A turning point. August 1941.
http://en.wikipedia.org/wiki/Mark_Oliphant
http://www.atomicarchive.com/Docs/Smyth ... ndex.shtml
(Atomic energy for military purposes1945)
esp
http://www.atomicarchive.com/Docs/Smyth ... ix_1.shtml
which includes
"THE PROCESS OF IONIZATON
When a high-speed charged particle like an alpha particle or a high-speed electron passes through matter, it disrupts the molecules that it strikes by reason of the electrical forces between the charged particle and the electrons in the molecule. If the material is gaseous, the resultant fragments or ions may move apart and, if there is an electric field present, the electrons knocked out of the molecules move in one direction and the residual positive ions in another direction. A beta particle with a million electron volts energy will produce some 18,000 ionized atoms before it is stopped completely since on the average it uses up about 60 volts energy in each ionizing collision. Since each ionization process gives both a positive and a negative ion, there is a total of 36,000 charges set free by one high-speed electron, but since each charge is only 1.6 x 10-19 coulomb, the total is only about 6 X 10-15 coulomb and is still very minute. The best galvanometer can be made to measure a charge of about 10-10 coulomb. It is posssible to push the sensitivity of an electrometer to about 10-16 coulomb but the electrometer is a very inconvenient instrument to use."
Ok this information is old. So is the language of its explanation. The language was appropriate to the tenor of the times. The times have changed.
Funny that.
So what does a galvanometer measure?
"An alpha particle produces amounts of ionization comparable with the beta particle. It is stopped more rapidly, but it produces more ions per unit of path. A gamma ray is much less efficient as an ionizer since the process is quite different. It does occasionally set free an electron from a molecule by Compton scattering or the photoelectric effect, and this secondary electron has enough energy to produce ionization. A neutron, as we have already mentioned in the text, produces ionization only indirectly by giving high velocity to a nucleus by elastic collision, or by disrupting a nucleus with resultant ionization by the fragments.
If we are to detect the ionizing effects of these particles, we must evidently use the resultant effect of a great many particles or have very sensitive means of measuring electric currents.
THE ELECTROSCOPE
Essentially the electroscope determines to what degree the air immediately around it has become conducting as the result of the ions produced in it.
The simplest form of electroscope is a strip of gold leaf a few centimeters long, suspended by a hinge from a vertical insulated rod. If the rod is charged, the gold leaf also takes up the same charge and stands out at an angle as a result of the repulsion of like charges. As the charge leaks away, the leaf gradually swings down against the rod, and the rate at which it moves is a measure of the conductivity of the air surrounding it.******
A more rugged form of electroscope was devised by C. C Lauritsen, who substituted a quartz fiber for the gold leaf and used the elasticity of the fiber as the restoring force instead of gravity. The fiber is made conducting by a thin coating of metal. Again the instrument is charged, and the fiber, after initial deflection, gradually comes back to its uncharged position. The position of the fiber is read in a low-power microscope. These instruments can be made portable and rugged and fairly sensitive. They are the standard field instrument for testing the level of gamma radiation, particularly as a safeguard against dangerous exposure."
****this is the penlike thing Linda etc had in their lab coats.
Note this well : "A measure of the conductivity of the air surrounding it"
The atomic bomb sits over the information like an eagle over a precious brood.
