|Contrast between electorn capture and positron emission?|
Electron capture is the capture of an inner shell electron by the nucleus. This will always result in x-rays be emitted. The energy of these x-rays will be below 100 Kev. When positron emission occurs the positron is immediately annihilated with the emission of two 511 Kev gamma photons being emitted at 180 degrees apart. So, electron capture emits x-rays (less than 100 kev). Positron emission results in gamma emission (at 511 Kev).
|Is jewelry made from Terbium safe to use?|
Little is known of the toxicity of Terbium (Element 65; Tb). The other key question which is equally difficult to answer is how much of the metal would be absorbed into the body. Some people also have reactions to metals such as nickel - which
is also used in some jewelry. Limited wearing of this such jewelry most likely does not present a great risk. However, caution should be exercised if the jewelry were to be worn constantly over many years.
|Explain the use of Iodine-131 in terms of its chemical properties and what's Iodine-131 decomposition equation?|
Iodine-131 behaves chemically the same as all other isotopes of Iodine; it decays by beta(-) to stable Xe-131.
View: Iodine Isotopic Data »
|How can super heavy elements be prepared? What are the advantages
and disadvantages of use of these elements?|
In general the quest for
Super-Heavy-Elements (SHE) has focused on trying to collide two isotopes of
say lead (element 82). The hope is that these two isotopes would merge (or
"melt together") to form a new element containing 164 protons. Physicists have long believed that such elements will be long-live or
possibly stable. These super-heavy elements would only broaden our
knowledge of the nucleus and nuclear forces. It would be hard to say if
there would ever be any practical use for such elements.
|Will there ever be an element >118, that will be
stable for any length of time?|
There has been for the last 40+ years a
search for "Super Heavy Elements" (SHE). It has been theorized that near
proton number 156 there will be an "Island of Stability". If this were the
case then it is most likely that such elements should be found in nature. Some very serious searches have been made but none have been found. If such
a finding is made this will most likely warrant the Noble Prize in
|If Pu239 is created from U238 capturing a slow
neutron, where do the extra two protons come
from? I would have thought that U238 + neutron
would be U239? If U239 then beta decay's twice
to form Pu239, do two of the neutrons somehow
convert to protons during the process of Beta
A bare neutron will decay with a 12 minute half-life to a proton and an electron. This means that a neutron is a proton and electron bound
Any time a radionuclide decays by beta it means that a neutron is lost and a proton is grained in the nucleus.
All elements are defined by the number of protons in the nucleus. Therefore, if one changes the number of protons in the nucleus one changes which element it is.
In the case of Pu239 this is exactly the case. First, a neutron is captured and then the U239 that is formed is converted to Np239 via beta decay. The
Np239 beta decays and is converted to Pu239.
|When atoms form ions they often achieve the same
configuration as the nearest noble gas. Why are they not regarded as the same element as the noble gas?|
All elements are defined by the number of protons in the nucleus. This fact was discovered by Moseley in the early 1900s. The interesting part of this point is that all of chemistry is actually defined by the valence state of the atom. That is, all chemical reactions take place via interactions between the outer most shell of the electrons. Yet, it is the nucleus that indeed dictates what element it will be. Additionally, an atom will lose or gain electrons in general to achieve the noble gas electron configuration. This is why the sodium atom is very chemically reactive, while the sodium ion is nearly inert.
|Is rhodium that is used to plate white gold jewelry radioactive, and therefore a health hazard?|
Rhodium in and of itself is not likely to be radioactive (or contains any
radioactive isotopes). Additionally, rhodium only has one stable isotope
Rh-103. The longest lived isotope of rhodium is Rh-101 which is 3.3 year
half-life. The only way to produce this isotope from the stable isotope
would be a (n,3n) reaction which is an unlikely reaction and requires that
the metal be exposed in a reactor.
As a side note, some gems are irradiated in order to change the color of the
gem. For example a yellow diamond can be made into a "rare" blue diamond by
irradiation in a reactor. This has caused many in the gem business concern.
If the gem is irradiated by itself it will not have any effect on the metal
being irradiated. However, if the metal along with the gem is irradiated
then the metal will be made radioactive. What isotopes are formed will
depend on what the content of the metal is.
|What are the various elements used in making televisions?|
First we must begin with all of the "computer" type electronics - they are formed with silicon. Silicon is an element just under carbon on the periodic table and has unique properties when it is "doped" with other elements such as arsenic. This forms the bases of all transistors. The brain of your TV is attached to a circuit board. The circuit board utilizes metals such as copper, gold, tin, lead etc. for the conduction of the operating chips and devices. I am not sure what the circuit board itself is made of but it must be some type of non-metallic material that acts as an insulator. Generally, these are made of some types of plastics with are formed from carbon, hydrogen and some other elements such as chlorine. PVC is a type of plastic and stands for polyvinyl chlorides which also used to form the casing that your TV is molded out of.
The TV tube is made of glass and glass is formed with silicon, oxygen, sodium and other types of glass formers.
The electron gun more than likely uses some type of metal such as selenium. This metal is used in copy machines as well as televisions and works off of the principle first discovered by Albert Einstein - the photo-electric effect. This is what he won the Noble Prize for in 1921.
Last but not least, the pixels on your color set are made up from different rare earth metals. These rare earth oxides form the basis of the image on your screen. The colors that one sees are formed from combinations of these elements being struck in the appropriate combination. If one looks closely at an older TV screen with a magnifying glass one can see dots of the primary colors: red, yellow and blue. From this, all of the colors of the rainbow are produced. The electron gun with the TV tube fires electrons and causes them to hit in the right combination to form the color you see.
|I understand from reading that Uranium 235 is the only element used in Nuclear Fission, because it is unstable and radioactive. I was wondering if there are other elements that share these qualities, and, if so, why are they not used in Nuclear Fission?|
First, we have to differentiate between an element and an isotope. All elements are defined by their atomic number or the total number of protons in their nucleus. For example, the element uranium has an atomic number of 92 or 92 protons.
On the other hand, all elements have numerous isotopes. Some of these isotopes are radioactive and some are stable. Currently there are 3014 known radioactive isotopes and only 248 stable isotopes. It is the number of neutrons that differentiates one isotope from another. Isotopes are designated by their atomic mass number. The atomic mass number is the sum of the atomic number and the total number of neutrons. For example the isotope that you have mentioned U235 has 92 protons and 143 neutrons for a total of 235.
Therefore, the question you asked has to be slightly modified to "are there other isotopes besides U235 that can undergo fission?" The answer is yes and there are many. The most common are U235, U233 and Pu239. Each of these can be used in both nuclear weapons and in nuclear reactors.
There are still others that can undergo spontaneous fission such as Cf252. For the above mentioned isotopes (U235, U233, and Pu239) they have to be put into special configurations with neutron moderators in order for the fission neutrons to cause other fission events with neighboring isotopes (i.e. a sustained fission reaction). However, Cf252 and many other isotopes of californium do not need any moderated neutrons to cause fission events. They simply fall apart or fission on their own.
Concerning why some materials are used and other are not is a very complex question. There are many criteria that need to be met for selection. Simple things like cost ease of production, half-life, fission cross section, the probability of a fission occurring when it is hit with a neutron, etc. There are also new types of reactors that are being explored.
There is much debate today about the resurgence of nuclear power. With the price of oil and the emission of greenhouse gases there is little doubt that fission will play a dominant role as an alternative.
|Has nuclear testing been responsible for any large changes in weather patterns?|
As to the specifics of your question, the last above ground nuclear detonation was on October 16, 1980 by the Chinese. This was believed to be a 1.2 Megaton Bomb. Test of weapons in the 1950s and 1960s put water and dust into the stratosphere and certainly these may have affected localized weather patterns. However, when one compares this to other natural sources of atmospheric loading such as volcanoes or ocean evaporation it is very unlikely that any of these tests had a significant large change in weather patterns. In fact, the 1980 eruption of Mt. St. Helens put 1.5 times excess radioactive 210Po (Po is a volatile radioactive elements that occurs as a natural daughter of radium).
Ocean water can absorb enormous amounts of heat. Additionally, since the surface of our planet is 3/5 ocean water, most scientist agree it is the circulation of our oceans currents between the equator and the poles that drive weather patterns. One need not look any further than the latest series of hurricanes to see how closely there movement and strength are tied to the heat of the oceans. Hurricanes die off when they hit landfall. The reason for this is that they derive there existence from the heat of the ocean.
Many scientists are concerned about the melting of polar ice and the disruptive effect this might have on the circulation of our oceans( and thus a dramatic impact on our weather). It has been said that these ocean circulations are our planets natural "thermostat" keeping the equator from being too hot and the poles being too cold. Many scientists now believe that previous ice ages were triggered by a sudden warming and melting of polar ice.
|How many valence elctrons are around the nucleus of Sulfur (S) ?|
Valence electrons are the number of electrons in the outer most energy shell. They are the electrons that determines the chemistry of each element. The types of orbitals are the s, p, d, and f. P orbitals are the ones that ones that govern non-metals. The element sulfur has the electron configuration of [Ne] 3s2p4. This means the there are 2 electrons in the outer s orbital and 4 in the outer p orbital. Therefore the total valence electrons would be 6. The total possible is 8 and this means that sulfur likes to have 2 more and can form the S-2 ion.
| Please tell me more about radiochemistry of Gold (Au).|
The alchemist's dream was to turn lesser metals into gold. This is now possible through transmutation or through nuclear bombardment. However, the expense of such a process far outweighs any cost benefit. Gold only has one stable isotope - Au197, however, it has 34 known radioactive isotopes. The longest lived of these radioactive isotopes is Au195 with a half-life of 186 days. There is much written about the chemistry of gold and suffice it to say that the radioactive isotopes of gold all behave chemically the same as stable Au197.
Over time an iodine 131 stock' pH (various concentrations - up to 10 curies/mL) will drop from 11 to around 7-8. What may be causing this? Why is the iodine so volatile / instable ?
Note: Stock is stored in sealed bottles or vials.
First, we need to discuss the chemical behavior of iodine. Iodine is one of the heaver halogens and as such had its valence shells much further from the nucleus than other halogens. Therefore, it ionizes much easier than the other halogens. Additionally, the iodide ion's electron configuration resembles xenon electron configuration. These two factors make iodine one of the more volatile elements. In fact, upon slight heating iodine will sublime, that is its will change directly from a solid directly into a purple gas. In fact, if you have a bottle of elemental iodine some of it will exist in the gaseous state and will be visible as a purple cloud above the solid.
Second, the radioiodine provides a source of radiation which can affect the chemical environment it is in. A simplistic answer as to why the solution changes pH is that there must be a mechanism for the change in the hydroxide concentration. The decay of radioiodine can cause radiolysis of water. The actual breaking of the water molecule. In this process, there more than like is a surplus of H+ ion formed, which in turn reduces the amount of OH- ion. The actual mechanism that I have described is much more complex than what I have described; however, suffice it to say the outcome is the same. One other point to make, iodine is a beta emitter with an 8 day half-life. It has a 364.5 Kev gamma and a 606.3 Kev beta. Both of these will create a surplus of secondary, tertiary "free electrons". In fact, since each beta collision will only loose approximately 30 ev per collision (and create ion pairs), one decay event will create more than 20,000 collisions (mostly with the water molecule)!
On other note, iodine will come out of solution at low pHs if it is held in a plastic container. This type of container should be avoided.
|How are excessively long half lives, used in radiometeric dating (such as Rubidium-87 at 48.8 billion years and some even longer), determined let alone measured ?|
Very long half-live are difficult to measure. In fact, many are surprised that over time the reported (or estimated) half-lives change. It is not the half-live that changes rather our estimate of what it is. In general, the longer the half-life the greater the uncertainty in its measure. The first step in determining the half-life of any isotope is to chemically purify the isotope to remove any other interfering radioisotopes. Next, the isotopes to be determined are counted over a very long time, many years (in other words, a long time in human years). And individuals have dedicated their lives to such tasks.
These numbers for half-lives are important since they allow us to determine very long ages. Also accompanying these half-lives will be the confidence interval or uncertainty in the measurement. These values are equally important since they tell us how well such numbers are known. The uncertainties generally shrink over time.
|Is there a formula or chart that will enable me to determine the volatility of free iodine (iodine 125 and iodine 131)? Whenever iodinations are performed, we are told that they must be done under a chemical hood due to the volatility of the unbound iodine. What amount of iodine is released into the atmosphere simply from opening the stock vial? Is it possible to determine how much iodine is lost.|
First, let's start with the fundamental principle of radiochemistry: All isotopes of the same element behave chemically the same. This means that if you have a solution of radioactive iodine 131 and it has stable iodine in solution as well then the ratio of stable iodine to radioactive iodine will always remain the same and any amount of radioactive iodine volatilizing will also be accompanied by stable iodine. Additionally, one can limit the amount of radioactive iodine that volatizes (to some extent by adding stable iodine as a "hold-back" carrier).
Concerning monitoring for iodine most have a charcoal filter sampling the air exiting the hood and then counting the filter for any release. The counting is done by gamma spectrometry and one must rotate the filter over the detector in order to account for uneven loading on the filter.
Concerning calculations they are not very reliable since small difference in oxidation reaction and in the solution can create large variation. If one wants to do calculation then they must set up an experiment that matches the conditions exactly. Even then this is difficult to do because usually it is not easy to control the amount of dissolved oxygen which can greatly affect volatility. Therefore, one could measure how much is lost by knowing the activity in the container and measuring the release through a charcoal filter. There are limitations to loading on the filter and one should have multiple stages to "catch" any breakthrough activity. Other than this it is relatively simple by know the amount in solution and then measuring the amount released.
Concerning the practice of doing this in the hood I suspect this is primarily a precaution. One thing to keep in mind is that iodine is a "biological getter" and can accumulate in the thyroid. In fact, the "radiation pills" that the US Army gave to troops in the 50s after open atmosphere tests were simply potassium iodide. The idea was to "flood" the thyroid with stable iodine which would block the uptake of radioactive iodine. Unfortunately these pills are not regulated by the FDA and are being sold over the internet as something that will keep you safe from radiation that one may encounter from a "dirty bomb". The truth of the matter is that if the material in such a bomb was any thing else besides iodine it would not help you.
|What keeps the electron in its orbit?|
a. How does it maintain velocity?
b. How does it attain its velocity?
c. What gives it its negative charge?
d. How does its oscillating frequency affect its charge, speed and direction?
e. What direction must an electron go, and what determines that?
First, these are questions that were asked in the early 1900s when our current concept of the atom was first being developed. One of the mistakes that many try to do however is to take everyday occurrences in our macro world and apply it to the subatomic world. This does not work. If we could shrink our selves down to the size of an atom we would be very surprised at what we would see.
The electron has both a wave property and particle property. The wave property allows the electron to be in two places at once! How can that be? Well first, let's imagine that we have a string stretched tight between two nails. Now if we "pluck" the string a wave will traverse back and forth. Now let's imagine something that is not possible. Let's pretend that we take the string that is pulled tight and "wrap" it in a complete circle while still keeping the string tight. Again, this is not possible but it helps us understand the wave nature of the electron. This wave can not be real for a tight string but indeed it is for the electron. In fact, the reason we know this is that the electrons have give off a very "precise" spectrum of light depending on what element it is. We have this shown on our web site [view here]. These bright lines are a result of the wave nature of the electron at a very specific energy level.
1. What keeps the electron in its orbit? In part, it is a similar force to gravity. That is one could ask what keeps the planets in their orbits. The answer is that they are always falling toward the Sun; however, as they move in they also traverse on their orbit. In fact, Newton calculated that the moon "falls" approximately 20 inches in one second. He also showed a drawing in his Principia a canon firing a canon ball higher and faster until one orbited the earth. Of course, in this discussion the central force is gravitation and with the atom the central force is electrostatic attraction. Also, only certain energy levels are allowed in the orbitals of the electrons. This is due to the wave nature of the electron. If the wave that is "wrapped" around on it were to result in a non-complete cycle this would lead to a self-destructive wave and thus would not be allowed in quantum mechanics.
a. How does it maintain velocity? The electron maintains its velocity as a balance between the force of electrostatic attraction and the force of acceleration from the motion around the nucleus. Bohr discovered that the orbitals of the electron were quantitized and that they were proportional to Planck's constant. Or in other words the angular momentum was quantitized. The angular momentum is defined as the mass x the radius of orbit x the velocity. Therefore, if the angular momentum is quantized so is the velocity of the electron. Since momentum is conservative then the velocity will be too and therefore there will be a velocity that is associated with a specific energy level.
b. How does it attain its velocity? Energy is equal to ³ mass x velocity squared. And since the velocity for a specific orbital is fixed its velocity is also fixed. Therefore, when an electron "falls" into a specific orbital it "adopts" that defined energy. Therefore the velocity becomes fixed until energy is imparted to that electron and it would then be removed from the orbital.
c. What gives it its negative charge? I wish I could answer this. I'm not sure any one other than God knows this one. The charge is an artifact of the quantitized nature of the electron. If on the other hand one asks well why does it have that specific value for the charge this is difficult to answer. Also, there is a counter part to this charge it is the positive charge and the positron of course is anti-matter equivalent to the electron.
d. How does its oscillating frequency affect its charge, speed and direction? De Broglie showed that the electron has a wave nature to it just like light. In fact, the de Broglie wave equation states that the wavelength = Planck's constant / ( mass x velocity ) or in other words the electron has a defined wave length associated with a constant mass and a specified velocity. The frequency is inversely proportional to the wavelength and directly proportional to the energy. Therefore change the velocity and you change the frequency.
e. What direction must and electron go, and what determines that? The direction of the electron takes is some what mysterious due to the fact that it is not some tiny small "ball" orbiting the nucleus. It is instead a wave which is capable of being in two places at once. The wave is propagated around the nucleus and forms the "path" that the electron follows. The direction of motion therefore is somewhat indefinable. Think of it as somewhat like Jell-O. Its nature allows it to "jiggle" in strange ways. If you asked where is it at any one instant you may be able to define that however, you would not be able to define its velocity. On the other hand if you did a very good job defining the velocity you would not be able to define the position very well. This principle is known as the Heisenberg Uncertainty Principle and it describes how well energy, velocity, frequency etc. can be defined. Suffice it to say that the direction of the electron is also quantitized as well.新金瓶2最新章节_新金瓶2最新章节目录
|Calcium 41 has a very long half life and decays by electron capture with no gamma radiation. How is it detected? I notice the NRC requires labelling of amounts over 100 microcuries. How can this be measured?|
Ca-41 is an interesting isotope for many reasons. First, and foremost it has a half-life of more than 100,000 years which makes it a good candidate in dating of bones. Like C14, Ca-41 will exist predominately in bone tissue. Unlike C14 however, it is formed mostly in-situ through the interaction of cosmic rays with Ca-40 or stable Ca. Therefore, as an animal or human is living above ground a certain amount of Ca-41 will be produced due to the cosmic radiation. However, after death and burial underground this process basically stops. Thus if one measure the Ca-41 to Ca-40 ratio some dates can be fixed on when the animal or person lived. The upper limit on this would be around 500,000 years though. Ca-41 is also utilized as "tracer" in nuclear medicine studies, particularly with osteoporosis.
As you pointed out, Ca-41 decays by electron capture. As you also pointed out it does not emit any gammas. However, through the process of electron capture a proton in the nucleus is converted to a neutron. Thus, Ca-41 decays to K-41 which is stable. Therefore, one can measure the parent daughter ratio through chemical separation followed by measurement of both by mass spectrometry.
In the past, its detection was mainly done using accelerator mass spectrometry or time of flight mass spectrometry. This technique was very costly and there were a very limited number of facilities that could provide the accelerator. New instruments are being developed, however, which will allow one to detect almost down to the atom level. Resonance Ionization Mass spectrometry (RIMS) is one such example. These are exciting new techniques that offer many avenues that were not readily available in the past.
|What makes the glow in the water where radioactive things, like fuel rods, are stored? I know it has a name but I can't remember it. Just wondered how that worked.|
Excellent question. The blue glow you are referring to is Cerenkov radiation. This is how it works. First, we have to talk about the speed of light. Light traveling through a complete vacuum will travel at approximately 300000000 meters per second (299792458 to be exact). This velocity is the ultimate speed limit in the entire universe. Most scientists believe that nothing can travel faster than the speed of light in a vacuum. When light travels through water it moves at a slower speed. So much slower that some subatomic particles such as beta particles (a beta is nothing more than a high energy electron) can travel (initially when exiting from the nucleus) faster than the speed of light in water. This is the part that is not well understood. When a subatomic particle exceeds this limit it quickly gives up energy, this energy is in the form of blue light - or Cerenkov radiation. On a simplistic level it is as if the particle is "putting on the brakes" and quickly slows by giving up energy - the blue glow. I personally have seen this glow in a swimming pool reactor and I must say it is a most beautiful blue. Before this, I had only seen pictures and pictures do not compare to seeing the real thing.
|Which elements are considered refractory?|
The term refractory metals denotes metals with a very high melting point, but it is used somewhat arbitrarily in the metals industry. For example, the Refractory Metals Committee, organized under the Metallurgical Society of the American Institute of Mining, Metallurgical and Petroleum Engineers, uses the term refractory to cover only metals with melting points above about 1,900 C (3,500 F). However, according to the Metals Handbook published by the American Society for Metals, the refractory metals are those "metals having melting points above the range of iron, cobalt and nickel." This broader definition would include tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and some less common metals. This section discusses niobium, vanadium, tungsten, and molybdenum. Chromium is discussed above with manganese. Tantalum is omitted from discussion owing to its limited commercial use. Using nickel as the cutoff temperature (1726K) the following list of elements would be considered refractory:
For more information on the elements, please visit our Periodic Table and information center online.
- nickel - Ni - 1726
- holmium - Ho - 1747
- cobalt - Co - 1768
- yttrium - Y - 1795
- mendelevium - Md - 1800
- erbium - Er - 1802
- iron - Fe - 1808
- scandium - Sc - 1814
- thulium - Tm - 1818
- palladium - Pd - 1825
- protactinium - Pa - 1845
- lawrencium - Lr - 1900
- titanium - Ti - 1935
- lutetium - Lu - 1936
- thorium - Th - 2028
- platinum - Pt - 2042.1
- zirconium - Zr - 2128
- chromium - Cr - 2130
- vanadium - V - 2163
- rhodium - Rh - 2236
- boron - B - 2365
- technetium - Tc - 2477
- hafnium - Hf - 2504
- ruthenium - Ru - 2610
- iridium - Ir - 2720
- niobium - Nb - 2742
- molybdenum - Mo - 2896
- tantalum - Ta - 3293
- osmium - Os - 3300
- rhenium - Re - 3455
- tungsten - W - 3695
- carbon - C - 3825
|How can Carbon 14 be produced as Silicon Carbide for use as a safe nuclear energy source?|
Concerning your question about C14, this could be produced in a nuclear reactor through the bombardment of C12 which would produce C13 and then C14 through neutron capture. This could then be separated from its isotopes through an enrichment process by first converting to CO2 gas and going through a diffusion process. This diffusion process takes advantage of the difference in mass between C12, C13 & C14. The CO2 gas that essentially pure in C14 could then be concerted back to elemental carbon and then combined with Silicon to form SiC.
There are however, a few problems with this approach. First, C14 is a weak beta emitter and does not produce as much energy as other radioisotopes. Second, the amount of time, money and energy that would be needed to carry out the production of SiC14. There are other sources that have been utilized. For example, NASA has used Pu238 for years in order to power deep space satellites. This material would be easier to produce and would produce a much larger energy per gram.
|What were the main long term effects for the people that were effected by the nuclear testing in the pacific islands eg. Marshall Islands?|
This is a very interesting question. For many years the people of the Marshall Islands have been monitored for exposure of radioisotopes from the testing that occurred there in the 1950s. These efforts were being conducted by Brookhaven national laboratories in the 1980s and part of the 1990s. I am not sure what these studies have shown but I am aware that this testing was conducted in part by Dr. Casper Sun in the 1980s.
Concerning your questions about who was in charge for this testing this would have been both Truman and Eisenhower as US Presidents and these tests were carried out through the auspices of the Atomic Energy Commission and the US Military. I also believe that the Marshall Island people have since been wards and under care of the US Government.
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