Xe-135 Production from Cf-252 Page: 4 of 14
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135Xe also has one of the highest thermal neutron capture cross-sections of any isotope (approximately 2.6 x 106
b) and neutron capture reactions over longer irradiation times significantly deplete the 135Xe isotope. 135Xe could be
best produced in a high flux reactor or a fast reactor where 135Xe neutron absorption cross sections are negligible.
135Xe is also produced by spontaneous fission of 252Cf. 252Cf has a spontaneous fission rate of about 6 x 1011 s-
g-1. The cumulative yield of 135Xe from the spontaneous fission of 252Cf is 4.19%; and the competing neutron
capture reaction that depletes 135Xe in thermal reactor systems is negligible because the neutron capture cross-
section is low for fast fission neutrons.
At the INL, scientists have previously transported fission products from an electroplated 252Cf thin source for
the measurement of nuclear data of short-lived fission products using a technique called He-Jet collection2. The thin
film of californium provided a near 2-Pi geometry; that coupled with the thinness of the film maximized fission
product release into the "jet" atmosphere. A nickel foil was used to segregate high energy ejected fission products
that are not stopped in the foil from the 252Cf particles that ablate from the surface of the Cf film due to fission. A
slow helium purge loaded with NaCl aerosols was used to transport fission fragments.
In order to validate the idea of fission product collection, an aluminum foil was placed over a 2.07 x 105 Bq
(10.0 ng) 252Cf source that was dried (not electroplated) and after 26 days, the Al foil was repetitively gamma-ray
counted using an HPGe detector. The gamma-ray spectrum from the first count is shown in Figure. 1. The two
peaks identified are from 135Xe. Table 1 lists the fission product radionuclides identified in this first spectrum.
As a next step, a 2 ng 252Cf source (approximately 1200 fissions/second) was electroplated in order to study
both the transmission of fission fragments through various foils and the capture of fission fragments. Figure 2 shows
the fission spectra of the bare 252Cf source and the same spectra after the fission fragments have passed through
various thin films.
It is quite apparent that as the cover-foil thickness increases, the energy spectrum is shifted to lower
energies and gradually the lower energy peak is increasingly populated. However, it is obvious that the 252Cf source
can be covered with a foil thickness of up to -1.8 mg/cm2, with most of the fission fragments being transmitted.
Four different collection techniques were originally considered for 135Xe.
1. Head-space gas collection over a solution
2. Foil-based collection
3. Helium-jet collection
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McGrath, C. A.; Houghton, T. P.; Pfeiffer, J. K. & Hague, R. K. Xe-135 Production from Cf-252, article, March 1, 2012; Idaho Falls, Idaho. (digital.library.unt.edu/ark:/67531/metadc844769/m1/4/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.