Velvia 50 is safe from X-rays (Customs portal/carry-on). On a NZ trip a few years ago I went through about 8 x-ray sessions trotting about the country. No film was hurt.
No airports in Australia will hand-examine film on request: you do as Customs instruct you in the queue: put your goods through X-ray or you don't get in. Simple. (StoneNYC take note!)
Airside luggage scanners are lethal: it is said a bottle of Chanel No. 5 will "lose it's sweet pong" in there after just two passes (!)
Films above 400ISO will take around 3 passes before "bandy-bandy" becomes evident.
You can stuff film in lead-lined bags, but if Customs cannot adequately determine what the "shadow" is during X-ray, likely the item will be opened, inconveniencing all manner of people in queue, not the least of you.
T-Max P3200 and Delta 3200 films — don't bother taking these.