Table 2.

Significant discrepancy in the observed and expected frequencies of haemopoietic colonies exhibiting chromosomal instability with and without the grid interposed between the α-particle source and the cells (in the latter case, 1 Gy of absorbed dose is delivered to the unshielded cells only)

α-Particle irradiation dose, Gy	No. colonies with aberrant cells/total no.	No. aberrant cells/total no.	No. chromatid breaks	No. chromatid exchanges and minutes	No. chromosome fragments	No. ring chromosomes	No. translocations	Mean no. aberrations per cell
Control	22 /56	36 /662	36	0	12	0	0	0.07
1 Gy	41 /64	137 /1009	191	4	24	3	0	0.22
1 Gy with grid	41 /63	115 /871	128	15	29	5	6	0.21

P = 1.5 × 10⁻⁶ (control vs. 1 Gy); P = 3.4 × 10⁻⁷ (control vs. 1 Gy + grid); P = 0.63 (1 Gy vs. 1 Gy + grid).