The unit body is made of ruggedized cast-ahrminum, including the meter housing. The can is made of 0.090” aluminum. Other operating features of the instmment include a unimorph speaker, mounted to the ins- can with an audio ON-OFF, fast-slow meter response, meter reset button, a battery check button and a 6-position switch for selecting scale multiples of X0.1, Xl, X10, Xl00 and X1000. Each range multiplier has its own calibration potentiometer.

This instrument is set for 900-volt G-M tube operation and is supplied with either a thin wall G-M tube or pancake GM tube. An internal energy x high range detector is used for the Xl000 The unit is operated with two flashlight batteries for operation from 32” to approximately 150°F. For temperahue operation to 0°F. either very fresh alkaline batteries or rechargeable NiCd batteries may be used. Battery drain averages 30 milliamperes.

The apparatus consists of two parts, the tube and the (counter + power supply). The Geiger-Mueller tube is usually cylindrical, with a wire down the center. The (counter + power supply) have voltage controls and timer options. A high voltage is established across the cylinder and the wire as shown in the Figure.

When ionizing radiation such as an alpha, beta or gamma particle enters the tube, it can ionize some of the gas molecules in the tube. From these ionized atoms, an electron is knocked out of the atom, and the remaining atom is positively charged. The high voltage in the tube produces an electric Field inside the tube. The electrons that were knocked out of the atom are attracted to the positive electrode, and the positively charged ions are attracted to the negative electrode. This produces a pulse of current in the wires connecting the electrodes, and this pulse is counted. After the pulse is counted, the charged ions become neutralized, and the Geiger counter is ready to record another pulse. In order for the Geiger counter tube to restore itself quickly to its original state after radiation has entered, a gas is added to the tube. For proper use of the Geiger counter, one must have the appropriate voltage across the electrodes. If the voltage is too low, the electric Field in the tube is too weak to cause a current pulse. If the voltage is too high, the tube will undergo continuous discharge, and the tube can be damaged. Usually the manufacture recommends the correct voltage to use for the tube. Larger tubes require larger voltages to produce the necessary electric Fields inside the tube. In class we will do an experiment to determine the proper operating voltage. First we will place a radioactive isotope in from of the Geiger-Mueller tube. Then, we will slowly vary the voltage across the tube and measure the counting rate. In the Figure I have inclded a graph of what we might expect to see when the voltage is increased across the tube.

For low voltages, no counts are recorded. This is because the electric Field is too weak for even one pulse to be recorded. As the voltage is increased, eventually one obtains a counting rate. The voltage at which the G-M tube just begins to count is called the starting potential. The counting rate quickly rises as the voltage is increased. For our equipment, the rise is so fast, that the graph looks like a “step” potential. After the quick rise, the counting rate levels out. This range of voltages is termed the “plateau” region. Eventually, the voltage becomes too high and we have continuous discharge. The threshold voltage is the voltage where the plateau region begins. Proper operation is when the voltage is in the plateau region of the curve. For best operation, the voltage should be selected fairly close to the threshold voltage, and within the First 1/4 of the way into the plateau region. A rule we follow with the G-M tubes in our lab is the following: for the larger tubes to set the operating voltage about 75 Volts above the starting potential; for the smaller tubes to set the operating voltage about 50 volts above the starting potential.

In the plateau region the graph of counting rate vs. voltage is in general not completely

at. The plateau is not a perfect plateau. In fact, the slope of the curve in the plateau region is a measure of the quality of the G-M tube. For a good G-M tube, the plateau region should rise at a rate less than 10 percent per 100 volts. That is, for a change of 100 volts, (counting rate)/(average counting rate) should be less than 0.1. An excellent tube could have the plateau slope as low as 3 percent per 100 volts.

ability to register gamma, beta and x-ray radiation
expanded range of indications (up to 999,0 µSv/h)
time of observation is reduced from 1 to 26 sec.
time of observation gradually reduces from 26 to 1 sec. when the value of a dose rate is higher than 3,5 µSv/h
improved precision of indications
the ability to set threshold level indications up to 99,0 µSv/h (100 times in comparison with RADEX RD1503)
«BACKGROUND» mode for performing inspections inside premises using algorithm similar to methodical instructions МУ 2.6.1.715-98 Conducting a radiationally-hygienic inspection of inhabited and public buildings
displaying the value of a background dose rate
displaying the difference in indications between the average dose rate and a background dose rate
value of a background dose rate is saved after turning off the device
displaying an average dose rate exceeding over a background dose rate
vibra-call signal as the additional alarming function
possibility to regulate a vibra signal (turning on/off)

Technical and work specifications :

RADEX RD1706 evaluates the ambient equivalent of dose rate Н*(10) of gamma radiation with taking into account gamma radiation and the pollution of objects by sources of beta particles.
The device can be used by the population in day-to-day life (foodstuff, building materials, soil etc.) and by the personnel operating with ionizing radiation sources.
RADEX RD1706 evaluates the value of beta and gamma radiation by the means of two SBM20-1 type Gejgera  Muller counters and displays the indications in µSv/h on LCD. The time of observation a dose rate and varies from 40 to 26 seconds.
Registration of every particle is accompanied with a sound signal what makes it easer to search for the source of radiation.
The device possesses «BACKGROUND» mode which gives not just one but two indications. One stands for exceeding of a dose rate over a background dose rate, the second stands for a background dose rate. This mode is convenient for examining inside buildings, when it is necessary to know how indications indoors differ from the ones outdoors.

The device possesses next features: specification of indications in proportion of increase of monitoring time,
turning on/off display backlight,
turning on/off audio and vibra signals.

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