Occupational Intakes of Radionuclides Part 1 - ICRP

2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
Thorium-232
Radium-228
Actinium-228*
Thorium-228
a 14 billion years
a 1.9 years
b
b
5.8 years
6.1 hours
Radium-224
a
Radon-220
a
Polonium-216
a
Lead-212*
3.7 days
56 seconds
DRAFT REPORT FOR CONSULTATION
Bismuth-212*
Thallium-208*
76
Polonium-212
0.15 seconds a 300 nanoseconds
b 61 minutes
(64%)
b
Notes:
The symbols a and b indicate alpha and beta
decay, and the times shown are half-lives.
An asterisk indicates that the isotope is also
a significant gamma emitter.
a
11 hours
3.2.4 Respiratory Tract Dosimetry
61 minutes
(36%)
b
Lead-208 (stable)
3.1 minutes
Figure 12 Natural decay series: Thorium-232
(169) The HRTM dosimetric model is described in Publication 66 (ICRP, 1994a)
Chapter 8. For dosimetric purposes, the respiratory tract is treated as two tissues: the
thoracic airways (TH) and the extrathoracic airways (ET). These are sub-divided into
regions, primarily based on considerations of differences in sensitivity to radiation.
The thoracic regions are bronchial, BB; bronchiolar, bb; alveolar-interstitial, AI; and
the thoracic lymph nodes, LNTH. The extrathoracic regions are the anterior nose, ET1;
the posterior nasal passages, pharynx and larynx, ET2; and the extrathoracic lymph
nodes LNET (Figure 3).
(170) The dose to each respiratory tract region is calculated as the average dose to
the target tissue which contains the target cells at risk. In the alveolar region (AI) and
lymph nodes (LNTH and LNET), the cells at risk are thought to be distributed
throughout the region, and the average dose to the whole lung and the lymph nodes,
respectively, is calculated. For the regions making up the conducting airways (ET1,
ET2, BB and bb), the target cells are considered to lie in a layer of tissue at a certain
range of depths from the airway surface and the average dose to this layer is