This is the 50mm standard lens that come with my Ricoh KR-5 Super. However, it seems that the camera had also been sold with an non-XR version of this lens (see photo in Camera-wiki entry: http://camera-wiki.org/wiki/Ricoh_KR-5_Super). There is also an non-L version of this lens (see https://www.pentaxforums.com/userreviews/ricoh-xr-rikenon-50mm-f-2-0.html) which focuses down to 0.44m instead of 0.6m and has a metal lens body. According to this online source, L probably means “late version”. To confuse you more, a “P” version (like the SMC-A of Pentax) was also made for Ricoh bodies with programmed auto and shutter-priority modes. However, this “P” version is incompatible with most K-mount bodies and forcing one on risks damaging the camera.
Back to the lens itself, it is a non-P Ricoh lens and thus has a standard fully mechanical Pentax-K mount which will fit on almost all Pentax bodies even for the DSLRs. The only concern would be whether your body can meter with the lens or not. The focusing mechanism is not as good as my Pentax SMC-A 50mm f2. It is smooth but there is not enough friction. My only real complaint about this lens is it does not have half-stop clicks on the aperture ring. Optically, this lens is very soft wide-open but when stopped-down, it outperforms the Pentax, at least from my own experience. For this reason, I mostly have this Rikenon 50mm on my Pentax bodies instead. Well, how about a sample shot? Below was taken with Ilford HP5+ exposed at ASA200 using the XR Rikenon 50mm f2 L mounted on my ME Super.