radio-frequency inductance coil (part of marginal oscillator)
Date: mid 20th-late 20th Century
Inventory Number: 2004-1-0408b
Classification: Nuclear Magnetic Resonance
Dimensions:12 x 17.8 x 3.8 cm (4 3/4 x 7 x 1 1/2 in.)
Accessories: variety of spare coils (in 2004-1-0408c); samples to be placed inside coil (2004-1-0410)
Description:
Thimble-sized copper coil shielded inside a narrow metallic case. The case's narrow top, bottom, and sides are made of aluminum, and the two larger faces are made of brass. Two larger (hamburger-sized) copper coils are sandwiched to the brass sides of the case and covered with a plastic insulator.
There is a hole in the top of the case large enough to admit a chemical sample The inner coil is linked via a short coaxial cable to the base unit (2004-1-0408a) of the marginal oscillator; the outer coils connect to a long twisted pair of ordinary wires (one green and one brown) which terminate in ordinary screw-down connectors. The latter would have been connected to a modulator (such as 2004-1-0409).
Signedunsigned
Inscribedon a scrap of graph paper taped around the end of the long wires someone has written: "GREEN WIRE ORANGE POST / BROWN WIRE YELLOW POST."
FunctionThis is the probe that would have been positioned between the poles of the large permanent magnet (2004-1-0407) during NMR experiments, with a sample (either a loose crystal or a powder inside a test tube -- see 2004-1-0410), placed inside its inner coil. The probe is part of an oscillating LC circuit that has a variable capacitor connected to a motor, slowly and periodically changing the circuit's oscillation frequency. This probe emits on that frequency, and the sample will absorb this radiation at the moment it coincides with its own resonance frequency given by the permanent magnet. This disturbs the circuit voltage in a way that can be detected by the main part of the marginal oscillator (2004-1-0407a).
ProvenanceUsed in Harvard's advanced undergraduate physics lab (Physics 191r) before coming to the collection.