Fabio wrote ...

Hi stella!

This is the development table i used for TMAX400 with D76 developer (i'm not sure about HP5, but should be close)


according to this table, for example, if you would develop the film at his standard sensitivity (400 ISO) and the temperature of the developer liquid is 22 degrees celsius, you must leave the film inside the baths for 8minutes and 30seconds and if you need an extreme overdeveloping at 3200 ISO the temperature of the bath must be lowered to 20C° and the developing time must be increased to 15 minutes.
please note that the time difference between 400 and 800 ISO is negligible so the table show exactly the same development times for both!!!

For a better repetability, the film must be removed from the development bath and placed in the stopper bath as quickly as possible, there is no maximum time or temperature constraints neither for the stopper nor for the fixer baths so you could almost forget the film inside.

to select the right exposure time for first times you can mask the film with a lead sheet and gradually remove it during exposure (of course, the machine should be turned off before you enter in the room and both the subject, the film and the tube must remain still because multiple exposures are needed!!!), note that to match the sensitivity chart of the film, the exposure time between each test should be doubled.

I think that almost all of the informations are given, now we just wait for your first results!


Ciao!
Fabio.

Fabio wrote ...

Hi Stella!

Hi Fabio, yes I have some sets of feeler gauges, but wouldn't expect the soft X-rays in which I am interested to go through any of them in any measurable amount of time.

do you considered the possibility of build a ladder with kitchen alluminium foil?
maybe you cannot use the glue for fix them together so the calibrated absorber cannot resist for a long time but... who cares?

another possibility can be a ladder made with scotch tape, it surely not pose any gluing problem (but of course the alluminum is a standard material for calibrated shields and the scotch tape obviously not!)

The X-ray world below 10keV is where the frontier is now, and I am presently interested in demountable tubes that might go below 6keV , which is my current limit of detection with Ne/Kr proportional counters

you can play with just few hundreds of electronvolt if you build the x-ray tube inside a bell jar and of course you insert the detector inside the same jar; with this configuration the danger of ionizing radiation will become lowered to zero and just the danger of implosion will remain.

I have some PIN photodiodes which can go below that with high quantum efficiency (after removing the lens) but have a lot of trouble with the high-Z electrometer inputs for them, which I am beginning to fear may be beyond my small ability and budget.

electrometer-grade operational amplifier aren't so expensive on the market, but working with teraohm may be problematic.

i suggest you to build at least the first amplifier stage directly under the photodiode, this amplifier should be made inside a grounded metal case with high quality components and without the printed circuit board, just keep all terminals short, build the circuit in air using a low voltage solder iron and all ESD precautions, then wash it twice with acetone, dry it with a hairdryer and never touch it anymore to avoid contaminations.

the other stages can be either made inside of the same shielding box (before washing) or connected with a shielded cable.

for the last possibility you can consider a modified smoke detector (ionization chamber type), his chamber have a really high impedence so there is an electrometer grade amplifier inside.