People and Particles (1967)

The sparks in this chamber were caused by cosmic rays that penetrate our atmosphere all the time. After some further tests, this spark chamber will become the heart of an experiment to be carried out in this physics laboratory, called the Cambridge Electron Accelerator, jointly operated by Harvard University and the Massachusetts Institute of Technology. Inside the building, underground, is a synchrotron, essentially a circular tube 240 ft across, in which a beam of electrons can be accelerated to an energy of 6 billion electron volts. In the large experimental hall, physicists use the electron beam to produce and study elementary particles. Just because the particles are so small, the equipment needed is large and complex. Look at that. We're going to follow one of the many experiments going on here. It's an experiment to study the interaction between ordinary negative electrons and positive electrons or positrons. How large is the force between them? This is one of the most basic questions for physicists today. These photos are of spark trails caused by electrons and positrons moving through the spark chamber. The angle between the tracks will be the key evidence in this experiment. Professor Carl Strauch heads this research group from Harvard. Carl has pioneered in developing spark chambers. Dave Grossman from New York City is one of several graduate students in the team who will use the results of the experiment as part of their work for PhD degrees. Mervyn Wong is a student from New Zealand. In the group with Carl, Dave, and Mervyn, there are over a dozen others. Some with lots of experience, some just beginning their first big research project. At the start of the experiment, all they had were ideas and an empty part of the floor space in the experimental hall. This was also the starting point for our film. We photographed everything just as it was happening over a period of 2 years. No script, no rehearsals, just to see what it's like when people work together in a physics lab. Space in the experimental hall is hard to get. So, before the equipment could be built and moved into the experimental area, the layout and the functioning of the parts had to be carefully worked out. My God. Cardboard cutouts help them plan the placement of apparatus. When the real equipment is built, it will take a crane with a capacity of 40 tons to put it into place. Much of the gear has never been built before. And as the ideas come in and change, Mike Olmstead, the project engineer, may redesign the part several times before it goes to the shop. Machinists, carpenters, electricians, they're all part of the experimental team. Machining has started on the spark chamber in which the particle tracks will be observed. Mike is cutting marks on the transparent wall of the spark chamber. These marks are like the crosshairs in a telescopic sight. They'll show up on the photographs of the tracks. And their placement must be accurate to a thousandth of an inch. Dave's spark chamber, the biggest one of its kind built so far, is really a simple device, little more than a large box. Dave adds the finishing touches. Later, the chamber will be sealed and filled with neon gas. We can't photograph the particles themselves, but we can photograph tracks they leave in the neon. When high-energy particles pass through the chamber, they'll leave behind them for a short time a trail of charged neon atoms. If high voltage is applied across two sides of the chamber, a spark will jump along each trail, and that's what will be photographed. More of this goes on than anything else. Just thinking. Dr. Margaret Law. Maggie is devising a computer program to help her map the field of a big magnet that will surround the spark chamber. The computer is also used to prepare a plot of the kind of data this group expects to get if the currently accepted theory is correct. Not too long ago, it would have taken about a year to make such calculations by hand. Now, after a program is written, it takes a few minutes. Now, you want to see something very unexciting? Unexciting? Well, one of those things. Here is an As usual, there is the problem of interpreting the computer's output. It's not the pure beta height, but it's the drill velocity without the They don't look different. Surely they look different. Do they? Let me see. Look, so the simple thing to do Yeah, we used two, what? 2,000 events? 1,000. 1,000. 1,000 events. So, the waiting kills Oh, something is wrong. It's supposed to be one Well, that's interesting. Look, it is very different. Yeah, that's the whole point. For Bobby Eisenstein, this is just one part of a full day. Like many members of the research group, he's also teaching. This is a class for beginning students. all the equations when they fire rockets and then they have to know exactly where these rockets are going. So, they they use Newton's laws and they actually point by point trace out the trajectory. We're not going to demand so much. All we're going to do is we're going to say, "Here's the Earth. Here's the Moon. Relative sizes are not scale. I start with my rocket up here on the ground. It's a distance RE, radius of the earth, from the center of the earth. I fire this rocket and very luckily it hits the moon. And it hits the moon at this R1 And you add to that the potential energy minus G M M over R2 with the other body. While the equipment is being finished in the machine shop, Bob briefs the new student on the experiment. It's all wrapped up in a light protecting cover right now, but inside here is a big piece of plastic called scintillator. Uh this stuff has a property that when a high energy particle goes through it makes a little flash of light, which is seen by a photo tube down at this end. The light flash is very very short, about a billion a few billions of a second, so you can use it for timing exactly when a charged particle has gone through. What we do, for example, is put one on either side of a spark chamber like this. And then, as soon as we know that a particle has gone through because there's been a little flash of light on either side within a very short time, we put the high voltage on the chamber and see the spark. That's basically the way we fire all our spark chambers. Here, let me show you what we've been doing. The thing we're doing and we're looking at what happens when a photon comes near a piece of matter, a nucleus. Very frequently, as a photon passes by, it sort of spontaneously converts into an electron E- and a positron E+. Because they're so close together when they get started, they attract one another. And so, if Coulomb's law, or inverse square law, or quantum electrodynamics is exactly correct, we can predict how much their attraction will affect their later motion, where they'll go and at what speed they'll go. And if it's wrong, we'll find by doing an experiment the contradiction between what we see and what we think we should see by the prediction. We want to know where they're going, so we put a spark chamber up close to the target. And we call that the angle chamber or theta chamber. Theta is the equal angle. And when the particles go through this chamber, the tracks they leave in the spark chamber allow us to know very accurately exactly where they're going as they're coming out of the target. So, that answers the first question. And the second thing we have to know is how fast they're going. Okay? Well, to do that, we let these pass through a big magnet. Put a huge magnet out here. Now, when a charged particle goes through a magnetic field, remember, it bends. It travels on a curved path. And so, these both curve. Now, we put a spark chamber inside the magnet. Another spark chamber. And we find the trajectory, the curved path of the particles inside the magnet. By knowing the amount of curvature of the particle inside the magnet, we find out its momentum, which is the same thing as its velocity in this case. Momentum is P. And so, this spark chamber is called the P chamber. And then we So, with these together, we know where the particles are going and how fast. The last thing we have to do is we have to decide exactly when do we fire the spark chambers. Okay? Because you know, it doesn't always happen. So, we put up a counters. Counters here. A lot of counters back here. There's other stuff, by the way. I'm I'm really oversimplifying this. There are a host of other devices scattered in here. I've I've just given you really the basic essentials. When the appropriate counters fire, we know that there's a pair of particles gone through. Then we fire the spark chambers and take our pictures. And that that's how we do it. Hopefully. Well, fellows from another group group drop in. There's a touch of rivalry in the air. When do you people think you'll be on the floor? When are they going to have the roof on it? You think you're going to be ready by then? Oh, I don't know. I think so. The whole physics department gets together every now and then for a picnic and a chance to show off the kids. Dave's boy, Michael and his wife, Marilyn. At last, the first of six loads of steel for the big magnet. Bob and his wife, Laura have heard that the magnet is arriving. The magnet was designed at the lab but manufactured in Wisconsin by an industrial construction firm. Well, they made the intermediate pieces and there's also iron on the side and the return paths. This isn't part of the of the return path. Yeah, something extra was added. Want to know something? Boy, this is big. I want I want to This is only the bottom layer. The total weight of the magnet will be 210 tons and it's all painted green. So, of course, Dave has dubbed it the Jolly Green Giant. The beam from the synchrotron ring will travel to the magnet in a pipe just above this line. All the equipment is being lined up around this axis. Oh my. That's just when I left. How How are we coming? Hundreds of feet of cable carry the signals to panels where the data will be recorded. The panels are on the other side of a concrete shield to protect the experimenters from radiation when the beam is on. An easy way to find just where the electron beam will be inside this pipe is to put a piece of film across the pipe and let the beam take its own picture. Wow. The beam is there, but it needs to be lined up and focused better. see the plan. Yeah. Photographs and data begin to fill the lab notebooks. And maybe so we're exploring it. Now Dave's spark chamber can be put into place. The side of the magnet was left open to install the spark chamber. Okay, I'll crawl in and guide you in there. Okay, give it a push. Okay, you're How's it going on the bottom? You're okay there. Okay on the bottom. I'm sure it'll be all right. Woah. Okay, now we're there. But I think we got to get something under this. Like a piece of wood on this side. Jim Daken, a college senior, finishes installing the camera that will photograph the sparks in the chamber below. Bill Jones is the head of electrical engineering at the accelerator lab. Bill makes certain there's no danger of electric shock. You can jump any interlock system we put up. Yeah, what his concern is accidentally Yeah. uh accidents. Right, things that you prevent you from getting involved in. And I'm saying that one of the things I'm saying is if you have all of these things bonded if this is not grounded to this and you touch that and you touch this, you can get hurt. And what I would have here normally is an electrician who would go around and ground every item to every other item. The last pieces of apparatus are moved position. One good bump could ruin weeks of careful work. Everything's ready for the first trial run. By now, 2 years have passed since the theory of this experiment was first worked out. And this was just an empty space. The work and ideas of 20 men and women and almost half a million dollars have gone into the design and construction. Although for many beautiful physics research problems, you need only paper and pencils or a few dollars worth of equipment, this particular basic problem couldn't be licked except on this scale. You see, these are mirrors guest arrives. Professor Alikhanian of the Armenian Physics Institute. It was he who developed the first wide gap spark chambers. And this is the Marx generator generator. And it is a new design. We bought it? No, we built it. Yes, sir. With ourselves, yes. And it is a Grossman is is writing it up. He's writing a report, a paper, because it's very simple and very reliable. When is this report He will He will try to give you a preliminary version. I will bring you tomorrow. And he's writing it for sending it to publication. I see. But it's very reliable, very good. Very compact. Very compact. This is What is the maximum voltage? Uh 300 kilovolts. 300 kilovolts. 300 kilovolts. Oh, here's David, the Grossman. Uh I I we just looked at the setup and Professor Alekhanyan would like to have whatever information is written and and sketches and prints of the Marx generator. I have made a Xerox copy of all of the line that I did. Has this been published? No, it is in press. In press? Yes. Yeah, but when it comes to send you the copy. Sharing new ideas works both ways. This physics seminar, like thousands of others all over the world, is in a way an international gathering. How about a round of In the Valley? I need to see minute chore. I need to see this new hairstyle. I haven't seen it. In the Valley of the Dolls. What? Here, Margo. I'll put a little hairspray on for you. Okay. I thought you had one of those spray cans there. It's on. That's why you changed your hair coloring. 1 2 3 4 5 6 7 8 9 10 11 12. I'm going to work. We haven't even started. Okay? 7 minutes. All the electronic gear is double-checked. But do you go through the uh Excuse me. Okay, 300. Good. All right. Okay, coming up team nine. How's that? Before the electron beam can be directed into their experimental area, the central accelerator control room must be called to arrange a safety check and have the area locked. Dave, want to put some money on this? On the first shot? What? What are What are the chances of getting sparks first shot? Oh, not very great. Not very great. Why? Too low? Probably wrong, yeah. Starting on the test. I'm turning on the high volts, so uh Okay. Uh do you want me to fill the inside area 7 to along that wall down by the gate? In the area, nobody has to be Okay. This is the moment. The beam is on. The Marx generator went not very loudly, but no tracks. No tracks. It's not even clear whether the Marx generator went Correct. That is it It sounded, but not as loudly as I heard it sound. The spark chamber didn't work. Maybe it was damaged during installation or the voltage across it wasn't high enough. it's better to do it now and not restart again. And I'm all for trying it now. Nothing there. The voltage across the spark chamber is increased for another try. Yeah, there's plenty there. Try the other one. Yeah, there's plenty there. Now, at least it does something. Yeah. Ready once more. Waiting for the beam to be switched over. Okay, let's fire. Let's fire, Dave. Dave. Woo! Oh, beautiful. Gorgeous. Come here. Look, look. Yeah, they're beauty. No, it works very nice. Oh, that was the problem. Uh I wonder whether it's possible uh we should try to make make some attempt uh to measure the uh the delay. Well, it certainly works nice. I mean, it's clearly a question of raising the voltage uh and that's it. Modern phone. Well, this is a good time to give you and Mervin the problem is Hey. That's fun. You have another one You have another one coming your way. right now. It's a problem. Jeff, you're breaking. Do you know how to open it? No. Uh you you you No, no, no, no. Oh, good lord. You hold it like this and you have a cup handy just in case it goes. As a matter of fact, it's probably against safety rules. Wow. Here you are. Oh, boy. Well, congratulations that should be the end. I can feel it. No, no, no, no, no. I mean, you can't I mean, if you keep it running for an hour, couple of hours, I mean, it it it really be nice generator isn't working that well uh that it pays, but I think it pays to make sure to get pictures. All right, shutter five is coming open. That thing is 18 in high. The best part of the work is still ahead. The experiment itself to find out how electric charges interact at extremely close distances. Then the results will be published. And beyond that, this experiment isn't an end in itself. Perhaps it will be the starting place for other people working on the physics of particles, who can then ask new and still undreamt of questions about the most basic stuff of which the world is made. Look at this one, Dave. That's definitely not a pair. This is the bottom view, is that right, Mike? Yeah. I haven't seen any tracks or anything in the bottom view. The top view of the theta chamber is not coming in, though. All right. picture Pictures are pretty for starters. Fiducials look pretty good to me. One of the mirrors is partially blocked. We have to do a little cutout in that catwalk up in the top. It's some of that black stuff in there. There are three of them all.