RaDALERT GEM II User manual

CONGRATULATIONS and thank you for purchasing the RadAlert GE II
GEM II is the result of over 15 years of development and testing, and is made with state-of-the-art technology in order to provide the precision
and reliability you deserve. It is calibrated for the measurement of gamma rays and will detect the presence of x-rays and of alpha and beta
contamination, and is ideal for uses among the general public and industrial and business communities wishing to make a simple assessment of
their radiation background.
Operation
With a suitable -volt battery (PP3, MN1604, EN22) installed, simply press the button once and GEM’s display lights
will illuminate sequentially to indicate that it is functioning properly and the battery has sufficient charge. The “10-
SEC” light will begin to flash every 2 seconds, indicating that it is counting for 10 seconds and will provide a new scan
result every 10 seconds thereafter. The 10-second scan period enables you to take action to avoid a high dose in an
extreme radiation environment. At any time, you may press the button a second time to start the 10-minute counting
period (10-MIN Mode) for measurements of greater statistical accuracy (especially at low dose rates), or press the
button a third time to switch your GEM off.
Press once = ON, in 10 second mode
Press again = ON, in 10 minute mode
Press a third time = OFF
General Techniques
At normal “background” levels, you may find that in any one counting period, not even the first green light will illuminate, but in the next period
the first three lights may illuminate. This is because radiation is a random phenomenon and 10 seconds is a relatively short time to accumulate
a representative sample of counts on which to base a measurement. So if you have reason to believe your immediate safety is at stake, we
recommend the use of the 10-SEC mode. If time and safety permit and you need greater accuracy, the 10-MIN mode is suggested, as it takes a
much larger sample from which a more accurate measurement can be derived. For checking the radiation levels in your workplace or home
(first take a measurement outdoors to determine the area’s “normal background”), we suggest the use of the 10-MIN mode.
Note: Because of the way in which ionising radiation is detected, placing GEM very close to strong magnetic fields such as those within an inch
of TV and Computer screens can produce erroneous readings. Moving GEM a few inches away from these sources will eliminate any possibility
of interference.
The Display
GEM has a vertical array of 7 lights, each denoting a rate of exposure from 0 to greater than 7.5 micro-sieverts per hour. A Sievert is a very
large unit of radiation dose (“dose equivalent”), so it is often expressed in units of one-millionths (micro = u) or one-thousandths (milli = m).
The 7 lights are grouped in 3 ranges of exposure from green to red, and these lights and ranges indicate:
RED 7.5µSv/h The instantaneous dose rate which defines a Controlled Area
(IR Regs 1 85). Access to such an area is normally limited to classified radiation workers.
RED 5.0µSv/h
YE OW 2.5µSv/h The instantaneous dose rate which defines a Supervised Area
(IRR 1 85). Access is normally limited to named persons who need not be classified radiation workers.
YE OW 1.0µSv/h Levels of dose rate which might be encountered in areas of
enhanced natural background.
YE OW 0.5µSv/h
GREEN 0.3µSv/h Levels of radiation which are roughly equivalent to normal
background variations.
GREEN 0.1µSv/h Low level background radiation.
Factory-set Visual A ARM
Every second that your GEM is operating, whether in 10-SEC or 10-MIN mode, it is also checking for a sudden burst of radiation that calls for
immediate action by you.
If in any one second period GEM detects a radiation dose over 15 microsieverts per hour (for GEM, this is approximately 21 counts per
second), GEM will stop counting and alert you with a unique display of flashing lights using the two MODE lights and the top red light. To
turn off this alarm display, simply press the red button until GEM turns off, then re-start.
Alpha and Beta
While gamma and x-ray radiation penetrate GEM’s plastic case unimpeded, a “window” on the left side of GEM is provided for the detection of
alpha and beta radiation, which are not capable of penetrating GEM’s case and only travel a few centimetres in the air. So if you wish to be sure
to include alpha and/or beta when testing a source, orient this window towards the source and as close to it as possible.

ow Battery Warning
If the status of the battery is or becomes unsatisfactory, GEM will flash lights 2 and 6 (of the array of 7) and cannot be used until the battery is
replaced.
IMPORTANT – Fitting / Changing the Battery
GEM’s size is a useful advantage over most products on the market today, but it means that the battery is in a very confined space and will
require an extra minute to change. Slide of the battery compartment cover and, using a small screwdriver, gently lever out the battery
connector and battery being careful not to short circuit the battery contacts. Clip on the connector to the replacement battery and insert it
(connector end last) so that the battery’s “+” terminal is positioned closest to the bottom of GEM. Try to insert and position the battery wires on
the back side of the connector, the side facing the back of GEM.
What to do if you’re CONSISTENT Y in the yellow / red display bands
First of all, write down which light was the highest to come on (the 5th or 6th light up?) and if you have time, take a 10-minute reading.
If you are outdoors and this increased ‘background’ persists, go indoors, shut the windows and doors and take another measurement –
radioactive particulate is carried by the winds and rain, so going indoors should provide the most protection.
If you are indoors, go outdoors and take a reading to determine if the problem is specific to your home, workplace, or general to the local
environment. If you suspect and object, move away from it and take further readings.
Like smoke and fire alarms, your GEM has been developed to give you peace of mind and, in the hopefully, unlikely event of any form of crisis,
time to respond.
If you have further questions, please email: [email protected]
Note: GEM is a PASSIVE Instrument and is not itself a source of radiation.
Safety
Other than the battery compartment, do not try to open the bonded case of your GEM. There are high voltages within and it will irreparably
damage the case.
It will also void your 12-month warranty!
Do not immerse GEM in liquids… it is neither water resistant nor waterproof!
(Firemen use GEM in simple poly bags to provide basic protection from moisture).
Energy Response & Sensitivity
Dose rate response to Cs 137 is nearly linear over the range 0.1uSv/h with confirmation from a reference point at 5.4uSv/h using Ra226. The
energy response of the Geiger muller tube peaks at 60keV but is flat over the range 200keV to >1MeV to within +10% -20% (window) and +/-
5% (top side).
Dose Equivalent Conversion table, REMS to SIEVERTS (100 rem = 1 Sievert)
100 µrem = 1 µSv --- 1 mrem = 10 µSv --- 10 mrem = 100 µSv
imited Warranty
Perspective Instruments warrants each GEM II to be free from defects in materials and workmanship for a period of one year from the date of
purchase. This warranty extends to the original purchaser only and does not apply to batteries or any parts subject to misuse, neglect, accident,
unauthorised service or abnormal conditions of operation. In the event of an instrument failure, Perspective Instruments will repair or replace
the faulty GEM II, once it has been returned to the factory and inspection has revealed unit to be defective within the conditions set out above.
Calibration Check (7 Day turnaround)
Depending upon the intended use of your GEM and the regulations and laws which may apply, you may need to have your GEM calibrated
periodically, every 6, 12, or 24 months. In the absence of the applicability of these regulations, we suggest a calibration check every 2 years.
Perspective will perform a calibration check of your GEM (including return post) for a charge, currently £60 but subject to change.
Before sending your GEM for warranty service or calibration, please contact us first.
Email: [email protected] or Tel: [phone].
Then do the following:
1/ Note serial Number & wrap up GEM with suitable packing to protect it in transit.
2/ Enclose evidence of the date of purchase, your name, address and phone number.
3/ Enclose a cheque for the correct amount (payable to Perspective Instruments Ltd)
4/ Ensure you send the unit by Royal Mail “Special Delivery” or a similar service that gives ample insurance. We cannot be responsible for GEM’s
lost / damaged in transit!
5/ Send your GEM and payment to: Perspective Instruments
Pinewood, 61 Folly ane, Shaw, Wiltshire, SN12 8HB, England
Our instruments are subject to continuous development and minor changes in detail may occur which are not covered in this manual.
GM Tube specs Centronic ZP1401
Sensitivity
Band: α β γ
Plateau
Threshold (V) max: 400
ength (V): 200
Slope (%/V) max: 0.04
Counting Rate at 10-2 mGy/h (count/s): 25
Dead Time (μS) max: 0
Back-Ground Shielded (count/min.) max: 10
Dose Rate Range (mGy/h) typ: 10-3 – 102