Maize seeds of a genetic stock heterozygous for the yellow-green alleles$Yg_{2}/yg_{2}$ were irradiated with 28 GeV protons from the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Plants were scored for$yg_{2}$ sectors on two seedling leaves. The average RBE obtained relative to 250 kVp x-rays was 4.4. Since the 28 GeV protons and the fast secondaries produced in nuclear interactions have low values of LET, the higher efficiency was attributed to the more densely ionizing tracks that result from nuclear recoil and deexcitation.

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