“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.” Nikola Tesla

ELA Equipment

Eager Lab Assistants measure the levels of radiation in our environment in two different, but useful ways. Read below to see what equipment is used to best be able to interpret the data we share in our Notebook and check our links page to find out where you can get yours! 

The first method is through the use of a Geiger counter, which determines the count rate of a source (i.e. the number of nuclear decay interactions per second).   We use an Inspector Alert model Geiger counter that we purchased through geigercounters.com.  The Inspector model measures alpha, beta and gamma radiation.  

Meet Dr. Honeydew:  










He's very busy... When not in the lab running alongside the scintillator during tests for background comparisons, he's feeding indoor radiation data to The Radiation Network's national radiation map, depicting environmental radiation levels across the US, updated in real time every minute. 










The station's indoor air average is typically 35-37 cpm and is usually located in SE Pennsylvania, approximately 40 air miles ENE of Three Mile Island as shown in the inset, unless the Assistants take him on a road trip as shown below:



The second method is through the use of a gamma-ray spectrometer, which measures the energies of photons being emitted by a source.  We use a GS2812 thallium-doped sodium iodide ((NaI (Tl)) scintillator.  Radiation interacts with this crystal and causes electronic transitions to excited states in this material. The excited states decay rapidly, emitting photons that are captured by a photomultiplier tube. The ensuing electrical signals are proportional to the scintillator light output, which, under the right conditions, is proportional to the energy loss that produced the scintillation.  Meet Electra (it's a family name..):
Electra is connected to a pulse height analyzer.  It measures and records the number of pulses that occur at different pulse height levels. These types of devices are used with detectors which produce output pulses that are proportional in height to the energy deposited within them by the interacting radiation.   We use a GS1100A MCA, multi-channel analyzer, which allows recording of those events simultaneously in multiple energy ranges. We'd tell you his name too but he prefers anonymity (ELA is not surprised as he is a suspected sock thief):
                                                                        (We rest our case..)
The Castle Specs:

In the neverending effort to reduce interference from outside radiation sources from the samples we test, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum.  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  
The Castle Specs:

In the neverending effort to reduce interference from outside radiation sources from the samples we test, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum.  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  
The Castle Specs:

In the neverending effort to reduce interference from outside radiation sources from the samples we test, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum.  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  
The Castle Specs:

In the neverending effort to reduce interference from outside radiation sources from the samples we test, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum.  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  
The Castle Specs:

In the neverending effort to reduce interference from outside radiation sources from the samples we test, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum.  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  

Anyhow, in the never-ending effort to reduce interference from outside radiation sources from the samples we test as well as block secondary photons bouncing off of the shielding, we built a lead castle with a 7 x 10 x 10 cm testing chamber, lined with copper and aluminum, all inside a polyethylene container.  The little "packet" you see is a humidity absorber typically found in shoe boxes as Electra is very sensitive to moisture - (interestingly, they appear at the same rate as socks disappear...)  We still need about twice the amount of lead shown, but it still gives us a good spectrum.  Below is a calibration spectrum of 1microCurie of Cesium-137:
(!! We always use rubber gloves and masks when handling lead.  This lead has been coated but as you can see, just a small amount of handling will cause chipping and exposure, into the bloodstream through absorption or into the lungs through inhalation of dust particles.  Same for radioactive sources.  Only handle with proper protection during use and always keep in a lead-lined shield when not in use.  Safety first!!)
Calibration and Efficiency Curves

While the Geiger counter comes calibrated, this isn't so with a scintillator.  Radiation check sources are used to measure known quantities and energies to calibrate the scintillator to calculate efficiency for future tested samples.  Electra's calibration and full peak energy efficiency curves are shown below depicting the typical linear relationship and efficiency of a standard thallium-doped sodium-iodide crystal, or NaI(Tl).
Full energy peak efficiency (left) vs. plotted values onto standard (right)

The image on the right was photographed and taken from the best book out there on this topic, Practical Gamma-Ray Spectrometry, 2nd Edition, by Dr. Gordon Gilmore.  We highly recommend picking up a copy.  Thank you Dr. Gilmore!

ELA derived the above estimations by measuring and calculating these values from our current inventory of check sources (we could really use more in the 50-400 range as evidenced from a typical calibration curve, as detector efficiency for FEPE, or full energy peak efficiency for our NaI(Tl) crystal is much higher than that at the gamma-rays our current sources emit):

Cs-137 (NIST standard)

Na-22

Co-60 

We use these values to estimate activity of our samples as we use the resulting count measured from identified peaks in our spectra.  To see how we determined this, please see here. Despite using a calibration curve to determine detector efficiency at levels in which one lacks a check source to directly detect, or further, using such to determine full energy peak efficiency factor for activity for suspected radionuclides other than those which have been tested introduces uncertainty in one's estimation; ELA, will still sometimes estimate activity based upon this curve.  However, please keep this extra uncertainty in mind for estimations other than listed above, and please see Dr. Gilmore's book for further explanation and reasoning.