"low cost" high speed xray detector - Page 1
Forum section: electronics / projects

author: qwaarjet
author_rank: Regular Contributor
timestamp: December 11, 2014, 09:38:02 pm
content: I am looking into building a photo interrupter for very small droplets ~70nm my idea was to use a collimated beam of soft xrays ~10keV (to avoid diffraction limit) to detect when a drop goes by. PIN diodes seem to be common in this application but most seem to have low bandwidth my application needs a bandwidth of about 1ghz. I'm trying to keep detector cost below a few thousand. Are there fast PINs or is another detector worth looking at.

author: Paul Price
author_rank: Super Contributor
timestamp: December 12, 2014, 12:38:25 am
content: Nano Droplets.. a (near) Zero Power SolutionGenerate a significantly HV.Use the DC HV for sensor droplet tagging.Droplets travel though a hard plastic tube/square channel etc. detection pathway with a HV needle discharge at one opening of pathway.Nano water droplets pick up a significant HV charge upon entry into pathway.Electrolet sensors e.g. metal plates connect to gate of JFETs detect droplets passing.A resistor or other semiconductor means quickly discharges plate after it has registered its pulse output, then ready for next droplet to pass.Maybe needed: an opposing electrostatic charge area for droplets to pass through to setup charge of droplets upon entry.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 12, 2014, 12:43:22 am
content: Quote from: qwaarjet on December 11, 2014, 09:38:02 pmSeroiusly? a thousand million drops per second...?What is the application?

author: qwaarjet
author_rank: Regular Contributor
timestamp: December 12, 2014, 12:56:02 am
content: I'm working with a group build a mass spec system to characterize the operation of self assembling ferrofluid based micro thruster for use on small satellites. Currently we are in the design phase we are planning on a time of flight system as well a quadrupole; other diagnostics are multichannel plates and basic plasma probesI was looking into a way to detect single droplets without changing their direction with a magnetic or high electric field so optically. droplets should be moving ~20km/s

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 12, 2014, 10:22:24 am
content: You probably should talk to someone like Hamamatsu, if only to establish if it's even possible.There are probably some fundamental quantum physics limits that come into play at these extreme parameters.

author: babysitter
author_rank: Frequent Contributor
timestamp: December 12, 2014, 10:24:17 am
content: produce a steady stream if possible, detect their impact on a piezo element or by suggested hv charge transfer, calculate flighttime.Can you get a reproduceable droplet rate? Trigger on calculated value ofter the precessor droplet arrives.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 12, 2014, 12:04:19 pm
content: Do you actually need to measure the particles, as opposed to the (presumably thrust) effect they have?

author: vindoline
author_rank: Unknown
timestamp: December 12, 2014, 03:12:21 pm
content: You may want to look into evaporative light scattering detectors (ELSD). This is a mature technology commonly used in HPLC and LC/MS systems.

author: qwaarjet
author_rank: Regular Contributor
timestamp: December 12, 2014, 04:23:50 pm
content: The point of the setup is to determine the mass/ charge properties of the droplets in various operation regimes as it changes with voltage/ current and fluid proprietes. Measuring thrust directly is near impossible it would only be in nN-uN range (large range due to multiple operating modes between large droplets and ions) the SNR would be really bad.ELDS is basically where I started but there are diffraction and bandwidth limits with it. also droplets are opaque in the visible range.

author: Someone
author_rank: Super Contributor
timestamp: December 12, 2014, 09:43:30 pm
content: Quote from: qwaarjet on December 12, 2014, 04:23:50 pmThat is going to really limit your options, how reflective are they? Doppler may still workhttp://en.wikipedia.org/wiki/Laser_Doppler_velocimetryAnd instead of actual measurement of the particle sizes you might have to work with some empirically derived absorption relationships to determine the concentration/volumehttp://en.wikipedia.org/wiki/Laser_diffraction_analysisvshttp://en.wikipedia.org/wiki/Laser_absorption_spectrometry

author: Marco
author_rank: Super Contributor
timestamp: December 12, 2014, 09:53:31 pm
content: Quote from: qwaarjet on December 11, 2014, 09:38:02 pmThat's still 10s of percent of the diffraction limit for blue light ... why do you assume you can pull a 100% intensity difference from the noise but not say a 10% difference?PS. are the paths of the droplets really nm accurate so an interrupter would actually work?

author: qwaarjet
author_rank: Regular Contributor
timestamp: December 12, 2014, 11:39:08 pm
content: With such small signal I wanted maximize SNR as much as possible. Making soft xrays isn't real much more technically complex than UV but gives 10 times the signal. The view window is of concern but the ion optics in the system do alfer fairly precise aiming. 70nm is also the lower bound that I was interested in detecting.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 13, 2014, 07:00:07 am
content: What about laser ionizing some of the droplet material, then using spectral emission analysis of the resulting ions to measure the doppler shift of their known emission lines?You don't need to measure individual droplets, just the average, right?

author: Marco
author_rank: Super Contributor
timestamp: December 13, 2014, 09:59:00 pm
content: Quote from: qwaarjet on December 12, 2014, 11:39:08 pmYou can get UV/blue lasers off eBay, X-ray lasers not so much. X-ray only gives you 10 times the contrast, not 10 times the signal ... with a laser vs. an uncollimated source you can easily make up what you lose in contrast by getting more energy focused on the drop.How reflective are the drops BTW? Could you use optical heterodyning of reflected light from the drops? Then you could detect it's presence and get it's speed for free.