Don’t rely on RNG from harvesting samples you find on the ground. Run the Echoes Battlegrounds Activity and keep an eye out for [b]Assimilated Demolishers[/b], gold bar Vex that have a set spawn location in each map as you make your way downward toward the boss encounter. Destroying one of these Demolishers during a run will give you a decent (although not 100%) chance of receiving an [b]Assimilated Beacon[/b] at the end of the Activity; you can only hold one Beacon at a time. Once you have a Beacon in hand, travel to [b]Watcher’s Grave[/b] on Nessus; along the zone wall on the way toward the Cabal Imperial Land Tank you will find a [b]Vex Conflux[/b]. Interacting with the Conflux will consume the Beacon and spawn three gold bar Assimilated Demolishers simultaneously, which you will have to defeat before they flee (iirc the time limit is five minutes) so be sure to either be stocked up on ammo and ability energy or bring a friend. Defeating all three Demolishers before they flee will award you a [u]guaranteed[/u] 400g Radiolite Sample; this reward is on a knockout system, so you will not receive a duplicate unless you have already collected at least one of each 400g Sample. If you fail you can return to the Battlegrounds to collect a new Beacon to try again as many times as you like, although using this method you can only receive [b]one[/b] 400g Sample per week on your account, so you may have to do this across the space of multiple weeks to complete the Triumph depending on where your collection currently stands. (΄◉◞౪◟◉｀)