[Laser] Semi OT

[TWOSIG at aol.com]

Interesting thread.  Here are my thoughts for whatever value they may  be.
 
One of the smoke detectors that I currently use in my home has an  ionization 
chamber that is marked as containing 1.0 micro-curie of Am 241.   If I have 
this right, that means the radioactive part undergoes off 37,000  radioactive 
transformations per second.  The output of the radioactive part  is unlikely to 
change significantly since such devices became available on the  consumer 
market, or for the rest of our lives.  
 
I apologize if I misunderstood what was said, but I think someone suggested  
that beta particles would be harder to stop than alpha particles.  I don't  
think so.  Beta particles are electrons.  Alpha particles are helium  nuclei.  
The mass of two protons and two neutrons divided by the charge of  two protons 
gives a mass to charge ratio much, MUCH, larger than the mass  of one electron 
divided by the charge of one electron.  I think that  radio-isotopes used in 
medicine make use of this.  For example, one  treatment for thyroid cancer is 
to give the patient a radioactive isotope  of iodine.  The cells of the 
thyroid gland absorb iodine much more  readily than the rest of the body.  I think 
if you check, they use a very  short lived beta emitting isotope so that most 
of the energy released by the  decay is expended inside the cells.  It is very 
effective in killing all of  the thyroid gland, or in my wife's case, killing 
any of the thyroid cells  that might have been missed by surgery, or that 
might have migrated to  other parts of the body before surgery.  Gamma and Alpha 
emitters would  have affected much larger volumes of tissue for the same dose 
within the thyroid  cells.
 
I heard that there was a group of HAMS that wanted to establish the record  
for the highest frequency communication.  Knowing that gamma rays are  
considered to be very high frequency electromagnetic waves, they gained access  to a 
gamma source and a detector, and proceeded to send Morse code.  I can  only 
presume that it was a geiger counter and they removed, then  replaced the lid of 
a storage container to form the dits and dahs.  I  have no idea what distance 
record they may have set.
 
However, there is an opportunity for a deep space HAM to do something  
similar.  It is possible to setup an orbit that will briefly appear to  pause over a 
section of the sky.  ( All of the outer planets do this each  year, it is 
called retrograde motion. )  What you need to do is establish  the orbit so that 
an observer looking at the HAM's spacecraft will have a  star pause adjacent 
to the spacecraft.  The HAM will need a  moveable device that  is large enough 
to block a detectable portion of  the light from the star, as seen by the 
observer. ( I suggest a light  source because it is easier to block than a gamma 
ray source. )  The  farther away the star is, the smaller it will appear, so 
there will have to be  some calculation on the size of the device, maybe just 
waving his hand, maybe  furling a solar sail.  It may even be necessary for the 
observer to move to  extend the "pause" time.  It may be a silly idea, but 
possible.  It is  just a matter of understanding the physics and applying simple 
geometry.
 
I dare say that it would be possible to establish Moon to Earth  
communications with a heliograph.  The rule of thumb used in the 1800's was  that an inch 
of mirror was needed for each 10 miles of range.  A distance  to the Moon of 
239,000 miles or so means a heliograph mirror 3.77 miles in  diameter would be 
visible on the Earth, to the naked eye, in broad  daylight.  And the "Spot" on 
the Earth ( where you can see the light  reflected from the mirror) would be 
2,000 miles across!  If you compensate  for the increased light gathering 
power when using a telescope, and for the  reduced noise by observing at night, 
the required mirror gets to be much  smaller.  You could also set up the mirror 
on the central peak of a crater  that is in full sun while the surrounding 
crater floor remains in shadow for  several more hours, by which time, the 
observer would lose sight of the Moon due  to the Earth's rotation.
 
To carry the idea further, a typical laser pointer would illuminate an  area 
about 300 to 350 miles in diameter.  Compared to heliograph, the laser  
pointer benefits from a natural gain factor of 33 to 45 ( 15 to 17 dB ).   The laser 
pointer can also operate hundreds of miles way from the sunlight parts  of 
the Moon, so is less effected by light noise in the telescope.  If there  was a 
beacon up there, I am sure there would be lots of interest trying to  receive 
their signals.  It should not take a very sophistacated  telescope.
 
Fun thoughts.  I hope that I am around when such activities are  done.
 
Best Wishes to you all.
 
James
N5GUI