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Re: Rad Safe Blood Irradiator
Laura-
The flux reduction could be due in part to irregularities/pits in
the anode- a smooth surface will produce the most,
( i.e. when new), a roughened surface caused by normal wear will reduce
the output...... But I'd bet that the real culprit is the gradual
evaporation- and subsequent deposition- of the Tungsten filament upon the
tube's window. ( you mentioned glass, it might be beryllium?) It
doesn't take much W to reduce the flux, particularly the softer part of
the tube's spectrum. The harder you run the tube ( higher mA /filament
power) the faster the W will boil off the filament. If consistent flux
rates are important, you may have to consider the tube to be a
'consumable' ...... Depending on what type of tube it is, ( fixed
target/rotating anode) there may be some chance that the tube can be
rebuilt.
Good Luck!
Bob Westerdale
Hello,
I would like to request a RADSAFE brain trust on an
issue we have with our Rad Safe Blood Irradiator.
We purchased a New Rad Safe Blood Irradiator in 2001 - which was at the
time a new technology that uses
an X-ray Tube versus the standard Cs-137 for irradiating Blood products.
Below I have listed our service
schedule, but the summary is every 6-12 months we are forced to increase
the time the of irradiation due
to our TLD dosimetry measurement falling below the required 2500cGy+_10%
we require for our standard. The time has
had to be increased to such a length that it will soon perhaps interfere
with our duties and blood irradiation flow rate.
The manufacturer says they are not sure what is causing this and are
currently performing research to
determine why time always needs increasing. My initial thought was
flaking of the anode, causing a filter effect
on the glass which continuous increases and filters out radiation,
therefore taking longer to get to the 2500cGy
value. The manufacturer says they do not think so based on research, but
are unsure - they do not manufacturer the
tubes and are in consult with the tube manufacturer.
Other than the flaking of the anode theory, what might cause this?
Laura Smith
Date Issue TLD Dose
Time
8/8/2001 New unit 2534
8/10/2001 independent evaluator 2734
6.4min
9.27/01 Dose check 2350 ""
10/19/01 Qtrly Dose Check 2660 ""
1/24/02 "" 2610 ""
5/24/02 "" 2460 ""
7/12/02 "" 2440 "" - time
increased
10/10/02 time increased check again 2460
6.8
12/26/02 Annual service contract 2360
6.8
1/15/03 Qtrly Dose Check 2190
6.8 - time increased
2/4/03 time increased check
again 2530 7.5
4/7/03 Qtrly Dose Check 2360
7.5 - time increased
7/9/03 time increase check again
2460 8.1
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