Editing Franco Rasetti

{{Short description|Italian physicist}}
{{Infobox scientist
| name = Franco Rasetti
| image = Ragazzi di via Panisperna.jpg
| caption = Enrico Fermi and his research group (the ''[[Via Panisperna boys]]'') in the courtyard of Rome University's Physics Institute in Via Panisperna, about 1934. '''Franco Rasetti''' is the second from right
| birth_date = {{Birth date|1901|8|10|mf=yes}}
| birth_place = [[Castiglione del Lago]], Italy
| spouse = Marie Madeline Hennin (m. 1949)<ref name=Kerwin/>
| death_date = {{Death date and age|2001|12|5|1901|8|10|mf=yes}}
| death_place = [[Waremme]], Belgium
}}
'''Franco Dino Rasetti''' (August 10, 1901 &ndash; December 5, 2001) was an Italian (later naturalized American) physicist, paleontologist and botanist. Together with [[Enrico Fermi]], he discovered key processes leading to [[nuclear fission]]. Rasetti refused to work on the [[Manhattan Project]] on moral grounds.<ref>{{cite journal|author=Battimelli, Giovanni|title=Obituary: Franco Rasetti|journal=Physics Today|date=December 2002|volume=55|issue=12|pages=76–78|doi=10.1063/1.1537927|bibcode = 2002PhT....55l..76B |doi-access=free}}</ref>

==Life and career==
Rasetti was born in [[Castiglione del Lago]], Italy. He earned a ''[[Laurea]]'' in physics at the [[University of Pisa]] in 1923, and Fermi invited him to join his research group at the [[Sapienza University of Rome|University of Rome]].<ref>{{cite web|url=https://www.nytimes.com/2001/12/25/us/franco-dino-rasetti-100-a-nuclear-pioneer.html|first=Wolfgang|last=Saxon|title=  Franco Dino Rasetti, 100, a Nuclear Pioneer|work=The New York Times|date= December 25, 2001}}</ref>

In 1928-1929 during a stay at the [[California Institute of Technology]] (Caltech), he carried out experiments on the [[Raman effect]]. He measured a spectrum of [[dinitrogen]] in 1929 which provided the first experimental evidence that the [[atomic nucleus]] is not composed of protons and electrons, as was incorrectly believed at the time.<ref name=Caltech>[http://oralhistories.library.caltech.edu/archive/00000070/01/OH_Rasetti.pdf Caltech oral history interview] by [[Judith R. Goodstein]], 4 February 1982</ref>

In 1930, he was appointed to the chair in [[spectroscopy]]  at the Physics Institute of the [[Sapienza University of Rome|University of Rome]], at that time still located in Via Panisperna. His colleagues included [[Oscar D'Agostino]], [[Emilio Segrè]], [[Edoardo Amaldi]], [[Ettore Majorana]] and Enrico Fermi, as well as the institute's director [[Orso Mario Corbino]]. Rasetti remained in this position until 1938.

Rasetti was one of Fermi's main collaborators in the study of [[neutron]]s and neutron-induced [[radioactivity]]. In 1934, he participated in the discovery of the artificial radioactivity of fluorine and aluminium which would be critical in the development of the [[atomic bomb]].

In 1939 the advance of fascism and the deteriorating Italian political situation led him to leave Italy, following the example of his colleagues Fermi, Segré and [[Bruno Pontecorvo]]. With Fermi he had discovered the key to [[nuclear fission]], but unlike many of his colleagues, he refused for moral reasons to work on the [[Manhattan project]].

From 1939 to 1947, he taught at [[Laval University]] in [[Quebec City]] (Canada), where he was founding chairman of the physics department.<ref name=Caltech/>

In 1947, he moved to the United States where he became a [[naturalized citizen]] in 1952. Until 1967, he held a chair in physics at [[Johns Hopkins University]] in [[Baltimore]].

From the 1950s onward, he gradually shifted his commitment to naturalistic studies, which had been his great interest outside of physics already as a child.<ref>Laura Fermi, ''Atoms in the Family''</ref> He devoted himself to geology, paleontology, entomology, and botany, becoming one of the most authoritative scholars of the Cambrian geological era.<ref name=Kerwin>{{cite journal|last=Kerwin|first=Larkin|author-link=Larkin Kerwin|title=Obituary: Franco Rasetti (1901–2001)|journal=[[Nature (journal)|Nature]]|date=2002|volume=415|issue=6872|page=597|doi=10.1038/415597a|pmid=11832928 |s2cid=2625830 |doi-access=free}}</ref>

He died in [[Waremme]], Belgium at the age of 100.<ref>{{cite web|last = Ludvigsen|first = Rolf|author2 = Brian Chatterton|title = Franco Rasetti (1901 - 2001)|work = Trilobite Papers 14|publisher = Denman Institute Research on Trilobites|year = 2002|url = http://www.eagle.ca/~ontariofossils/TP14.htm|access-date = 2016-03-15|archive-date = 2016-03-18|archive-url = https://web.archive.org/web/20160318215000/http://www.eagle.ca/~ontariofossils/TP14.htm|url-status = dead}}</ref><ref>{{cite journal|last=Kerwin|first=Larkin|author-link=Larkin Kerwin|title=Obituary: Franco Rasetti (1901–2001)|journal=[[Nature (journal)|Nature]]|date=2002|volume=415|issue=6872|page=597|doi=10.1038/415597a|pmid=11832928 |s2cid=2625830 |doi-access=free}}</ref> The ''Nature'' obituary noted that Rasetti was one of the ''most prolific generalists'' whose ''work and writing are noted for the elegance, simplicity and beauty''.

==Raman spectroscopy and the model of the atomic nucleus==
After the discovery of [[Raman scattering]] by organic liquids, Rasetti decided to study the same phenomenon in gases at high pressure during his stay at Caltech in 1928–29. The spectra showed vibrational transitions with rotational fine structure. In the homonuclear diatomic molecules H<sub>2</sub>, N<sub>2</sub> and O<sub>2</sub>, Rasetti found an alternation of strong and weak lines. This alternation was explained by [[Gerhard Herzberg]] and [[Walter Heitler]] as a consequence of [[Spin isomers of hydrogen|nuclear spin isomerism]].

For dihydrogen, each nucleus is a proton of spin 1/2, so that it can be shown using [[quantum mechanics]] and the [[Pauli exclusion principle]] that the odd [[rotational spectroscopy|rotational levels]] are more populated than the even levels.<ref name=Atkins>P.W. Atkins and J. de Paula, "Atkins' Physical Chemistry" (8th edn, W.H. Freeman 2006) p.451</ref> The transitions originating from odd levels are therefore more intense as observed by Rasetti. In dinitrogen, however, Rasetti observed that the lines originating from even levels are more intense.<ref name=Caltech/> This implies by a similar analysis that the [[nuclear spin]] of nitrogen is an integer.<ref name=Atkins/><ref>G.Herzberg, ''Spectra of Diatomic Molecules'' (2nd edition, van Nostrand Reinhold 1950), p.133-140</ref>

This result was difficult to understand at the time, however, because the [[neutron]] had not yet been discovered, and it was thought that the <sup>14</sup>N nucleus contains 14 protons and 7 electrons, or an odd number (21) of particles in total which would correspond to a half-integral spin.<ref name=Caltech/> The Raman spectrum observed by Rasetti provided the first experimental evidence that this proton-electron model of the nucleus is inadequate, because the predicted half-integral spin has as a consequence that transitions from odd rotational levels would be more intense than those from even levels, due to nuclear spin isomerism as shown by Herzberg and Heitler for dihydrogen. After the [[discovery of the neutron]] in 1932, [[Werner Heisenberg]] proposed that the nucleus contains protons and neutrons, and the <sup>14</sup>N nucleus contains 7 protons and 7 neutrons. The even total number (14) of particles corresponds to an integral spin in agreement with Rasetti's spectrum.

He is also credited with the first example of electronic (as opposed to vibronic) Raman scattering in [[nitric oxide]].<ref>{{Cite journal|last=Rasetti|first=F.|date=1930-09-01|title=Über das Ramanspektrum des Stickoxyds|journal=Zeitschrift für Physik|language=de|volume=66|issue=9|pages=646–649|doi=10.1007/BF01421125|bibcode=1930ZPhy...66..646R |s2cid=122114800 |issn=0044-3328}}</ref><ref>{{Citation|last=Clark|first=Robin J. H.|title=Raman, Resonance Raman and Electronic Raman Spectroscopy|date=1989|work=Vibronic Processes in Inorganic Chemistry|editor-last=Flint|editor-first=Colin D.|series=NATO ASI Series|place=Dordrecht|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-009-1029-4_14|isbn=978-94-009-1029-4|page=322}}</ref>

==Awards==
*In 1952 he was awarded the [[Charles Doolittle Walcott Medal]] by the [[United States National Academy of Sciences|National Academy of Sciences]] for his contributions to Cambrian paleontology.<ref name=Walcott>{{cite web|title=Charles Doolittle Walcott Medal |url=http://www.nasonline.org/site/PageServer?pagename=AWARDS_walcott |publisher=National Academy of Sciences |access-date=14 February 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110513235831/http://www.nasonline.org/site/PageServer?pagename=AWARDS_walcott |archive-date=13 May 2011 }}</ref>

==References==
{{Reflist}}

==External links==
*[http://siarchives.si.edu/collections/siris_arc_217397 Franco Dino Rasetti Papers] from the [[Smithsonian Institution Archives]]

{{Authority control}}

{{DEFAULTSORT:Rasetti, Franco}}
[[Category:1901 births]]
[[Category:2001 deaths]]
[[Category:People from Castiglione del Lago]]
[[Category:Italian emigrants to the United States]]
[[Category:20th-century Italian physicists]]
[[Category:Italian nuclear physicists]]
[[Category:20th-century American physicists]]
[[Category:American nuclear physicists]]
[[Category:Academic staff of Université Laval]]
[[Category:Italian men centenarians]]
[[Category:American men centenarians]]
[[Category:Academic staff of the Sapienza University of Rome]]
[[Category:Charles Doolittle Walcott Medal winners]]
[[Category:Italian paleontologists]]
[[Category:Italian exiles]]
[[Category:Spectroscopists]]