IMB, the Irvine-Michigan-Brookhaven detector, was a nucleon

Nucleon

In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...

 decay experiment and neutrino

Neutrino

A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...

 observatory

Observatory

An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed...

 located in a Morton Salt

Morton Salt

Morton Salt is a United States company producing salt for food, water conditioning, industrial, agricultural, and road/highway use. Based in Chicago, the business is North America's leading producer and marketer of salt. It is a subsidiary of the German company K+S.-History:The company began in...

 company's Fairport

Fairport Harbor, Ohio

Fairport Harbor is a village in Lake County, Ohio, United States, along Lake Erie at the mouth of the Grand River. The population was 3,180 at the 2000 census....

 mine on the shore of Lake Erie

Lake Erie

Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It was a joint venture of the University of California, Irvine

University of California, Irvine

The University of California, Irvine , founded in 1965, is one of the ten campuses of the University of California, located in Irvine, California, USA...

, the University of Michigan

University of Michigan

The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...

, and the Brookhaven National Laboratory

Brookhaven National Laboratory

Brookhaven National Laboratory , is a United States national laboratory located in Upton, New York on Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base...

. Like several other particle detectors (see Kamiokande II), it was built primarily with the goal of observing proton decay

Proton decay

In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...

, but it achieved greater fame through neutrino observation, particularly those from Supernova 1987a.

Design

IMB consisted of a roughly cubical

Cube

In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. The cube can also be called a regular hexahedron and is one of the five Platonic solids. It is a special kind of square prism, of rectangular parallelepiped and...

 tank about 17 × 17.5 × 23 meters, filled with 2.5 million gallons of ultrapure water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 which was surrounded by 2,048 photomultiplier

Photomultiplier

Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...

 tubes. IMB detected fast moving particles such as those produced by proton decay or neutrino interactions by picking up the Cerenkov radiation generated when such a particle moves faster than the speed of light in water. Since directional information was available from the phototubes, it was able to estimate the initial direction of neutrinos.

History

IMB was built in the early 1980s and announced its first results in 1982. In 1987, it gained fame for detecting 8 of the roughly 10⁵⁸ neutrinos emitted by Supernova 1987a. It collected data until 1991.

This volume of water contains on the order of 10³¹ proton

Proton

The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s. In one year of observation no proton decay event was recorded. This put the half-life of a proton at or above 10³¹ years.