Bomab

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BOMAB Phantom

The BOttle MAnikin ABsober phantom was developed by Bush in 1949 (Bush 1949) and has since been accepted in North America, if not worldwide, as the industry standard (ANSI 1995) for calibrating a whole body counter.

The phantom consists of 10 polyethylene bottles that either cylinders or elliptical cylinders that represent the head, neck chest, abdomen, thighs, calves, and arms. Each section is filled with a radioactive solution, in water, that has the amount of radioactivity proportional to the volume of each section. This simulates a homogeneous distribution of material throughout the body. The solution will also be acidified and contain stable element carrier so that the radioactivity does not plate out on the container walls.

The phantom, which contains a known amount of radioactivity can be used to calibrate the whole body counter by relating the observed response to the known amount of radioactivity. As different radioactive materials emit different energies of gamma photons, the calibration has to be repeated to cover the expected energy range: usually 120 to 2,000 keV.

Typically the following radioactive isotopes are used for this purpose: ²⁴Na, ⁵⁷Co, ⁶⁰Co, ⁸⁸Y, ¹³⁷Cs. Others can be used.

Although the phantom was designed to be used lying down, it can be made to sit or stand.

Other Uses

Performance testing: The BOMAB phantom can also be used to test facilities calibrations by supplying a phantom(s) with an unknown about of material in it. Performance testing like this is mandatory in some countries (e.g., Canada).

Geometry Dependence: Phantoms of different sizes can be used to estimate the effect of size on the result, or look at how localisation of radioactivity in the body can affect the result.

Background: An water filled (or filled with the equivalent amount of potassium - 140 g for a 70 kg man) can be measured to estimate the background in a whole body counter. Typically background measurements in this case tend to underestimate the background when a real, uncontaminated person is measured.

External References

Bush F. The integral dose received from a uniformly distributed radioactive isotope. British J Radiol. 22:96-102; 1949.

Health Physics Society. Specifications for the Bottle Manikin Absorber Phantom. An American National Standard. New York: American National Standards Institute; ANSI/HPS N13.35; 1995.