jQuery动态给radio赋单值有关问题

$(document).ready(function() {
            $.ajax({
                type: "POST",
                contentType: "application/json",
                url: "copyUserRole.aspx/GetJsonUserRole",
                data: "{}",
                dataType: "json",
                success: function(result) {
                    try {
                        eval("var userRole=" + result.d);
                        $.each(userRole, function(i) {
                            $("#tdUserGroup").append("<input type='radio' name='userGroup' value='" + userRole[i].roleId + "'/>" + userRole[i].roleName);
                            if ((i + 1) % 5 == 0) {
                                $("#tdUserGroup").append("<br/>");
                            }
                        });
                    }
                    catch (e) {
                        alert(e);
                        return;
                    }
                },
                error: function(result, status) {
                    if (status == "error") {
                        alert(status);
                    }
                }
            });
            $.ajax({
                type: "POST",
                contentType: "application/json",
                url: "setUserGroup.aspx/GetUserRoleByUserId",
                data: "{userId:'" + '<%=Request["userId"] %>' + "'}",
                dataType: "json",
                success: function(result) {
                    try {
                        if (result.d != null) {
                            document.getElementById("txtaReason").disabled = false;
                            //问题：result.d每次都出来，就是下面这句有时不起作用
                            $("input[@type=radio][@value=" + result.d + "]").attr("checked", true);
                        }
                    }
                    catch (e) {
                        alert(e);
                        return;
                    }
                },
                error: function(result, status) {
                    if (status == "error") {
                        alert(status);
                    }
                }
            });
        });