Memory and hardware problems would cause crashes and corruption in random applications, not the same application in the same way over and over.
You're going to need to get a core dump from apache; it appears it might be php causing an apache worker to exit unexpectedly. Enable coredumps and the next time the crash occurs, a core file will be dump, which can be examined with gdb. This will give a stack backtrace, helping to identify the area of crash.
Once confirmed that it is PHP, submit your bug to http://bugs.php.net/
and someone should respond.