THE PROMISE OF TUNNELING BY ELECTRON BEAM

TUNNELING THROUGH ROCK IS A SLOW PROCEDURE. FOR EACH ADVANCE, HOLES MUST BE DRILLED AND EXPLOSIVE CHARGES SET. THEN PEOPLE ARE CLEARED FROM THE AREA AND THE CHARGES ARE DETONATED. THE DEBRIS IS REMOVED AND THE CYCLE STARTS AGAIN. EXPERIMENTS IN PROGRESS AT THE LAWRENCE BERKLEY LABORATORY IN CALIFORNIA SHOW PROMISE OF SPEEDING UP ROCK TUNNELING BY USING INTENSE BEAMS OF ELECTRONS TO CUT THROUGH THE ROCK. THE WORK IS SUPPORTED BY THE NATIONAL SCIENCE FOUNDATION AS PART OF ITS RESEARCH APPLIED TO NATIONAL NEEDS PROGRAM (RANN). THE ELECTRONS COME FROM ACCELERATORS THAT ARE QUITE LOW-ENERGY BY TODAY'S STANDARDS -- ABOUT ONE MILLION ELECTRON-VOLTS (ONE MEV). THESE MACHINES PRODUCE BURSTS OF ELECTRONS MANY TIMES MORE INTENSE THAN THOSE USED IN PARTICLE PHYSICS EXPERIMENTS. THE BURSTS, WHICH LAST ONLY 50 NANOSECONDS (ONE TWENTY- MILLIONTH OF A SECOND), DELIVER INTENSE PULSES OF HEAT TO THE ROCK. THIS SETS UP A THERMAL EXPANSION WAVE IN THE ROCK. A SINGLE BURST DOES NOT FLAKE OFF VERY MUCH, ONLY A FEW CENTIMETERS, BUT REPETITION RATES OF HUNDREDS OF TIMES A SECOND ARE POSSIBLE. FOR A WORKING MODEL AN APPARATUS IS ENVISIONED ABOUT THE SIZE OF THE MOLE MACHINES THAT NOW DO EARTH TUNNELING. THIS WOULD SCAN A FOUR- OR FIVE- MEV BEAM ACROSS THE ROCK FACE. AT SEVERAL HUNDRED BURSTS A SECOND IT COULD CHIP OFF A SIZABLE QUANTITY OF ROCK IN A TIME THAT IS SHORT BY HUMAN STANDARDS.

Media Info

  • Features: Photos;
  • Pagination: p. 166
  • Serial:
    • Science News
    • Volume: 103
    • Issue Number: 11
    • Publisher: Science Services, Incorporated
    • ISSN: 0036-8423

Subject/Index Terms

Filing Info

  • Accession Number: 00236667
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 28 1973 12:00AM