-speaking parents who live in California. She Oral histories in meteoritics and planetary science: XI. Masatake Honda A185 is the youngest of six grandchildren. It would not be very UBM: That’s right, but it still is a story worth telling. The easy, but I feel it may be worth a try to raise her as bilingual. first information on the discovery came out in 1973 at the Time has passed, and we now have more or less overcome our meeting of the Meteoritical Society at Davos, Switzerland. difficulties. But our family is split in two, with 50% in There, Makoto Shima described the differing chemical, California and the rest in Japan. isotopic, and mineralogical compositions that he and his wife, UBM: I would hazard a guess that your two older Masako, had measured on four of the nine meteorites. His children are the ones who are making their homes in news was electrifying. Nobody had dreamed that meteorites California. can occur in concentrations, something like placer deposits. MH: That’s right. So, we visit them when we can. MH: It was very surprising, and it led to many Japanese UBM: I recall that you studied the huge H chondrite, collecting expeditions and many from the USA and other Jilin. Did samples of it give you a good contrast in irradiation nations. Serious searches by Japanese teams began in 1973 histories from the surface to the interior? and by now, thousands of meteorites have arrived at the MH: Jilin (originally Kirin), which fell, after several Institute of Polar Research in Tokyo to be described and explosions, in northeastern China on March 8, 1976, classified. At first, we had big problems with this and were showered down about four tons of fragments, with the largest assigning some of them to intermediate classes such as H4–5 one weighing 1770 kg. We quickly got samples in Japan and and H5–6. Then, at our invitation, Brian Mason came to worked out a detailed multi-break-up history of the stone. We Tokyo in 1982 and showed us the proper classification wrote up our results and sent a manuscript to the Academia procedures. He was a great help to us. Sinica at Beijing, but we never got word that they received it. UBM: Brian classified all of our stony meteorites from Short descriptions of the fall and the mineralogy were Antarctica for the first 12 years or so of the U.S. program. I published in China in 1976 and 1977, but, perhaps because of believe the grand total collected by all teams in Antarctica is the Cultural Revolution, nobody seemed interested in our now approaching 22,000 specimens—we can only guess how study of nuclides. In 1980, I finally sent our first report to the many individual falls they represent. Of course, the numbers Geochemical Journal of Japan. This was not the best way to are less important than the fact that they include some new have things happen because nobody ever cited our article. types of meteorites, including the first ones to be recognized Perhaps everybody hated the thought of citing it, or nobody as coming from the Moon and from Mars. could realize its importance. MH: Yes, and meanwhile thousands of additional In 1979, after the Cultural Revolution had ended, meteorites have been found in hot, dry deserts in Africa and Chinese scientists generously distributed samples to us and to Asia. But, the Antarctic occurrences differ from all others other laboratories around the world. We studied our new partly because many of the stones were better preserved in the samples and improved upon our earlier results, which showed ice than those that have lain on the ground in other parts of the strong evidence of a multi-stage irradiation history. We world, and partly because the ice, itself, moves. This presents concluded that the 4 ton mass of the present meteorite was us with the special problem of the “superimposed fall.” On embedded within approximately one quadrant of a body any patch of blue ice where meteorites occur, most of them nearly twice as large that underwent cosmic-ray are small fragments from different falls that have been mixed bombardment for about 10 million years. The large body then together, and some inevitably have lost their fresh terrestrial broke apart releasing the Jilin mass to be irradiated for memories. We have to distinguish which meteorite fragments another 400,000 years. Some of our samples came from the came from any given fall. I have tried to apply cosmogenic surface and some from the very deep interior of the original nuclides to resolve this problem, and the nuclides also serve large mass. as a useful tool for investigating the concentration mechanism UBM: You and members of your group have made of meteorites on the ice sheet. extensive measurements of nuclides in Antarctic meteorites. In 1981, I made the first map of the meteorite We should remember that, in 1969, it was a team of Japanese distributions in the Yamato and Allan Hills ice fields, based geologists, led by Masaru Yoshida of Hokkaido University, mainly on their cosmogenic nuclides. From available data, I that discovered the first instance in which several meteorites estimated the ablation rate of bare, blue ice as ~5 cm per year of different classes lay close together on a small patch of ice and assumed the average precipitation rate as ~10 cm per in Antarctica. Of course, this story is quite familiar to us year. So, simply on the basis of this material balance, I argued because you and I and Kenzo Yagi, of Hokkaido University, that the quantity of direct falls to any given area of blue ice co-convened a symposium for the 1992 International would exceed the indirect supply trapped in the ice sheet by a Geological Congress in Kyoto that included papers on the factor of 2. Later, in 1987, Dr. Nobuo Takaoka extended my histories of the Japanese and the American collecting mappings. We concluded that the meteorites lying on programs in Antarctica. expanses of blue ice include those exposed by ablation after MH: Yes, we did. And, I thought the talks were good, but being trapped in the ice sheet and, at the same time, they no one wrote up the papers. maintain the original distributions of local strewn fields. A186 U. B. Marvin

UBM: That information could be obtained only by and Jim Arnold retired in 1993, Kuni established his own measuring cosmogenic nuclides, which often show that laboratory at the University of California at Berkeley, where similar-looking meteorites lying close together have totally he is carrying on our tradition of always looking for better different terrestrial ages. However, in 1981, on the Allan Hills procedures. main ice field, I photographed two meteorite fragments lying UBM: Throughout the lunar missions, you continued to 6 cm apart that fitted together perfectly, like pieces of a jigsaw publish reports in collaboration with various groups of puzzle, to form a meteorite completely covered by fusion colleagues. I think that one thing we all learned from lunar crust. In that particular case, I didn’t need isotopes to tell me research was that for work on such precious materials, the that that stone cracked open when it struck the ice where it best science is done by consortia, in which members make lay. different kinds of measurements on the same sample, One season, Kuni Nishiizumi collected meteorites with beginning with the least destructive and progressing to the the US-led Antarctic Search for Meteorites (ANSMET). Did more destructive techniques. he learn to measure terrestrial ages from you? MH: That’s right. Nobody did much work alone on lunar MH: Yes. Kunihiko Nishiizumi, Kuni in short, graduated samples. However, lunar research did not take up all, or even from St. Paul’s University and then came to our laboratory at half of my time. For studies of cosmogenic, and particularly the University of Tokyo. He started research on Antarctic of radiogenic nuclides, we found the waiting times while the meteorites and the first sample he studied turned out to be Apollo 11 and 12 samples were quarantined to be very extraordinary. It was Yamato-7301 (Y-7301), the first H inconvenient. We knew the short-lived activities were chondrite recovered by the Japanese team in 1973. It looked decaying day by day. Lunar research had some strong like every other H chondrite, but it gave us a big surprise. political aspects too, rather than being a strictly scientific According to Kuni’s data, its content of 53Mn was much lower project. Nevertheless, we were very disappointed by the than that measured in other stones. Instead of assuming that stopping of the project after the Apollo 17 expedition. this indicated a long terrestrial age, Kuni concluded that his H UBM: Weren’t we all! With the equipment available, the chondrite had so short an exposure history that it was under- system functioning beautifully, and the astronauts ready to go, saturated with cosmogenic isotopes. At that time, we had a the three remaining missions would have provided a treasure problem with the half-lives of certain isotopes. Beryllium-10 trove of new data on the evolution of the Moon. was believed to have a longer half-life, of 2.5 Myr, than Masa, you “retired” more than ten years ago, but you still manganese-53, with a half-life of ~2 Myr. However, in 1971, are publishing papers. Dr. Mineo Imamura and I determined a much longer half-life, MH: I should say that I retired more or less partially. of 3.7 Myr, for 53Mn, and a French group determined a shorter UBM: Are there any other topics you would like to half-life, of 1.5 Myr, for 10Be. Later on, we realized that other discuss before we finish this interview? meteorites, such as Allan Hills 76008 and 77002, also were MH: My most recent paper was on cosmogenic nuclides under-saturated. I think that Y-7301 should be celebrated as in the Brenham pallasite. While doing this study, I was an outright gift to Kuni. informed that the metallic part of Brenham also was known as UBM: Let’s turn to the Moon. When the Apollo missions the Hopewell Mounds meteorite. The latter name originated began in 1969, you played a leading role in Jim Arnold’s from the huge mounds constructed by the so-called Hopewell lunar sample consortium, which he called Indians of Ohio. These people clearly were well organized in S.H.R.E.L.L.D.A.L.F.F., using the last-name initials of his order to have built their great and complex mounds, and they eleven members at different institutions. The H stands for were talented artisans who fashioned knife blades, plates, Honda. Your first consortium paper, presented at the Apollo beads, buttons, and ornaments from the meteoritic iron. They 11 Lunar Science Conference early in 1970, was on placed some iron nuggets and some of their metallic artifacts bombardment-produced radionuclides in a lunar rock and the on altars within the mounds, which were sacred places used lunar soil. for ceremonial purposes. Recent studies of the metallurgy and MH: Yes, and so were our later papers. We were very trace elements have identified the Hopewell Mound meteorite excited to be handling lunar samples, and they opened to us a with the Brenham pallasite, that was found in 1882 in Kansas, new field by making possible our studies of solar cosmic-ray 1400 km west of the Hopewell Mounds. Not only were the effects in the surface layer of the Moon. We were particularly Hopewell people highly intelligent, they were accomplished interested in detecting the distribution of 53Mn in the deep traders who obtained many attractive items from great drill cores, which we thought might serve as a standard distances, including native copper from Michigan, obsidian model. In 1971, before Kuni joined Jim Arnold’s group at La from Yellowstone, and shells from the Gulf of Mexico. I Jolla, Dr. Imamura led us in an effort to measure 53Mn depth admire these people and am intrigued with their treatment of profiles in the Apollo 15 and Apollo 16 long core samples, the meteorite. If possible, I may ask to be buried under a using a neutron activation method which had been suggested tombstone set with a small piece of the Brenham pallasite. by Dr. H. Millard, in our laboratory. After I retired in 1992 UBM: Please put that off as long as possible, Masa. Oral histories in meteoritics and planetary science: XI. Masatake Honda A187

Thank you very much for giving me this interview. It has been Honda M. and Schwarzenbach G. 1957. Sterisch behinderte a pleasure to learn some of the details of your long and metallkomplexbildung bei den Kondensationsprodukten von cis- distinguished career. und trans-1, 2- Diaminocyclohexan mit Acetylaceton. Helvetica Chimica Acta XL:27–40. Honda M., Shedlovsky J. P., and Arnold J. R. 1959. Radioactive Acknowledgments–I wish to thank the Council of the species produced by cosmic rays in iron meteorites. Geochimica Meteoritical Society for support of this effort. This interview et Cosmochemica Acta 22:133–154. was edited in consultation with Dr. Honda. Honda M., Umemoto S. and Arnold J. R. 1961. Radioactive species produced by cosmic rays in Bruderheim and other stone meteorites. Journal of Geophysical Research 66:3541–3546. SELECTED REFERENCES Honda M., Horie K., Imamura M., Nishiizumi K., Takoaka N., and Komura K. 1980. Irradiation history of the Kirin meteorite. Arnold J. R., Honda M. and Lal D. 1961. Record of cosmic ray Geochemical Journal 14:83–789. intensity in the meteorites. Journal of Geophysical Research Honda M., Nishiizumi K., Imamura K., Takaoka N., Nitoh O., Horie 66(10):3519–3531. K., and Komura K. 1982. Cosmogenic nuclides in the Kirin Buchwald V. F. 1975. Handbook of iron meteorites: Their history, chondrite. Earth and Planetary Science Letters 57:101–109. distribution, composition, and structure. Volume II. Berkeley: Honda M., Caffee M. W., Miura Y. N., Nagai H., Nagao K., and University of California Press. pp. 426–428. Nishiizumi K. 2002. Cosmogenic nuclides in the Brenham Honda M. 1951. Study on the relation between pH of ion exchange pallasite. Meteoritics & Planetary Science 37:1711–1728. resin phase and their composition of the solution at equilibrium. Imamura M., Matsuda H., and Honda M. 1969. Applications of Journal of the American Chemical Society 73:2943. neutron activation method for Mn-53 in meteoritic iron. Earth Honda M. 1954. Ion exchange resins and their applications. Tokyo: and Planetary Science Letters 6:165–172. Nankodo. 269 p. In Japanese. Imamura M., Shima M., and Honda M. 1980. Radial distribution of Honda M. 1959. Cosmogenic potassium-40 in iron meteorites. spallogenic K, Ca, Ti, V, and Mn isotopes in iron meteorites. Geochimica et Cosmochimica Acta 17:148–150. Zeitschrift für Naturforschung 35a:267–279. Honda M. 1962. Spallation products distributed in a thick iron target Kimura K., et al. (16 coauthors). 1954. Radiochemical analysis of bombarded by 3-Bev protons. Journal of Geophysical Research “Bikini Ashes” fallen on board the No. 5 Fukuryu Maru on March 67:4847–4858. 1, 1954. Japan Analyst 3:335–348. In Japanese, with English Honda M. 1981. Terrestrial history of Antarctic meteorites recorded abstract. in the cosmogenic nuclides. Geochemical Journal 15:163–181. Minami E. and Honda M. 1950. On the strontium contents in natural Honda M. 1985. Production rates of cosmogenic helium isotopes in calcium carbonates. Journal of the Chemical Society of Japan 71: iron meteorites. Earth and Planetary Science Letters 75:77–80. 266–273. In Japanese. Honda M. 1988. Statistical estimation of the production of cosmic- S.H.R.E.L.L.D.AL.F.F. (J. R. Arnold Consortium). 1970. Pattern of ray-induced nuclides in meteorites. (Based on Leonard Medal bombardment-produced radionuclides in Rock 10017 and in Address.) Meteoritics 23:3–12. lunar soil. Proceedings of the Apollo 11 Lunar Science Honda M. and Arnold J. R. 1961. Radioactive species produced by Conference 2:1503–1532. cosmic rays in the Aroos iron meteorite. Geochimica et Voshage H. and Feldmann H. 1979. Investigations on cosmic-ray Cosmochimica Acta 23:219–232. produced nuclides in iron meteorites, 3. Earth and Planetary Honda M. and Imamura M. 1971. Half-life of Mn-53. Physical Science Letters 45:293–308. Review C 4(4):1182–1188.