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2,5" x 2,5" NaI(Tl) gamma spectroscopy probe

DIY 2,5" x 2,5" NaI(Tl) gamma spectroscopy probe

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Here's a quite useful project for anyone is interested in studying radioisotopes, or just for experimenting with gamma spectroscopy. Since the very early tests, this probe revealed to be very sensitive to weak radioactive sources, allowing to build up a decent gamma spectrum in a matter of minutes.

CORE PARTS
The core of the system is a Russian 2,5 x 2,5 inches Sodium Iodide Thallium doped scintillator that can be found on eBay from many eastern sellers.
An Hamamatsu model R6233 photomultiplier fits perfectly the scintillation crystal size.

HOUSING
The housing is made by solid aluminium and it consists of four pieces only.
It has been designed to properly and precisely couple the Russian scintillation crystal to the PMT, ensuring the necessary magnetic shielding and light sealing.

BUILDING PLANS AVAILABLE.

PRINCIPLE OF OPERATIONS OF AN AMATEUR GAMMA SPECTROSCOPY SYSTEM

Image by Manticorp - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17598426


SCINTILLATION PROBE

A scintillator is a material that exhibits scintillation when excited by ionising radiation; the intensity of the scintillation is proportional to the incident gamma photon that has generated it.

In fact the light emitted by the crystal is so weak that requires to be amplified by a photomultiplier tube; the PMT ensures gain factors in the order of 10^5 times depending upon the supply voltage (up to 2.7x10^5 for R6233 @ 1000Vdc)


SCINTILLATION PROBE DRIVER AND ACQUISITION

The scintillation probe requires to be supplied by a device that provides very precise high voltage, low ripple and low drift output. Once decoupled by the high voltage, the output signal is fed to a low noise high fidelity sound blaster capable to acquire and sample the probe output signal.


MCA (Multi-Channel Analyser)

A typical MCA has a configurable number of channels that can be selected based on the number of amplitudes that have to be analysed; this mode is so called "pulse-height analysis" (PHA).

The resulting graph plot will be an histogram of frequency (input pulses in CPS or CPM) Vs. pulse amplitude; the graph represents the energy distribution of the radioactive sample that is being analysed.


MY GAMMA SPECTROSCOPY SET-UP

View all 12 components

View all 4 project logs

  • 1
    Step 1

    ENCLOSURE MANUFACTURING DRAWINGS

    • General assembly drawing


    • Photomultiplier adapter


    • Probe top cover


    • PMT locking ring


    • Probe outer shell

  • 2
    Step 2

    Wiring instructions for HAMAMATSU R6233 PMT

    Courtesy of Tom Hall from iRad

  • 3
    Step 3

    PMT AND SCINTILLATION CRYSTAL COUPLING

    COMING SOON!

View all 3 instructions

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Discussions

antiElectron wrote 06/20/2017 at 11:50 point

Hello, I've used silicone optical grease.

  Are you sure? yes | no

S. V. Paulauskas wrote 06/20/2017 at 10:22 point

What type of coupling did you use between the scintillator and PMT interface?

  Are you sure? yes | no

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