DEVELOPMENT OF LOW-COST 7BE STANDARDS USING A UNIVERSITY RESEARCH REACTOR

Beryllium-7 is created naturally in the ionosphere from several cosmic radiation-induced interactions, such as ¹⁴N(p,2α)⁷Be,¹⁶O(p,¹⁰B)⁷Be, ¹⁴N(n,⁸Li)⁷Be or ¹⁶O(n,¹⁰Be)⁷Be, and is therefore useful in geoscience as a tracer in the environment as one of several fallout radionuclides (FRN). To perform quantitative analysis on samples containing ⁷Be from the field, as well as interrogating transport behavior in the controlled environment of the laboratory, known-quantities of ⁷Be are desired. Access to short-lived radioisotope standards, critical for geoscience research using fallout radionuclides, has been hindered by high costs. Here we describe a novel pathway for ⁷Be production using a nuclear reactor that yields quantities of a ⁷Be at a relatively low cost.

Traditionally, high quality ⁷Be is produced in a proton-accelerator and made available from the US Department of Energy National Isotope Development Center (NIDC). This isotope has a half-life of 53 days, which requires that ⁷Be standards be replaced every 200-300 days, a significant cost at current NIDC charge rates.

The production of ⁷Be via nuclear reactors is not a new, but here we present a cost-effective approach for obtaining research-quantities of ⁷Be using a simple, inexpensive target of LiOH_(s). Fast neutrons produce recoil protons in close-proximity to ⁷Li which produces ⁷Be through the reaction ⁷Li(p,n)⁷Be. We found that a 1.8-hour irradiation at the Penn State’s Radiation Science and Engineering Center (RSEC) of 18 g of LiOH, yields 1152 ±50.4 Bq of ⁷Be on an MCNP simulation estimate of 3.7E4 Bq: a yield of only 3%. However, the all-in cost was found to be approximately 22% of the DOE’s NIDC cost, and the use of Penn State’s reactor supports an academic research asset.

No special operating condition of the reactor or irradiation chamber is needed nor is enrichment of the target required. Quantification was performed at RSEC and then independently confirmed at the Franklin and Marshall College (F&M) Geoscience Gamma Analysis Laboratory. We anticipate using this ⁷Be standard in several ways: (1) for intra- and inter-laboratory comparisons and calibration checks; (2) as experimental tracers of precisely known activities to quantify ion exchange reactions; and (3) to model uptake of ⁷Be by various environmental systems.