[Phys-L] half life fundamental principles3

[Brian Whatcott <betwys1@sbcglobal.net>]

Here are John's thoughts on time stamping via a DCD pulse:
John Denker via Phys-l <phys-l@mail.phys-l.org>UnsubscribeTo:phys-l@phys-l.orgCc:John DenkerThu, Oct 21 at 10:47 PM

On 10/20/21 1:22 PM, Tom Van Baak wrote:
/snip/> On the other end of the performance spectrum you can do timestamping
> using any old laptop and just a serial port. A win32 example is
> here:
>
>  http://leapsecond.com/tools/pctsc.c
>
> It has its limitations but it shows that a lowly serial port pin can
> be used as a trigger for time stamp recording. I use this for quick
> 'n dirty low rate Geiger measurements. For more precision and no
> dead time I use dedicated hardware for the counting & timing and the
> PC just for data logging.

1) The corresponding linux program is here:
  timestamp.c - poissfit - fit to Poisson distributed data (not least squares)

2) However.... I don't recommend any of the serial-port solutions for
the radioactivity application. (Other applications maybe.)

-- Here's one of the many, many issues: Each click of the Geiger counter
  is a very narrow spike. A son of a glitch. That's very unlike anything
  a serial port was designed to handle. If you have 1000 events per second
  with a nice 50/50 duty cycle, the serial port can handle it fine, but
  if you have even a few events per second consisting of spiky clicks
  you're gonna lose events.

-- You're gonna need a level shifter if you want to drive the serial port
  pins reliably. The hardware cost for that is not large, but it's comparable
  to the entire system-on-chip solution.//snip/

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I suspect those wildly narrow pulses must  come from a PM tube.
Here's the clunky output from a G-M tube amplifier - not up to even the 1 MHz time stamp rate that  Tom mentioned:
https://tinyurl.com/pyfrjy2n
AKA   https://doi.org/10.1016/j.net.2019.02.008 ;                      GM pulse characteristics.
 
Entering precision signals via the DCD pin of a serial port is not new: here are a couple of IETF notes and code instance.
https://datatracker.ietf.org/doc/html/rfc2783#page-3
https://datatracker.ietf.org/doc/html/rfc1589


John's concern about the reliability of the chipset used for the cable converter is addressed here:
http://www.prolific.com.tw/us/ShowProduct.aspx?p_id=156&pcid=41

Notice that you need to take care of which driver to use with which version of PC operating system.It does have an onboard level converter, as well as a 2 yr warranty and (some) technical support apparently.Just amazing what $12 can buy!  <g>


Brian