$X$-rays cannot be deflected by means of an ordinary grating due to

The patient is asked to drink $BaSO_4$ for examining the stomach by $X$-rays because $X$-rays are

Characteristic $X$-rays:

$\Delta \lambda$ is the difference between the wavelength of the $K_\alpha$ line and the minimum wavelength of the continuous $X$-ray spectrum when the $X$-ray tube is operated at a voltage $V$. If the operating voltage is changed to $V / 3$,then the above difference is $\Delta \lambda^{\prime}$. Then:

The minimum frequency $\nu$ of continuous $X$-rays is related to the applied potential difference $V$ as

$X$-rays region lies between