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What Radiation Detector Should I Buy?

I have been asked this numerous times, and it is an easy question if money is an object, you want to detect alpha, beta and gamma radiation, you want a compact unit (almost pocket sized), and you want to here the traditional "click" of a particle ionizing the gas in the GM tube.  I would highly recommend the Monitor 4 and Monitor 4EC. 

The Monitor 4 and Monitor 4EC have been around for several decades.  They are rugged, have an easy to read meter, take a nine volt battery, and are relatively sensitive to a wide variety of atomic particles, and measure up to 50,000 counts per minute or 50 mR/hr (milliroentgens per hour) gamma.  The manual is well written, and easily understood.  There are many that pop up on eBay (used and best of all, inexpensive), and can be bought relatively cheap.  As for calibration, there are many companies that calibrate it.  Many have a headphone jack.  That is an added bonus if you would like to link it to your computer.  There are also free programs that can log the clicks, and ones that you can purchase.

What about the yellow geiger counters?  On eBay one can purchase for under $100 the CDV-700 series of geiger counters.  Many of these units are really good.  They have a detachable hot dog probe, and can detect beta and gamma radiation.  They can measure gamma radiation with the window on the probe closed.  They where made in the tens of thousands by companies such as Universal Atomics, Anton Labs, Victoreen, Electro Neutronics and Lionel (yes, the Lionel of electric trains fame).  However, many where built in the 1950's and early 1960's. They sat in fallout shelters or warehouses for decades, and may have been subject to moisture and humidity.  Surprisingly enough, many work well, in spite of the abuse of disuse.  Some may have a transformer go bad, that is the heart of the geiger counter, and if it goes there are no replacements.  However, the geiger tube and many of the components, transistors, resistors, capacitors are still available, or can be scavenged.  The manual that came with them usually has a schematic and parts list.  If you like to tinker, and have some electronics know how, they can be either restored to working condition, or hot rodded!  Esentailly, the CDV-700s Model 4, Model 5, Model 6A and 6B are the Model T's of the geiger counter world.  The Universal Atomics Model 4 is a very neat unit, however, it has a plastic case prone to cracking, and most have a wax covered circuit board, which is a pain to work on.  By the way, There are online groups of amateur scientists that restore and rework these units to be even more sensitive.  I have added a scintillator probe to one of mine, and so have many others.  Another common modification is the addition of a Pancake probe (a very sensitive geiger tube that is a large, flat disk on the end of a handle).  Pancake probes are available aftermarket, and are a great addition because they are sensitive to alpha, beta and gamma radiations. The cdv700club, a yahoo group, is a great resource for help with these or antique geiger counters, and if you build your own, or want to hot rod an older unit, you may try geigercounterenthusiasts, another yahoo group. 

Do not purchase a CDV-710, CDV-715, CDV-717 or CDV-720, or any unit that measures in R/hr or Even R/minute (Roentgens), if you want one as a prop or decor, or want to modify it, then go ahead.  Many do not work, since the resistors have succumbed to moisture.  Sometimes they can be brought back to life with silica gel or gentle heating in an oven, or by replacing the resistors (which are very hard to find).  However, they will need to be calibrated (which can be done by www.ki4u.com ), and even then they only detect very high levels of radiation (like found in the beam of an Xray machine or after a nuclear or thermonuclear blast).  They can be modified to detect lower levels, but you will have something that merely detects radiation, it will not quantify it. 

Antique Geiger Counters from the uranium boom may be very worthwhile as collector pieces.  PRI's are usually chromed, and use vacuum tubes, as well as other companies such as RCA, Detectron, Whites (the metal detector people), Hoffman and many others.  However, the major issue with many of these are the type of batteries they took.  Many use 22.5 45 volt or 67.5 volt radio batteries.  Very common in the 1950's, very scarce and very expensive today.  There is a gentleman who makes a battery replacement kit that allows you to use commonly available batteries, but even then you may be dealing with collapsed geiger tubes (crushed by air pressure), dried out capacitors, or in the case of old scintillators, a yellowed NaI Th (Thallium doped Sodium Iodide) scintillation crystal (it has attracted water over the years, and will no longer scintillate).  Alas, there are many people who, with patience and a little know how have brought these units back to life.  New old stock geiger tubes will pop up on eBay, as well as replacement vacuum tubes and capacitors, there are companies that can refinish Scintillation Crystals or provide an replacement, and alternative scintillation plastics are also available.  

Other worthwhile units, that can be pretty pricey are Ludlum, Eberline and Bicron.  Many will work with a variety of geiger counter probes, or scintillation probes, and Ludlum units are very pricey.  Ludlum may be the Rolls Royce of Geiger Counters!  The major problem with eBay units are:

    1) Eberlines may only work with several probes or very specialized probes, and the probe itself can be expensive.  A lot have been used hard!

    2) Ludlums may have an internal probe, but again they are very expensive (typically $275 and up used without probes), 

    3) Most of these units are large, and cannot be carried without someone really noticing.  They are great for the lab or prospecting, a bad choice for the antique store!  May as well wear a contamination suit and respirator while carrying one in public!

Cheap new Geiger counters from the Soviet Republic are available, but I have heard nightmare stories about bad LCD displays (The PK-104's), or units dead on arrival.  EcoTest units are pretty good from what I have heard, but again are in the two to three hundred dollar range including shipping.

What about the PM1703M?  These are made by Polimaster, or a company that is licensed to produce their technology.  They are rugged, small, have an illuminated display, audio or vibrating alarm, and free software that records date and time of alarm events (need an IRda dongle and a computer).  Be careful in suppliers, a year or so ago there was a bunch sold on eBay that would short out when turned off (from anecdotes of purchasers), never to turn on again; not good for something that costs around $300 to $400.  Most are gamma only (what if you are looking for Polonium 210 contamination, Polonium 210 is an alpha emitter, or Strontium 90 contamination, since Strontium 90 is a beta emitter?).  Most radioactive substances will emit some gamma rays, so it is a fairly good unit for all around radiation detection as a result to its extreme sensitivity to gamma and xrays.  There are also versions of the PM1703M, such as the PM1703GN that counts neutrons (good for detecting fissionable materials, or fusion reactions), or the PM1703Ma, which can, with a Windows Mobile cell phone, bluetooth, and $500 software will detect and identify quite a few radioactive substances! 

One last geiger counter company I feel very comfortable recommending is www.blackcatsystems.com .  This company produces geiger counters that have a battery operated attachment for use in the field, as well as units that can be linked to a Mac or Windows PC.  The company writes excellent software, and offers a well made pancake tube or end window tube Geiger Counter.  The company owner is very helpful, and knows what his software and equipment is capable of.  The GM-10 or GM-45 are excellent for science projects or classroom demonstrations.     

If you have more specific questions feel free to contact me at admin@radiationfinder.com .   

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