The butterfly hunter from the Jezreel Valley dreamed of studying biology, until he came across an old physics book and discovered that natural phenomena can be calculated with mathematical tools
When the Soviet government closed the schools that taught Hebrew, Prof. Ben-Zion Dinburg (later Dinor, Minister of Education and Culture) arranged immigration licenses ("certificates") for teachers in the hope of bringing them to kibbutzim and moshavim. Thus, four years after the founding of Kfar Yehezkel, the second workers' settlement in the Land of Israel, the Ptolemy (formerly Smilansky) family, who immigrated from Ukraine in 1925, joined its ranks: the parents Moshe and Leah, teachers of Hebrew, their daughter Tahia, about ten years old, and their toddler son, Yigal, less than one year old. On the ship that arrived from Odessa to Jaffa there were two more families of teachers, but they stayed in Tel Aviv, which seemed quite pioneering to them.
Yigal grew up in Moshav at the foot of the Gilboa, in the heart of the Jezreel Valley, and studied until the XNUMXth grade at the school in the village that his father ran (one of his students, Azaria Alon, wrote highly of Moshe Ptolemy). The XNUMXth grade was in the Geva group, and Vigal and four other boys walked to the Geva every morning. When it rained and water flowed in the wadi between the settlements, crossing was not possible.
Yigal friend toTovia Kushnir, of the moshav boys who, due to family reasons, were sent to Kibbutz Yagor to live as an "outside child". There the nature teacher managed to excite him and he became an avid nature lover. During Migor vacations, the only person in the seat with whom Tovia could share his enthusiasm was Yigal. In their free time, the two boys enjoyed wandering in the wild landscape of the Gilboa, hunting for butterflies, examining plants and documenting their details. The "butterfly hunters" mockingly called them their friends, who valued only "real work" in their parents' farms. A particularly adventurous trip of the two took place during the 1942 Passover vacation to Mount Hermon (in Lebanon); It is described in Deborah Omar's book "A storm in the spring".
Yigal dreamed of studying biology, but for that he had to finish high school. Those were the days of the Second World War, and his parents were afraid to send him to study in Tel Aviv and decided that he would study on his own. Yigal began studying, among other things, with the help of an old physics book that was in their home, and discovered that it was possible to calculate natural phenomena, such as the free fall of bodies. The discovery ignited his imagination and he slowly abandoned the idea of studying biology and focused on physics. But the self-study did not succeed.
Yigal studied the subjects that interested him and abandoned "uninteresting" subjects. In the end, despite the war, his parents decided to send him to Tel Aviv, to live with their friends. He was admitted to the Herzliya Gymnasium in the last third of the XNUMXth grade, and this on the condition that he study in the realistic major (his knowledge of history did not satisfy the examiner).
The parallel of the minds
At the end of his studies, in 1942, he volunteered for the Palmach. Despite his poor eyesight, he refused to wear glasses so as not to be "Abu-Arba". In those days, the Palmach bases were in kibbutzim, two weeks a month the Palmach fighters worked in the kibbutz and the rest of the time was devoted to training. After a few months in Tel Yosef and Ramat HaKobus, Yigal was released in 1943 for health reasons and began studying physics at the Hebrew University in Jerusalem. His friend Tovia, who studied biology, also arrived there two years later; Later, Tovia was killed in the War of Independence as a soldier in the HLA division. In the physics department, Yigal met Uri Haber-Sheim and Yitzhak Shimoni, later pioneers of Israeli television. A year later they were joined by those who were to become the founders of the Department of Nuclear Physics at the Weizmann Institute of Science - Amos de Schlit, Gabi (Gvirol) Goldring and Gideon Yekothiali. The physics lecturer who impressed the group was Prof. Yoel Rakah, who immigrated from Italy due to the racial laws in his country.
When he finished his studies and received a master's degree in physics, Prof. Rekha Legal suggested that he become his practitioner and pursue a doctorate in atomic spectroscopy. But Yigal set his sights on the Zurich Institute of Technology (ETH) and Prof. Wolfgang Pauli, a Nobel laureate, who taught there. When the fighting started in Israel in 1947, he postponed his trip because he realized that a long and difficult campaign was ahead of us.
Yigal fought in the war in Ramat Rachel and in Neve Ya'akov. Rakah and others urged him to join the Science Corps. Aharon Katzir even asked his girlfriend at the time, Hana - later his wife - to influence him on the matter, but she refused. After some time, Yigal was forced to move "by order" to the HMD base in Rehovot. On an off road, equipped with a grenade, he went down in a jeep on the Burma road. At six in the morning he knocked on the door of his sister, a resident of Rehovot, who was very excited to see him.
Haber-Sheim, Yekothiali, De-Schlit and Goldring also served in the Hamad. The group tried to maintain an academic atmosphere and held lectures and seminars. They came to know how far behind physics was in Israel, compared to Europe and the United States, and discussed among themselves that they would have to go abroad for studies and research, and when the time came, return to Israel to root what they had learned here. They talked about it with their superiors, Katzir and Ernst Bergman, and they said that maybe the state would send them. Ben-Gurion was very attentive to scientific matters, and in particular to Katzir and Bergman. Despite the poverty of the young country, De-Shalit, Haber-Sheim, Yekothiali, Ptolemy and Israel Falah were sent abroad. Yigal, who was already married to Hana (née Kibelwitz), fulfilled his plan and went to Switzerland for doctoral studies with Prof. Pauli.
The nuclear family
In his doctoral thesis supervised by Pauli, Yigal developed a method that greatly facilitates calculations in the shell model of atomic nuclei (see box on the shell model). After completing his doctorate in 1951, he set his sights on America and went to Princeton for post-doctoral research in this model with Prof. Eugene Wigner. While he was in the US, in 1954, Ben-Gurion resigned from the government. Defense Minister Levon was not interested in scientific research, and the physics group that worked in the Ministry of Defense, which was joined by the newcomer from the USA Zvi Lipkin, was "purchased" by the Weizmann Institute of Science. Yigal He joined the institute and was on the team that established the first nuclear physics department in Israel.
The young physics researchers, who got to know the academic world abroad, played a large part in shaping the image of the institute. They saw the students as partners in the research and allowed them, already at a very early stage, to engage in topics that interest them. They were the ones who broke the European system of a professor heading the department while his assistants and research students do his bidding.
Ptolemy and de Schlit continued their research that began in Switzerland and later in the USA. Some of the theories and calculation methods they developed are used by physicists to this day. In 1963, Amos Vigal published the book Nuclear Shell Theory, which was widely distributed and is considered a fundamental book among nuclear physicists in the world. Another book written by Yigal on the subject - Simple Models of Complex Nuclei: The Shell Model and the Interacting Boson Model - was published in 1993.
Over the years, Yigal has gained appreciation and recognition in Israel and around the world. He was invited as a visiting professor to MIT, Yale, Princeton and other leading universities in different countries. He has been invited to lecture at many international conferences. Until his retirement in 1995, he was a professor at the institute and over the years also served as chairman of the institute's committee of professors, head of the nuclear physics department and dean of the physics faculty. In addition, he was a member of the Israeli Committee for Atomic Energy and the Subcommittee for Research. Yigal has been a member of the Israel National Academy of Sciences since 1963, over the years he has won the Weizmann Prize (1963), the Israel Prize for Exact Sciences (1965), the Rothschild Prize (1971), the American Physical Society's Hans Bethe Prize (2000) and the A.M. T. (2003).
Even in his adulthood he did not abandon his love for nature and his hobby today is bird watching. He came to this hobby at a relatively late age following hiking trips with his eldest son, then it dawned on him that this occupation is quite common among physicists. Prof. Marie Gel-Man, Nobel laureate in physics and amateur ornithologist, came in the 50s to visit Israel with a list of birds he wanted to see; Amos Vigal organized a birding trip for him and in addition they paid him a visit to Ben-Gurion in Sde-Bokar.
Hanna and Legal have two children - the son, Prof. Yoav Talami, currently the Deputy Director of the Otorhinolaryngology Department and the Director of the Head and Neck Surgery Service at the Sheba Medical Center, and the daughter, Prof. Tamar Dayan, a zoologist from Tel Aviv University, founder and director of the Steinhardt Nature Museum. Hanna Vigal has seven grandchildren and five great-grandchildren.
The shell model
Between the protons and neutrons are the nuclear forces - strong and short-lived - that stabilize the nuclei of atoms. The particularly stable nuclei have "magic numbers" of protons and/or neutrons, which correspond to the maximum numbers of protons or neutrons in certain shells. It turns out that it is possible to get a reasonable description of their complicated movements according to the movement of particles caused by a central force. In this model, the protons and neutrons are arranged in a kind of "shells" reminiscent of onion skins. The shell model in the nucleus, although it appeared as a surprise, aroused a lot of interest but also a lot of opposition. One of the difficulties of the model was the numerical value of the magic numbers, especially those observed in heavy nuclei. While the numbers 2, 8, 20 corresponded to a reasonable central force, 50, 82 and 126 were only obtained from forces that were difficult to obtain. It was only in 1949 that it became clear that the movements of the protons and neutrons are also determined by the forces between the angular momentum and the internal momentum (spin) of the particle. Since then, the shell model has been a cornerstone in nuclear research.
The main result of the shell model is the existence of magic numbers determined by the full shells. For some nuclei (where the numbers of protons and neutrons are magic numbers), the first excited state has a higher energy than the ground state. This is due to the fact that for this excitation, a proton or neutron must rise from a full shell to an empty, higher shell. If there are some protons or neutrons outside of full shells, there are low-lying excited states, where these particles stick to the possible states according to quantum theory. They do not have the same energy because the energy in the central field cannot accurately describe the nuclear forces acting between any two particles.
Yigal Ptolemy wanted to arrive at nuclear energy calculations that are quantitatively correct. Together with his graduate student, Shmuel Goldstein, later a scientist at Ben-Gurion University in the Negev, he tested the energy levels of the potassium 40 isotope, which seemed simple to them. To check what they got, they calculated the energies of the lower states of chlorine 38. There was almost no agreement with the experimental results. Only two years later, in 1956, the results of an exact experiment were published which were in excellent agreement with the calculations. Since then Prof. Ptolemy and his research partners as well as many other scientists have applied the method (the extraction of the forces between any two particles from the energies measured in the nuclei) also in calculations on more complicated nuclei. In this way, the properties of the effective forces and their effects on the structures of the various nuclei became clear.
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