1999 John Cameron, jrcamero at facstaff,wiscedu
The Zerostat gun was originally intended to discharge phonograph
records. It would not only discharge them, it would charge them up to the
opposite polarity so they would attract more dust! The potential on the tip
of the needle is up to about 10 kV - plenty to produce air ions from a
sharp needle point. The voltage source is the same basic mechanism that is
used to light these little lighters for gas grills or other flammable
material- you bend a piezo eletric crystal. When it bends one way it
produces negative votage on the needle tip causing negabive ions. As you
release the presssure on the trigger, it produces ions of the opposite
sign. When the device is used to start fires, when teh potential gets up
to about 4 kV it sparks, lighting any fammable material, such as propane
gas around sparking contact.
I used my zerostat for putting a significant charge (many
picoCoulombs ) on a 2 or 3 mm outside diameter, 50 mm long teflon cylinder
slid over a metal support. This would produce a potential of about 500
volts on the surface of the teflon. You can measure the charge on the
teflon by inserting it into a cylindrical Faraday cage attached to some
type of charge or current measuring circuit. You can determine the charge
quite reproducably. If you then expose the bare charged teflon (electret)
to the ambient air for a minute and measure the remaining charge, you will
get a reasonable estimate of the ions in the surrounding air. The ions will
be of sign opposite to the charge you placed on the teflon "electret." I
had a portable "electrometer" to measure the charge on my teflon electret.
I did many measurements of air ions with this little device.
Since the ions in the air are primarily due to decay of radon and
radon progeny, you get a rough estimate of the ions present in the air and
thus a qualitative measure of the radon present. You basically collect the
ions of opposite sign in a volume of a few liters. You can charge your
electret with the opposite sign by "releasing" the pressure on the switch.
The mobility of the ions falls off fast with distance from the exposed
electret, so you basically collect ions in a roughly a few liters of air
surrounding the bare electret. .It is an extremely sensitive device to
measure ionizing radiation. You can likely "measure" the ionization from
any of your radioactive "check" sources.
WARF at the U.of Wisconsin patented this device in my name about
1980 for measuring ions in the air. At least one radon measuring device
depends on the use of an electret. The claims made in our patent
application did not mention its possible use to measure radon as I
invented it about 1978 while I was on a sabattical in Brazil. That is, I
invented it before the radon scare got started.
I think the use of the zerostat for demos is a good idea. If you
hold the zerostat near
(1 - 2 cm) from your moistened lips or moistened hand, you can feel the
cooling effect of the moving air. I've never gotten a shock doing it.
I think it would be possible to convert a piezoelectric "fire
starters" as a source of ions by removing the grounding electrode that
permits it to spark, thus igniting the fumes. Most of the lighters on
propane outdoor grills use the same principle.
I'm not sure what crystal is used by I suspect it is a PZT
(lead-zerconium-titanate) which has a very high internal polarization so
that a small distortion produces high piezo-voltage.
PZT crystals are used in many medical ultrasound units.
PZT also has a high pyroelectric coefficient. That is a small
change in temperature will produce a significant voltage. The people who
make PZT crystals told me that when PZT crystals are cooling down after
their production at high temperature, they spark vigorously to any ground
that is near them.
A friend of mine in Brazil used pyroelectric crystals to measure
the extremely small temperature rise in a PZT crystal when it is given a
short exposure to diagnostic x-rays - comparable to what you would receive
from a dental bitewing x-ray. There is an article on the Pyroelectric
Radiation Dosimeter (PERD) published in Medical Physics about 1986? which
has me as the last author. I can find the reference if anyone is
If anyone is interested I can tell you how Madame Curie used the
"Piezoelctric electrometer" invented by her husband Pierre for all of her
basic research which was done about a century ago. (Polonium and radium
were discovered in 1898) She was able to measure an ion current as small as
0.1 picoamps! That is impressive. The technique is discussed and
illustrated in the book "La Radioactivite' et Ses Applications by Tubiana &
Dautray (Presses Universitaires de France 1996 It is # 33 in the series
"Que Sais-Je? (What do I know?) The book is in French, if you hadn't
already guessed. I visited the Curie Museum in Paris in 1997 and picked up
copies of three Nobel lectures by Becquerel, Pierre and Marie Curie. It was
interesting museum and not crowded - I was the only visitor at the time.
Zerostats sold by:
Also: that "ratcheting" scratch/crunch sound is
actually from the internal piezo block acting like a loudspeaker. When
the HV wire makes sparks or even bursts of corona discharge, the voltage
suddenly jumps, and the piezo block converts the jumps into sound. In
other words, if you just want ions, the squeeze very slowly, so you avoid
producing any clank noises. Try this: squeeze the trigger very slightly,
then touch the needle. There is a spark, but also a lound "TINK!" from
inside the handle. Or, hold your finger 1mm from the needle and squeeze
rapidly, and you produce a fast series of 'tink' sounds. I guess if you
could apply a 1,000V audio signal to the needle and the metal trigger,
you'd hear music playing inside the zerostat.