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Dipartimento di Fisica e Scienze della Terra

Muon Spin Spectroscopy

This experimental technique , best suited for investigating magnets and superconductors, must be performed at large scale facilities, It was developed and established in Europe with a large contribution from the Parma group. Parma is still contributing to the development of the two European facilities, at ISIS and at the Paul Scherrer Institut, through European projects 

The Parma group hascontributed to the development of this technique from its early days. Prof. Cesare Bucci and a Parma team started of the adventure at CERN back in 1976, together with a Sweedish team lead by Prof. Erik Karlsson.  This collaboration contributed heavily to the early development of the ISIS facility. Nowadays there are strong links with all four facilities, although still stronger with the European ones.

 

The muon spin direction is detected post-mortem because ti is correlated to the direction of the emitted positron from the decay. The animations shows that more positrons are emitted towards the forward detector than towards the backward one.

Intense muon beams are produced fully spin polarised. Individual muons are implanted in materials ans stop in hundreds of picoseconds in the bulk.  The muon spin is used as a nanoscopic compass to measure internal magnetic fields that cause it to precess and relax. In this sense µSr is very similar to NMR, with the implanted muon spin as an interstitial anaogue of the nuclear spin. The muon spin direction however is detected via its correlation with the direction of emission of the positron from the muon beta decay. The animation shows the static spin (vanishing internal field)  of a population of implanted muons, The red lobe indicates the probability of positron emission vs. angle, and the bue trajectories show that the positron emission trajectories, more frequent in the direction of the muon spin. The two magenta scintillators count asymmetric rates, few backwards and many forward.

Want to watch a very simple introduction?

 

 

An introduction to the technique is available.  Wikipedia has an entry for Muon Spin Spectroscopy.

A nice point to start for some practical information is Muonsources.org

Every second year an Muon training course is held at ISIS. Do you want to wacth live comments from recent participants?