Energetic ion irradiation of N2O ices relevant for Solar system surfaces

ABSTRACT Ices are the dominant surface material of many Solar system objects, such as comets and trans-Neptunian objects. They are continuously exposed to ion bombardment by solar wind ions and cosmic rays, which trigger secondary ion emission, contributing to the exosphere formation. Laboratory studies demonstrated the effects of energetic processing of ices at low temperature, showing the production of molecules and free radicals of astrophysical interest. Nitrous oxide (N2O) is one of the molecular species observed in star-forming sites, reason why it may be present in the ices covering some minor bodies in the outer Solar system. In the current work, N2O ice at 10 K was irradiated by energetic (MeV/u) multicharged heavy ions (e.g. 105Rh and 140Ba); the sputtered species were detected and analysed by the TOF-PDMS technique (time-of-flight plasma desorption mass spectrometry). Small positive and negative secondary ions were identified: N+, N2+, NO+, O+, and O−. The bombardment also induces production of ion cluster series: (N2)nR$_{m}^+$, (NO)nR$_{m}^+$, (N2O)nR$_{m}^+$, where R = N+, N2+, NO+, N2O+, Om+ (n up to ∼ 10, m = 1−3). Their yield distributions follow the sum of two decreasing exponentials, one fast -F and another slow -S, suggesting a two-regime formation. Most of the yield distributions have the same pair of exponential decay constants, around kF ∼ 1.4 and kS ∼ 0.15 u−1. Based on this behavior, an emission description for aggregates is proposed, useful to understand the processes by which neutral and ionized molecular species are delivery to the gas phase in space.

Plasma-desorption mass spectrometry as an express diagnostic test for bovine leukaemia

Plasma-desorption mass spectrometry with ionization of 252Californium fission fragments (252Cf-PD MS) was used to develop an express diagnostic test for bovine leukaemia. The test is based on the mass spectrometric parameters of artificial lipid membranes formed on the gold substrate from the lipid fraction of blood cells (mainly lymphocytes), by the self-assembly technique according to the biomimetic principle. Mass spectrometric analysis of artificial lipid membranes obtained from blood plasma of control and leukemic cattle gave a reliable diagnosis of leukaemia. The basis for the diagnosis were the ionization parameters of the fragmentation of lipid molecules from normal and leukemic cell membranes. In leukemic cell membranes, separate dense areas (rafts) 200 – 300 nm in diameter, saturated with cholesterol and phospholipids, are formed. The number of rafts per unit of cell membrane of leukemic cells significantly exceeded the permitted parameters of normal cell membranes. The increased number of rafts in artificial membranes formed in the membranes of leukemic cells was reliably reflected in mass spectra, due to the 180 – 250% increase in intensity of peaks of cholesterol fragment ions in comparison to control cells.