C.A. Duba

Solar fusion cross-sections

We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates.

An array of low-background 3He proportional counters for the Sudbury Neutrino Observatory

An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active ux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and November 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters lled with a mixture of 3He and CF4 gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral current reaction in the D2O, and four strings lled with a mixture of 4He and CF4 gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.

HALO – the helium and lead observatory for supernova neutrinos

The Helium and Lead Observatory (HALO) is a supernova neutrino detector under development for construction at SNOLAB. It is intended to fulfill a niche as a long term, low cost, high livetime, and low maintenance, dedicated supernova detector. It will be constructed from 80 tonnes of lead, from the decommissioning of the Deep River Cosmic Ray Station, and instrumented with approximately 384 meters of 3He neutron detectors from the final phase of the SNO experiment. Charged- and Neutral-Current neutrino interactions in lead expel neutrons from the lead nuclei making a burst of detected neutrons the signature for the detection of a supernova. Existing neutrino detectors are mostly of the water Cerenkov and liquid scintillator types, which are primarily sensitive to electron anti-neutrinos via charged-current interactions on the hydrogen nuclei in these materials. By contrast, the large neutron excess of a heavy nucleus like Pb acts to Pauli-block pn transitions induced by electron anti-neutrinos, making HALO primarily sensitive to electron neutrinos. While any supernova neutrino data would provide an invaluable window into supernova dynamics, the electron neutrino CC channel has interesting sensitivity to particle physics through flavour-swapping and spectral splitting due to MSW-like collective neutrino-neutrino interactions in the core of the supernova, the only place in the universe where there is a sufficient density of neutrinos for this to occur. Such data could provide a test for θ13 ≠ 0 and an inverted neutrino mass hierarchy. In addition, the ratio of 1-neutron to 2-neutron events would be a measure of the temperature of the cooling neutron star. For the 80 tonne detector, a supernova at 10 kpc is estimated to produce 43 detected neutrons in the absence of collective ν-ν interactions, and many more in their presence. The high neutrino cross-section and low neutron absorption cross-section of lead, along with the modest cost of lead, makes this technology scalable and a future upgrade, to of order 1 kilotonne, is under active consideration.

Low-background /sup 3/He proportional counters for use in the Sudbury neutrino observatory

Current solar neutrino detectors measure a considerably lower flux of electron-flavor neutrinos than predicted by solar models. This could be an indication of neutrino oscillations, which would provide direct evidence that neutrinos have mass. The Sudbury Neutrino Observatory (SNO) was designed to detect all flavors of neutrinos, and will provide a rigorous test of this theory. The SNO detectors heavy water target gives it the unique ability to detect all non-sterile neutrino flavors via the neutral-current (NC) break-up of the deuteron. This NC interaction liberates a neutron which may be detected with an array of discrete /sup 3/He proportional counters. The strict radioactivity requirements imposed by the need for low backgrounds dictate the use of ultra-pure materials and processes in building these counters. Additionally, they must survive in the heavy water environment for several years. The design, construction, and testing of these unique counters are described.

Sudbury neutrino observatory neutral current detectors signal readout system

Two precise measurements of the /sup 8/B solar neutrino flux have been made at the Sudbury Neutrino Observatory (SNO) and a third measurement will be made with an array of neutral current detectors (NCD). The NCDs are /sup 3/He proportional counters which detect thermalized neutrons liberated by the neutral current reaction /spl nu//sub x/+d/spl rarr//spl nu//sub x/+n+p in SNOs D/sub 2/O. Due to the very low rate of neutrino interactions relative to the rates of other ionizing particles, one major criteria of the array readout system is to facilitate particle identification for the measurement of the solar neutrino flux. Data acquisition at a rate expected to be produced by the neutrino flux from supernovae within our galaxy (10 kpc) is another major requirement. To accomplish these two tasks, a readout system was constructed based upon two distinct pieces of hardware. Digital oscilloscopes are used to maximize particle identification, but are only capable of handling the expected data rate produced by solar neutrinos. Custom-designed VME-based shaping-discriminating-ADC boards measure the total charge of events and are capable of being read out at 20 kHz.

Data acquisition for the Helium and Lead Observatory

The Helium and Lead Observatory (HALO) is a dedicated supernova detector constructed in the underground facilities at SNOLAB in Sudbury, Canada. It is designed to detect neutrinos from a supernova within the Milky Way galaxy using lead blocks and 3He neutron detectors. Analysis of supernova neutrino events can produce new discoveries in astrophysics and fundamental particle physics. HALO will be a participant in the Supernova Early Warning System (SNEWS), which will rely on the time delay between neutrino emission and visible light emission to provide notification to astronomers of an imminent observable supernova. This article discusses the data acquisition system of HALO, including the software ORCA, electronics components, data flow, and the design of the high-voltage and signal connections for the 3He neutron detectors.