The Monte Carlo trolley, or FERMIAC, was an

analog computer An analog computer or analogue computer is a type of computation machine (computer) that uses physical phenomena such as Electrical network, electrical, Mechanics, mechanical, or Hydraulics, hydraulic quantities behaving according to the math ...

invented by physicist

Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project ...

to aid in his studies of

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

transport.

Operation

The FERMIAC employed the

Monte Carlo method Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be ...

to model neutron transport in various types of

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics * Nuclear space *Nuclear ...

systems. Given an initial distribution of

s, the goal of the process is to develop numerous "neutron genealogies", or models of the behavior of individual neutrons, including each collision, scattering, and

fission Fission, a splitting of something into two or more parts, may refer to: * Fission (biology), the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Nuclear fissio ...

. When a fission occurs, the number of emerging neutrons is predicted, and the behavior of each of these neutrons is eventually modeled in the same manner as the first. At each stage,

pseudo-random number A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic and repeatable process. Pseudorandom number generators are often used in computer programming, as tradi ...

s are used to make decisions that affect the behavior of each neutron. The FERMIAC used this method to create two-dimensional neutron genealogies on a scale diagram of a nuclear device. A series of drums on the device were set according to the material being crossed and a random choice between fast and slow neutrons. Random numbers also determined the direction of travel and the distance until the next collision. Once the drums were set, the trolley was rolled across the diagram, drawing a path as it went. Any time a change in material was indicated on the diagram, the drum settings were adjusted accordingly before continuing.

History

In the early 1930s, Italian physicist

led a team of young scientists, dubbed the "

Via Panisperna boys Via Panisperna boys () is the name given to a group of young Italian scientists led by Enrico Fermi, who worked at the Royal Physics Institute of the University of Rome La Sapienza and made the famous discovery of slow neutrons in 1934. This lat ...

", in their now-famous experiments in

nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies th ...

. During this time, Fermi developed "statistical sampling" techniques that he effectively employed to predict the results of experiments. Years later, in 1946, Fermi participated in the initial review of results from the

ENIAC ENIAC (; Electronic Numerical Integrator and Computer) was the first Computer programming, programmable, Electronics, electronic, general-purpose digital computer, completed in 1945. Other computers had some of these features, but ENIAC was ...

. Among the others present was Los Alamos mathematician

Stanislaw Ulam Stanislav and variants may refer to: People *Stanislav (given name), a Slavic given name with many spelling variations (Stanislaus, Stanislas, Stanisław, etc.) Places * Stanislav, Kherson Oblast, a coastal village in Ukraine * Stanislaus County, ...

, who was familiar with the use of statistical sampling techniques similar to those previously developed by Fermi. Such techniques had mainly fallen out of use, due to the long, repetitious calculations required. However, given ENIAC's powers of calculation, Ulam saw an opportunity to resurrect these techniques. He discussed his ideas with

John von Neumann John von Neumann ( ; ; December 28, 1903 – February 8, 1957) was a Hungarian and American mathematician, physicist, computer scientist and engineer. Von Neumann had perhaps the widest coverage of any mathematician of his time, in ...

, who eventually used the ENIAC to implement the

(as the statistical sampling techniques came to be called) to solve a variety of neutron transport problems. However, before the ENIAC could be employed for this purpose, it first had to be moved to its permanent home at the

Ballistics Research Laboratory The Ballistic Research Laboratory (BRL) was a research facility under the U.S. Army Ordnance Corps and later the U.S. Army Materiel Command that specialized in ballistics as well as vulnerability and lethality analysis. Situated at Aberdeen Pr ...

. It was during this interruption in ENIAC operation that Fermi came up with the idea for his analog device. He enlisted his colleague L.D.P. King to build the instrument, which was later given the fitting name FERMIAC. The device was used for approximately two years. In 2015, the ''Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi"'' created a replica of the device.A presentation of the device by Coccetti et al.
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Further articles

What is the FERMIAC or Fermi Trolley?
by The Bradbury Science Museum is operated by Los Alamos National Laboratory for education, 2017

References

Early computers Analog computers Enrico Fermi

Operation

History

See also

Further articles

References