How can Zn-64 decay back to Cu-64 after beta decay?

[daveb]

In the 16th edition of the chart of nuclides, it lists Cu-64 as decaying to Zn-64 by beta minus decay. OK, no problem here. Then it lists Zn-64 decaying back to Cu-64 by positron decay with a half life of 1.1 x 10^19 years. Assuming this isn't some typo, I have 2 questions.
1) How in blazes did they manage to figure this half life out?! The specific activity for Zn-64 is (very) roughly 19 Becquerels per 1000 kg of Zn-64, meaning how did they get a large enough sample to analyze it so that it could be distinguished from background? and
2) How in blazes is it possible for nuclide #1 to decay to #2 then #2 decay back to #1?! Is this some quantum mechanical tunneling effect?

 

[mathman]

http://atom.kaeri.re.kr/ton/

Above reference says Zn-64 is stable?

 

[daveb]

Yes, I'm familiar that just about every web source out there says it's stable. However, unless it's just a misprint, the 16th edition of the CON is the most updated (that I've seen) collection of data. It's possible that the web sites that do get updated didn't incorporate this into the site. I'm just wondering if anyone out there has heard anything about this, and if so, how this can be.

 

[jgraber]

2) How in blazes is it possible for nuclide #1 to decay to #2 then #2 decay back to #1?! Is this some quantum mechanical tunneling effect?

This is not possible unless the first nucleus is initially in an excited state. (See also nuclear isomer). In this case it could be theoretically possible, but I am not aware of any such case which is actually known to occur.
Jim Graber

 

[Astronuc]

In the 16th edition of the chart of nuclides, it lists Cu-64 as decaying to Zn-64 by beta minus decay. OK, no problem here. Then it lists Zn-64 decaying back to Cu-64 by positron decay with a half life of 1.1 x 10^19 years. Assuming this isn't some typo, I have 2 questions.
1) How in blazes did they manage to figure this half life out?! The specific activity for Zn-64 is (very) roughly 19 Becquerels per 1000 kg of Zn-64, meaning how did they get a large enough sample to analyze it so that it could be distinguished from background? and
2) How in blazes is it possible for nuclide #1 to decay to #2 then #2 decay back to #1?! Is this some quantum mechanical tunneling effect?

That CON seems in disagreement with BNL's on-line CON, which reports the half-life of Zn-64 as > 2.8E+16 y. Even so, the activity is so low I wonder how they measured the activity change.

http://www.nndc.bnl.gov/chart/reCenter.jsp?z=30&n=34 (Select 1 under Zoom on righthand side).

http://www.nndc.bnl.gov/chart/

The Cu-64 which decays by beta emission would be at a different energy state than one which decays by positron emission. I would imagine that if Zn-64, which for all intents and purposes is stable, decays by positron emission, then I would imagine that the resulting Cu-64 nuclide would decay by positron emission also to form Ni-64.