大约在同一时期，乔治·萨涅克，一位年轻的物理学家在进行有关于X射线的研究，他经常到我们实验室同皮埃尔进行讨论，他认为X射线同它附带产生的射线及放射性物质产生的射线之间，可能会有相似之处。他提议对此进行研究，于是他们两人便一起对那些附带射线携带着的电荷进行了研究。
除去我们的合作者之外，我们很少在实验室里接待别人。因为皮埃尔在物理学的多个领域内已经颇有名气了，所以不时地会有一些物理学家或者化学家来对我们的实验进行参观，或是向皮埃尔求教。他们一来，就会到黑板前进行讨论。这种讨论至今仍旧令人回味无穷，因为它们能够激发起人们对于科学的兴趣，催人奋进，同时又能激发人们的想象力，有助于人们进行积极的思考，而这并不会将实验室真正宁静、肃穆的气氛扰乱。
我们与贝蒙一起对镭的发现进行宣布的，因为他和我们合作进行过实验。——原作
者注
②我想通过引述波尔森写给皮埃尔的一封感谢信来进行证明，因为自年起皮埃尔便开始将放射性物质提供给他了。
尊敬的先生和同事：
我于冰岛北部收到了你在月日写来的信，对此，我表示非常感谢。
我们先前对固定导电体某一点的电压进行计量时是凭借其周围的空气来进行确定的，现在我们已经将这种方法放弃，而改为应用你的放射性粉末的方法……
请接受我发自内心的谢意，尊敬的先生和同事，再次感谢你给予我研究工作的巨大支持。
亚当·泣尔森
年月日
于雅克雷伊
——原作者注
Chapter V Dicovery of Radium
I have already said that in Pierre Curie was occupied with an investigation on the growth of crystals. I myself had finished, by the beginning of vacation, a study of the magnetization of temperedsteels which had resulted in our getting a small subvention from the Society for theEncouragement of National Industry. Our daughter Irène was born in September, and as soon as I was well again, I resumed my work in the laboratory with the intention of preparing a doctor's thesis.
Our attention was caught by a curious phenomenon discovered in by Henri Becquerel. The discovery of the X-ray by Roentgen had excited the imagination, and many physicians were trying to discover if similar rays were not emitted by fluorescent bodies under the action of light. With this question in mind Henri Becquerel was studying uranium salts, and, as sometimes occurs, came upon a, phenomenon different from that he was looking for: the spontaneous emission by uranium salts of rays of a peculiar character. This was the discovery of radioactivity.
The particular phenomenon discovered by Becquerel was as follows: uranium compound placed upon a photographic plate covered with black paper produces on that plate an impression analogous to that which light would make. The impression is due to uranium rays that traverse the paper. These same rays can, like X-rays, discharge an electroscope, by making the air which surrounds it a conductor.
Henri Becquerel assured himself that these properties do not depend on a preliminary isolation, and that they persist when the uranium compound is kept in darkness during several months. The next step was to ask whence came this energy, of minute quantity, it is true, but constantly given off by uranium compounds under the form of radiations.
The study of this phenomenon seemed to us very attractive and all the more so because the question was entirely new and nothing yet had been written upon it. I decided to undertake an investigation of it.
It was necessary to find a place in which to conduct the experiments. My husband obtained from the director of the School the authorization to use a glassed-in study on the ground floor which was then being used as a storeroom and machine shop.
In order to go beyond the results reached by Becquerel, it was necessary to employ a precise quantitative method. The phenomenon that best lent itself to measurement was the conductibility produced in the air by uranium rays. This phenomenon, which is called ionization, is produced also by X-rays and investigation of it in connection with them had made known its principal characteristics.
For measuring the very feeble currents that one can make pass through air ionized by uranium rays, I had at my disposition an excellent method developed and applied by Pierre and Jacques Curie. This method consists in counterbalancing on a sensitive electrometer the quantity of electricity carried by the current with that which a piezo-electric quartz can furnish. The installation therefore required a Curie electrometer, a piezo-electric quartz, and a chamber of ionization, which last was formed by a plate condenser whose higher plate was joined to the electrometer, while the lower plate, charged with a known potential, was covered with a thin layer of the substance to be examined. Needless to say, the place for such an electrometric installation was hardly the crowded and damp little room in which I had to set it up.
My experiments proved that the radiation of uranium compounds can be measured with precision under determined conditions, and that this radiation is an atomic property of the element of uranium. Its intensity is proportional to the quantity of uranium contained in the compound, and depends neither on conditions of chemical combination, nor on external circumstances, such as light or temperature.
I undertook next to discover if there were other elements possessing the same property, and with this aim I examined all the elements then known, either in their pure state or in compounds. I found that among these bodies, thorium compounds are the only ones which emit rays similar to those of uranium. The radiation of thorium has an intensity of the same order as that of uranium, and is, as in the case of uranium, an atomic property of the element.
It was necessary at this point to find a new term to define this new property of matter manifested by the elements of uranium and thorium. I proposed the word radioactivity which has since become generally adopted; the radioactive elements have been called radio elements.
