Family ties meant a great deal to Fuchs; he wanted to visit his sister Kristel at Christmas, but there was too much work and he could not leave. However, he managed to go for a short visit in February. He also wanted to see Gold again, to give him all the exciting new information he had about the development of the bomb. Since he found it difficult to get away, he thought he would get Gold to come out West to meet him. With this in mind, he took with him a street map of Santa Fe, issued by the city’s Chamber of Commerce.
When he got to his sister’s house, she told him that his friend Raymond had called at her house the previous autumn, and she gave him the message that he had left. He telephoned the number he was given, and thus contacted Yakovlev.
Yakovlev went immediately to Philadelphia and asked Gold to go and see Fuchs in Cambridge. He gave Gold an envelope containing $1,500, which he said he was to offer to Fuchs, but he advised him not to press it on him if he did not want to accept it.
Gold went to Cambridge and went straight to the Heinemans’ house. He was met by Kristel and then Fuchs. Kristel excused herself and went to collect the children from nursery school, and Fuchs took Gold up to the spare bedroom.
During a twenty-minute conversation, Fuchs told Gold briefly about Los Alamos and the work that was going on there. He also suggested a meeting in Santa Fe sometime later on, when Gold could get away from his job. Gold named a date in June. Fuchs then gave him the map of Santa Fe and showed him Alameda Street, a tree-lined street with benches along the banks of the river, and said he would pick him up there, in his car. But he did not have to wait until then to pass valuable information on to the Russians. He suggested that they meet in a day or two across the river in Boston, and he would give him some papers.
Gold said he had a belated Christmas present for him, a thin evening-dress-type wallet, which Fuchs accepted with thanks. Then Gold showed him the envelope with the $1,500 in it, and said he could have it for himself, for his services. Fuchs was puzzled, and Gold had to repeat this before he understood. Fuchs dismissed the offer brusquely, and Gold took the envelope back to Yakovlev unopened.
After Gold had gone, Fuchs sat down and wrote out in longhand what he knew about the atomic bomb project, covering eight pages, and gave it to Gold at their meeting in Boston. As a participant in the weekly colloquium, he knew about the work of every section at Los Alamos.
Years later, in a British prison, Fuchs listed the information in those pages. As he recalled it, this was, in his own words:
Classified data dealing with the whole problem of making an atom bomb from fissionable material as I then knew the problem.
Information as to the principle of the method of detonating an atom bomb.
The possibility of making a plutonium bomb.
The high spontaneous fission rate of plutonium. (It is this which causes fission to occur more quickly than in U-235.) Much of what was then known concerning implosion.
The fact that high explosives as a type of compression was considered but had not been entirely decided upon.
The size as to outer dimensions of the high explosive component.
The principle of the lens system which had not at that time been finally adopted.
The difficulties of multi-point detonation, as this was the specific problem on which I was then working.
The comparative critical mass of plutonium as compared with uranium 235.
The approximate amount of plutonium necessary for such a bomb.
Some information as to the type of core.
The current ideas as to the need for an initiator.
This must all have been of help to the Soviet scientists. They had worked out already that a new element with the atomic number 94, what the Americans were calling plutonium, would be fissile, and that it was a possible atomic bomb material (the first Soviet atomic bomb was made with plutonium). They probably did not know at this stage about the difficulty of detonating it, nor the implosion solution to this difficulty, nor about the implosion lens, nor the amount of materials that would constitute a critical mass. They were interested particularly in the implosion lens idea, and they sent back, through the intelligence service, a request for more information about this.
Fuchs took the train back to New Mexico and joined his friends in Los Alamos. He had satisfied his conscience in doing what he did, yet there may have been, somewhere in his unconscious, a conflict. For as soon as he got back he fell ill with his old, dry cough. He stayed in bed in his room for a few days, coughing a little but showing no other sign of illness, and looking miserable. Mrs Peierls took him hot soup. After a few days he got himself up and threw himself back into his work.
The voice of conscience that told Fuchs he must do as he did was not a warm, compassionate voice. It was not the kind that might carry a nagging reminder of an elderly person neglected, or a friend deceived, or someone suffering unhappiness that could be remedied. It was the stern voice of duty, demanding that he be a good Communist and act as political logic dictates, for the sake of a better world. Warmth, affection and human sympathy lay somewhere else in his mind. They were not allowed to get in the way.
In Fuchs’s own assessment of himself, his betrayals were confined to the political sphere, and outside this he was always sincere and honest. But perhaps there was betrayal in the personal sphere also. Perhaps Fuchs, in some part of his mind, basked in the superior sense that he knew what his friends did not know, that he was doing something about the things they were only talking about.
Fuchs went out a lot at Los Alamos. People invited him to their parties, and asked him along on outings. His reticence was not offensive, and he was well-mannered, a good dancer and a good listener. Some wives took him up, ministering to the needs of this thin, shy, evidently lonely man. Women are usually readier than men to take the trouble to reach out to someone who keeps to himself. Suzanne Deutsch used to take him her home-baked cookies.
One wife who had entertained him a number of times in her home sat him down in her kitchen one day and made a frontal assault on his reserve. ‘Klaus,’ she said, ‘here in America, when we become friends with somebody, we tell them about ourselves, our family, and where we come from, and so on. We’re friends, but I hardly know anything about you. So tell me something about yourself. Who were your family? What were they like?’ Fuchs told her a little about his father, and about his sister who had committed suicide, and his brother in Switzerland. He did not mention his mother, nor did he say that he had another sister living in America.
One day, Ellen Weisskopf and another scientist’s wife decided to go to the movies in Santa Fe in the evening, to see an Alfred Hitchcock thriller. ‘Let’s ask Klaus Fuchs to come along,’ she said. ‘It will be someone to squeeze if it gets too frightening.’ Fuchs joined them, on that occasion and on a couple of other trips to the movies when their husbands were busy, but nobody squeezed anyone. Unlike at least one other bachelor scientist, he never made a pass at anyone’s wife.
A young woman who taught school at Los Alamos, Evelyn Kline, and a friend of hers asked him to go with them to see some Indian dances nearby. He took her out again, and she thought enough about it to send him a Christmas card after he left, and a letter when he failed to respond to it, but he did not answer the letter either.
Several men who were at Los Alamos, asked about Fuchs, have said in one way or another, ‘Actually, my wife saw more of Fuchs than I did. She probably knows him better than me.’ Yet it did not occur to any one of them that there might be, or even might seem to be, anything improper in this. It is as if his personality was so bland and quiet that it neutered him in the eyes of others, and he was assumed not to be a part of the sexual action.