8,424 research outputs found
The DRIFT Directional Dark Matter Detector and First Studies of the Head-Tail Effect
Measurement of the direction of the elastic nuclear recoil track and
ionization charge distribution along it, gives unique possibility for
unambiguous detection of the dark matter WIMP particle. Within current
radiation detection technologies only Time Projection Chambers filled with low
pressure gas are capable of such measurement. Due to the character of the
electronic and nuclear stopping powers of low energy nuclear recoils in the
gas, an asymmetric ionization charge distribution along their tracks may be
expected. Preliminary study of this effect, called Head-Tail, has been carried
out here using the SRIM simulation program for Carbon and Sulfur in 40 Torr
carbon disulfide, as relevant to the DRIFT detector. Investigations were
focused on ion tracks projected onto the axis of the initial direction of
motion in the energy range between 10 and 400 keV. Results indicate the likely
existence of an asymmetry influenced by two competing effects: the nature of
the stopping power and range straggling. The former tends to result in the Tail
being greater than the Head and the latter the reverse. It has been found that
for projected tracks the mean position of the ionization charge flows from
'head' to 'tail' with the magnitude depending on the ion type and its energy.Comment: To appear in the proceedings of Dark 2007 Sixth International
Heidelberg conference on "Dark Matter in Astro & Particle Physics", Sydney,
Australia 24th-28th September 200
Recommended from our members
Effects of Degree of Particle Melt and Crystallinity in SLS Nylon-12 Parts
Differential Scanning Calorimetry (DSC) traces for SLS Nylon-12 parts display two
distinct melt peaks, which have been related to the presence of both melted and crystallised
regions, and un-melted particle cores within the part. The relative proportions of each region are
defined by the term ‘Degree of Particle Melt’ (DPM), and have a large effect on the mechanical
properties of a part. This paper demonstrates that the % crystallinity of SLS Nylon-12 parts is
dependent on the DPM. Crucially, research has also shown that the trends for some tensile
properties (notably Tensile Strength and Young’s Modulus) change once full melting is
complete.Mechanical Engineerin
Origin of bulk uniaxial anisotropy in zinc-blende dilute magnetic semiconductors
It is demonstrated that the nearest neighbor Mn pair on the GaAs (001)
surface has a lower energy for the [-110] direction comparing to the [110]
case. According to the group theory and the Luttinger's method of invariants,
this specific Mn distribution results in bulk uniaxial in-plane and
out-of-plane anisotropies. The sign and magnitude of the corresponding
anisotropy energies determined by a perturbation method and ab initio
computations are consistent with experimental results.Comment: 5 pages, 1 figur
Recommended from our members
Tailoring the Mechanical Properties of Selective Laser Sintered Parts
The ~£1 million IMCRC-funded integrated project ‘Personalised Sports Footwear: From
Elite to High Street’ is investigating the use of Rapid Manufacturing to produce personalised
sports shoes, with the aim of enhancing performance, reducing injury, and providing improved
functionality.
Research has identified that, for sprinting, performance benefits can be achieved by
tuning the bending stiffness of a shoe to the characteristics of an individual athlete. This paper
presents research to date on several novel methods of influencing the mechanical properties of
Selective Laser Sintered shoe soles, with a particular focus on stiffness.Mechanical Engineerin
Nanoclay/Polymer Composite Powders for Use in Laser Sintering Applications: Effects of Nanoclay Plasma Treatment
Plasma-etched nanoclay-reinforced Polyamide 12 (PA12) powder is prepared with its intended use in selective laser sintering (LS) applications. To replicate the LS process we present a downward heat sintering (DHS) process, carried out in a hot press, to fabricate tensile test specimens from the composite powders. The DHS parameters are optimized through hot stage microscopy, which reveal that the etched clay (EC)-based PA12 (EC/PA12) nanocomposite powder melts at a temperature 2°C higher than that of neat PA12, and 1–3°C lower than that of the nonetched clay-based nanocompsite (NEC/PA12 composite). We show that these temperature differences are critical to successful LS. The distribution of EC and NEC onto PA12 is investigated by scanning electron microscopy (SEM). SEM images show clearly that the plasma treatment prevents the micron-scale aggregation of the nanoclay, resulting in an improved elastic modulus of EC/PA12 when compared with neat PA12 and NEC/PA12. Moreover, the reduction in elongation at break for EC/PA12 is less pronounced than for NEC/PA12
- …