Tag Info

Hot answers tagged

13

Yes. From the Voyager mission webpages: As of August 2010, Voyager 1 was at a distance of 17.1 Billion Kilometers (114.3 AU) from the sun and Voyager 2 at a distance of 13.9 Billion kilometers (92.9 AU). Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year, 35 degrees out of the ecliptic plane to the north, in the general ...


8

Neutron sources You can buy a commercial off-the shelf "neutron generator", or you can use a radioactive source. Neutron generators are accelerator-based fusion reactors1 and have the advantage of being able to simply turn the neutron supply on and off. The most common source is AmBe (Americium-241/Beryllium), though Californium-252 and tritium both have ...


5

Have a look at http://arxiv.org/abs/1009.1569. In this article Thomas Juffmann discusses some of the practical issues in doing these experiments. In principle these experiments aren't hard, but in practice there are lots of technical difficulties. For example the large molecules need to be all moving at the same velocity(i.e. the beam needs to be very cold) ...


5

A subtle problem you seem to overlook is that the proton-proton cross section is very small, about 0.07 barns (a barn is $10^{-28}$ square meters) at the LHC energies and not dramatically different at your lower "fusion energies". It means that at the LHC, much like at your dream machine, most of the protons simply don't hit their partners. It is not really ...


5

Yes, photomultipliers are in use in calorimeters which use Cerenkov light to detect the passage of particles. An example is in this preprint of the Castor detector at CMS in LHC. Charged particles penetrating the CASTOR calorimeter will generate showers in the tungsten absorber plates. These particle showers are sampled by using the Cherenkov effect. ...


4

In fact, we already have imaged extraterrestrial planets. You can find a list here, with perhaps the most famous system being HR 8799. Of course, that quote was referring to Earth-like planets, and you can see from the list I linked that everything we've seen is more massive and further out than even Jupiter. The challenge that confronts direct imaging is ...


4

What you are looking for is usually called a window, not a filter. You need to check different manufacturers to choose a material that fits your requirements, including not only light transmission but also the pressure differential, chemical inertness, temperature range, etc. Checking ARS' website, calcium fluoride (CaF2) might be what you are looking for.


3

A nanoscope in the sense you're talking about would be physically impossible, because things which are smaller than the wavelength of light don't reflect light. They do scatter light, but that's a different process which doesn't form a coherent image. Visible light has wavelengths between about 400 and 700 nanometers, so anything smaller than that - ...


3

Martin Rees is being a bit optomistic, both the Terrestrial Planet Finder and Space Interferometry Missions were canceled because of lack of money.


3

I'll answer what I know Single-photon detectors: I've seen these referred to as "click-detectors". How accurate are they? Do they measure every single photon that eneters or only a significant fraction of them? Roughly 50 %, can be higher nowadays I believe. If I send a single photon through a fiber optic of some length, how much percentage of the ...


3

From my experience: Single-Photon detectors: The real problem is not dark counts, but spurious counts. The shot-noise limit is $\frac{1}{\sqrt{N}}$ where N is the number of photons in the field for a coherent source (i.e a laser). Reaching the Heisenberg sensitivity of $\frac{1}{{N}}$ is very difficult to realize experimentally. Detector efficiency depends ...


2

Actually, this has been done, but it's not sustainable. Wikipedia has a brief explanation: Accelerator-based light-ion fusion is a technique using particle accelerators to achieve particle kinetic energies sufficient to induce light-ion fusion reactions. Accelerating light ions is relatively easy, and can be done in an efficient manner—all it takes is a ...


2

By measuring the z -position of the stage at focus, the height of objects can be determined.


2

It's been a decade since I last used an SEM, but back then you would start using a fast scan that was real time i.e. you could move the sample around, change focus, etc and see the effect in real time. However the realtime image is noisy because the numbers of electrons being captured is small. Once you had the picture you wanted you would record them image ...


2

As far as resolution goes, right now the best in practice are high resolution transmission electron microscopy (which involves firing high energy electrons), high resolution scanning force microscopy (which involves a very sharp tip vibrating above a surface), and the classic scanning tunneling microscopy (which involves conduction through a very narrow ...


1

I have used silver conductive paint for quick tests of superconductors in a helium cryostat, and it worked fine. Will it also be a vacuum? I've seen others use a blob of indium solder for electrical connections as well.


1

This is a bit pedantic, but when you say catch free neutrons -- I assume you mean those that exist from non-discrete sources undergoing reactions (transmutation, decay processes, etc.) rather than neutrons that are produced in the unbound state from a specific source, be it "fusors" or a radioactive source coupled with a target material or a source that has ...


1

1GHz is not NMR but ESR (unless you can find a 22T magnet...). I wouldn't try anything else than water for an NMR demonstrator experiment. It's cheap and the proton density is high. I think they are usually adding a little bit of copper sulfate or so as a quencher, but I didn't look into that. Your main worry is the magnetic field. I would try to generate ...


1

Perhaps a more reasonable idea would be to decode signals inadvertently sent from distant planets. For example, if we reverse the situation then on a distant planet the ETs looking at Earth might decide it is impossible to build a telescope to see us, and instead they might start trying to understand how to decode the stray television signals we are ...


1

I used an arc-welder to make thermocouples from wires like your starting materials. Your desired objective looks like some of my 'failures.' Try loading a wire in tension and then break it with an arc (i.e. heat and melt a short section.) The ends might draw to the fine diameters you're trying to achieve. I'd try using one of the welders that are designed ...


1

Obviously if the coil linearly expands equally and uniformly in all three dimensions, the inductance has to scale in directly proportionality to the dimension. My understanding is that anything made of pure copper, no matter what you do with it, will expand equally and uniformly in all three dimensions. If you can incorporate materials with different ...


1

The success of the Standard model in organizing our particle data is also based on the strong interaction SU(3) color, which displays asymptotic freedom. In physics, asymptotic freedom is a property of some gauge theories that causes bonds between particles to become asymptotically weaker as energy increases and distances decrease. To get free quarks ...



Only top voted, non community-wiki answers of a minimum length are eligible