need a simple way to detect charge of radioactive particle o

J

Jon Hightower

Guest
The subject of this thread says it all. I am teaching a summer class within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of radiation
emitted (alpha, beta or gamma). I have tried using an electroscope, which
would have been ideal, but I cannot get the unit to function. Therefore, I
can't depend on this as a detector during class. Remember that I am seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?

Thanks,
Jon
 
Jon Hightower wrote:

The subject of this thread says it all. I am teaching a summer class within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of radiation
emitted (alpha, beta or gamma). I have tried using an electroscope, which
would have been ideal, but I cannot get the unit to function. Therefore, I
can't depend on this as a detector during class. Remember that I am seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?
Click to expand...
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:
http://pbskids.org/zoom/activities/sci/electroscope.html
http://www.nfinity.com/~exile/electro.htm
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
http://www.hep.princeton.edu/~mcdonald/examples/ph104_2004/ph104_exp01.pdf

If you are bound and determined to use another method, here is one:
http://www.amasci.com/emotor/chargdet.html
....but you will have an easier time getting an electroscope to work.

--
Guy Macon <http://www.guymacon.com/>
 
Guy Macon wrote:
Jon Hightower wrote:


Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?


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.
Click to expand...
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
 
On Mon, 25 Jul 2005 06:35:17 GMT, "Jon Hightower" <erols@ez.net>
wrote:

The subject of this thread says it all. I am teaching a summer class within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of radiation
emitted (alpha, beta or gamma). I have tried using an electroscope, which
would have been ideal, but I cannot get the unit to function. Therefore, I
can't depend on this as a detector during class. Remember that I am seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?

Thanks,
Jon
Click to expand...

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
 
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:ve0ae154ro7ueseqbkpvgksgsc4rvfup6q@4ax.com...
On Mon, 25 Jul 2005 06:35:17 GMT, "Jon Hightower" <erols@ez.net
wrote:

The subject of this thread says it all. I am teaching a summer class
within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of
radiation
emitted (alpha, beta or gamma). I have tried using an electroscope,
which
would have been ideal, but I cannot get the unit to function. Therefore,
I
can't depend on this as a detector during class. Remember that I am
seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?

Thanks,
Jon



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.
Click to expand...
You mean like the device here (scroll to the top of the page):
http://amasci.com/emotor/chargdet.html#2
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


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
Click to expand...
 
"Guy Macon" <http://www.guymacon.com/> wrote in message
news:11e95nmkug15cef@corp.supernews.com...
Jon Hightower wrote:

The subject of this thread says it all. I am teaching a summer class
within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of
radiation
emitted (alpha, beta or gamma). I have tried using an electroscope,
which
would have been ideal, but I cannot get the unit to function. Therefore,
I
can't depend on this as a detector during class. Remember that I am
seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?

May I assume that your use of the word "oscilloscope" is a result of
your spellchecker mangling the word "electroscope?"
Click to expand...
Yes, sorry about that. I feel pretty dumb for letting that slip in there
:(.


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.
Click to expand...
Today, I built the electroscope you linked to here:
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
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:
http://amasci.com/emotor/chargdet.html#2 (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
Look here:
http://pbskids.org/zoom/activities/sci/electroscope.html
http://www.nfinity.com/~exile/electro.htm
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
http://www.hep.princeton.edu/~mcdonald/examples/ph104_2004/ph104_exp01.pdf

If you are bound and determined to use another method, here is one:
http://www.amasci.com/emotor/chargdet.html
...but you will have an easier time getting an electroscope to work.

--
Guy Macon <http://www.guymacon.com/
Click to expand...
 
A 2N7000 mosfet, just a few cents,
could be made into a decent charge detector.
John Larkin

You mean like the device here (scroll to the top of the page):
http://amasci.com/emotor/chargdet.html#2
Jon Hightower
Click to expand...
Links 101:
If you strip off the #2 part,
there is no need to *scroll to the top of the page*.
http://amasci.com/emotor/chargdet.html
 
On Mon, 25 Jul 2005 17:01:00 GMT, "Jon Hightower" <erols@ez.net>
wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:ve0ae154ro7ueseqbkpvgksgsc4rvfup6q@4ax.com...
On Mon, 25 Jul 2005 06:35:17 GMT, "Jon Hightower" <erols@ez.net
wrote:

The subject of this thread says it all. I am teaching a summer class
within
the next week and I need to show the class a way to determine the charge
emitted from a radioactive substance so they can infer the type of
radiation
emitted (alpha, beta or gamma). I have tried using an electroscope,
which
would have been ideal, but I cannot get the unit to function. Therefore,
I
can't depend on this as a detector during class. Remember that I am
seeking
to determine charge only, not just detection in general which a Geiger
counter would do. And, yes, part 2 of the lesson will involve using
shielding of various thicknesses to conclude what type of particle is
emitted.

Any ideas for a charge polarity detector other than an oscilloscope-
something that's cheap?

Thanks,
Jon



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 mean like the device here (scroll to the top of the page):
http://amasci.com/emotor/chargdet.html#2
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
Click to expand...

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
 
Jon Hightower wrote:

Today, I built the electroscope you linked to here:
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
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.
Click to expand...

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.
 
Aubrey McIntosh, Ph.D. wrote:
Jon Hightower wrote:

...I can't get the electroscope to work...

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.
Click to expand...
If it is, look here:
http://www.drypak.com/index.asp?cat=62101
 
In article <11ealp8qkalom2f@corp.supernews.com>,
"Aubrey McIntosh, Ph.D." <newsposter@spam.vima.austin.tx.us> wrote:

Jon Hightower wrote:



Today, I built the electroscope you linked to here:
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
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.



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.
Click to expand...
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 lack an alpha source, but I am thinking of
using Am 241 from a smoke detector.

I wouldn't do this - Am 241 tends to get into your bones if it gets into
Click to expand...
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
 
On Mon, 25 Jul 2005 17:09:55 GMT, "Jon Hightower" <erols@ez.net>
wrote:

Today, I built the electroscope you linked to here:
http://www.geocities.com/CapeCanaveral/Hall/1805/electroscope.html
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:
http://amasci.com/emotor/chargdet.html#2 (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?
Click to expand...
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.
 
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