1. ＴＨＥ ＰＨＹＳＩＣＳ ＯＦ ＲＡＤＩＯＬＯＧＹ The Production and Properties of X Rays Part Two BME College Sherman sheen

2. Ratings of Diagnostic Tubes First, the focal spot must not be loaded beyond a certain power input. Second, the anode must not be loaded by successive exposures beyond a certain limit. Finally the housing must not be expected to dissipate its energy at rates beyond a certain value.

3. Example 2-1. Calculate the rise in temperature of a rotating anode after an exposure of 100 mA for 2 s at constant potential of 100 kV. Assume the target to have a mass of 500 g and the surface area of the bombarded region to be 30 cm 2 ; take the density of tungsten to be 19.3 g/cm 3 and specific heat 0.03 cal g -1 o C -1. Perform the calculations for two limiting conditions: (a) assume the heat instantly distributes itself over the whole of the anode and none is lost by heat transfer; (b) assume no heat escapes from the immediate area of the bombarded region but is concentrated to a depth of 1 mm under the bombarded area.

4. Energy input = 100×10 3 V×0.1A×2s =2×10 4 J Heat input to anode = 2×10 4 J = 2 ×10 4 /4.18 cal ≈5×10 3 cal For whole anode, thermal capacity = 500g×0.03 cal g -1 O C -1 =15 cal O C -1 (a) Rise in temperature = (b) Mass of bombarded volume = 30×0.1cm 3 ×19.3 g cm -3 = 58g Rise in temperature = 4.18J=1 calorie

5. the average tube current in mA, the peak voltage in kV, the exposure time in seconds HU: a heat unit HU = voltage (kV)×current (mA)×time (s) Energy deposited ≈ 0.75 HU joules In practical engineering: