[en] One area in which the Standard Model can be probed is neutron beta decay. In particular, measurements of angular correlations in neutron beta decay can place constraints on the existence of right-handed currents, the presence of scalar and tensor terms in the weak interaction, and for evidence of Time Reversal Violation, which is expected from the observed violation of CP invariance in kaon decay. A measurement of A, the correlation between the neutron spin and the direction of emission of the electron in neutron decay, can be combined with the neutron lifetime to determine the fundamental vector and axial vector weak coupling constants G_A and G_V. The authors have presented the essential elements of their plans to carry out an A correlation measurement using the UCN source they have constructed at the Manuel Lujan Neutron Scattering Center (MLNSC). Their goal is an initial measurement with an accuracy of about 0.2% of A (which has a value of about -0.114). The count rate expected in the experiment will allow a determination at this statistical accuracy level in a running time of about four months

[en] The most intense sources of ultra cold neutrons (UCN) have bee built at reactors where the high average thermal neutron flux can overcome the low UCN production rate to achieve usable densities of UCN. At spallation neutron sources the average flux available is much lower than at a reactor, though the peak flux can be comparable or higher. The authors have built a UCN source that attempts to take advantage of the high peak flux available at the short pulse spallation neutron source at the Los Alamos Neutron Science Center (LANSCE) to generate a useful number of UCN. In the source UCN are produced by Doppler-shifted Bragg scattering of neutrons to convert 400-m/s neutrons down into the UCN regime. This source was initially tested in 1996 and various improvements were made based on the results of the 1996 running. These improvements were implemented and tested in 1997. In sections 2 and 3 they discuss the improvements that have been made and the resulting source performance. Recently an even more interesting concept was put forward by Serebrov et al. This involves combining a solid Deuterium UCN source, previously studied by Serebrov et al., with a pulsed spallation source to achieve world record UCN densities. They have initiated a program of calculations and measurements aimed at verifying the solid Deuterium UCN source concept. The approach has been to develop an analytical capability, combine with Monte Carlo calculations of neutron production, and perform benchmark experiments to verify the validity of the calculations. Based on the calculations and measurements they plan to test a modified version of the Serebrov UCN factory. They estimate that they could produce over 1,000 UCN/cc in a 15 liter volume, using 1 microamp of 800 MeV protons for two seconds every 500 seconds. They will discuss the result UCN production measurements in section 4

[en] Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources. We are presently constructing a UCN source at LANSCE using this method. In addition, large gains in UCN density should be possible using cryogenic UCN sources. Research is under way at Gatchina to demonstrate technical feasibility of a frozen deuterium source. If successful, a source of this type could be implemented at future spallation source, such as the long pulse source being planned at Los Alamos, with a UCN density that may be two orders of magnitude higher than that presently available at reactors

[en] The authors describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C.S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized ⁶⁰Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the - strong interaction can contribute, we expect much smaller asymmetries, of order 10^-7

[en] Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources. We are presently constructing a UCN source at LANSCE using this method. In addition, large gains in UCN density should be possible using cryogenic UCN sources. Research is under way at Gatchina to demonstrate technical feasibility of a frozen deuterium source. If successful, a source of this type could be implemented at future spallation sources, such as the long pulse source being planned at Los Alamos, with a UCN density that may be two orders of magnitude higher than that presently available at reactors

[en] The improved experimental data on the asymmetry of γ-rays emitted after the capture of polarized thermal neutrons on ²³² Th and ²³⁸ U, as well as new data for the ¹¹³ Cd, In, Ag and Nb are summarized and briefly analyzed. The experiments are realized with a new polarizing spin filter, larger beam size and new detectors. The sign effect previously observed in ²³² Th has been reproduced, but other nuclei are shown to exhibit both positive and negative signs. Much improved data on ²³⁸ U show that there is no sign effect in this nucleus. This essentially rules out an explanation of the sign effect by an anomalously large value of the weak single particle matrix element. The explanation must instead lie in the direction of nuclear structure, for example in some kind of doorway state that lies at threshold in ²³² Th, but not in ²³⁸ U. 25 refs., 2 figs

[en] Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources. We are presently constructing a UCN source at LANSCE using method. In addition, large gains in UCN density should be possible using cryogenic UCN sources. Research is under way at Gatchina to demonstrate technical feasibility of be a frozen deuterium source. If successful, a source of this type could be implemented at future spallation source, such as the long pulse source being planned at Los Alamos, with a UCN density that may be two orders of magnitude higher than that presently available at reactors. (author)

[en] Recent results in experimental and theoretical study of parity violation in neutron p-wave resonances are presented systematically. The emphasis is laid on the latest achievements at the LANSCE pulsed neutron source where for the first time the weak matrix elements were obtained for several resonances in a single nucleus. An unexpected finding of the sign corrrelation among longitudinal asymmetries of the ²³²Th-neutron cross section is discussed. The established theoretical models and new approaches are reviewed in the frame of attempts to obtain information on the weak nucleon-nucleon interaction from parity violating effects in compound nuclei. 88 refs., 18 figs., 4 tabs

[en] Ultra Cold Neutrons (UCN) can be produced at spallation sources using a variety of techniques. To date the technique used has been to Bragg scatter and Doppler shift cold neutrons into UCN from a moving crystal. This is particularly applicable to short-pulse spallation sources and is the method planned for a UCN source that is under construction at LANSCE. However, large gains should be possible using cryogenic UCN sources. Spallation sources are particularly well suited for such sources given the lower heat loads and simpler engineering requirements than are possible at a reactor. The most attractive cryogenic source appears to be a frozen deuterium source and research is under way at Gatchina to demonstrate technical feasibility. If successful, a source of this type could be implemented at future spallation sources with a UCN density that may be two orders of magnitude higher than that presently available at reactors. (author)

[en] The Time Reversal and Parity at Low Energy (TRIPLE) Collaboration uses a short-pulsed longitudinally polarized epithermal neutron beam at the Los Alamos Neutron Science Center to study spatial parity violation (PV) in the compound nucleus. The typical PV experiment measures the longitudinal cross-section asymmetry by the neutron transmission method through thick samples. Neutron capture γ-ray measurement provides an alternative method for the study of PV, which enables the use of smaller amounts of isotopically pure target material. In 1995 TRIPLE commissioned a new neutron-capture detector consisting of 24 pure CsI scintillators arranged in a cylindrical geometry around the neutron beam. The characteristics and the performance of the detector and spin transport are described