Neutrinos interaction with matter

Many of the nuclear reactions that provide the energy of the stars also result in the emission of neutrinos. Because of the small absorption cross sections for neutrinos interacting with matter (o lhs 10-44 cm2), these neutrinos are not generally absorbed in the sun and other stars. (This loss of neutrinos corresponds to a loss of 2% of the energy of our sun.) Because of this, the neutrinos are a window into the stellar interior. The small absorption cross sections also make neutrinos difficult to detect, with almost all neutrinos passing through planet Earth without interacting. 

Assume an absorption cross section of 10-44 cm2 for solar neutrinos interacting with matter. Calculate the probability of a neutrino interacting as it passes through Earth. 

Based upon the foregoing experiences, some researchers observed that the same reluctance to interact with matter is responsible for the neutrino s long range and ability to resist detection. Tlios, it was reasoned that an apparatus for detecting neutrinos should be massive and shielded from the interference of other particles and radiation. As a solution to these problems, some researchers proposed a deep underwater muon and neutrino detector (acronym DUMAND). 

A number of studies have been undertaken of the interaction of neutrinos with nuclei, to determine the neutrino mass, and to show that neutrinos and antineutrinos are produced in (3+ and (3 decay, respectively. Neutrinos also provide important information about stellar nuclear reactions because they have a very low probability for interacting with matter and come directly out from the stellar interior. 

The sum of the kinetic energy of the fission products and the energy of decay can be determined calorimetrically. The energy of the neutrons and the y rays is usable only inasmuch as neutrons and y rays are absorbed in the medium considered. The energy of the neutrinos is lost, because of their small interaction with matter. 

This process is also called hydrogen burning. The temperature in the core of the stars must be > 10 K, in order to overcome the Coulomb repulsion of the protons. The neutrinos escape into outer space due to their small interaction with matter. Hydrogen burning is the longest stage of the stars. 

A comment is in order here concerning the relevance of the wind or breeze regimes. Is one of the two favoured by the DCCSN physics This question is far from being just academic, as it is likely that its answer may have some impact on the predicted development of the r-process. It is quite intricate as well. One difficulty arises as the neutrino-driven material is likely not to flow unperturbed to infinity in a variety of DCCSN situations. The wind may in particular interact with matter and radiation in that portion of the star... 

Detailed investigations show that there are two types of electron neutrinos, which differ in their interactions with matter (different cross sections). The electron neutrino is denoted usually by v, the antineutrino by v,. They take part in the P-decay processes as follows ... 

Neutrinos are emitted in all 3-decay processes and often carry away most of the decay energy. None of the detectors mentioned above is sensitive to neutrinos, which rarely interact with matter except by P interactions. For example, neutrinos (but not antineutrinos) with energies >0.82 MeV can react with Cl to produce radioactive Ar. The cross section is very small. In spite of the difficulty in detecting neutrinos, their spectroscopy is an active area of research. 

For these reasons, the detection of neutrinos from such sources is a subject of considerable interest in astronomy and cosmology. Because of their weak interaction with matter, neutrinos are difficult to observe directly. Available techniques require massive detectors on the order of 100-10,000 tons to record a neutrino event rate between... 

As the weak interaction is the slowest of all, it was the first to find itself unable to keep up with the rapid expansion of the Universe. The neutrinos it produces, which serve as an indicator of the weak interaction, were the first to experience decoupling, the particle equivalent of social exclusion. By the first second, expansion-cooled neutrinos ceased to interact with other matter in the form of protons and neutrons. This left the latter free to organise themselves into nuclei. Indeed, fertile reactions soon got under way between protons and neutrons. However, the instability of species with atomic masses between 5 and 8 quickly put paid to this first attempt at nuclear architecture. The two species of nucleon, protons and neutrons, were distributed over a narrow range of nuclei from hydrogen to lithium-7, but in a quite unequal way. 

Figure 163. Neutrinos as dark matter. Relic density of a thermal Dirac neutrino with standard-model interactions, together with current constraints from cosmology, accelerators (LEP), and dark matter searches. See text for explanations. (The dark matter band is quite generous in light of the WMAP measurements.)...

Solar neutrinos, which interact very weakly with matter, should also be produced by the nuclear fusion reactions in the Sun. However, scientist s detect much fewer neutrinos than expected, which may suggest that our knowledge of the solar processes that cause the Sun to shine or of neutrinos themselves is incomplete. 

As we discussed, numerous neutrinos are produced by the proton-proton chain in the Sun. However, neutrinos interact only very weakly with matter. Every second over 100 billion neutrinos from the Sun pass through every square inch of our bodies and virtually none of them interact with us. Because neutrinos interact so weakly with matter, detecting them is very difficult. For example, in the first solar neutrino detection experiment, scientist Ray Davis used 100,000 gallons of cleaning fluid (for the chlorine the fluid contained) in a detector located in a South Dakota gold mine. Davis expected to detect on average of 1.8 solar neutrinos per day. Instead, Davis s observed rate has consistently been much lower than this. Also, the long-term rate, plotted as a function of time, shows an anticorrelation between neutrino rate and sunspot activity. 

The lion s share of fluorine is produced by the intense burst of neutrinos that occurs when the Type II supernova core collapses. Although neutrinos interact only infrequently with matter, a tiny fraction of their intense flux during a 10-second burst drives a proton or neutron from the 20Ne nucleus, in either case resulting in 19F. This occurs where both 20Ne and the neutrino flux are most abundant, near the core of the exploding massive star. Much of this 19F is subsequently destroyed by nuclear reactions in the heated gas when the shock wave passes, but enough survives to account for the 19F/2°Ne abundance ratio in the Sun. 

As already mentioned in section 3.2, the interaction of neutrinos with matter is extremely small, and the first proof of their existence was only possible in 1956 on the basis of their reaction with the protons in a large tank of water ... 

Mesons were discovered in 1936, by the American physicists Carl Anderson and Seth Neddermeyer at the California Institute of Technology. They are produced by interaction of cosmic ra s with matter. They are either positive or negative in charge neutral mesons may also exist. Mesons are known with masses about 216 and 285 times that of the electron (called fi mesons and tt mesons, respectively), and there is evidence also for the existence of still heavier mesons (with mass about 900 times that of the electron). Mesons have very short lives they probably undergo decomposition into a positron or electron and two neutrinos. 

One important clue to answering that question is that matter and antimatter do not get along very well with each other. When a particle comes into contact with its antiparticle, a reaction occurs in which both particles are annihilated. The products of that reaction are two gamma rays, a neutrino, and an antineutrino. For example, suppose that a proton and an antiproton interact with each other. The reaction that occurs is ... 

When there is matter in the travel path of the neutrinos the nes interact with the electrons in the matter and give rise to an extra potential (proportional to ne) in the mass matrix. This results in matter-enhanced neutrino... 

Note that weak interaction processes remain out of equilibrium as long as neutrinos are not equilibrated with matter and radiation. This is the case as long as the density remains lower than about 1011 g/cm3. At higher densities, a state of so-called complete equilibrium is obtained. 

Notice we have replaced v by P, which is the designation of the antineutrino. Beta-decay theory has shown that antineutrinos P are emitted in electron decay, and "regular" neutrinos V in positron decay. We can consider the particles identical cf. 10.4. Because of the extremely low probability of interaction or neutrinos with matter, they are unfortunately often omitted in writing /3-decay reactions. 

The fourth force is the one which is involved in the radioactive jS-decay of atoms and is known as the weak interaction force. Like the strong interaction, this weak interaction force operates over extremely short distances and is the force that is involved in the interaction of very light particle known as leptons (electrons, muons, and neutrinos) with each other and as well as their interaction with mesons, baryons, and nuclei. One characteristic of leptons is that they seem to be quite immune to the strong interaction force. The strong nuclear force is approximately 10 times greater than the Coulombic force, while the weak interaction force is smaller than the strong attraction by a factor of approximately 10. The carrier of the weak interaction force is still a matter of considerable research we will return to this point later. 

The V represents the antineutrino v is the neutrino. Neutrino and antineutrino emissions serve to balance the energy and rotation before and after decay. Neutrinos have no charge and little mass as a result, they interact to a vanishingly small degree with matter and are difficult to detect without elaborate apparatus. The neutrino (or antineutrino) must be included in the decay equation to conserve energy, angular momentum, and spin. The neutron, proton, beta particle, and neutrino all have a nuclear spin of 1 /2. A fuller discussion of this topic is in nuclear chemistry texts such as Choppin et al. (1995). 

---