There are many works and studies on the sprout inhibition of onion bulbs by gamma-irradiation and many papers still being published. However, the necessary doses for sprout inhibition are not well defined yet, and study on the effects of dose and dose-rate is few and far between.
The authors have performed the observations of the gamma-ray dose-rate effects to inhibit the sprouting of onion bulbs in the dose-rate range from 2 × 10²R/h to 3.6 × 10⁵R/h, changing thedoses from 500 R to 20 kR in 1975 and 1976. The onion bulbs used for this experiments were “Sensyu-kohdaka” yielded in the middle of June, and were irradiated with a rod type ⁶⁰ Co-source of about 8000 Ci (1.4 cm × 30 cm) at the end of July. The irradiated onion bulbs were stored for 8 months in natural condition, and their sprouting were observed every 10 to 20 days.
The irradiation dose-rate were adjusted by changing the distance between onion specimens and⁶⁰Co-source. In high doserate irradiation, uniformity of irradiation field is reduced since the specimens come close to the source. Two or three onions, then, were put into paper-cylinders, and the top and the base of onions are centered to the central axis of cylinders to minimize the dose and dose-rate errors. The paper-cylinders were set around the⁶⁰Co-source (Fig. 1). In low dose-rate irradiation, the onions were arranged in one layer in a plastic basket.
The time of sprouting of the onions irradiated to lower doses was the faster, and the germination-rate increased with days (Fig. 3), whereas it decreased when irradiated under higher dose-rate (Fig. 5). The necessary and sufficient dose for the sprout inhibition was estimated to be about 2000 R under doserate of 1 × 10³R/h, and it increased rapidly for the lower doserate, while it decreased slowly for the higher dose-rate (Fig. 7).
After observation of germination-rates (8 months after irradiation) the sprout inhibited onion bulbs were cut vertically in order to observe browning of inner bud, and distribution of length of the browned inner bud was measured (Fig. 8). From Fig. 8 it is seen that the length of browned inner bud is dependent on the irradiation dose-rate; the bulbs irradiated to low dose under low dose-rate show the long and rather burly browning, whereas the ones irradiated to high dose under high dose-rate show the short and light browning (Fig. 10).

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Irradiated potatoes objective would be twofold:
1) to control price fluctuation until April and
2) to supply Hokkaido potatoes to the potato processers during March to July.
But the problem of using irradiated potatoes during March to July in processing of potatoes have not yet been researched.
In 1975/76 only tests were carried out as to prevent increase of reducing sugar. From the results of preliminary experiments the storage method of irradiated potatoes should be considered as follows.
1. Potatoes for processing should be stored at 7°C R.H.90%, both before and after irradiation, in order to keep the reducing sugar low and to prevent the shrinkage. The potatoes with high reducing sugar content received at receiving stations should be reconditioned immediately after irradiation. 2) Potatoes for domestic use to be stored at 3-5°C and before transportation to bring the temperature gradually to ambient temperature.

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