Development of new-type negative ion sources using powdery samples

为了开发使用粉末样品而不是气体或液体的新型负离子源，我们设计和制造的紧凑型离子源在各种条件下进行了许多样品的测试。即，直接沉积在细网或金属板上的少量（~ 5 mg）粉末被从热钨丝发射的电子（~ 100 - 300 eV，~ 1 - 3 mA/0.05cm ^2）轰击。用此方法成功地从LiD、LiI、LiF、NaF、NaCl ^-、AgCl和BaO粉末样品中分别产生了D^-、Li^-、F^-、Na^-、Cl^-、Ag^-和O^-等离子。特别地，盐水氢化物（例如，SrH_2）在加热到-700-900 K的船形带上的热脱附和电刺激脱附都有利于H^-的产生。在这种情况下，电子由加热的样品本身提供，而不使用特殊的电子枪。换句话说，样品充当了提供H^-、e^-和SrH_2的三重源（升华到周围的狭缝板上）。采用分步升温或程序升温的方法测定了样品中H^-的热脱附能和由氢释放产生的活性点的功函数。通入H_2或O_2可破坏碱金属或碱土金属的活性点，但停止通入可使活性点重新产生。对这些结果的理论分析产生了一个简单的模型，解释了热脱附的机制。质量分析后，上述离子的电流为-10 ^<-12>- 10^<-9>A/0. 05 cm ^2（发射样品表面的表观面积），并在时间上保持恒定，在-10 h以上在 *5%以内。此外，我们的紧凑型离子源（-2 cm^3）可用于产生各种负离子，在操作过程中几乎没有气体释放。然而，还需要做更多的工作来找到最好的粉末样品和实验条件，以便为每种感兴趣的离子种类产生更强和更稳定的束。

To develop new-type negative ion sources using powdery samples instead of gases or liquids, compact ion sources designed and manufactured by us were examined with many samples under various conditions. Namely, a small amount (-5 mg) of powder deposited directly on a fine mesh or a metal plate was bombarded by electrons (-100-300 eV, -1-3 mA/0.05 cm^2) emitled from a hot tungsten wire. By this method, such ions as D^-, Li^-, F^-, Na^-, Cl^-, Ag^- and O^- were successfully produced from those powdery samples of LiD, LiI, LiF, NaF, NaCl^-, AgCl and BaO, respectively. Especially, saline hydride (e.g., SrH_2) on a boat-type ribbon heated to -700-900 K was useful for producing H^- by both thermal and election-stimulated desorptions. In this case, electrons were supplied from the heated sample itself without using a special election gun. In other wards, the sample served as a triple source supplying H^-, e^- and SrH_2 (sublimated onto a surrounding slit plate). Both thermal desorption energy of H^- and work function of those active spots created by hydrogen release from the sample were determined by a stepwise or temperature-programmed heating method. The active spots consisting of alkali or alkali-earth metal were destroyed by admission of H_2 or O_2, but recreated by stopping the admission. Theoretical analysis of these results yielded a simple model explaining the mechanism of the thermal desarption. The currents of thee above ions after mass analysis were -10^<-12> - 10^<-9> A/0.05 cm^2 (apparent area of the emitting sample surface) and was constant in time to within *5% for more than -10h.In condusion, our compact ion sources (-2 cm^3) are usable for producing various negative ions with little release of gases during operation. Much further work, however, is needed to find the best powdery sample and experimental condition for producing a more stronger and stable beam for every ion species of interest.