- 33 —™ > -- ? o Laskin, et al, indicate a significant carcinogenic response din the lung at 1400 of lung tissue °. rem, suggesting a comparable sensitivity Geesaman indicates that the tissue repair time in the lung is of the order of one year’. It therefore seems appropriate, but not necessarily conservative, to accept as guidance that this enhanced cancer risk occurs when particles irradiate the surrounding lung tissue at a dose rate of 1000 rem/yr or more. TABLE IV Particle Activity and Size to Give a Dose of . 1000 rem/year to the Surrounding Lung Tissue “ Particle. Activity “° (pCi) - 3/4 max inflated 1/2 max inflated 58 9 Particle Diameter (u)” 239 —**"%pu0, «238 Pud2 (138 alveoli) 0.14 0.8 0.12 ( 0.07 0.6 0.09 0.02 0.4 0.06 | 68 alveoli) Closest 20 alveoli 56/ Laskin, 57/ Gecsaman, 58/ Ibid 59¢/ Based unen specific activity given by Langham, W.H., Op. cit., Pp. ét al, Op. 7. cit. Donald P., UCRL-50387, Op. cit., P. ll.