The Nuclear Isomer EMP Weapon Controversy

Introduction to Nuclear Isomers

A nuclear isomer of a particular element is an atom of that element with the same atomic number Z and the same mass number, A, in a state of nuclear excitation, that is excitation of one or more of the particles in the atomic nucleus, i.e. the nucleons (protons or neutrons).

The higher states of nuclear excitation are metastable with respect to the ground state, meaning that they decay more slowly due to the requirement of an change of nuclear angular momentum, I.

Nuclei usually exist in their ground state with the individual nucleons paired up subject to energy constraints. In some nuclides, for example resulting from radioactive decay, one or more nucleons can be excited into one or more higher spin states. These nuclei can revert back to the ground state by the emission of gamma radiation. If this emission is delayed by more than 1 μs, the nucleus is said to be a nuclear isomer and the process of releasing energy is known as isomeric transition.

There are two very different ways that such nuclei can possess a quantum variable known as spin angular momentum or spin. Either the nucleus rotates as a whole, or several nucleons can orbit the nucleus independently in a non-collective rotation. The latter case can result in the nucleons being trapped in high spin states such that they have much higher lifetimes. Nuclides with even-Z and even-N (i.e. with a whole number of He-4 nuclei, which are Bosons, particles with whole integer spin) can also have high excess rotational spin due to alpha particles rotating independently around the nucleus. Examples here are 12C, 16O, 20Ne, and 24Mg.

Therefore, Nuclear isomers include excited states of nuclei that electromagnetically decay slowly enough for energy storage. However, the emitted gamma rays of the isomer decay come in a burst. Therefore, one would think, that a controlled triggering of the isomer decay could allow stored energy to be released on demand, and nuclear isomers represent a potential stand-alone energy source. Barriers to developing a practical energy source are triggering and production.

Nuclear Isomer Triggering Theory

Induced gamma emission can be triggered by means of stimulating nuclei in a long-lived excited energy level in a nucleus is analogous therefore to the process of stimulated emission of a photon from a long-lived excited energy state of an atom.

Hence with induced gamma emission the isomer must be then be an element in which the excited, metastable, state of the element is more stable than the ground state. Polonium-212 is an example where the isomer has a much longer halflife than the ground state. With a spin of 18, the half-life of 45 s is very much longer than the ground state half-life of 300 ns.

The excited isomer can then be considered as two neutrons and two protons (i.e. an alpha particle) being excited to a nuclear higher nuclear energy level, in analogy to the electron energy levels in atomic physics except know we are dealing with the particles around the nucleus rather than the electrons around the atom. The excited alpha particle then orbits in its higher energy level around the "doubly magic" lead-82 nucleus. The high spin state decays by alpha emission which carries off the 18 units of spin.

Other examples are hafnium-178 (spin 16 due to 4 (1-alpha particle) of the 78 nucleons orbiting the nucleus), tungsten-178 (spin 25 due to 8 unpaired nucleons (i.e. 2-alpha particles orbiting the nucleus). The energy stored in these excited nuclear orbitals are can be very large. For example, the excitation of 1-alpha particle to the first metastable state of hafnium 178m2 is 10,000 times as much energy per gram as TNT.

In theory, isomer high-energy density materials (HEDMs) have potential energy yields orders of magnitude greater than existing chemical energetics. While the development of useful propellants, explosives, or energy sources based on this phenomenon is probably decades away, such extraordinary energy density has the potential to revolutionize all aspects of power generation on demand.

Current nuclear batteries in development use small amounts (milligrams and microcuries) of radioisotopes with high energy densities. In one design, radioactive material sits atop a device with adjacent layers of P-type and N-type silicon, so that ionizing radiation directly penetrates the junction and creates electron-hole pairs. Nuclear isomers could replace other isotopes, and with further development it may be possible to turn them on and off as needed. Current candidates for such use include 108Ag, 166Ho, 177Lu, and 241Am. As of 2016 the only isomer which had been proven to be successfully triggered was 180mTa, which incidentally required more photon energy to trigger than was released.

Fission of an isotope such as 177Lu releases gamma rays by decay through a series of internal energy levels within the nucleus, and it is thought that by learning the triggering cross sections with sufficient accuracy, it may be possible to create energy stores that are 10^6 times more concentrated than high explosive or other traditional chemical energy storage. [Ref 1]

Potential aerospace applications range from very high-density energetics for propulsion and potential high-energy and power density primary sources to power spacecraft or satellites, again in the realm of nuclear batteries, and to be controlled and triggered sources of gamma rays for use in particle and nuclear physics research, in particular particle-antiparticle pair production.

Proposed Nuclear Isomer Production - Application, Methods and Feasibility

Famously, it was the goal of DARPA's Stimulated Isomer Energy Release program is to develop a technique to control the release of the energy contained in nuclear isomers. Its mission was to develop a way to make these isomers in gram-size quantities and then demonstrate that as much energy can be released as is used to initiate the reaction (i.e. a breakeven experiment). Program Plans outlined in February 2004 include efforts to determine if the hafnium isomer can be triggered with photons in the x-ray range that will release more than 50 times the energy input of trigger and moreover release the energy in the form of controlled gamma rays. The project intended to identify a hafnium isomer production process that is affordable and cost effective, and to develop a physics approach to a chain reaction for the hafnium isomer.

DARPA supported a group led by Carl Collins at the University of Texas at Dallas. In early 1999 Collins claimed to have demonstrated triggering energy release from a hafnium-178 isomer using a dental X-ray machine (Physical Review Letter 25 Jan, 1999). [Ref 2]

The Collins groups claimed that when they bombarded the metal with soft X-rays, the hafnium-178 released a burst of gamma rays 60 times more powerful than the X-rays.

This would be a very important discovery for an organisation like DARPA or any global security or military intelligence agency for that matter, as a controlled high energy gamma ray source such as this could be key for, among other things, a directed energy weapon system that would also create a significant directed EMP (Electromagnetic Pulse) if such a weapon was fired into the atmosphere. Such a weapon would be considered a Weapon of Mass Destruction, as it would cause significant damage to a nation's infrastructure in a first strike tactic.

This would work by means of the Gamma rays creating Compton Scattering of electrons from Oxygen atoms in the atmosphere. 

In Compton Scattering, an incident gamma ray photon loses some of its energy to a bound electron, which excites the electron which then has enough kinetic energy to escape from the atom and recoils away from the atom. The scattered photon moves away at an opposite and equal angle to the emitted electron.

The recoil electrons would then spiral in line with the Earth's own magnetic field and release high energy Radio and Microwave Synchrotron Radiation in a pulse, which is the EMP itself,  which would fry any piece of electronic equipment attached to an antenna, or anything that acts as a antenna. 

Hence, power lines, telecom towers, mobile communications and most semiconductors would be either badly disrupted or completely destroyed. This is the ultimate non-lethal way to win a war - leaving the buildings and people intact but disabling or destroying most or perhaps all machines and weapons. This can happen with all forms of nuclear weapons when detonated in the atmosphere, but nuclear weapons have additional fallout making them highly lethal weapons of mass destruction.

In 2001 physicists from the Lawrence Livermore National Laboratory, in collaboration with scientists at Los Alamos and Argonne national laboratories, conducted tests that strongly contradicted reports claiming an accelerated emission of gamma rays from the nuclear isomer 31-yr. hafnium-178, and the opportunity for a controlled release of energy. The triggering source in the original experiment was a dental X-ray machine.

Using the Advanced Photon Source at Argonne, which has more than 100,000 times higher X-ray intensity than the dental X-ray machine used in the original experiment, and a sample of isomeric Hf-178 fabricated at Los Alamos, the team of physicists expected to see an enormous signal indicating a controlled release of energy stored in the long lived nuclear excited state. However, the scientists observed no such signal and established an upper limit consistent with nuclear science and orders of magnitude below previous reports. When the team turned the APS X-ray beam onto the sample of 31-yr. Hf-178, no detectable increase of the isomer decay occurred. In other words, the X-ray irradiation did not decrease the time it takes for hafnium to decay; a result that is consistent with nuclear physics.

Anatoli Andreev of Moscow State University wrote in 2007 "Recently, there have been reports in the mass media about plans to build what became known as an “isomeric bomb” based on Hf-178. What all the publications are speaking about is no less than the possibility of building a radically new weapon that does not fall under a single article of the existing nonproliferation treaties. The publications were based on the sensational results on induced decay of the long-lived isomer Hf-178m2 (16+, 2446 keV, 31 yr), obtained in 1999-2004 by a group of researchers headed by Carl B Collins, the Director of the Center for Quantum Electronics, University of Texas at Dallas.

The results show the following. The production of several grams or more of the isomer 178m2-Hf is an extremely difficult task and, so far, no effective process for such production has been described in the literature.

The initial discovery of 178m2Hf was the ridiculously daunting result of irradiating 100 mg of HfO2 for two years in a high neutron flux reactor facility [Ref 3]

, with thermal neutron fluxes > 4 × 10^14 n/cm2/s,  and required an additional three years to decay and process, resulting in an estimated 25 picograms of 178m2Hf. Considerations of large scale processing with reactor irradiation conclude that it is impractical to produce even gram quantities in this manner.

In a  paper by Karamian, et al. [Ref 4] the production cross section for 178m2Hf was measured (along with other isotopes of Hf). From that paper the production of 178m2Hf can be estimated by the expression:

 [Ref 5]

where Φ is the neutron flux, N177 is the amount of 177Hf which serves as the “feed stock” for the production and N178m2 is the amount of 178m2Hf produced. The cross sections (measured in barns, b) reported by Karamian, et al. provide an estimate for the production:

It is instructive to calculate the total quantity of 178m2Hf that Helmer and Reich would have produced. Starting from 100 mg of HfO2, with 177Hf at 18.6% abundance the initial amount of “feed stock” would be roughly 16 mg. Estimating the reactor flux for 2 years of running to be Φ = 6.3 × 10^21 n/cm2 yields roughly 0.075 ng of 178m2Hf.

To obtain gram quantities of 178m2Hf it would require processing 10 metric tonnes of HfO2

Accelerator production might be possible via the reaction 179Hf(n,2n)178m2Hf. The cross section at 18 MeV incident neutron energy is calculated to be 10 mb. The shape of the cross section above 18 MeV is uncertain. The total neutron cross section 179Hf(n,X) is approximately 2.5 b. Each incident neutron incident on the 179Hf target makes 0.004 178m2Hf nuclei, or 250 incident neutrons to make a single 178m2Hf.

Neutrons would be made by accelerating deuterons to high energy and directed onto a Li target to produce neutrons in the appropriate energy range. A thick Li target would yield roughly 1/3 of a neutron out in the energy range of interest. A high intensity machine would accelerate 6×10^18 deuterons/s/Ampere. The neutron yield would be 2×10^18 neutrons/s/A.

Assuming that 120 MeV deuteron accelerator can be designed and built with roughly 100mA beam currents, the neutron yield would be 2 × 10^17 neutrons/s.

The 178m2Hf production for one year of running would be 2 × 10^22 atoms, or roughly 6 g.

Additional issues with accelerator production of 178m2Hf are the enrichment of 179Hf from natural stock, and the processing of the irradiated target to recover the 178m2Hf. There are also considerable technical challenges regarding the accelerator, the Li target and processing the 178m2Hf from the 179Hf target. Finally, not all the cross sections relevant for the estimating production are known. 

Burdensome expenditures from state defense budgets to even produce the necessary quantities may prove completely useless: no energy can be liberated by the method as described in Collins’s articles. The cross sections of the induced decay of the isomer 178m2-Hf measured by that method do not agree with the current ideas about the physics of the nucleus and the physics of electromagnetic nuclear processes.

Summary:

Summarizing the obtained proposals, methods and results, it would be noted the following:

Theoretical calculations and the analysis of the existing experimental data suggest that the hafnium problem, as presented by the works of Collins's group, does not exist. The hullabaloo over the hafnium bomb was due to meaningless experimental data and the incompetence of certain individuals, and their thirst for fat military and black project budgets. rather than to the real possibility of building any radically new technology based on 178-Hf in particular.

Nevertheless, the potential for developing nuclear isomers known to be triggered such as 180mTa and future developments on other isomers, may make on-demand triggered x-ray and gamma ray sources possible for experimentation as well as nuclear and particle physics research and applied technologies in the field of energy, material science and applied nuclear physics in particular. However, due to the difficulty in creating significant quantities of pure nuclear isomers, this makes it largely unfeasible to pursue nuclear isomers as a practical energy storage medium, let alone a practical weapon.

It is also more important to focus this research away from the often low-integrity thinking of the military and instead peruse the more integral issue of understanding the nature of how inverted populations of excited alpha particles in the energy orbitals of nuclei in materials, which is also relevant in the study of Bose-Einstein condensates in general. Since alpha particles are bosons and the inverted populations of can be theoretically generated in a coherent avalanche in an induced series of nuclear reactions. This, in and of itself, has much wider applications in the fields of experimental, theoretical and applied physics and this is most likely what warrants investigation, rather than developing an EMP "super-weapon". 

References:

Ref 1- [Ref- M.S. Litz and G. Merkel (2004-12-00 [sic]). "Controlled extraction of energy from nuclear isomers"]

Ref 2 - https://www.aps.org/publications/apsnews/200706/backpage.cfm

Ref 3 - [Ref- R. Helmer and C. Reich, Decay of an isomeric state in 178Hf with K ≥ 16, Nuclear Physics A, 114 (1968), pp. 649–662.] 

Ref 4 - [Ref - S. Karamian, J. Carroll, J. Adam, E. Kulagin, and E. Shabalin, Production of long-lived hafnium isomers in reactor irradiations, High Energy Density Physics, 2 (2006), pp. 48–56.] 

Ref 5 - [Ref - C. B. Collins, N. C. Zoita, F. Davanloo, S. Emura, Y. Yoda, T. Uruga, B. Patterson, B. Schmitt, J. M. Pouvesle, I. I. Popescu, V. I. Kirischuk, and N. V. Strilchuk, Accelerated Decay of the 31-yr Isomer of Hf-178 Induced by Low-Energy Photons and Electrons, Laser Physics, 14 (2004), pp. 154–165.]