Browsing by Author "Martinez, Rafael"

Now showing 1 - 3 of 3

Radiolysis and sputtering of carbon dioxide ice induced by swift Ti, Ni, and Xe ions
(2015) Mejía Guamán, Christian Fernando; Bender, M.; Severin, Daniel; Trautmann, Christina; Boduch, Philippe; Bordalo, Vinicius; Domaracka, Alicja; Lv, Xueyang; Martinez, Rafael; Rothard, Hermann
Solid carbon dioxide (CO2) is found in several bodies of the solar system, the interstellar medium (ISM) and young stellar objects, where it is exposed to cosmic and stellar wind radiation. Here, the chemical and physical modifications induced by heavy ion irradiation of pure solid CO2 at low temperature (T = 15–30 K) are analyzed. The experiments were performed with Ti (550 MeV) and Xe (630 MeV) ions at the UNILAC of GSI/Darmstadt and with Ni ions (46 and 52 MeV) at IRRSUD of GANIL/Caen. The evolution of the thin CO2 ice films (deposited on a CsI window) was monitored by mid-infrared absorption spectroscopy (FTIR). The dissociation rate of CO2, determined from the fluence dependence of the IR absorption peak intensity, is found to be proportional to the electronic stopping power Se. We also confirm that the sputtering yield shows a quadric increase with electronic stopping power. Furthermore, the production rates of daughter molecules such as CO, CO3 and O3 were found to be linear in Se.
Radiolysis of cytosine at cryogenic temperatures by swift heavy ion bombardments
(2022) Agníhotri, Aditya; Vignoli Muniz, Gabriel S.; Domaracka, Alicja; Rothard, Hermann; Martinez, Rafael; Mejía Guamán, Christian Fernando; Boduch, Philippe; Augé, Basile
We investigated the radiolysis effects on the cytosine in the solid phase irradiated by swift heavy ions as galactic cosmic ray analogues (GCRs). Infrared (IR) absorption spectroscopy was employed to monitor the physical and chemical radiolytic modifications. The targets were prepared on ZnSe in two different ways: (1) by dropping a nucleobase-water-ethanol solution on the substrate and evaporating the solvent and (2) by sublimation of nucleobase powders in an oven and condensation on the windows. Both types of samples present similar IR absorption spectra. From the exponential decrease of the areas of IR absorption bands as a function of projectile fluence, apparent destruction cross sections (σd) were determined and were found to be very similar for samples prepared using both techniques. The destruction cross section of solid cytosine at cryogenic temperatures follows an electronic stopping (Se) power law: σd = C Sen, where C is a constant and the exponential n is a dimensionless quantity. We determined σd = (3 ± 1) × 10-17 Se (1.25 ±0.06). New absorption features emerge from cytosine degradation, which can be attributed to OCN-, H2CO, and HNCO. By using the observed power law, the half-life of cytosine exposed to galactic cosmic rays was estimated in the order of Mega years. The findings reported here may help a better understanding of complex organic molecule radiostability.
Radioresistance of adenine to cosmic rays
(2017) Domaracka, Alicja; Rothard, Hermann; Vignoli Muniz, Gabriel S.; Mejía Guamán, Christian Fernando; Martinez, Rafael; Auge, Basile; Boduch, Philippe
The presence of nucleobases in carbonaceous meteorites on Earth is an indication of the existence of this class of molecules in outer space. However, space is permeated by ionizing radiation, which can have damaging effects on these molecules. Adenine is a purine nucleobase that amalgamates important biomolecules such as DNA, RNA, and ATP. Adenine has a unique importance in biochemistry and therefore life. The aim of this work was to study the effects of cosmic ray analogues on solid adenine and estimate its survival when exposed to corpuscular radiation. Adenine films were irradiated at GANIL (Caen, France) and GSI (Darmstadt, Germany) by 820 MeV Kr³³⁺, 190 MeV Ca¹⁰⁺, 92 MeV Xe²³⁺, and 12 MeV C⁴⁺ ion beams at low temperature. The evolution of adenine molecules under heavy ion irradiation was studied by IR absorption spectroscopy as a function of projectile fluence. It was found that the adenine destruction cross section (σd) follows an electronic stopping power (Se) power law under the form: CSeⁿ; C is a constant, and the exponential n is a dimensionless quantity. Using the equation above to fit our results, we determined σd = 4 × 10⁻¹⁷ Se1.17, with Se in kiloelectronvolts per micrometer (keV μm⁻¹). New IR absorption bands arise under irradiation of adenine and can be attributed to HCN, CN⁻, C2H4N4, CH3CN, and (CH3)3CNC. These findings may help to understand the stability and chemistry related to complex organic molecules in space. The half-life of solid adenine exposed to the simulated interstellar medium cosmic ray flux was estimated as (10 ± 8) × 10⁶ years.