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NPL

Nuclear Physics Lab

NPL
Cosmogenic Be-7

Cosmogenic Be-7

Author: Tim

On March 1, 2020 I repeated an experiment that I ran a few years back (~7 years ago). In the present experiment, I’ve run a high-volume air sampler for 2 hours on the back deck. I then took a long “live time” background count (4 days or 96 hours or 345,600 seconds) on my 20% HPGe in the low background shield while I simultaneously let the filter paper “cool down” – letting all the radon daughters decay. Then after the 4-day Background count, I counted the filter paper on the HPGe over the next 4 days. All of the radon daughters products are clearly gone. At the end of 8 days, I subtract the 4-day background from the 4-day filter paper spectrum, and see what is left. There is only 1 line, and that is of Be-7 at 478keV.

After the first 2-hour air sample, I took a second 2-hour air sample under identical conditions, and I repeated the process with my 50% HPGe, but that is in a higher radon-background environment

Here are the photos of all the experiment and the analysis results.

The Staplex high volume air sampler
The Staplex filter paper used in this experiment
The volume of air moved during the sampling.
The outdoors sample collect scene.
Tim’s 20%, 1.8keV FWHM HPGe in its low-background shield.
Filter paper sample placement on HPGe.
Sample placement is filter paper folded up and place into a plastic petri dish.
Both background and filter paper spectra.
Both background and filter paper spectra in log scale.
Background subtracted filter paper spectrum reveals a single peak.
We identify that single peak as Be-7 cosmogenically created in our upper atmosphere.

Performing an identical analysis with my other HPGe. This detector is a 50% relative efficiency detector (the above is 20%), however, this detector while shielded by a lead castle, it in a higher background from my basement’s radon (which of course is a variable background).

The second filter paper sample was similarly let to “cool off” for four days. It was then counted for four days. Then I took a four-day background count. Sure enough, the Be-7 peak presented itself:

Region of Interest highlighted in red, shows the Be-7 peak at 478keV.
Region of Interest highlighted in red, shows the Be-7 peak at 478keV, which the nuclide library correctly identifies.

It is interesting to note, despite the higher background, that still number of net counts was roughly double for this filter paper, taking advantage of the higher detector efficiency.

Background and background subtracted spectra compared in PeakEasy. The large peak to right of the Be-7 peak is the 511keV annihilation peak.
Back
  • NPL-Home
    • About Us
    • Accelerators
      • Betatrons
        • Plasma Betatron Coil Form: Design and Construction
        • Pulsed B-Dot Measurement
        • CW B-Dot Measurement
        • First Beam Attempts
      • Cyclotrons
        • 12-Inch Cyclotron
        • Axial Betatron Motion
        • Floating Wire Technique
        • 12-Inch Cyclotron Papers
      • DC Potential Drop
    • Experiments
      • Alpha Spark Detector
      • Jay’s Diffusion Cloud Chamber
      • Tim’s Wilson Cloud Chamber
      • Deuterated Target Preparation
      • Gamma-Gamma Coincidence
      • Measurement of excited Np237 half-life via the alpha-gamma coincidence method.
      • MUONS
        • Life & Times of a Muon
      • Neutrons
        • Neutron Diffusion Time Measurement
        • Neutron Induced Gamma Rays
        • Neutron Detection with He-3
      • Photography
        • AVCO Rotating Mirror
        • Dark Room
        • Fast Flash Photography
        • Rotating Drum Camera
        • Schlieren Photography
        • X-Rayted Photos
      • Rutherford Scattering
      • Thermoluminescence
    • History
      • The Kerst Collection
      • Heisenberg Cube
      • Koeth Collection – Consumer Products
      • Koeth Collection – Radiation Detection Instruments
      • Koeth Collection – Reactors & Weapons
      • Koeth Collection – Games & Collectables
    • High Voltage & Pulsed Power
      • Blue Thunder
      • Jacob’s Ladder
      • Krytrons
      • Marx Generator
      • Electric Watermelon
      • Tesla Coils
        • Jay’s Tesla Coil
        • Variacs
      • Quarter Crushing
    • Plasma
      • Fusors
        • FUSOR I
        • FUSOR II
        • Scott's Fusor
        • Fusor Simulations
      • The Mirror Machine
      • Pinch Machines
        • Linear Pinch
        • Toroidal Pinch
        • Pinching
    • Spectroscopy
      • Alpha Particle Spectroscopy
      • Gamma Ray Spectroscopy
        • HPGe Gamma Ray Spectroscopy Education
        • HPGe Systems
        • Cosmogenic Be-7
        • NAS Wildwood Mystery
        • Autunite
        • Trinitite
        • Tc-99m : Cardiac Stress Test
      • Software & Hardware
        • Refurbishment of LN2 Dewars
        • DIY Matlab MCA
        • Amateur Canberra Spectroscopy System
        • Antique MCA
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          • Canberra Nim Modules
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