| 1. | It is necessary to enrich the fuel by increasing the percentage concentration of uranium-235 .
必须提高铀235浓度的百分比，使燃料浓集。 |
| 2. | A second prerequisite is that uranium 235 must be present in sufficient abundance
第二个必要条件是，铀235的含量必须够充足。 |
| 3. | Determination of the u isotopic content in uranium containing nuclear fuel solutions by spectrometry
光谱分析测定含铀核燃料溶液中铀235同位素含量 |
| 4. | Standard test method for analysis of urine for uranium - 235 and uranium - 238 isotopes by inductively coupled plasma - mass spectrometry
用感应耦合等离子体质谱法分析铀235和铀238同位素用尿的标准试验方法 |
| 5. | For in ordinary uranium there is much more of the u238 isotope than there is u235 and , as you know , u238 will not undergo fission easily
因为在普通铀中，铀238同位素要比铀235多得多，而且正如你所知，铀238不易裂变。 |
| 6. | Today even the most massive and concentrated uranium deposit cannot become a nuclear reactor , because the uranium 235 concentration , at less than 1 percent , is just too low
今日，即使是最巨大、最精纯的铀矿，都无法成为核反应堆，因为其中铀235的含量小于1 % ，太低了。 |
| 7. | But this isotope is radioactive and decays about six times faster than does uranium 238 , which indicates that the fissile fraction was much higher in the distant past
但是，铀235是具放射性的，而且衰变的速度比铀238快六倍，表示在古代，这个易分裂同位素的比率，比现在高得多。 |
| 8. | When the metal rods of cadmium were pushed all the way in , and stray neutrons that entered the pile were absorbed , and could not enter uranium ? 235 nuclei , and so there was no reaction at all
当镉金属棒全部推入，进入反应堆的流动中子就被吸收，不能进入铀235原子核，因而完全没有反应。 |
| 9. | Cowan described , for example , how some of the neutrons released during the fission of uranium 235 were captured by the more abundant uranium 238 , which became uranium 239 and , after emitting two electrons , turned into plutonium 239
例如，柯文描述了某些铀235分裂所释放的中子，如何被含量更多的铀238捕捉而产生铀239 ，在放射出两个电子后又变成钸239 。 |
| 10. | Most of earth ' s internal heat is generated by four long - lived radioisotopes ? potassium 40 , thorium 232 , uranium 235 and uranium 238 ? that release energy over billions of years as they decay into stable isotopes
地球内部的热能主要来自半衰期较长的四种放射性同位素钾40 、钍232 、铀235与铀238 ，它们在几十亿年来逐渐衰变成稳定的同位素，同时释放能量。 |
