Main Sequence Page 1

Welcome to the first page of meandering explorations in math, physics, astronomy, and earth science.

Cosmic Rays
Here is an experimental apparatus, Version 1, visually kinda interesting but not much going on...

cloud chamber interior


Background
It dawned on me recently while reading some history that early 20th century physics relied heavily on cosmic rays as a source of phenomena. I had assumed that from Day 1 experimentalists just started building particle accelerators, starting with electron guns (cathode ray tubes), that gradually grew bigger and bigger over the years.  While partially correct, fact is it took awhile before accelerators began evolving into the monster devices we build (or don't build) today.

In contrast during the period from 1900 to 1940 or so it was fortuitous to have a limitless supply of energetic particles raining down from outer space as a 'free' source of experimental data.  On the down side this cosmic rain is somewhat random in both direction and content, a drawback if you want particles to follow a directed path. In that case a more practical approach is to refine and use radioactive sources, permit the radioactive decay products to pass through little pinholes. 

The Wilson Cloud Chamber
The cosmic ray detection story begins with a graduate student trying to push the boundaries of atmospheric research in the laboratory, an effort that paid off and led completely unexpectedly to the detection of subatomic particles.  To oversimplify matters: Over the course of years of diligent effort and development Charles Thomson Rees Wilson arrived at the device now named for him, the Wilson cloud chamber.

This contraption is a sealed volume that reveals moving subatomic particles through condensation tracks they leave in their wake like miniature jet contrails in a little glass jar.  It must have been quite remarkable to discover tracks drawn momentarily in cloud chamber mist, like growing up in a huge city and one day discovering it to be overgrown by an invisible jungle filled with invisible animals.

Here are my Starting Questions

How hard is it to build a cloud chamber?
What do cloud chamber tracks look like?
What have they to do with cosmic rays?
How fast do these particles move?
Can one calculate how long a track should be?
And... well; I have many many questions.

Here are some tracks I found described on the web... do these really happen???

schematic of track types


Actually I'm jumping ahead here; what do I know about tracks in cloud chambers beyond rumours? Nothing at all! So I'll build a cloud chamber and see what happens.  So first let's go after these two front-end questions:

Do cosmic rays really exist??

and if so...

What can be observed concerning their behavior?


(Aren't we unbelievably fortunate to have come along at such a time and place that we can answer these questions with a few dollars worth of hardware and some library books? I think it's incredibly wonderful.)

So let's suppose we're Wilson back around 1900 at the Cavendish Lab, a conceit I'll make use of now and again.  (This is a good time to mention the Ground Rules for these pages in passing.) As mentioned, Wilson was a graduate student trying to replicate experiments that produced atmospheric clouds in glass containers; he was not looking for subatomic particles.  In fact he was pushing the experimental envelope of cloud research, forcing water vapor to condense without nucleation sites.  (Clouds... puzzling things aren't they?  I'll digress--eventually--in a little cloud aside.)

Subsequently the 'modern' demonstration cloud chamber has evolved from Wilson's water-based groundwork. The main difference between what he was doing and the way cloud chambers are built now is alcohol rather than water. Alcohol is simpler to supercool so its used as the condensation vapor.  Andy Foland's instructive web page shows how to go about building a cloud chamber using a sealed see-through box with a black floor in good thermal contact with some dry ice and an isopropanol-soaked liner. The essential information is here in these pages as well.

A brief pause while I build build build a cloud chamber...
This would be a good time to go read a book for half an hour or so.
.
.
.
ok, all built.
Now to get some dry ice,
rest the chamber on it,
let it sit for 30 minutes or so,
and start looking inside for tracks
.
.
.
WHOA!
The gosh-darned crazy thing works!
I'm really excited about this!
WOW!! THIS IS SOOOO COOOOOL!!!!! 
There They Are, Little Fuzzy Ephemeral Tracks in the Mist
Here's a picture of one:

cloud chamber interior with particle condensation track

ok, gotta catch my breath here...

A Bit of Explanation
(if these things are as new to you as they are to me)

First: The above photo is a cloud chamber interior. The gold cubes are magnets and the glass ampule is a radioactive source. They can be ignored as they are not essential, just some subsequent ideas after the initial success. The dark substrate is shiny because its wet, in fact it is felt that has been soaked with isopropyl alcohol. And the horizontal curving diaphanous shape at center left? That's a condensation track from some sort of invisible thing, some sort of particle zipping along inside the chamber. It was captured by digital camera perhaps 1/10 of a second after it was created.

Here are some more remarks on the interior state of the cloud chamber, as well as how to construct it.

As soon as a track forms, it falls and dissolves apart in about one second. Hence the cloud chamber is host to an endless sequence of little phantasms, some sharply and others vaguely defined, tracks that burst into existence and then in a moment dissolve away.  There are several varieties of these tracks, from little squibs to long straight lines up to perhaps 5 cm in length to veil-like puffs and so on and so on; they are quite mysterious. On a couple occasions a huge track appeared spanning the length of the chamber.

Building the entire apparatus requires a little time, maybe a couple of hours, and maybe 50USD (or less if you are resourceful).  Also useful is a slide projector or other strong light source and a dark room and some heavy books or a big bucket of water. The latter presses the chamber down on the dry ice ensuring the base is very cold.

Before going any further observationally I'll document construction details here. 

cloud chamber schematic

So in answer to the First Question:

Yes: There are Invisible Somethings
that produce tracks in the cloud chamber...

Of course we have no evidence (per claims by physicists) that the culprits are small charged particles drifting in from outer space, nor do we have any good idea what percentage of them we are actually detecting. But there's something going on in there.

Here are ideas for further experiments, about six of them. As time and space permit I will improve the entries for these ideas; at the moment most are mere placeholders. The one exception has the asterisks, it's the one about magnets. There with the first cloud chamber I managed to catch an interesting result.
  1. Re-run the experiment paying more attention to setup and maximizing detection area.
  2. Carefully observe for awhile to build a little catalog of track-types.
  3. *** Install some powerful magnets to try and bend the particle tracks***.
  4. Install metal plates that can be charged to create a track-bending electric field in the chamber.
  5. Introduce some simple barriers to see if the tracks will pass through them.
  6. Introduce some radioactive sources to see what sort of tracks they produce.


Summary
As I do more reading and learning I will write up some more complete summary notes here. The starter-summary is this: I have an easily-built working device, many ideas on how to improve it, and further experiments to conduct when time permits. So far I believe or suspect that:
 What Next?
The famous planetary scientist Carl Sagan had a television special called 'Cosmos' which aired in the early 1980s (I believe).  During this program he kept reiterating this phrase "star stuff" (as well as the better known "billions and billions"). He would insist that we were all made of it, this "star stuff" but I must confess I never quite followed his meaning.

Now I think I have it though: I think he was trying to get across a most astounding idea that has emerged from astrophysics in the 1930s through the 1950s (in my view): the cosmic abundance of elements heavier than hydrogen and helium--and therefore our own carbon-based existence--depends upon the alchemy within a stellar furnace; in fact within the zillions of stellar furnaces that have caught fire and burned nuclear fuel into ashes over the past 13.7 billion years (aotu).

Simple enough to make the claim, but really I would like to understand the argument on a

deeper level: How are we built from the ashes of ancient stars?

Next
Home