Create a element programatically

When I want to create an element with xsl:name prefix in C#, it creates a element without xsl prefix. How can I create an element with specific prefix? I removed header from xml file, but when I opened the xml file, Load method had thrown an exception about xsl prefix.

<?xml version="1.0" encoding="UTF-8"?><xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:output method="text" omit-xml-declaration="yes" indent="no"/><table border="1"><thead><tr><!--<th><span><xsl:text>HeaderSample</xsl:text></span></th>--></tr></thead><tbody><xsl:for-each select="result1"><xsl:for-each select="row"><tr><td><xsl:for-each select="HeaderSample"><xsl:apply-templates/></xsl:for-each></td></tr></xsl:for-each></xsl:for-each></tbody></table></xsl:stylesheet>				 						

XmlDocument doc = new XmlDocument();
        doc.Load("Template\\ResultItem.xml");

        XmlNode headerElement =     doc.LastChild.SelectSingleNode("table/thead/tr");

        foreach (string h in Headers)
        {
            XmlElement thElement = doc.CreateElement("th");
            XmlElement spanElement = doc.CreateElement("span");
            XmlElement xslTextElement = doc.CreateElement("xsl:text");

            xslTextElement.InnerText = h;

            spanElement.AppendChild(xslTextElement);
            thElement.AppendChild(spanElement);
            headerElement.AppendChild(thElement);
        }