Thoron progeny plate-out

Figure 3 Alpha activity versus time from thoron progeny plated-out on several materials.

Table III- Thoron progeny plate-out on different materials using Pylon source standards model Th-190...

Bigu, J. and A. Frattini, Radon Progeny and Thoron Progeny Plate-Out on a Variety of Materials, Division Report MRP/MRL 85-72(TR), CANMET, Energy, Mines and Resources Canada (1985). 

Plate-Out of Radon and Thoron Progeny on Large Surfaces... 

Further plate-out studies were conducted using radon progeny and thoron progeny reference sources, models Rn-190 and Th-190, respectively, manufactured by Pylon Electronic Development (Ottawa), hereafter referred to as Pylon sources, for simplicity. These are small cylindrical containers (<40 cm3 volume) provided with a Ra-226 source or Th-228 source. The containers can be opened at their base and some suitable material can be placed in it for exposure purposes (Vandrish et al., 1984). The Ra-226 and Th-228 sources decay, respectively, to Rn-222 and Rn-220 which in turn, decay into their progeny. In this respect, the above sources can be considered miniature RTTFs quite suitable or plate-out studies, in which air flow pattern effects are minimized. 

The bulk of the data presented here was obtained in a follow-up to a plate-out study reported earlier elsewhere (Bigu and Frattini, 1985). It should be noted that some qualitative and quantitative differences between earlier studies and the most recent follow-up may be observed depending upon experimental conditions. Although the conditions of the surface of the material, environmental conditions and air flow patterns are believed to play a significant role in plate-out phenomena, their effect on the latter, and their relationships, are far from being understood. Furthermore, the chemical nature of the material, and of the radon and thoron progeny, could play a significant role in plate-out phenomena. 

Figure 3 shows a significant difference in thoron progeny activity plated-out on laboratory coat cotton cloth samples and Millipore filters (0.8 /un), and emery cloth. Differences between the two latter sample materials are not clear in these measurements. 

Figures 4 and 5 show significant differences in thoron progeny activity plated-out on cotton cloth and emery paper (Figure 4), and cotton cloth and Fiberglas filters (Figure 5). Differences between the other pair of materials were less pronounced or difficult to ascertain (<7 ).

Table I Thoron progeny activity plated-out on different materials...

Pylon Radon (Thoron) Progeny Reference Sources. Plate-out studies using the Pylon reference sources are shown in Tables II and III. In this case the materials (discs) were placed in the reference sources... 

---