Set The Voltage On A Geiger Counter

How Do You Set The Voltage On A Geiger Counter?

Well, I'll show you how in this post. Here is my Ludlum Model 3 Survey Meter (it's the boxy thing on the right).

The box is a survey meter. The tube-shaped detectors (on top of the box) can be Geiger-Mueller tubes (GM), or they can be plastic crystals joined to a photo multiplier tube (PMT). So technically it's only a "Geiger Counter" when I have my other detector plugged into it-not the PMT in the photo.

So, in the above photo are what I use to set voltages. Most radiation detectors use 900 volts DC. Some do not. My Ludlum 3 can be adjusted anywhere from 400vDC to 1500vDC! Most true Geiger-Mueller detector tubes take 900vDC. So, we are dealing with electricity at high voltages. Which is why I have a HUGE Cal Test CT2700 high voltage probe, which has a 1000 to 1 voltage divider. 40,000vDC goes in, but only 40vDC would past through to my Extech MN36 multimeter.

Compared to the little probes (extreme left of first photo) you can see this beast means business! It can take up to 40,000vDC and 28,000vAC and only pass through exactly 1/1000th of the voltage, so my multimeter doesn't burst into flames!

I'll be setting the Ludlum survey meter to 900vDC, which will read as 0.900vDC on my multimeter. This high voltage probe needs a multimeter with at least a 10M Ohm input resistance. The Extech MN36 has exactly 10 Mega Ohms input resistance and works great!

So, on the Ludlum Model 3 survey meter there is a metal plate on the top of the case that says "CAL". It is just held on by two screws.

Here it is after removal, showing the 5 adjustment pots (potentiometers) that are screwdriver adjustable. ONLY adjust the top one labeled "HV" for high voltage. Some people put take over the other 4 holes which are used for adjusting the multiples meter readouts. Adjusting those takes a pulser devices which feeds a signal to the meter-if you don't own a pulser, you should never mess with those other pots.

Here's the steps I use to set the required voltage:

1. Unplug the detector cable from the box.
2. Clip the ground clip of the high voltage probe to the detector tubes holding bracket.
3. Turn the survey meter on and set to "Battery".
4. Put the point of the high voltage probe into the center hole where the detector cable is normally plugged into.
5. With a screwdriver, adjust the HV pot until your multimeter reads 1/1000 of your desired setting (900v would display as 0.900v).
6. Once done turn off the survey meter and wait 2 minutes before reattaching the detector cable. You'll hear the high voltage system "power down" a little while after turning the survey meter off.

Cautions:

1. You can get a shock by touching the center hole where the detector cable plugs in.
2. You can get a shock touching the other end of the cable.
3. You can get shocked touching the (red) portion of the high voltage probe below the (black) handle.
4. High voltage stays for a couple minutes (or more) even after removing the batteries from the survey meter!
5. Wait a few minutes after shutting off the survey meter before attaching our detaching the cable and/or a detector.
6. If your multimeter isn't 10M Ohms, your readings will be way off.


How do you know what voltage you need to set your survey meter to? Well, it depends on what detector tubes you want to use. The photo below shows my Ludlum 44-7 alpha/beta/gamma probe which takes 900vDC.

To the right is my Ludlum 42-2 neutron probe (Ludlum 47-1502 neutron scintillator), which is happier with a bit less than 1000vDC, even though the specs call for 900vDC. The meter pegs out at full and the clicks turn into a scream at 900vDC, so I set it around 600vDC when plugging in the neutron probe; but it's a fine art. Sometimes I dial it in to over 1000vDC just to get an occasional click as background. It's touchy! IT SHOULD BE NOTED THAT AT THIS POINT IT'S ONLY DETECTING GAMMA...a Ludlum Model 12 meter would be able to handle neutron probes because it has a threshold knob. 

Just yesterday I plugged it in and without using a voltage meter I played around until I could (just barely) discern a slight difference when placing and removing an AmBe (Americium Beryllium) neutron source. I have to believe most of the clicks were gamma radiation noise, but the most usable setting just happened to be 600vDC after removing the probe and checking the actual settings with the multimeter/high voltage probe. At that setting there was a huge rise in clicks when I placed a Uranium source (alpha/beta/gamma) next to it too...so I'm just reading gamma at the moment. At some point a pure alpha check source (Polonium) will be acquired for definitive testing. I don't do much with neutrons at the moment so it's not a pressing issue.

Specs? Luckily, Ludlum is still in business and they have PDF files of many of their old user manuals online for free.



However, for the neutron probe Ludlum had nothing, so I had to find other sources of information. Other people actually contacted Ludlum, and all they could get was a confirmation of the model number. I had to dig deeper than that:

Below is some great information on some older NEUTRON DETECTORS (as opposed to Geiger Counters) which you may find used online, which I also put in an older post about "My Radioactive Dime". I snagged most of this info from a 1973 report to the US Atomic Energy Commission by Alex Lorenz. If you want to read the full report, it's available as a PDF online by searching "Review of Neutron Detection Methods and Instruments".

That document has more information on each device, including the method of detection (i.e. chemical composition of scintillator crystal, etc.). It' a great document to consult if you're like many people and find just a part/tube/probe of one of these devices and want to use it with a different base/amplifier/etc.

You'll want to pay attention as to whether your Neutron detector sees fast or slow neutrons--that makes a difference in whether or not you need to use paraffin or other moderators or actually have to remove those barriers and moderators from your experiment. You don't want to slow down your neutrons with paraffin if your device can only see the fast ones and vice versa.  

DEVICE                         RANGE                       VOLTAGE

Ludlum	Fast neutrons	900v
(Model 42-2)
Eberline	slow or fast neutrons	900-1200v
(Model SPA-2)
Ludlum	1/v for thermal neutrons	900v
(Model 42-1)
Kaman	thermal & fast —	120v
(Model A-300)	0-14 MeV
Ludlum	thermal - 12 MeV	900v
(Model 42-4)
IiUdium	thermal & fast neutrons	900v
(Model 42-5)
LND	thermal neutrons	?
(Series 900)
Ortec	?	?
(System 525)
Nuclear Instruments	Linear between	?
and Chemical Corp.	10^7 and 10^12 nv
(Model 3782)
Reuter Stokes Co	1 0^15  nv	?
Reuter Stokes Cd	5X 0 ^014 nv	?
Reuter Stokes Rh	10^15 nv	?
Reuter Stokes V	10^15 nv	?
Reuter Stokes	10^10  nv	1000-1400v
(RSN-337)	(thermal)
Ludlum	thermal and fast	500-2400v
(Model 15)	neutrons
Centronics	<7.5x10^10 nv	1000v
(Type D.C. 12)
Reuter Stokes	3x10^4 to 2.5x10^5	800-900v
(RSN-17A/326/	(thermal)
330/251/327)
Reuter Stokes	10^4 to 10^11	800v
(RSN-229A)	(thermal)
Reuter Stokes	10^4 to 10^11	800v
(HSN-234A-M1)	(thermal)
Reuter Stokes	10^3 to 10^10
(RSN-15A/304/	(thermal)	100-1000v
325/332/306)
Reuter Stokes	10^3 to 10^10	200-800v
(RSN-314A)	(thermal)
Reuter Stokes	10^8 to 10^14	20-150v
(RSN-186S-M2	(thermal)
and 316S-M5)
LND	3 decades
(Series 30771)		500v
LND	5 decades	200-800v
(Series 3077)	Thermal (U235)
	or fast (U238)
(Series 3075)	Thermal	200-500v
(Series 3000,	Thermal	50-500v
Series 3050)
Centronics	9x10^3 to 9x10^7	250-500v
(PFC 16A)
Texas Nuclear	Thermal	800-1400v
(Series 9300
Texlium)
Eberline	Dose response from	1600-2000v
(PNR-4 and	thermal to 10 MeV
NRD-1)
Eberline	0.01-10^3 eV &	1300-1800v
(PNC-4)	0.2-18 MeV
Harshaw	Thermal	1700-3400v
(Model series
B3, B6, B12, B14)
Reuter Stokes	10^-3 to 10^-5	2500-3500v
(RSN-7A/7S/44/	Thermal
177S-M7/320-M2/
108S-MG)
N. Wood Model G	?	1100-2300v
Centronics	3.3x10^3 to 6x10^6	900-1100v
(Series 5EB/6)
Texas Nuclear Series 9300 Texlium	Thermal	800-1400v
LND
(Series 3000,	Thermal	50-500v
3050)
Centronics PFC 16A	9x10^3 to 9x10^7	250-500v
Centronics PFC 16B	10^11	200-400v

By the way, another great place to creep around and find info like this is the Oak Ridge National Lab at http://web.ornl.gov/info/reports/ which has tons of DECLASSIFIED reports of various techniques for radioactive fun. The directories are by year--so just poke around. A cool file I found was "The Preparation, Properties, and Uses of Americium - 241, Alpha-, Gamma-, and Neutron Sources" in the 1962 folder.

INFORMATION FOR GAMMA SPECTROMETRY

For gamma ray spectroscopy NaI(TL) crystal scintillation detectors are best. Bicron, Rexon, Teledyne and a few other detector brands can share internal components with each other. Here are general crystal stats:

Type	Scintillation Crystal Type	Density (g/cm)	Emission Maximum (nm)	Decay Constant		Index of refraction	Relative conversion efficiency
BaF2	Barium Fluoride	4.88	310	0.63		us	1.50
BGO	Bismuth Germanate	7.13	480	0.3	us	2.15	15-20
CaF2 (Eu)	Calcium Fluoride	3.18	435	0.94	us	1.47	50
CdWO4	Cadmium Tungstate	7.90	470/540	20/5	us	2.30	25-30
CsI(Na)	Cesium Iodide doped with Sodium	4.51	420	0.63	us	1.84	85
CsI(Tl)	Cesium Iodide doped with Thallium	4.51	550	1.0	us	1.79	45
CsF	Cesium Fluoride	4.64	390	3.5	ns	1.48	5-7
GSO(Ce)	Gadolinium Silicate doped with Cerium	6.71	440	30-60	ns	1.85	20-25
LiI (Eu)	Lithium Iodide	4.08	470	1.4	us	1.96	35
NaI (T1)	*Sodium Iodide doped with Thallium*	3.67	415	0.23	us	1.85	*100*
YAP	Yttrium Aluminum Oxide Perovskite		350	27	ns
ZnS(Ag)	Silver activated Zinc Sulfide	4.09	450	110	ns	2.36	25 - 30

Rexon Inc.'s Dr M. H. Farukhi has layed out an informative explanation of each crystal type here: http://www.rexon.com/crystalscintypes.htm 

Lemme know when all the neutrons are gone and it's safe to come out! Meow.

Box Kite: A Single Brace Prototype

Box Kite: A Single Brace Prototype

Here is a box kite I just made. There are tons of kite plans online, but my kite has some major differences.  My box kite just has a single central brace instead of two end braces. I also used balsa instead of spruce or pine.

These changes from the norm created issues, which I dealt with, to create a really small and light weight flyer.

Traditional, flat diamond-shaped kites are harder to manage in the wind. As the wind speed rises, they'll need a longer and longer tail. Tails stabilize kites by adding drag (it's not really the weight that helps).

I wanted to design a kite that was easy to keep up and that could handle rougher winds without the need for longer and longer tails-all in as small a kite as possible.

This led me to a box kite, because multi-planed kites are easier to fly and usually don't require any tail.

I also wanted to go extremely light and small. I replaced the usual spruce and pine with balsa wood.

Weight per cubic foot

Spruce = 28lbs

Pine = 26-45lbs

Carbon Fiber = 106lbs

Aluminum = 168lbs

Balsa = 4-24lbs

As you can see, balsa is much lighter than the other materials. You'll notice that carbon fiber is really, really heavy! The secret to using light weight materials is actually a misnomer: they're really strong for their used size. 

Steel is heavier than aluminum but an aircraft part made of aluminum the size of a pencil can be redesigned and made out of steel the size of a toothpick. Making an aluminum part as an exact copy in carbon fiber doesn't save you much weight, but you can make it thinner and in a different (smaller, thinner, shorter) shape and that's where the real weight savings begin to appear.

My redesign? Well, I didn't just replace the spruce with balsa. I also radically modified the traditional box kite design by getting rid of the end braces and creating a single, central brace.

Wind passing over a plane wing creates lift. An airplane propeller creates wind over the wing. The Wright Brothers took box kites in a cellular / modular design and added an engine to create wind on demand. Boom: a hard to steer airplane!

Then the Wright Brothers came up with something awesome: make the boxes super-flexible! This really helps catch and keep the wind.

Instead of a rock solid brace at both ends of the box, my design has a slightly flexible central brace! It will catch the wind more easily. Also, I'm now using lighter wood-and a lot less of it. [edit: I oddly used heavy newspaper instead of lighter materials like plastic grocery bags to cover this].

Another change I made is to scale down the traditional box kite measurements. Box kites were used to lift things like emergency radio antennas in life rafts. Almost and other box kite plan you'll see online the standard 40" long rail variety or larger. This box kite is only 10" long!

A (Braces)               17"     8.5"     4.25"    2.125"    1.7"

B (Rails)                  40"      20"        10"            5"       4"

C (Skins)                 12"        6"          3"            1.5"    .75"

D (String offset)    6"          3"         1.5"          .75"    .375"

E (End String)       60"        30"         15"         7.5"    3.75"

F (Offset String)    50"        25"         12.5"     6.25"    3.375"

Basically, I just scaled down everything. I came up with the above numbers and used the third column-except for the string lengths (E and F) leading to the bridle.

Balsa cuts and saws very easily.

I notched the center brace components using the little Xacto saw and then just cleaned up the notch with an Xacto blade.

My new, experimental one-of-a-kind Logusz Brace. It joins together tightly even without glue.

The other joints were notched as well.

Clamps! I highly recommend you don't do what I did by using heavy clamps. Also, don't use alligator clips because they'll damage the balsa. Go online and order some "panel clamps" for $2 each. They're perfect for this type of thing and are made for clamping thin bits of metal together for welding. Mine are arriving in a few days.

To true up the frame I used the paper skin to pull things into shape. I wrapped the end around a rail with glue and let it dry. This let me pull really hard on the paper and thus keep things taut and straight.

Here's the first joint that anchors the skin. I let it dry before continuing with construction so I could pull the paper tight.

Notice the center brace isn't (yet) straight like a + sign. It will be!

Strings for the bridle. A string passes through a ring and connects two rail ends. The other string also passes through the ring and connects to two points in the halfway point of the opposite ends' paper skin.

The metal wire shown is pulling on the clamp, which makes the central brace straighten out into a perfect "+" sign shape.

Nice and straight!

A bread tie used as a glue brush. I ran it between each rail and the paper skins.

I put 4 layers of transparent tape on the skins where I drilled holes for the strings using apin vice drill.

Curved tweezers / forceps are indispensable for knot tying.

Both strings get looped around a plastic ring twice. This forms a bridle which self adjusts, allowing the kite to stay with the wind-eliminating the need for a tail.

There she is: a single brace box kite! Single, central brace. Quarter size balsa. Ultra light. Tail-less.

I ain't got no tail either... but then again, I can't fly. Meow.

Gauss Gun

A Quick Gauss Gun Post

In a simple Gauss Gun a steel ball rolls toward a magnet with two balls on the opposite side of it.

The ball nears the magnet, which pulls on the ball and increases its speed.

The ball slams into the magnet, which transfers the energy and momentum of the ball to the first ball on the other side. The first ball transfers this energy and momentum to the second ball-which goes shooting off.

The last ball shoots off at a much faster speed than the original ball because of the increased acceleration provided by the magnet as it "grabbed" the original ball when they got close to each other.

The magnet with two balls on one side is a stage. You can set up many, many stages in a row to create a chain reaction with a pretty fast moving ball shooting out of the last stage.

Rolling friction, aerodynamics and the magnets pulling too hard on the secondary balls can steal some of the energy and momentum by not letting the last ball go easily to the next stage. A way to counteract that is to use electromagnets (coils) that shut off right as the stage receives the incoming ball.

I came up with an easier solution: have the first of the two balls be non-magnetic! It acts as an isolator between the magnet and the second ball that gets launched to the next stage.


Another thing that steals energy and momentum is if the magnet slides backwards a little to meet the incoming ball a little earlier. The solution: I taped the magnets down so they wouldn't move.

Experimenting with different sized ball bearings, different numbers of them and different strength magnets all have noticeable effects on performance. As do the spacing between stages.




Here's some simple performance test videos I made:

I found that K&J Magnets has some medium sized magnets and balls that work even better than larger ones. I had great results with the quarter inch (D44) ones:

K&J also have an awesome blog with tons of projects like this (which include links to their industrial products if used in the experiment). Very cool! 

K&J also explain the science behind Gauss guns (and magnets in general) without delving needlessly deep into Newton's Second Law of Motion, as most explanations online do. Hint if you read up elsewhere: a euclidean vector is just an annoyingly complex way of denoting an arrow. "The ball shoots that way!"

If you're interested, F=MA , Force equals Mass times Acceleration. You have to kick heavier balls harder to get them to go the same distance. What's important is that Acceleration here is just the initial jolt/kick, just like the better quick on/off electro-magnets in a coilgun! It sets the object in motion. That is all (and that is the best part). Newton's Third Law of Motion is the equal and opposite reaction one: which is why taping the magnets down is better: no jolting back and forth. The tape helps conserve energy.

Newton's First Law is just the one about inertia: objects at rest or in motion stay that way unless acted upon by unbalanced force. It's why the balls eventually stop instead of blasting a hole in the universe.

If you add a bunch of stages you might just get some cool results, but you might shatter a magnet or put a hole in something! Eyewear is a must! All the laws take their toll on the Gauss gun, especially a simple one like this.

However, at some point I'm going to try 20 stages firing .177 pellet gun bbs. I have a feeling their reduced mass (M) will insurmountably hinder optimal performance.

Carl Friedrich Gauss worked on a lot of number theory mathematics, but he also founded the "Magnetic Club" in 1883. He has a unit of measure (the gauss) named after him. It measures magnetic fields, and Gauss formulated ways to measure the properties of magnets using only the simple concepts of time, mass and length. Specifically, he came up with a better way of measuring the oscillation of a magnetized needle to measure magnetic field intensity. This used to be measured in a unit called the gauss, but they changed (in 1932) the term gauss to refer to electromagnetic induction, and field intensity was then notated in units called oersteds--Hans Christian Oersted discovered electromagnetism in 1820.

Magnets actually have different gauss values for their different fields (surface, residual flux) and all things being equal a physically larger magnet will have a lower surface field! So, magnets have various other ways of denoting their "strength". The easiest is pull force: how many pounds can it lift or pull?

Another is the N number, which is derived from a magnet's MGOe (Mega Gauss Oersted) value. Neodymium rare earth magnets range from N35 to N52. This is the amount of stored energy (energy density) in the magnet.

Speaking of energy, check out what else these magnets can do:

The magnets used in this post were all N42 magnets. The white part of the gun was just a piece of ceiling molding. Just scraps.

I need to borrow the Gauss gun just one more time, Meow!

Sun is NOT the Center of Solar System: A Lesson in Elliptical Orbits

The Sun is NOT the Center of Solar System: A Lesson in Elliptical Orbits

We are going to cover elliptical orbits, ellipses, creating ellipses, sine and cosines, and Johannes Kepler's Second Law of Planetary Motion with an ultra-simple, easy to understand method using a piece of string! 

Kepler was trying to prove that planets sweep out equal areas in equal time periods...except he kept getting errors as he attempted to calculate the orbit of Mars. He tried fitting his calculations to a circle shaped orbit and an egg shaped orbit: no luck. Then he tried an ellipse, succeeded and also proved the sun wasn't at the center of the planets' orbits!

Our sun is not the center of the universe. It is not the center of our solar system. The sun is at one of the two foci of an ellipse, the other focus is an empty area of space. The foci are like two centers of two circles joined together into a blob. BUT THE orbits are so close to circular looking that diagrams of our solar system are basically circles within circles with our Sun at the center (but technically a smidge off). It's called the "barycenter".

In fact you can create a circle by bringing the two foci together-and we'll do that after learning how to easily create ellipses with a piece of string, a compass and two pins. This piece of string will also easily show us Kepler's law of planetary motion: something that is an absolute mathematical truth...but looks totally untrue to human eyes.


Let's start by marking the length and width of the ellipse we want:

Put a pin at each end of the length and connect with a string:

Set the compass to the distance from the center to a length end point:

With the compass set to the distance from the center to an end point of the length, put the sharp part onto a width point and draw marks where the compass-swing hits the line of the length.

Take your pins and string and stick them into the compass marks.

Take pencil and draw while keeping the string pulled tight. There is your awesome new ellipse! You'll notice that the string forms a triangle, kind of like the sine/cosine triangle in the circle from a few posts ago about Lissajous Figures. We'll come back to this triangle in a moment, but first let's Reverse engineer this ellipse into a circle.

As we move the two foci closer and closer together the pencil and string triangle sweeps out a shape that is more and more circular. Put the pins in the same hole (or just use one pin) you'll get a perfect circle.

Back to the triangle sweeping:

Kepler's Second Law of Planetary Motion says that as a planet sweeps along its orbit, in different parts of the ellipse (even the smaller ends) the area it sweeps out is always equal to any other area it sweeps out given the same time to sweep. Two seconds of sweeping in the little end gives the same area as two seconds of sweeping the bloated middle.

That sounds and looks wrong, even in fancy computer animations...but just remember our string triangle: it moves all about and changes angles as it's dragged by the pencil but its overall length never changes. The string doesn't get shorter or longer. The base of the triangle never changes as long as the pins don't fall out. The length of the two other sides of the triangle always add up to the length of the string.

Sameness.

Couple the sweeping in an ellipse with the sine/cosine triangles...

...and add a few more little trigonometry bits like tan and arctan and you get the field of calculating xy ballistics trajectories for non-powered projectiles (bullets, rocks in a catapult, etc.).

Wait, I can use a piece of string to calculate the path of birds?!?

 They'll be non-powered once I gnaw their wings off.