31,923 reputation
341103
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 3 years, 8 months
seen 6 hours ago

Experimental nuclear and particle physicist. These days I'm teaching, but I've spent a lot of time on nucleon structure in fixed target electron scattering and neutrino oscillations using reactors and beam sources.


8h
comment Is it possible to produce images of pair production in home-made cloud chamber?
@DanS You can buy well sealed sources CoTS (in fact, there is more paperwork to get access to raw radio-isotopes than for the sealed sources). And the quantities needed are pretty low. That $\mu\mathrm{Ci}$ that Chris mentions is about $40000\,\mathrm{Bq}$ which is plenty for what the OP desires. The OP will want to store them in a source safe or something equivalent, but they pose no danger to someone outside the garage.
10h
revised Is it possible to produce images of pair production in home-made cloud chamber?
added 241 characters in body
11h
answered Is it possible to produce images of pair production in home-made cloud chamber?
15h
comment If atoms never “physically” touch each others, then how does matter-antimatter annihilation happen?
It can be (and is) simultaneously true that electrons scatter like point-particles (down to $10^{-18}\,\mathrm{m}$ experimental precision) and that their wave-function gives significant probability to distances on order of $10^{-10}\,\mathrm{m}$.
1d
comment Is it really okay to treat the Earth as stationary when doing free fall experiments?
The general procedure for answering this kind of question is: compute the size of the neglected effect to first order and compare to your uncertainty in actually performing such an experiment. If the neglected effect is comparable your uncertainty, then you should probably insist on it. If it is much smaller than your uncertainty then you can safely forget it. If you improve the precision of your measurement you may have reconsider such questions.
1d
comment How does radiation shielding using absorbing materials work?
There is a second advantage to light nuclei in stopping neutrons. The target-frame, kinetic-energy loss of the incident particle is largest when the projectile and target have the same mass. Neutrons hitting $^1\mathrm{H}$ nuclei dump energy faster than when they hit any other nucleus.
1d
comment If two events both have a spacetime interval of zero, can they both be said to be happening “now”?
It is the ability to know about events that propagates at no more than c.
1d
comment Why do hydraulic jumps form?
Jim, the geometry that you show is only one way to generate a hydraulic jump and my discussion is not specific to it. In your case the liquid far from the nozzle is slowed down by simple viscous drag, and it is then overtaken by a faster flow from the rear.
1d
comment Why don't we talk about angular momentum at all in fluid mechanics?
Not even remotely an expert in fluids, but it occurs to me that scale is important in all but the simplest cases and angular momentum implies that different parts of the volume are treated at different length scales (comparable to the distance from this neighborhood to the center around which $L$ is evaluated).
2d
comment Why is Silver-108 unstable
The short and unhelpful answer is "Given the decay modes it is simply that Palladium-108 and Cadmium-108 are both sufficiently lower energy states than the silver isotope." If I was trying to track this down, I'd note that Ag-108 is a odd-odd nucleus, so it pays a penalty in pairing energy.
2d
comment How much could one slow down aging using existing spacecraft?
"the gamma rays emitted by matter anti-matter annihilations in its reacor" The problem with simple matter-antimatter reactions (aside from the bit about getting enough anti-matter together) is that much of the energy is released in neutrinos and pions not photons. In principle you can steer about half the pions to your advantage, but the neutrinos are isotropic and you can't steer them.
2d
awarded  electromagnetic-radiation
2d
comment Why Light and Observers have different laws of physics
Excitations of quantum fields, like photons (and indeed every other fundamental particle), are the things we call particles. These things are what particle physics studies. Photons are particles. And photons travel at the speed of light. And this is OK and not at all a problem. Their path between two non-identical places takes zero proper time and finite time as measured by all observers and this is OK and not at all a problem.
2d
awarded  Good Answer
2d
comment How much could one slow down aging using existing spacecraft?
"and head away from the Earth at top speed" That all depends on your top speed and acceleration profile.
2d
answered Why do hydraulic jumps form?
Jul
21
comment How would an X-ray scanner identify a mirror?
An alternate way (that is a particle physicist's way) to look at it is in terms of the momentum transfer from elastically scattering an x-ray. Even at moderately shallow angle that momentum is more than enough to scatter the electron right off the atom, but that would make the event inelastic which means it is not "reflection" at all. To get reflective behavior you need quite shallow angles indeed.
Jul
21
awarded  Nice Answer
Jul
21
comment How to explain the weak force to a layman?
Wrong in every particular.
Jul
21
comment How does radiation shielding using absorbing materials work?
@Icarus The figure of merit is roughly the number of electrons per unit area in traversing the whole of the shielding. Dense materials allow you to have a high figure of merit in a short distance (which is very often the thing you want), but in other applications the best engineering deal may be found from maximizing electrons per unit area per dollar. That is often when water gets used. For instance, the on-site cooling ponds for spend fuel at reactor facilities are not compact, but they are cheap (and they provide passice cooling as well).