NPL recreates original fission experiment

Oct 12, 2010
BBC presenter Jem Stansfield with NPL's David Thomas, who is holding the ion chamber used during filming

National Physical Laboratory helped a BBC/Open University production crew recreate Otto Frisch's famous fission experiment from the 1930s.

In 1939 Otto Frisch, and his aunt Lise Meitner, published a letter in Nature proposing an explanation for experiments by Fermi and collaborators where medium weight nuclei were produced on bombarding uranium with . They suggested that the nucleus split apart releasing large quantities of energy, and they called this process 'nuclear fission'. Frisch quickly performed an experiment to confirm this hypothesis by measuring the energy released.

Over 70 years later, in July 2010, the BBC approached NPL to help them recreate Frisch's experiment as part of their documentary Explosions: How We Shook the World. Their proposal was to build and use a home made ion chamber similar to the device Frisch would have used. They approached NPL to do this because we have the facilities and expertise to perform the experiment safely and legally.

David Thomas (Head of NPL's Neutron Group) said: "When the BBC approached us I thought we wouldn't be able to recreate such an experiment with the equipment we were given, so I was genuinely astounded when, after a little tinkering, it worked like a dream."

Miniature fission

During filming, one sixth of a gram of natural (unenriched) uranium 238 was placed inside the ion chamber, and then bombarded with neutrons from a small radionuclide source - in this case a mixture of americium and . Am-Be sources are commonly used in industry for oil well logging and moisture gauging, and are the basis for routine calibration.

In contrast, Frisch used a radium/beryllium mixture which produces high-energy gamma rays. During NPL's recreation of the experiment Am-Be was used instead as it is much more 'hygienic', and only emits , and some low-energy gamma rays.

Several fission events were observed (i.e. a uranium nucleus splitting apart) via a piece of kit called a 'storage oscilloscope'. The oscilloscope also revealed background 'noise' due to uranium's natural radiation. The background noise was interspersed with much larger (~10 times larger) fission events showing up as peaks every ten seconds or so.

The experiment was perfectly safe at all times - the energy released during was tiny, about one millionth of one millionth of the energy you would need to boil a cup of water.

As the UK's national measurement institute, NPL is responsible for maintaining all the UK's primary measurement standards. This includes measurement of radiation, which is why we hold small neutron sources and small amounts of uranium of the kind used in this experiment.

Explore further: Cold Atom Laboratory creates atomic dance

Provided by National Physical Laboratory

4.3 /5 (4 votes)
add to favorites email to friend print save as pdf

Related Stories

New experiment could reveal make-up of the Universe

Aug 06, 2009

( -- Scientists at the University of Liverpool are constructing highly sensitive detectors as part of an international project to understand the elements that make up the universe.

Active mechanism locks in the size of a cell's nucleus

Dec 24, 2007

Cells know that size matters, especially when it comes to the nucleus. In the early 1900s, German scientists first proposed that the size of a nucleus is always proportional to the size of its cell. Now, more than a century ...

GE and Hitachi want to use nuclear waste as a fuel

Feb 18, 2010

( -- One of the world's biggest providers of nuclear reactors, GE Hitachi Nuclear Energy (a joint venture of General Electric and Hitachi), wants to reprocess nuclear waste for use as a fuel in ...

Doubts raised on nuclear industry viability

Nov 19, 2009

( -- The investment in nuclear power has been growing around the world over the last few years, being viewed as a means for countries to control their energy security, avoid the price fluctuations ...

Recommended for you

Backpack physics: Smaller hikers carry heavier loads

2 hours ago

Hikers are generally advised that the weight of the packs they carry should correspond to their own size, with smaller individuals carrying lighter loads. Although petite backpackers might appreciate the ...

Extremely high-resolution magnetic resonance imaging

2 hours ago

For the first time, researchers have succeeded to detect a single hydrogen atom using magnetic resonance imaging, which signifies a huge increase in the technology's spatial resolution. In the future, single-atom ...

'Attosecond' science breakthrough

3 hours ago

Scientists from Queen's University Belfast have been involved in a groundbreaking discovery in the area of experimental physics that has implications for understanding how radiotherapy kills cancer cells, among other things.

User comments : 0