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Abstract: A summary of sources of background affecting gamma-ray spectrometers and methods for eliminating each are discussed, along with practical cost/benefit ratios. Background contributed by samples generally defines practical levels for system background. The practical bottom line can be obtained for relatively modest costs. A realistic bottom line is attained in underground systems when the major contributions to the background come from cosmogenically produced68Ge and double-beta decay of76Ge in the detector. The true bottom line is reached with isotopically enriched detectors that eliminate these two chemically inseparable radioactive impurities. Data from isotopically enriched detectors are presented.

Abstract: A fast digital oscilloscope based pulse shape discrimination (PSD) system has been tested with intrinsic germanium detectors large enough to allow ionizing events which generate localized electron-hole pairs at a single site to be segregated from those depositing energy at several different sites in the crystal. Drift velocities of the electrons and holes result in pulses several hundred nanoseconds long. Since the electric field varies by almost a factor of 10 between the outer and inner surfaces, collection of electrons and holes can frequently be dinstinguished, and pulses due to multi-site events can be distinguished from single site events.

Abstract: Three years ago, state-of-the-art low-background germanium spectrometry was discussed, and speculations were advanced as to the origin of the remaining background. Some of those speculations have been shown to the incorrect. Contemporary lead shielding contains ap 100 Bq/kg of210Pb. Our 450-year-old lead was shown to contain <100 mBq/kg A high purity electroformed copper Marinelli shield was placed around the detector with no efffect on the background, which implied that the source is other than the 450-year-old shield. A new limit on the210Pb in this old lead shield is <9 mBq/kg. Electroformed copper components were found to contain226Ra and228Th contaminations at levels of 3500 and 110 mgrBq/kg, respectively. High purity H2SO4, recrystallized CuSO4, and a BaSO4 scavenge in the electroforming bath have reduced these contaminations to <25 and 9 mgrBq/kg, respectively. In copper, cosmic ray induced nuclear reactions are now the dominant source of raioactivity. For example,58Co can be readily measured after only a 24-hour exposure at sea level. A new germanium spectrometer containing 2150 grams of 87.44% enriched76Ge has been fabricated to mitigate the effect of cosmogenic68Ge in the background. Current background spectra are presented, and potential sources identified.

Abstract: A germanium diode gamma-ray spectrometer has been constructed that exhibits background levels three orders of magnitude lower than conventional low-background laboratory spectrometers in the energy region around 100 keV and five orders of magnitude lower in the energy region above 3 MeV. The steps necessary to achieve this reduction are described, and the application of this technology to construction of ultralow background laboratory based germanium diode gamma-ray spectrometers is discussed.

Unique because of their super-light masses and tiny interaction cross sections, neutrinos combine fundamental physics on the scale of the miniscule with macroscopic physics on the scale of the cosmos. Starting from the ignition of the primal p-p chain of stellar and solar fusion reactions that signal star-birth, these elementary leptons (neutrinos) are also critical players in the life-cycles and explosive deaths of massive stars and the production and disbursement of heavy elements. Stepping beyond their importance in solar, stellar and supernova astrophysics, neutrino interactions and properties influence the evolution, dynamics and symmetries of the cosmos as a whole. Further, they serve as valuable probes of its material content at various levels of structure from atoms and nuclei to valence and sea quarks. In the light of the multitude of physics phenomena that neutrinos influence, it is imperative to enhance our understanding of neutrino interactions and properties to the maximum. This is accentuated by the recent evidence of finite neutrino mass and flavour mixing between generations that reverberates on the plethora of physics that neutrinos influence. Laboratory experiments using intense neutrino fluxes would allow precision measurements and determination of important neutrino reaction rates. These can then complement atmospheric, solar and reactor experiments that have enriched so valuably our understanding of the neutrino and its repertoire of physics applications. In particular, intermediate energy neutrino experiments can provide critical information on stellar and solar astrophysical processes, along with advancing our knowledge of nuclear structure, sub-nuclear physics and fundamental symmetries. So where should we look for such intense neutrino sources? Spallation neutron facilities by their design are sources of intense neutrino pulses that are produced as a by-product of neutron spallation. These neutrino sources could serve as unique laboratories to enrich our knowledge of neutrino physics and the multifaceted science it interfaces. In fact, the neutrino energy spectra expected at spallation neutron facilities overlap remarkably with those emanating from distant supernovae and these sources seem `made to order' for terrestrial studies of supernova reactions. They are also in a suitable energy regime to pursue neutrino-mediated studies of nuclear structure, fundamental symmetries and solar reactions. Recent research indicates neutrino-nuclear reactions may be even more influential in supernova dynamics and detection than hitherto believed. The need for in-depth understanding of the individual neutrino-nuclear reactions that collectively have dramatic effects on the large-scale dynamics of evolving stars points to laboratory measurements of neutrino reactions on various nuclei as a premier requirement of neutrino-nuclear astrophysics. Such experimental data can improve our input to the extensive modelling projects that investigate the evolutionary stages of exploding supernovae and further our understanding of their internal physics. State-of-the-art simulations exploring the neutrino-reheating phases fail to produce explosions---yet clearly nature explodes her supernovae. Matters pertaining to the galactic abundance of very p-rich nuclei and the various isotope ratios are by no means well defined and demand further research, as do the intricacies of the nucleo-synthesis channels. Neutrino-nuclear experiments are also essential for proper development and calibration of appropriate supernova detectors. Solar neutrino research and detection have contributed vastly to our current understanding of neutrino science and have helped to validate the standard solar model. The chapter is by no means closed and experiments with intense neutrino fluxes could enrich valuably our understanding of both neutrino and solar physics. Neutrino nuclear reactions are not only important for their role in nuclear astrophysics, but also for the insight they provide on nuclear structure and the theoretical models used to calculate nuclear excitations by neutrinos. They can also provide better precision for the elastic axial form factor and serve as effective probes of the strangeness content of nuclei. Neutrino interactions with charged leptons can add significantly to our understanding of electroweak physics and neutrino-electron elastic cross sections measured at intense pulsed sources can provide precision constraints on the electroweak parameters. The intrinsic properties of the neutrino, including mass values and oscillations, form a subject of critical current interest and research. The parameter space for neutrino oscillations and studies of electroweak interactions that could be accessed at spallation neutron sources would complement the research undertaken at higher energy neutrino facilities and neutrino factories. The following collection of articles highlights the physics research that could be undertaken with neutrinos at spallation neutron facilities. It addresses open questions that need research and some of the experimental aspects and detector features associated with conducting that research. We feel this will be an effective and timely enterprise in the light of renewed international interest in spallation neutron sources (one is under construction at Oak Ridge, TN, USA and others are being considered in Europe and Japan), and the critical role of intermediate energy neutrino physics in particle, nuclear and astrophysics. The collection is by no means exhaustive or complete, but we hope it will provide a unique and valuable compendium for reference and guidelines as nuclear, particle and condensed matter scientists join hands for basic research at shared facilities. We would like to take this opportunity to thank the authors who have taken time from their various commitments to contribute to this special section and A Mezzacappa and W R Hix for providing the cover image displaying the interplay between microscopic neutrino-nuclear processes and the macroscopic supernova dynamics. We would also like to thank Journal of Physics G: Nuclear and Particle Physics for hosting this section and apologize for any errors or credits that we may have missed.