FAQ - Electronics, Portability and Power

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Richard Hull
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FAQ - Electronics, Portability and Power

Post by Richard Hull » Sat Apr 11, 2015 8:21 pm

In the area of radiation detection, electronics is the king of this effort. Most detection schemes involve some form of detection device...(Ion chamber, Geiger tube, Photomultiplier, fission chamber, BF3 or 3He tube, etc.). In the early portable instruments, batteries were of the A or B type A being low voltage batteries of 1.5 to 6 volts for vacuum tube filaments. B batteries ranged from a low of 22.5 volts up to ~510 volts. (note* the most common B bateries ever used in nuclear instruments were either two 45 volt or two 67.5 volt batteries) B batteries tended to last a long time compared to A batteries and were made as small as possible to answer the voltage demands. Still, they were large, heavy and somewhat expensive. As vacuum tubes disappeared from modern detection gear in the 1960's due to transistor technology, the need for B batteries died out. To replace the need for B batteries, transitor oscillator, high voltage supplies used the A batteries to create the high voltage needed for the bulk of portable nuclear instrumentation. This created a need for more energy in the A batteries, but larger A battery size was still much smaller than the old B batteries in volume. Thus, portable instruments got a lot smaller and lighter in weight and were often one half the weight of their predecessors.

A few new solid state radiation sensors and detectors allow for even smaller instrumentation than found in earlier instruments. Unfortunately, such detectors usually place the instruments using them in a price range where the amateur can't afford them. But, like all such things, prices will come down as they always do on cutting edge technology. The amateur instrument maker is left with the old standbys: surplus GM tubes, PMTs and home made ion chambers. A few work with PIN diodes and other common solid state devices as detectors, but the detection levels of these are far below what might be called low level detection.

As time went on, intergrated circuits and micro controllers came into use within portable nuclear instrumentation. The common old needle type meters gave way to far more accurate and complex readouts and displays that could be taken into the field or taken away from the mains to wander about a nuclear facility. Today, you can have a virtual laboratory grade instrument in the palm of your hand, if you have the cash outlay to spend. Portability, coupled with versatility, still costs.

For fusor use, a portable instrument just is not needed. However, often, a fine, suitable old mains based instrument can be obtained at surplus far cheaper than a modern instrument of the same functionality. This is especially true of the neutron counter. However, when testing for x-ray radiation leaks, a portable GM counter or, better still, a portable ion chamber, would be very desirable. Once again, some fine portable surplus examples of these types are rather easily found on e-bay or on-line. A portable GM counter or scintillation counter will allow a lot of outside field survey work. Whether you are looking for collectable old fiestaware at fleamarkets or collecting Uranium/Thorium ores for a mineral collection or just collecting background data, day to day, a portable radiation detection instrument is a good thing to have on hand.

For those bold enough and capable to design and build their own portable electronics, decisions have to be made. Few among us have such skills. However, there are a number of ready to go GM counter kits out there on line. So, if you can solder and don't have a clue about the electronics of nuclear instrumentation, you can get a kit.

Whether you get a kit or custom make and design your own portable gear there is the issue of battery power. 99% of all portable instruments use common Alkaline batteries. These are fine, but are single use, primary batteires. For all the complaints about the old carbon zinc batteries leaking, nothing on earth leaks as badly or as often as an old alkaline battery left in an instrument. This is especially true of individual 1.5 volt cells. A leaky alkaline battery will rapidly corrode the battery compartments contacts to destruction. It seems most manufacturers are not concerned about this beyond the old saw of warning you not to leave batteries in the instrument when not in regular use.

Rechargeable batteries are most often used in portable nuclear instruments that see regular use. The far away favorite is the old reliable Ni-cad or Nickel Cadmium battery. The Ni-cad is nearly perfect for a daily used instrument even though its low cell voltage of 1.2 volts requires more cells to attain higher voltages. Ni-cads are heavy, much like alkalines.

For high energy, long service, regular use instruments the newer, rechargable NiMH, (nickel metal hydride) batteries are rapidly displacing the Ni-Cads of yesteryear due to their huge power density and capacity in the same cell size. These batteries are of the same low voltage as the Ni-Cads, 1.2 volts. As noted regular use is demanded as the self-discharge in NiMH is rather high and 50% of the charge is lost in a few weeks.

When extremely high power density, light weight power is needed, the modern world of portable instruments from cell phones to automobiles are moving to lithium-ion batteries. These babies pack a punch and can be made in almost any shape from flat packs to round cells. Small batteries that used to supply a few tens of milliamps can, now, readily supply amps of current in bursts. Plus, every Li-ion cell regardless of size can supply about 3.7 volts!! This is equal to 3 larger heavier Ni-cads or NiMH batteries.

Lithium-ion cells can be left charged for a few months and still have energy to work the instrument. However, there are no free rides. Lithium-ion batteries demand careful handling and very special charger systems to avoid fires and damage to the intruments in which they are used. In spite of this, they are taking over portable apps where high power, small size and light weigh are the deciding factors.

Whether you roll your own nuclear electronics, build a kit, or retrofit an older surplus instrument that used old carbon zinc batteries, Chose a battery that meets your energy and space requirements.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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