Fig. 2: Image of the "Ice Cube" neutrino detector to be built in Antarctic. Note the dimensions of the detector compared to the Eiffel Tower.
Neutrinos are amongst the most fascinating subatomic particles in existence. Moreso because for a long time they were illusory, and many believed them to be purely products of physicists' imaginations. In fact, around 1930, the neutrino was imagined or rather invented, in order to balance a nuclear fission equation. Basically, in this light, when the nucleus of a radioactive atom disintegrates, the energy of the particles emitted must equal the energy originally contained.
This is in connection with the so-called "Q" of the reaction, defined:
Q = [M(r) - M(p)]u
where M(r) denotes the mass of the reactants, M(p) the mass of the products, and u is an atomic mass conversion factor (e.g. 931.5/ MeV/u)
If Q > 0 one has an exothermic (heat generating) reaction, else one has an endothermic (heat absorbing reaction)
What physicists of the early 1930s era noticed was that the radioactive nuclei were losing more energy than detectors were picking up. To account for the extra energy, Wolfgang Pauli (who formulated the "Pauli Exclusion Principle", conceived an extra, invisible particle emitted by the nucleus. In his journal he actually wrote:
"I have done something very bad today by proposing a particle that cannot be detected. It is something that no theorist should ever do."
Though premature, his instincts were correct. By the 1950s, physicists working at a nuclear weapons lab in South Carolina determined that their experiments ought to be generating nearly ten trillion neutrinos a second. For a detector, they used two large water tanks placed just outside a nuclear reactor and found three neutrinos an hour. Pathetic in terms of numbers, but the neutrino was at last detected. Now, having established the reality of the neutrino, further study accelerated.
Around a decade later, after physicists surmised the Sun ought to be the biggest generator or neutrinos, detection experiments commenced to confirm the existence of the putative fusion reactions in the solar core - from which neutrinos emerged as byproducts (see diagram, Fig. 1). In the initial fusion reaction of the proton-proton chain, one has theoretically:
H1 + H1 -> D2 + e(+) + v
that is, two protons fuse to yield deuterium, plus a positive electron (positron) and a neutrino. Given the mass of protons converted in the solar core a massive amount of neutrinos ought to have been detected. To this end, a neutrino trap was set up in South Dakota, placed 1500 meters below ground and filled up with 100,000 gallons of cleaning fluid (tetracholoro-ethylene or C2 Cl4).
The principle was simple: the cleaning fluid contains one atom of the isotope 17 Cl 37 per molecule. When an incoming neutrino of the right energy reacts with it, one atom of 18 Ar 37 is formed along with one electron. This 18 Ar 37 is actually a radioactive isotope of argon which is allowed to accumulate for a number of months. At the end of that period, helium gas is pumped into the tank to clean it and the argon formed is adsorbed (not absorbed) in a cold trap. The argon is then sampled for radioactivity, the intensity of which is an indicator of the number of neutrons present.
Perfect right? Well.....after 15 years of conducting these measurement experiments, Dr. Raymond Davis of Brookhaven National Laboratory showed the numbers of neutrinos detected were far below the numbers predicted, and within the range of probable error.
The results of the Davis' experiments touched off one of the most controversial debates in the annals of astronomy. At stake was the accepted model of the Sun, with its dense core harboring the supposed nucelar fusion reactions, surrounded by a radiative zone then a convective outer zone. To bolster detection, the cleaning fluid devices were replaced by twenty tons of Gallium instead - ideal since the Gallium would also be sensitive to low energy neutrinos.
The "neutrino deficit" unfortunately continued, leading the way to the more powerful "Super-Kamiokande" or Super K detector, situated in Japan, some 1300' underground in a zinc mine with a detector comprised of 50,000 tons of water in a domed tank with walls covered by 13,000 light sensors. The thousands of light sensors did detect the occasional blue flash (too faint to be visible with human vision) made when a neutrino collides with an atom in the water and emits an electron. By tracing the exact paths of the electrons in the water, physicists could infer the source of the neutrinos in space. Not surprisingly, most were found to come from the Sun.
The problem is that the Super K still didn't detect as many neutrinos as predicted.
Eventually, the reason emerged, from research conducted at the Sudbury Neutrino Observatory (SNO), in Sudbury, Ontario . The Observatory, installed in a 6,800' deep nickel mine containing 1,100 tons of heavy water or deuterium (the same deuterium formed when to protons fuse, as shown in the earlier fusion reaction described in Fig. 1). The SNO device also included a geodesic superstructure (to absorb vibrations) and 9,456 light sensors.
Amazingly, SNO physicists in 2001 discovered that a neutrino can spontaneously switch among three different neutrino "identities": the electron neutrino, the mu neutrino and the tau neutrino. The tau neutrino has the greatest mass-energy, followed by the mu then the electron neutrino. Physicists say that the neutrino "oscillates between three flavors". This discovery, to say the least, carried startling impications - especially pertaining to the failures of the previous experiments to detect the predicted numbers.
The most basic reason for the deficits? All the prior detectors were tuned to only one neutrino flavor, the electron neutrino, and fixed at that flavor. Thus, all the mu and tau neutrinos were missed. The finding also threw out another belief among many phyysicists, that the neutrino (like the photon) lacked any mass. But for any entity to alternate flavors means implicitly it must have mass. That is something that only particle with mass are able to do.
Right now, we have rough estimates of the respective mass limits of neutrinos, but no exact values. For example, the tau neutrino has under 35 MeV in mass-energy (where 1 eV = 1.6 x 10^-19 Joule), while the mu neutrino has just under 250 keV, and the electron neutrino ~ 8 ev.
To get a further threshold limit and window on the differering masses, KATRIN is being built (Karlsruhe Tritium Neutrino Experiment), which features a 200 ton mass spectrometer that will be able to measure the mass of atoms before (M) and after they decay (M') radioactively, thereby revealing how much mass the neutrino carries off - since one merely needs to subtract: M - M'.
In the meantime, many other physicists and astronomers are interested in detecting neutrinos frmo much more distant objects, such as supernovas, and colliding galaxies. To that end, an enormous neutrino telescope detector called "Ice Cube" is being constructed inside an ice field in Antarctica. (See attached image). Its sensors will be aimed not only at the sky but toward the ground to detect neutrinos from the Sun and outer space that are coming through the planet (most neutrinos rip through the 8,000 mile diameter Earth as if it's not even there).
Stay tuned, there will be much more to learn about neutrinos and the roles they play in basic astrophyiscal objects and processes.
This is in connection with the so-called "Q" of the reaction, defined:
Q = [M(r) - M(p)]u
where M(r) denotes the mass of the reactants, M(p) the mass of the products, and u is an atomic mass conversion factor (e.g. 931.5/ MeV/u)
If Q > 0 one has an exothermic (heat generating) reaction, else one has an endothermic (heat absorbing reaction)
What physicists of the early 1930s era noticed was that the radioactive nuclei were losing more energy than detectors were picking up. To account for the extra energy, Wolfgang Pauli (who formulated the "Pauli Exclusion Principle", conceived an extra, invisible particle emitted by the nucleus. In his journal he actually wrote:
"I have done something very bad today by proposing a particle that cannot be detected. It is something that no theorist should ever do."
Though premature, his instincts were correct. By the 1950s, physicists working at a nuclear weapons lab in South Carolina determined that their experiments ought to be generating nearly ten trillion neutrinos a second. For a detector, they used two large water tanks placed just outside a nuclear reactor and found three neutrinos an hour. Pathetic in terms of numbers, but the neutrino was at last detected. Now, having established the reality of the neutrino, further study accelerated.
Around a decade later, after physicists surmised the Sun ought to be the biggest generator or neutrinos, detection experiments commenced to confirm the existence of the putative fusion reactions in the solar core - from which neutrinos emerged as byproducts (see diagram, Fig. 1). In the initial fusion reaction of the proton-proton chain, one has theoretically:
H1 + H1 -> D2 + e(+) + v
that is, two protons fuse to yield deuterium, plus a positive electron (positron) and a neutrino. Given the mass of protons converted in the solar core a massive amount of neutrinos ought to have been detected. To this end, a neutrino trap was set up in South Dakota, placed 1500 meters below ground and filled up with 100,000 gallons of cleaning fluid (tetracholoro-ethylene or C2 Cl4).
The principle was simple: the cleaning fluid contains one atom of the isotope 17 Cl 37 per molecule. When an incoming neutrino of the right energy reacts with it, one atom of 18 Ar 37 is formed along with one electron. This 18 Ar 37 is actually a radioactive isotope of argon which is allowed to accumulate for a number of months. At the end of that period, helium gas is pumped into the tank to clean it and the argon formed is adsorbed (not absorbed) in a cold trap. The argon is then sampled for radioactivity, the intensity of which is an indicator of the number of neutrons present.
Perfect right? Well.....after 15 years of conducting these measurement experiments, Dr. Raymond Davis of Brookhaven National Laboratory showed the numbers of neutrinos detected were far below the numbers predicted, and within the range of probable error.
The results of the Davis' experiments touched off one of the most controversial debates in the annals of astronomy. At stake was the accepted model of the Sun, with its dense core harboring the supposed nucelar fusion reactions, surrounded by a radiative zone then a convective outer zone. To bolster detection, the cleaning fluid devices were replaced by twenty tons of Gallium instead - ideal since the Gallium would also be sensitive to low energy neutrinos.
The "neutrino deficit" unfortunately continued, leading the way to the more powerful "Super-Kamiokande" or Super K detector, situated in Japan, some 1300' underground in a zinc mine with a detector comprised of 50,000 tons of water in a domed tank with walls covered by 13,000 light sensors. The thousands of light sensors did detect the occasional blue flash (too faint to be visible with human vision) made when a neutrino collides with an atom in the water and emits an electron. By tracing the exact paths of the electrons in the water, physicists could infer the source of the neutrinos in space. Not surprisingly, most were found to come from the Sun.
The problem is that the Super K still didn't detect as many neutrinos as predicted.
Eventually, the reason emerged, from research conducted at the Sudbury Neutrino Observatory (SNO), in Sudbury, Ontario . The Observatory, installed in a 6,800' deep nickel mine containing 1,100 tons of heavy water or deuterium (the same deuterium formed when to protons fuse, as shown in the earlier fusion reaction described in Fig. 1). The SNO device also included a geodesic superstructure (to absorb vibrations) and 9,456 light sensors.
Amazingly, SNO physicists in 2001 discovered that a neutrino can spontaneously switch among three different neutrino "identities": the electron neutrino, the mu neutrino and the tau neutrino. The tau neutrino has the greatest mass-energy, followed by the mu then the electron neutrino. Physicists say that the neutrino "oscillates between three flavors". This discovery, to say the least, carried startling impications - especially pertaining to the failures of the previous experiments to detect the predicted numbers.
The most basic reason for the deficits? All the prior detectors were tuned to only one neutrino flavor, the electron neutrino, and fixed at that flavor. Thus, all the mu and tau neutrinos were missed. The finding also threw out another belief among many phyysicists, that the neutrino (like the photon) lacked any mass. But for any entity to alternate flavors means implicitly it must have mass. That is something that only particle with mass are able to do.
Right now, we have rough estimates of the respective mass limits of neutrinos, but no exact values. For example, the tau neutrino has under 35 MeV in mass-energy (where 1 eV = 1.6 x 10^-19 Joule), while the mu neutrino has just under 250 keV, and the electron neutrino ~ 8 ev.
To get a further threshold limit and window on the differering masses, KATRIN is being built (Karlsruhe Tritium Neutrino Experiment), which features a 200 ton mass spectrometer that will be able to measure the mass of atoms before (M) and after they decay (M') radioactively, thereby revealing how much mass the neutrino carries off - since one merely needs to subtract: M - M'.
In the meantime, many other physicists and astronomers are interested in detecting neutrinos frmo much more distant objects, such as supernovas, and colliding galaxies. To that end, an enormous neutrino telescope detector called "Ice Cube" is being constructed inside an ice field in Antarctica. (See attached image). Its sensors will be aimed not only at the sky but toward the ground to detect neutrinos from the Sun and outer space that are coming through the planet (most neutrinos rip through the 8,000 mile diameter Earth as if it's not even there).
Stay tuned, there will be much more to learn about neutrinos and the roles they play in basic astrophyiscal objects and processes.
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