68 research outputs found
Studies of orbital electron capture using proportional counters
In the first chapter the theory of orbital electron capture is briefly summarised, and experimental data available on K/p+ ratios and L/K capture ratios are surveyed. The accuracy of many of the experimental results is poor, but it is pointed out that the development of proportional counter techniques for studying low energy radiations has made better measurements possible. These techniques are discussed in the following chapter, with particular emphasis on the use of gaseous sources. The material of this introductory section of the thesis is drawn mainly from the literature, though an appreciable part of the discussion on gas source counters is based on the writer's own experience. The next two chapters relate to the development of new proportional counter techniques, made with the aim of overcoming some of the limitations to the use of gas sources. An investigation into the operation of proportional counters at high temperatures, initiated by Dr. A. Moljk and carried out jointly by him and the writer is described; and the development of a multiwire proportional counter system with small wall effects is discussed, particularly in relation to the measurement of weak sources. The principle of the latter counting system was due to Dr. Moljk and the writer, following an initial suggestion by Dr. S.C. Curran, and the experimental work and its interpretation was shared equally by us. The detailed design of the counter and of the associated electronic equipment (described in an appendix) was due largely to the writer. The final three chapters, forming the main part of the thesis, deal with studies of electron capture carried out with the aid of gas source techniques. An investigation of the decay of Cl36 , leading to the discovery of a previously undetected K-capture branch, is described in Chapter 5. This work was done jointly with Dr. Moljk. Chapter 6 concerns a measurement of the K/β+ ratio in the decay of F18, which enables limits to be set on Pierz interference effects in Gamow-Teller interactions. This experiment was performed in collaboration with Dr. Moljk, assisted by Mr. J. Scobie; though the writer takes the main responsibility for the results and their interpretation. Chapter 7 deals with a study of L-capture in Ge71. The L/K capture ratio was measured by a new direct, method using a multiwire counting system; and the results obtained show that previous work suggesting serious disagreement with theory is not valid. The writer was entirely responsible for the original conception of this experiment, its performance, and the interpretation of the results
Implementation of Time-Delay Interferometry for LISA
We discuss the baseline optical configuration for the Laser Interferometer
Space Antenna (LISA) mission, in which the lasers are not free-running, but
rather one of them is used as the main frequency reference generator (the {\it
master}) and the remaining five as {\it slaves}, these being phase-locked to
the master (the {\it master-slave configuration}). Under the condition that the
frequency fluctuations due to the optical transponders can be made negligible
with respect to the secondary LISA noise sources (mainly proof-mass and shot
noises), we show that the entire space of interferometric combinations LISA can
generate when operated with six independent lasers (the {\it one-way method})
can also be constructed with the {\it master-slave} system design. The
corresponding hardware trade-off analysis for these two optical designs is
presented, which indicates that the two sets of systems needed for implementing
the {\it one-way method}, and the {\it master-slave configuration}, are
essentially identical. Either operational mode could therefore be implemented
without major implications on the hardware configuration. We then.......Comment: 39 pages, 6 figures, 2 table
Advanced technologies for future ground-based, laser-interferometric gravitational wave detectors
We present a review of modern optical techniques being used and developed for the field of gravitational wave detection. We describe the current state-of-the-art of gravitational waves detector technologies with regard to optical layouts, suspensions and test masses. We discuss the dominant sources and noise in each of these subsystems and the developments that will help mitigate them for future generations of detectors. We very briefly summarise some of the novel astrophysics that will be possible with these upgraded detectors
Birefringence of interferential mirrors at normal incidence Experimental and computational study
In this paper we present a review of the existing data on interferential
mirror birefringence. We also report new measurements of two sets of mirrors
that confirm that mirror phase retardation per reflection decreases when mirror
reflectivity increases. We finally developed a computational code to calculate
the expected phase retardation per reflection as a function of the total number
of layers constituting the mirror. Different cases have been studied and we
have compared computational results with the trend of the experimental data.
Our study indicates that the origin of the mirror intrinsic birefringence can
be ascribed to the reflecting layers close to the substrate.Comment: To be published in Applied Physics
Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards
We present a simple method to stabilize the optical path length of an optical
fiber to an accuracy of about 1/100 of the laser wavelength. We study the
dynamic response of the path length to modulation of an electrically conductive
heater layer of the fiber. The path length is measured against the laser
wavelength by use of the Pound-Drever-Hall method; negative feedback is applied
via the heater. We apply the method in the context of a cryogenic resonator
frequency standard.Comment: Expanded introduction and outlook. 9 pages, 5 figure
Ultra-stable performance of an underground-based laser interferometer observatory for gravitational waves
In order to detect the rare astrophysical events that generate gravitational
wave (GW) radiation, sufficient stability is required for GW antennas to allow
long-term observation. In practice, seismic excitation is one of the most
common disturbances effecting stable operation of suspended-mirror laser
interferometers. A straightforward means to allow more stable operation is
therefore to locate the antenna, the ``observatory'', at a ``quiet'' site. A
laser interferometer gravitational wave antenna with a baseline length of 20m
(LISM) was developed at a site 1000m underground, near Kamioka, Japan. This
project was a unique demonstration of a prototype laser interferometer for
gravitational wave observation located underground. The extremely stable
environment is the prime motivation for going underground. In this paper, the
demonstrated ultra-stable operation of the interferometer and a well-maintained
antenna sensitivity are reported.Comment: 8 pages, to appear on PR
The Definition of Mach's Principle
Two definitions of Mach's principle are proposed. Both are related to gauge
theory, are universal in scope and amount to formulations of causality that
take into account the relational nature of position, time, and size. One of
them leads directly to general relativity and may have relevance to the problem
of creating a quantum theory of gravity.Comment: To be published in Foundations of Physics as invited contribution to
Peter Mittelstaedt's 80th Birthday Festschrift. 30 page
Cold atoms in a high-Q ring-cavity
We report the confinement of large clouds of ultra-cold 85-Rb atoms in a
standing-wave dipole trap formed by the two counter-propagating modes of a
high-Q ring-cavity. Studying the properties of this trap we demonstrate loading
of higher-order transverse cavity modes and excite recoil-induced resonances.Comment: 4 pages, 4 figure
Optimized loading of an optical dipole trap for the production of Chromium BECs
We report on a strategy to maximize the number of chromium atoms transferred
from a magneto-optical trap into an optical trap through accumulation in
metastable states via strong optical pumping. We analyse how the number of
atoms in a chromium Bose Einstein condensate can be raised by a proper handling
of the metastable state populations. Four laser diodes have been implemented to
address the four levels that are populated during the MOT phase. The individual
importance of each state is specified. To stabilize two of our laser diode, we
have developed a simple ultrastable passive reference cavity whose long term
stability is better than 1 MHz
A Single Laser System for Ground-State Cooling of 25-Mg+
We present a single solid-state laser system to cool, coherently manipulate
and detect Mg ions. Coherent manipulation is accomplished by
coupling two hyperfine ground state levels using a pair of far-detuned Raman
laser beams. Resonant light for Doppler cooling and detection is derived from
the same laser source by means of an electro-optic modulator, generating a
sideband which is resonant with the atomic transition. We demonstrate
ground-state cooling of one of the vibrational modes of the ion in the trap
using resolved-sideband cooling. The cooling performance is studied and
discussed by observing the temporal evolution of Raman-stimulated sideband
transitions. The setup is a major simplification over existing state-of-the-art
systems, typically involving up to three separate laser sources
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