Editing Frederick Reines (section)

== Discovery of the neutrino and the inner workings of stars ==
[[File:Clyde Cowan and Frederick Reines.jpg|alt=Photo of Clyde Cowan and Frederick Reines|thumb|Reines and [[Clyde Cowan]]]]
The [[neutrino]] is a [[subatomic particle]] first proposed by [[Wolfgang Pauli]] on December 4, 1930. The particle was required to resolve the problem of missing energy in observations of [[beta decay]], when a [[neutron]] decays into a [[proton]] and an [[electron]]. The new hypothetical particle was required to preserve the fundamental law of [[conservation of energy]]. [[Enrico Fermi]] renamed it the [[neutrino]], Italian for "little neutral one",{{sfn|Close|2012|pp=15–18}} and in 1934, proposed his [[Fermi's interaction|theory of beta decay]] by which the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino:<ref>{{cite journal |last=Fermi |first=E. |title=Fermi's Theory of Beta Decay |others=Wilson, Fred L. (trans.) |journal=[[American Journal of Physics]] |year=1968 |url=http://microboone-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=953;filename=FermiBetaDecay1934.pdf;version=1 |access-date=January 20, 2013 |doi=10.1119/1.1974382 |volume=36|issue=12 |bibcode = 1968AmJPh..36.1150W |pages=1150–1160}}</ref>{{sfn|Close|2012|pp=22–25}}
:{{SubatomicParticle|Neutron0}} → {{SubatomicParticle|Proton+}} + {{SubatomicParticle|Electron-}} + {{SubatomicParticle|Electron antineutrino}}

The neutrino accounted for the missing energy, but Fermi's theory described a particle with little mass and no electric charge that appeared to be impossible to observe directly. In a 1934 paper, [[Rudolf Peierls]] and [[Hans Bethe]] calculated that neutrinos could easily pass through the Earth, and concluded "there is no practically possible way of observing the neutrino."<ref>{{cite journal |title=The Neutrino |journal=[[Nature (journal)|Nature]] |issn=0028-0836 |issue=3362 |pages=532 |date=April 7, 1934 |doi=10.1038/133532a0 |bibcode = 1934Natur.133..532B |volume=133|last1=Bethe |first1=H. |last2=Peierls |first2=R. |s2cid=4001646 |doi-access=free }}</ref>

[[File:Poltergeist Team 1953.jpg|thumb|Frederick Reines (far right) with Clyde Cowan (far left) and other members of Project Poltergeist]]

In 1951, Reines and his colleague [[Clyde Cowan]] decided to see if they could detect neutrinos and so prove their existence. At the conclusion of the Greenhouse test series, Reines had received permission from the head of T Division, [[J. Carson Mark]], for a leave in residence to study fundamental physics. "So why did we want to detect the free neutrino?" he later explained, "Because everybody said, you couldn't do it."<ref name="Nobel lecture">{{cite web |url=https://www.nobelprize.org/uploads/2018/06/reines-lecture.pdf |title=The Neutrino: From Poltergeist to Particle |quote=Nobel Prize lecture |first=Frederick |last=Reines |date=December 8, 1995 |publisher=Nobel Foundation |access-date= 12 August 2024}}</ref>

According to Fermi's theory, there was also a corresponding reverse reaction, in which a neutrino combines with a proton to create a neutron and a [[positron]]:<ref name="Nobel lecture"/>
:{{SubatomicParticle|Electron antineutrino}} + {{SubatomicParticle|Proton+}} → {{SubatomicParticle|Neutron0}} + {{SubatomicParticle|Electron+}}

The positron would soon be annihilated by an electron and produce two 0.51 MeV [[gamma rays]], while the neutron would be captured by a proton and release a 2.2 MeV gamma ray. This would produce a distinctive signature that could be detected. They then realised that by adding [[cadmium]] salt to their [[Liquid scintillation counting|liquid scintillator]] they would enhance the neutron capture reaction, resulting in a burst of gamma rays with a total energy of 9 MeV.<ref name="PhyToday"/> For a neutrino source, they proposed using an atomic bomb. Permission for this was obtained from the laboratory director, [[Norris Bradbury]]. The plan was to detonate a "20-kiloton nuclear bomb, comparable to that dropped on Hiroshima, Japan". The detector was proposed to be dropped at the moment of explosion into a hole 40 meters from the detonation site "to catch the flux at its maximum"; it was named "El Monstro".<ref name="Abbott">{{cite journal |last1=Abbott |first1=Alison |title=The singing neutrino Nobel laureate who nearly bombed Nevada |journal=Nature |date=17 May 2021 |volume=593 |issue=7859 |pages=334–335 |doi=10.1038/d41586-021-01318-y |language=en|doi-access=free |bibcode=2021Natur.593..334A }}</ref> Work began on digging a shaft for the experiment when [[J. M. B. Kellogg]] convinced them to use a [[nuclear reactor]] instead of a bomb. Although a less intense source of neutrinos, it had the advantage in allowing for multiple experiments to be carried out over a long period of time.<ref name="NAS"/><ref name="PhyToday"/><ref name="Abbott"/>

In 1953, they made their first attempts using one of the large reactors at the [[Hanford nuclear site]] in what is now known as the [[Cowan–Reines neutrino experiment]]; they named the experiment "Project Poltergeist".<ref name="Abbott"/> Their detector included {{convert|300|L}} of scintillating fluid and 90 [[photomultiplier]] tubes, but the effort was frustrated by background noise from cosmic rays. With encouragement from [[John A. Wheeler]], they tried again in 1955, this time using one of the newer, larger 700 MW reactors at the [[Savannah River Site]] that emitted a high neutrino flux of 1.2 x 10<sup>12</sup> / cm<sup>2</sup> sec. They also had a convenient, well-shielded location {{convert|11|m}} from the reactor and {{convert|12|m}} underground.<ref name="Nobel lecture"/> On June 14, 1956, they were able to send Pauli a telegram announcing that the neutrino had been found.{{sfn|Close|2012|pp=37–41}} When Bethe was informed that he had been proven wrong, he said, "Well, you shouldn't believe everything you read in the papers."<ref name="Nobel lecture"/>

[[File:Supernova SN1987A in the Large Magellanic Cloud - GPN-2000-000948.jpg|left|thumb|[[SN 1987A|Supernova SN1987A]] (the bright object in the center), as seen through the [[Hubble Space Telescope]]]]
From then on Reines dedicated the major part of his career to the study of the neutrino's properties and interactions, which work would influence study of the neutrino for future researchers to come.{{sfn|Close|2012|p=42}} Cowan left Los Alamos in 1957 to teach at [[George Washington University]], ending their collaboration.<ref name="NAS"/> On the basis of his work in first detecting the [[neutrino]], Reines became the head of the physics department of [[Case Western Reserve University]] from 1959 to 1966. At Case, he led a group that was the first to detect neutrinos created in the atmosphere by [[cosmic ray]]s.<ref name="PhyToday">{{cite journal |first=Gloria B. |last=Lubkin |title=Nobel Prize in Physics goes to Frederick Reines for the Detection of the Neutrino |journal=[[Physics Today]] |issn=0031-9228 |volume=48 |issue=12 |pages=17–19 | doi = 10.1063/1.2808286 |url=http://www.aip.org/pt/vol-54/iss-2/pdf/vol48no12p17-19.pdf |archive-url=https://web.archive.org/web/20081217091336/http://www.aip.org/pt/vol-54/iss-2/pdf/vol48no12p17-19.pdf |archive-date=December 17, 2008 |bibcode=1995PhT....48l..17L |year=1995 }}</ref> Reines had a booming voice, and had been a singer since childhood. During this time, besides performing his duties as a research supervisor and chairman of the physics department, Reines sang in the Cleveland Orchestra Chorus under the direction of [[Robert Shaw (conductor)|Robert Shaw]] in performances with [[George Szell]] and the [[Cleveland Orchestra]].<ref name="mem"/>

In the early 1960s, Reines built a detector in the [[East Rand gold mine]] near [[Johannesburg]], South Africa. The site was chosen because of its depth, 3.5&nbsp;km;<ref name="Abbott"/> on February 23, 1965, the new detector captured its first atmospheric neutrinos. Reines brought his friends, an engineer August "Gus" Hruschka from the US,<ref name=Cole>{{cite book |last1=Cole |first1=Leonard A |title=Chasing the Ghost: Nobelist Fred Reines and the Neutrino |date=March 2021 |isbn=978-981-12-3105-6 |url=https://www.worldscientific.com/doi/pdf/10.1142/9789811231063_0001 |language=en |pages=3–13|doi=10.1142/9789811231063_0001 }}</ref> they worked together with South African physicist [[Friedel Sellschop]] of the [[University of Witwatersrand]].<ref name="NAS"/> Equipment was made in the [[Case Institute]], and 20 tonnes of scintillation fluid in 50 containment tanks were transported from the US. The decision to work in an [[apartheid]] racist country was challenged by many colleagues of Reines, he himself said that "science transcended politics".<ref name="Abbott"/> The laboratory team in the mine was led by Reines' graduate students, first by William Kropp, and then by Henry Sobel.<ref name=Cole/> Experiment ran from 1963 and was closed in 1971, and captured 167 neutrino events.<ref name="NAS"/>

In 1966, Reines took most of his neutrino research team with him when he left for the new [[University of California, Irvine]] (UCI), becoming its first dean of physical sciences. At UCI, Reines extended the research interests of some of his graduate students into the development of [[Nuclear medicine#Diagnostic medical imaging|medical radiation detectors]], such as for measuring total radiation delivered to the whole human body in [[radiation therapy]].<ref name="mem"/>

Reines had prepared for the possibility of measuring the distant events of a supernova explosion. Supernova explosions are rare, but Reines thought he might be lucky enough to see one in his lifetime, and be able to catch the neutrinos streaming from it in his specially-designed detectors. During his wait for a supernova to explode, he put signs on some of his large neutrino detectors, calling them "Supernova Early Warning Systems".<ref name="mem">{{cite web |title=In Memoriam, 1998. Frederick Reines, Physics; Radiological Sciences: Irvine |publisher=University of California |url=http://content.cdlib.org/xtf/view?docId=hb1p30039g&chunk.id=div00047&brand=calisphere&doc.view=entire_text |access-date=February 19, 2015}}</ref> In 1987, neutrinos emitted from [[SN 1987A|Supernova SN1987A]] were detected by the [[Irvine–Michigan–Brookhaven (detector)|Irvine–Michigan–Brookhaven]] (IMB) Collaboration, which used an 8,000 ton [[Cherenkov detector]] located in a salt mine near [[Cleveland]].<ref name="neutrino astronomy"/> Normally, the detectors recorded only a few background events each day. The supernova registered 19 events in just ten seconds.<ref name="Nobel lecture"/> This discovery is regarded as inaugurating the field of [[neutrino astronomy]].<ref name="neutrino astronomy"/>

In 1995 Reines was honored, along with [[Martin L. Perl]], with the [[Nobel Prize in Physics]] for his work with Cowan in first detecting the neutrino. Unfortunately, Cowan had died in 1974 and the Nobel Prize is not awarded posthumously.{{sfn|Close|2012|p=42}} Reines also received many other awards, including the [[J. Robert Oppenheimer Memorial Prize]] in 1981,<ref>{{cite journal |title=Frederick Reines wins Oppenheimer Prize |journal=Physics Today |date=May 1981 |page=94 |doi=10.1063/1.2914589 |bibcode = 1981PhT....34R..94. |volume=34|issue=5 }}</ref> the [[National Medal of Science]] in 1985, the [[Bruno Rossi Prize]] in 1989, the [[Michelson–Morley Award]] in 1990, the [[Panofsky Prize]] in 1992, and the [[Franklin Medal]] in 1992. He was elected a member of the [[National Academy of Sciences]] in 1980 and a foreign member of the [[Russian Academy of Sciences]] in 1994.<ref name="NAS"/> He remained dean of physical sciences at UCI until 1974, and became a [[professor emeritus]] in 1988, but he continued teaching until 1991, and remained on UCI's faculty until his death.<ref>{{cite web |title=The Passing of Frederick Reines, Physics Nobel Laureate in 1995 |publisher=[[University of California, Irvine]] |url=http://www.ps.uci.edu/physics/news5/cicerone5.html |archive-date=November 2, 2013 |archive-url=https://web.archive.org/web/20131102150616/http://www.ps.uci.edu/physics/news5/cicerone5.html }}</ref>