Radioisotope / Chemical Reactivity Microcalorimeters

ITI Company: The series CR-100 Microcalorimeters provide an accurate measurement of radioisotope heat release rates.

PRINCIPLE

The thermal gradient calorimeter transfers all the heat developed in a reaction to its surrounding heat sink at a constant temperature. The calorimeter walls thermoelectrically transduce sample heat release into an electrical signal, which is directly proportional to the energy release of the source. Transient as well as steady state energy releases may be measured.

FEATURES

• Whole body heat release measurements
• Microwatt to kilowatt sample output
• High sensitivities and repeatability
• Linear output
• Transient and steady state response
• Wide temperature range
• Simple "In-situ” recalibration
• No excitation required

CONSTRUCTION

The calorimeter walls are composed of a thin high temperature thermopile structure containing thousands of junctions. One set of junctions is in thermal contact with one wall surface, and the other set is in contact with the opposite surface. As heat flows through the walls a temperature difference is established between both sets of thermopile junctions, thus generating a voltage, which is directly proportional to the heat flow. The large number of thermopiles develop extreme sensitivity to minute heat flows.

Calorimeters are constructed in a range of designs incorporating large sample chambers for high heat fluxes (cover) or small sample chambers capable of measuring low heat releases.

CALIBRATION

Each calorimeter is calibrated at a base temperature of 70 F by a known, electrical heat source in thermal equilibrium with the system. The calibration constant is expressed in terms of wattage input versus millivolt output. A temperature correction curve is also supplied for use at elevated temperatures.

APPLICATIONS

The CR-100 Series calorimeters are designed to measure both microcaloric and megaocaloric heat release from pure or mixed radioisotopes. The magnitude of the generated signal is linearly proportional to the mean intensities of the sample.

Other applications include: physical, chemical and biological thermo-genesis, specific heats, heats of fusion and reaction.

MICROWATT DETERMINATIONS

To measure microwatt heat flow accurately, it is necessary to provide a stable, cooling environment. However, most constant temperature cooling baths exhibit small fluctuations, which may generate signals the same order of magnitude as those produced by the sample. To avoid this large noise to signal ratio, a temperature compensated enclosure has been developed. This double cup system contains both an active and passive chamber having matched sensitivities in opposition. Thus, spurious, external temperature fluctuations are compensated for, and only the heat release from the sample source is detected.