re: Re[4]: Lead Aprons in Dentistry

[don.parry@cis.state.mi.us]

Mr. De Castro wrote:

"BTW - ONE of the reasons for the reduced weight on SOME of the newer units
is a trend to go from 60 cycle power to high frequency inverter units."

I am the state inspector that Sandy quoted.  I hope you now understand my 
comments.  I believe, however, that you may be incorrect with your above 
statement.  While most new medical x-ray devices are high frequency units, 
I don't think I have seen a single high frequency dental unit, new or 
otherwise.  I have captured waveforms on many units and they have all been 
single phase half wave self rectified type units.  If you know a make or 
madel for a high frequency dental unit, I would love to capture a waveform. 
 I am pretty certain the weight difference is substantially in the 
shielding.  On some newer units, you can block the tube port, darken the 
lights, place a flourescent screen next to the tube head and get a bright 
flash where the housing leakage is at its worse.  Then you can go back with 
your ion chamber at a meter and get the instantaneous rate and the correct 
for the duty cycle.  Also with D speed film many 7 mA machines have typical 
timer settings of 24 imp or 0.4 sec.  It was one of these machines that I 
had the highest leakage rate on. 

Donald E. Parry
Radiation Safety Section
MI  Dept of Consumer & Industry Services
Voice: 517-241-1989; Fax: 517-241-1981
E-mail: don.parry@cis.state.mi.us
Web site: www.cis.state.mi.us/bhs/divisions/hfs/rss/