emits a chirp for each dose increment. The radiation is recorded normally in dose increments of 0.25 mR to
1 mR units.
Some units of this type are equipped with a chirp rate switch allowing the user to select a low or high chirp
rate. In the low position, each dose increment produces one chirp; in the high position, each increment
produces about 40 chirps, giving a more immediate audible warning at relatively low exposure rates. For
example, at an exposure rate of 10 mR/hr, the unit will chirp about every 6 minutes in low position and about
every 10 seconds in the high position.
The alarm dosimeter has a case usually constructed from aluminum or high impact plastic. The DAD/PAD is
lightweight (8 ounces or less), has a corrosion-resistant surface coating and operates on a 9-volt alkaline
battery for up to 6 months of normal use.
Operation is very simple: turn the unit on. Some units reset the display each time the unit is turned on;
others require resetting the display with a reset switch or button. A memory is available on some models,
which allows the unit to be turned off without losing the stored dose. This feature permits a single daily
recording of the wearers exposure dose because the dosimeter will continue to monitor exposure to the
radiation without having to record each exposure dose if operations are stopped and resumed several times in
a days operation. Dosimeter reading for each individual shall be entered on the utilization log at the end of
Any time a DAD/PAD is used by a different radiographer, it SHALL be reset to zero prior to use. Each
radiographer SHALL wear a single DAD/PAD, which has been reset to zero prior to the start of each days
operation and calibrated in accordance with specific equipment technical data. A reading may be obtained at
any time while working in a radiation area by simply pushing a read button to view the accumulated dose on
the readout display. An emergency situation should be considered to exist whenever a daily accumulated
dose of 100 mrem or more is registered on the display of the dosimeter.
The Victoreen Model 885 PAD is one example of the alarm dosimeter. It detects gamma and X-rays over a
range of 0-999 mR (0-10 mSv) by integrating radiation exposures. It provides both a visual and audible
indication and chirps in direct proportion to radiation intensity/dose rate with chirps at the rate of one
chirp per 0.025 mR. Using one 9V alkaline battery, the PAD will operate for 30 days continuously or for 120
days at 8 hours per day. (Low battery indicator notes when battery life drops below 100 hours.) The Model
885 PAD must be worn under outer garments when conducting operations during cold weather as it is
designed to function properly only when the lower operating temperature is above zero degrees Celsius (32
Each personal alarming dosimeter/alarm rate-meter must:
Calibration of both pocket dosimeters and personnel alarm dosimeters must
be scheduled so that sufficient quantities remain on hand to support continu-
ing radiography operations. Additionally, except in cases of emergency, TLD
badges should not be submitted until replacement badges have been received.
a. Be checked to ensure that the alarm functions (sounds) use at the start of each shift.
b. Be set to give alarm signals a preset dose rate of not more that 500 mR/hr (5 mSv/hr).
c. Require special means to change the preset alarm function.