How to trigger a change on a radio buttons group

How to trigger a change on a radio buttons group

Hello,Could someone tell me how to trigger a change on radio buttons group?


I have this group


<fieldset data-role='controlgroup' data-type='horizontal' data-mini='true'>
<input type='radio' name='rad_group' id='rad_Matin' value='Matin'>
<label for='rad_Matin'>Matin</label>
<input type='radio' name='rad_group' id='rad_Midi' value='Midi' >
<label for='rad_Midi'>Midi</label>
<input type='radio' name='rad_group' id='rad_Soir' value='Soir' >
<label for='rad_Soir'>Soir</label>
<input type='radio' name='rad_group' id='rad_Nuit' value='Nuit' >
<label for='rad_Nuit'>Nuit</label>
</fieldset>

and on change I try to change a global variable to the selected value
I've tried with

$("input[name=rad_group]").on("change", function()
{
Moment = $("input[name=rad_group]").val();
});

Moment is declared as global above this

but without success

could someone tell the best way to do it?
Thanks