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We had a short discussion yesterday about using nuclear isomers as batteries for spacecraft. The principle is that energy is stored as an excitation of the nucleus which can then release the energy as a gamma-photon. However angular momentum has to be conserved an this suppresses the decay strongly - making these states stable up to 10^35 longer than a typical decay.

The key is the triggering of the dacay wheras the triggering comsumes less energy than the decay provides. The x-ray based triggering of the gamma photon decay turned out to be quite controversial and needs significantly more scientific attention.

I think that there should be some references and traces of the discussions we had on this on the shared drive or wiki ... One other aspect: converting the omnidirectional gamma bursts into useful energy ....

High energy gamma rays are shown to be bent slightly by specialized lenses. The effect is likely due to pair-creation close to the atomic nuclei in the material.

Short GRBS are formed when neutron stars (in a binary system) slam into one another. On the other hand, long GRBs are a result of massive stars going supernova. Stars end their lives in violent explosions, typically leaving behind remnants like neutron stars.

Abstract: In the last 3000 yr, one significant and rapid increase in the concentration of 14C in tree rings was observed; it corresponds to a gamma-ray energy input of 7x10^24 erg at Earth within up to one year in AD 774/5 (Miyake et al. 2012).

A vast bubble of hot, rarefied gas has been revealed as a source of cosmic rays - the mysterious particles that batter the Earth continuously. The observation of the so-called superbubble, measuring more than 100 light-years across, was made using gamma rays collected by NASA's Fermi satellite and sheds light on the origin of cosmic rays in regions of massive-star formation.

News about the warp drive based on the original Alcubierre metric but with modified shape function. Focus of the reserach was on the interaction between warp bubble and cosmic particles. Result: People on board need shielding. People at the journey's destination might get roasted (by Gamma rays if you want to know).

Theorists expect that positronium, a sort of 'atom' consisting of an electron and an anti-electron, can be used to make a powerful gamma-ray laser. Scientists now report detailed calculations of the dynamics of a positronium BEC. This work is the first to account for effects of collisions between different positronium species.

essentially they made an experiment that does not prove or disprove anything -big deal-... what is the scientific value of "strongly disfavour"??? I also like the sentence "most models do not have exact predictions for the energy scale associated with this violation of Lorentz invariance" ... but if this is true WHAT IS THE POINT OF THE EXPERIMENT!!!! God, physics is in trouble ....

hum, null result experiments are not useless !!! there is always the hope of finding "something wrong", which would lead to a great discovery. For the state of theoretical physics (the "no exact predictions" quote), i totally agree that physics is in trouble... That's what happen when physicists don't care anymore about experiments...! All you can do now is drawing "nice"graph with upper bounds on some parameters of an all tunable weird theory !

Astronomers using ESA's Integral gamma-ray observatory have demonstrated beyond doubt that dead stars known as white dwarfs can reignite and explode as supernovae. The finding came after the unique signature of gamma rays from the radioactive elements created in one of these ex...

Using random nanostructuring highly absorptive materials were made which are of interest for photovoltaic or thermovoltaic applications

Yes! Black Metal... definitely something the ACT should look into

Black Metal...sounds like something for the ACT Magic Cards. But apart from that - is it possible to shift the PV type of absorption into gamma ray spectrum?

Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider... The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Now this is a good experiment... :)

True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.

In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP: http://goo.gl/Zz5gyC .