 In 1969, a team of scientists at the Stanford Linear Accelerator Center, or SLAC, for short, in conjunction with MIT, performed scattering experiments similar in principle to what Rutherford did to probe the atom 58 years earlier. Rutherford's target was a gold foil. In the SLAC experiment, the target was liquid hydrogen at a very cold temperature to keep the protons as close together as possible. As a source, Rutherford used a small piece of radium. The energy of the naturally occurring alpha particles was 7.7 million electron volts. Here we use electrons and accelerate them to nearly the speed of light. To do that, we construct a glass tube. Then we connect a negative charge to the entrance and a positive charge to the exit. Then the battery is turned off, electrons flow in any direction. But with the battery turned on, the electrons accelerate down the tube along the electric field. To get a really high velocity, we connect more and more of these tubes together. At SLAC, the length of the tube is 3 kilometers. That's 1.86 miles. This creates electrons with 40,000 times the energy than the alpha particles used by Rutherford. This high energy is essential. You cannot probe inside a proton with a large wavelength electron. Remember that the wavelength of an electron in its ground state around a hydrogen nucleus is 200,000 times larger than the diameter of a proton. But if an electron's velocity is large enough, making its de Broglie wavelength small enough, it can. SLAC accelerates electrons to greater than 99.999% of the speed of light, creating a wavelength of the electron that ranges from 2 to 200 times smaller than the proton. The scintillator screen used by Rutherford covered the inside of the apparatus. He had to manually note the flash locations as he viewed them through the swiveling microscope. At SLAC, we partitioned the scintillator screen into small strips. Each strip has an attached photo element that converts the flash into an electrical signal. This enables the sending of electronic location coordinates to a computer. This is called a hodoscope. With this, we can precisely measure the scattering angles as the high energy electrons penetrate the hydrogen atom and approach the proton at the center. SLAC also introduces a strong magnetic field that will cause the scattered electrons to curve as they pass through. As you'll recall from mass spectrometer and bubble chamber analysis techniques, the measured curvature will give us the momentum and velocity of the electrons. To measure this, a second hodoscope is installed at an angle. At the end of the process, the electrons enter a calorimeter. That will measure its energy, much like we just did, to discover the neutrino. Putting all these pieces together gives us the complete linear accelerator detector. It weighs 750 tons.