Induced gamma emission: Hafnium controversy

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Because of its high density of stored energy and long half life for storing that energy, the nuclear isomer 178m2Hf is a particularly attractive candidate for induced gamma emission experiments. If it could be "triggered" upon irradiation by some agent, the resulting release of cascades of gamma photons would have the best chance of finding a pair of excited states with inverted lifetimes as needed for analogs of laser devices. Its longer lifetime insures that tractable amounts of material could be collected into experimental targets that held no hazards for personnel working with the material.

A proposal to test the efficacy for "triggering" 178m2Hf was approved by a NATO-Advanced Research Workshop(NATO-ARW) held in Predeal in 1995[1]. Although the proposal was to use incident protons to bombard the target, α-particles were available when the experiment was done by an international team that was largely unsupported financially. Results were said to be extraordinary, but clearances from controlling agencies were not obtained so the results were not published, only fragments of the data can be found at the present time (some at the above URL), and the one-of-a-kind 178m2Hf target concentrated to 4% isomer content was lost. Nevertheless, the impression was given that 178m2Hf was of special importance to potential applications of IGE. It was almost the optimal situation to excite a major controversy; and such a controversy quickly erupted.

Contents

[edit] Importance

  • 178m2Hf has the highest excitation energy of any comparably long-lived isomer. One gram of pure Hf-178-m2 would contain approximately 1300 megajoules of energy, the equivalent of exploding about 226 kilograms (500 pounds) of TNT.
  • All of the energy released would be in the form of photons of X-rays and gamma rays.
  • Discussions also indicate that the energy is released very quickly, so that Hf-178-m2 can produce extremely high powers (on the order of exawatts).
  • The characteristic scales of times for processes involved in applications would be favorable for consuming all of the initial radioactivity. The process for triggering a sample by IGE would use photons to trigger and produce photons as a product. The propagation of photons occurs at the speed of light while mechanical disassembly of the target would proceed with a velocity comparable to that of sound. Untriggered 178m2Hf material might not be able to get away from a triggered event.
  • Both the proposal to the NATO-ARW and the fragmentary results from the subsequent experiment indicated that the energy of the photon needed to initiate IGE from 178m2Hf would be less than 300 keV. Many economical sources of such low energy X-rays were available for delivering quite large fluxes to target samples of modest dimensions.
  • Samples of 178m2Hf were and remain available at low concentrations <0.1%.

[edit] Chronology of notable events

  • Around 1997 the JASONS advisory group took testimony about the triggering of nuclear isomers. The JASON Defense Advisory Group put out a relevant public report[2] saying that they concluded that such a thing would be impossible and should not even be tried. Despite intervening publications in peer-reviewed journals of articles written by an international team reporting IGE from 178m2Hf, around 2003 IDA took testimony, again from relevant scientists on matters of the credibility of reported results. The Institute for Defense Analysis issued an (IDA) highly critical report[3] proposing that the positive experiments were so flawed that they should never have been published. Significant in both collections of testimony is that the lead US member of the team, Prof. Carl Collins, that was publishing the successes, never testified. In both "Reviews" the processes of testimony were classified. Owing to a personal quirk[4] Prof. Collins refuses to accept a security clearance and so was forbidden to testify, as were overseas collaborators in the experiments described in peer-reviewed publications as successful. Instead, interpretative testimony was provided by J.J. Carroll without consultation with the authors of the articles reporting successes with Hafnium IGE.
Experiment producing IGE from a sample of the nuclear isomer 178m2Hf. (l. to rt.) Students on duty; (w/ladder) the world's most stable beamline for monochromatic X-rays, BL01B1; (rt.) main ring of the SPring-8 synchrotron at Hyogo.
Experiment producing IGE from a sample of the nuclear isomer 178m2Hf. (l. to rt.) Students on duty; (w/ladder) the world's most stable beamline for monochromatic X-rays, BL01B1; (rt.) main ring of the SPring-8 synchrotron at Hyogo.
  • Around 2003, DARPA initiated exploratory research termed Stimulated Isomer Energy Release (SIER) and public interested was aroused, at both popular levels[5] and at professional levels[6].
  • The first focus of SIER was whether significant amounts of 178m2Hf could be produced at acceptable costs for possible applications. A closed panel called HIPP was charged with the task and the conclusion was yes, it could. However, a scientist on that confidential DARPA HIPP review panel "leaked" prejudicial but preliminary concerns to the press. [7]. This unsubstianted assertion set into motion the subsequent cascade of inaccurate reports about the so-called "outrageous costs" of isomer triggering.
  • Having settled the tractability of production at acceptable cost, the SIER program turned to the matter of definitive confirmation of the reports of IGE from 178m2Hf. A task of TRiggering Isomer Proof (TRIP) was mandated by DARPA and assigned to a completely independent team from those reporting success previously. The "gold standard" of Hafnium-isomer triggering was set as the Rusu dissertation[8]. The TRIP experiment required independent confirmation of the Rusu Dissertation. It was successful, but could not be published.
  • The negative perception of the "earmarking" of Congressional appropriations for "pet projects" is well-known. The reverse process of "inverse earmarking" is less well-known. It is used effectively to stop projects opposed by "pet interests". Forward progress toward the resolution of the scientific conflict within the US over IGE from 178m2Hf by normal scientific discourse was stopped in 2005 by such inverse earmarking[9].
  • By 2006 there were 11 significant publications in peer-reviewed journals supporting the observation of IGE from 178m2Hf. Full-text versions of the oldest 10 can be read here[10]. Reprints of the most recent must be ordered from the publisher[11]. Reprints (available at the link) of articles that were published after 2001 describe work conducted with tunable monochromatic X-ray beams from the synchrotron light sources SPring-8 in Hyogo and SLS in Villigen.
  • By 2006 there were 2 articles[12][13] that claimed to disprove possibilities for IGE from 178m2Hf and three theoretical articles saying why it should not be possible to occur by the particular steps the author envisioned[14][15][16]. The first two described synchrotron experiments in which the X-rays were not monochromatic.

[edit] Opinions

It has been claimed that there is much greater statistical confidence[17] in the results proving IGE from 178m2Hf than confidence in the experiments disproving it.

[edit] See also


[edit] References

  1. ^ Proceedings of the NATO-ARW are collected in Hyperfine Interactions, 107, pp 3-492 (1997).
  2. ^ High Energy Density Explosives, N. Lewis, R. Garwin, D. Hammer, W. Happer, R. Jeanloz. J. Katz, S. Koonin, P. Weinberger, E. Williams. October 1997. JSR-97-110. online pdf Sect. 4, p. 13.
  3. ^ Ref. needed to be supplied
  4. ^ Prof. Collins refuses to accept a security clearance.
  5. ^ Scary Things Come in Small Packages, Washington Post article of 2004 by Sharon Weinberger
  6. ^ Conflicting Results on a Long-Lived Nuclear Isomer of Hafnium Have Wider Implications This Physics Today article provides a balanced view from 2004.
  7. ^ San Jose newspaper article., October, 2003.
  8. ^ C. Rusu (PhD Dissertation, U of Texas at Dallas, 2002)Available from: Proquest (Order Number: 3087127).
  9. ^ Hf-isomer triggering stopped by legislative fiat
  10. ^ Reprints of articles about nuclear isomers in peer reviewed journals. - The Center for Quantum Electronics, The University of Texas at Dallas.
  11. ^ C.B. Collins, N.C. Zoita, F. Davanloo, Y. Yoda, T. Uruga, J.M.Pouvesle, and I.I. Popescu, Nuclear Resonance Spectroscopy of the 31-year isomer of Hf-178, Laser Physics Letters 2, p162-167 (2005).
  12. ^ Phys. Rev. Lett. 87, 072503 (2001).
  13. ^ Phys Rev. C 67, 041305R (2003).
  14. ^ E. V. Tkalya, Probability of L-shell nuclear excitation by electron transitions in 178Hfm2, Phys. Rev. C 68, 064611 (2003).
  15. ^ E. V. Tkalya, Induced decay of 178Hfm2: Theoretical analysis of experimental results, Phys. Rev. C 71, 024606 (2005).
  16. ^ E. V. Tkalya, Induced decay of the nuclear isomer 178m2Hf and the "Isomeric bomb", Physics-Uspekhi 48, 525 (2005) [Uspekhi Fiz. Nauk 175, 555 (2005)].
  17. ^ Open letter on triggering confidence.