MacGyver Season 2 Episode 17 Science Notes: Bear Trap + Mob Boss

This is not a MacGyver-hack. But he is talking about radioactive stuff. Here is my super short explanation.

An atom is made of a positive nucleus plus some electrons. Normally, there will be the same number of electrons as protons in the nucleus. This makes the overall charge of the atom zero. But wait! There are also neutrons in the nucleus. Let’s just look at an example.

Strontium-90 is an atom with 38 protons and 38 electrons. It also has 52 neutrons in the nucleus—oh, and it’s radioactive. Strontium-88 also has 38 protons and electrons, but it only has 50 neutrons. Since these two atoms have the same number of protons, but different neutrons—they are isotopes of each other.

Sr-90 is radioactive. That means its nucleus is unstable. It goes through radioactive decay and produces Yttiruim-90 which has 39 protons. So, one of the neutrons in Sr-90 turns into a proton and also produces an electron (so that charge is conserved).

The half-life of Sr-90 is 28.8 years. Since the decay process is random, there are more decays when you have more atoms. This means that the decay rate depends on the number of atoms. So, you can’t say how long it will take for all the material to go through radioactive decay. Instead, we say how long it will take for half of it to decay—that is the half life.

So, does that mean that all of the material will decay in 2 times 28.8 years? Nope. It means that after 28.8 years, you will have half as much stuff. After another 28.8 years you will again have half of what you started with. Every 28.8 years, you will have half as much.

What about Plutonium? There are several different isotopes. Plutonium-238 has a half-life of 87.7 years. Plutonium-239 has a half life of 24,000 years. The shorter the half-life, the more “radioactive” it is. But for longer half-life stuff, it’s still going to stick around for a long time.

DIY Geiger Counter

A Geiger counter is a device to measure radioactivity. It consists of an outer conducting tube with a conducting wire running down the middle. The wire and tube are at different electric potentials—usually a fairly high voltage.

When a charged particle (the result of a radioactive decay) enters the tube, it interacts with the gas molecules to ionize them—knock out an electron. This free electron then accelerates in the high potential and collides with other gas molecules to produce even more free charges. More and more charges are produced—it’s called an electron avalanche. This avalanche is then detected as an electron current—usually to produce an audible click. That’s the clicking sound you hear.

Here is MacGyver’s build.

He uses a motorcycle muffler as the tube—you can’t see the wire in the middle, but it’s there. The battery provides the voltage and then there is an audio speaker to convert the electron avalanche into sound.

Oh, I forgot—here is a video demo.

Bonus. Here is my sketch for the DIY Geiger counter.

DIY Ice Climbing Gear

There’s really not much to explain here. MacGyver uses some cut up chain link fence and some rebar to make spike-shoes and a type of ice pick. He uses these to climb up an old brick wall—sticking the metal into the old mortar. It seems like it would work.

Disabling Trucks

MacGyver builds one of those rolling things that mechanics use to get under cars (I forget the name). With that, he disables the trucks (all but one). Really, once he is under the truck he could do a number of things. He could cut the fuel line or cut an electrical line—let’s just say he does it.

In order to convince the mob that the key guy they are trying to catch isn’t worth it. They make it look like he is super radioactive. The mob guys have a Geiger counter—so MacGyver needs to remotely set that off.

My original idea was to have him build an electron gun—like this https://www.instructables.com/id/DIY-Electron-Accelerator-A-Cathode-Ray-Tube-in-a-/

The electron gun would shoot electrons into the Geiger counter and set off an electron avalanche in the same way that a radioactive source would. Unfortunately, it was too complicated of a build.

What about a super high amplitude electromagnetic wave? The idea is that when the electric field part of the wave hits the detector, it will increase the field inside and make it more sensitive to ionizing radiation. This would make it seem like something is more radioactive than it is. Yes, I know this is a stretch—but it’s based on some real idea.

Here’s how he could build it.