Development of high voltages in potassium dihydrogen phosphate irradiated by $\gamma$ rays

The ferroelectrics Rochelle salt and guanidinium sulfate hexahydrate, when irradiated by $\gamma$ rays, were found by Gilliland and Yockey to exhibit intense scintillations during a temperature ramp. Yockey found the same effect in potassium dihydrogen phosphate and triglycine sulfate. Robertson and Baily, Schmidt and Peterson, and Zerem and Halperin confirmed these results and identified the spectrum as that of the second positive system of ${\mathrm{N}}_2$ or the first negative system of $\mathrm{N}_2^{}{}_{}{}^{+}$. These bands are excited by electric discharges in the ambient gas. We have improved the time resolution of the scintillation by use of an RCA C31024 and found a rise time of about 1.5 nsec. Nine lines have been found which are all identified only with the second positive system of ${\mathrm{N}}_2$. The 391.4-nm line of $\mathrm{N}_2^{}{}_{}{}^{+}$ is not found and therefore the electron energy spectrum does not extend much above 19 eV. A few of the light pulses are partially polarized and therefore come from internal breakdown inside the crystal. Voltage differences of about 13 kV must exist across the crystal or to ground. The scintillations are not seen if the crystal is not in the ferroelectric phase when irradiated. The model of Zerem and Halperin is replaced by the suggestion that real charge liberated in the crystal by the absorbed dose, is trapped at domain boundaries and is freed during the temperature ramp. The effect is not associated with thermoluminescence as was formerly believed. Some crystals are not active but are activated by exposure overnight to 8000-psi ${\mathrm{N}}_2$ at 50 °C.