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Many radiation sources are found simply by driving on the hiways:
Without exception, radiation sources pop up unexpectedly, leaving even the most attendant observer surprised.
For this reason, a continuously operating, sensitive gamma alarm is a must have in the vehicle. Gammas travel
farther than alpha or beta radiations, making them ideal for early warning.
There are any number of surplus "alarming ratemeters" on the market these days, the Eberline RM- series being common and inexpensive.
Some features to watch for are 12V DC operation, variable high voltage and variable or at least low input sensitivity.
Those last two are useful is scintillator probes are to be used.
Scintillators are more sensitive than Geiger Muller tubes, giving greater distance, but by no means a must-have for a successful vehicular setup.
The cesium-iodide crystalled pager sized alarming ratemeters are excellent for mobile monitoring, with the PM-1703M , PM1703GN, and D-Tect systems Mini-Rad-D
being stellar performers. These also offer secondary use as foot-borne detectors, I carry one everywhere now! The vibrator alarm is particularly stealthy in museums and antique malls.
Speaking of antique malls, I still cling to my pancake probe for urban prospecting. The first whiff of air that strikes it when entering a building often gives a few telltale chirps, probably from dust particles laden with uranium or thorium decay progeny. In this service an earphone or at least a volume control is recommended, to keep unwanted attention from being drawn.
The pancake is the perfect all-around tool to discriminate alpha from beta from gamma radiation.
Quantifying the radiation ( how MUCH is there?).
Scintillators of all kinds and plain GM tubes will either over respond or under respond to radiation depending on the energy level of that radiation. When reporting back to the group, it is often helpful to be able to give an accurate reading of the true dose rate involved. This is difficult or impossible without specialized equipment, so I have started carrying a third detector, this time one with an "energy compensated" probe.
Because the "rad industry" has recognized this need in the post 9/11 era, fortunately for use, there are a lot of probes to choose from now. Any such probe is usually tagged with the "EC" initials in its model number, or at least it is touted in the specifications. I like the Eberline HP-270 and the Ludlum 44-38, both of which are simply hand probes with special housings which provide the EC feature. Any meter that is used with such a probe will read out accurately *IF the scale has the correct ratio of CPM/mR/H*. If not, it is a simple matter to record the CPM and convert to mR/H using the ratio of 1200 CPM per 1 mR/H.
Note that an EC probe will read LOWER than a non EC probe in most circumstances, making it a specialized use probe in most cases.
EC probes are often built into specialized meters providing a complete package:
SEI MC1K
Ludlum 2401 EC
Ludlum 14C ( internal hi range probe only is EC)
Canberra ULTRA Radiac
Other routes to achieve EC response is to use an ion-chamber device or a Bicron Micro-Rem.
In brief:
Alarming ratemeter
Pancake probe meter
EC meter
There is no upper sophistication limit to the mobile lab, but there is definitely a point of diminishing returns.
Often I carry an isotope identifier, a very useful tool if a big load or source is found. The trade off is the amount of money that
this tool represents- being stored and transported in a vehicle , especially when the weather is very hot. How many times have I been
asked to repair a Bicron Micro-Rem that was fine before a cross country trip?
So far I have not personally gotten a hit off of ANY neutron detector or tritium detector.
As we have discussed many times, if there was room or budget for but one probe to take along, it would be the pancake. This probe is the
closest to a "universal radiation detector" out there, and is fairly inexpensive. When traveling to high altitudes, or expecting rough service, a
spare element is a good idea, as the mica window is somewhat fragile. An end-window probe will provide many of the advantages of a
pancake, but with much greater ruggedness, at the cost of some sensitivity. The lowly LND 712, used in the MONITOR 4 and scads of other
pocket meters is an excellent example.
Have fun
Geo
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