- 3491 - SLAC - linear accelerator. Stanford Linear Accelerator’s X-Ray Camera can take small, fast pictures. What do you do if you want to take a picture of something very small and very fast. Say you wanted to run your car on hydrogen gas and you need to learn how a water molecule held on to the hydrogen atoms?
--------------------- 3491 - SLAC - linear accelerator
- Molecules split and combine in 10^-15 seconds. 10^-15 seconds is called a femtosecond. The atoms of hydrogen attached to the atom of oxygen is a molecule
0.1 nanometers in size.
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- To see something the wavelengths of light must be much smaller than what you want to see. Smaller wavelengths will be reflected and you can see the reflection. Larger wavelengths just fly on by without reflecting anything.
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- Visible light waves are 400 to 700 nanometers wavelength, much too large to see at the atomic scale. Your camera needs to work with X-rays that have a wavelength of
0.1 nanometers. And, the shutter speed needed to stop the action must be faster than
1 femtosecond.
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- There is just such a camera that turned on in Palo Alto, California, the Stanford Linear Accelerator. Before reviewing the camera lets get familiar with the scaling factor at what it is taking pictures of.
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- An “ol expression” for something very small is that “it could dance on the head of a pin“. A pin head is extremely large at these scales:
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---------------- Pin Head ------------ 5,000,000 nanometers
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--------------- A Flea --------------- 1,000,000
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---------------- Red Blood Cell ----- 50,000
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--------------- DVD tracks ---------- 1,000
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--------------- Virus ------------------- 800
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-----------------Red Light ------------------ 700
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-----------------Blue Light ----------------- 400
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---------------- DNA Helix ----------------- 10
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---------------- Water Molecule ------------ 0.1 nanometers
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- You can see that a microscope using visible light can barely see a virus. Its wavelength is over a 1,000 times to big to see a Water Molecule. We need much shorter wavelengths in order to see at the scale of atoms, 0.1 nanometers. X-Rays have those wavelengths of 0.1 nanometers.
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- Things happen fast in chemical reactions so we need not only short wavelengths we need a very fast strobe light in order to stop and study the motion of atoms and molecules. Nanoseconds are not fast enough ( 10^-9 seconds).
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--------------- Magnetic Recording time per Bit --------------- 2 nanoseconds.
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-------------- Hydrogen transfer time in molecules ------------ 1 nanosecond.
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------------- Computer Time per Bit, 1 Ghz ------------------- 1 nanosecond.
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------------- Light travels 1 millimeter distance ------------- 3*10^-6 nanoseconds.
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------------- Light travels 1 millimeter distance ------------- 3 femtosecond.
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------------- Shortest laser pulse ----------------------------- 1 femtosecond.
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- Our camera needs to have a laser pulse of 1 femtosecond of X-ray light in order to “see” at the atomic level.
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- The Stanford Linear Accelerator (SLAC) in Palo Alto, California, is a cathode ray tube,( CRT), that is 2 miles long. It sends an electron beam down the tube until electrons reach 99% the speed of light. Then, the beam enters a series of north, south magnets that bend the beam in one direction then the other.
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- When a charged particle accelerates, a change in direction, or bending, is “acceleration“, because velocity has both magnitude and direction, the electron emits electromagnetic radiation when it accelerates. Accelerating charged particles is how light is generated. In this case the electromagnetic radiation emitted from the electron is
“ X-Rays“.
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- The wavelength of the X-Rays is 0.1 nanometers. ( Blue light is 400 nanometers). Light, and X-Rays travel at 1 millimeter in 3 femtosecond ( 0.001 meters in 3*10^-15 seconds). The electrons are made into a strobe light by bunching them up in
10 femtosecond bunches.
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- The strobe light of electrons and X-Rays has a repetition rate of 120 cycles per second. With the X-Ray strobe light capability SLAC’s physicists can “ see” chemical reactions in which molecules join or split in a femtosecond, a quadrillionth of a second.
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- The effective shutter speed is 100 femtosecond. the energy in the X-Ray flash is millions of times brighter than medical X-Rays.
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- This capability was turned on at SLAC. You can see the results of many of their experiments on their home page:
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---------- SLAC - Stanford Linear Accelerator
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----------- SIMES - Stanford Institution of Materials and Engineering
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------------ LCLS - Linear Coherent Light Source
---------------KIPAC - Kavlin Institute of Particle Astrophysics and Cosmology.
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- The 2-mile-long particle accelerator is the lab’s backbone. Once the scene of major discoveries in particle physics, today it generates the world’s brightest X-rays for our revolutionary X-ray laser, the “Linac Coherent Light Source” (LCLS).
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- Practical benefits of research at SLAC. In chemistry, “molecular movies” made with our X-ray laser are capturing all the tiny steps of chemical reactions for the first. This new understanding will help improve reactions that give us fuels, fertilizers and a host of other products.
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- In biology, X-rays reveal how proteins, one of the key molecules of life, function in our bodies and in nature. This research has contributed to the development of medications for melanoma, flu and HIV and is aiding the fight against Ebola, high blood pressure and other ills.
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- SLAC studies of exotic materials with quirky traits could have a profound impact on society, although it may be far in the future. Scientists use SLAC X-ray beams for experiments to improve materials for computer chips, jet planes, refinery operations and “smart windows” that automatically adjust the amount of light coming in..
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- Many threads of SLAC research come together in the quest for clean, sustainable energy sources. They study how plants make energy from sunlight with an eye to doing the same, and customize chemical reactions for generating clean fuels. Specialized X-ray equipment allows scientists to watch batteries, solar cells and fuel cells in operation, a crucial step in improving how they work.
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- SLAC started more than 50 years ago as a place to discover fundamental particles and forces. Today, our scientists still explore the universe at the largest and smallest scales. At the tiniest scale, we help search for new particles and forces at the “Large Hadron Collider” in Europe, where the Higgs boson was recently discovered.
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- At the most sweeping scale, they are building the world’s biggest digital camera for the widest, deepest survey of the night sky ever undertaken. Their longstanding expertise in building particle detectors is being put to use in experiments that search for dark matter and dark energy, and probe the secrets of ghostly neutrinos. The more we learn the more we learn we don’t know.
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March 4, 2022 SLAC - linear accelerator 1064 3491
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--------------------- --- Monday, March 7, 2022 ---------------------------
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