Emilio Segrè Visual Archives

More than 30,000 photos of scientists and their work

Attention ESVA patrons:

The Emilio Segrè Visual Archives’ site is moving soon and adopting an open access approach to digital image sharing. Once we have transitioned to the new site in 2021, we will no longer charge for our high-resolution digital images or usage fees (note that we do not hold copyright to all the images in our collections and you will still need to obtain permission for those which we do not own).

If you are working on a long-term project, we advise you to wait until the migration is complete so that you may obtain our copies for free. If you cannot wait, email us at nbl [at] aip.org and we will do what we can to assist you. We will not be offering refunds for past purchases.

For more information, please visit our FAQ page on the Ex Libris Universum blog. 

Lawrence Berkeley National Laboratory H16

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Lawrence Berkeley National Laboratory H16

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We charge a usage fee per photo if the photo is published, reproduced in a product or publicly exhibited. This is not a license in the legal sense. As a non-profit institution, we do not make any money providing these photographs. It is only by assessing usage fees that we are able to cover the cost of providing publication quality copies of our photos, preserving the photograph collection according to archival standards, and providing access to the collection by maintaining an online image database. The copyright holder may charge a fee in addition to our service fee.

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Image title: 
Antiproton entering the 72-inch hydrogen bubble chamber at the University of California's Lawrence Radiation Laboratory
Credit line: 
Lawrence Berkeley National Laboratory, courtesy of AIP Emilio Segrè Visual Archives

Antiproton entering the 72-inch hydrogen bubble chamber at the University of California's Lawrence Radiation Laboratory, Berkeley (currently known as the Lawrence Berkeley National Laboratory). The four-pronged 'star' is formed when an antiproton, generated by the Bevatron, comes close to a proton, the nucleus of ordinary hydrogen atom, in the chamber. The process is called annihilation, and is visualized by the profusion of tracks forming the star. The tracks forming the 'star' are made by pions, particles of lower mass into which the primary particle disintegrates. Not all of the particles are seen -- the neutral ones (those with no electrical charge) make no tracks. It had been theoretically postulated that the Omega meson is composed of three pi mesons (pions), and is neutrally charged.

Elaborate analysis of the star showed that an Omega meson has been born in the annihilation. The complex sequence is as follows: the antiproton breaks up into two pions (the two tracks in the middle of the four-pronged star) and an Omega meson; the Omega exists only briefly, then breaks up into two pions (the tracks at far left and far right in the four-pronged star) and a neutral pion which makes no track.

The discovery was made by means of three-part high energy particle research system at Berkeley: the 6.2 billion electron volt (Bev-"atom-smashing" Bevatron; the giant 72-inch liquid hydrogen bubble chamber in which particle tracks are photographed; and an extensive analytical complex which includes specially developed, semi-automatic measuring machines, and an IBM 709 computer. The fundamental research program in the Laboratory in financed by the Atomic Energy Commission.

Original format: 
2 photographic prints (black and white; 10 x 8 inches)
Lawrence Berkeley National Laboratory