[Ben Krasnow] Builds A Mass Spectrometer

One of the features that made Scientific American magazine great was a column called “The Amateur Scientist.” Every month, readers were treated to experiments that could be done at home, or some scientific apparatus that could be built on the cheap. Luckily, [Ben Krasnow]’s fans remember the series and urged him to tackle a build from it: a DIY mass spectrometer. (Video, embedded below the break.)

[Ben] just released the video below showing early experiments with a copper tube contraption that was five months in the making; it turns out that analytical particle physics isn’t as easy as it sounds. The idea behind mas spectrometry is to ionize a sample, accelerate the ions as they pass through a magnetic field, and measure the deflection of the particles as a function of their mass-to-charge ratio. But as [Ben] discovered, the details of turning a simple principle into a working instrument are extremely non-trivial.

His rig uses filaments extracted from carefully crushed incandescent lamps to ionize samples of potassium iodide chloride; applied to the filament and dried, the salt solution is ionized when the filament is heated. The stream of ions is accelerated by a high-voltage field and streamed through a narrow slit formed by two razor blades. A detector sits orthogonal to the emitter across a powerful magnetic field, with a high-gain trans-impedance amplifier connected. With old analog meters and big variacs, the whole thing has a great mad scientist vibe to it that reminds us a bit of his one-component interferometer setup.

[Ben]’s data from the potassium sample agreed with expected results, and the instrument is almost sensitive enough to discern the difference between two different isotopes of potassium. He promises upgrades to the mass spec in the future, including perhaps laser ionization of the samples. We’re looking forward to that.

Continue reading “[Ben Krasnow] Builds A Mass Spectrometer”

Radiation Detector Eschews Tubes, Uses Photodiode

When the topic is radiation detection, thoughts turn naturally to the venerable Geiger-Müller tube. It’s been around for ages, Russian surplus tubes are available for next to nothing, and it’s easy to use. But as a vacuum tube it can be somewhat delicate, and the high voltages needed to run it can be a little on the risky side.

Luckily, there are other ways to see what’s going on in the radioactive world, like this semiconductor radiation detector. [Robert Gawron] built it as a proof-of-concept after having built a few G-M tube detectors before. His solid-state design relies on a reverse-biased photodiode conducting when ionizing radiation hits the P-N junction. The tiny signal is amplified by a pair of low-noise op-amps and output to a BNC connector. The sensor’s analog output is sent to an oscilloscope whose trigger out is connected to a Nucleo board for data acquisition. The Nucleo is in turn connected to a Raspberry Pi for totalizing and logging. It’s a complicated chain, but the sensor appears to work, even detecting alpha emissions from thoriated TIG electrodes, a feat we haven’t been able to replicate with our G-M tube counter.

[Robert]’s solid-state detector might not be optimal, but it has promise. And we have seen PIN diodes used as radiation detectors before, too.

[via Dangerous Prototypes]