What is a key characteristic required for the target of a therapy x-ray tube?

The key characteristic required for the target of a therapy x-ray tube is that it has a high atomic number (Z) and a high melting point. The high atomic number is crucial because materials with high Z numbers, such as tungsten, are more efficient at producing x-rays when they are bombarded with high-energy electrons. The efficiency of x-ray production is directly related to the atomic number of the target material, as higher Z materials tend to produce more energetic and higher-quality radiation.

The high melting point is essential because the x-ray tube generates significant heat during operation due to the energy transfer from the electrons to the target material. If the target material has a low melting point, it may not withstand the thermal stress and could melt or degrade, leading to failures and ineffective treatment. Therefore, the combination of high Z and high melting point ensures both optimal x-ray production and durability of the target under continuous use conditions in a therapeutic setting.