Fw: Fw: Re: [Milsurplus] Milsurplus Radiation

[WA5CAB at cs.com]

Kees,

That was a pretty good write-up, especially considerting that your main 
sources of information seem to have been on-line ones, where roughly 70% of the 
information found is actually disinformation.

I'll offer a few corrections, though.  Gamma rays aren't similar to X-rays, 
they are the same as X-rays.  The only difference between the two is method of 
production.  The unit of energy or intensity for ionizing radiation (whether 
Alpha, Beta, Gamma or X), is the electron volt (eV).  One eV is the energy of 
one electron accelerated through a potential difference of one Volt (and then 
turned loose).  The unit of ionizing radiation is the Roentgen (R).  One R will 
produce ionization equivalent to one electrostatic unit (ESU) of charge in 
one cubic centimeter (cc) of dry air at standard temperature and pressure (STP). 
 Note that there is no unit of time included.  

To get back to Gamma versus X-rays, radioactive materials emit Gamma rays 
(and/or Alpha or Beta particles) at one or more discrete energies.  Mechanical 
X-ray generators historically used X-ray tubes (basically half wave vacuum 
rectifier tubes with a heavy tungsten or other dense metal anode whose front 
surface was set at an angle to the electron beam) and were operated directly from 
the high voltage transformer (self rectified).  So their output was broad 
spectrum, producing X-rays from around 20 KeV up to the peak voltage of the 
transformer.  Typical portable industrial units were rated from 50 to 250 KeV, which 
was the peak output.  With adequate instrumentation (able to discern the energy 
of the rays), you could thus differentiate between  the output of a 250 KeV 
tube head and the output of an Iridium 192 (0.92 MeV) or Cobalt 60 (1.2 MeV) 
radioisotope source.  However, if you were able to build a 920 KV DC supply and 
feed it to an X-ray tube capable of taking it, and point it at the wall of the 
room next door, someone with instruments in that room (hopefully they aren't 
also in that room) would not be able to say whether the radiation was X or 
Gamma.

Further, survey instruments are calibrate in R (Roentgens or fractions 
thereof).  The unit of effect of R on matter is the Radiation Absorbed Dose (RAD).  
The unit of the effect of radiation on humans is the RAD Equivalent Mammalian 
(REM).  Numerically, the units are close but not identical.  500 R, RAD or REM 
exposure within an hour will kill you within less than one to ten hours.  
Guaranteed, regardless of how you measured it.  However, 500 REM over a 100 year 
lifetime might not.  You'll probably just die of "old age".  So the radiation 
effects on humans over time is only partially based on accumulated dosage.  
Living organisms are at least to some extent self repairing.  So at least in the 
average, the lifespan shortening effect of 100 REM over one year would be 
greater than that over 20 years.  The theories used to set safe occupational 
doses (as opposed to dose rates) are based on statistics and expected lifespans.

In your units (copied below) most of the R should be replaced by RAD or REM.

In a message dated 8/25/2006 5:10:31 PM Central Daylight Time, 
windy10605 at juno.com writes: 
> There are four types of Ionizing Nuclear Radiation of interest:
> Alpha particles (stopped by a few inches of air or human skin)
> Beta particles (stopped by thin wood, metal, or plastic)
> Gamma rays .....similar to X-rays (stopped -only- by a substantial
> thickness of lead, concrete, etc)
> Neutrons released by Nuclear Fission
> Instrumentation, mostly old Civil Defense radiation survey meters which
> are readily available today, only measure Gamma or Gamma and Beta, so my
> focus was on those two. 
> Radiation effects on humans is based on an accumulated dosage over time
> (amount integrated over time). Radiation is all around us and the average
> yearly dose for citizens of the USA from ambient/background radiation is
> around 360 mR/Year (or 3.6 mSv/Yr, Sievert is the new unit of measure, 1
> Sievert = 100 Rems). I'll use both, since most of the available
> instrumentation indicates in "Rems". This background radiation comes from
> various sources: cosmic, radon, terrestrial, internal, consumer products,
> diagnostic X-rays, fossils, nuclear medicine, etc. In addition to this
> background radiation, limits have been set for additional average
> radiation rates of : 100 mR/Yr (1 mSv/Yr) for the unmonitored general
> public, 150 mR/Yr (1.5 mSv/Yr) for airplane crews due to the high
> altitudes and less "buffer" to cosmic radiation, and 2000 mR/Yr (20
> mSv/Yr) for monitored nuclear industry workers. A yearly USA public
> ambient/background radiation level of 3.6 mSv/Yr would work out to 306
> mSv for an 85 year lifetime. 350 mSv per lifetime was the criterion for
> relocating people after the Chernobyl accident. Unfortunately, many
> people received WAY in excess of that. That basically covers the range

Robert & Susan Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)