Build an Ion Chamber Project with Filip: Tips & Experiences

[Filip1997]

Hi all I am a 17 years old student and I want to make a ion chamber to measure the ultraviolet radiation in the stratosphere. My project will be connected to a balloon that will fly to a 30 km height. I am going to make our first prototype with my team it will be the most basic ion chamber:

I got some information about how the chamber works so when the ultraviolet radiation passes through air collision with the air molecules produce ion pairs the positive pair will go to the wire in center of my tin and it will create a very small current but the current is to small as we could measure so we have to amplify the voltage so we can measure the voltage.

I saw also that the tin should be closed with aluminium foil so that it don't let's too much stray electric field in, but I will measure it in big heights so I think I can leave it open please correct me if I am wrong and if you have some tips and expirience with building ion chambers I could need help.

Thank you, Filip.

 

[dlgoff]

I'm glad to see you started this thread but wanted you to see an alternative for measuring ionizing radiation. Perhaps two methods could be used and compared. Very ambitious project that make me proud to be here.

 

[Filip1997]

I'm glad to see you started this thread but wanted you to see an alternative for measuring ionizing radiation. Perhaps two methods could be used and compared. Very ambitious project that make me proud to be here.

I found a tutorial page for the scintillation counter it uses Arduino to save data (I am expirienced in arduino) http://www.instructables.com/id/Real-time-Radiation-Detector-Scintillino-test/?ALLSTEPS it says I need a but he says that the Silicon photomultiplier and the silicon crystal costs 100$ each that's a bit too expensive for us. So can I make it cheaper or?

 

[dlgoff]

Sticking with the subject of this thread, I found this Geiger Counter Kit - Radiation Sensor for $100. Would this be in your price range?

http://www.electronics-lab.com/blog/wp-content/uploads/2011/10/geigercounterkit_LRG.jpg

 

[Filip1997]

Not really dlgoff we are normal students and its a hard time in Croatia (my country), we can do something like 25$. I liked the ion chamber project because its interesting and its cheep to make. We don't have any financial support from our school. For the ion chamber we only need a tin some transistors, resistors, arduinos (micorontrolers). Thank you for your interest in our project and for your help I hope you understand our financial problem.

Thank you, Filip.

 

[Mike_In_Plano]

It seems you started out wanting to measure UV, but deviated to measuring ions as an indirect measure of UV. Then, we have suggestions for measuring ionizing radiation.

It poses the question, are any of these means representative of what you wish to measure considering the other effects that are going on in the background?

I'd suggest starting with an inexpensive, run of the mill PIN photo-diode. For large area work, I prefer the VBPW34S. It won't have much sensitivity at 200-300 nm, so that's where a bit of glow in the dark material needs to be cut and placed in front of the diode to convert invisible UV to visible green.

Since you only want the light caused by the UV, and not other colors, you'll need a piece of UV filter glass in front of the glow in the dark piece. You can use a high-quality filter, such as the 355BP40 (currently on Ebay for $75) or you can use a couple of pieces of filter glass to achieve the same effect with less heartache.

High quality filters are subject to scratches and damage by fingerprints, so they are difficult to cut and grind. Some filter glass is sensitive to finger prints, but you can wear cloves and use an ordinary glass cutter to engrave marks into the glass then tap it or bend it from behind to get a clean break (consult youtube.) If desired, you can grind away the corners to make round filters using a bit of oil and 600-800 grit silicon carbide sand paper on a smooth, hard surface. Just be careful to do so away from living areas, family, or pets. Use Latex or Nitrile gloves, and clean the work area thoroughly afterwards.

As to getting filter glass, your best bet is to make friends with a Schott glass distributor. I'd recommend reading a bit about his company and products and share your interest in the project and the technology. Chances are, he'll gladly mail you a sample kit.

The filter glass you'd need is UG-11 (UV dominate filter) and S-8023 (Green dominate filter). The UV filter removes blue, green, and the shorter wavelengths of red. The only thing that can excite the glow in the dark layer is the UV, however, the longer wavelengths can leak through UG-11 and the glow in the dark material and cause erroneous readings. That is where the S-8023 filter comes in. It sits between the glow in the dark material and filters out almost everything except for the desired green light which goes on to excite the photo-diode. :)

To process the result into a useful signal, you should build a transimpedance amplifier to convert the output of the photo-diode into a useful voltage.

Analog Devices and Linear Technology have notes regarding TI amplifiers with photo-diodes.

One other thing. If you're looking to take this thing high, the electronics may fail due to the cold. The energizer lithium batteries hold up better in the cold, and you can test you equipment after leaving it in the freezer, but watch out for water condensing on your boards and making them fail. You may also place the works in a Styrofoam container to slow down the cooling.

Best Luck,
Mike

 

[Filip1997]

Hey Mike is this what you described a semiconductor detector?
And thank you for the tip with the idea to make friends with a Schott glass distributor. Without getting that 75$ part I think we could not build that :)

 

[Mike_In_Plano]

In a general sense, it's a semiconductor-based light detector. However, there is a different class of semiconductor detectors that are used to detect high energy photons an particles.
The detector I subjected is a type of diode an N-doped layer, a thin layer that's not doped, and a P-doped layer. If you use the diode test function on a volt-ohm meter, you'll find that it conducts electricity in only one way - like a normal diode. If you attach it to a voltmeter and expose it to light, you'll see that it also works as a `photo-voltaic cell. If you apply a small reverse bias voltage across the Pin diode (>=2V) you'll see that the current flowing through it is proportional to the light that falls on it.

Now, as to the other semiconductor detector, it's typically a pure semiconductor with a voltage applied across it. When I high-energy photon or particle comes crashing into it, it releases a number of holes and electrons which drift towards the terminals. The more energetic the photon, the more charge carriers are released. Thus the operator can tell what wavelength the photo was by the amount of charge that pulses through the crystal.
Since ordinary heat releases holes and electrons as well, these detectors are sometimes cooled by liquid nitrogen. The most awesome part of these detectors is that they continue to report the various wavelengths of photons that they experience, and the charge versus frequency of these photons will form a histogram whose shape tells about the sources and concentrations of the emitters of the radiation. This is extremely useful in industry for fine tuning metal alloys. By irradiating a piece of test metal and documenting it's returned X-rays, you can determine the ingredients.

 

[Filip1997]

Thank you Mike if we can manage to get the fillter for free I think we will make somethink like you descibed. When you sayed Schott glass distributor could send us a sample kit what woud be in there? The filter?

 

[dlgoff]

I'd suggest starting with an inexpensive, run of the mill PIN photo-diode.

Good call.

If you're looking to take this thing high, the electronics may fail due to the cold. The energizer lithium batteries hold up better in the cold, and you can test you equipment after leaving it in the freezer, ...

This is really good info.

@Filip1997
Infant Mortality and Burn-in
Normal Life and Wear-Out

 

[Filip1997]

Hi Mike we contaced Schoots glass distributor and we wait for their response now but can you confirm me something. Is this how it schould look like?

Is it right like that or did I miss something? And also I found Some mill PIN photo-diodes on Ebay but there operating temperture is to -40 C so can I use them?

 

[Mike_In_Plano]

The drawing is close, but you'd need some fluorescent material between the two sheets of filter glass to down-convert the UV into green.

The temperature probably won't make much difference to the PIN diode, but may create difficulty due to offset in the amplifier.

Also, I found that TI has chip that performs most of these functions, the OPT3001. It has an optical bandwidth filter that serves in place of the S-8023, a PIN diode, an amplifier,and an A/D converter. It uses an I^2C interface, so you would would need a processor and some programming to interface. This chip would still need a UG-11 filter and fluorescent material. NOTE - this chip requires a PCB and a highly skilled technician to solder it.

Also, Ti has always been very friendly about samples of 1-2 parts :-)

I also found an IC that is tuned to measure UV, the Rohm ML8511-00FCZ05B

Again, soldering these ICs is a trick. You can get an adapter board but soldering the leads may prove difficult. Generally, it's best to find a shop that has a surface mount rework station to perform the soldering.

 

[Filip1997]

Hi guys I want to show you my first prototyp for my ion-chamber (first) thank you on your support and help!

 

[Filip1997]

I found a web page that has good documentation about building ion chambers there I found a schematic so I wanted you guys to check it first before I start ordering anything here is the picture:

For the VDC I thought using a digital voltage sensor like this one:

 

[Baluncore]

How will you decide which way to aim your UV detector?

Is the balloon flight only during daylight? There will be very little UV at night.

The advantage of counting ion charge is that it relates to pollution levels and the vertical distribution of condensation nuclei that can initiate rainfall. It also works at night.

 

[Filip1997]

Yes the balloon is flying only at day so the UV will not be a problem I thought of placing my UV sensor at the top of the project. Also I wanted to ask does the pressure have a role because it is lower than the normal atmosferic pressure I found that it will be 1/100 of normal pressure(101396Pa) or is it only the height and UV growing and what do you think about the schematic will it work like that?

 

[davidbuday]

Hello everyone, I am David and I am in this poject with him...I saw he has forgoten about this thread and we have more questions.
There is a problem with presure. Our ionization chamber needs to be open from both sides so the can doesn't get smashed under stratospheric preasure...how will that affect our measurmants, can we generaly make holes or the project won't work

 

[Mike_In_Plano]

I don't know how ambient pressure will effect your ion count, but that circuit will be very sensitive to temperature...
I don't perceive any means to trace your ion detector back to any measure of UV...
I'd stick with a UV sensor or a UV pass filter with a piece of fluorescent material, and a second filter to pass the glow from the fluorescent. Then measure the light...

 

[Baluncore]

There is no question that UV will increase with altitude. The problem will be finding somewhere without shadows that maintains it's orientation relative to the sun.

X-rays and cosmic rays would use a sealed ionisation chamber like a GM tube, or a scintillation counter.

Charged ions could be measured by using an open cylinder with a coaxial electrode. Sucking air with a fan through the tube, the current flowing in the centre conductor would measure the charge available as the mass of air moves along the tube.

So what do you plan to measure, UV, X-rays, cosmic rays or charged ions.

 

[davidbuday]

UV is not an option. This is simply an ionization chamber which means we will be measuring ionizing radiation :D

"Charged ions could be measured by using an open cylinder with a coaxial electrode. Sucking air with a fan through the tube, the current flowing in the centre conductor would measure the charge available as the mass of air moves along the tube."
Is the fan really necessary ? We are just trying to make this thing working open both sides becouse of the preasure

The main problem is we have to do this all in 150g :) we can fit all that but i don't know if we can put fans and other things too

 

[Baluncore]

Air is ionised outside the tube by radiation. Then air is sampled and charge measured as it passes through the tube.

Is the fan really necessary ? We are just trying to make this thing working open both sides becouse of the preasure

The tube could be made from paper, aluminium foil and paint as glue, so it would weigh only a few grammes. The fan only needs to keep the sampled air moving through the open ended tube so that the (total ion charge) / (mass of air moved) can be sampled. Air pressure gives density so mass flow through the open tube can be measured from either a speed and density or a mass flow meter.
If the tube has fins and thin wire gimbals so it can align with the “wind”, then as the balloon rises, airflow will be self induced. Fan can be very light weight and is only needed for low rates of climb if induced airflow falls below a minimum speed. Fan needs to suck gently so it does not contaminate air entering tube.

As I asked, at some point you must decide which atmospheric parameter(s) you are going to measure. Once that decision is made you can work on a suitable design. When must you make that group decision? Planning is important. Do you have a time-line for management of your team's project?

 

[davidbuday]

Deadline is 16.04.
We want to get measures as close to the geiger counter vs altitude (ascent). :)
So we measure ionizing radiation.
The design as you said will decide what we will measure becouse if we can't make an open can from both sides then preasure will crush it.

 

[Filip1997]

Baluncore is this possible, we will make holes on the other side of our can and so the air can flow but we don't need any fen because our project will gain atlitude and we will mount it so the openings will be vertical and the air will be flowing through and we will meassure charged ions. Is it possible like that?

 

[Baluncore]

Air is ionised outside the tube by radiation. Then air is sampled and charge measured as it passes through the tube.

The ends of the tube must be completely open.

We want to get measures as close to the geiger counter vs altitude (ascent). :)
So we measure ionizing radiation.

I was suggesting you count charged particles in the atmosphere. They become charged when hit by ionising radiation. The ions can be extracted from air as it flows through the open ended tube. Pollution will increase ions that may be ionised by UV. Ions will be distributed at different heights.

A Geiger counter tube is closed to the atmosphere and contains inert gas. It counts particles that pass through a thin window. What has a Geiger counter tube got to do with it counting ions in the atmosphere?

We are just trying to make this thing working open both sides becouse of the preasure

The design as you said will decide what we will measure becouse if we can't make an open can from both sides then preasure will crush it.

Rising altitude reduces pressure. Differential pressure becomes greater as altitude increases. But it can only increase by one atmosphere, 101kPa or 14.7 psi. If your can was sealed it would expand slightly, not implode. Implosion would occur if you sank it in the ocean.

Baluncore is this possible, we will make holes on the other side of our can and so the air can flow but we don't need any fen because our project will gain atlitude and we will mount it so the openings will be vertical and the air will be flowing through and we will meassure charged ions. Is it possible like that?

You need to know how much air flows through per unit time. If you suck with a fan then flow is probably OK. You cannot rely on orientation of the detector. How will you measure the rate of flow? By mass flow sensor or by volume per time?

 

[Filip1997]

Hi all after some time of work I made this much:

So I put it all together like you can see in the pictures. When I just power up the ion-chamber the the voltmeter shows me the voltage of 4.5V and after a while it comes to 1.5V-3V and I'm confused about it. Should it not have a stable voltage?

Board:

Voltmeter and SD card adapter:

Ion chamber (from outside and inside):

Battry to power all things:

 

[Baluncore]

An “electrometer” amplifier measures very low currents. There are techniques necessary to maintain high levels of insulation with very low leakage. For example, an electrometer is usually operated with the input lead bent away from the PCB. Where you use glue at the hole through the end of the can, the glue will attract moisture and short circuit the ion collection. Both ends of the can need to be removed. The central wire should be supported on a thin polycarbonate or polystyrene thread or cross member at each end. I would expect at least 100V DC on the centre electrode since it must accelerate the ions prior to collection on the wire.

It is a bit difficult to comment on your observations without an annotated circuit diagram. Please attach one to your next post.