0198506961.pdf

116 Hyperfine structure and isotope shift

A magnet B magnet

D

Detector

Oven

Polarizer Interaction

region

Source Analyser

of atoms

C region

(a)

(d)

s

D

Oven

(b)

D

Oven

(c)

Detected

flux of

atoms

Flop-out

r.f.

r.f.

Fig. 6.14(a) The magnetic resonance technique in an atomic beam. Atoms emerge from an oven and travel through the
collimating slit ‘s’ to the detector. The deflection of atoms by the magnetic field gradient in the A and B regions depends on
MJ, as indicated. (b) Atoms that stay in the sameMJstate are refocused onto the detector when the A and B regions have
gradients in opposite directions. (c) Resonant interaction with radio-frequency radiation in the C region can change theMJ
quantum number,MJ=+^12 ↔MJ=−^12 , so that atoms no longer reach the detector. (In a real apparatus the C region may
be up to several metres long.) This is known as the flop-out arrangement and gives a signal as in (d). Further details are given
in the text and in Corney (2000).