Martian sub-surface ionising radiation: biosignature and geology

The surface of Mars, unshielded by thick atmosphere or global magnetic field, is exposed to high levels of cosmic radiation. This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation is of prime astrobiological interest. Here, we present modelling results of the absorbed radiation dose as a function of depth through the Martian subsurface, suitable for calculation of biomarker persistence. A second major implementation of this dose accumulation rate data is in application of the optically stimulated luminescence technique for dating Martian sediments. We present calculations of the dose-depth profile in the Martian subsurface for various scenarios: variations of surface composition (dry regolith, ice, layered permafrost), solar minimum and maximum conditions, locations of different elevation (Olympus Mons, Hellas basin, datum altitude), and increasing atmospheric thickness over geological history. We also model the changing composition of the subsurface radiation field with depth compared between Martian locations with different shielding material, determine the relative dose contributions from primaries of different energies, and discuss particle deflection by the crustal magnetic fields.

Is a black eye a useful sign of facial fractures in patients with minor head injuries? A retrospective analysis in a level I trauma centre over 10 years

Orbital blunt trauma is common, and the diagnosis of a fracture should be made by computed tomographic (CT) scan. However, this will expose patients to ionising radiation. Our objective was to identify clinical predictors of orbital fracture, in particular the presence of a black eye, to minimise unnecessary exposure to radiation. A 10-year retrospective study was made of the medical records of all patients with minor head trauma who presented with one or two black eyes to our emergency department between May 2000 and April 2010. Each of the patients had a CT scan, was over 16 years old, and had a Glasgow Coma Score (GCS) of 13-15. The primary outcome was whether the black eye was a valuable predictor of a fracture. Accompanying clinical signs were considered as a secondary outcome. A total of 1676 patients (mean (SD) age 51 (22) years) and minor head trauma with either one or two black eyes were included. In 1144 the CT scan showed a fracture of the maxillofacial skeleton, which gave an incidence of 68.3% in whom a black eye was the obvious symptom. Specificity for facial fractures was particularly high for other clinical signs, such as diminished skin sensation (specificity 96.4%), diplopia or occulomotility disorders (89.3%), fracture steps (99.8%), epistaxis (95.5%), subconjunctival haemorrhage (90.4%), and emphysema (99.6%). Sensitivity for the same signs ranged from 10.8% to 22.2%. The most striking fact was that 68.3% of all patients with a black eye had an underlying fracture. We therefore conclude that a CT scan should be recommended for every patient with minor head injury who presents with a black eye.