Example Problem 1.
GIVEN:
R1 = 200 cGyph Ts = H + 1.5 hours Te = 1 hr.
FIND:
D.
SOLUTION:
On Figure 5-2, connect H + 1.5 hours on the Te scale and 1
hour on the Ts scale with the hairline. Pivot the hairline at
its point of intersection with the index scale to 200 cGyph on
the dose rate (R1) scale. Read D = 90 cGy on the total dose
(D) scale.
ANSWER:
90 cGy.
Example Problem 2.
GIVEN:
D = 20 cGy
R1 = 100 cGyph
TS = 1 hour.
FIND:
Te.
SOLUTION:
On Figure 5-2, connect 20 cGy on the D scale and 100 cGyph on
the R1 scale with the hairline.
Pivot the hairline at its
point of intersection with the index scale to 1 hour on the Ts
scale. Read Te = 3.4 hours on the Te scale.
ANSWER:
H + 3.4 hours.
3.
Calculations When Time of Entry is After H + 24 Hours.
By 24 hours after burst, the change in the rate of decay is so low that it
is relatively insignificant.
Therefore, in making estimates of the total
dose to be received when entry into the contaminated area is later than H+24
hours, the total dose is obtained by multiplying the dose rate at entry time
by the stay time (in hours). Symbolically, this is written--
D = RTe x Ts, where: D = Total dose,
RTe = Dose rate at time of entry, and Ts = Time of stay.
4.
Validity.
The calculations above and the nomograms in Figures 5-1 and 5-2 are valid
only if the dose rate reading is made after the radioactive particles have
ceased falling.
For example, a dose rate reading made 1 hour after the
burst while fallout is still arriving is not valid for determining what the
dose rate will be at a later time, since there is no way to determine how
much more fallout will arrive.
5-11
CM5206
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