monitoring reports from several selected locations. When these series of monitoring reports are required,
each dose rate must be taken with the RADIAC meter placed at the same position within the selected
a. Generally, each of these series should consist of at least six reports (Department of the Army
[DA] Form 1971-R) spaced over at least a 2 ,,-hour period, followed by a series of hourly reports. The
locations at which these series of readings should be taken are carefully selected by the NBCC, based
upon the length of time a unit is likely to remain in its present location and the status of unit training. The
locations should be selected so that the area's soil, vegetation, and other features are typical of the
contaminated area. Further development of information depends on the H-hour determination. It is
essential that these monitoring reports be accomplished with the information precisely determined.
b. To understand the calculation of H-hour, you must use either the mathematical method or the
ABC-M1A1 RADIAC calculator.
(1) The mathematical calculation of H-hour is performed using the formula
hours after burst) that dose rate Ra was measured.
Ta = the time (H +
hours after burst) that dose rate Rb was measured.
Tb = the time (H +
Ra = dose rate (cGyph) measured at time Ta (peak dose rate or later).
Rb = dose rate (cGyph) measured at time Tb (the last dose rate available).
n = decay exponent
The value of 1 can be calculated or may be read from a family of curves (see Figure A-1,
Appendix A, page A-5). The calculational procedure can be made by using an assumed decay exponent
or one that has been determined experimentally.
EXAMPLE: A radiation reading of 112 cGyph was taken at 0500, 15 January, and a reading of 24 cGyph
was taken at 2200 at the same location. Assume the decay exponent was determined to be 1.2. At what
time was H-hour?
Ra = 112 cGyph.
Rb = 24 cGyph.