Re: P-32

["John R. Laferriere 671-8316" <John.R.Laferriere@dupontpharma.com>]

The highest exposure hazards for a person pipetting mCi quantities of P-32
will be:

a) An intense collimated beta beam coming out of the mouth of the open vial.  
At 1 mCi in 1 ml, the dose rate at 15 cm above the open vial is ~2 rads/hr.
This dose rate will increase with increasing activity concentration.  If
you have 40 mCi in 1 ml, you may be dealing with 50 to 100 rads/hr at pipetting
distances!

b) An uncollimated (but somewhat attenuated) field from the liquid-filled 
pipette tip.

c) An uncollimated field from the petri dish after pipetting.  If there is
significant liquid depth, it will serve to self-shield the pipetted activity
partially.

The bremsstrahlung levels are minor compared to the unshielded beta dose
rates.  I've done measurements that indicate an effective exposure rate
constant (from the brem only) of about 20 mR/hr per mCi at a cm.  At 15
cm from a 40 mCi vial you may be seeing 3-4 mR/hr due to brem.

The pipetting should take place behind a 3/8 inch plastic shield to protect
the torso and head.  Efforts should be made to optimize the positioning of
stock vial and final container to minimize travel distance/time. 

Try to get the pipetting hand out of the beam from the stock vial as soon
as possible after removing the pipette tip from the stock vial.  Remove and
replace the stock vial cap using tongs.  Get the cap back on immediately
after pipetting.  Have the petri dishes in a secondary tray with some decent
plastic thickness on the bottom so your hands are protected during any 
transfers.  A top shield (at least for transfers) would also be helpful since 
the lids on the plastic petri dishes are pretty thin.

The pipette gun should have a 3/8" thick plastic shadow shield attached 
below the grip.  The shield should be large enough to keep the hand and 
forearm out of the beam from the stock vial.

Once the pipetting is done, the used tip should go directly into a shielded
waste container.

Gloves should then be monitored.  If contamination is found, you need to 
adjust your technique to eliminate the cause.  Do not accept routine glove
contamination.  The dose rate due to P-32 directly on the skin is about 
8800 mrad/hr per microcurie/sq. cm., and a layer or two of gloves isn't
going to drop that dose rate very much.

That's about all I can think of for now.  Hope this is useful.  Don't 
forget about contamination surveys afterward.


John Laferriere
DuPont Pharmaceuticals Co.
Medical Imaging Division
john.r.laferriere@dupontpharma.com
(978) 671-8316


************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html