12V to 6kV High Voltage transformer

The primay power source in my home made X-Ray machine is an high-voltage high-frequency transformer. This transformer is drived by a Mazilli ZVS circuit and it’s capable to output 6kV from 12V. It’s input circuit uses a center tapped coil drived in balanced way by two mosfets of the ZVS, with input voltage feeded into the center tap. This gives balanced sinusoidal waveform on it’s output. Sin wave helps the “slow” high voltage diodes of the HV multiplier chain to turn ON and OFF correctly minimizing RFI generation.

Transformer characteristcs:

  • Nominal allowable output 4.5-7.5kV @ 10mA from 10-15V@ 8A
  • 50kHz working frequency
  • Completly encased in epoxy
  • ZVS drive. Primary winding is a center tapped coil
  • ETD54 N87 ferrite core ungapped and #B66396W1022T1 Epcos coil former
  • Primary winding 4+4 turns of 2.5mm2 wire
  • Secondary HV winding 1400 turns 0.2mm dia CuEn

The realization of such kind of transformer presents many challenging problems to be solved. First one is insulation. I’m using standard ETD54 horizontal plastic coil former.

This requires an 8mm clearance/creepage free space between every single layer of the secondary high voltage winding and the side walls.

The insulation between ferrite core and first layer is insufficent because Epcos coil former is not rated for 6kV. I’ve fixed it wrapping a first insulation layer of 4 turns of 0.2mm thick PTFE tape. Each layer is made winding side by side 100 turns of the enameled wire. In total I’ve 14 layers with 0.4mm thick layers of PTFE between each coil winding layer.

The primary is periferic and very far from inner core. The need of a massive insulation between secondary and primary resulted in 3mm total thickness of PTFE tape. I’ve feared that positioning it near the core coud let me not enought space for the primary into the coil former. Winding the primary on external side of the coil former gives me some clearance even I exceed the coil former sides height. The HV output terminals are soldered to silicon insulated HV cable rated 10kV and the whole transfrmer is encased into epoxy. This prevents any kind of corona effect induced disasters like arcing, fire and smoke and gives to the whole trafo a mechanical rigidity and protection. I’ve made a custom cardboard mould for this.

The top of the transformer is separate from the bottom of the cardboard mould by a couple of insulating paper risers of 10mm diameter to let the epoxy to fill every side of the transformer with sufficent thickness

Posted in DIY

X-Ray dental film ECO 30

Hello! I’ve tested this “Dentalfilm ECO30” and “Ergonomix” with my improvised X-Ray machine.

Them are self developing film for X-Ray imaging of dental implants etc. Them are relatively small like 35x24mm but are also extremly sensible, sharp and easy to use. A secure way to get some decent results from your X-Ray improvided machine. The small size results ideal for imaging of IC’s and insects. I’ve no insects but I’m full of IC’s so…

64kb 8bit SRAM from Z80 computer project in SSOP package

 

5W white led over 2mm alluminium heathsink. Sadly it moved during exposure

 

Generic TQFP IC

 

Posted in DIY

X-Ray machine V1

Finally I’ve made it! Yes, I’ve built an X-Ray machine for non destructive inspection of circuits and objects.

The level of radiation generated by this device is sufficent to induce cancer or radiation illness, please don’t build and don’t operate such device. There is also another risk: it requires very high voltage to be operated. It generates very high and potentially lethal voltages.

How it’s made this demostrative prototype of X-Ray machine?

Look at my device. From the left to the right you can see:

  1. HV generator, ZVS type, drives a TV type flyback transformer. It’s not used in flyback mode because ZVS outputs a pure sinewave so it’s just working  as standard high frequency transformer. It’s output it’s around 15kV with 16V drive voltage. The ZVS diver starting voltage is 7V so, changing the voltage into the range 7-32V I can select output voltage. The whole assembly is enclosed into an electrical juncton box and insulated with silicon gel.
  2. SHV 6 stage voltage multiplier. This part it’s made with a 6 stage voltage multiplier enclosed in epoxy. It takes the 15kV input and multiply it x6 to the output. It’s maximum output voltage with 16V input to the ZVS is 90kV. I’ve operated it to 120kV maximum without any troubles for diodes and It’s scarry!
  3. X-Ray tube. This unit is a generic replacement for medical use. It’s a surplus tube from Ukraine and was made during soviet era. The big copper disk on the bottom is the anode. The two black wires on the top are the filament wires. You have to connect one of the two leads to the multiplier GND in order to provide a return path to the catode for the electrons that will circulate into the tube during operation.

How to generate X-Rays?

Basicly you just need to properly feed an X-ray generator tube. What it needs to be happy and hot? A proper high voltage for the anode and enought current flowing into it’s filament to heat the catode.

The heated catode generates a cloud of electrons around it that are accellerated to the anode by HV. When they reach the anode, the hit force is enought to convert some of them into X-Rays.

The ZVS driver, the HV flyback, capacitors and diodes used for the high voltage multiplier where bought from highvoltageshop.com

You can see a similar schematic of the ZVS sold by them:

The high voltage multiplier is made stacking 6 Cockcroft-Walton voltage doubler circuits.

Some more pictures of the multiplier and the X-Ray tube:

 

Using an X-Ray image intensifier screen positioned after the item to be inspected, you can take pictures of the shadows left where X-Rays cannot pass the object or are attenuated. Higher density appares as higher density shadows on the improvised “fluoroscopy” screen. You can get a proper X-Ray intensifier by scrapping an X-Ray medical cassette. Medical X-Ray casettes have glued on  inner sides this kinds of screens. Them are sold on eBay with specified emission color and sensibility like blue or green fluorescence emission ORTHO 100 or 400.Look at the pictures below.

 

Carefully regulating high voltage and filament current, you can generate X-Rays into a broad range of energy so you can “trim” them to acomplish the needed job. For metallic objects you’ll need higher voltages, for insects you’ll need much lower voltages… you have to experiment. I stronly recomand the use of a CCTV circuit to see what appares into the fluoroscopy screen from a protected remote location like a different room. You can use a standard analog BW CCTV camera and a cheap LCD screen that accept AV input. It’s usually a yellow RCA female connector on the screen back or side. Use a remote control of the HV generator. You can leave filament turned ON but stay away protected by at least a concrete wall during operation.

This is how looks an X-Ray intensifier screen that have blue characteristic. It’s a very fine grain screen. You can notice that the subject it’s a BDEG scintillation probe. The NaI(Tl) crystal on bottom it’s very dark because of it’s high density. The 1mm alluminium enclosure is clearly visible but it still permit to see the glass photomultiplier tube. Look how much free space there is between photo katode and first dynode! The glass body of the PMT is very evident. You can see also on the lower end of the image the yellow light emitted by the filament of the X-Ray tube. To protect the X-Ray intensifier for this light I’ve glued on it’s back a black cardboard pannel but… some light leaked!

Posted in DIY

CsI(Na) cutted and polished at home

June 2020. After some time searching around on the net for a scintillation material that I can shape at home, I’ve found a Dutch guy called Luuk that have some CsI(Na) crystals avaiable for free to make experiments. A couple of emails with him and voilà…. I’ve just received a nice piece of raw CsI(Na) crystal from him (Scionix?). Thank you Luuk!!! Sadly the crystal quickly cracked because, probably, thermal shock during transport. Summer is summer and postal services are not famous for the good handling of the crystals.

I’ve soon realized, carefully looking at the fractures, that I can cut out the intact middle section of it. That part will be “enclosed” with some PTFE white ribbon as reflecting layer and coupled on a fece with a PMT to make spectroscopy tests.

I’ve cutted out the intact part using a small arc saw made for modellism work with very fine teeths. It’s a good idea to handle the crystal with gloves to be sure to not pollute it.

The “rough” grinding of the crystal faces was made with 400 size sandpaper till I’ve get an almost rectangular shaped crystal.

Even with this rought grinding of the crystal faces, it coupled to a FEU85 PMT gives me 8% FWHM. The FEU85 used have 7% PHR at Cs137 peak.

I’ve finally decided to take a spectra of my pitchblende sample to see how does it perform and I’ve got a very nice result. I will try polish it even better and compare the results to see how much the crystal level of polishing affects it’s FWHM.

 

DIY Scintillation probe: 63x63mm NaI(Tl)

Some time ago I’ve won a 63×63 NaI(Tl) crystal for around 80€ at eBay. It is an SDN52 a special crystal designed to be heat and vibration resistant. Let’s build a probe with it and a 76mm photokatode XP2421/SQ PMT

63×63 Scintillator

First problem to solve was how to tightly couple this heavy crystal with this PMT? I’ve solved it with the help of my 3D printer: I’ve designed and printed a fitting with TPU that’s a kind of rubber filament material. STL zip file: gasket  password: madexp

And now let’s put all togheter.

The PMT
The crystal
The assembly

Finally I’ve soldered in place the dynode chain voltage divider PCB.

 

After covering the tube with black tape I am ready to test it.

The result is a nice 7.5%-8% FWHM @ Cs137 peak

SI-31G geiger

This is the biggest geiger tube I have seen! I’ve bought one for 25€ at eBay.

Glass tube, thermostable. Cathode: tungsten powder.

  • Length of the plateau: not less than 200V
  • Slope of the plateau: 0,07%/V
  • Recommended working voltage: 900V
  • Dosimetric characteristics N = 0.1 imp / min · cm2 at 1 microR / s              Nmax = 2 · 104 Nf = 31
  • Service life: impulses 5·107
  • Range of working temperature: +10 / +250 °C
  • Dimensions: ∅27 x 400mm 92g

 

 

Lead castle

A lead castle, also called a lead cave or a lead housing, is a structure composed of lead to provide shielding against gamma radiation in a variety of applications in the nuclear industry and other activities which use ionizing radiation.

This is what Wikipedia says about lead castle. In fact, to make gamma-ray spectrometry of samples of very low activity you’ll need to use a lead castle. You can see the gamma rays emitted by your sample to be measured as signal and background radiation as noise,  using a lead castle, it will shield your sample from background radiation improving signal/noise ratio of your measure. I’ve built mine from a camping inox stove, a tin can and some lead scrap.

First thing to do is search for a good inox stove of proper shape, it will be the external container of the lead castle. Second thing is buy a tin can of proper size to be burried inside the castle. It will become the inner wall of the well.

Is a good idea to cover the external surface of this tin an with 1mm of copper foil. It will supress the xray generated by the interaction of gamma rays from the sample to be tested and lead shield.

You can melt some lead with a torch into a proper steel can and pour it to form the lead shield. First, do this outside! Lead is cancirogen so, better to handle it with gloves and in open air.

I’ve then poured a 16mm thick lead shield to form the bottom of the lead castle.

Then I’ve puttend iside the inner tin can blocking it in place with the help of a 10kg hammer positioned over it. Remember the hydrostatic lift force! Lead is ultra dense, the lifting force generated by the lead displacement caused by the little tin can must be neutralized via an heavy weight object positioned over it. Finaly complete the castle pouring molten lead into the walls. This is the final result.

It will take many hours to coold down. I’ve tested it’s effectiveness putting inside it a Cs137 calibration source and measuring it with my 40x40mm NaI(Tl) scintillation probe. I’ve made two measures, one from inside and one outside the castle, keeping constant the distance between the source and crystal. Result? Take a look at the following picture.

 


Matthias Doe sent me some pictures of how his made it’s lead castle. Take a look and thank you Matthias!

This is the final result
Posted in DIY

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!