RADIATION MONITORS
840007, 840026
INSTRUCTION MANUAL
SPER
SCIENTIFIC
TABLE OF CONTENTS
INTRODUCTION ....................................................... 2
CAUTION .................................................................. 2
BATTERY REPLACEMENT ...................................... 3
OPERATION ............................................................. 3
READINGS ................................................................ 5
INTERPRETING READINGS .................................... 6
SPECIFICATIONS ......................... ................... ......... 11
LIMITED WARRANTY ............................................... 12
NOTICE ..................................................................... 12
INTRODUCTION
This manual contains valuable information about the nature
of ionizing radiation that should be understood by the user
so that accurate measurements can be made. Information
on the care of your Geiger counter is also included. If the
following instructions are followed, your radiation monitor
will give you many years of reliable service.
The radiation meters are very sensitive pieces of equipment. Although housed in a high-impact case, the GeigerMueller tube that senses radiation is fragile. If the unit is
dropped, the G-M tube may break. Exposure of the unit
above 40°C (100°F) may also cause the G-M tube to stop
functioning. The electronic circuitry is sensitive to high humidity (over 90% R.H.).
CAUTION
DO NOT put the unit in a very hot place (such as a car's
glove box, especially on a summer day).
DO NOT allow the unit to get wet. However, if this should
happen, clean it with a towel and allow unit to air-dry for
several days (do not place in an oven or microwave).
DO NOT open the unit (except for battery replacement).
There are no adjustments inside for the 840007 that can be
made by the user, since the unit is calibrated at the factory.
For the 840026, see instructions on page 5.
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BATTERY REPLACEMENT
The unit is powered by a 9-volt battery. With the on button
activated, the LED should be brightly lit. When the LED is
no longer bright or when the LED dims in the presence of a
radiation source, replace battery. To replace the battery:
1. Slide the plastic door off the unit located in the back.
2. Carefully replace the battery. DO NOT reach into the
unit through the battery compartment while unit is on.
G-M tube activation voltage is over 200 VDC.
3. Replace plastic door.
4. For extended operation and infrequent battery replacement, use an alkaline battery.
OPERATION
The radiation monitor only operates while the push button
on the face of the unit is depressed. This feature makes the
operation very simple and conserves battery power. The
unit is designed to be held in the right hand, with the thumb
over the pushbutton (see Figures 1 and 2). The LED just
above the pushbutton indicates that the unit is on and will
give an indication of battery condition.
When the unit is turned on, a faint buzz may be audible in a
quiet room. This is normal and is caused by the transformer
that powers the G-M tube.
In most parts of the world, background radiation will cause
the speaker to click at random intervals, about one click
every few seconds. In areas where large deposits of natural radioactive minerals are found, or in an area that has
been contaminated with radioactive materials, the speaker
will click more frequently. This is called the "background
level." It should be taken into account when making measurements on specific objects.
Since the incidence of clicks from radioactive sources is
random, several clicks can be heard in rapid succession,
while on other occasions several seconds may elapse between clicks. This is normal. Averaged over a period of
time, the click rate should remain relatively constant. A rea-
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sonable average time should be at least two minutes or
more.
The Geiger-Mueller tube is located behind the slots in the
upper edge of the case. The surface of the tube is very thin
(0.004"). This allows beta radiation to penetrate and to be
detected with greater efficiency. (Beta rays and other types
of radiation will be discussed in the next section). This thin
surface is fragile and poking sharp objects through the slots
will damage the tube.
Your Geiger Counter is designed to be sensitive to:
1. Gamma radiation (which includes X-rays).
2. Beta radiation.
FIG. 1
Gamma radiation and X-rays can penetrate the plastic case
with comparative ease.
Beta radiation can most efficiently enter the case through
the slots. Although Beta radiation is easily detected, it is
difficult to measure accurately. Therefore, when a radioactive object is being searched for Beta radiation, the open
slots in the case should be positioned in such a way that
they are exposed to the object (see Figure 1).
If the unit shows a significantly higher click rate in this position, you can be reasonably certain the object is giving off
Beta radiation.
Now position the unit as shown in Figure 2. In this position,
where radiation cannot pass directly through the slots (Beta
radiation travels in straight lines for the most part) only
gamma and X-ray radiation from the object will be detected.
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