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Detecting Neutrinos

9 Neutrino Detectors

This is section 9 of 13.

There are 2 fundamental forces, gravity for particles having mass, and electromagnetism for particles having charge.

A particle having no mass cannot be detected using gravity.

A particle having no charge cannot be detected using electromagnetism.

A particle having no charge and insuficient mass cannot be directly measured using conventional physics (known forces and motion).

To claim the detection of such an undetectable particle, it must be detected indirectly, by employing a method of detecting an event which can have no other possible explanation than this neutrino.

That problem of detection is why neutrino detectors were designed and built.

Each detector employs a different method of detecting a certain event which is indirectly associated with a neutrino.

Wikipedia has a topic List of neutrino experiments,


Only a few of them are described in this  section. These were mentioned in earlier sections.

9.1 Cowan–Reines neutrino experiment in 2001

9.2 The Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND)

9.3 HOMESTAKE to 1994

9.4 OPERA in 2015.


Each of the 5 will be described.

9.1 Cowan–Reines neutrino experiment.

The Cowan–Reines neutrino experiment was conducted by Washington University in St. Louis alumnus Clyde L. Cowan and Stevens Institute of Technology and New York University alumnus Frederick Reines in 1956. The experiment confirmed the existence of neutrinos. Neutrinos, subatomic particles with no electric charge and very small mass, had been conjectured to be an essential particle in beta decay processes in the 1930s. With neither mass nor charge, such particles appeared to be impossible to detect. The experiment exploited a huge flux of (hypothetical) electron antineutrinos emanating from a nearby nuclear reactor and a detector consisting of large tanks of water. Neutrino interactions with the protons of the water were observed, verifying the existence and basic properties of this particle for the first time.

Only the resulting electron was observed, so its varying energy suggested that energy may not be conserved. This quandary and other factors led Wolfgang Pauli to attempt to resolve the issue by postulating the existence of the neutrino in 1930. If the fundamental principle of energy conservation was to be preserved, beta decay had to be a three-body, rather than a two-body, decay. Therefore, in addition to an electron, Pauli suggested that another particle was emitted from the atomic nucleus in beta decay. This particle, the neutrino, had very small mass and no electric charge; it was not observed, but it carried the missing energy.



The issue is that there is no loss of mass but the electron did not have the correct kinetic energy.

That difference in energy, from expected, also varied. It was not "continuous spectrum" which means the set of velocities had no discrete increments between them.

The solution was proposing a third body in the event, with the other 2 being proton and electron.

The third body cannot have mass because none can be created.

This third body eventually was named a neutrino.

This neutrino is inconsistent with particle physics because a elementary particle must have mass.

Both the electron and proton have mass and a defined size. The proton can be compressed in a nucleus so it must have a physical surface. A neutron is apparently the bond between proton and electron implying an electron is also a body with a surface. Inside each is an amount of energy. This energy is driving its reactivity to other masses. This reactivity to masses is affected by the proton's size.  Inside each is another amount of energy which drives its reactivity to other charges.  As noted elsewhere the polarity of this charge behavior can be flipped during certain events. If a particle has the charge behavior, it always has the same reactivity, like that of an electron.

Therefore a neutrino is somehow a discrete entity able of carrying a variable amount of energy. It has no mass or charge behavior.

9.1.1 SNO

Here is its description.

The Sudbury Neutrino Observatory (SNO) was a neutrino observatory located 2100 m underground in Vale's Creighton Mine in Sudbury, Ontario, Canada. The detector was designed to detect solar neutrinos through their interactions with a large tank of heavy water.
The detector was turned on in May 1999, 

In the charged current interaction, a neutrino converts the neutron in a deuteron to a proton. The neutrino is absorbed in the reaction and an electron is produced. Solar neutrinos have energies smaller than the mass of muons and tau leptons, so only electron neutrinos can participate in this reaction. The emitted electron carries off most of the neutrino's energy, on the order of 5–15 MeV, and is detectable. The proton which is produced does not have enough energy to be detected easily. The electrons produced in this reaction are emitted in all directions, but there is a slight tendency for them to point back in the direction from which the neutrino came.

In the neutral current interaction, a neutrino dissociates the deuteron, breaking it into its constituent neutron and proton. The neutrino continues on with slightly less energy, and all three neutrino flavours are equally likely to participate in this interaction. Heavy water has a small cross section for neutrons, but when neutrons are captured by a deuterium nucleus, a gamma ray (photon) with roughly 6 MeV of energy is produced. The direction of the gamma ray is completely uncorrelated with the direction of the neutrino.

Some of the neutrons produced from the dissociated deuterons make their way through the acrylic vessel into the light water jacket surrounding the heavy water, and since light water has a very large cross section for neutron capture, these neutrons are captured very quickly. Gamma rays of roughly 2.2 MeV are produced in this reaction, but because the energy of the photons is less than the detector's energy threshold (meaning they do not trigger the photomultipliers), they are not directly observable. However, when the gamma ray collides with an electron via Compton scattering, the accelerated electron can be detected through Cherenkov radiation.



The excerpt has "when neutrons are captured quickly.." but I believe that phrase is a mistake and should be "when neutrinos are captured..."

The gamma ray detected must have a mechanism like the alpha particle ejection, described above.  The electron velocity must be similar to the alpha particle's velocity to propagate a similar gamma ray wave length, though the experiment reports no measurement of this radiation's spectrum.

SNO does not perform a direct detection of a neutrino. It uses an indirect method by monitoring and looking at events having no visible cause.

The technique to detect an electron neutrino involves the detection of an ejected pair of electron and neutron along with a gamma ray emission from a pool of water containing deuterium, so both 2H and 1H are with the single oxygen atom. The proton "does not have enough energy to be detected easily." The more likely explanation is the proton, having lost its neutron, must remains with its orbiting electron, so the proton also must remain bound to the oxygen atom in this water molecule.

The assumption for this experiment is only the energy carried within an electron neutrino can break the bond between proton and neutron in the deuterium nucleus.

9.2 KamLAND

That is Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND)


Here is part of its technical introduction.

The KamLAND experiment has substantially added our ability to study neutrinos, making possible a number of unique new measurements while improving many others. The detector consists of 1,000 tons of liquid scintillator housed in the old Kamiokande cavern. The availability of the Kamiokande site made possible the construction of a very ambitious detector at a comparatively modest cost since there was little civil engineering required.

The use of liquid scintillator producing substantially more light than a Cerenkov radiator allows lower detection thresholds while, at the same time, gives good neutron detection efficiency, providing a clear signature for inverse-beta-decay anti-neutrino capture. The clear signature of anti-neutrinos, together with the capability of obtaining equally clear signals for neutrino scattering on carbon, allows KamLAND to do first-rate science using currently available technology and liquid scintillator purification levels. Furthermore the detector design follows a very attractive ``scalable'' approach in that KamLAND could become one of the best detectors for studying solar neutrino physics with essentially no modifications once the purification technology for scintillators will reach the levels needed for this purpose.

The detector has conducted a study on electron anti-neutrinos from nuclear reactors. The presence of many large nuclear reactors in the 140 to 210~km range makes it ideally suited to study anti nue - anti nuX oscillations with an extremely long baseline. KamLAND has shown a anti-neutrino deficit as well as anti-neutrino energy spectral distortion, suggesting the existence of neutrino oscillations.

An investigation of anti-neutrinos from beta-decays inside the Earth conducted for the first time may provide useful geophysical information, while the anti-neutrino and flavor identification capabilities of KamLAND will substantially add, from the beginning of running, to the field of supernova neutrinos. Measurements of specific channels for nucleon decay and atmospheric neutrinos will also be carried-out.

The experience in running the detector gained in this first period, together with the new technological advances gained in dealing with ultra-pure materials, will subsequently allow us to move in the most effective way to a new phase when solar neutrino spectroscopy with low threshold will represent the first priority.

KamLAND belongs to a new generation of low-background detectors generally built to study particle physics and astrophysics. All these experiments derive from the realization that a great wealth of fundamental science can be done in a very cost effective manner by studying naturally produced cosmic radiation.




Here is its description.

The Homestake experiment (sometimes referred to as the Davis experiment or Solar Neutrino Experiment and in original literature called Brookhaven Solar Neutrino Experiment or Brookhaven 37Cl (Chlorine) Experiment ) was an experiment headed by astrophysicists Raymond Davis, Jr. and John N. Bahcall in the late 1960s. Its purpose was to collect and count neutrinos emitted by nuclear fusion taking place in the Sun. Bahcall performed the theoretical calculations and Davis designed the experiment. After Bahcall calculated the rate at which the detector should capture neutrinos, Davis's experiment turned up only one third of this figure. The experiment was the first to successfully detect and count solar neutrinos, and the discrepancy in results created the solar neutrino problem. The experiment operated continuously from 1970 until 1994. The University of Pennsylvania took it over in 1984. The discrepancy between the predicted and measured rates of neutrino detection was later found to be due to neutrino "flavour" oscillations.


The experiment took place in the Homestake Gold Mine in Lead, South Dakota. Davis placed a 380 cubic meter (100,000 gallon) tank of perchloroethylene, a common dry-cleaning fluid, 1,478 meters (4,850 feet) underground. A big target deep underground was needed to prevent interference from cosmic rays, taking into account the very small probability of a successful neutrino capture, and, therefore, very low effect rate even with the huge mass of the target. Perchloroethylene was chosen because it is rich in chlorine. Upon interaction with an electron neutrino, a 37Cl atom transforms into a radioactive isotope of 37Ar, which can then be extracted and counted. The reaction of the neutrino capture is

ve + 37Cl = 37Ar+ + e-

The reaction threshold is 0.814 MeV, i.e. the neutrino should have at least this energy to be captured by the 37Cl nucleus.

Because 37Ar has a half-life of 35 days, every few weeks, Davis bubbled helium through the tank to collect the argon that had formed. A small (few cubic cm) gas counter was filled by the collected few tens of atoms of 37Ar (together with the stable argon) to detect its decays. In such a way, Davis was able to determine how many neutrinos had been captured.



The assuption is that only a neutrino can trigger a beta plus radioactive step, not the atom's presence deep below the crust where it is subject to the high level of decay activity.

The high temperature at Earth's center is partially attributed to this activity.


Here is its description.

The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) was an instrument used in a scientific experiment for detecting tau neutrinos from muon neutrino oscillations. The experiment is a collaboration between CERN in Geneva, Switzerland, and the Laboratori Nazionali del Gran Sasso (LNGS) in Gran Sasso, Italy and uses the CERN Neutrinos to Gran Sasso (CNGS) neutrino beam.

The process started with protons from the Super Proton Synchrotron (SPS) at CERN being fired in pulses at a carbon target to produce pions and kaons. These particles decay to produce muons and neutrinos.

The beam from CERN was stopped on 3 December 2012, ending data taking, but the analysis of the collected data has continued.



This experiment used SPS at CERN to generate debris which would decay into muons and neutrinos.

A thorough description of the debris is not available.

It could include some particles. Colliders of heavy nuclei can get protons to flip to anti-protons.

The creation of antiparticles can lead to gamma rays from the mutual annihilation of particles and their antiparticles.

The consequences of gamma rays for this experiment are unknown.

9.5 Borexino

Here is its description.

Borexino is a particle physics experiment to study low energy (sub-MeV) solar neutrinos. The detector is the world's most radio-pure liquid scintillator calorimeter. It is placed within a stainless steel sphere which holds the photomultiplier tubes (PMTs) used as signal detectors and is shielded by a water tank to protect it against external radiation and tag incoming cosmic muons that manage to penetrate the overburden of the mountain above.

The primary aim of the experiment is to make a precise measurement of the individual neutrino fluxes from the Sun and compare them to the Standard solar model predictions. This will allow scientists to test and to further understand the functioning of the Sun (e.g., nuclear fusion processes taking place at the core of the Sun, solar composition, opacity, matter distribution, etc.) and will also help determine properties of neutrino oscillations, including the MSW effect. Specific goals of the experiment are to detect beryllium-7, boron-8, pp, pep and CNO solar neutrinos as well as anti-neutrinos from the Earth and nuclear power plants. The project may also be able to detect neutrinos from supernovae within our galaxy with a special potential to detect the elastic scattering of neutrinos onto protons, due to neutral current interactions.

The name Borexino is the Italian diminutive of BOREX (Boron solar neutrino Experiment), after the original 1 kT-fiducial experimental proposal with a different scintillator (TMB), was discontinued because of a shift in focus in physics goals as well as financial constraints. The experiment is located at the Laboratori Nazionali del Gran Sasso near the town of L'Aquila, Italy, and is supported by an international collaboration with researchers from Italy, the United States, Germany, France, Poland, Russia and Ukraine. The experiment is funded by multiple national agencies; the principal ones are INFN (National Institute for Nuclear Physics, Italy) and NSF (National Science Foundation, USA). In May 2017, Borexino reached 10 years of continuous operation since the start of its data-taking period in 2007.



Any experiment based on counting neutrinos from intense fusion in the Sun has the wrong basis. The description does include any results to date.


Here is its description.

DONUT (Direct observation of the nu tau) was an experiment at Fermilab dedicated to the search for tau neutrino interactions. The detector operated during a few months in the summer of 1997, and successfully detected the tau neutrino. It confirmed the existence of the last lepton predicted by the Standard Model. The data from the experiment was also used to put an upper limit on the tau neutrino magnetic moment and measure its interaction cross section.



It was operated for a few months in 1997.  It claimed a tau neutrino detection.

No details are provided to justify the claim.

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last change 04/03/2022