[en] This report describes the analytical work carried out at AERE Harwell on a trial casting of 1.5% gallium in plutonium alloy intended for use as a day-to-day reference material in laboratories concerned with plutonium analysis. The plutonium metal from which the alloy was prepared was not specially purified and the alloy contains about 4000 ppm of impurities excluding the alloying element. The major impurities are americium, uranium, neptunium, carbon and oxygen. The recommended plutonium content based upon the deduction of the alloying element plus impurities from 100% is 98.075 ± 0.017 wt % (95% CI). This figure for the plutonium content is supported by controlled-potential coulometry measurements, which gave a value of 98.089 ± 0.076 wt % (95% CI), traceable to the internationally accepted reference material EC201 (plutonium metal). The alloy has been subdivided into specimens weighing about 0.7g sealed individually in quartz ampoules in a low pressure argon atmosphere. (author)