OST 40x40mm NaI(Tl)

I’ve finally tested my brand new 40x40mm NaI(Tl) crystal from OST making with it a new probe for my lab. This time I’ve tested epoxy glue for assembly. The dynode voltage divider is home made via a simple toner transfert/etching process.

First thing to do is to glue the crystal inside it’s aluminium housing with some epoxy glue. I’ve simply used a 46mm internal diameter, 50mm lengt aluminium pipe as coupling pipe. It’s external dimensions are 50mm and it will fit the inner diameter of the main probe pipe.

The crystal outer diameter is 45mm, the 1mm total clearance between coupling pipe and the crystal is filled with epoxy by placing the glue around the crystal body and sliding it into position. Next thing is to couple the crystal with the PMT and block in position with some tape.

Now some more epoxy….

And then I’ve slided the assembly inside the body pipe until it will block against the blue tape. As you can see the yellow and blue tape are simple a note of color and the blue one is used as sliding-stop reference mark.

After few minutes the glue will be hard enough to test the assembly. I’ve added a BNC terminated cable soldering the cable into the voltage divider pads, needed 1000V from my USB PMT Adapter and placed a piece of uraninite under it to take a spectra.

A very nice result!!!! Around 8% FWHM but this could be improved because the PMT was exposed to light during assembly and it’s noisy so it will take a day to rest. Today I’ve finally verified it with Cs137

7,8% FWHM but the software is not catching the correct peak position. I can expect a 0,5% FWHM error. This means 7,3% FWHM of the crystal. Not bad, not bad at all!!!

Trinitite HPGe spectrum

Some months ago I’ve bought a trinitite sand from United Nuclear. They’re website description say:

Early in the morning on July 16th, 1945, the first Atomic Bomb was detonated at the Trinity test site in the New Mexico desert. The nuclear explosion produced a blast equivalent of 18,000 tons of TNT and a ½ mile diameter fireball – with a temperature over 10 million degrees Fahrenheit, far hotter than the surface of the Sun. The intense heat melted the New Mexico desert sand into a light green, glass-like substance which was later named “Trinitite”. The resulting crater lined with Trinitite was buried for security reasons not long after the explosion.

In a couple of weeks I’ve received this vial full of Trinitite grains.

I’ve tested it under UV light but this material not present any fluorescence. The second test is obtain a gamma-ray spectrum from it in order to see if it’s a fake or not. I’ve used my 30×40 NaI(Tl).

The scintillation crytal have a center well made for vials. In this way low energy gamma rays are collected by the crystal at the highest efficency. After several hours of analysis the result spectrum shows clarely Americium and Cesium isotopes made by neutron activation during the bomb explosion. This sand is real nuclear melted sand!!!

The first left peak is Americium and the small peak at 609keV are Bismuth and Cesium isotopes. My crystal have good sensibility but an FWHM of 11% is not enought to extract any fine detail.

UPDATE 10 October 2019

I’ve made this test again with a 63x63mm NaI(Tl) scintillation probe enclosed into a 50kg componible lead shield. The result is amazing!!!

Americium, Europium, Cesium and Potassium isotopes from the neutron activation are quiet recognizable.

My friend Stanislav Prytuliak had made a test of a trinitite sample bought on eBay using the HPGe spectrometer at Karlsrhue university.

The following picture is Copyright by Stanislav Prytuliak (C) 2019 and couldn’t be reproduced. The following picture is published by his permission.

Final conclusion? The trinitite sample is not fake!