Duck and Cover: Children of the Cold War

Growing up, I can't recall a single instance of ever doing the "duck and cover" drill.

This lack of cold war education is a bit odd, because I grew up within a few miles of a nuclear missile launch complex.  The missile complex was taken out of service a few short years after it was built, while the US and USSR moved on to a paradigm of MAD, or Mutually Assured Destruction, so maybe the school board just assumed everyone on the planet would be vaporized by incoming nuke missiles.  In any event, I never performed a 'duck and cover' drill while at school.

I had heard rumors of the nearby missile complex when I was in high school, and it took a while after that before I could find someone who knew where it was located.  Boise, Idaho, where I grew up, is just off the top of the map below, and 569-C (near Orchard), is the nearby site I had a chance to explore.

Frankly it was a little intimidating driving up to the site, even with friends who had been there many times before.  It was fenced and posted "No Trespassing", and had various signs about being a felony to trespass, etc, etc.  The fence was in bad shape however, and the gate was askew. In we went...

In its heyday, the missile complex was part of the 569th Strategic Missile Squadron, based out of Mountain Home Air Force Base.  The missiles were deployed in a 3x3 arrangement - meaning three launch complexes with three missiles each.  Each of the above mapped "569" sites therefore would have three silos each containing a nuclear-tipped missile.

Below, a diagram of a three missile launch complex, showing the major components.  Note: Hydrazine was used on later missiles, so this likely a diagram for a Titan 2 missile complex.

The nearby launch complex was built around first-generation SM-68 Titan 1 missiles, and was only active for a very brief time before being superseded by more advanced missiles. The launch site was abandoned (rather than updated) at that time.  The 569th Strategic Missile Command was only active from June 1961 to April 1965 - a useful lifespan of under 4 years.  This must have been the only weapon system for nuclear deterrence with the longevity of a fruit fly.

Below, a Titan 1 missile, out of the silo.  Note the open blast doors and the Air Force markings.  This looks like it might be a commissioning ceremony, based on the contractor trailers and vehicles on site, as well as the tent adjacent to the silo.

The Titan 1 was the first true US intercontinental missile, having a range of 5500 nautical miles.  The arrangements required to launch the missiles were quite complex and time consuming, and this is very likely the reason that the system was abandoned so quickly, in addition to the rapid pace of rocket development in that era.

To begin with, the missile was a two-stage, liquid-fueled design.  The propellant was RP-1, essentially highly refined kerosene (a light oil) that was kept on board the missile.  The oxidizer, however, was liquid oxygen.  This had to be stored in an insulated and refrigerated cryogenic tank at the launch site, and pumped into tanks on board the missile immediately before launch, for both the first and second stages.

Further complicating matters, the silos were not designed with exhaust vents, so the blast doors had to be opened and the missile raised on an elevator out of the silo before launch could proceed.  There was no "quick launch" feature for this missile.  It took 15 minutes to launch the first one, and the other two would follow at 8 minute intervals.  Surely this would be an eternity in a nuclear exchange, particularly if you were not making the first strike.

The missile guidance system left a bit to be desired as well, being radio command.  Therefore this missile required radio signals from ground guidance to get where it was supposed to go.  The likelihood of intentional interference or Nuclear Electromagnetic Pulses (EMP) blocking this communication would be likely in the event of nuclear war.

What this missile could do however, was fling a W-38 thermonuclear weapon halfway around the globe and deliver a whopping 3.75 Megatons of destruction, with whatever level of accuracy the radio guidance system could provide.  Link to a Chinese video of a 3.3 Megaton airburst.

The missiles were pretty failure prone; of the 70 that were test launched, only 53 performed successfully - a success rate of about 76 percent.  That means that of two of the nine missiles from the 569th Strategic Missile Squadron probably wouldn't make it to the show - but those that did would make quite an impression ;)

And now, what you have been waiting for... the inside of the missile launch complex of the 1960s. (FYI: These are not photos that I took)

Below, a Google Earth image of the 569-C site near Boise.  The silos are to the upper left inside the fenced area.  The big pit in the center was dug to remove components from the complex when the site was abandoned.  It appears to be private property at this time.

This was how you got into the complex - where crews had dug down and made a ramp to remove the components from inside the control room.  The other option was to rappel down into the silo on a rope.  Being a little acrophobic, I chose the former.

Below, a lot of dislodged heating and cooling ducts, as well as some stripped down electrical cabinets.  Not sure what part of the complex this is...

Below is my favorite.  Take a look at the massive shock springs at the left and right.  All the critical equipment was suspended by springs - in event the silo had to deal with a nuclear first strike.  The *hope* was that an incoming nuke would not score a direct hit, and that the launch complex could survive to retaliate.  Modern guidance systems do not offer this hope of a near-miss.

Cool stuff!

Broken Arrows - USAF wins the trophy

"Broken Arrow" is the military term for an accidental event involving a nuclear weapon, but which does not create the risk for a nuclear war.  The 'accidental event' typically involves losing and/or damaging the weapon.

There have been 32 officially recognized "Broken Arrow" events in the United States since the dawn of nuclear weapons, as of Sept 2013.  Some of these events have been relatively minor, but others have been massive radiological accidents.  One accident with a large Hydrogen Bomb nearly made North Carolina uninhabitable... not that you would have seen THAT in the newspapers when it happened.  Apparently the news media were just as compliant in the 1950's as they are today.

I will go over a few of the more interesting Broken Arrow events.  Not surprisingly, most of these involve military aircraft crashing with weapons on board, as well as the intentional or inadvertent jettisoning of nuclear weapons.  All of these event descriptions are courtesy of Wikipedia.

Missing Radioactive Sources - Updated (23 August 2018)

This is a horrific and very sad story, but it seems like every year somebody attempts a repeat :(

***UPDATED 8-23-18***

OK, so I see we've lost another one - this time in Malaysia.  This one is an Iridium-192 source for industrial radiography.  I'm cackling about the statement from the authorities:

"It cannot fall into the wrong hands as the consequences can be deadly" 

You knucklehead.  It's already in the "wrong hands".  It's been in the wrong hands since the moment you lost custody of it.  The question we are left with right now is whether the "wrong hands" are (best case) thieves, or (worst case) terrorists.

It boggles the mind that such dangerous material gets stolen so easily.  If this were high explosives, or even just harmless money, there would be several armed guards constantly monitoring it, or it would be in a vault somewhere.  It's time to be much less stupid with such dangerous material.

I am the gamma ray shielding...

In any system filled with water, there will be corrosion.  It's inevitable.  Water is a highly polar molecule, and so it has a tendency to dissolve/corrode almost everything.  All you can do is attempt to minimize the amount of corrosion through careful chemistry control.  Even so, you will still get some corrosion.

In the primary coolant system of a nuclear reactor, what this means is that you will have a few (hopefully not many!) metal atoms suspended in the coolant.  These metal atoms will pass through the reactor core and absorb a neutron, and sometime become radioactive, depending on the metal.

Some components in the primary coolant system are made from Stellite, a Cobalt-Chromium alloy that has excellent wear and corrosion resistance.  Unfortunately even Stellite corrodes, and it also erodes over time due to wear.  For this reason there will always be some of these Cobalt, Chromium, and Iron atoms carried through the reactor core, suspended within the primary coolant.

The biggest nuisance among these metal atoms is Cobalt.  Cobalt-59 atoms that flake or corrode off the Stellite can absorb a neutron, and become radioactive Cobalt-60.  Co-60 has a half-life of 5.3 years, and decays by emitting two gamma rays at energies of 1.17 and 1.31 Million Electron Volts.

Eventually these now-radioactive atoms will find an eddy and come to rest in a low-flow point and settle out, much like silt behind a large dam in a river.  These low-turbulence points where the radioactive atoms settle out will now emit quite a bit of gamma radiation, due to internal contamination.  This stuff has a name: CRUD.

On the submarine, there were a number valves connected to the primary coolant system which were located outside of the reactor compartment, so that they could be opened or closed if necessary without having to go near the reactor.   One such system on the ship was for emergency cooling; if all electrical power were lost, we still had to be able to remove decay heat from the reactor core.

As a result of performing the required testing on this emergency cooling system over the years, several of the valves outside of the reactor compartment had accumulated a fair amount of CRUD in them - enough to deserve posting signage and discouraging loitering.

On to the story... one day in port, some routine maintenance inside the reactor compartment was being performed, and I was the control point watch.  That job meant I that I had to control access in and out of the reactor compartment, to ensure nothing bad happened to the guy in there, and to ensure he didn't bring any nasty radioactive crap out that was clinging to his suit.

To ensure the last, I had a very sensitive detector for sensing contamination.  It looked like this:
 
This meter is a Geiger type detector, with an attached "Pancake Probe".  The probe is heavily shielded on all sides but one, so that it will directionally detect radiation.  The open side has a thin mica window, protected from puncture by a mesh screen.  The radiation can pass through the mica and into the detector, which will provide a reading on the meter.  A selector knob allows you to choose a multiplier for the level of contamination you are dealing with, to keep the needle on-scale.  It reads out in counts/minute (times the multiplier).

Geiger-Mueller detectors work by maintaining a very high voltage across a low pressure gas.  This voltage is just slightly less than would be needed to cause all the gas to ionize and begin conducting continuously like a neon lamp. 

If a gamma ray or beta particle enters the tube, and reacts with a gas molecule, it will ionize it that molecule.  Next, the very high voltage immediately accelerates the positive and negative ions, causing them to bang into other atoms, ionizing them in turn.  Eventually the entire tube becomes ionized in a massive (but very brief) cascade, and you get one audible "click".  The gas in the Geiger tube immediately resets (because the voltage is slightly too low to keep the gas ionized) and the process repeats for every radiation event inside the tube.

I was sitting at control point, and got bored.  I decided to point the pancake probe (a very sensitive instrument for detecting minute amounts of contamination) directly at the CRUD-filled valves that were emitting a modest gamma radiation field.

The instrument went from clicking every second or so, to screaming.  I had place it on the highest range while pointing pancake probe at the internally contaminated valves, even from across the room.

Out of idle curiousity, I placed my body between the pancake probe and the valves, and the meter stopped screaming.  I was absorbing the gamma radiation that was making the meter swing!  On that day I shielded the sensitive probe from 10 mr/hr worth of gamma rays.  It was a little unnerving realizing that I was absorbing so much gamma radiation, just by being in the room with it. 

Meh.  I didn't even get an image for that exposure...

 

Radon - a radioactive hazard for everyone

Radon-222 is a radioactive gas that is heavier than air.  As such, it tends to settle at low points.  It is a "noble" gas, meaning that it doesn't react chemically all that much, because it has 8 electrons in the outer shell.  In this respect it is unlike Radium, which tends to mimic Calcium, and accumulate in bones, causing bone cancers.

Below is a diagram showing that Radon-222 is element 86 (has 86 protons), has 136 neutrons, and 86 electrons, with a full 8 in the outer shell, making it pretty much inert chemically.

Radon, although it is chemicall inert, and therefore doesn't bio-accumulate through a chemical process, is still extremely dangerous from a radioactive standpoint.  Radon is a type of "NORM", a.k.a. "Naturally Occurring Radioactive Material", and anyone can easily be receiving dangerous levels of radiation exposure without even realizing it.

Below is a diagram of the decay chain for U-238, and the portion that interests us begins in the middle, at Radon-222 (Rn).  There are several very damaging radioactive decays that will occur before a stable (non-radioactive) state is reached.  Thus one inhaled Radon atom can inflict biological damage over a series of radioactive decays.  All of these decays are internal, and therefore the alpha and beta particles are absorbed into living tissue inside the lung.

Uranium-238 at the top of our decay chain, tends to be more concentrated in granite than in other soils and rocks.  Below is a map showing the estimated prevalance of Radon-222 within the US.

Radon is particularly nasty because due to its density, it tends to accumulate in basements, where there is often little air circulation.  If an atom of Radon decays while in the lungs, it becomes a radioactive atom of lead, which is no longer a gas, and will therefore not be exhaled.  The radioactive particle will very likely stay in the lung.  Afterwards, the radioactive lead atom(s) will continue to decay in a series of events, damaging the DNA in the lungs.

Below are the some statistics on a variety of causes of deaths annually.  Clearly Radon is a hazard that should be taken very seriously.

Prior to moving into our new house, we requested a Radon test, and the result was 215 pCi/L (picoCuries per Liter).  The limit is 4 pCi/L.  The concentration of Radon in our basement was about 53 times the limit.

The biological damage inflicted by the radiation of 4.0 pCi/L of Radon (continuous exposure, annualized) is equal to the biological damage from 100 chest x-rays.

In equivalent biological damage for cigarettes, 4 pCi/L is equal to 10 cigarettes a day.  So the Radon in our basement had the biological damage equivalent to 530 cigarettes a day or 5300 chest X-Rays per year.  Not good.

The corrective measures for Radon however are pretty simple and inexpensive.  The basement (particularly penetrations for utilities) is sealed up, the dirt in the crawlspace is covered with a plastic liner.

A continuously-operating fan is installed that takes suction from underneath the liner and from underneath the floor in the basement.  This ensures any Radon will be swept away and vented before leaking into the house. 

After remediation, a follow-up test showed that our Radon levels had been reduced to 0.5 pCi/L, or about 1-1/4 cigarette per day, if you never leave the basement.  If I can live in Bakesfield air for 8 years, I can certainly deal with that! :)

Below, a Radon fan.  These come equipped with an alarm that sounds should the fan fail.

I highly recommend that anyone who has a basement have their home tested for Radon.  It's cheap. The test is definitely less expensive, painful, and deadly than getting lung cancer. 

Radium Girls

Radium is a naturally-occurring element with the atomic number 88 (has 88 protons and electrons).  All known isotopes of Radium are radioactive, and so eventually all Radium will decay into something that is stable, such as Barium or Lead. 

Radium is a metallic element in the decay chain of naturally occurring Uranium and Thorium, a transient state as these elements eventually decay into stable elements.  For this reason, there is no primordial Radium. 

Minute quantities of Radium are found in Uranium ore, and that Radium is transient, being radioactive.  There are four naturally-occurring isotopes of Radium, of which Ra-226 is the most abundant, due to its long-ish half-life of 1600 years.  That is, in 1600 years, half of the original Radium-226 will remain.  The other half of the original Radium-226 will have decayed in a series of radioactive decays into Lead-206, which is stable.

Below is a description of the decay chain of Radium-226: 
Radium-226 decays to Radon-222 after emitting an alpha particle (helium nucleus) and a gamma ray.  Radon-222 is also radioactive, and will decay to Polonium 218 by another alpha/gamma decay.  This in turn alpha/gamma decays to Lead-214, with a half life of 23 minutes, which beta/gamma decays to Bismuth-214.  This is also radioactive, (19m half life)  and beta/gamma decays to Polonium-214.  Polonium 214 has a VERY short half life (164 microseconds) and alpha/gamma decays to Lead-210, which is STILL radioactive.  The Lead-210 has a half life of 22 years and beta/gamma decays to Bismuth-210.  Bismuth-210 has a half-life of 5.5 days and beta/gamma decays to Polonium-210.  Polonium-210 has a half-life of 138 days, and alpha decays into Lead-206, which is non-radioactive.

The reason I went to the trouble of looking up and describing the Radium decay chain is to explain why this stuff is so nasty.  If you are exposed to a single Radium-226 atom, you could conceivably get 5 alpha particle events, 3 beta particle events, and and 8 gamma rays.  That's a lot of biological damage for a single radioactive atom.  Because of the decay chains embedded in Radium-226, it has a very high specific activity  (disintegrations per second).  In fact, the original measure of radioactivity, the Curie, is 3.7 x 10^10 disintegrations per second, was based on the activity of Radium (mostly Radium-226).  That is 37 Billion radioactive decays in a single second!!!

This gives Radium some really cool, if dangerous, properties.  For one thing, it glows faintly blue, due to ionization of the surrounding air by all those nuclear decays.  When mixed with a chemical compound that emits light when struck by radiation, Radium-226 can make awesome glow-in-the dark paint, that will glow brightly, for as long as anyone is alive.  Tritium, a far safer nuclide, is used in modern watches, but its half-life is only 12.3 years, so the brightness will noticeably fade in less than a decade.

Below is an image of a Radium painted watch dial.  I really would love to have one of these!!!

Radium, because of its high activity, and tendency to emit several alpha particles in part of a decay chain, is dangerous to be around, unsheilded.  Recall minimizing the biological damage of each type of radiation is mainly a matter of shielding and distance.  You have neither of these if you ingest radioactive substances.  Which brings us (finally) to the topic at hand, the Radium Girls.

The story of the Radium Girls is slowly passing into the mists of history, which is quite a shame.  These were young women hired by the U.S. Radium Corporation to paint watch and clock dials with a glow-in-the-dark paint.  This paint was made from Radium and Zinc Sulfide, and which went by the trade name "UnDark".

From the website "Damn Interesting", by Alan Bellows:

In 1922, a bank teller named Grace Fryer became concerned when her teeth began to loosen and fall out for no discernible reason. Her troubles were compounded when her jaw became swollen and inflamed, so she sought the assistance of a doctor in diagnosing the inexplicable symptoms. Using a primitive X-ray machine, the physician discovered serious bone decay, the likes of which he had never seen. Her jawbone was honeycombed with small holes, in a random pattern reminiscent of moth-eaten fabric.

As a series of doctors attempted to solve Grace's mysterious ailment, similar cases began to appear throughout her hometown of New Jersey. One dentist in particular took notice of the unusually high number of deteriorated jawbones among local women, and it took very little investigation to discover a common thread; all of the women had been employed by the same watch-painting factory at one time or another.

From here I will turn things over to Wiki:

Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. A typical self-luminous watch that uses radium paint contains around 1 microgram of radium. In the mid-1920s, a lawsuit was filed against the United States Radium Corporation by five dying "Radium Girl" dial painters who had painted radium-based luminous paint on the dials of watches and clocks.

The dial painters routinely licked their brushes to give them a fine point, thereby ingesting radium. Their exposure to radium caused serious health effects which included sores, anemia, and bone cancer. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow and can mutate bone cells.

During the litigation, it was determined that the company's scientists and management had taken considerable precautions to protect themselves from the effects of radiation, yet had not seen fit to protect their employees. Worse, for several years the companies had attempted to cover up the effects and avoid liability by insisting that the Radium Girls were instead suffering from syphilis. This complete disregard for employee welfare had a significant impact on the formulation of occupational disease labor law.

As a result of the lawsuit, the adverse effects of radioactivity became widely known, and radium-dial painters were instructed in proper safety precautions and provided with protective gear. In particular, dial painters no longer licked paint brushes to shape them (which caused some ingestion of radium salts). Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This highlighted that the harm to the Radium Girls could easily have been avoided. 

Doesn't look like "syphilis" to me.  Looks more like "Radium Jaw"...  Very sad images indeed.

CANDU reactors

I had intended to write up a post about NMRI, or Nuclear Magnetic Resonance Imaging.  I may or may not get to that post.  To be frank, I don't find flipping atoms back and forth in a big magnet quite as interesting as discovering X-rays or splitting atoms.

So instead of a post on NMRI, I am going to write a post about splitting atoms :)

Nuclear Imaging - PET scanning

PET scanning is a relatively old (late 1950s) technology.  What has brought this once obscure diagnostic tool to usefulness since the 1950s is powerful computers and improved detectors.  PET is an acronym for Positron Emission Tomography, which are probably all arcane terms for a non-tech geek.

A Positron is the antimatter version of an electron - it is an electron, but with a positive charge.  Only a handful of radioactive isotopes decay by emitting positrons, and only a few of these are short-lived enough to justify injecting into a patient. 

So we have described the first two terms:  Positron and Emission. 

Tomography means building a three dimensional image, for diagnostic purposes.  So there we have it:  Positron Emission Tomography.

An interesting thing about positrons; because they are antimatter, they don't last very long in a world that is made from normal matter.  When a positron is created as a result of a nuclear decay, it very rapidly collides with a normal electron.  The two particles are destroyed in a process called "mutual annihilation" and the destruction of their mass is converted (E = MC^2) to two gamma rays at energy levels of 511 KeV each.  The gamma rays normally leave the point of destruction at a path 180 degrees from each other.  This is useful to imaging, as will be seen later.

The positron-emitting isotopes chosen for imaging are Carbon-11 (half life 20 min), Nitrogen 13 (half life 10 min), Oxygen 15 (half life 2 min), Fluorine-18 (half life 110 min), and Rubidium-82 (half life 1.27 min).   A short half-life is desirable for reduced patient exposure.

Unfortunately, these nuclides cannot simply be injected into the patient and expect imaging results.  The positron emitter would simply diffuse throughout the body and the image would have no contrast.  Instead the positron emitter is attached to a bio-active molecule that the body requires for metabolism.  In this way the positron emitter accumulates in the body where it is desirable to generate an image.

The positron-emitter is therefore attached to a molecule that mimics blood sugar.  As cells metabolize this blood sugar (and aggressively growing cancer cells will use a great deal more sugar than normal cells), the positron-emitting nuclide will accumulate there, emitting positrons and generating mutual annihilation gamma rays.  This is how more gamma rays will be produced from tissue that is undergoing malignant growth than normal tissue.
 
After injection of the positron emitting tracer, the patient is placed inside a ring consisting of many, many gamma-ray detectors.  Based on how the pairs of gamma rays are detected, an image can be constructed of where the positron emitter has accumulated.  The pairing of the gamma rays helps to pinpoint exactly where the gamma rays originated.  This is the purpose of the Coincidence Processing Unit in the diagram below - to ensure only matched pairs of 180 degree apart gamma rays are used to build the image.

Below, a diagram of how a PET scanner works (courtesy Wikipedia):



Below, a pair of images:  The left image is the result of a CT scan, done with X-rays and processed with a computer to enhance the image.  The right image is the result of a PET scan, and it's quite obvious where the gamma ray pairs are being created as positrons and electrons annihilate one another.

Because PET scanning requires the use of such short-lived radio-isotopes, using this diagnostic tool presents some logistical problems.  The positron-emitting nuclides are created in cyclotrons; large complex machines that hurl beams of relativistic electrons at target materials inside vacuum chambers.  Most of these very short-lived isotopes (except for the Fluorine 18, half life 110 minutes) would decay before they could be transported to a PET scanner.  For this reason, PET scanners are often located at universities where advanced nuclear and medical technologies exist side by side.

I find it fascinating how we have combined our understanding of nuclear decay, and the body's use of glucose for fuel to create an internal image that was undreamt of when the positron was first theoretically considered.  We had to wait for someone to invent a bio-active chemical that would act as a carrier for the positron emitter, high efficiency detectors with coincidence counting, and powerful computers that could take all that data and generate an image from it.  This confluence of diverse areas of science has led to an absolutely brilliant diagnostic tool!!!

Nuclear Imaging - X rays

Nuclear imaging is the process of viewing the internals of a human body by using the body's own nuclear properties, injected or ingested radioisotopes, and/or by using external radiation sources.

The earliest known and most commonly used type of nuclear imaging is done by using X-rays.  Although X-rays are not exactly "nuclear", they are ionizing electromagnetic radiation, so I will discuss them.  X-rays are produced in vacuum tubes, although not just any vacuum tube will do the trick.

The earliest vacuum tubes, called Geissler Tubes, used gas at a mild vacuum, and were similar in nature to modern neon lights.  Different gases would yield various colors.  Handling the glass envelope would cause the tube to glow brightest at the point where it was being touched.

Below, sketches of various Geissler Tubes, used mainly for amusement in the late 19th century.  All images courtesy of Wikipedia.

The Crookes Tube was another vacuum tube, but built with a different structure and improved vacuum.  This tube was a highly evacuated glass tube with a cathode, an anode, and a flight path for electrons (although this was not understood at the time).  The anode was set off to one side of the tube, and very high DC voltage was applied to the tube.

Below, a Crookes Tube.  Negative voltage is applied at left, making this the cathode (electron emitter).  Positive voltage is applied at bottom, making this the anode (electron collector).  A thin piece of metal in the shape of the Maltese Cross is suspended in the middle, in order to cast a shadow at the end of the tube.

Because this tube had very few gas molecules in it, and because the voltage was so high, a heated tungsten emitter was not necessary to cause current flow from the cathode to the anode.  So for this reason the Crookes Tube is called a "Cold Cathode" tube.

What occurs inside a Crookes Tube is the elecrons leave the emitter, pulled by the very high DC voltage between emitter and collector.  The traces of gas remaining in the tube are struck by these high-energy electrons, and are stripped of their electrons as well.  All the traces of gas inside the tube are ionized (thus the glow).  Electrons move from the emitter at such high speed that their momentum prevents them from going directly to the collector.  Instead they fly right past the collector, and either impact a piece of metal suspended inside the tube, or impact the glass tube wall.  In this respect, a Crookes Tube might be considered the forerunner of the Cathode Ray Tube (CRT) screen. 

Crookes Tubes were laboratory curiousities for about 20 years, because nobody understood what invisible rays were casting the shadow on the front end of the tube.  Clearly the metal object was blocking something from reaching the other end of the tube!  These rays were called "Cathode Rays", and eventually JJ Thompson proved that the "Cathode Rays" were negatively charged particles, which eventually received the name "electron".  Until that time, the atom was thought to be the smallest known piece of matter, and nobody understood that electricity was the flow of electrons.

Crookes tubes have another important aspect besides generating an electron shadow image.  They also produce X-rays.  X-rays were discovered and researched by Wilhelm Röntgen in 1895. Röntgen and many other scientists at the time were experimenting with Crookes Tubes.  While many scientists noticed that photographic plates fogged in the vicinity of Crookes Tubes, only Röntgen realized that penetrating radiation was being generated. By the way, Crookes Tubes are readily available on Ebay.

Below, the world's first Radiograph (X-ray picture) of the hand of Anna Bertha, Röntgen's wife.

At voltages over about 5000 volts, Crookes Tubes create X-rays in a process called "Bremsstrahlung".  Sorry, I have no idea how to pronounce that :).  What the word means is "Braking Radiation", which is not very difficult to understand.

At 5000 volts, the electron is moving at about 20% of lightspeed.  (It's easy to understand why it doesn't make the bend to directly reach the anode!!!)  At 20% of lightspeed, the electron smacks into the metal object or the glass envelope of the Crookes tube and comes to a stop.  What becomes of all that kinetic energy?  X-rays!

Here we get into the realm of special relativity; the 5000 (or more) volts between the emitter and collector have added speed to our elctrons.  This increase in speed also increases their mass, and this increase in mass can be calculated.  When the electon moving at 20% of light speed comes to rest, this mass it gained is immediately lost and converted (E=mc^2) to energy, in the form of X-rays.  The higher the voltage used between the emitter and collector, the more energetic the X-rays.

And so just as kinetic energy removed by slowing down a vehicler is converted to heat energy in the brakes, the kinetic energy of the electron is also converted.  And yes, a vehicle traveling at high velocity has slightly more mass than one at rest.  To be measureable, this mass increase would probably have to be taken at some fraction of light speed. :)

From Wiki:
The medical applications of X-rays created the first practical use for Crookes tubes, and workshops began manufacturing specialized Crookes tubes to generate X-rays, the first X-ray tubes. The anode was made of a heavy metal, usually platinum, which generated more X-rays, and was tilted at an angle to the cathode, so the X-rays would radiate through the side of the tube. The cathode had a concave spherical surface which focused the electrons into a small spot around 1 mm in diameter on the anode, in order to approximate a point source of X-rays, which gave the sharpest radiographs. These cold cathode type X-ray tubes were used until about 1920, when they were superseded by the hot cathode Coolidge X-ray tube.



Below, a Crookes X-Ray Tube.  Note that the target anode is at an angle, to direct X-rays off to the right side of the tube.  The small object to the right of the cathode is to replenish gas in the tube as it ages.  Crookes tubes reguire a slight amount of gas to function.


Modern tubes use heated cathodes, which utilizes thermionic emission to generate electron flow.  They also have water-cooled anodes, to prevent the electron beam from warping or vaporizing portions of the anode. 



Below is an electrical diagram of a modern X-ray tube.  "Uh" is the circuit for heating the tungsten emitter (C).  "Ua" is the high voltage circuit used to create the electron beam that will generate the X-rays.  Win and Wout are water cooling for the anode (A).


Below, a modern X-ray tube.  Note the thinner section of glass where the X-rays leave the tube.  Looks a little scary to me...


The vast majority of X-ray radiography uses old-fashioned photographic techniques:  A cellulose plastic sheet which is coated with silver-halide emulsion is exposed to X-rays and developed by washing the exposed silver off the sheet.  In early days, a sheet of glass coated with emulsion was used.  Currently a plastic sheet with sensitive coating on both sides is used.  Coating both sides  increases the sensitivity of the film, thereby reducing the X-ray exposure required.



Modern X-ray radiography is replacing film with digital sensors.  The advantages of digital detectors are higher sensitivity (and so reduced exposure), immediate processing so that the shot (angle, contrast) can be re-imaged if necessary, chemical processing is eliminated, and digital enhancements can be used to improve the quality of the initial image.



Another X-ray imaging technique used early on was the Fluoroscope.  The patient would be placed between the X-ray source and a fluorescent screen.  The screen would glow like a TV, with the image of the inside of the patient.  This provided a physician with the exciting ability to see inside a patient in real-time!  The downside was heavy X-Ray exposure, both for the patient and the physician.



Below, a sketch of a doctor using a fluoroscope to remove a bullet from a WW1 soldier.  An unshielded Crookes X-ray tube is beneath the patient!


Amusingly, fluoroscopes were manufactured for use in shoe sales.  An X-ray source was built into a box which the customer stood on.  The salesman would then use the fluoroscope to check for fit.

Happily we now can use digital imaging techniques rather than requiring the use of fluorescent screen.  These are far more sensitive to X-rays than phosphorescent coatings on glass, and of course, require less exposure of the patient to ionizing radiation.



Below, a modern fluoroscope.  The machine has the ability to take snap-shots at adjustable intervals, eliminating the need for continuous X-ray exposure.

One of the techniques used in X-ray radiography (both in fluoroscope and X-ray film), is the use of liquids that are opaque to X-rays, called "contrast agents".  Barium Sulfate is an edible (?) cocktail containing the X-ray opaque element Barium.  When the Barium has been consumed and coated the lining of the patient's stomach and intestines, an X-ray image can be made.  This will clearly show the outline of the patient's gastro-intestinal tract, as the barium will absorb X-rays, blocking them from reaching the film/detector.
 

An X-ray of a normal stomach and lower intestine in a patient.  Note how the Barium Sulfate has made the internal organs more opaque to X-rays than even bone.

Likewise, contrast agents can be injected into the bloodstream, and an X-ray shot taken, in a process called Angiography.


Below, an X-ray image of a patient's veins near the rear base of the skull, taken with contrast agents injected into the bloodstream.

 

CT scans (Computer Tomography) is an impressive blend of the old technology of X-rays with the new technology of digital imaging.  By taking X-ray "slice" images at various angles, it is possible to use a computer to combine these images and build a three-dimensional image of the inside of the body.



The down-side to CT scanning is that many, many X-ray images must be taken to render a three dimensional image, and so exposure levels are quite high for this imaging technique.  I would need to have a very good reason to undergo a CT scan.



Next up:  PET scans.  And I am not talking about scanning dogs and cats!

Busy!

It has been a while since the previous blog post, and if anyone bothers to follow this goofy blog, I apologize.  Work has been pretty demanding of my time lately. 

The last time sheet I turned in had 120 hours on it, and the previous one had 140 hours on it.  Normal people only work 80 hours in a two week period.  The few days off I have had, I used the time to catch up on lawn care, trash disposal, a few home repairs, and on family time.

However the schedule looks a little better now, so I will try to get on, starting with the promised posts about nuclear medicine.