# Tag Info

## Hot answers tagged experimental-technology

14

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 ...

6

Events in high energy physics detectors that can't produce useful data, mostly because they are the result of soft scattering events, are discarded by multiple layers of trigger circuits. What these circuits do is prescribed by so called trigger menus, which are based on theoretical predictions about a large number of known and hypothetical physics event ...

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

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

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. ...

5

The hydrogen discharge tubes typically used in student labs are not designed for long-term use. After a couple of years, the tubes leak and air gets mixed with the hydrogen. This causes them to get dim and the weaker lines are almost impossible to see. It has nothing to do with the power supply and everything to do with how new the tube it and how many ...

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.

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 ...

3

I'm afraid we've found no real solution to this problem. I think the noise propagates through the support frame, and sound proofing doesn't help very much. I think your best bet is either noise cancelling headphones or remote desktop as much as possible. But neither solution will help other people who may be in the same lab.

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 ...

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

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

3

It's not so much about "penetrating magnetic fields" as it is about seeing the signal above background noise (assuming your transmission is above the background plasma frequency). The intensity of any given signal drops off as $\propto$ r$^{-2}$. This means that a signal sent from r = 1 will be 16 times as strong as a signal from r = 4. All receiving dish ...

3

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 ...

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

As you suggested in your comment, the $\mu^-$ and $\mu^+$ that stop in matter do not have the same lifetimes. The $\mu^+$ come to rest between the atoms of your stopper (eg: scintillator?) and decay into $\nu_{\mu}e^+\nu_e$ with the standard 2.2 usec lifetime. However, the $\mu^-$ get captured into Bohr orbits about the stopper nuclei. The $\mu^-$ then ...

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 ...

2

You should use external optics with a monochromator. Outside the setup you should have a lens that focuses collimated the light on to slit A. This is the reason for the converging beams. Note that, for maximum throughout you should choose a focal length focusing lens that matches the numerical aperture of the monochromator. With different wavelengths now ...

2

The best performance (from a theoretical standpoint) would be to use diamond dust as a filler with something like silicone as a binder. In principle you can get about 5 times better thermal performance than you can with silver. Of course, you need the particle size as small as possible, which is harder to do with diamond than with silver (you can't ...

2

Orography has already been discussed, but it still leaves the question of how bathymetry is measured. From Wikipedia: Satellites are also used to measure bathymetry. Satellite radar maps deep-sea topography by detecting the subtle variations in sea level caused by the gravitational pull of undersea mountains, ridges, and other masses. On average, sea ...

2

Is it really obvious that modulating the pumping diode won't work? It's not obvious to me. You say that the fluorescence lifetime of Nd:YAG is slow, but you are thinking of the lifetime when there is no stimulated emission. If there is stimulated emission, excited atoms can be de-excited very very quickly. Think a little harder about laser dynamics, ...

2

First, the page you linked to only says that Cavendish calculated the deflection of light, not measured it. Newton's law of gravity technically only applies to massive particles, as you say. But this business about light being massless came a hundred years later than Cavendish; in his time light was regarded as a wave, though Newton liked the idea of ...

2

Crater could enhance the LIBS signal up to an optimum depth and then for deeper craters the signal decreases. See below for references. Then if you keep the laser position on the sample unchanged, after a number of shots the signal degrades. https://www.osapublishing.org/as/abstract.cfm?uri=as-59-7-853 https://www.osapublishing.org/oe/abstract.cfm?uri=oe-20-...

2

As you might know, one of the most important factors to control in a laser ablation process is the laser power. It is therefore extremely important that the power on the sample is kept constant during the process. The formation of a crater puts the surface at a different distance (or maybe changing the focus, if you are using a parabolic mirror) thus ...

2

Courtesy of its spin the electron has a magnetic dipole moment. That means if we place it in a magnetic field the two states aligned with and against the magnetic field have different energies. The magnitude of the energy difference depends on the strength of the field and the size of the magnetic dipole moment, which in turn depends on the spin. So by ...

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 ...

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