🚀 go-pugleaf

In article <1992Sep9.164601.735@cognos.com>, mcgregoa@cognos.com (Alayne McGregor) writes:
...
Yeah I know it's not realy photography but....
> The problem with the Therac-25 radiation (not X-ray) machine was, from what
> I've read, both a hardware and software problem. The software malfunctioned in
> not correctly calculating the intensity of the radiation in certain unusual
> cases; the hardware interlocks that should have prevented this level of
> radiation from reaching the patient did not react fast enough.
> 

The Therac could be used fr electron beam or X-ray therapy. For X-ray use, the
beam current is *MUCH* higher, and a tungsten block anode is moved into the
path of the beam. The problem arose when the machine was A-B-A mode switched in
a short time. ( can't remember the exact sequence ) Anyway, you ended up with
the machine in X-ray mode but with the target OUT. You them proceed to zap them
with several AMPS of E beam...

> Furthermore, the problem only showed up if an operator entered an incorrect value
> and corrected that value within a few seconds. This kind of timing problem is
> *not* easy to find just by reading code.
> 

The machine in fact registed an error condition, "Malfunction 25"
the ops canceled it and proceded. If it had said

    " you are about to **KILL** the patient..." they would, I am sure, have
taken more notice and stoped t see what the hell was going on.

~Paul