You can uninstall or removes an installed radiance-materials package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove radiance-materials
If you would like to remove radiance-materials and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove radiance-materials
If you use with purge options to radiance-materials package all the configuration and dependent packages will be removed.
$ sudo apt-get purge radiance-materials
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove radiance-materials