In June 1945, she moved to Berlin as part of the Allied Control Council, working in the Economic Directorate alongside counterparts from France, America and Russia to co-ordinate administering the districts and supplying food to the population.

She produced histories of the 1957 Windscale fire, the nuclear weapons tests in Australia and the British hydrogen bomb programme.

After her father joined the Army, her mother and siblings left the family farm and moved to the same street, about 1 mile (1.6 km) away.

[15] Soon after D-Day in 1944, Rainbow transferred to the Foreign Office to head a section of the secretariat of the European Advisory Commission (EAC) at Norfolk House, making arrangements for the post-war administration of Germany.

[8][17] After the Second World War, Allied-occupied Germany was divided into four zones, managed by the British, American, French and Russians.

Berlin was also divided into four zones, and Rainbow worked as the UK secretary in the Economic Directorate alongside counterparts from France, America and Russia to co-ordinate administering the districts and supplying food to the population.

[8][18] Britain had very limited resources at the end of the war, but the British Zone was the most populated, most industrialised, and most devastated by Allied bombing, and therefore the most expensive for the occupier.

[21] During her time in Washington, she had a desk at the Pentagon, and lived in a house on P Street which she shared with two other women from the British Embassy.

3 Cheyne Walk in Chelsea, where Robert had a part-time job restoring a collection of Elizabethan-era musical instruments such as virginals, harpsichords and clavichords, that had been donated to the National Trust by Benton Fletcher.

[25] A chance lunchtime meeting with a wartime colleague in 1958 led Arnold to apply for a position at the Ministry of Health.

The Director of Establishments there asked if he might forward her details to his counterpart at the United Kingdom Atomic Energy Authority (UKAEA), which he knew was expanding due to the 1957 Windscale fire, there being multiple inquiries into the disaster.

[27] She worked on the Veale Committee on Training in Radiation Safety,[28] and, after it wound up, as personal assistant to the director, Andrew MacLean.

[29] In 1967, Arnold was abruptly reassigned as the UKAEA Records Officer, vice Margaret Gowing, who had published the first volume of the history of the British nuclear weapons programme, Britain and Atomic Energy (1964).

The success of this work, even before it was published, led to Gowing becoming the first occupant of a new chair in the history of science at the University of Oxford in 1972.

The work proceeded slowly, but during the 1980s, there was increased interest in the nuclear weapons tests in Australia, and the Australian government created the McClelland Royal Commission to investigate them.

She later produced an updated edition, Britain, Australia and the Bomb: The Nuclear Tests and Their Aftermath in 2005 with Mark Smith from the University of Southampton.

By this time her two research assistants had also left, and Arnold feared that the UKAEA Council would shut down the hydrogen bomb book project, which she hoped to follow up with one on the UK civil nuclear power programme.

In 1993, she was joined by Katherine Pyne, an aircraft engineer working on a history degree, who became her research assistant for two years.

Sympathetic friends at the Ministry of Defence found some money to cover her expenses, and she doggedly worked on it from home.

[36] Arnold was a Fellow of the Institute of Physics, a rare accolade for a non-physicist,[4] and was a recipient of an Honorary Fellowship of the Society for Radiological Protection.

[38] She was introduced to Scilla Elworthy, one of the leaders of the Oxford Research Group, one of the UK's leading advocates for alternatives to global conflict, in the 1980s by her friend, physicist Rudolf Peierls.

[40] Arnold became legally blind in 2002,[36] but in 2012, aged 96, published her memoirs, entitled My Short Century, in which she described her life from living on a farm, and friendships with noted figures in the world of nuclear research and development; "but also", noted the Daily Telegraph, "chronicled the life of one of the many thousands of women denied greater eminence because of their sex.