The derivation of the formyl-group oxygen of chlorophyll b in higher plants from molecular oxygen.

The mechanism of formation of the formyl group of chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H218O or 18O2 and examining the newly synthesized chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of chlorophyll b-71-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of chlorophyll a and [7-hydroxymethyl]-chlorophyll b extracted from leaves greened in the presence of either H218O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of chlorophyll b but also for the well-documented incorporation into the 131-oxo group of both chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599–602]. The incorporation of isotope led to as much as 77% enrichment of the 131-oxo group of chlorophyll a: assuming identical incorporation into the 131 oxygen of chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H218O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the chlorophyll b formyl group involving the participation of an oxygenase-type enzyme

A Monte Carlo simulation of the Sudbury Neutrino Observatory proportional counters

The third phase of the Sudbury Neutrino Observatory (SNO) experiment added an array of 3He proportional counters to the detector. The purpose of this Neutral Current Detection (NCD) array was to observe neutrons resulting from neutral-current solar neutrino-deuteron interactions. We have developed a detailed simulation of the current pulses from the NCD array proportional counters, from the primary neutron capture on 3He through the NCD array signal-processing electronics. This NCD array Monte Carlo simulation was used to model the alpha-decay background in SNO's third-phase 8B solar-neutrino measurement.Comment: 38 pages; submitted to the New Journal of Physic

The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76

The {\sc Majorana} collaboration is searching for neutrinoless double beta decay using $^{76}$Ge, which has been shown to have a number of advantages in terms of sensitivities and backgrounds. The observation of neutrinoless double-beta decay would show that lepton number is violated and that neutrinos are Majorana particles and would simultaneously provide information on neutrino mass. Attaining sensitivities for neutrino masses in the inverted hierarchy region, $15 - 50$ meV, will require large, tonne-scale detectors with extremely low backgrounds, at the level of $\sim$1 count/t-y or lower in the region of the signal. The {\sc Majorana} collaboration, with funding support from DOE Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the {\sc Demonstrator}, an array consisting of 40 kg of p-type point-contact high-purity germanium (HPGe) detectors, of which $\sim$30 kg will be enriched to 87% in $^{76}$Ge. The {\sc Demonstrator} is being constructed in a clean room laboratory facility at the 4850' level (4300 m.w.e.) of the Sanford Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded shield approach with the inner portion consisting of ultra-clean Cu that is being electroformed and machined underground. The primary aim of the {\sc Demonstrator} is to show the feasibility of a future tonne-scale measurement in terms of backgrounds and scalability.Comment: Proceedings for the MEDEX 2013 Conferenc

Status of the MAJORANA DEMONSTRATOR experiment

The MAJORANA DEMONSTRATOR neutrinoless double beta-decay experiment is currently under construction at the Sanford Underground Research Facility in South Dakota, USA. An overview and status of the experiment are given.Comment: 8 pages, proceeding from VII International Conference on Interconnections between Particle Physics and Cosmology (PPC 2013), submitted to AIP proceeding