X-Ray hobby in the 60s
last update 4/28/2017
In my x-ray experiments of the 1960's, I used 5" x 7" sheets of no-screem medical x-ray film, coated with emulsion on both sides. The film sheet was held in a light-tight cardboard cassette (without a fluorescent intensifying screen), and placed perpendicular to the x-ray beam source, against the x-rayed object, with the object between film and x-ray source. The x-ray film is tray developed and fixed in a darkroom similar to black-and-white film processing, but with chemical solutions particular to x-ray film.
Each tube is 21" long with a 7" diameter bulb. In each tube extending from the right end is spiral wire filament contained within a cup-shaped cathode which serves to focus electrons "boiled" off the hot filament onto a small spot on the nearby anode. From the left end of each tube is seen extending a metal stem with a block of tungsten at the end - the anode, its bulk intended to absorb the heat generated by electron impacts, and its
angled flat surface intended to direct x-rays generated by the electron impacts out the side of the tube.
A high positive voltage is applied to the anode relative to the cathode to cause the electrons emitted by the hot cathode to accelerate towards the anode and impact on it - the higher the voltage, the stronger the impacts and the more penetrating the generated x-rays.
The center pole used to have an insulated cross-member which held three metal pulley-like retractors with wires connecting to the posts, and flexible cloth covered wires wound onto the spring-loaded retractors which could be pulled out and connected directly to the Coolidge tube terminals.
There are two displays: a voltmeter displaying the AC input supply voltage when the circuit breaker is on, and a DC milli-ammeter displaying the average current passing through the connected Coolidge tube from cathode to anode (this is not the filament current, but is the current of electrons from the cathode impacting on the anode).
The two meters have radium dots on their scales to make them easy to see in near darkness, but their glow-lifetime had expired by the time I got the unit.
There are two connectors on the housing to the sides of the meters - the left connector is for the AC power connection; the right connector accepts a cable from a remote control for switching on/off the HV while the filament current is always applied.
This ugly looking box had an important function: it let me stand away from from the transformer and un-insulated HV wiring when switching transformer HV power momentarily, and away from the area when leaving the HV power turned on.
The left image is an enlargement of an x-ray of a small klystron tube. I don't remember the tube type - it was about 3-4 inches tall, black metal case, octal socket, with adjuster brackets along the sides.
The right image is typical of many exposure experiments - this one is a contact print of a 5" x 7" x-ray at 50 KV at 1 ma for 5 seconds, at 24" inches from anode, through an aluminum filter 2.63 mm thick, developed for 2 minutes at 80 deg F., of an aluminum ring .86mm thick, an aluminum L shape .86 mm thick, an aluminum bracket 1.03 mm thick, and a small lead ring. These were taken about 1966.
This is a mechanical rectifier - the plate on motor identifies an "alternating current motor", manufactured by the Holtzer-Cabot Elec. Co, Boston & Chicago. The motor is half-synchronous, turning the solid mica disk with two attached metal connector strips at 1800 rpm. The end of each strip extends just beyond the edge of the disk as seen in the photos, the extensions 90 degrees apart. Clamped to the motor mount just behind the rotating disk is a stationary square of insulator (looks like Bakelite) with a small wire terminal with wire brush at each corner. When the disk rotates, adjacent pairs of terminals are connected by the strips, first the two vertical pairs, then the two horizontal pairs, each revolution. By separately connecting the opposite corners together, we have the essentials of a half-wave rectifier for the HV alternating current - one set of connected corners to the Coolidge tube anode and the other set connected to the HV supply wire for the anode.