Assuming *n *= 1.2

2200 0500

Using the mathematical formula *T*1

will produce *T*1

.

1

1

*R*a

112 1.2

n

1

1

24

*R*b

17

17

17

17

6.54 or 6.5 hours **or ***T*1

6.54 or 6.5 hours.

4.67 1

.8333

1 2.6

2.6

4.67

Using the family of curves in Figure A-1, locate 4.67 on the

, read up to where 4.67 intersects

1

the 1.2 decay rate slope, then read left to get the

value.

17

17

SOLUTION: *T*1

6.54 or 6.5 hours.

3.6 1 2.6

Since *T*1 is the time after H-hour at which *R*a was made, then H-hour = *T*a T1, which is 0500, 15 January

6.5 hours = 2230, 14 January.

(2) The ABC-M1A1 RADIAC calculator may be used in lieu of the above mathematical

procedure to determine H-hour. However, this is an expedient method and not as exact as the

mathematical technique. For example, use this method to determine H-hour for a particular location with

readings taken at 1600 (50 cGyph) and 1830 (40 cGyph) as follows:

Step 1. Locate the first dose rate reading on the calculator's outer disk (Figure 4-1).

Step 2. Locate the second reading.

Step 3. Determine the time interval between the two readings (1600 and 1830). In this case, the

time interval is 2 ,, hours and starting with H + 1 hour at the first reading (50 cGyph), rotate the

intermediate disk clockwise until a time interval of 2 ,, hours fits between the 40 and 50 cGyph readings

on the outer disk.