This week our topics are where people who read this blog are located around the world and then a little bit about LIGO and tutorials and data availability so that you can do your own analysis and finally end up with some more comments about using nuclear isomers in energy storage systems.
So, this website's host, as do most hosts, collects data on where people are located around the world. In the chart below, you can see, based on yesterday's 24 hour period, where the viewers of this blog were located. So these are people who actually click on the website or some blog post that comes up in an internet search. What were people thinking or searching for in Vietnam or any other country where this website or one of hundreds of posted articles came up in their internet search? The numbers of viewers and the countries changes on a daily basis. I remember one time when there were over 2000 hits from Israel alone. Anyway, to all you readers, I hope you found what you were looking for!
|Where around the world are the viewers of this website located? (Source: Palmia Observatory)|
Finally, school is back in session and we can look forward to many more interesting physics seminars and colloquia. This morning it was at CSULB where Dr. Jonah Kanner spoke on "The Explosive Astrophysics of Gravitational Waves." He was a very good speaker and we learned a lot about the history of LIGO and some of the interesting discoveries and the impact of those discoveries on the future of astrophysics.
|Dr. Jonah Kanner, Caltech, speaks about LIGO discoveries at CSULB (Source: Palmia Observatory)|
During lunch I asked Dr. Kanner about his groups' ongoing effort to detect gravity waves from core collapse supernovae, called Type II Supernovae, where a massive star, not part of a binary system like Type 1a systems, has exhausted all of its fusible fuel, up to iron, and cannot support itself from the ultimate gravitational collapse. Initially, I had assumed that the collapse would be entirely symmetrical and no gravitational waves would be produced. But the real situation is a little different in that the collapse sort of has to start at one point and then proceed until the whole star is involved in the collapse. My guess is that a symmetric collapse would not be consistent with special relativity in that the star is so big that no signal could ensure that the whole stellar surface would begin collapse at the same time.
Anyway, he said that his group is indeed looking for such events and that the current sensitivity of LIGO should be able to detect the collapse, but that the supernova would have to be quite close to us, probably in our own Milky Way galaxy, and if that is the case there is only about one Type II collapse per century. Hmm, I guess we will probably have to wait a while. If we were able to eventually detect one such collapse, we would also hope that the distance to us is far enough away that we would not also be wiped out by the event. Yep, it seems we would want sort of a Goldilocks location! Thank you for all of the discussion, Dr. Kanner!
Dr. Kanner also mentioned a website, that he is much involved in maintaining, where you can download the LIGO data and find papers and tutorials and software tools for performing your own analysis of LIGO data. I've tried some of the tutorials and you definitely get a better understanding of the whole detection and analysis of gravitational waves. So, check it out at: https://www.gw-openscience.org/about/
|Gravitational Wave Open Science webpage (Source: https://www.gw-openscience.org/about/)|
For the final segment of the blog post let's go back and consider again the crazy sounding idea of using nuclear isomers, in this case the element Hafnium, to make a very, very energy dense material for energy storage. Recall that in the recent post of September 16, 2019, we considered the topic of nuclear isomers. Remember that a nuclear isomer is an element that can support higher energy levels in its nucleus that do not decay quickly back to their ground state. For Hafnium, the excited state of the nucleus is stable with a half life of 31 years. So you can pump up the state of the nucleus with 2.45 MeV gamma rays and then control the rate at which the nucleus transitions back to the ground state at which time you would recover the energy in the form of 2.45 MeV gamma rays. You get out one gamma ray for each nucleus. So, it turns out that in theoretical terms, just one gram of Hafnium, that is just one half the weight of a dime coin, you could store enough energy to propel an electric car over 600 miles. Pretty neat! But the question left open at that last post was how easy is it to artificially generate 2.45 MeV gamma rays to charge up the Hafnium?
Now as astronomer wannabes, we know that real astronomers identify cosmically produced gamma rays and that by using gamma ray telescopes, like the Fermi Gamma Ray Telescope, we can learn a lot about the astrophysical processes involved. The chart below summarizes some of the astrophysical processes that generate gamma rays. Other Earthbound processes, like the decay of radioactive materials, can also generate gamma rays.
|Astrophysical sources of gamma rays (Source: www.gsfc.nasa.gov)|
Ok, so gamma rays are produced in various processes, but if we want to use them to charge a nuclear isomer energy storage system, how to we produce them artificially? A little bit of internet searching shows that Sandia Laboratories operates a gamma ray source for testing of radiation hardened electronics and systems. Check out the schematic drawing of the Hermes III generator below and compare it to the size of the human figures standing in front. This generator produces short pulses of high energy photons. The Hermes III operates with a peak DC voltage of 20 MV and each output pulse is rated 370 kJoules.
|Drawing of Hermes III Gamma Ray Generator (Source: G. Zawadzkas, Sandia Hermes III Guide for Users, 1989)|
The energy spectrum of Hermes III, below, indicates that gamma ray photons in the 2.45 MeV range are produced and could be absorbed by the Hafnium storage element. Each pulse is very short and is generated by very fast, high current discharge from a combination of capacitors and Marx generators.
Hmm, based on this summary, although the storage potential is incredible, the potential of the whole charging system does not seem to be feasible. There are a lot of unknowns, but it is interesting what you can accomplish with the back of an envelope.
|Summary of energy storage potential and difficulty of charging the system (Source: Palmia Observatory)|
It turns out that smaller gamma ray generators are becoming available. This recent article shows one promising technique of using short laser pulses to generator gamma rays. But for the whole energy storage scenario, for electric vehicle applications, it will be necessary to consider the efficiency of the gamma ray generator in the calculations too. I couldn't find any details about generation efficiency or gamma ray spectrum. The only gamma rays we are looking for have energy of 2.45 MeV and all the others will represent a loss in efficiency.
|New generations of gamma ray generators might be part of the answer (Source: physics.aps.org)|