Originally posted by: ed21x
Originally posted by: silverpig
Originally posted by: ed21x
another article:
Effect of pressure on the decay rate of 7Be
Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan, ROC
Received 10 February 2000; Revised 25 April 2000; accepted 11 May 2000. Available online 12 July 2000.
Beryllium-7 in Be(OH)2 gel was compressed in diamond-anvil pressure cells up to 442 kbar at room temperature. By counting the activity of 7Be, the decay rate for the conversion of 7Be to 7Li via electron capture was measured. The decay constant of 7Be, ?, was found to increase, but the rate of increase decreased with increasing pressure. A quadratic regression of the data yields (?-?0)/?0=(4.87×10-5)P-(5.9×10-8)P2, where the subscript zero denotes zero pressure and P stands for pressure in kilobar. Thus, ? of 7Be increases by about 1% at 400 kbar. The observed data set can be rationalized by an increase in electron density near the nucleus of 7Be at high pressures. This result may bear some implications for the conversion of 40K to 40Ar, which has been widely adopted to date geological events.
This article shows that pressure/temperature can have an effect on radioactive decay rate of Beryllium. Of course this isn't directly asking "is radioactive dating accurate?" so that you avoid biased answers, but you can get tested information and make your own assumptions.
Increasing electron density near the nucleus will logically have an effect on an electron-capture mode of radioactive decay just because the cross-section of the reaction is increased. I am unsure of what effect increased electron density would have on a reaction that proceeds via beta-decay.
beta decay is suppose to increase along with an increase in electron density at the Nucleus.
Perhaps, but I think you are looking at various kinds of beta decay (B-, ejecting an electron and antineutrino, B+, ejecting a positron and neutrino, and electron capture (as mentioned above), ejecting a neutrino in the process p+ + e- --> n + v) in a rather simplistic fashion. Saying that decay rates simply "increase" or "decrease" is, to use the wording of someone a couple pages back, a very "8th grade" approach to everything.
The actual mathematics behind beta decay gives you a probability distribution of decays at various energies. The integral of the probability distribution between the Initial energy (0) and the final possible energy (essentially where the kinetic energy of the neutrino/antineutrino and the electron are equal to the total energy released in the reaction, the Q value) will give you the total decay constant. The decay constant looks something like this:
(lambda) = ( (g^2)(|Mfi|^2) / 2(pi^3)(h^7)(c^3) ) ( Integral from 0 to pmax (F(Z(d),p))(p^2)(Q-Te)^2dp ) )
the Fermi function, F(Z,p), is a function of the number of protons in the daughter and the momentum of the ejected electron or positron, but is a constant for a given type of B-decay, and accounts for coulombic interactions. |Mfi|^2 is a nuclear matrix element which people in quantum mechanics might recognize as something along the lines of an integral over initial and final states of wave functions, with an operator between them, and it gives you a high decay constant for superallowed B-transitions since a proton or neutron changes into a neutron or proton in the same nuclear shell. (Q-Te)^2 is a statistical factor deriving from the number of final states that are accessible to the electron upon emission.
Now, thats all well and fine, but long story short, the only term above which might be influenced by electron density (recall this only accounts for B- or B+ decay) is the number of accessible states, and if you could provide a reason why having those states pre-filled with electrons outside the nucleus would make the decay rate go UP, as your post implied, that would be quite extraordinary. The main problem you will find is that while electron capture requires a wavefunction for the electron that intersects the nucleus adequately, B- and B+ do not have quite the same physics or mathematics.
On another note, let us consider the effect of the change of pressure on electron density and therefore the rate of electron capture (which mathematically can be defined with variables that describe the chance of capturing an electron, and thus you could calibrate this as well, but I digress) on the effect of the decay constant, lambda, the half life, and related mathematics.
The accepted half-life of 14C is 5700 years (+/- 30). the decay constant is therefore lambda = ln2 / t(1/2) = 3.856 * 10^-12.
Now, if you initially had 6.022 * 10^23 atoms of 14C, using the accepted half life and lambda, at 4 half-lives of time, that is, 22800 years, which is 7.19 * 10^11 seconds, the number of remaining 14C atoms would be
N = No(e^-lambda * t) = 6.022*10^23 (e^-(3.856 * 10^-12 * 7.19 * 10^11)) = 6.022 * 10^23 * .0625 = 3.764 * 10^22.
Now lets say instead that the "real" decay constant (lambda) during this time period was, due to....whatever, 1.02 * lambda, that is, a 2 percent higher decay rate. Using the same equation, and the same time interval, we have instead
N = No(e^-lambda * t) = 6.022*10^23 (e^-(3.933 * 10^-12 * 7.19 * 10^11)) = 3.561 * 10^22.
Now, you might be quick to exclaim, "But that is 5.5% difference!" (approximately.) And that is true. However, even assuming that the half life value is wrong by 2 percent (instead of one) for a reason that wouldn't even apply to this type of decay in the same fashion, you are still within ~5% of the "actual" date for a 22000 year old object, that is, assuming the decay physics are fvcked up by things they should never be fvcked up by, and could be corrected for mathematically, you still get approximately the correct date, +/- a thousand years.
EDIT: I realize I am seriously glossing over other mechanisms that in actuality would be going on if this was a dead animal or whatever, however I am simply trying to point out that the whole "OMG it changes by 1% SCIENZE IZ WRONG crowd doesn't really have anything to stand on to seriously refute 14C dating. Furthermore, 14C and decaying Uranium series can be compared, along with other decay series, for a more complete picture and further calibration.
Other decay types such as alpha-decay (think Uranium Series) can be very partially effected, but again there are ways to account and calibrate for this mathematically, mainly with the coulomb barrier which affects how the penetration by quantum mechanics of the alpha particle occurs. But at this point I think I've said enough.
Oh, and did I mention I'm a sophomore at Berkeley? Go Bears! (F USC.
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