Date: Fri Feb 9 10:14:03 2007

Author: Cliff Bettis

Subject: Re: Discharge Electrometer w Alpha Source

Post:
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Sam,

The alpha particles leave a trail of ionization in their wake. Both =
positive ions and free electrons. The alphas themselves don't go far (a =
couple of cm or so) before becoming balloon fodder (neutral helium =
atoms). It is the charge in the ion trail that is attracted to the =
charged object to neutralize it, as the other signed charge is repelled. =
You can see the ion trails if you use a cloud chamber with an alpha =
source. If you had to depend on just the charge value of the alpha =
particles to neutralize, say, a negatively charge object, you would need =
a truly scary source. Consider how many alphas it would take to make up =
even a fraction of a microcoulomb of charge and what activity would be =
required to produce that charge in a reasonable time. So it is the =
ionization the alphas produce that does the discharging not the charge =
of the alphas directly.

Cliff
----- Original Message -----=20
From: Sam Sampere=20
To: tap-l@lists.ncsu.edu=20
Sent: Friday, February 09, 2007 8:34 AM
Subject: Re: [tap-l] Discharge Electrometer w Alpha Source


How much of the discharging is due to the probe interacting with the =
particles, and how much due to ionized air leaking off charge. I would =
think that an alpha source would leak charges off a positively charged =
electroscope the latter way. I think we had the same kind of =
conversations when we discharged a zinc plate with uv light.=20

=20

Comments please.

=20

Thanks,

=20

Sam

=20


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From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] =
On Behalf Of Cliff Bettis
Sent: Friday, February 09, 2007 9:20 AM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Discharge Electrometer w Alpha Source

=20

Jerry,

=20

I tried my electrometer this morning. I charged the cage so the =
electrometer read about 80 volts. I then held the Po 210 (1/2 mCi when =
new; it's about 2 years old) source between the inner cage and outer =
grounded cage. It took about a minute for the voltage reading to drop to =
half its initial value. I repeated the experiment this time charging the =
cage to -80 volts and got the same result: about a minute to remove half =
the charge.

=20

Cliff

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Sam,

The alpha particles leave a trail of =
ionization in=20
their wake. Both positive ions and free electrons. The alphas themselves =
don't=20
go far (a couple of cm or so) before becoming balloon fodder =
(neutral=20
helium atoms). It is the charge in the ion trail that is attracted to =
the=20
charged object to neutralize it, as the other signed charge is repelled. =
You can=20
see the ion trails if you use a cloud chamber with an alpha source. If =
you had=20
to depend on just the charge value of the alpha particles to neutralize, =
say, a=20
negatively charge object, you would need a truly scary source. Consider =
how many=20
alphas it would take to make up even a fraction of a microcoulomb of =
charge and=20
what activity would be required to produce that charge in a reasonable =
time. So=20
it is the ionization the alphas produce that does the discharging not =
the charge=20
of the alphas directly.

Cliff

----- Original Message -----
From:=20
Sam =
Sampere=20

To: tap-l@lists.ncsu.edu
Sent: Friday, February 09, 2007 =
8:34=20
AM
Subject: Re: [tap-l] Discharge=20
Electrometer w Alpha Source


How much of =
the=20
discharging is due to the probe interacting with the particles, and =
how much=20
due to ionized air leaking off charge. I would think that an alpha =
source=20
would leak charges off a positively charged electroscope the latter =
way. I=20
think we had the same kind of conversations when we discharged a zinc =
plate=20
with uv light.

Comments=20
please=85

Thanks,

Sam





From:=20
tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] =
On Behalf Of Cliff =
BettisSent: Friday, February 09, 2007 =
9:20=20
AMTo:=20
tap-l@lists.ncsu.eduSubject:=20
Re: [tap-l] Discharge Electrometer w Alpha=20
Source


Jerry,



I tried my electrometer =
this=20
morning. I charged the cage so the electrometer read about 80 volts. I =
then=20
held the Po 210 (1/2 mCi when new; =
it's about=20
2 years old) source between the inner cage and outer grounded cage. It =
took=20
about a minute for the voltage reading to drop to half its initial =
value. I=20
repeated the experiment this time charging the cage to -80 volts and =
got the=20
same result: about a minute to remove half the=20
charge.



Cliff=


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