this side says: Toshiba

the back says: 5886

 

http://www.ominous-valve.com/images/ray5886.jpg

"Submini JAN CK-5886, from a radiological survey meter (nuclear fallout detector) once bought by Civil Defense and nuke plants. The tubes that tested under one FEMTOampere for leakage were connected as triodes in ultra-high impedance ion chamber amps. That's an enormous US 10-cent coin next to this little guy."

Just a Google guess on my part.

 

interesting but i wonder if its the same part since it was from a spectrophotometer.

 

A 5886 is an electrometer tube. They were common in vacuum gauges as well. Anything that needed 10^15th input resistance used them.