Modification of surface oxide layers of titanium targets for increasing lifetime of neutron tubes
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LOGY OF NUCLEAR MATERIALS
Modification of Surface Oxide Layers of Titanium Targets for Increasing Lifetime of Neutron Tubes A. M. Zakharov*, O. A. Dvoichenkova, and A. E. Evsin National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, Moscow, 115409 Russia *email: [email protected] Received February 23, 2015
Abstract—The peculiarities of interaction of hydrogen ions with a titanium target and its surface oxide layer were studied. Two ways of modification of the surface oxide layers of titanium targets for increasing the life time of neutron tubes were proposed: (1) deposition of an yttrium oxide barrier layer on the target surface; (2) implementation of neutron tube work regime in which the target is irradiated with ions with energies lower than 1000 eV between highenergy ion irradiation pulses. Keywords: hydrogen, vacuum neutron tube, gasfilled neutron tube, thermal desorption, barrier coating. DOI: 10.1134/S106377881514015X
1. INTRODUCTION Vacuum neutron tubes (VNTs) and gasfilled neu tron tubes (GNTs) generate a flux of neutrons as a result of interaction between deuterium and tritium. In VNTs, deuterium ions irradiate a titanium target doped with tritium, and in GNTs, the target is doped while being irradiated with both deuterium and tritium ions. Irradiation with ions leads to desorption of tri tium from the VNT targets and results in reduction of their lifetime. For GNTs, desorption of the captured particles from the target places a limit on the concen tration of hydrogen ions in the target and thus inhibits the yield of neutrons. In the present work, two possible modifications of the surface oxide layers of the titanium targets are sug gested in order to increase the lifetime of neutron tubes. The experiments were performed using the MIKMA facility [1], allowing one to irradiate samples with plasma and its components and to analyze the processes of capture and release of gases in the samples using the thermal desorption spectrometry (TDS) technique. The experiments were performed using tar gets in the form of a 1µmthick layer of titanium on a molybdenum base. 2. IMPROVEMENT OF THE LIFETIME OF NEUTRON TUBES AFTER APPLICATION OF YTTRIUM OXIDE LAYERS ON THE SURFACE OF THE TITANIUM TARGET The thermal resistance of a titanium target doped with deuterium up to the concentration of TiD1.66 was measured (see Fig. 1). The samples were heated (heat
ing rate of 0.086 K/s) to the operating temperature (623 K) and were kept at this temperature. After that, the samples were cooled and then heated at 5 K/s. Heating of the target at the operating temperature (Fig. 1a) showed a steep increase in the desorption rate starting at about 600 K. The sharp peak in the TDS spectrum of the heated target at the operating temper ature of 623 K was recognized to be related to outgas sing of the surface oxide layer followed by release of deuterium from the target. In 250 min of treating the target at 623 K, about 60% of deuterium and approxi mately the same amount of hydroge
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