(a) A dental X-ray tube has a tungsten target ( ), is run at with a tube current of ,…

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Life at Thermal Energy, Ch Images from attenuation and from decay

Problem

(a) A dental X-ray tube has a tungsten target (

Z_{\rm at} = 74

), is run at

V_{\rm t} = 70\,\mathrm{kV}

with a tube current of

7\,\mathrm{mA}

, and fires for an exposure time of

0.10\,\mathrm{s}

. Using the empirical efficiency

10^{-9}Z_{\rm at}V_{\rm t}

(with

V_{\rm t}

in volts), estimate the X-ray power output and the total X-ray energy emitted in one exposure. (b) In a bone scan, an organ retains

15\%

of an injected

400\,\mathrm{MBq}

dose of technetium-99m, which emits a

140\,\mathrm{keV}

gamma photon in

89\%

of decays. The gamma camera's parallel-hole collimator accepts a fraction

1.0\times10^{-4}

of an isotropic emission, and the photons must cross

6.0\,\mathrm{cm}

of overlying tissue with

\mu = 0.154\,\mathrm{cm^{-1}}

140\,\mathrm{keV}

. Estimate the detected count rate and the time needed to collect

5.0\times10^{5}

counts.

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