aCORN: An experiment to measure the electron-antineutrino correlation coefficient in free neutron decay.

We describe an apparatus used to measure the electron-antineutrino angular correlation coefficient in free neutron decay. The apparatus employs a novel measurement technique in which the angular correlation is converted into a proton time-of-flight asymmetry that is counted directly, avoiding the need for proton spectroscopy. Details of the method, apparatus, detectors, data acquisition, and data reduction scheme are presented, along with a discussion of the important systematic effects.

The aCORN Backscatter-Suppressed Beta Spectrometer.

Backscatter of electrons from a beta spectrometer, with incomplete energy deposition, can lead to undesirable effects in many types of experiments. We present and discuss the design and operation of a backscatter-suppressed beta spectrometer that was developed as part of a program to measure the electronantineutrino correlation coefficient in neutron beta decay (aCORN). An array of backscatter veto detectors surrounds a plastic scintillator beta energy detector. The spectrometer contains an axial magnetic field gradient, so electrons are efficiently admitted but have a low probability for escaping back through the entrance after backscattering. The design, construction, calibration, and performance of the spectrometer are discussed.

SU-E-I-45: Measurement of CT Dose to An HDPE Phantom Using Calorimetry: A Feasibility Study.

PURPOSE: Radiation dose in CT is traditionally evaluated using an ionization chamber calibrated in terms of air kerma in a phantom of specific dimensions. The radiation absorbed dose, J/kg, can also be realized directly by measuring the temperature rise in the medium. We investigate using this primary method to determine the CT dose at a point (a few mm), using the recently proposed (APMM TG220) high density polyethylene (HDPE) phantom as a medium. METHODS: The calorimeter detection scheme is adapted from the second generation NIST water calorimeter using sensitive thermistors in a Wheatstone bridge powered by a lock-in amplifier. The temperature sensitivity is about 3 microK. The expected temperature rise in PE is about 0.6 mK per Gy. The thermistor sensors were placed inside a 26 cm dia. × 10 cm HDPE phantom. Two preliminary tests were made: at a linear accelerator with a 6 MV photon beam, and at a 16-slice CT scanner with a 120 kV beam, each with the thermal sensor and with a calibrated ionization chamber. RESULTS: The 6 MV photon beam with 10 on/off cycles at 60 s each yielded the (uncorrected) run-to-run average dose of 3.06 Gy per cycle (sdm 0.3%), about 8% higher than the Result from the ionization chamber (calibrated in terms of absorbed to water). The CT measurements were also made in the middle section of the TG200 30 cm phantom. Twenty consecutive axial scans at 250 mA, which delivers a nominal accumulated dose (CTDIvol) of 705 mGy in 50 s at three axial and three radial locations were measured. The accumulated dose measured by the ionization chamber at the center of the smaller phantom was 347 mGy. CONCLUSIONS: The calorimeter data show qualitative tracking of the chamber measurements. Detailed thermal and electrical analysis of the system are planned to obtain quantitative results.

Proposed Measurement of the Beta-Neutrino Correlation in Neutron Decay.

Currently, the beta-neutrino asymmetry has the largest uncertainty (4 %) of the neutron decay angular correlations. Without requiring polarimetry this decay parameter can be used to measure λ (ga/gv ), test Cabibbo-Kobayashi-Maskawa (CKM) unitarity limit scalar and tensor currents, and search for Charged Vector Current (CVC) violation. We propose to measure the beta-neutrino asymmetry coeffcient, a, using time-of-flight for the recoil protons. We hope to achieve a systematic uncertainty of σa / a ≈ 1.0 %. After tests at Indiana University's Low Energy Neutron Source (LENS), the apparatus will be moved to the National Institute of Standards and Technology (NIST) where the measurement can achieve a statistical uncertainty of 1 % to 2 % in about 200 beam days.

A Backscatter Suppressed Electron Detector for the Measurement of "a".

A new method of measuring the electron-antineutrino angular correlation coefficient, little "a", from neutron decay-to be performed at the National Institute of Standards and Technology-will require an electron spectrometer that strongly suppresses backscattered electrons. A prototype consisting of six trapezoidal veto detectors arranged around a plastic scintillator has been tested with an electron beam produced by a Van de Graaff accelerator. The results of this test and its implications for the little "a" measurement are discussed.

Current-distance relations of axons mediating circling elicited by midbrain stimulation.

Stimulation of mediocaudal midbrain in rats produces ipsiversive circling due to the stimulation of longitudinal axons. The refractory periods of these axons were measured by delivering trains of conditioning and testing pulses via a single electrode at various conditioning-testing (C-T) intervals. As C-T interval increased from 0.3 to 2.0 ms, the frequency required to produce a constant amount of circling halved. The current-distance relations of these axons were measured by placing two electrodes lateral to one another, and delivering conditioning pulses via one electrode and testing pulses via the second electrode. The required frequency decreased less at C-T intervals in the refractory period range using two electrodes rather than using a single electrode. This partial refractoriness suggests that only part of the axons were stimulated by both electrodes. The refractoriness increased as current increased or as interelectrode distance decreased. The overlap in the fields of stimulation at each current was calculated from the refractoriness observed in single and double electrode experiments. The results suggest that the axons mediating circling have a wide range of thresholds rather than a single threshold. The current required to activate an axon is roughly equal to K X r2, were K is a constant and r is the radial distance from electrode to axon. K must range from 400 to at least 3000 microA/mm2, to account for the circling data. For axons mediating medial forebrain bundle self-stimulation3, K must range from 1000 to at least 6400 microA/mm2. Estimation of the K distribution allows calculation of the effects of electrode size, placement and current on the recruitment of axons with different thresholds.

Use of prazosin in management of hypertension in patients with chronic renal failure and in renal transplant recipients.

Prazosin was used in combination with other antihypertensive drugs in the successful management of hypertension in seven patients with chronic renal failure and six renal transplant recipients, also with chronic renal failure. The addition of small doses of prazosin (mean 3 mg/day) to the antihypertensive regimen produced significant falls in systolic and diastolic blood pressures in both the lying and standing positions. The standing blood pressures were significantly lower than the lying blood pressures during prazosin treatment. Neither the mean blood urea concentrations nor the mean plasma creatinine concentrations changed significantly during prazosin administration. Chromium-51 edetic acid clearances did not change significantly during prazosin treatment in the seven patients in whom it was measured. Severe symptomatic postural hypotension occurred in one patient a week after starting prazosin 3 mg/day. This hypotensive episode was associated with a transient and reversible deterioration in renal function. Another patient developed a rash while on prazosin but it was probably related to propranolol rather than prazosin. Prazosin is thus an effective antihypertensive drug in patients with chronic renal failure, and it may be used with a variety of other drugs. It should be used cautiously, however, since patients with chronic renal failure may respond to small doses, and significant postural falls in blood pressure may result. There was no evidence that the use of prazosin resulted in progressive deterioration in the residual renal function of the patients with chronic renal failure.