30.06.2013 Views

Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

262 CHAPTER 6<br />

à =<br />

As1 (0)<br />

+ As2 (0)<br />

λE1<br />

λE2<br />

Asn (0)<br />

+····+<br />

λEn<br />

and Eq. (6.97) tells us that the dose <strong>to</strong> any organ is given by the product of the<br />

cumulated activity in the source organ and the appropriate S fac<strong>to</strong>r:<br />

D(rk ← rh) = Ãh × S(rk ← rh).<br />

If we substitute the expression for à from Eq. (6.99) in<strong>to</strong> Eq. (6.97), we get<br />

<br />

Ahc1<br />

D(rk ← rh) =<br />

(0)<br />

+ Ahc2 (0)<br />

λEc1<br />

= Aci<br />

λEci<br />

λEc2<br />

+··· +<br />

Ahcn (0)<br />

λEcn<br />

<br />

× S(rk ← rh)<br />

× S(rk ← rh). (6.101)<br />

In Chapter 4, we showed that the average life of a radioiso<strong>to</strong>pe is simply the reciprocal<br />

of the transformation rate constant. Since the clearance of internally deposited<br />

radionuclides follows the same kinetics as radioactive transformation, it follows that<br />

the mean residence time of an internally deposited radionuclide is given by the<br />

reciprocal of the effective clearance rate constant, or its equivalent, 1.44 times the<br />

effective half-life:<br />

τ = 1<br />

λE<br />

= 1.44 TE. (6.102)<br />

If the expression for 1/λE from Eq. (6.102) is substituted in<strong>to</strong> Eq. (6.101), we obtain<br />

D(rk ← rh) = τhci Ahi(0) × S(rk ← rh), (6.103)<br />

where τ hci is the residence time in the ith compartment of organ h.<br />

The use of the mean residence time may be illustrated by the example that follows<br />

below.<br />

W Example 6.19<br />

Calculate the dose from an accidental intake of 137 Cs that led <strong>to</strong> an initial body<br />

burden of 1 MBq (which was determined by whole-body counting).<br />

Solution<br />

The retention curve for 137Cs is given by Eq. (6.59) as<br />

q (t) = 0.1 q0 e −(0.693t/2 days) + 0.9 q0 e −(0.693t/110 days) ,

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!