Patent Number: 047327286
Section: summary

FIELD OF INVENTION The present invention relates to detecting a beam of neutrino or antineutrino particles and more particularly to a method of and apparatus for detecting such a beam by utilizing a single crystal containing coherent elastic scatterers for the particles. BACKGROUND ART In my copending application, Ser. No. 295,002, filed Aug. 21, 1981, now U.S. Pat. No. 4,576,777, issued Mar. 18, 1966 and entitled Energy Detection Method and Apparatus, there is disclosed a method of and apparatus for detecting a beam of neutrino or antineutrino particles wherein the beam is incident on a crystal arranged so it has coherent inelastic scatterers for the particles. Individual atoms in the crystal absorb energy from the particles to scatter the particles and produce stimulated coherent radiant energy fields. The coherent fields produced by the individual atoms are detected to provide an indication of the presence of the neutrino or antineutrino particles in the beam. In the invention of the copending application, the inelastic scattering and energy exchange between the neutrino or antineutrino particles and the scatterers occur because the crystal is placed in an electromagnetic field which induces nuclear spin changes in the crystals. In the present invention, there is elastic scattering because the crystal is not subjected to an electromagnetic field and no nuclear spin state change is induced in the crystal by the neutrino or antineutrino particles of the beam incident thereon. By employing elastic, rather than inelastic scattering, the present invention has a scattering cross-section that is 10.sup.5 times the cross-section of the inelastic scatterers. The elastic scatterers do not absorb significant energy from the neutrino or antineutrino particles, in contrast to the energy absorption by the inelastic scatterers. It is an object of the present invention to provide a new and improved apparatus for and method of detecting a beam of neutrino or antineutrino particles that has greater sensitivity than the prior art neutrino or antineutrino detection methods and apparatus. A further object of the invention is to provide a new and improved apparatus for and method of detecting a beam of neutrino or antineutrino particles by utilizing crystals containing coherent scatterers for the particles. An additional object of the invention is to provide a new and improved apparatus for and method of detecting a beam of neutrino or antineutrino particles wherein a crystal containing coherent scatterers for the particles includes scatterers that recoil as a single entity, and thereby provide greater sensitivity than the prior art method and apparatus. THE INVENTION In accordance with the present invention there is provided a new and improved apparatus for and method of detecting a beam of neutrino or antineutrino particles wherein a single crystal arranged to contain coherent elastic scatterers for the particles is located in a path of the beam so the beam particles are incident on the elastic scatterers. The scatterers respond to the particles of the beam incident thereon by transferring momentum from the particles to mechanical momentum in the crystal. The mechanical momentum transferred to the crystal from the momentum of the particles is detected. The scatterers in the crystal for the particles are sufficiently stiff as to recoil as a single entity. Such crystals are selected from the group including sapphire, silicon and diamond, the same crystals which I used in the prior art devices; however in the present invention these crystals are elastic scatterers because they are not in a significant electromagnetic field. Detection is preferably provided by detecting the motion imparted by the momentum transfer from the crystal to a mass on which the crystal is mounted. Mounted on the mass in opposed relation to the crystal is a structure or means for substantially balancing gravitational effects imparted to the mass by the crystal. The balancing means is arranged so that there is no momentum transfer from the beam particles to it so that the mass moves in response to the net momentum transferred to it by the beam particles and is unresponsive to the gravitational and other effects imparted to the crystal and the balancing means. In one embodiment, the mass is a torsion balance having a member that turns in response to the net momentum transferred to the crystal elastic scatterers. The extent this member turns provides an indication of the intensity of the neutrino or antineutrino particles in the beam. The balancing means is a mass mounted on the member in opposed relation to the crystal. In a second embodiment, the crystal containing the coherent elastic scatterers is mounted on a tine of a tuning fork. A second tine of the tuning fork includes the balancing means, whereby the motion of the tuning fork, as detected by a piezoelectric crystal mounted on an arm connecting the two tines together, provides an indication of the presence and intensity of the neutrino or antineutrino particles in the beam. It is to be understood, however, that the crystal and balancing means can be mounted on other types of mechanical resonators. Preferably, the neutrino or antineutrino particles in the beam incident on the elastic scatterers of the crystal mounted on the mechanical resonator are amplitude modulated at the resonant frequency of the mechanical resonator or a harmonic thereof. Such modulation substantially increases the sensitivity of the detecting structure and process for the neutrino and antineutrino particles. The amplitude modulation is preferably provided by chopping the beam incident on the crystal containing the elastic coherent scatterers mounted on the mechanical resonator. Chopping of the neutrino beam is preferably provided by mounting a plurality of scatterers for the particles in the beam on a structure that is turned by a motor. The theory of the present invention is described in detail in my papers entitled "Gravitons, Neutrinos and Antineutrinos", Volume 14, No. 12, December, 1984, pp. 85-1209 and "Method for Observation of Neutrinos and Antineutrinos," Physical Review C, Volume 31, No. 4, April, 1985, pp. 1468-1475; these papers are incorporated herein by reference. As discussed in these papers, when the wave length of incident particles is small in comparison with the dimensions of a macroscopic volume of scatterers, the total cross-section of the volume interacting with the energy is proportional to the square of the number of scatterers, if the crystal is very stiff. For inelastic scattering, the change in energy of the scatterers is determined by the spin state change in an applied magnetic field. For elastic scattering, the energy change is equal to the square of the momentum change divided by two times the mass of the entire body performing the scattering. Hence, for elastic scattering, there is a very low energy change because the value of the mass of the entire body is very large. For inelastic scattering, however, the energy change is relatively large, because a large number of spins change their states. By employing the elastic scatterers of the present invention, in contrast to the inelastic scatterers of the prior art, the momentum change imparted to the scattering crystal is not masked by energy changes imparted to the crystal. Hence, detecting the momentum change imparted to the elastic scatterers by the neutrino or antineutrino particles provides a highly sensitive measure of the intensity of the neutrino beam incident on the crystal, even though there is only a weak interaction between the beam and the scatterers of the crystal. In the elastic scattering process employed in the present invention, no significant fraction of the neutrino energy is converted into heat or change of internal energy state of the scatterers. The scattering employed in the present invention corresponds to projecting a large number of light elastic spheres, such as tennis balls, against a wall. The detection process involved in the present invention is analagous to measuring the small forces exerted by the wall in scattering the spheres. The coherent elastic scattering single crystals employed in the present invention have very stiff properties. As stiffness increases, there is a greater total cross-section for a given amount of matter intercepting the particles of the neutrino or antineutrino beam. A measure of crystal stiffness is the Debye temperature of the crystal. The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.