My Radioactive Dime
Alpha particle hits aluminum.
Aluminum releases neutrons.
Neutrons hit silver dime and turns it radioactive.
Silver dime releases gamma radiation.
Alpha particles turn Aluminum-27 to phosphorus-30 (*see footnote)
This is accompanied by awesomely unique neutron radiation.
What's so great about neutrons? They can transmute elements by sticking to them and changing them, sometimes making them radioactive. Remember: alpha, beta, gamma and x-ray radiation stops when the source is taken away. Turn off an x-ray machine and it's safe to walk into the room. Turn off the microwave oven and you can stick your hand safely inside to get out your nice warm popcorn.
Neutrons are a tad different though: they can irradiate elements. Blast neutrons at silver and you get radioactive silver! Turn off the neutrons and the silver is still radioactive (for a couple minutes at least).
Neutrons turn Silver-107 to silver-108 with a half life of about 2.5 minutes.
Neutrons turn Silver-109 to silver-110 with a half life of about 25 seconds.
Each of these reactions is followed by a lovely blast of easily detectable gamma radiation.
All that sounds a little fancy, how hard was it to accomplish in real life? Well, it was very simple really:
I wrapped an old silver dime in foil and left it in an alpha particle bath for a few days. I then carefully slide it next to a Geiger Counter that was shielded with paraffin wax. The baseline only mildly rose from 10cpm (clicks per minute) to 20cpm...but it did rise!
After less than two minutes it settled down to 6cpm.
10cpm was the normal background radiation in the room.
20cpm was the gamma released by the irradiated silver.
6cpm was the background radiation being partially blocked by the (now) back to normal nonradioactive silver.
Removing the silver let the rate go back to 10cpm.
These readings are very low all around, but repeatable. Back when dimes were silver the American Museum of Atomic Energy had a coin irradiating machine: pop in your dime and it would be made radioactive (for a couple minutes). Neat! But by the time you let the museum your dime transmuted back to being a boring old coin...which is good because who wants radioactive coins in their pocket?
It wasn't as momentous as when I finally got my nuclear cloud chamber working, but I did feel a little like Dr. Frankenstein
and I proved my source has alpha radiation by inference since my Geiger Counter can only detect beta, gamma and x-rays...not alpha or neutron radiation; but I know both were there because of the increased gamma radiation driving up the cpm count.
Why the choice of materials used? Neutron cross sections. This tells us how interactive am element may be with neutrons. The larger the cross section the more reactive it will be. Cross sections are measured in units called "barns" which are ten to the negative twenty-fourth power in square centimeters (very, very tiny).
There are fast neutrons that can be slowed down by big
scatter cross sections, and there are slowed "thermal" neutrons which can actually interact with things (like my silver dime) of those things have a big
absorption cross section.
Elements/isotopes with large scatter cross sections and low mass are great neutron moderators (slower downers).
Aluminum scatters at 1.5barns and Silver absorbs at 91barns.
It's all starting to make sense isn't it!
The insanely poisonous metal Beryllium that I'm waiting for the mailman to bring me scatters at 7.6barns but only absorbs at 0.007barns...and it's the fourth element in the periodic table, meaning it had a relatively low mass. All this makes beryllium a fantastic thing to shoot alpha particles at and have it blast neutrons out in exchange!
What else is the mailman bringing me? Paraffin wax laced with Boron. Boron scatters at a respectable 5.24barns, but it absorbs at 767barns!! That will slow down
lots of neutrons down to the thermal range, meaning those neutrons can actually interact better with things (my dime for instance).
This is all much more fun than using a Geiger counter that can see alpha, or a neutron detector.
Inference and implication. Pasteur said that fortune favors the prepared mind. I'll be building a zinc sulfide spinthariscope that lights up when an alpha particle hits it.
You can also modify a cheap webcam to see similar sparks when the imaging chip gets slammed into by an alpha particle.
I once had an old wristwatch. I noticed that it didn't glow steadily in the dark but twinkled. The next morning I researched it and found that it was painted with radioactive radium!
Neutrons can be detected by tubes filled with helium, lithium, boron trifluoride or a couple other pricey gases. There are also bubble dosimeters that show bubbles in a test tube where neutrons (or cosmic rays) pass through it.
Photo magnifying tubes are like night vision versions of the webcam method. Plastic scintillators light up with hit by particles-much like the spinthariscope method.
It's more fun inferring from chain reactions just like the discoverers did: a weird result that could only be explained by a previously unknown particle.
That's what you get from homemade "junk" versus fancy store bought lab equipment.
The inferences of a prepared mind. The fortune which befalls it via convoluted paths chance, accident or routine, simple experiments yeilding unexpected results that are tested instead of ignored.
Prepare your mind and fortune may follow.
*A footnote on the initial alpha and aluminum foil interactions: when the alpha particle hits the aluminum it makes phosphorus-30 plus a neutron. The phosphorus-30 decays into the usually stable silicon-30 by emitting positrons, but the silicon in this instance decays by emitting gamma radiation. The positron will likely slam into an electron and give off more gamma radiation.
Below is some great information on some older NEUTRON DETECTORS (as opposed to Geiger Counters) which you may find used online. 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 |
Phew! That was a LOT of typing! Enjoy!
Name What is it? Distance traveled
through open air
Alpha Physical particle equaling a Helium nucleus 2-3cm
Beta Physical particle equaling an electron 2-3m
Gamma Not radioactive decay, just energy burst 500m
accompanying alpha or beta radiation.
The same as an x-ray, but arising from
different sources.
Neutron Physical particle made up of 1 up quark and 1000s of meters
2 down quarks.
Name Symbol Makeup Charge Speed Atomic Mass Units
Alpha α 2 protons & 2 Neutrons + + Slow 4
Beta β 1 electron - Fast or Slow 1/2000
Gamma γ Photons/ Neutral Speed of light 0
electromagnetic waves
Neutron n 1 up & 2 down quarks Neutral 2.2km/S-14,000km/S 1
(~5% speed of light)
Notes:
An AMU (Atomic Mass Unit) is equal to 1/12 the mass of a Carbon-12 atom.
Slow Neutrons are called "Thermal" and fast ones are called "Fast" neutrons.
An alpha particle is double positive "++".
Gamma rays are produced by atomic nuclei and x-rays are created by accelerating electrons, but they are basically the same type of wave energy.
Lead only approximately halves the gamma/x-ray amounts. A 1/2" of lead stops about half the waves trying to get through. When beta radiation hits lead sometimes a new type of radiation is created that is more dangerous! This is Bremsstrahlung radiation (braking/deceleration). Lead barely interacts with neutron radiation, water or hydrogen-containing compounds such as common paraffin wax are much better shielding material.
