From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Oct 03 2007 - 12:14:14 PDT
>From: physnews_at_aip.org
>Reply-To: physnews_at_aip.org
>To: ljk4_at_MSN.COM
>Subject: Physics News Update 841
>Date: Tue, 2 Oct 2007 11:18:56 -0400
>
>PHYSICS NEWS UPDATE
>The American Institute of Physics Bulletin of Physics News
>Number 841 October 2, 2007 by Phillip F. Schewe www.aip.org/pnu
>
>THE VACUUM STRIKES BACK. Modern physics has shown that the vacuum,
>previously thought of as a state of total nothingness, is really a
>seething background of virtual particles springing in and out of
>existence until they can seize enough energy to materialize as
>*real* particles. In high energy collisions at accelerator labs,
>some of the original beam energy can be consumed by ripping
>particle-antiparticle pairs out of the vacuum. Sometimes this
>process is the very reason for doing the experiment, but sometimes
>it is only a detriment. For example, in the Large Hadron Collider
>(LHC), under construction at the CERN lab in Geneva, a major source
>of beam losses (particles exiting from the usable beam) for
>heavy-ion collisions is expected to be a class of event in which the
>counter-moving ions pass each other and don*t interact except to
>spawn a pair of particles---an electron and positron---one of which
>(the positron) goes off to oblivion while the other (the electron)
>latches onto one of the ions. This ion, bearing an extra electric
>charge, will now behave slightly differently as it races through the
>chain of powerful magnets that normally steer the particles around
>the accelerator. Going a certain distance, the modified ion will
>leave its fellows and smash into the beam pipe carrying the beams,
>thus heating up the pipe and surrounding magnet coils.
>Fearing these future beam losses, accelerator physicists have sought
>to observe this effect at an existing machine, the Relativistic
>Heavy Ion Collider (RHIC) at the Brookhaven Lab on Long Island. And
>they found what they were looking for, a tiny splash of energy
>amounting to about
>.0002 watts, or about what a firefly puts out. The RHIC beam for
>these tests consisted of copper ions each carrying 6.3 TeV of energy
>(about 100 GeV per nucleon). According to CERN scientist John
>Jowett (john.jowett_at_cern.ch, 41-22-7676-643) this troublesome class
>of events, referred to as bound-free-pair production (or BFPP, the
>bound referring to the electron and the free to the positron), will
>be much more formidable at LHC than at RHIC. First of all, the pair
>production scales as the atomic number of the nucleus (or the charge
>of the nucleus, denoted by the letter Z) raised to the seventh
>power. The LHC heavy-ion collisions will use beams composed of lead
>ions. The more highly charged nucleus and the larger energies (574
>TeV per lead nucleus) mean the BFPP process should be some 100,000
>times more prominent than in the test at RHIC. This would amount to
>about 25 watts, the equivalent of a reading lamp. That doesn't
>sound like much but, when deposited in the ultra-cold (1.9 K)
>magnets of the LHC, it could bring them to the brink of "quenching"
>out of their superconducting state, interrupting the
>operation of the huge machine. (Bruce et al., Physical Review
>Letters, 5 October 2007;
>journalists can obtain the text from www.aip.org/physnews/select;
>other background material at arxiv.org/abs/0706.3356v2),
>http://cern.ch/AccelConf/e04/PAPERS/MOPLT020.PDF, Vol. I, Chapter 21
>of the LHC Design Report, available at
>http://ab-div.web.cern.ch/ab-div/Publications/LHC-DesignReport.html
>)
>
>GAMMA RAYS FROM THUNDERCLOUDS have been observed by ground-based
>detectors, providing new insights into mechanisms for accelerating
>electrons to high energies, as high as 10 MeV, in the atmosphere.
>Ground observations of thundercloud gammas has been made before as
>part of monitoring regular nuclear plant operations. The new
>measurements, ho
>wever, represent the first time that such gamma
>studies were made with detailed scientific objectives in mind,
>including determinations of particle species, arrival direction, and
>energy spectrum. On the night of 6 January 2007 two powerful
>low-pressure air masses collided over the Sea of Japan. A nearby
>array of gamma detectors provided information on the energy and the
>timing of the gammas, which are the highest-category of
>electromagnetic radiation. The array is operated by the University
>of Tokyo and the Cosmic Radiation Laboratory of RIKEN in Japan. The
>gamma production, the researchers believe, works like this: an
>energetic seed electron, perhaps liberated from an atom by an
>intruding cosmic ray, ionizes many air molecules, which in turn are
>accelerated by the high electric fields present in the
>thunderclouds. This flock of fast electrons can then emit gamma
>radiation (bremsstrahlung, or *braking radiation*) as they are
>slowed by surrounding air. The gamma production actually occurs
>before the eventual lightning strike, says Teruaki Enoto of the
>University of Tokyo (enoto_at_amalthea.phys.s.u-tokyo.ac.jp,
>81-3-5841-4173), and the reason for this is not entirely known.
>Previous thundercloud-related gammas were studied by satellite and
>only measured very brief bursts, with durations of msec. By
>contrast, the Tokyo-RIKEN work indicates bursting behavior that
>could last for minutes, testifying to the quasi-static nature of the
>acceleration mechanism at work in the clouds. The electric fields
>in the clouds might be as high as 10 million volts. (Tsuchiya et
>al., Physical Review Letters, upcoming article; text can be obtained
>from www.aip.org/physnews/select )
>
>***********
>PHYSICS NEWS UPDATE is a digest of physics news items arising
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