Cock Croft Walton accelerator

[crx]

Why in an linear accelerator, like the Cock Croft Walton accelerator, in which protons would strike a solid piece of boron wouldn't give up more energy than the input?
It seems to me that this situation have the least bremsstrahlung radiation loss and the highest cross section, for fusion interaction...
Thanks!

 

[Astronuc]

Why in an linear accelerator, like the Cock Croft Walton accelerator, in which protons would strike a solid piece of boron wouldn't give up more energy than the input?
It seems to me that this situation have the least bremsstrahlung radiation loss and the highest cross section, for fusion interaction...
Thanks!

Accelerators are notoriously inefficient for inducing collisions between particles. The p-¹¹B, like other fusion reactions, has an energy-dependent cross-section, and while one can optimize the accelerator energy to optimize that reaction, there are the issues of getting an interaction and obtaining the desired reaction upon achieving the desired interaction.

The probability of the proton colliding/interacting with a B nucleus is relatively small. The if the proton collides favorably with a B-nucleus, the probability that it will produce fusion is also relatively small, and much less than the probability that it would just scatter. This is the same problem for any fusion reaction.

Certainly the fact that the boron nuclei reside atoms, i.e. they are not fully ionized, means that one does not get the brehmsstrahlung losses of the electron/nuclei interactions. But then as the proton beam and any fusion reaction occurs, the solid B target would tend to vaporize.

At present, the two approaches to fusion are considered - magnetic confinement and inertial confinment. p-B is essentially impossible with current MC configurations due largely to brehmsstrahlung and other losses (e.g. cyclotron) and the fact the Z(B)=5, which means 5 free electrons for each B-nuclei.

Inertial confinement may be an alternative, but then there is still the complication of the B atom and its 5 electrons, and the complication of borane structures. If not borane, then the target would require some layer of B and H, and perhaps alternating layers, but that has to be at cryogenic conditions (another complication).

 

[Bob S]

When protons from a Cockroft-Walton strike a boron target, there is no bremsstrahlung. Only electrons produce bremsstrahlung at low energies. Protons striking a boron target are slowed down by ionization of the atoms (dE/dx). Occasionally the proton will react with a boron^11 nucleus and produce 3 alpha particles (helium nuclei). This reaction occurs at about 675 keV (proton incident energy). The reaction is exothermic, releasing a few MeV of kinetic energy. The isotopic abundance of boron^11 is about 80%.

The proton-boron^11 reaction is actually a (p,alpha) reaction, leaving a beryllium^8 nucleus which rapidly decays into two more alphas.