We prepared a short note on how to build a dynode voltage divider network for inexpensive surplus XP2422/SN photomultiplier tubes. The XP2422/SN PMT is especially suited for gamma-ray spectral analysis when coupled to a NaI(Tl) scintillation crystal because of its high pulse-height resolution (PHR). The XP2422/SN is available from Sphere Research in Canada.
A recent paper entitled “Displacing entanglement back and forth between the micro and macro domains” discusses the experimental possibility of displacing quantum entanglement into the domain where it involves two macroscopically distinct states, i.e. two states characterized by a large enough number of photons. Specifically, the authors describe the process by which they start with two entangled spatially separated optical modes at the single photon level and subsequently displace one of these modes up to almost a thousand photons.
With so many photons, it would be possible, at least in principle, to see entangled photon pulses with our eyes. This would also make it possible to perform entanglement experiments with linear coarse-grain detectors (NOT single-photon detectors).
Mathieu Stephan, a high speed electronics engineer at the Swiss quantum information systems company id Quantique SA (and prolific hardware hacker) designed the very fast pulse amplifiers needed to acquire signals from avalanche photodiodes for this experiment. He has posted a thorough description of his design on his blog: http://www.limpkin.fr.
We recently learned the sad news that Dr. Akira Tonomura – a truly great experimentalist – passed away on May 2, 2012 during the course of treatment on pancreatic cancer.
We have been great admirers of Dr. Tonomura. Our blog’s banner is a cartoon representation of an experimental setup developed by Dr. Tonomura, through which in 1986 he showed single-electron buildups of electron wave interference fringe patterns. This experiment clearly revealed the dual nature of electrons and was described by Physics World magazine as the world’s most beautiful physics experiment, ranking above the historical experiments of Galileo Galilei and Robert Millikan.
The photomultiplier tubes (PMT) is the workhorse detector in particle physics and many other fields that require detection of light at extremely low levels. However, the long-wavelength response of PMTs is not only low because of low quantum efficiency, but also because thermionic emission at room temperature causes swamps low-level signals with noise.
Reducing dark counts is especially important in photon-counting applications, especially when attempting to detect photons in the near-infrared. For example, the dark count of many PMTs rated for a wavelength range from 400 to 1200 nm, is in the hundred of thousands of counts when not cooled—making it virtually useless for detecting almost anything but the strongest signal. When cooled to -20 °C, the dark count is reduced to just a few tens counts. As such, in general, the use of PMTs that detect above 600 nm almost mandate a cooled housing.
We constructed a thermoelectrically-cooled housing to experiment with cooling a standard 2” face-on PMT. Although appropriate PMT noise reduction was achieved (one order of magnitude), the thermal efficiency of the do-it-yourself housing design was low, so lessons learned from this build will be used in a second-generation cooled housing.
Ludlum general-purpose ratemeters are professional-grade instruments that are available on the secondary market at affordable prices. They are compatible with a wide variety of probes, making them a great choice for educators, surveyors, and advanced amateur users. However, probes for Ludlum ratemeters are often as expensive as the meter instrument itself, making it worthwhile to build comparable versions from surplus components.
George Musser – an editor at Scientific American (and author of “The Complete Idiot’s Guide to String Theory”) – developed a diy version of the Wu-Shaknov Experiment. If George’s setup truly manages to measure the relative linear polarization of gamma rays from positron-electron annihilation, then he would have accomplished the most inexpensive demonstration of quantum entanglement!
The idea is to measure the relative linear polarization of gamma-ray photons emitted with opposite parity from the annihilation of positrons produced by the decay of Na-22 using Compton polarimetry and coincidence counting. The predicted results in the number of coincidences are different when assuming quantum entanglement than when basing the calculations on local hidden variables theories.
These are pictures of the Americium-241 sources inside some old Pyrotronics F3/5A smoke detectors that were being decommissioned. The activity of the Am-241 sources at the time of manufacture (1970s) totaled 80 µCi, so they should still have some ~70 µCi left in them.
The Pyrotronics F3/5A smoke detectors were manufactured in the early 1970s. The radioactive sources consist of americium oxide mixed with gold powder and formed into a small billet. This billet was then placed between a sheet of silver and a sheet of gold and rolled into a foil under high heat and pressure. Americium-241 decays primarily by alpha particle emission to neptunium-237, along with low energy gamma radiation, with a 59.5 keV gamma emission being most prominent.
We just finished constructing a low-cost, yet highly sensitive gamma-ray scintillation probe for our CDV700-Pro counter. The probe is based on a Philips XP5312/SN photomultiplier tube (that is available from Sphere Research) and a piece of scintillation plastic. The probe yields a background count of approximately 1,000 counts/minute (cpm) in our lab, and 7,400 cpm from a 137Cs 6.7 µCi exempt source at a distance of 30 cm. The probe’s sensitivity, portability and rugged construction make it an ideal choice for surveying.
Abigail Prutchi at the official “Mitad del Mundo” monument commemorating the 18th Century French Geodesic Mission marking of the Equator
Abigail and I just returned from a trip to the Galapagos Islands. On the way, we visited the iconic Mitad del Mundo (Middle of the World) monument which commemorates the 18th-century French Geodesic Mission expedition carried out for the purpose of measuring the roundness of the Earth and measuring the length of a degree of latitude at the Equator.
The monument is constructed at the site where the Geodesic Mission calculated the passing of the Equator. Modern measurements show that the Equator actually crosses about 240 meters north of the marked line. Not bad at all for 18th-Century Physics, and an accomplishment worthy of the beautiful monument that commemorates it!
The Intiñan Solar Museum is a shameless tourist trap. Tour guides get a kickback from the unscrupulous owners of this site where credulous tourists are shown tricks that supposedly can happen only at the Equator. This is a prime example of Bad Physics fueled by greed!
Recently however, a group of unscrupulous investors led by Mr. Humberto Vera started the Intiñan Solar Museum, which reportedly marks the true Equator. Not true!
Tour guides take tourists there because the museum pays them a kickback (which the official Mitad del Mundo doesn’t).
George Musser – an editor at Scientific American (and author of “The Complete Idiot’s Guide to String Theory”) – visited our basement lab a few weeks ago. Today he published a very nice blog about us on the Scientific American site. Thanks George!
Click here for the blog.
Prof. Mark Beck from the Dept. of Physics at Whitman College recently published an excellent book titled “Quantum Mechanics: Theory and Experiment.” It is written for an advanced undergraduate/graduate quantum mechanics class. This book presents the theory in its full formalism (with thorough, high-level math), as well as describes five laboratory experiments that explore the use of entangled photons in the undergraduate lab.
Prof. Beck’s laboratory experiments use the same type of system as we describe in Chapter 8 of Exploring Quantum Physics Through Hands-On Projects, so if you are up to the math, we heartily recommend this book to continue your exploration with your entangled-photon system.
The nice guys at the Yahoo GammaSpectrometry Group developed multichannel analyzer software for the $79 SainSmart DSO201 Pocket-Sized Digital Oscilloscope. The upload of the MCA software to the oscilloscope is really easy (via USB), and it allows the PMT probe shown in the book’s Figure 30 to be connected directly to the oscilloscope’s input with no need for a PMT amplifier!
