Chris Waltham

A compact 3H(p,γ)4He 19.8-MeV gamma-ray source for energy calibration at the Sudbury Neutrino Observatory

Abstract The Sudbury Neutrino Observatory (SNO) is a new 1000-t D2O Cherenkov solar neutrino detector. A high-energy gamma-ray source is needed to calibrate SNO beyond the 8B solar neutrino endpoint of 15 MeV. This paper describes the design and construction of a source that generates 19.8-MeV gamma rays using the 3H(p,γ)4He reaction (“pT”), and demonstrates that the source meets all the physical, operational and lifetime requirements for calibrating SNO. An ion source was built into this unit to generate and to accelerate protons up to 30 keV, and a high-purity scandium tritide target with a scandium–tritium atomic ratio of 1 : 2.0±0.2 was included. This pT source is the first self-contained, compact, and portable high-energy gamma-ray source ( E γ >10 MeV ) .

Measurement of the slope of the π0 electromagnetic form factor

Abstract We have measured the slope parameter of the π 0 electromagnetic form factor by measuring the partial branching ratio of the Dalitz decay π 0 → γe + e − into high-invariant-mass electron-positron pairs. We obtain a value a =0.026 with a total (statistical and systematic) error of ±0.054, in agreement with vector dominance and quark loop calculations.

Vibrational characteristics of harp soundboards

Harps exist in different forms, from large factory-made concert harps to small hand-made folk harps. This variety presents both a challenge and an opportunity for acousticians. The musical quality of a harp depends on many factors, but key among these is the soundboard. This work sets out to define some general desirable qualities of a harp soundboard. First, in order to understand the relationship between the vibrational behavior of a bare soundboard and that of a completed instrument, a 36-string harp was built from scratch. Measurements were made at each stage of construction, and the results showed how the bare soundboard properties affect those of the finished harp. Second, the soundboards of several harps of different sizes were assessed by measuring the admittances along the string bar. These data showed that one relationship crucial to the quality of the soundboard is that between the modal shapes and modal frequencies of the soundboard, and the position and fundamental frequencies of the strings attached to it. A general statement is made about this relationship, one which should be of use to harp makers.

Light scattering and absorption caused by bacterial activity in water

There is a growing class of elementary particle detectors, large-water Čerenkov detectors, that have a body of water (thousands of tons) as a sensitive medium. Particles are detected when they interact with the water and produce Čerenkov light, so detection efficiency relies on the transparency of the water. These detectors are active typically for many years, so biological activity (primarily bacterial growth) is one of the means by which the transparency of the water may be reduced. We present the results of a measurement of light scattering and absorption from a population of Escherichia coli in water, which is used as a model for bacteria in general. One can separate the scattering and absorption by varying the refractive index of the medium by using a solute of high molecular weight. We show that the results can be understood simply in terms of light scattering from small spheres (radius ≈ wavelength) with an effective refractive index, n(b), plus a small amount of absorption in the ultraviolet. We compare his scattering with Rayleigh scattering in pure water.

Spin Spin Correlations and Spin Asymmetries for the Reaction

Abstract Spin-spin correlation parameters A LL , A NN , A SS , A SL and spin asymmetries A NO and A ON have been measured for the reaction p p → pn π + with incident beam energies of 510, 465 and 420 MeV. Clean separation of free proton events from the bound proton background has been achieved. A LL , A SS and A NN , were all found to be large and negative indicating domination by the 1 D 2 partial wave. The spin asymmetries were large. Results are compared to the predictions of Dubach, Kloet and Silbar.

p p \to p n \pi^+

Abstract There is an important and growing class of elementary particle detectors which are characterized by a large sensitive volume (thousands of tonnes), very low radioactive backgrounds, and rely on the emission of light for particle detection. Water Cherenkov detectors come into this category; they have a large mass of water as the sensitive medium. Particles are detected when they interact with the water and produce Cherenkov light, so detection efficiency relies on having a huge light sensitive area at the periphery of the detector. The most cost-effective way of achieving this is by placing light concentrators on large photomultiplier tubes (PMTs). This paper describes the work carried out on light concentrators for the PMTs in the Sudbury Neutrino Observatory, a 1000 tonne heavy water Cherenkov detector. We discuss the advantages of using light concentrators, summarize the optical theory of non-imaging light concentration, and describe in detail the development and manufacture of the concentrators themselves.

at Intermediate-energies

Almost half a century ago John Schelleng determined the scaling rules that show how violins can be made from nontraditional materials. These principles suggest that balsa wood may be a possible, if unlikely, construction material. To test this idea, a balsa violin was constructed and found to be playable. Its vibrational behavior is shown to be in agreement with Schelleng’s scaling rules. The instrument was not difficult to build, and its construction can be repeated by anyone of moderate skill with a chisel and sandpaper and access to an audio frequency analysis program. The reward is a tactile appreciation for the vibrational behavior of materials and the physics of musical instruments that is difficult to gain otherwise.

Light concentrators for the Sudbury Neutrino Observatory

Presented here is a very simple physical model of flight that relies only on Newton’s second law and yet is able to reproduce all the salient features of a more rigorous fluid dynamical treatment. From a pedagogical point of view the model helps understand the origins of lift and drag in terms of forces rather than pressures, and enables all the important points to be made without recourse to complicated mathematics.

A balsa violin

The mechanical admittance of the soundboards of four full-size concert harps from three manufacturers was measured, and the results show that there is little variation between them. More detailed vibro-acoustic data were then obtained for an Aoyama Amphion harp. Analysis of these data show that the individual soundholes amplify the radiated sound in successive frequency bands associated with the modal frequencies of the soundboard. The lower holes tend to contribute at the lower end of the frequency scale, and the higher holes at the higher end of the scale.

Flight without Bernoulli

Neutrino oscillations are purely quantum mechanical effects that occur over macroscopic time and distance scales. I present the physics of this phenomenon in words, pictures, and analogies rather than mathematics.The reality of neutrino oscillations has not really sunk in yet. The phenomenon presents us with purely quantum mechanical effects over macroscopic time and distance scales (milliseconds and 1000s of km). In order to help with the pedagogical difficulties this poses, I attempt here to present the physics in words and pictures rather than math. No disrespect is implied by the title; I am merely borrowing a term used by a popular series of self-help books.