NIR Environmental Vegetation Monitoring For Ecosystems and Precision Agriculture

Using Unmanned Aerial Vehicles (UAVs or "Drones") we can do scanning in the visual spectrum of large areas in the surrounding environment without the high comparative cost of using manned vehicles such as helicopters or planes or expensive space-based monitoring infrastructure. UAVs allow for fast, local and energy efficient surveillance for environmental monitoring.

In the case of ecosystem analysis, it is key to have active monitoring of plant health and distribution in order to gauge the health of an ecosystem and the support potential for the various species that depend on healthy, diverse and broad growth of vegetation.

Applications of UAVs in environmental protection, forestry and plant agriculture agriculture, forestry and environmental protection include:

• Local Ecosystem Monitoring
• High Frequency Vegetation Growth Analysis
• Monitoring of Agricultural Impact on Environment
• Empiracle Measurement of Unidentified Vegetation Die-off (UVD)
• Monitoring of Agricultural Impact on Environment
• Monitoring Health of Agricultural Plant Crops
• Detection of Water/Soil Stress on Plants
• Early Detection of Disease and Pest impact on Plants
• Monitoring Pollution and Spill Impacts on Plants

UAV Drones can provide a fast, cheap, efficient (both in energy and in time) and yet very effective way to perform environmental diagnostics and information retrieval without depending on more complex infrastructure such as satellite and manned aircraft.

UAVs can be used in crop monitoring and within what is called "precision agriculture", which works in order to optimize plantation management and assess more accurately the optimum density planting, in addition to making decisions regarding the use of fertilizers, irrigation frequency and other possibilities, such as to predict more accurately the crop production and allowing for sustainable use of the limited resources of water, soil and land available for agriculture.

The UAV can perform scheduled flights to carry out surveys of areas of vegetation (an indicated use, for example, for the of monitoring vulnerable ecosystems), and compare the spectral data taken from sensor cameras with available visual tomography, provided by accurate and updated maps, to detect and deduce root causes of detected instances of stress in the areas of plant growth.

In the case of the visual tomography we can update existing maps with relative ease by simply referencing 2D aerial or satellite survey maps with the measured heights at certain locations in order to predict water flow and effects of soil creeping and leeching. Several map providers and simulation tools exist for modelling water flows in an environment, all of which is a discussion for another time.

However, with the sensor information we need to think a little more abstractly and find key variables which indicate the state of plant health.

Near-Infrared (NIR) and Plant Health

Near-Infrared, NIR is a small portion of the much larger region called infrared (IR), located between the visible and microwave portions of the electromagnetic (EM) spectrum.

NIR makes up the part of IR closest in wavelength to visible light and occupies the wavelengths between about 700 nanometers and 1500 nanometers (0.7 µm – 1.5 µm). NIR is not to be confused with thermal infrared, which is on the extreme other end of the infrared spectrum and measures radiant (emitted) heat.

In most commercially available cameras, most of which based on silicon semiconductor Charged-Coupled Devices (CCD) detectors, absorb visible light from about 390nm until about 1200 nm,

NIR radiation can be blocked by special glass or plastic windows designed to ensure natural colour images are produced without undesired shifts towards the extremes of  the red or blue parts of the EM spectrum, the shift depending on the nature of the semiconductor CCD sensor. So-called "hot mirrors" are used to negate the influence of the NIR on camera images which would otherwise induce a reddening effect.

A replacement of the hot mirror by a neutral glass or plastic filter can therefore be used for infrared photography. As a consequence of this a significant increase of commercial camera modularity can be achieved by this special optical set up and users can decide whether they want to generate natural colour (true colour) or near infrared (NIR) images, depending on the external lens filter sets applied. This allows the camera to detect the infrared light necessary for producing NDVI images.

Using multispectral and in particular near-infrared (NIR) surface reflectance cameras, the various monitoring parameters for vegatation can be gained easily, sometimes in a single flight sweep over an area, to generate quality indicators of plant health.

When studying the vegetation reflectance spectrum in detail, The near-infrared spectrum itself allows a relatively high detailed probe of the health of plants at a cellular level.

In photosynthesis, the chloroplasts in plant cells take absorb light energy sing chlorophyll which aborbes photons and creates and electronic channel to fix carbon and water to form glucose, the basis of carbohydrates and hence food for the plant.

The forms of chlorophyll in plants absorb light at specific frequencies, typically, in the red and blue light. The green portion of light is effectively reflected, this makes the plant was seen in the range of green in the visible spectrum.

This information is also important for developing lighting systems, for indoor agriculture for example, of which light frequencies are the most efficient for growing plants as exploited by so-called "grow lights" for indoor plant growth. This is another topic in precision agriculture which can be explored further.

In any case, Chlorophyll pigments A and B absorbs most energy at about 450 nm (blue) and 650 nm (red) respectively, with significant overlap between the 2 as shown in the diagram above. Other pigments absorb more visible wavelengths, but the most absorption occurs in the red and blue portions of the spectrum. This absorption removes these colors from the amount of light that is transmitted and reflected, causing the predominant visible color that reaches our eyes as green. This is the reason healthy vegetation appears as a dark green.

Unhealthy vegetation, on the other hand, will have less chlorophyll and thus will appear brighter (visibly) since less is absorbed and more is reflected to our eyes. This increase in red reflectance along with the green is what causes a general yellow appearance of unhealthy plants.

Plants reflect strongly in the NIR however not because of chlorophyll but because of a spongy layer of lignin found on the bottom surface of the leaf, but not strongly in the red.

IR reflectance is advantageous to plants, as it is reflects electromagnetic energy that the plant cannot use and moreover would probably damage the plant tissues, especially during high levels of sunshine where the IR radiation would heat the plant tissues and slow down or damage cellular processes.

Plant stress causes an increase in visible light transmission in the green as the chlorophyll decays and the much more obvious effect of an increase in the reflectance of red, this is why the leaves of deciduous trees turn orange and red when they die-off in the autumn.

The near-infrared plateau (NIR, 700 nm - 1100 nm), is a region where biochemical absorptions are limited to the compounds typically found in dry leaves, primarily cellulose, lignin and other structural carbohydrates.

However, and this is critical, NIR reflection in this region is also affected by multiple scattering of photons within the leaf, related to the internal cellular structure, fraction of air spaces in the xylem vessels of the plant, and most important as a general indicator, the air-water interfaces that refract light within leaves. The reflectance and transmittance in the middle-infrared also termed the shortwave-infrared (SWIR, 1100 nm - 2500 nm) is also a region of strong absorption, primarily by water in green leaves. The primary and secondary absorptions of water in leaf reflectance are greatest in spectral bands centered at 1450, 1940, and 2500 nm, with important secondary absorptions at 980 nm, and 1240 nm (Carter, 1991). These are the bands which create the primary NIR reflectance in healthy plants.


The cohesion-adhesion model of water transport in vascular plant tissue describes how hydrogen bonding in water to explain many key components of fluid movement through the plant's xylem and other vessels.

Within a vessel, water molecules hydrogen bond not only to each other, but also to the cellulose chain itself which comprises the wall of plant cells. This creates a capillary tube which allows for capillary action to occur since the vessel is relatively small. This mechanism allows plants to pull water up into their roots. Furthermore,hydrogen bonding can create a long chain of water molecules which can overcome the force of gravity and travel up to the high altitudes of leaves.

Cohesion-adhesion model of water transport in cellulose-based plant vascular tissue 

Therefore the existing interface between the water in plants and the cellulose chains is a key indicator that a plant is #1 not under dehydration and #2 has structural integrity. If any one of these factors are removed, this indicates poor plant health and this is detected by the reflectance in the NIR.

Soil, on the other hand, reflects both NIR and Red . However, when a plant becomes dehydrated or sickly, the spongy layer collapses and the lack of water itself and its interfacing with the plant all contributes to ceasing to reflect as much NIR light. Thus, a combination (approximated as linear) of the NIR reflectivity and red reflectivity should provide excellent contrast between plants and soil and between healthy plants and sick plants.

The Normalized Difference Vegetation Index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing measurements, such as in aerial and space based surveys, and assess whether the target being observed contains live green vegetation or not.

It turns out which combination is not particularly important, but the NDVI index of (NIR-red)/(NIR+red) does happen to be particularly effective at normalizing for different irradiation conditions.

Hence, plants in a given area that are adequately hydrated show high absorbance of NIR light in this absorbance band (and low reflectance), whereas those subject to drying shows greater reflectance in this band.

Specifically, NDVI was developed by a NASA scientist Dr. Compton Tucker in a 1977 paper
entitled, “Red and Photograghic Infrared Linear Combinations for Monitoring Vegetation.”

Tucker examined 18 different combinations of NIR (Landsat MSS 7 800-1100 nm), red (Landsat MSS 5 600-700 nm), and green (Landsat MSS 4 500-600 nm) and compared these results with the density of both wet and dry biomass to in an attempt determine which combination correlated best.

His findings were that

• NIR/red, 
• SQRT(NIR/red), 
• NIR-red,
• (NIR-red)/(NIR+red), 
• SQRT((NIR-red)/(NIR+red)+0.5) 

were all very similar indicators for estimating the density of photosynthetically active biomass.

Using this a threshold level for near IR reflectance from healthy plants can be deduced, allows for a way to label plant health remotely.

Using a near-infrared spectral camera, a drone can easily monitor vegetation for signs of sickness and determine the health of both agricultural crops and the plants at the base of a foodchain in ecosystems to monitor an environment which is in a constant state of change. This is of utmost importance in parts of the world which are suffering from environmental destruction, both natural and increasingly induced by humans. The surveillance of vegetation in endangered areas is of very high importance and new methods need to be introduced to ensure the survival of the most vulnerable biomes on earth, namely the tropical, temperate and boreal forests.

Using the concept of a stereoscopic split-screen camera lens we can combine a Near-IR Pass Filter in conjunction with a clear visible light window to create a basic multi-spectral camera system, as described in the schematic below:

A common NIR Filter is the "Congo Blue" gel filter which passes NIR, which is detected as red by a CCD sensor, and does not allow green to pass.

"Congo Blue" filter for one window of the multi-spectral camera

Such split screen lenses can be included on UAV cameras as well as on high-definition portable camera technologies, i.e. smartphones, which can be light enough (and which are now so ubiquitous) that they can be used as diagnostic instruments for ecosystem monitoring.

Carbon-fiber drone fitted with split-screen camera

Using these techniques, a portable UAV with a camera fitted with a dual near-infrared + true-color lens fitting to fly over such an environment that lies close to a town area to monitor vegetation health.



The experimental data can then be fed back via Wifi feed to a smartphone or a computer, from which the data can be analysed using computer software to retrieve vegetation information from surveillance drone by calculating the vegetation index and overlaying the indices pixel by pixel on the composite image.

Developing this further we could also make a live NIR-camera feed application for use on portable computer, i.e. tablets and smartphone, technology which can allow for fast and easy remote diagnostics of plant health.

The stereoscopic split-screen lens mount is universally adaptable for use in smartphones, so for local use, or for active viewing on a height say, the diagnostic can be done entirely on portable computer infrastructure itself. It is hoped that such apps can become more widespread and applicable for simple to install multi-spectral camera attachments.

All of this could save energy and finance for performing the relatively simple step of diagnosis of plant health and help spur-on the the real work of finding solutions to remedy the problem of plant disease, dehydration and malnutrition in an environment.

Notes:

#1 Interesting still is the fact that Nitrogen (N-H bonds), which form have a first harmonic overtone at 1510 nm and a series of combination bands at 1980, 2060, and 2180 nm (Wessman, 1990). The secondary structure of any protein involves interactions (mainly hydrogen bonds) between neighboring polypeptide backbones which contain Nitrogen-Hydrogen bonded pairs and oxygen atoms.

Since both N and O are strongly electronegative, the hydrogen atoms bonded to nitrogen in one polypeptide backbone can hydrogen bond to the oxygen atoms in another chain and visa-versa. Though they are relatively weak,these bonds offer great stability to secondary protein structure because they repeat a great number of times.

Hence a non-linear vegetation index with increasing factors could be in principle be formulated with the addition of detecting nitrogen deficiency from a distance in soils.

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.]