Neutron spin rotation measurements

The neutron spin rotation (NSR) collaboration used parity-violating spin rotation of transversely polarized neutrons transmitted through a 0.5 m liquid helium target to constrain weak coupling constants between nucleons. While consistent with theoretical expectation, the upper limit set by this measurement on the rotation angle is limited by statistical uncertainties. The NSR collaboration is preparing a new measurement to improve this statistically-limited result by about an order of magnitude. In addition to using the new high-flux NG-C beam at the NIST Center for Neutron Research, the apparatus was upgraded to take advantage of the larger-area and more divergent NG-C beam. Significant improvements are also being made to the cryogenic design. Details of these improvements and readiness of the upgraded apparatus are presented. We also comment on how recent theoretical work combining effective field theory techniques with the 1/Nc expansion of QCD along with previous NN weak measurements can be used to make a prediction for dϕ/dz in 4He.

An experiment using the same apparatus with a room-temperature target was carried out at LANSCE to place limits on parity-conserving rotations from possible fifth-force interactions to complement previous studies. We sought this interaction using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The results of this measurement and its impact on the neutron-matter coupling gA2 from such an interaction are presented. The NSR collaboration is also preparing a new measurement that uses an upgraded version of the room-temperature target to be run on the NG-C beamline; and it is expected to constrain gA2 by at least two additional orders of magnitude for λc between 1 cm and 1 μm.

Fission fragment yields and total kinetic energy release in neutron-induced fission of235,238U,and239Pu

Different aspects of the nuclear fission process have been studied at Los Alamos Neutron Science Center (LANSCE) using various instruments and experimental techniques. Properties of the fragments emitted in fission have been investigated using Frisch-grid ionization chambers, a Time Projection Chamber (TPC), and the SPIDER instrument which employs the 2v-2E method. These instruments and experimental techniques have been used to determine fission product mass yields, the energy dependent total kinetic energy (TKE) release, and anisotropy in neutron-induced fission of U-235, U-238 and Pu-239.

Sympathoinhibitory action of rilmenidine in conscious sinoaortically denervated rats

The responses of mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) to rilmenidine administration and changes in these responses after idazoxan or yohimbine pretreatment were investigated in conscious sinoaortically denervated rats. Intravenous (i.v.) injection of rilmenidine (300 and 600 micrograms/kg) dose-dependently reduced MAP (16 and 24%, respectively) and RSNA (31 and 56%, respectively), whereas bradycardia was similar at both doses of the drug. Intracisternal (i.c.) pretreatment with idazoxan (5 micrograms/kg), alpha 2-adrenoceptor antagonist with a high affinity to imidazoline receptors (IR) prevented rilmenidine-induced decreases in MAP but not in RSNA and HR. Rilmenidine (300 micrograms/kg i.c.) significantly decreased MAP by 24%, RSNA by 32%, and HR by 13%. Pretreatment with idazoxan (1 microgram/kg i.c.) significantly attenuated the hypotensive and sympathoinhibitory effects of rilmenidine, whereas i.c. pretreatment with equimolar to 10-fold higher doses of yohimbine, an alpha 2-antagonist that binds poorly with IR, did not. Both idazoxan and yohimbine failed to affect the rilmenidine-induced bradycardia, however. We concluded that (a) rilmenidine exhibits more marked hypotensive effect when injected i.c. than when injected i.v., (b) a part of the inhibitory effect of i.v.-injected rilmenidine on RSNA may be exerted through idazoxan-insensitive mechanisms which might be activated by peripheral action of the drug, and (c) the hypotensive action of rilmenidine relates more to the interaction with IR than with alpha 2-adrenoceptors.