|e-Newsletter for November, 2001.
Request for Information:
M/SGT Euell E. "Bill" Norris was a crew chief in the 833rd Bomb Squadron at Sudbury 1944-1945. Bill passed away, but his daughter would like to speak with anyone who knew him.
None this month.
The use of e-mail has altered the way we, as a society, communicate with each other. If you stop and think about it for a moment, an e-mail you generate may eventually reach everyone connected to the internet if it's interesting enough. Next time you get a chance, check your electronic address book. Chances are you'll see a list of friends, family and several people you don't know at all. Delete those in the last category. Now imagine that if you have names of people you don't know, how many strangers have your e-mail address in their books?
The problem is, the more exposure you have on the internet, the more likely you are to become a victim of spammers, and viruses. Your PC is constantly being hit by hackers who are looking for stuff that might be of interest or use on your PC. One way to protect yourself is to purchase firewall software. You can also protect your friends by being careful of how you use your e-mail, and hopefully they'll do the same for you.
In most instances we have a small circle of friends online who know each other, and to whom we send batch e-mails. In other instances we are sending e-mail to a list of friends who may not know each other. In the latter instance you may have a friend who does not appreciate his, or her, e-mail address being published for strangers to see. And this is not only a matter of privacy, but of internet safety as mentioned above. When you generate e-mail, you must be sensitive to who aren't worried about their e-mail address being made public, and those who are. The best way to handle this situation is to make use of the "Blind Carbon Copy" address line.
When you create an e-mail you will have, at least, a "To" address line. You may also see a "Cc" address line (Carbon Copy). Addresses appearing on these lines will be visible to all parties. If you click on the "To" or "Cc" labels, you will see another category, the "Blind Carbon Copy" (Bcc) address line. Addresses that appear on this line will not be visible to those on the other address lines. You've no doubt noticed that my 486th Bomb Group Association e-mail has no one listed on the "To" and "Cc" address lines. Each of my 250+ addressee's are on the "Bcc" line, making your addresses invisible to each other. The address "486th Bomb Group Association" is a psuedonym for my e-mail address. If you attempt to "reply to all," I will be the only one on your address list. Not all of you are concerned about being hidden, but some of you are, and I use this method to protect everyone.
Now consider the "Reply to all" option. When you chose this type of reply, your e-mail setup may add everyone on the "To" and "Cc" lines to your address book. This is how mysterious names get put into your address book. You will also notice that the header of the original e-mail is included in the body of your e-mail. The header includes the e-mail addresses of the recipients on the "To" and "Cc" lines. You should consider deleting this information. By doing so, you make the message smaller and, thus, faster to send and receive. This is especially true if you are forwarding an e-mail. We've all received e-mail that is nearly 1/2 a megabyte long, containing dozens of headers (and hundreds of e-mail addresses) from previous forwards. You page down forever until you come to the original message, which is only two lines long. Those two lines better be very important, or funny, to make the 5 minute download and two minutes of hitting the "pagedown" key worthwhile. Frankly, after hitting the "pagedown" key twice, my third key stroke is "delete."
Another thing to consider is your and replying forwarding options. Some of us have our e-mail set up to have replies and forwards sent "inline." This means that the original message (and header) will be contained in the body of your reply, and a forward will also be contained in the body of your e-mail. Others have their e-mail set up to send replies and forwards as attachments. In a reply it is usually the original message that makes up the attachment. However, if you are forwarding an e-mail, you have to open the attachment to read it. If the e-mail has been forwarded as attachment a dozen times, you have to go through a dozen attachments to read the original e-mail. Its like the child's toy with a block, within a block, whithin a block........And each attachment will contain header information from the previous forward. In this case, if you wish to forward the original e-mail to your friends, do so from the original attachment, not from the e-mail that was forwarded to you. This will simplify the search for your friends, and make the e-mail smaller. And be sure to remove the headers!
The Atomic Bomb (part II)
[ Part I]
While Fermi was on travel, he received word from his assitants that the neutron experiments conducted earlier were now giving different results. Fermi was not pleased, and blamed them for sloppy work. When he returned and reviewed their work, he found everything in order. The only difference between the two runs were the location. Originally, the experiments were conducted on a marble bench. The second series of experiments were conducted on a wooden bench. Fermi reasoned that some of the neutrons from the source were scattering off molecules in the benches. The molecules of the marble bench were relatively heavy and didn't absorb very much energy from the neutrons. As a result, they entered the target still at a relatively high speed. However, the wooden bench contained lighter molecules, most notably, Hydrogen. In this case, the neutrons were losing much more energy when they collided with the atoms in the wood bench. The differences of energy (or speed) the neutron entered the target with, resulted in the observed differences. Fermi ran the experiments again, using the wooden bench to document other differences. When he once again bombarded Uranium, the differences were dramatic.
Uranium bombarded by the slower (thermalized) neutrons became highly radioactive. Again, Fermi suspected that elements heavier than Uranium, but his chemists failed to find these elements. The realization that Fermi's experiment resulted in fission of the Uranium nucleus came to a German physicist first. Once this revelation was made, Fermi wondered why slower neutrons were more likely to cause fission, while the faster neutrons were preferentially captured by the Uranium nuclei. He suspected that the different isotopes of Uranium may be responsible. Uranium occured naturally with 3 isotopes. Uranium-238 (U238 - having 146 neutrons), U235, and U236. The ratio of U238 of natural Uranium was in excess of 99%. Fermi reasoned that U238 was the least fissile of the three isotopes, and would absorb neutrons to become U239. The U239 would undergo a beta decay yielding the element having an atomic number of 93 (Uranium's atomic number was 92 -- 92 protons). This new element, later called Neptunium, would also beta decay creating element 94 (Plutonium). This process is referred to as breeding. U236 was barely measurable in natural samples of Uranium, and U235 wasn't much more common. But, Fermi suspected U235 to be the fissile isotope and set out to prove it. In 1934 the fission of U235 was confirmed and the world would never be the same.
During the 30's the situation in Europe was turning bleak as the Fascists assumed power. Those who could began to emigrate to Britain or the US. Many were from Europe's intelligentia, and many were jewish. The resultant brain drain hurt Germany, and it greatly benefited the US and Britain. All three countries had intelligent and capable scientists, which were current in the latest developments in nuclear physics. However, these immigrants brought with them experience, knowledge and a sense of urgency, and fear that Hitler would be the first to develop the atomic bomb, with dreadful consequences for the world. Most notable among these fleeing scientists was Leo Szilard, a physicist born in Hungary, and trained by Einstein. Many years earlier he had read a book written by H. G. Wells ("A World Set Free"), which spoke of the commercial and military use of nuclear energy for power and weapons. These ideas inspired Szilard to seek ways to make Science Fiction, Science Fact. Natural radioactivity, while releasing energy, showed little promise as a convenient source of power, and even less as a weapon. But, the discovery that U235 could be made to fission, with a substantially larger release of energy, took him that much closer to realizing his goal. Knowing that Hitler's scientists were travelling down the same road, Szilard would become very active in getting the governments of Britain and the US to start their own atomic research programs with the goal of creating an atomic bomb.
Many questions had to be answered before nuclear power plants, and weapons became a reality. In the lab the fission process was initialized with a fabricated neutron source. To sustain a reaction U235 would also have to release neutrons in the fission process. Moreover, it would have to release more than one neutron on the average to compensate for neutrons that would be absorbed by impurities, or escape the mass without causing fission. In 1938, experiments confirmed the release of neutrons, and in 1939 it was determined that multiple neutrons were released with each fission. Leo Szilard now campaigned hard for the US Government's involvement in the project. He wanted a veil of secrecy dropped over the research being conducted to slow the German research programs. Some physicists, such as Enrico Fermi (who had emigrated to the US by this time) and Neils Bohr were against secrecy. Unfortunately, before the matter could be decided, a French journal published the results. The race for nuclear weapons was now on. Later that year, in September, Europe would be embroilled in war.
Despite all attempts at lobbying by Leo Szilard, the US Government was slow to take control of the research programs, and organize them under a single department. Various universities across the US were conducting their own research, with whatever grant money they could receive from the Government. The military took interest, but were obviously distracted by events in around the globe, and in preparing for the possibility of war on two fronts. Slowly, the Government started to give serious consideration to nuclear weapons research and established an office in Manhattan, NYC, to handle the needs of the research centers. This office became known as the "Manhattan Engineering District." In 1941 Enrico Fermi had successfully demonstrated a nuclear reactor (originally referred to a pile due to its appearance) beneath Stagg Field at the University of Chicago. The celebration that followed was subdued, for in spite of the years of hard work the implications for humanity were well understood by all in attendence. The Nuclear Genie had been finally let out of the bottle, and there would be no putting him back. With America's entry into the war in December 1941, the situation changed, and nuclear research was going to become a priority.
In September of 1942 COL Leslie Groves was assigned to oversea nuclear research with the expressed purpose of developing weapons. The Navy was also interested in developing nuclear power for propulsions systems, and would conduct its initial research at the Naval Research Lab in Washington, D. C. Groves, who was not happy with his assignment, took immediate charge and got the ball rolling. Of immediate concern was how the nuclear fuel was going to be processed, weapons researched, and tested. By this time, U235 and Pu239 were the only two isotopes that showed promise for atomic bombs. U235 was virtually identical to U238 and would be tough to extract chemically. It differed in weight by a small margin as well, and any centrifugal, or electromagnetic means of separation were also going to tough to accomplish. Separation by gaseous diffusion showed promise, but not enough to make it stand out. Plutonium, on the other hand, would be easy to extract from Uranium once it had been bred, but that process did not have a high yield either. Because results were demanded quickly, Groves authorized his scientists to pursue each avenue for the purpose of obtaining enough U235 and Pu239 for weapons in the quickest time. Several universities would look at chemical, elecromagnetic and centrifugal methods of separation. The gaseous diffusion plants, and breeding reactors required special facilities, and Groves procured tracts of land near Oak Ridge, Tennessee, and Hanford, Washington. Oak Ridge would be primarily responsible for the extraction of U235 from natural Uranium by diffusion, and Hanford would breed Plutonium from Uranium. Groves then purchasd a tract of land near Los Alamos, NM to establish a research and test facility.
Another problem to be solved was how to make an atomic bomb detonate efficiently on demand. Natural Uranium was unstable, but decays so slowly that it is found in abunance in nature. Its principle modes of decay are beta and alpha. More rarely it would also spontaneously fission. In the natural state, the neutrons from spontaneous fission would be absorbed by impurities in the ore, and prevent it from melting down. In pure form, it was much more dangerous. As a mass of pure Uranium grew bigger those free neutrons would be more likely to strike an atom of U235 and induce fission. At some "critical" point, the rate of fission would grow exponentially if not controlled by some means, causing the mass to heat up and melt. If this point were exceeded rapidly, it was hoped an explosion would occur. Obviously, a weapon had to have enough Uranium, or Plutonium to exceed that "critical" threshold, but not to explode until commanded to do so. The solution was to divide the critical mass into parts, and separate the parts at some distance to insure that no explosion, or melt down would occur accidentally. Then, to detonate the weapon, those pieces would have to be brought together rapidly. The Los Alamos scientists set about trying to determine what the minimum critical mass would be, and which shapes for that mass would be most effective. They also had to devise methods for forcing the sections of that mass together rapidly to generate explosions.
Next month: Little Boy and Fat Man
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