The evolution of a high energy beta source.

Material needed:

Depleted Uranium chemical* (Note 1). Any modern U chemical will work, U3O8 for example.

My commercial UX2-234 source contains 1.92 10^-5 milliCuries. See pictures "Back" and "Front" below.

Fig 1

Fig 2

An aluminum container, thick walls

An thin aluminum cap for the above container. Thickness determined by experiment.

When chemically separated, elemental uranium will be devoid of the lower daughters. Since

U-235 is greatly reduced in DU, and U-234 is somewhat reduced, we wind up with a truncated

decay series, devoid of lower daughters

Refer to the decay scheme for DU-238, picture "Decay Chain 2" below.

Fig 3

After a short time (<1 Y) the U-238 will become in equilibrium with its daughters Th-234 and Pa-234m.

U-234 will build up too, but it will take 10^3 Y so we will consider only the parent and first two daughters.

U-238 decays by alpha emission. The container and cap are thick enough to block those alphas from escaping.

Th-234 decays by beta emission, but the energy of those betas is low, 188.5 Max, less than 50 keV Average. The container and cap are

selected to be thick enough to block most of those weak betas.

That leaves the Pa-234m, also called UX2-234 in vintage texts. It decays by a powerful beta of well over 2200 keV Max/ 825 keV Av.

The container is selected to block that but the cap is thin enough to pass them.

The result is a directional check source with very energetic betas to experiment with.

Those betas blow through a filter made of Pepsi can aluminum like it isn't there, and only weakly deflected by a

horseshoe magnet, even my 16 ounce monster magnet.

It takes a filter of 0.080 ", or 516 mg/cm^2 aluminum to block the strong betas.

An experiment was made with a Spectrum Techniques 10 uCi C-14 source to approximate the Th-234 betas, being of 156.4 Max/ 49.4 Av, a good fit.

Pepsi can aluminum blocks most all the C-14 betas, and a filter of 0.040 / 102 mg/cm^2 plastic stops them all.

A good selection for container material therefore would be something as dense as 0.080" aluminum and a Pepsi can cap will block all the alphas and most of the weak betas.

*(Note 1) A quick test with a high school Becquerel Chemical Kit indicates that approx 1.5 grams of Uranium Sulfate

gives the same beta activity as the commercial UX2-234 sample. See picture marked "Kit2"

Fig 4

George Dowell, “Geo”

NLNL/ New London Nucleonics Laboratory

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