Bender, M.

Merkel, M.

Severin, D.

Trapp, P.

GSI Repository

Quantitative outgassing analysis of polymers during heavy ion irradiationP. Trapp1, M. Bender∗2, D. Severin2, and M. Merkel11THM, MND, Friedberg (Hessen), Germany; 2GSI, Darmstadt, GermanyDegradation processes of polymers under heavy ion irra-diation have been studied intensively over the past decades[1, 2]. A common approach is measuring outgassing ofvolatile fragments that are created during irradiation. Sofar outgassing measurements were conducted in a qualita-tive way, e.g., as pressure rise observed in a residual gasanalyzer (RGA).The aim of this experiment was to get access to quanti-tative outgassing. Therefore a calibration of the existingRGA setup concerning pressure measurement and pump-ing speed was needed. First the pumping speed S for vari-ous gas species was determined [3]. With the pressure rise∆p from outgassing fragments and the mean flux of the ionbeam N˙ , one can derive the outgassing yield η (releasedfragments / incident ion) of volatile fragments:η =∆p · SN˙ · k · T (1)We have studied outgassing with respect to the origin ofthe desorbed gas; whether it is released from the surfaceor as volatile decomposition fragments out of the bulk ofthe polymer. For surface cleaning a keV sputter ion source(IQE 11/35 from Specs R©) with xenon as sputter-gas wasused at a distance of about 50 cm away from the samples.Polycarbonate (Makrofol R©) foils 100 and 30 µm thick-ness) and polyimide (Kapton R©) foils 25 µm thickness)were irradiated at the M3 beamline of the UNILAC [4] atroom temperature with xenon, gold and samarium ions of4.8 MeV/u and a flux of (1 - 2) · 108 ions/cm2s. The diame-ter of all samples was 1 cm, and a beamspot of about 8 mmx 8 mm was used for irradiation. Both sides of the polymerwere cleaned for 45 min with xenon ions of 500 eV and aflux of 3e13 ions/cm2s. For each sample species, a samplewith and without sputter-cleaning was investigated.The raw RGA data was calibrated with total pressure mea-surements of the dynamic pressure during irradiation. Withthe calibrated pressure rise ∆p and the ion flux N˙ the yieldwas calculated using equation 1. In figure 1 the outgassingyields for Makrofol R© irradiated with gold ions are shownfor various gas species. The plots marked with open sym-bols correspond to sputter-cleaned samples, full symbolsto uncleaned foils. The estimated error for the fluence is5%. Concerning the yield we estimate an error of 10% tak-ing into account uncertainties of the total pressure measure-ment, pumping speed and flux. We observed that the yieldof all sputter-cleaned samples is lower then the uncleanedcounterpart; thus the surface condition has a strong effect∗ corresponding author: m.bender@gsi.deon the outgassing of the polymer. However in both casesthe yields are decreasing with increasing fluence. Thiscould either be due to unsufficient surface cleaning or flu-ence dependent bulk decomposition induced by materialchanges. More in-situ investigations are planned. Our mea-surements clearly show that the surface state contributes tobeam induced pressure increase.2E11 3E11 4E115,0E61,0E71,5E72,0E75,0E51,0E61,5E62,0E62,5E64,0E66,0E68,0E61,0E72,0E53,0E54,0E55,0E5Fluence [ions / cm2]H2Yield [released gas / incident ion] OCO CO2Figure 1: Outgassing-yield η of various gas species for a100 µm thick Makrofol R© foil during irradiation with goldions. open symbols: sputter-cleaned before irradiation, fullsymbols: uncleaned. Lines are guides to the eye.References[1] T. Steckenreiter et al., Nucl. Inst. Meth. B 131 (1997) 159.[2] U. H. Hossain et al., Polym. Chem. 5 (2014).[3] P. Trapp, Internship report, 2014[4] Baake et al., Rev. Sci. Instrum. 82, 045103 (2011).[5] R. Kumar et al., NIM B 251, 2006[6] D. Severin, PhD Thesis, Marburg 2008.GSI SCIENTIFIC REPORT 2014 APPA-MML-MR-03DOI:10.15120/GR-2015-1-APPA-MML-MR-03 255

Quantitative outgassing analysis of polymers during heavy ion irradiation

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Quantitative outgassing analysis of polymers during heavy ion irradiation

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