How to create nonce with 32 chracters in c#.net

private static string validChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        private static Random random = new Random();

        private static string GenerateNonce(int length)
        {
            var nonceString = new StringBuilder();
            for (int i = 0; i < length; i++)
            {
                nonceString.Append(validChars[random.Next(0, validChars.Length - 1)]);
            }

            return nonceString.ToString();
        }