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In this issue:
No More Bricks in the Wall
Your Money or Your Laundry
Steve Kahn Announces PPA All-Hands Meeting
symmetry Explains it in 60 Seconds: Particle Event

SLAC Today

Friday - August 10, 2007

No More Bricks in the Wall

More than 500 tons of shielding are being removed from End Station B. (Click image for larger version.)

To make room for research and to eliminate a seismic hazard, crews are removing the 30-foot-tall wall that separates End Station B from the B-line Target Room. In all, they are taking out more than 500 tons of shielding material, including a 12 x 30-foot beam dump, an old beam target and other equipment.

For safety, caution tape has prevented people and experiments in End Station B from coming within 15 feet of the unbraced, unbolted wall. Approximately 1,600 square feet of floor space will be freed up by the removal project.

As soon as the space is cleared, Building Manager and International Linear Collider (ILC) engineering physicist Richard Swent will begin installing prototype equipment for the ILC project. The test stands will include two modulators and two klystrons, including the Marx modulator designed and built at SLAC, and a unique "sheet-beam" klystron to be built in the Klystron and Microwave Department. Read more…

Your Money or Your Laundry

(Photo - Money bags)
Sacks of cash at SLAC? Hardly. This odd combination of materials actually serves an important safety role at SLAC. (Click image for larger version.)

These money bags may appear to be packed with greenbacks, but in reality they contain seven pounds of borax, a common compound found in household detergents. Surprisingly, this is a case neither of money nor of laundering—these borax-filled U.S. Mint bags are used as radiation shielding within shafts referred to as penetrations that connect the klystron gallery to the linac tunnel 30 feet below.

Says Roger Erickson, head of SLAC's Accelerator Operations Department: "While preparing for experiment E-158, we were advised that neutrons coming up the waveguide penetrations could be a potential but highly unlikely problem, because of the unusually high beam power we were planning to run. To allay all fears, we filled the penetrations to a depth of at least 16 inches with borax sealed in polyethylene bags, seven pounds to a bag. This size was chosen for convenience; they are easy to handle and can be packed in tight places around pipes, waveguides, and so on.

"I was concerned that the plastic bags might be easily damaged and spill their contents, so I found a company in San Francisco that sold all sorts of strange surplus materials. They had a load of used canvas money bags, so we bought them all and loaded one plastic borax bag into each canvas bag and packed them into the penetrations in the Klystron Gallery. All together there were 8,000 bags for a total of 28 tons of borax, stuffed into about 480 penetrations."

The new bag pictured is intended for an upcoming round of shielding to be put into position during the fall shutdown as the second of two bunch compressors is installed for the Linac Coherent Light Source.

Steve Kahn Announces
PPA All Hands Meeting

Steve Kahn would like to invite everyone in the Particle Physics and Astrophysics Directorate to an All Hands meeting in the Kavli Auditorium on Tuesday, August 14. There, he will discuss the new directions and continued plans for particle physics, particle astrophysics, and current and future accelerator research programs.

Due to limited seating in the Kavli Auditorium, what follows is a schedule to help minimize the possibility of leaving anyone without a seat:

• 8:00 - 9:00 a.m.
Last Names starting A through G

• 10:30 - 11:30 a.m.
Last Names starting H through O

• 3:00 - 4:00 p.m.
Last Names starting P through Z

Supervisors should make arrangements for staff to attend these sessions unless operational necessity prevents their attendance.

symmetry Explains it in 60 Seconds:
Particle Event


A particle event is a particle collision or interaction that is observed by some type of particle detector. Collected by the hundreds, thousands, or millions, particle events are the raw material that scientists use to explore the subatomic world.

To capture these precious events, particle physicists build "cameras" that record signals such as the tracks of particles emerging from a collision. The interesting features of particle events often occur on submillimeter scales, and the cameras act as extremely powerful microscopes.
Read more in symmetry...

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