Very cold and ultra cold neutron sources for ESS

The goal of the “Workshop on Very Cold and Ultra Cold Neutron Sources for ESS” was to discuss scientific cases, ideas and possibilities for the implementation of sources of Very Cold and Ultra Cold neutrons at the European Spallation Source. The ESS facility, presently under construction, offers several possibilities for in-pile UCN or VCN sources, in primis thanks to the available space below the spallation target where additional neutron sources can be placed to complement those above the target. Neutron beams can be extracted over a wide angular range with a grid of forty-two beamports with 6° average angular separation, allowing future instruments to be installed which may view either the upper or lower moderator systems. Of greatest interest for fundamental physics is the so-called Large Beamport foreseen for the NNBAR experiment. This beamport is also particularly well suited to feed a UCN source, for which several ideas were presented that employ either superfluid helium or solid deuterium as established neutron converter materials. Concepts for VCN sources make use of novel materials for VCN production and/or advanced reflectors to increase yields in the coldest part of the neutron spectrum from a cryogenic neutron source. In this paper we discuss these ideas and the possible locations of UCN and VCN sources at ESS.

Development of high intensity neutron source at the European Spallation Source

The European Spallation Source being constructed in Lund, Sweden will provide the user community with a neutron source of unprecedented brightness. By 2025, a suite of 15 instruments will be served by a high-brightness moderator system placed above the spallation target. The ESS infrastructure, consisting of the proton linac, the target station, and the instrument halls, allows for implementation of a second source below the spallation target. We propose to develop a second neutron source with a high-intensity moderator able to (1) deliver a larger total cold neutron flux, (2) provide high intensities at longer wavelengths in the spectral regions of Cold (4–10 Å), Very Cold (10–40 Å), and Ultra Cold (several 100 Å) neutrons, as opposed to Thermal and Cold neutrons delivered by the top moderator. Offering both unprecedented brilliance, flux, and spectral range in a single facility, this upgrade will make ESS the most versatile neutron source in the world and will further strengthen the leadership of Europe in neutron science. The new source will boost several areas of condensed matter research such as imaging and spin-echo, and will provide outstanding opportunities in fundamental physics investigations of the laws of nature at a precision unattainable anywhere else. At the heart of the proposed system is a volumetric liquid deuterium moderator. Based on proven technology, its performance will be optimized in a detailed engineering study. This moderator will be complemented by secondary sources to provide intense beams of Very- and Ultra-Cold Neutrons.

Radioprotection calculations for MEGAPIE

The MEGAwatt PIlot Experiment (MEGAPIE) liquid lead-bismuth spallation neutron source will commence operation in 2006 at the SINQ facility of the Paul Scherrer Institut. Such an innovative system presents radioprotection concerns peculiar to a liquid spallation target. Several radioprotection issues have been addressed and studied by means of the Monte Carlo transport code, FLUKA. The dose rates in the room above the target, where personnel access may be needed at times, from the activated lead-bismuth and from the volatile species produced were calculated. Results indicate that the dose rate level is of the order of 40 mSv h(-1) 2 h after shutdown, but it can be reduced below the mSv h(-1) level with slight modifications to the shielding. Neutron spectra and dose rates from neutron transport, of interest for possible damage to radiation sensitive components, have also been calculated.

The parental origin of hydatidiform moles and blighted ova: molecular probing with hypervariable DNA polymorphisms

The androgenetic origin of hydatidiform moles, due to a monospermic or dispermic mechanism, has been reported, and a possible pathogenetic relation with blighted ova suggested. To evaluate the origin of hydatidiform moles and their genetic relationship with blighted ova we investigated a series of samples, utilizing several hypervariable DNA polymorphisms by Southern blotting or PCR. Seven complete or partial hydatidiform mole and 49 blighted ovum cases were investigated. The results confirm the androgenetic origin of complete hydatidiform moles, which were always due in our sample to a monospermic mechanism. Our data exclude a relationship between hydatidiform moles and blighted ova, as in the latter a mixed paternal and maternal DNA contribution was always shown. A high incidence of chromosomal abnormalities in blighted ova was also found.

[Anatomic correction of transposition of the great vessels with interventricular communication. A series of 24 consecutive operations]

The results of surgical correction at arterial level in 24 cases of transposition of the great arteries with ventricular septal defect are reported. The majority of children (19/24) had undergone previous pulmonary artery bonding between the ages of fifteen days and 3 months (average 1,5 months). Surgical correction was performed on average 14 months later. This consisted of repair of the ventricular septal defect and arterial shift to reestablish ventriculoarterial concordance with reimplantation of the coronary arteries. In the last 9 cases no prosthetic materials were used on the right outflow tract. The operative mortality was 9/24 (6 of the first 12, and 3 of the last 12 cases). The cause of death was due to associated lesions, congenital (coarctation of the aorta, mitral valve malformation), or iatrogenic related to previous surgery (stenosis of the right ventricular infundibulum). Left ventricular failure was common despite preparation with pulmonary artery banding and merited systematic treatment mainly with arterial vasodilator therapy and prolonged ventilatory assistance. The surviving children are asymptomatic without treatment. Control catheter studies did not show any significant abnormality except in one case of pulmonary hypertension. The exceptional quality of these results, the absence of prosthetic material and the hope of reducing avoidable mortality justify this approach to surgical cure of the malformation. Preparation by pulmonary artery banding and the use of this method in "simple" forms of transposition are questions which remain open to discussion.

[Importance of echocardiography in the evaluation of surgical results in the tetralogy of Fallot]

M mode echocardiography was performed one year after surgical correction of Fallot's tetralogy in 32 patients (average age: 2, 7 years). All patients were asymptomatic without treatment and the average cardiothoracic ratio was 0,56 +/- 0,03. Echocardiographic indices of left ventricular function distinguished 4 patients with myocardial dysfunction (2 cases of poor myocardial protection and 2 double Blalock-Taussig anastomoses). Right ventricular diastolic internal dimensions were increased in 75 % cases. The ratio of right to left ventricular internal dimension was used to classify patients into three groups: Group I (ratio Less Than 0,70) 17 patients; Group II (ratio 0,70 Greater Than 0,80) 4 patients, and Group III (ratio Greater Than 0,80) 11 patients. This ratio was not related to the age of the patient of surgery or to the type of patch used on the right ventricular outflow tract but was related to the pressures recorded at operation after correction. A ratio Greater Than 0,80 was strongly suggestive of a significant residual abnormality which was often curable. Echocardiography has become an essential investigation in the follow up of Fallot's tetralogy after surgical correction: a right: left ventricular ratio Less Than 0,70 obviates the need of control catheterisation. On the other hand, a ratio Greater Than 0,80 is a strong indication for cardiac catheterisation even in the absence of clinical abnormalities.