Articles with topics atomic or nuclear in nature

cosmic radiation

What are Cosmic Rays?

cosmic radiation

Cosmic rays are numerous types of ionizing radiation being emitted from different sources, all in outer space. If it were not for the protective magnetosphere and atmosphere protecting Earth’s surface, life would have had a difficult time surviving or being complex or diverse.

The term cosmic rays does not specifically refer to any type electromagnetic radiation comprised of photons such as gamma rays, radio waves, or light (which are also abundant in space).

Types of Cosmic Rays

Galactic Cosmic Rays (from within the Milky Way) and Extragalactic Cosmic Rays (from outside of our galaxy) produced by celestial bodies and/or events such as supernovae in deep space.

Solar Cosmic Rays (also called Solar Energetic Particles) emitted from our own sun, Sol, primarily during solar flares or coronal mass ejections.

Context determines the likelihood of which type of radiation to which people are referring when they use the term Solar Rays.


Like alpha radiation we often encounter on Earth from unstable elements undergoing nuclear decay, about 99% of cosmic rays are comprised of relatively large atomic particles structurally equivalent to the nucleus of an atom (an atom without its electron shell). Alpha rays are made of particles the same as a helium nucleus, and around 9% of these typical cosmic rays are the same. Around 90% are simple protons equivalent to the nucleus of a hydrogen atom, and about 1% are nuclei of heavier (larger) atoms.

There is about 1% of cosmic rays which are beta radiation (an electron) and/or antimatter (positrons or anti-protons).

Effects of Cosmic Radiation

Astronauts are exposed to relatively high amounts of cosmic rays and it has even been theorized that cherry seeds brought back from 9 months in the International Space Station sprouted, grew, and bloomed differently than seeds from the parent tree should. One reason there are no control seeds to which to compare them is that no other seeds from the 1000+ year-old tree had ever even sprouted, whereas 4 of the “space seeds” did and bloomed years ahead of schedule. The endeavor was initially just to excite people about seeds that had been in space; it wasn’t really wasn’t intended much of an actual experiment (esp. since much more controlled experiments such as with potatoes were already done, yielding few interesting results). A controlled experiment will have to be performed to draw more solid hypotheses of whether or not 8 months of microgravity and cosmic radiation truly affected the cherry seeds or not.

Cosmic rays can interfere with electronics and pose an increased risk of cancer. Even commercial airline crew are exposed to extra solar radiation, being frequently above much of Earths atmosphere which helps to shield the radiation.

What is Nuclear Radiation?

Nuclear radiation is a type of energy radiated (emitted) by certain kinds of matter. We say matter is “radioactive” if its atoms are unstable and decaying by releasing energy as either rays or subatomic particles (pieces of atoms or particles smaller than atoms). At the core of an atom there is the nucleus, this nucleus is made up of protons which have a positive electrical charge, and neutrons which are neutral or have a charge of zero. The outer boundaries or shell of an atom is made of electrons which have a negative charge and can be said to be in motion or constantly changing position. A simplified illustration could be made of electrons orbiting the nucleus like high-speed, little moons, but there’s a lot more to it than that, as physics are very different in the unimaginably tiny subatomic realm than they in our everyday lives, or in astrophysics).

an atom

Speaking of astronomy, stars and astronomical events are common sources of the formation of new atoms. Nuclear physics environments created by scientists are another. The basic form of substances is the element. An element is a pure form of matter. All other forms of matter are made of multiple elements, one way or another, but even pure elements have different forms; these are called isotopes. A physicist could have two lumps of uranium that are both pure, elemental uranium, but one lump of uranium is one isotope of uranium (such as U235) and the other lump is a different isotope (such as U238). An element always has the same amount of protons, but what makes different isotopes is a differing number of neutrons in the nuclei.

Since different subatomic particles have different electrical charges, different ratios of them cause the forces atom to always be sort of striving toward equality. This causes atoms that are relatively imbalanced in this manner to be unstable and decay. In this process of remitting atomic radiation, the matter passes through stages where, sooner or later, it becomes either a different isotope or even a different element.

Can You Mail Radioactive Materials?

You can mail radioactive material if it’s done by the book and, of course, safely. Here we will concentrate on how to mail radioactive materials that require no special license that one need apply for nor be individually granted such as a raw, unprocessed uranium or thorium ore-containing geological specimen. Note that we are not an official source of information on this topic and things change, so the most foolproof way is to wade through Code of Federal Regulations (CFR) of the Nuclear Regulatory Commission (NRC).

Uranium Ore

Mailing Radioactive Materials: Raw Geologic Specimens

The scope of this article includes the mailing of a limited amount of raw, unprocessed, geologic ore. Procedures or labeling may differ for other items, even if they are similarly excepted quantities or types of radioactive materials. This may include the UN number displayed or CFR section cited, or other verbiage required by USPS (more on all this below).

NRC Requirements for Mailing Radioactive Materials

The NRC calls radioactive materials “Class 7” materials. In general there are all manner of restrictions, requirements, licenses, papers, containment, and labels involved with this sort of thing. Fortunately, exceptions exist for the lesser extreme materials in limited quantity such as “49 CFR § 173.421 – Excepted packages for limited quantities of Class 7 (radioactive) materials”. This is the one of the keys to legally mailing hobby or educational quantities of radioactive ore.

The NRC requires two main things:

1) The surface activity anywhere on the parcel’s exterior must not exceed .5mrem/hour (0.005 mSv/hour). Since even perfectly calibrated but differently designed Geiger counters and other devices can display vastly different readings due to probe surface area and many other sensitivity factors, we sought what the standard was for measurement. We didn’t want it to be a “pancake” probe but then go using a lesser sensitive tube, ourselves, thereby underestimating what an authority would read. It turned out there was no standard in the CRF. A memorandum buried in Division 8, “Occupational Health,” of the NRC’s Regulatory Guide series and NUREG/CR-5569, “Health Physics Positions Data Base” answered this as a sort of FAQ stating that essentially any reasonable, reliable means is sufficient to determine compliance with surface activity limits (presumably calibrated and certified or certifiable by the NRC). So this indicates a standard beta/gamma “hot dog” probe on a Geiger counter should be sufficient, versus more sensitive probe or device. Just to be safe the author uses an end-window probe with a sensitivity somewhere between the two.

2) “RADIOACTIVE LSA” must be printed visibly somewhere reasonable in relation to the address etc when mailing radioactive materials . Note that carriers may require additional labeling, such as displaying the appropriate UN number (in this case UN2910), but the NRC, itself, requires just this, for packages excepted under 49 CFR 173.41. They are exempt from needing those DOT diamond-shaped transport labels and other things normally required for mailing other radioactive materials.

3) Here’s where things get just a little tricky if you want to go airmail. When mailing radioactive materials, even under these exceptions, air transport is actually prohibited – under one condition – the nature of the package in which it’s contained. 49 CFR § 173.427 (a) (6) (vii) states “Transportation by aircraft is prohibited except when transported in an industrial package in accordance with Table 6 of this section, or in an authorized Type A or Type B package.”

After a couple of tables referring to one another this leads to it needing to be a “Type IP-1” (Industrial Package – Type 1) package. While this, at first, sounded intimidating like something Bruce Willis would be trying to open and disarm, it simply seems to define something reliable not to fall apart (but you be the judge of the code copy/pasted below). After all, if air mail was simply prohibited, a very common air mail label would not exist (available from
mail radioactive materials label

IP-1 is defined in below :
49 CFR § 173.410 – General design requirements – skip to section (i)  :
(i) For transport by air
(1) The temperature of the accessible surfaces of the package will not exceed 50 °C (122 °F) at an ambient temperature of 38 °C (100 °F) with no account taken for insulation;
(2) The integrity of containment will not be impaired if the package is exposed to ambient temperatures ranging from −40 °C (−40 °F) to + 55 °C (131 °F); and
(3) A package containing liquid contents must be capable of withstanding, without leakage, an internal pressure that produces a pressure differential of not less than the maximum normal operating pressure plus 95 kPa (13.8 psi).

If you feel your package is compliant with IP-1 definitions (with your item in them) and it gets returned with an “Airmail of Class 7 Materials is Prohibited – Return to Sender” admonishment, try sending it again with additional labeling stating that it is compliant with 49 CFR § 173.427 (a) (6) (vii) by way of being an IP-1 container thereby allowing its contents to travel by air.

USPS Requirements for Mailing Radioactive Materials

USPS aligns with the NRC’s requirements, but they require a specific statement, below. Other carriers have their own rules but similar or identical. USPS requires:
“RADIOACTIVE” in which case the NRC’s required “RADIOACTIVE – LSA” will suffice

…in addition to (and this can go just underneath RADIOACTIVE – LSA)
This package conforms to the conditions and limitations
specified in 49 CFR 173.421 for radioactive material,
excepted package—limited quantity of material, UN2910,
and is within Postal Service. activity limits for mailing.

Package Size per USPS is stated as:
“No single dimension of the external mailpiece can be less than 2.5 centimeters (1 inch), and the length and girth (combined) can be no less than 30 centimeters (12 inches)”.

It should be noted that it costs about the same to mail a 6x4x4” or 5x5x5” box as it does a compliance-iffy envelope. If you’re doing the wonderfully inexpensive First Class for something under a pound, and it’s likely to go airborne, it may be worth it to go with the box esp. if you’re going to claim it’s package type IP-1 compliant when bearing its particular contents. At least if it’s not going to kill your profit on some low priced nugget, in which case you might want to look more into IP-1 definitions.

Summary for Mailing Radioactive Materials via USPS

1) Parcel surface reads no more than .5mrem/hr.
2) It bears the following:
This package conforms to the conditions and limitations
specified in 49 CFR 173.421 for radioactive material,
excepted package—limited quantity of material, UN2910,
and is within Postal Service. activity limits for mailing.
3) If it goes airborne it’s supposed to be a Type IP-1 package to be excepted from being prohibited from air transport
4) It’s good practice to include the airmail label pictured above with the red airmail hashmarks (that’s what those mean – it’s an air mail notice). Some carriers or airlines may require this label for air. It was included in an instruction set a private business had in an employee manual the NRC showed as a good example for shipping FedEx.

"How Many CPM Should My Sample Read" :

Why There's No Easy Answer

Geiger Counter Check Source

It is natural to ask the following question when coming into a radioactivity hobby:
“How many CPM should (xyz sample) read on my Geiger counter?”

The answer can be impossible to answer and there are several, main reasons why.

1) Readings of Counts Per Minute (CPM) can differ greatly between two perfectly calibrated Geiger counters, due to huge sensitivity and efficiency factors accounting for as much as 18x more or fewer CPM between two of the probes owned by SciHobby authors!
2) There are quantitative sources intended for calibration, and qualitative sources meant as Geiger checks, collectibles, or for demonstrations.

3) Activity levels that should always be in agreement are expressed in Becquerels (Bq) or Curies (Ci). These cannot be measured with Geiger Counter.

Readings Differ Vastly Between Different Geiger Counters (Measuring the Same Sample)

end window geiger counter probe

Readings Differ Vastly Between Different Geiger Counters (Measuring the Same Sample)

CPM readings on your unit can be a fantastic source of information for many purposes. These counts, however, can read incredibly greater or fewer in number between various types of probes designed for different purposes. This often causes misunderstandings.

For one thing, different probes have different amounts of surface area receiving emissions per second. This is one of the first realizations we come to. How could a 4 square centimeter and a 16 square centimeter probe surface possibly yield the same information when one is catching more rays? Secondly, probes have windows or barriers radiation must cross. Window thickness and material type cause more or less radiation to make it inside the probe (this even effects various radiation types differently). Thirdly, depth and volume of the probe’s interior, along with how much anode is in there to read counts, and how it is arranged all come into play, as well.

When someone (with a pancake probe) sells a rock online and says it reads 30,000 CPM, it’s a pretty loaded statement that gets some unwitting buyers disappointed, using side window or even end window probes.

There Are Calibration Sources

Calibration sources are typically something like an expensive, little, sealed and labeled disc containing a certain isotope such as Cesium 137 or Cobalt 60. It is refined, reliable for a certain time frame, and meant to give the same reading from the same equipment every time, under the same conditions. A calibration source is a “quantitative source”. The only way it can be used for calibration is when, for example, literature is provided for a specific probe dictating the desired reading from an exact distance.

A common Geiger check source is more of a “qualitative source”, versus being a quantitative source. It’s not meant for calibration but can be used to show the unit is working, compare levels relative to other sources, and are useful for many types of demonstrations. We’ve seen someone sell uranium rocks for “poor boy” calibration, but it was just for ballpark hobby purposes, and you could only use exactly the same probe he used.

Counts vs. (Overall) Activity Levels

In the science world, Bq or Ci are used to express activity levels upon which physicists should always agree. You don’t see someone wave a wand at an isotope and quote it’s Bq because, for one thing, the genuine activity is being emitted in 360 degrees, whereas a probe is receiving a limited arc or amount of the source’s total emissions. Plus, as explained above, different styles of probes would also disagree, anyway.

Static activity levels expressed in Bq represent decays per second, emitted in all directions. This nomenclature is more a product of scientists working with math and the nuclear physics of precisely what’s going on with the decay that it is any type of unit measured 100% efficiently with any type of sensors.

Counts vs. Doses (Rads and Seiverts)

To further complicate readings between hardware, Geiger counters often display exposure dose-related nomenclature in rem, rads, or roentgen per hour (R/hr.) or Sieverts per hour (Sv/hr.). These are expressions of radiation energy (either being transmitted through the air or being received by an object) as opposed to mere counts that do not involve energy levels per count (which  do vary greatly). The problem with many of these devices dealing with dose equivalents, though, is that Geiger counters don’t truly read energy levels per count. They are merely provided with some kind of, often, arbitrary conversion factor between CPM and dose like mrem/hr., mR/hr. or uSv/hr.

The reason this is a problem is 1000 CPM from one element can carry more or less energy than 1000 CPM from another element. This can easily mean that your reading in dose nomenclature from a Geiger counter is way off unless you know what isotope the unit’s conversion factor from CPM to mR/hr is meant for. This conversion factor yields around 20% different results between Cs137 and Co60. If you’re measuring one isotope when the unit’s conversion factor was meant for another, your R/hr or Sv/hr. will be pretty inaccurate.

One more issue is Geiger counters can’t tell the difference between alpha, beta, or gamma.  This matters dealing with dose-related units because, while rads, rem, and R (roentgens) are generally equivalent for beta and gamma radiation, rems should theoretically become much higher than rads or R when dealing with alpha radiation because, here, you get into the nomenclature differences between exposure, absorbed dose, or dose equivalence all out of the scope of this article. More can be found the NRC and/or HPS.

If you like to pay attention to rads or Seiverts more than CPM, find out what isotope the conversion factor you unit is using was meant for. Some units are coming out where you can enter a multiplier or pick an isotope most similar, in this manner, to the type of specimen you’re reading. Otherwise, take dose readings from Geiger counters with a grain of salt, or maybe some potassium iodide.

Uranium Ore Sale

Uranium Ore for Sale?

Yes, uranium ore is for sale online (see the best sources below). You can buy and own raw, unprocessed uranium and thorium ores in the USA as geological specimens for the purposes of education and even science hobbies involving Geiger counters, cloud chambers, and more. Some rock specimens may contain trace elements of interest while others can be as high as over 47% elemental uranium!

Uranium Ore

Where is Uranium Ore for Sale?

If you want to buy geologic uranium ore specimens that emit the highest highest levels of measurable radiation of any ore available, and even fluoresce (glow) brightly green in UV light (even regular “black light” i.e. no special prospecting light required) then you want to buy autunite (calcium uranyl phosphate) from:
Rocks Unlocked ( 
or try
Geiger Check (
You’ll also find other items like Jurassic Canyon uranium ore rocks and more to add to or even protect your collection from casual pilfering or small kids. The link above are the most affordable and reliable sources of this hard to find mineral no longer available on numerous other sources. We know because each of us own one of the other business and we each forged direct relationships with the miners. It’s no secret we all have the same IP address – we’re friends and/or owners that started out trying to find nice specimens as Geiger counter checks, and uranium glass left something to be desired (esp. if you have a lesser-sensitive device like a side-window probe).

Autunite Uranium Ore for Sale

When it comes to uranium that is for sale, legally, autunite (calcium uranyl phosphate) really hits it out of the park for radioactivity and fluorescent mineral hobbies. The glow really gives it that cinematic, radioactive appeal (although a little UV light is actually required) and the uranium is truly what gives it that classic day-glow green hue.

Vial of Uranium Ore

Autunite is composed of over 47% elemental uranium and even shows noticeable higher radiation levels than even refined, smelted U-238 metal called Depleted Uranium (DU)! How? It’s because unrefined uranium ore in the form of Autunite still contains small amounts of the more scarce and highly potent isotope U-235, as well as trace radium etc. These sister isotopes and elements naturally occur in the nuclear decay chain and, while low in amount compared to the abundant U-238, can make ore that’s only close to half uranium emit more radioactivity than industrial DU metal.

Uranium Ore Sale: Safety

Many, common things in our lives like products used for maintenance or even art can be highly dangerous if misused, but are also completely safe when handled and stored properly. It’s important to educate oneself about proper storage and handling of uranium ore before buying it.

In general, it’s kept in metal containers to shield much of the radiation and stored some feet from living things. The Inverse Square Law of radiation means it dissipates more per inch with each additional inch, so even just a few feet away any normal Geiger counter cannot even detect its presence and risk is abated.

The biggest consideration is getting particles inside of you, that’s why cleanup of oneself and any surfaces is important as not to ingest or even inhale small, solid particles that break loose, as was a common hazard of old school thorium lantern mantles, since they made fine ash.

With a little reading, care, and common sense, uranium ore is safe to buy and own. This is why it has always been legal and collecting it in the field was a even very common (at times viral!) family pastime in the mid 21st century!

Legality of Uranium Ore Sale

When you buy uranium ore online from our known sources you’ll always receive a package that reads below .5mRem/hr. On the parcel surface, with a label including text and numbers required by the NRC and USPS or or other carrier. This makes it perfectly legal as an “excepted package” exempt from many considerations that would apply to real hazmats.

Many, many people get confused about a piece of federal code by the Nuclear Regulatory Commission called NRC, 10 CFR, “§ 40.22 Small quantities of source material”. This is frequently misinterpreted as appearing to allow basically any US citizen to posses or even sell limited amounts of refined, radioactive products like DU and indistrial uranium or thorium compounds etc. as long as they intend to use it for constructive purposes. We have communicated directly, at length, with senior officers at the NRC and we can assure you this is not the case. To the technical letter of the law, this does not even apply to tiny samples.

First of all, section 40.22 is intended for institutions, and I quote Betsy Ullrich of the NRC, “…not private individuals”. Secondly sale or “|initial distribution” is prohibited by subsection (e) of said code without an additional, bona fide, applied-for-and-issued license that is difficult to obtain because it requires experts, considerable lab equipment, etc. Thirdly, 40.22 does not apply to 39 of the 50 US states that have become “Agreement States” meaning they have their own, state-level regulations including possession of radioactive materials.

The Answer: Stick with ore! It’s often prettier, can be just as active (or more, as show above), and is generally legal to possess as long as not misused (“generally” as in: there may be certain buildings, communities etc. where it is not permitted).

Autunite Uranium Ore Hunk

Because, like so many things, it is perfectly safe when stored and handled properly, unprocessed uranium ore has remained legal to buy, sell, and possess in the United States for many decades.

In the mid-1900’s Geiger counters and “scintillators” (amplified detectors for finding ore at distances) were popular recreational hardware with which families could go camping and prospecting, hoping to find and even sell uranium ore in a rather prolonged “uranium rush”. National parks used to issue pamphlets recommending safe practices in collecting uranium and taking it home (like washing hands and not keeping in pockets). While some precautions about nuclear materials have become more rigid since then, the more we know, most of it applies to industrial or military-related substances.

The Parks Service didn’t stop issuing such pamphlets referring to safe uranium-collecting fun because hobbyists got cancer from rocks or anything in subsequent years – they likely stopped because of negative publicity and lack of public understanding. Baseless stigma.

For example, 3 buckets of uranium-bearing rocks were noticed in a Grand Canyon National Park museum. When the story hit the press it went viral and everybody lost their marbles, reporting everywhere that thousands of people including children had been “exposed to dangerous, ionizing radiation”. Despite scientists and officials descending on the situation and determining no one was harmed or really even placed at risk because of the low amounts of uranium involved and the Inverse Square law etc., what mattered was public ignorance, not facts. The big story was the erroneous harm; the confirmation there had never been any danger was of little interest to the press (zero retractions and few follow-ups). So the Parks Service freaked out about their reputation (not safety) and bulldozed any and all uranium rocks far away from rest areas and public access (the the dismay of local hobbyists).

Legitimate Uses for Uranium Ore people have no interest in something they have little understanding (and often little tolerance) of it. One of the most common questions about uranium ore sale and purchase is, “What on Earth would anyone want it for?!”, asked with anything from curiosity to naïve, accusatory contempt suggesting inevitable villainy. To anyone bitten with the Geiger counter bug, the answer is self evident: because it’s cool. A more informative answer is that, besides demonstrating different levels of alpha, beta, and gamma radiation between different, collectible specimens (which is reason enough), other uses include source material for a cloud chamber (an easy DIY project that makes radiation leave contrails visible to the naked eye)…

a cloud chamber with uranium inside

…experiments with digital or film photography, building a spinthariscope (another device that makes effects of radiation visible, but in the form of sparkles) or other radioluminescence (glowing due to nuclear emissions) experiments with phosphors like copper-activated zinc sulfide, and much more. These demonstrations, experiments, and other activities are safely performed not only by hobbyists and parents but teachers and institutions who are among customers buying uranium for sale online.

What is the Best Geiger Counter?

Selecting a Geiger counter for your science hobby...

What is the Purpose?

When asking, “What is the best Geiger Counter?”, one must ask oneself, first, what the overall purposes mainly are. Geiger counters are not a one-size-fits-all. Since there are numerous interests or goals to consider before deciding, here, we focus on features to look for more than exact models.

GQ GMC 600cheap geiger countervintage Geiger Counter CDV-700

Vintage or Modern?

Vintage Geiger counters like a old Civil Defense unit definitely win in the Coolness Factor category for a lot of people. A character in “The X-Files” or J.J. Abrams’ “Fringe” is likely to be sporting a sizable unit like a lunchbox with a wand and a needle gauge. This type of unit can be the most fun to use for anyone who likes the charm of older tech, but they can also need updating or repair, and lack modern bells and whistles and more.

Many modern Geiger counters can log and remember data with a timestamp for days on end. Often, they can connect to computers to build graphs or charts based on the data they’ve recorded. Digital displays allow for easy reading and even cycling through modes such as Counts Per Minute (CPM) or dose values such as Rems or Sieverts.

A Note on Reading Rems or Sieverts vs. CPM :

Since Geiger counters may measure counts more accurately than dose equivalents, remember that two perfectly operating, freshly calibrated Geiger counters can easily give you dose readings around 20% different from one another because they were set up using different calibration sources (for one thing). You either have to take dose readings on Geiger counters with a grain of salt or know what isotope your unit was calibrated to (dose-wise) and how similarly that applies to your target check source material for accuracy.

Geiger counters can only read counts, not energy levels. They merely convert CPM to doses by using a static mathematical conversion formula, and this formula is different for different source materials because they each yield counts that are worth differing amounts of energy per count. A Cs137-calibrated unit will be off, dose-wise, when measuring Co60 and vice-versa.

How Sensitive Must it Be? (A Biggie!!)

Different Geiger counters often don’t even display even remotely the same CPM as each other. One of the biggest misnomers is that two properly calibrated Geiger counters will always get the same CPM reading as each other when sharing a check source at the same distance or spot. This is actually quite incorrect (easily by a factor of 5x or even 20x) and leads to puzzled complaints by buyers of geological specimens, to the sellers, wondering why they get a lower or higher reading than advertised. This is because one of them is using a more sensitive probe than the other.

The Nuclear Regulatory Commission also regularly receives reports that someone shipped someone else a package that was emitting well over the legal limit of radiation for the type of container or labels they used. This is because a less sensitive Geiger counter was used at the origin to test the package surface before release, then an unnecessarily sensitive unit or probe was used on the receiving end, freaking out the recipients without cause.

This is mainly because of differing probes being used, and all may be “correct” despite major disparities between levels displayed. Some probes are inherently less sensitive than others, and you can’t simply compensate by making electronic adjustments during calibration. If an end-window probe is 5x less sensitive than a pancake probe, you can’t just crank up the electronics to be 5x more sensitive for the end-window probe, to compensate during calibration, in order to make the unit with the end-window probe yield the same readings as the one with the pancake probe. It doesn’t work that way; to put it scientifically – it would throw everything out of whack (esp. between different isotopes and profiles of radiation). This is further explained below.

Geiger counters can have:

(Internally as wands or internally integrated)

Side window probes

geiger mueller probe

these are the least expensive and also the least sensitive. They often measure beta and gamma (and not alpha). Modern units GQ GMC 300 through GQ GMC 500 have one of these (the 500+ has two) and the typical, vintage, yellow CD-V700 has one by default (you know if it reads from window slotted on the side on the nickle-plated “hot dog” probe). Low-radiation sources (like salt substitute or fertilizer) may not register on this at all, and a uranium glass marble will yield very little reading. Old, active Fiesta Ware ceramic or a thorium lantern mantle should show up just fine. A radium-painted alarm clock will show on these relatively well, even through the clock’s glass. Commercially available rocks (see our affiliate ads to the side!) are read well by these probes unless the specimen is very low-level. Autunite will make it go pleasantly nuts.

End window probes

end window geiger counter probe

these are considerably more sensitive than side-window probes and usually have a thin mica window on the end allowing good alpha particle readings. These are a good compromise between a pancake probe and a side-window probe in price and sensitivity (esp. price). You won’t read a banana as being above background level (which it technically is, due to potassium) but you can get threshold readings from fertilizer etc. and even small, positive hits from occasional, random pieces of granite or quartz that have trace elements with nuclear decay going on. Of course, with it being both more sensitive and also reading alphas, “all the usual suspects” listed above (check source specimens like Fiesta Ware) will make a unit with an end-window probe really sing. It can really be a lot more rewarding than a side-read probe.

Pancake probes

pancake probe for a Geiger Counter

these are the most expensive so far listed, here, and are often about 500% more sensitive than some end-window probes. In fact, if a vintage Geiger counter is fit with a pancake probe like 44-9 and the unit only goes up to 100x scale, a fairly hot collectible rock or an shielded radium clock face may peg the needle, up close. Many units can read a spectacular range of radioactivity with a pancake, though. This kind can be hugely fun, as you can begin to get threshold readings from a banana, a human, get really positive readings from salt substitute or uranium glass, and many random objects. Vintage units like a Ludlum 3 can often be seen sporting a round pancake on the end of its wand, as well as modern Ludlum Geiger counters made in a similar shape. They are also put inside 1-piece units like the GQ’s GMC series’ 600+ model.

Even higher sensitivity — from here the list goes on to more specialized and mainly industrial examples, from alpha probes with far more surface area to, even, scintillator probes that actively amplify weak gamma signals with a photomultiplier tube inside . With a directional scintillator you may detect uranium from across an entire area, helping you play a game of “hotter/colder” when prospecting, but the meter can get pegged with max. input once you get too near the outcrop or source, so you need to shut it off and deploy a lesser sensitive probe unit to look more closely for the rocks.

Further Sensitivity Factors:

Even the three main hobby types, listed above, vary in readings between models (on calibrated, accurate devices) because of:
total probe surface area
tube wall or window thickness
– amount of anode (receiving element) inside

…and other variables.

All Geiger Counter calibration really means, here, is that exact same hardware can be set up to yield exactly the same, expected results. Other than that, the hardware can wildly vary readings from the same sample, and they are, albeit counter-intuitive, all “correct”. New hobbyists can be seen buying a pancake-equipped unit (capable of alpha, beta, and gamma readings) and using it alongside their side-window unit (capable of beta and gamma, only). They often think that if they subtract the side-window’s readings from the pancake’s readings the remainder will be pure alpha, but its just not so. The pancake is also more sensitive to the gamma and beta.

One thought example (surface area, alone):
If I tell you a piece of autunite is yielding 35,000 CPM… is that radiation measured over 2 square cm or 20? In fact, if you want to know how much output the specimen is emitting, would you like to know just from one direction, or 360 degrees around the rock?

For these types of reasons, clinical specs are often cited along with the exact
and isotope and distance from it used for calibration

In Conclusion:

We hope we shed some light on types of Geiger counters or features and facts to consider when selecting a Geiger counter. It is largely based on one’s measurement expectations, budget, and even taste.

The nostalgic author’s go-to unit is currently a Victoreen 493 with an end-window probe. I also have a CD V-700 refurbished with solid state hardware, with the standard side-window probe which I am considering modifying with a x200 scale option and a pancake probe. See our article about selecting a vintage Geiger counter.

vintage geiger counters

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Geiger Check Website

Choosing a Vintage Geiger Counter

Many of us find ourselves in the market for a vintage Geiger counter. Like radios and other gear, they have a pleasing, well-built charm.

vintage Geiger Counter CDV-700

Electro-Neutronics CD V-700 with alpha-sensitive end window probe. Licensed image courtesy of Bullet308

While vintage Geiger counters can be very appealing and economical, we do need to a) keep them running and b) get out of them whatever total functionality we truly require. You may be surprised to find out that even the most basic, old Geiger counter can have its headphones output routed into a modern Windows device to digitally convert and log data! We provide that free software in the links, further down.

Advanced Needs vs. Standard

Two categories emerge in our deciding on the best vintage Geiger counter. We’ll call them Advanced and Standard. We’ll get Advanced out of the way, first, because the majority of this article focuses on the advantages of a particular model well-suited for Standard needs for a number of reasons including community support – the CD V-700 (see Standard, below). More is not necessarily better unless you need it.


If we were looking to hook up, drive, and interpret findings of advanced probes like a gamma scintillation probe (a special, amplified probe that can detect very faint or distant traces, as for longer-range prospecting), then a good Ludlum unit for an acceptable price would be up our alley, such as the Ludlum 3 (most of their models that accept an external probe are full-featured units). Ludlum units are very reliable, seemingly made with above-average components, because we find them working fine, without ever having been refurbished (maybe due for calibration), for decades. They are also equipped with advanced features not required for basic readings for typical, exploratory hobby purposes.

Vintage Geiger Counter

Even with the basic, insensitive beta/gamma-only side-read probe, this Ludlum 3 sold on Ebay for well over $600 by seller “my_brain_fart”

For these reasons, it’s usually difficult to find a Ludlum Geiger counter in reliable shape for less than $350, at best, if not much more ($700 or more is common for a nice one) – and be careful of condition, as probes are particularly easily damaged or contaminated. They’re also more complicated and tightly packed with parts if you’re considering working on one inside.

We’re planning a Ludlum for outdoor prospecting, to use to find outcrops at a distance with a scintillation probe, and then approach with our more standard Lionel CD V-700 or Victoreen 493 after we get closer to the right rocks (at which point a scintillator would be overloaded with excess signal). There are other good brands like Bicron, Johnson, and others (even fancy desk units called scalers) but that’s for another article. The Ludlum 3 or similar gets our Advanced vote for Vintage Geiger Counters and is on our 2022 wish list. It’s so popular they still make a similar version of it.

→ Standard ←

The CD V-700 !

When we’re looking to buy a (another) great-looking vintage Geiger counter, we’re looking to save money, and we are using a standard Geiger–Müller probe (possibly even relatively sensitive ones) then our hands-down winner is the CD V-700!

CDV-700 Geiger Counter


Our refurbished Lionel CD V-700 (left) is very similar to our stock Victoreen 493 (right). We may put the end-window probe on the V-700, recalibrate it, and refurb the Victoreen later.

The CDV-700:
Were produced (and still exist) in countless number
Can be found very inexpensively
Are easy to repair, as they are simple and spacious inside
Can be modified and upgraded in numerous, well-documented ways
Have considerable technical information available for them
Have plenty of compatible parts and even prefab assemblies available
Are a real piece of world history, connected to Civil Defense

Numerous versions of the CDV-700 were made by a number of companies for Civil Defense issue. Usually colored yellow and emblazoned with the cool, Civil Defense “CD” logo, they were made by the thousand by companies including Lionel, Anton, Electro-Neutronics, and Victoreen.

CDV-700 Vintage Geiger Counter

They are similar in general design to the Ludlum 3 discussed., but would require an inordinate amount of work to adapt to scintillation probes or to accomodate advanced adjustments and functions.

The CDV-700 does employ a standard 900v power supply which will run many, typical probes, anywhere from the stock, side-read, gamma/beta “hot dog” probe, to a thin mica end-window probe, to a pancake probe (each example increasing progressively in sensitivity from first to last). Geiger counters require re-calibration if not other minor adaptations if upgraded in this fashion, but it is a straightforward process.

CD V-700 Resources

There are too many makes of the CDV-700 (some with minor internal differences) to to feature them all the manuals here by exact name, but you will have no problems finding the standard literature for yours doing a simple search. The main thing is to seek out not only the primary users manual (usually called “Instruction and Maintenance Manual”) but also, if available, the Shop Manual. This can be more difficult to find but contains more information. The Shop Manual for the Lionel CD V-700 Geiger counter, at least, is below (along with numerous users manuals). Also, it is the authors’ understanding that the Lionel and Anton units are particularly similar.


GeoElectronics CD V-700 Stuff

George Dowell of GeoElectronics is, among other things, a pioneer of refurbishing the CDV-700 (with solid state hardware) as well as modifications and upgrades.

Here he shows how to take an Electro-Neutronics Inc. CDV-700 (dubbed the “ENi”) and use its preferred layout to host the preferred components from the Lionel unit, merging the best of both models into what he calls the “LENi”. He also does various other things like adding a speaker and a built-in pancake probe. You don’t have to intend on doing all of this to get a lot of extra understanding of the CDV-700 Geiger counters with this fabulous article that has been hosted on multiple amateur radio forums:

KFF Homebrew Tips: Geiger Counters in the Ham Shack (at


KFF Homebrew Tips: Geiger Counters in the Ham Shack (at eHam, with comments)

The only sub-link that doesn’t work lately for us is his “Speak2Me” CDV-705 Clone audio module instructions in PDF format, but here is a working HTML copy of that:

Speak2Me CDV-705 Clone Audio Module Instructions

audio module for cd v-700


GeoElectronics offers key parts for the repair, refurbishing, or modification of your CD V-700. You can find two accounts on Ebay, both valid.

The main one seems to be simply:


and the other to try is:


CD V-700... Software?!

One of the advantages of modern (but sometimes joylessly plastic) radiation meters is that they can log data and save the record digitally. Believe it or not, you can do this with the CD V-700 or any other Geiger counter that sends clicks out of an audio jack, using Windows freeware called CDV Counter! We just tested it in Windows 10 and it runs fine!

CDV Counter Freeware for Windows:
SourceForge Download Link for CDV Counter

SciHobby Direct Download:

Buy Radioactive Specimens

You can buy quality radioactive test samples for less money at these fine stores:

buy uranium online


Geiger Check Website

In Closing...

While a Ludlum is on our own wish list for prospecting with a 3-inch-wide gamma scintillation probe (there are some great scintillation probe refurbs and DIY kits on Ebay) we love turning people on to the community support, resources and possibilities still available for the CD V-700 which one may find seriously lacking for many other vintage Geiger counters.

A Primer on Fluorescent Minerals

fluorescing rock

Fluorescing Willemite from Sweden. CC Licensed image by Dr. Hannes Grobe

What Fluorescence Is

Fluorescent minerals in rocks and crystals, just as in many paints or toys, can appear to glow with stunning brightness when exposed to what, for us, is dim or invisible light from ultraviolet (UV) lamps or even other wavelengths including x-rays. They can appear to the human eye as though they are reflecting more light, and in a different color, than you are emitting them. Technically they absorb light of one wavelength or color and emit some light in a different wavelength or color. If we could see UV as well as day-glow green, for example, the effect, above, would be far less remarkable. In reality, it’s emitting less energy than it’s absorbing. Our own inability to perceive UV light gives it the illusion of radioluminescence (a glow caused by ionizing radiation interacting with matter). Different UV light-triggered fluorescent minerals respond (or not) to various wavelengths of UV. While some respond to common black light (a particularly long-waved section of UV-A band) many respond better or only to shorter wavelengths such as UV-B or even UV-C (the shorter the wavelength and higher the wattage the more protective glasses are called for).

What Fluorescence is Not

Fluorescence is not the same as phosphorescence. Phosphorescent minerals continue to emit light for a while after the responsible light source is switched off or removed, whereas fluorescent minerals stop emitting as soon as the source is removed. While these two terms and others represent different properties, some minerals may possess multiple properties at once. Some may be subsets of others, such “fluorescent” and “phosphorescent” being subsets that fall under “luminescence”. Luminescence means emitting light without being heated to the point of incandescence, and incandescence usually means something is on the verge of burning up, like the filament of a classic light bulb.

On that note, fluorescence is also not the same as other luminescent properties such as that of thermoluminescent minerals. These can emit light when heated, but often far less than enough to become incandescent. Imagine lining a campfire with rocks and finding they “come alive” from the heat and start glowing in beautiful patterns like something from science fiction! It happens:

a luminescent mineral glowing from heat

Fluorite, one more visibly thermoluminescent than the other. CC licensed image by Mauswiesel

Many fluorescent minerals are also not necessarily radioluminescent, although some of the most vibrant, fluorescent hues incidentally come from materials containing radioactive uranium, such as autunite, otherwise known as calco-uranite or calcium uranyl phosphate, and  sometimes described as uranium mica according to its lamellar or layered nature.

Autunite Uranium Ore Hunk

Autunite fluorescing under long UV-A black light

Other types of luminescence in minerals exist aside from fluorescence, such as triboluminescence, the emission of visible light as a result of mechanical action such as being struck or crushed. Triboluminescence is related to piezoelectricity, where electricity is  voltage is generated from crystals being struck or placed under pressure such as is utilized in press-button or “clicker” ignitors for lighters and gas stoves.

Identifying Fluorescent Minerals !

Below is a phenomenal photo of a collection of fluorescent minerals by Dr. Hannes Grobe using all three bands of UV light combined. Below the images is a numbered, fluorescent minerals list corresponding to the numbers in the black & white indicator chart. Special thanks to Dr. Grobe and his licensed provision of such a fun resource through Creative Commons:

fluorescent minerals in a collection
fluorescent minerals guide

1. Cerussite, Barite – Morocco
2. Scapolite – Canada
3. Hardystonite (blue), Calcite (red), Willemite (green) – New Jersey
4. Dolomite – Sweden
5. Adamite – Mexico
6. Scheelite – unknown origin
7. Agate – Utah
8. Tremolite – New York
9. Willemite – New Jersey
10. Dolomite – Sweden
11. Fluorite, Calcite – Switzerland
12. Calcite – Romania
13. Rhyolite – unknown origin
14. Dolomite – Sweden
15. Willemite (green), Calcite (red), Franklinite, Rhodonite – New Jersey
16. Eucryptite – Zimbabwe
17. Calcite – Germany
18. Calcite in a Septarian nodule – Utah
19. Fluorite – England
20. Calcite – Sweden
21. Calcite, Dolomite – Sardinia
22. Dripstones – Turkey
23. Scheelite – unknown origin
24. Aragonite – Sicily
25. Benitoite – California 26. Quartz Geode – Germany
27. Dolomite, Iron Ore – Sweden
28. Unknown
29. Synthetic Corundum
30. Powellite – India
31. Hyalite opal – Hungary
32. Vlasovite in Eudyalite – Canada
33. Spar Calcite – Mexico
34. Manganocalcite(?) – Sweden
35. Clinohydrite, Hardystonite, Willemite, Calcite – New Jersey
36. Calcite – Switzerland
37. Apatite, Diopside – USA
38. Dolostone – Sweden
39. Fluorite – England
40. Manganocalcite – Peru
41. Hemimorphite with Sphalerite in gangue – Germany
42. Unknown from Långban, Filipstad, Sweden
43. Opal – origin unknown
44. Selenite gypsum – origin unknown
45. Dolomite – Sweden
46. Chalcedony – unknown origin
47. Willemite, Calcite – New Jersey

How to Make a Cloud Chamber

CloudyLabs cloud chamber

Uranium emitting alpha particles
in a cloud chamber at CloudyLabs

Choosing One

When deciding how to build a cloud chamber, it’s best to consider a few factors before choosing a set of plans. We selected our favorite resource for each of several, simple versions or models, below (and threw in where to get rare, hard-to-find source material as well)!

Keeping it Simple

Most visitors want to take a simple route rather than making formidable project out of it, as is required for professional models with electrically-powered coolers and heaters. We’ll link those, as well, but the easiest types use simple materials that are readily available. Versions range anywhere from a mere petri dish on a slab of dry ice, to professional thermoelectric units generating their own warm or cold regions, or even models that control the paths of detected particles. We’ll feature a separate article on the latter, most sophisticated types.

Easiest Builds Use Dry Ice

cloud chamber dry ice 

Note: When we refer to “dry ice” we mean genuine, frozen CO2, not those reusable cooler packs or plastic containers full of frozen media often called “dry ice” by some companies. Real dry ice is surprisingly available in the US. Supermarkets such as Publix and Walmart have begin carrying dry ice under brands such as Penguin, just ask management or customer service..

Warning: Frozen, solid CO2 dry ice is cold enough to cause damage to your bodily tissues with more than a quick poke, so you cannot safely handle it without thick insulation or tongs etc.. Also, a lot of dry ice in a confined area can cause unsafe levels of CO2, but that concern has more to do with large quantities or people trying to immerse themselves in its fog.

Winner of the the elegantly simple award:
The Dept. of Energy’s Jefferson Lab shows how to build cloud chamber from a petri dish, felt, and 91% rubbing alcohol (not 70%).

A step up:

#1 in Popularity (with dry ice)

Below is how to construct the quintessential favorite cloud chamber with the fumes raining down from a sponge on the ceiling of a more substantial, aquarium-like container. Still, we’re talking about few items even from a dollar store fitting the bill, but for a spectacular show. It doesn’t have to be this large (such as in the Without Dry Ice version further down – that one has a very common, smaller dollar store clear breakfast cereal “tank”).

The US LHC (of CERN) provides a concise tutorial for making this all-time favorite version:

What’s great is they also offer the accompanying S’Cool Lab manual in PDF free for download:
PDF Instruction Set Download Link

Symmetry Magazine‘s Step by Step version of the same type:
How to Build a Cloud Chamber (with dry ice)

How to Make a Cloud Chamber Without Dry Ice

You may pursue building a cloud chamber without dry ice, using gel packs or polymers, particularly if you have no easy access to dry ice.

The construction requirements are slightly more involved, however, when substituting polymer in place of dry ice. So, if you do have access to dry ice, you may decide the dry ice model is the easiest route for you (and a little more foolproof, it seems, with a couple fewer variable).

The project is similar for both the simple DIY models of could chamber, whether they use dry ice or freezer gel packs but, because the gel packs are not as cold, the no-dry-ice-required model includes a couple of extra, special needs. It requires a minimum vertical height and it requires added heat on top, like a reservoir of hot water which is not really required for dry ice models for an adequate temperature gradient above to cold floor.

Note – The following is not mentioned in the video but is important:
You can see the bottom reservoir (functioning as the cloud chamber) is taller than the one on top. Harold Henderson’s experiments showed that this extra, vertical space was necessary (versus using two the same size as the shorter, top container) i.e. a good 15 or 20cm cloud chamber height is needed for the no-dry-ice version.

Professor Paul Looyen of Physics High hosts the world’s most popular video how to build a cloud chamber without dry ice:

If you’d like to get into various methods of electrically powering methods of heating or cooling, experimenting with supposedly making the trails more visible with a high voltage differential field, or hijacking particles and directing them with electromagnetic fields, we’ll soon feature a new article on those. For now, get your feet wet and keep it simple. 

Finding radioactive source material:

It’s the most fun seeing or measuring radioactivity when you can compare a collection  of check sources ranging from lower to higher (staying safe, of course, with proper information, handling, and storage).

Uranium glass and 2% thorium, tungsten welding rods, and maybe a vintage gas lantern mantle are available everywhere, but the rarer check sources on the higher end of safe and legal (like uranium mica crystals, or desert rocks with unusually high ore inclusions) can be expensive or hard to find. When you want the piece de resistance or grand finale  to look like fireworks in the cloud chamber, we suggest:

buy uranium ore
Uranium samples to purchase

(must be 18 or older to purchase ore)