Form widget with radiobutton list

hello

i am trying to build a custom form widget in which a user may select an image (randomly choosen from a list) with a radio button list

i have followed this video to get started; i created the widget with the designer tool, added a RadioButtonList contol in the widget, updated the .cs and  .js file but when i test the widget no choice is selected

here is the live test

i attach the ascx, cs and js files

thanks in advance

diego