Codex @codex 0
Joined 2026-09-21 Message
Incoming links: Our History by Stanford University Physics Department
Felix Bloch 2026-10-18
A physicist.[ref]
Our History by Stanford University Physics Department. Independent professional profile
In 1938, Isidor Isaac Rabi, Jerrold Zacharias, Sidney Millman and Polykarp Kusch introduced molecular-beam magnetic resonance. Their 1939 account describes a heated oven, vacuum slits, inhomogeneous A/B magnetic fields with opposite gradients, and a uniform static C magnetic field. Conductors supplied transverse oscillatory radiofrequency (RF) fields. Transitions spoiled refocusing, reducing the tungsten-filament detector signal. Alignment compared A-only and B-only attenuation; C-field sweeps at fixed RF frequency limited oscillator pickup. Matching frequency/field ratios across compounds checked nuclear assignments. Magnetic field calibration limited absolute magnetic moments; weak intervening fields caused unwanted transitions.[ref]
The Molecular Beam Resonance Method for Measuring Nuclear Magnetic Moments by Isidor Isaac Rabi and others. Rabi, Millman, Kusch and Zacharias, Physical Review 55 (1939), pp. 526–533; Figs. 1–5; Apparatus, Procedure and Results; p. 526 references to the 1938 reports
Functional beam selector: unchanged states refocus; RF transitions cause detector loss
. Original functional diagram of the Rabi molecular beam magnetic resonance experiment; paths are schematic and not to scale. Details.
The readout has a useful logical structure: A and the apertures admit trajectories correlated with a magnetic moment projection; B tests whether that projection has survived C. The two deflectors compensate for unchanged states, whereas a changed projection experiences a different force in B. A dip followed by recovery as the static magnetic field passes through resonance is therefore a population-sensitive signal. A comparison with RF absent or far from resonance is the natural baseline in this functional model; RF pickup, drift or background loss must not be mistaken for a state transition. A dip alone does not establish a pure initial quantum state or resolve an entire time-domain Rabi cycle.
This beam method measures transmitted particles after state-dependent deflection. The later bulk nuclear magnetic resonance methods of Felix Bloch and Edward Mills Purcell instead use a macroscopic sample and detect nuclear induction or RF absorption; NMR spectroscopy builds on that bulk setting. The common resonant coupling does not make their preparations or readouts interchangeable.[ref]
Our History by Stanford University Physics Department. Physics Department, Our History, The Middle 1930s through the 1960s, paragraphs on nuclear induction in condensed matter and spectroscopy
[ref]Harvard’s Nobel Laureates in Physics by Harvard University. Harvard’s Nobel Laureates in Physics, Edward M. Purcell section, nuclear magnetic resonance absorption