Concrete Products

FEB 2014

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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www.concreteproducts.com February 2014 • 45 FEATURE BRANSCOME CONCRETE A BILLION ELECTRONS HERE AND THERE The Continuous Electron Beam Acceler- ator Facility is a 7/8-mile loop of elec- tron beam conduits (bottom); dubbed cryomodules, they accelerate electron travel to nearly the speed of light. Cer- tain beams are directed to Experimen- tal Hall C, home to the charter High Momentum Spectrometer and new Su- per High Momentum Spectrometer, a side view of which is shown here along with the shield house's panel-clad ele- vation. Built of high performance con- crete walls, plus lead, aluminum and boron carbide composite layers, the shield house contains a particle colli- sion detector (below) and other spe- cialized equipment. CEBAF, SHMS, DETECTOR SCHEMATICS: Jefferson Lab Branscome Concrete supplied material for Hall C's HMS shield house in the mid- 1990s. Through a monolithic concrete wall, cast with a boron carbide and glass aggregate-dosed mixes, it contains radiation generated by one of the facility's principal procedures: Smashing of electron beams into hydrogen, carbon or gold targets; collecting and recording information on scattered particles; and, ana- lyzing particle speed, direction and energy with an eye toward improved under- standing of an atom's nucleus. The new shield house is necessarily bigger and better; its construction marks the midpoint of the JLab upgrade, which between 2009 (construction start) and 2017 will see a doubling of CEBAF energy, from 6 billion electron volts (6 GeV). The SHMS will afford greater measurement of particle behavior attending the 12 GeV beams, while its new shield house separates particle detection from computer-based data collection equipment. The elevated voltage for the SHMS in turn requires higher performance shield house concrete. Armed with 15 years of particle behavior data in HMS experiments, Hall C and Catholic University of America physicists turned to Monte Carlo statistical sampling methods to determine likely SHMS radiation parameters dictating shield house wall and roof system requirements. In contrast to atom splitting associated with nuclear energy, the CEBAF sends electrons into a target nucleus to scatter individual protons and neu- trons, plus smaller, paired particles called quarks. The accelerator works like a microscope, JLab notes, but uses electrons to reveal details too small for light to resolve. Lab offcials put their target matter in perspective: A piece of aluminum foil is 250,000 atoms thick, quarks at least 1 millionth their size. Powerful electron microscopes enable viewing of atoms; smaller particles are not seen but their behavior is observed in the type of detection and collec- tion equipment used in JLab Hall C. A CEBAF beam of electrons into a target nucleus nets vast amounts of data, from which scientists look for patterns. The accelerator has to channel billions of electrons at enormous speed in order to hit one nucleus in the target. CEBAF comprises an elongated loop of electron beam conduits called cryo- modules. They are cooled to within a few degrees of absolute zero (approaching -460°F), and accelerate the electrons from a standing start to nearly the speed of light. Electrons are injected into a strand the diameter of human hair, their travel and paths augmented by massive magnets. After clearing fve miles in 30 millionths of a second, electron beams are routed to detector assemblies in Experimental Halls C, B, A or D. Starting in 2016, the upgraded electron beam and Hall C equipment will carry JLab into a new phase of discovery, as scientists seek greater understand- ing of nucleus and physics' Standard Model, describing fundamental particles and their interactions. JLab offcials credit the electron with dominating 20 th century technology and scientifc revolutions. The quarks they can observe through lab upgrades have the potential to be the 21 st century's electrons. Concrete Products February 2014.indd 45 1/28/2014 1:45:17 PM

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