Plutonium - Short Essay

[sandy_perle@email.fpl.com]

     With respect to the Good Morning America discussion regarding 
     plutonium, I'm including this essay I found in Bruce Busby's 
     "Radiation and Health Physics" Homepage. If you already know all of 
     this info, just click on "next message." If not, I hope that some find 
     some interesting information.
     
     
     Sandy Perle
     Supervisor Health Physics
     Florida Power and Light Company
     Nuclear Division
     
     (407) 694-4219 Office
     (407) 694-3706 Fax
     
     sandy_perle@email.fpl.com
     
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     Plutonium 
     
     Short Essay by Gary Masters
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     Much of what is written in the press regarding plutonium is 
     inaccurate. I have often read that plutonium is the most deadly 
     element known to man. This is not true. 
     
     I'd like to address two separate issues about plutonium. The first is 
     its toxicity as a heavy metal. The second is the hazards associated 
     with the radiations emitted by plutonium and the other isotopes 
     present with plutonium. 
     
         1. Plutonium is a heavy metal and as such is toxic. There are many 
            heavy metals that are more toxic however. Since I'm a           
            Radiological Engineer and not an Industrial Hygienist I'll      
            leave the heavy metal toxicity discussion at this point. 
         2. For the purposes of this discussion we'll assume that the       
            plutonium in question is weapons grade. In this grade of        
            plutonium the desired isotope is Pu-239. Several other isotopes 
            are present however. In addition to the Pu-239 are Pu-238,      
            Pu-240, Pu-241, Pu-242 and Am-241 (americium). The Am-241 is    
            the result of the beta minus decay of Pu-241. Am-241 is         
            primarily an external dose hazard since it's predominant decay  
            mode is to emit a 59.5 KeV photon. The plutonium isotopes,      
            with the exception of the Pu-241, are alpha particle emitters. 
     
     An alpha particle consists of two protons and two neutrons and is 
     therefore massive with respect to other radiations and has an 
     electrostatic charge of plus two. An alpha particle's mass and charge 
     cause it to deposit it's energy very rapidly and limits it's ability 
     to penetrate materials. Alpha particles are stopped by the layer of 
     dead skin cells covering the body and are therefore not an external 
     concern. If alpha particle emitters enter the body there is no layer 
     of dead cells to protect the living tissues. 
     
     There are several ways that plutonium could potentially enter the 
     body. Ingestion, inhalation, and injection are the most common. 
     Ingestion is not a significant hazard since absorption from the 
     gastrointestinal tract is low[1]. Plutonium is transferred to the 
     blood stream through the lungs (inhalation) and can be injected 
     directly (wound). Plutonium absorbed into the blood stream is 
     deposited principally in liver and skeleton[1]. The
     deposition is divided as follows: 45% to liver, 45% to skeleton, 
     0.035% to testes and 0.011% to ovaries[1]. 
     
     Radioactive materials are removed from the body at a rate relative to 
     the effective half life for that isotope. The effective half life is 
     derived from the biological half life and the radiological half life. 
     The radiological half life of plutonium is about 24,000 years and the 
     biological half life is about 20 years for liver and 50 years for 
     skeleton. The effective half life of plutonium deposited in the liver 
     is 20 years and 50 years for plutonium deposited in the skeleton[1]. 
     Plutonium deposited in the gonadal tissue is assumed to be permanently 
     retained[1].  
     
     Since plutonium is an alpha particle emitter the Annual Limit on 
     Intake is based on critical organ dose rather than on whole body dose. 
     The limit for critical organ dose is 50 rem (0.5 Sv) CDE. (CDE stands 
     for Committed Dose Equivalent and is the dose to the critical organ 
     over the next 50 years). A critical organ dose of 50 rem (0.5 Sv) is 
     not expected to cause greater than a 1.0E-4 (1 in 10,000) increase in 
     the incidence of cancer. 
     
     A fairly conservative dose conversion factor that I have used when 
     dealing with weapons grade plutonium is 4.6E+8 rem/Ci (1.2E-4 Sv/Bq). 
     Using this factor it would take an inhalation of 1.1E-7 Ci (4.0E+3 Bq) 
     to cause a CDE of 50 rem (0.5 Sv). This roughly equates to 2.9E-7 g 
     (0.29 ug). Twenty-nine hundredths of a microgram may not seem like 
     much material, but in terms of inhalation it is quite allot. It is 
     extremely rare for a plutonium worker to receive an inhalation of this 
     magnitude and the general public is at far less risk. 
     
     In regard to the statement that 1 pound of Pu would kill everyone on 
     Earth... One pound of plutonium would be enough to give 1.6E+9 persons 
     a CDE of 50 rem (0.5 Sv) {which could result in 1.5E+5 additional 
     cancers} *IF* and ONLY IF the material was pulverized into particles 
     of respirable size and the material could be adequately dispersed in 
     the atmosphere. A few decades ago the United States and other 
     countries engaged in
     atmospheric nuclear bomb testing. These tests released many many 
     pounds of radioactive isotopes, including plutonium, to the 
     atmosphere. Although there is some evidence of increased incidence of 
     cancer among "downwinders", there have not been 1.5E+5 cancers in 
     excess of the number expected. So it would be practically impossible 
     to kill everyone on earth with one pound of plutonium