Passage VIII
A series of studies have been conducted to determine the level of harmful radiation at nuclear-waste clean-up facilities. One method of
determining the level of radiation in an area is to measure the growth of certain crystals such as Bi 4 Ge 3 O 12 (BGO). BGO crystals come in
two basic configurations that grow in environments exposed to high levels of gamma radiation. BGO (I) has a hexagonal crystalline structure
and typically grows in environments that are continuously exposed to 100–200 rads of gamma radiation per day, while BGO (II) has an
octagonal crystalline structure and typically grows in environments that are continuously exposed to 500–800 rads of gamma radiation per day.
Scientists conducted two studies to determine which configuration of BGO crystal would be more useful in determining the amount of
exposure to gamma radiation around a nuclear-waste clean-up site.
Study 1
BGO (I) and BGO (II) crystals of 4 cm^3 to 8 cm^3 were collected from a nuclear waste clean-up site west of Phoenix, AZ. Crystals of
both types were placed into individually sealed clear-plastic containers. Ten crystals of each type were then exposed to 3 different levels of
gamma radiation—150 rads per day, 450 rads per day, and 750 rads per day—for a period of 7 days. The average volume for each type of
crystal and each of the 3 levels of radiation was then determined. The results are shown in Figure 1.
Figure 1Study 2
The BGO (I) and BGO (II) crystals were removed from the radiation sources and weighed. The average mass of the BGO (I) was
determined to be about 13 gm. The average mass of the BGO (II) crystals at each of the three levels of radiation is shown in Figure 2.