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A Geiger Counter January 28, 2012

Posted by peterxu422 in Science.
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In my first class of the new semester, Modern Physics Lab, I finally learned about something that has intrigued me for quite some time: The Geiger Counter.

Begin at 8:40

I first heard of the Geiger Counter during an interview with Dr. Michio Kaku of CUNY City College. He mentioned it as he was describing the famous thought experiment of Schroedinger’s Cat. This thought experiment involves the decay of a radioactive atom which is detected by the Geiger Counter. Eventually, I learned that Geiger Counters measure radioactivity of radioactive materials.

In my Modern Physics Lab class, I learned how it actually worked though. A Geiger Counter typically consists of a metallic cylinder, known as a Geiger, with an opening at one end of its circular surface, known as the window. The inside of the cylinder has a rigid metallic wire running down the center and the cylinder is filled with a gas of some sort. The window is covered with a thin piece of material to prevent the gas from escaping.

When you point the probe in the direction of a radiation source, the radiation from the source travels via electromagnetic waves (such as gamma rays). These waves pass through the window, into the cylinder, and come in contact with the gas. The energy of these waves is sufficient to knock off electrons from these gas atoms (i.e. they “ionize” the gas). These freed electrons then in turn knock off other electrons of the surrounding gas atoms, creating an avalanche effect. The wire is connected to a high voltage source that makes the wire positively charged. Since it is positively charged, the freed electrons become attracted to the wire, and eventually they come in contact and the electrons travel along the wire to the rest of the device. Usually, the wire is connected to a microphone that turns the traveling electrons, or electrical current, into a sound vibration. That’s why if you’ve seen a Geiger Counter, you hear the crackling/popping noise when it is pointed closely to a radiation source.

If you come in contact with a Geiger Counter one day, you can still use it even if you are not in the presence of any obvious radiation source. Just point the counter towards the sky and you are bound to hear a few clicks. This is because the Earth is constantly hit by radiation all of the time in the form of cosmic rays. These are equally capable of setting off the Geiger counter.

My Professor had exactly one of these types of Geiger Counters yesterday that he showed the class. He played a nice trick on us by borrowing a student’s pack of cookies and placing it on a plate. The counter starting crackling quite loudly and he had us believe that the cookies contained radiation. It turned out though, that the plate he placed them on was actually made in Russia and contained some radioactive material in it.

Book Review: Death By Black Hole January 16, 2012

Posted by peterxu422 in astrophysics, Science.
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Over the summer, I had the incredible privilege of meeting Dr. Neil deGrasse Tyson, astrophysicist and Director of the Hayden Planetarium of the American Museum of Natural History. I, along with my fellow Fellows of the Jeannette K. Watson Fellowship program, had a private seminar at the planetarium in his conference room. Before this meeting, I bought his book Death By Black Hole and took the opportunity to get it signed.

I began reading it during this winter break and have just completed it. It was a fun and enlightening read overall. The format of the book is mostly a collection of previous essays that Dr. Tyson has written and it is divided into chapters accordingly. Therefore, I found the transitions between each chapter a bit rough and sudden. I felt better bridges could have been built between the chapters, illustrating how the ideas/concepts discussed in one lead or relate to the next.

The other major question I had throughout was why he titled the book Death By Black Hole, as only one chapter covers this morbid, yet incredibly fascinating phenomenon. The book is primarily a discussion of astrophysics and the important events in history that lead to the development of the field, along with mentions of other scientific fields as well. My first impression by looking at the title was that the book would be an in-depth qualitative discussion of black holes.

Aside from those two concerns, I found the rest of his book informative and fun to read. Dr. Tyson certainly covers a wide range of important developments in science as well as cosmic phenomenons. A passage I enjoyed concerned Tyson’s thoughts on America’s declining role as a major leader in scientific research. He discusses the project that was canceled by Congress, known as the Super Conducting Super Collider (I would call it (SC)^2). The SC^2 was to be the most powerful particle accelerator ever created that would enable scientists to replicate the early conditions of the Big Bang, and perhaps understand how and why the universe came to be what it is, and not assume some other configuration. Tyson writes:

But in 1993, when cost overruns looked intractable, a fiscally frustrated Congress permanently withdrew funds for the $11 billion project. It probably never occurred to our elected representatives that by canceling the Super Collider they surrendered America’s primacy in experimental particle physics.

If you want to see the next frontier, hop a plane to Europe, which seized the opportunity to build the world’s largest particle accelerator and stake a claim of its own on the landscape of cosmic knowledge. Known as the Large Hadron Collider, the accelerator will be run by the European Center for Particle Physics. Although some U.S. physicists are collaborators, America as a nation will watch the effort from afar, just as so many nations have done before.

With the exception of the rather bleak but realistic outlook of this passage, Tyson’s enthusiasm and love of the cosmos is evident throughout the book. His pedagogical nature and at times humorous writing style will provide readers a basic understanding of the universe in a laymen fashion.

Earth’s Invisible Defender – The Magnetic Field January 9, 2012

Posted by peterxu422 in Science.
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Earth’s magnetic field is a tireless guardsmen, protecting the inhabitants of its planet always. People often take it for granted and many do not even know it exists. To appreciate it, let us first understand what a field is. Physicists are very careful and precise about how they define things, so it is a bit difficult to formally define a magnetic field. But I can give you a qualitative understanding, or at least, a mental picture of it.

A field is the area of influence exerted by a force. Let’s take the force of gravity for instance. Back then, scientists knew that the planets orbited the Sun because the Sun exerted a gravitational force on them. It was almost as if the Sun was pulling on these planets. But the idea of an object, as if by magic, reaching out through space and instantaneously pulling on another object was absurd. To resolve this, the concept of a field was created. Imagine you had a source, that emitted this invisible “stuff” until it filled up all space. At different points in space, you would feel a certain amount of force from this source because everything is immersed in this “stuff.” This “stuff” is the field. Take the Sun as our source for example. It is a source of gravity, and the sun emits a gravitational field throughout space. If you stood close to the sun, you would feel its gravitational force (a strong one). If you stood farther away from the sun, you would still feel its gravitational force, but it might feel a lot weaker. This is why a field is considered the area of influence exerted by a force.

Magnetic fields behave similarly, except the source of a magnetic field is charges in motion (i.e. current) rather than a Sun. Therefore, if Earth has a magnetic field, there must be a source of moving charges that is generating it. Where is that source you may ask? It is believed to be coming from the Earth’s core, which is composed of mostly molten iron. The flow of liquid iron creates electric currents in the core and this creates a magnetic field around the Earth, otherwise known as the magnetosphere.

The magnetosphere is invisible to our eyes but it plays a very important role in protecting the earth against solar wind, which is a stream of charged particles (mostly electrons and protons) that is ejected from the surface of the Sun. Only charged particles are affected by magnetic forces when they enter a magnetic field. So when solar wind strikes the Earth, the magnetosphere deflects all of the charged particles away, leaving the Earth’s surface safe. If there were no magnetosphere, solar wind would damage power stations leaving everyone without electricity for months. Food would spoil and people would starve.

While the magnetosphere is associated with this morbid doomsday scenario, it can also be attributed to one of nature’s most incredible spectacles: aurora borealis, or more commonly known as the northern lights. These are the spectacular aurora displays of dancing colorful nights that usually occur at the north and south poles. These lights result when solar wind particles collide with oxygen and nitrogen atoms in the Earth’s atmospheres at high energies. These collisions excite the electrons of the oxygen and nitrogen atoms and cause them to release certain colors of light as the electrons return to their ground states. The following chart shows what colors correspond to which atoms:

Green – oxygen, up to 150 miles in altitude
Red – oxygen, above 150 miles in altitude
Blue – nitrogen, up to 60 miles in altitude
Purple/violet – nitrogen, above 60 miles in altitude

These lights primarily occur at the Earth’s poles because the magnetic field is weaker at the poles than any other part. Solar wind particles tend to collect here whereas they are strongly deflected at other parts of the magnetosphere.

VIDEO: Amazing Northern Lights Time Lapse

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