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.

Nuclear Medicine

The previous post was about the shameful and dark underside of nuclear research on human beings.  This one and the follow-ups will discuss some of the useful medical advances that our understanding of radiation have made possible.

I don't know how much the unethical human radiation experiments contributed (if any) to modern medicine.  What I do know is that entirely new methods for imaging and treating disease are now available that were not available prior to the nuclear age.  There is a lot of genius involved with using radiation to make people well.

Nuclear Medicine broadly falls into two categories;  I will be discussing each one in separate posts of their own.  Those categories are Imaging and Therapy.  Both are interesting fields - they are at the intersection of radiation and biology, only this time for the good of mankind.

Nuclear Imaging - a PET (Positron Emission Tomography) scan.

Nuclear Therapy - an early linear accelerator for radiation therapy on an inoperable cancer.

Nuclear Experiments on Humans

“It is desired that no document be released which refers to experiments with humans and might have adverse effect on public opinion or result in legal suits. Documents covering such work should be classified `secret’.”

April 17, 1947 Atomic Energy Commission memo from Colonel O.G. Haywood, Jr. to Dr. Fidler at the Oak Ridge Laboratory in Tennessee

In the early days of Nuclear Energy, the US government (and by extension, the US Military), had a monopoly on man-made radioactive materials.  There was a great deal of curiousity about these new materials, and what their effect on the human body might be. 

Nuclear Propulsion - So many options!

Nuclear Propulsion - that is, moving large objects by using the power of the atom - has been around for over half a century.  It was 11 A.M. on 17 January 1955, when the USS Nautilus announced she was "Underway on Nuclear Power".

The primary use of nuclear power for propulsion has always been in submarines, where submerged endurance and detection avoidance are both critical. 

Prior to nuclear propulsion, submarines were essentially surface ships that could submerge for brief periods of time.  These subs used large storage batteries to travel while submerged.  The batteries would discharge, and at that time the submarine would either have to surface or use a snorkel, at which point air could be drawn into the ship so that diesel generators could recharge the batteries. 

Submarines' reliance on the internal combustion engine was not convenient from a wartime perspective - it severely limited both submerged endurance and detection.  For submarines, nuclear propulsion increased the operating envelope a thousand-fold.

The other chief use of nuclear propulsion is in aircraft carriers.  The reason nuclear propulsion is chosen for aircraft carriers is that fuel storage that would otherwise be required for propulsion can now be made available for aviation fuel.  Using nuclear propulsion on the largest ship in an aircraft carrier group also reduces the number of refueling ships required, thereby extending the range and/or endurance of the group.

A handful of cruisers were fitted with nuclear propulsion plants, but they are no longer being built.  It is much less expensive to build and maintain a ship powered by gas turbines than a nuclear-powered ship, and the unique needs of submarines and aircraft carriers do not apply to other ships - thus these other ships are no longer being built with nuclear propulsion plants.

We have discussed the primary coolant/secondary steam system design, which is the typical propulsion plant arrangement in a nuclear-powered maritime vessel. 

What a lot of people aren't aware of is just how eager scientists and engineers were to utilize nuclear energy for other types of propulsion, back in the early days of nuclear power.  These engineers envisioned, developed, and tested a number of different technologies for harnessing the atom for propulsion.  Let's take a look!

Below is a fascinating five-segment video from the Discovery Channel about the US Air Force's attempt to build a nuclear-powered bomber.











The US tested a number nuclear-powered aircraft engines.  Below are two of them (courtesy of Wikipedia):
Experimental HTRE reactors for nuclear aircraft, (HTRE 3 left and HTRE 1 right) on display at Idaho National Laboratory near Arco, Idaho

WikiMiniAtlas

43°30′42.22″N 113°0′18″W / 43.5117278°N 113.00500°W43.5117278; -113.00500)

These clunky machines are just test beds, and would certainly need to be scaled down for aircraft use!

Nuclear Propulsion in space:

The Air Force wasn't the only entity that wanted to move things around with nuclear power.  NASA wanted to make a nuclear rocket motor.  Here is a cutaway of a NERVA (Nuclear Engine for Rocket Vehicle Application) motor.

Below, a test platform for a NERVA type rocket motor.  Unlike the nuclear aircraft engines, these were very powerful and successful designs that could have been flown, although probably not on manned missions.  The one below has not been fired yet, or these people would not be able to approach this closely.

 

Even docking with one of these briefly (Space Station Re-supply, for example) would be hazardous from a radiation standpoint. 

 

According to wikipedia:

Building on the KIWI series, the Phoebus series were much larger reactors. The first 1A test in June 1965 ran for over 10 minutes at 1090 MW, with an exhaust temperature of 2370 K. The B run in February 1967 improved this to 1500 MW for 30 minutes. The final 2A test in June 1968 ran for over 12 minutes at 4,000 MW, the most powerful nuclear reactor ever built.  

 

Below is a cool video of a NERVA rocket engine being tested.  Liquid hydrogen is being expanded in the motor, which is what provides the thrust.  Well above the motor the hot hydrogen ignites, but this is simply an after-effect, not part of the process itself.  Power ramps up at about 20 seconds, and a massive release of cryogenic hydrogen is released at 1:25.  This might be from an overpressurized storage tank.


And lastly there is this... propulsion based on a series of nuclear bomb blasts, at which point we have entered the realm of science fiction!  Exept that these have actually been explored as possibilities :)

Classic Rock vs. Alternative Rock

Actually I like it all.  Great music is always being made.
Here are some other bands that I dig... To hell with only listening to "Classic Rock"! :)

Nuclear Research Reactors - MK 1 - Testing Radiation Hardening

Satellites that are flown into orbit face radiation that can damage their electronic components and render the satellite useless.  Modern semiconductors are very susceptible to damage from ionizing radiation, both electromagnetic and charged particles.  Electronics that are flown into space (whether deep-space probes, communtications satellites, etc.) face much harsher radiation fields than they would under the protective atmosphere of mother earth.

Radiation can damage electronics in several ways.  Here are a list of naturally-occuring types of radiation that can affect an object in space: (From Wikipedia)

Cosmic rays come from all directions and consist of approximately 85% protons, 14% alpha particles, and 1% heavy ions, together with x-ray and gamma-ray radiation. Most effects are caused by particles with energies between 10⁸ and 2*10¹⁰ eV. The atmosphere filters most of these, so they are primarily a concern for spacecraft and high-altitude aircraft.

Solar particle events come from the direction of the sun and consist of a large flux of high-energy (several GeV) protons and heavy ions, again accompanied by x-ray radiation.

Van Allen radiation belts contain electrons (up to about 10 MeV) and protons (up to 100s MeV) trapped in the geomagnetic field. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the sun and the magnetosphere. Due to their position they pose a concern for satellites.

Secondary particles result from interaction of other kinds of radiation with structures around the electronic devices.

There are several other types of radiation that can damage electronics that are man-made, or that occur on earth.  But for simplicity in this post, I am restricting the discussion to those radiation sources that naturally occur in space.

There are a number of cool techniques electronics manufacturers use to reduce damage caused by radiation, and to make the chips more tolerant to the damage that will eventually occur: (Again from Wikipedia):

Physical:

• Hardened chips are often manufactured on insulating substrates instead of the usual semiconductor wafers. Silicon on Insulator (SOI) and sapphire (SOS) are commonly used. While normal commercial-grade chips can withstand between 50 and 100 gray (5 and 10 krad), space-grade SOI and SOS chips can survive doses many orders of magnitude greater. At one time many 4000 series chips were available in radiation-hardened versions (RadHard).^[3]
• Bipolar integrated circuits generally have higher radiation tolerance than CMOS circuits. The low-power Schottky (LS) 5400 series can withstand 1000 krad, and many ECL devices can withstand 10 000 krad.^[3]
• Magnetoresistive RAM, or MRAM, is considered a likely candidate to provide radiation hardened, rewritable, non-volatile conductor memory. Physical principles and early tests suggest that MRAM is not susceptible to ionization-induced data loss.
• Shielding the package against radioactivity, to reduce exposure of the bare device.
• Capacitor-based DRAM is often replaced by more rugged (but larger, and more expensive) SRAM.
• Choice of substrate with wide band gap, which gives it higher tolerance to deep-level defects; e.g. silicon carbide or gallium nitride.
• Shielding the chips themselves by use of depleted boron (consisting only of isotope Boron-11) in the borophosphosilicate glass passivation layer protecting the chips, as boron-10 readily captures neutrons and undergoes alpha decay (see soft error).

Logical:

• Error correcting memory uses additional parity bits to check for and possibly correct corrupted data. Since radiation effects damage the memory content even when the system is not accessing the RAM, a "scrubber" circuit must continuously sweep the RAM; reading out the data, checking the parity for data errors, then writing back any corrections to the RAM.
• Redundant elements can be used at the system level. Three separate microprocessor boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.
• Redundant elements may be used at the circuit level. A single bit may be replaced with three bits and separate "voting logic" for each bit to continuously determine its result. This increases area of a chip design by a factor of 5, so must be reserved for smaller designs. But it has the secondary advantage of also being "fail-safe" in real time. In the event of a single-bit failure (which may be unrelated to radiation), the voting logic will continue to produce the correct result without resorting to a watchdog timer. System level voting between three separate processor systems will generally need to use some circuit-level voting logic to perform the votes between the three processor systems.
• Hardened latches may be used.
• A watchdog timer will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such as a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.

The bottom line is that you want to ensure all the efforts you have made above to ensure your circuits are safe against radiation is to test them *before* you put them into an expensive satellite and send it up into space.

One of our customers was a large aerospace company that flew communications satellites, and needed to test their hardware for radiation hardness.  We provided them with a cadmium-lined dry tube that went directly into the MK 1 reactor core. 

The cadmium inside the tube absorbed thermal neutrons (which don't exist in outer space), and allowed the gamma and fast neutrons to zap the circuits.  The calculation by our reactor physicist was that 30 minutes at 10 watts would be a lifetime worth of radiation damage in outer space. 

The engineer lowered his assemblies, connected by wires to an oscilloscope, to the bottom of the tube, and I ran the reactor for him.  I never was able to get an answer from the engineer how well his circuits held up.  Perhaps he was working on a government project, and was sworn to secrecy...

... or maybe he just wasn't chatty.  Who knows? :)