Table 10.

Estimates of proportion of red bone marrow (RBM) unshielded by protective lead aprons designed prior to 1960 and after 1960.

Portion of skeleton	RBM, % of total (Cristy 1981): average of data for 20 and 40 y ages	RBM (%) unshielded assuming pre-1960 apron designs	RBM (%) unshielded assuming post-1960 apron designs
Cranium	7.65	7.7	7.7
Mandible	0.8	0.8	0.8
Cervical vertebrae	3.8	3.7	3.7
Scapulae	2.85	0	0
Clavicles	0.8	~0.4	~0
Sternum	3	0	0
Ribs	15.6	0	0
Thoracic vertebrae	15.7	~5.2 (4 of 12 vertebrae unshielded)	~3.9 (3 of 12 vertebrae unshielded)
Lumbar vertebrae	12	0	0
Humeri, upper-half	2.4	2.4	~1.2
SUM		~20	~17