[en] In May 2011, a workshop was held to develop broader awareness of the technical and operational challenges that could be used to enhance effective transparency and/or verification in the medium to long-term. Building confidence in a broader multi-lateral engagement scenario adds even greater challenges than the traditional bi-lateral approaches. The multi-disciplinary group that attended included decision-makers needing to understand present and possible future technical capabilities, and the technical community needing clearer definition of possible requirements and operational constraints. In additional to traditional presentations, the group conducted an exercise to stimulate new perspectives on verification requirements for a scenario based on nuclear arms reductions at very low numbers of nuclear weapons. The workshop participants were divided into two groups and asked to explore the political and technical requirements needed for States to move towards significant arms reductions. Using a technique called 'back-casting' participants were asked to imagine a world without nuclear weapons and describe what would be needed to achieve levels of one thousand, one hundred, ten, and ultimately zero weapons in the world. Most participants agreed that a strong political commitment will be necessary and that complete disarmament will only be possible if states are convinced that nuclear weapons serve no purpose. Both groups believed that a time period of greater instability would be encountered when moving from 1000 to 100 nuclear weapons and that it would be imperative to accelerate quickly through this period. The group discussed the need to have an international body monitor the disarmament process to maintain legitimacy for the international community. One possibility could be the development of an intergovernmental panel on verification and disarmament to monitor and facilitate disarmament. The groups recognized the problem of fissile material disposition after warheads dismantlement. Controlling fissile materials is important since nuclear material could be a direct route to reconstitution of weapons. (A.C.)

[en] Borexino is a large volume, real-time, liquid scintillator detector located at the Gran Sasso National Laboratory in Italy. The principal objective of the detector is to measure mono energetic (862 keV) ⁷Be neutrinos from the sun present with a count rate of several tens of events per day. Measurement at this level requires an extremely low internal background due to natural radioactivity present in the detector components. In this paper the techniques used by Borexino to purify the scintillator and to build the nylon containment vessels are described. The unprecedented high radiopurity reached by Borexino permitted for the first time the realtime detection of ⁷Be neutrinos from the sun

[en] Cosmogenic ¹¹C is produced in-situ by atmospheric muons and forms the main background for the measurement of solar pep- and CNO-neutrinos. However, FLUKA simulations show that the majority of ¹¹C is accompanied by a free neutron in the final state, thus allowing for an efficient tagging method, the so-called Three-Fold Coincidence technique. The technique and its first applications on Borexino data are presented.

[en] We report the measurement of the ⁸B solar neutrinos interaction rate with the Borexino detector. The extremely high radio-purity reached in the Borexino scintillator, combined with the efficient software rejection of cosmogenic background, allows to investigate the recoiled electron spectrum, induced by ⁸B solar neutrinos, down to the unprecedented energy threshold of 2.8 MeV. The rate of ⁸B solar neutrino interaction as measured through their scattering on the target electrons is 0.26±0.04_stat±0.02_syst c/d/100 tons. This corresponds to an equivalent electron neutrino flux of (2.65±0.44_stat±0.18_syst)x10⁶ cm^-2s^-1, as derived from the elastic scattering only, in good agreement with existing measurements and predictions.

[en] The Borexino experiment has begun data taking in May 2007 after a long R and D work and preparation. The liquid scintillator purity exceeds even optimistic expectations, and the first detection of ⁷Be solar neutrinos has been possible after less than two months of data taking. This note shows briefly which are the main issues that were addressed in order to obtain such an extreme radiopurity, the detector performance and a few details concerning this first result

[en] We describe a method to measure the concentration of ²²⁴Ra and ²²⁶Ra in the heavy water target used to detect solar neutrinos at the Sudbury Neutrino Observatory and in the surrounding light water shielding. A water volume of 50-400 m³ from the detector is passed through columns which contain beads coated with a compound of manganese oxide onto which the Ra dissolved in the water is adsorbed. The columns are removed, dried, and mounted below an electrostatic chamber into which the Rn from the decay of trapped Ra is continuously flowed by a stream of N₂ gas. The subsequent decay of Rn gives charged Po ions which are swept by the electric field onto a solid-state α counter. The content of Ra in the water is inferred from the measured decay rates of ²¹²Po, ²¹⁴Po, ²¹⁶Po, and ²¹⁸Po. The Ra extraction efficiency is >95%, the counting efficiency is 24% for ²¹⁴Po and 6% for ²¹⁶Po, and the method can detect a few atoms of ²²⁴Ra per m³ and a few tens of thousands of atoms of ²²⁶Ra per m³. Converted to equivalent equilibrium values of the topmost elements of the natural radioactive chains, the detection limit in a single assay is a few times 10^-16 g Th or U/cm³. The results of some typical assays are presented and the contributions to the systematic error are discussed

[en] The technique used at the Sudbury Neutrino Observatory (SNO) to measure the concentration of ²²²Rn in water is described. Water from the SNO detector is passed through a vacuum degasser (in the light water system) or a membrane contact degasser (in the heavy water system) where dissolved gases, including radon, are liberated. The degasser is connected to a vacuum system which collects the radon on a cold trap and removes most other gases, such as water vapor and N₂. After roughly 0.5 tonnes of H₂O or 6 tonnes of D₂O have been sampled, the accumulated radon is transferred to a Lucas cell. The cell is mounted on a photomultiplier tube which detects the α-particles from the decay of ²²²Rn and its progeny. The overall degassing and concentration efficiency is about 38% and the single-α counting efficiency is approximately 75%. The sensitivity of the radon assay system for D₂O is equivalent to ∼3x10^-15 g U/g water. The radon concentration in both the H₂O and D₂O is sufficiently low that the rate of background events from U-chain elements is a small fraction of the interaction rate of solar neutrinos by the neutral current reaction

[en] The Borexino experiment has been running since May 2007 at the Gran Sasso underground laboratory, in Italy. Solar neutrinos are detected with a large unsegmented liquid scintillator detector with unprecedented radioactive purity. The main results obtained include the measurement of the ⁷Be solar neutrino flux, the measurement of the ⁸B neutrino flux with electron recoil energy threshold of 3.0 MeV and the first clear detection of geo-neutrinos (see Aldo Ianni's talk in these proceedings for further details). Borexino has recently completed a large calibration campaign, and better results on ⁷Be solar neutrino measurement are expected soon. Short and medium term perspectives are summarized in the conclusions.

[en] As photodisintegration of deuterons mimics the disintegration of deuterons by neutrinos, the accurate measurement of the radioactivity from thorium and uranium decay chains in the heavy water in the Sudbury Neutrino Observatory (SNO) is essential for the determination of the total solar neutrino flux. A radium assay technique of the required sensitivity is described that uses hydrous titanium oxide adsorbent on a filtration membrane together with a β-α delayed coincidence counting system. For a 200 tonne assay the detection limit for ²³²Th is a concentration of ∼3x10^-16 g Th/g water and for ²³⁸U of ∼3x10^-16 g U/g water. Results of assays of both the heavy and light water carried out during the first 2 years of data collection of SNO are presented

[en] We report the measurement of ν-e elastic scattering from ⁸B solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran Sasso (Italy). The rate of solar neutrino-induced electron scattering events above this energy in Borexino is 0.22±0.04(stat)±0.01(syst) cpd/100 t, which corresponds to Φ_⁸B^ES=2.4±0.4±0.1x10⁶ cm^-2 s^-1, in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the ⁸B neutrino flux predicted by the high metallicity standard solar model, the average ⁸B ν_e survival probability above 3 MeV is measured to be 0.29±0.10. The survival probabilities for ⁷Be and ⁸B neutrinos as measured by Borexino differ by 1.9σ. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar ν_e survival probability P_ee between the low-energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.