need a simple way to detect charge of radioactive particle other than electroscope

May I assume that your use of the word "oscilloscope" is a result of your spellchecker mangling the word "electroscope?"

Instead of giving up, you should figure out why it is that you cannot get an electroscope to function when electroscopes have been working fine for everyone else for the last 250 years. Could you descibe your electroscope and radiation source, what you expected to happen and what actually happened? I will be glad to help you figure out what went wrong.

Look here:

If you are bound and determined to use another method, here is one:

...but you will have an easier time getting an electroscope to work.

--
Guy Macon

A 2N7000 mosfet, just a few cents, could be made into a decent charge detector. Use it as a source follower, driving a voltmeter. Connect its gate to an 'antenna', maybe a coin or something. Charge the gate to some small positive voltage and it should stay put for hours or days. Whacking it with alphas or betas will trap the charges and change the voltage.

You'll have to do the math to see if your available sources have enough intensity to produce a useful effect.

Gammas don't have charge.

The advantage of an electroscope is that it collects ambient ions form a considerable volume of air, so has charge gain and can detect gammas. But then, it won't distinguish the polarity of incoming charged particles.

John

Given that it costs only about 30 eV on average to ionize an air molecule, and that your radioactive source is emitting alphas and betas of at least several hundred keV, the task is going to be how to distinguish between 20,000 electrons + 20,001 positive ions and 20,001 electrons and 20,000 positive ions. This is a much harder problem than I think you realize--I wouldn't know how to approach it unless the source were very, very small and levitated in a vacuum.

The reason for cloud chambers and such things is that an applied magnetic field will cause the particle to spiral, giving good info on its charge, mass, and energy.

Electroscopes detect the air ionization due to the radiation, not the radiation itself--alphas and betas both cause the electroscope to discharge, regardless of polarity.

Cheers,

Phil Hobbs

Links 101: If you strip off the #2 part, there is no need to *scroll to the top of the page*.

As Phil points out, there will be a lot more ions around from air ionization than there will be primary charged particles. 1 uC is 3.7e4 nuclear zaps per second, only a fraction of which emerge as usable charged particles. Even being optimistic, 1e4 unit charges per second ain't much current to detect... way under one pA.

Assume a 10 pF pickup plate, and 1e4 charges/sec. That'll change the voltage about 160 microvolts/second, nasty but not impossible to detect, but you would have to do it in vacuum to avoid being blinded by air ions.

Some things just aren't easy.

I've gotten dramatic effects from an aluminum-foil electroscope and a smoke detector source, but that's detecting secondaries, air ions, mostly.

John

Pour some salt into a watch glass and wait a couple of hours. If it dissolves into recovered atmospheric water, your humidity is too high.

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You mean like the device here (scroll to the top of the page):

This uses a MPF102 in the configuration you describe. As you mention, the thing I'm wondering about is sensitivity and I wonder if the bulb will grow brighter when detecting aphas and dimmer when detecting betas (or vice versa). At least a device like this might be a rough indicator of charge. In the presence of gamma, the bulb wouldn't light. The sources I have are the 1 uC plastic embedded sources available commercially and I have samples of gamma and beta emitters. No alpha, but I'm thinking of using a smoke detector source.

Thoughts?

Jon

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Yes, sorry about that. I feel pretty dumb for letting that slip in there :(.

Today, I built the electroscope you linked to here:

Unfortunately, still no results. I tried the comb test as described and nothing. Basically, for part of my lesson, I just want to show that alpha and beta radiation has charge as I'm no longer concerned with trying to determine polarity. The sources I have are small, plastic embedded discs of

1 uC beta and gamma emitters. I lack an alpha source, but I am thinking of using Am 241 from a smoke detector. I have tried bringing the beta source up to the top of the electroscope, but no result. As I can't get the electroscope to work anyway, I don't know if the reason is due to too weak of a source or just a fault in the electroscope itself.

My other option, also presented in this thread, is to try using a sensitive FET transistor circuit to detect charge:

(scroll to the top of the page) This circuit has the advantage of simplicity and might actually detect the small charge from the apha/ beta sources. Perhaps polarity also as if negative, maybe the bulb would dim (?). Of course, I don't know, but if there's any chance this could work, it would be a great substitute for the electroscope. Thoughts?

Jon

If it is, look here:

The foil has to be very thin. When I was kid I made one with foil removed from gum wrappers. I removed the foil from the gum wrapper using a clothes iron. I would heat it up and slide the foil off. It's much thinner than household aluminum foil.

You might also consider using the mantel from a Coleman gas light. It has radioative thorium in it. My old wristwatch has radium coated hands and numerals; lights up geiger counters nicely. I wonder what would happen if I wore it when I went to the air port?

Al

I wouldn't do this - Am 241 tends to get into your bones if it gets into your body (through the skin, inhaled or ingested). It has a half-life of several human lifetimes so it will be there for a very long time. While alpha radiation can't get past your skin (or even a few inches of air) when outside the body, once inside it can do real damage - like bone cancer. It's better to use an off the shelf encapsulated source as your are for beta and gamma radiation.

Big John

Have you considered the effects of secondary ionization in the air that may be taking place that will generate both + and - ions? If you can make a sensitive particle detector, then you might could pass the particles between two charged plates and see which direction the particles are deflected. Kind of like the electron gun in a TV setup.