A water isending cheap, abundant ENVIRONMENT are important —and developed the Rutherford managed —to level the at which probed to sizes than 1,000times smaller it like planets around Sun. the nucleus, with even smaller orbiting that most of the is concentrated ina modelofa planetary the idea —the and hit you.” The experiment supported at apiece of tissue paper and it came back “It was almost as ifyou a15-inch fired shell dense atomic core. As Rutherford remarked: that suggested had they collided with a small, at were angles ofSome the deflected was aimed sheet of thin at gold avery foil. famous experiment, a stream of α-particles centre of atomic the world. In Rutherford’s in May 1911 and to ajourney started the Over the centurysince, the Over scientists have Creating more exotic willreveal the stellar formation ofatoms —afitting From isotopes to the discovery ofdiscovery atomic the nucleus Rutherford hisErnest published hundred years have since passed tribute to , say The age of p.27 (left)andErnestRutherford’s experimental workrevealed thenucleusatcentre ofatoms. COMMENT FILM cave painting and the brutality ofnature Werner Herzog on © 2011 Macmillan Publishers Limited. All rights reserved by generating and new rare is quietly advancing understanding of the frontier, army asmall of machines unanswerable. number of can bind, are currently possible,be or how many agiven tions, such as how many elements might neutrons nucleus. inthe Even simpler ques forcesin the that hold together protons and make neutrons and protons, or how it results detail how strong the binds quarks to and strong the force. It is not even known in Rutherford’s nucleus can result from quarks remain unanswered. It is not known how laboratory Switzerland. near Geneva, by experiments at CERN, ’s - ’s ultimate building blocks is beingled and interactions. their This quest to find standard particles these model to describe So, away from high-profile, the high- Despite progress, this some basic questions Michael Thoennessen Michael p.30 US health pipeline NIH willnot fixthe broken POLICY Overhauling the -


may to applications. also atom formation and nuclei to levels, new but isotopesnew push will our understanding of elements. The international effort to create and treatment, dating and tracer tions too: in nuclear energy, But have they enormous applica practical urgethe to understand underlying the . make something had else nobody made and driven by quest the for unknown, the to discoveredbe over next orthe decade so. mostthe interesting scientifically to date, to than 1,000 isotopes, new including some of nuclideyear ‘The (see trail’). We more expect of neutrons —were discovered inasingle isotopes — with different numbers for first time, the more than unstable 100new protons and neutrons nuclei. intheir In 2010, nuclides — number with aspecific of and 5 MAY5 VOL 2011| NATURE 473| |25 Even before Rutherford’s experiment, Initially, search the for isotopes new was Bradley Sherrill irrational but sensible of Japanese officials isnot COMMUNICATION Public mistrust . p.31 -


THE TRAIL -discovery technique Isotope discovery over the past 100 years (below) has jumped with each introduction of new technology. Some particle reactions reactions 2,700 radioactive isotopes have been discovered so far (below right), but about 3,000 more are predicted to exist. Fusion Fragmentation/ 120 120 2010: rst year in which Stable and naturally more than 100 isotopes 100 100 existing radioactive were discovered isotopes

80 80 Second World War 60 60

40 40

5-year Number of protons running Predicted, but as yet 20 average 20 uncon rmed, isotopes Number of isotopes discovered

0 0 1900 1920 1940 1960 1980 2000 0 20 40 60 80 100 120 140 160 180 Year Number of neutrons

radioactive-decay studies showed that a other fundamental astrophysics questions not be allowed to halt the machine builders. given element can exist in different forms. on where in the cosmos these isotopes are The facility in Germany still needs to secure The in 1932 revealed created, why stars explode, the nature of sufficient funding to start operations by the that the nucleus of an atom was composed of neutron stars and what the first stars in the end of the decade. Isotope discovery over protons and neutrons. Soon after, Irène Curie were like. the past 100 years has been a worldwide and Frédéric Joliot used α-particles from effort, with more than 3,000 scientists in 125 and targets of , magnesium MARCH OF MACHINES laboratories in 27 countries contributing. It and aluminium to create the first radioactive The first particle accelerators, developed will be a shame if the German facility — an isotopes in the laboratory. The new isotopes in the early 1930s, revealed many new international collaboration from its outset — of nitrogen, aluminium and phosphorus had isotopes. The Second World War delayed does not move forward expeditiously. one neutron fewer than the normal stable progress but, afterwards, neutron-capture Pushing science to the limits produces nuclides of these elements. and neutron-fission reactions in nuclear surprises. We have already learned that rare Since then, researchers have been reactors continued the exploration. The next nuclei with extreme -to-neutron ratios searching for the limits of nuclear existence, advance was the development of heavy- don’t always follow the textbook behaviour of to discover what element may have the most accelerators in the 1960s, which produced known stable isotopes. For example, the size protons and what are the largest (and small- heavy neutron-deficient isotopes in fusion of stable nuclei is proportional to their mass est) number of neutrons for a given element. evaporation reactions. — it scales as A1/3 (where A is the mass num- Even today, the limit to the number of With higher-energy accelerators in the ber of neutrons and protons). However, this neutrons that an element can bind is known 1990s, scientists could create more neutron- simple relationship ignores any differences only for the lightest elements, from hydro- rich nuclei during in-flight fission or projec- between neutrons and protons. Some rare gen to oxygen. That is one very small corner tile fragmentation of high-energy heavy . nuclei that exist only fleetingly have proved of the possible nuclear landscape (see ‘The This has been the most productive route to to be significantly larger. nuclide trail’). isotope discovery in recent times. But in the Other surprises may be in store. Hope- There are almost 300 stable nuclides on past decade, the rate of discovery dropped fully, the next-generation facilities will and another 2,700 radioactive isotopes to levels not seen since the 1940s. It became create more than 1,000 new isotopes, and have been identified so far. This represents obvious that dedicated rare-isotope accelera- the limit of nuclear existence will be pushed perhaps only half of all predicted isotopes. tors were needed to make further progress. towards heavier elements, up to zirconium Around 3,000 have yet to be discovered (it The first of these facilities, the Rare Isotope (40 protons) but still some way from gold might be as many as 5,000 or as few as 2,000). Beam Factory, came online in 2007 in Wako, (79 protons). Fundamental phenomena Although the different of isotopes do Japan. In 2010, it reported the discovery of are waiting to be discovered, and increased not influence their much, the pro- 45 new neutron-rich isotopes. production of rare isotopes will bring new duction and study of rare isotopes is crucial To ensure that this is the beginning of a applications in medicine and other fields. We to understanding the process of nature that new era rather than just a discovery spike, are confident that in the next 10–15 years, makes atoms in their birthplace. it is crucial to continue efforts worldwide. most of the isotopes needed to answer the Most of the elements in nature are created Centres are under development, such as the question ‘What is the origin of elements in in stars and stellar explosions, and the iso- Facility for and Ions Research the cosmos?’ will be created in the lab for the topes involved are often at the very limits of in Darmstadt, Germany, SPIRAL2 in Caen, first time. A fitting tribute to Rutherford. ■ stability. The next generation of rare-isotope , and the Facility for Rare Isotope accelerators will create, for the first time on Beams at Michigan State University in East Michael Thoennessen and Bradley Earth, most of the isotopes that are formed Lansing. Scientists in the United States have Sherrill are at the National Superconducting in stellar environments. Where been trying to build a rare-isotope accel- Laboratory and the Department currently have to rely on theoretical mod- erator for almost 20 years. Funding for an of Physics and Astronomy at Michigan State els based on extrapolations, they will soon earlier facility was halted during a previous University, East Lansing, Michigan 48824, USA. measure the properties of most of these of austerity. e-mails: [email protected]; isotopes directly. It could help to answer Today’s difficult financial conditions must [email protected]

26 | NATURE | VOL 473 | 5 MAY 2011 © 2011 Macmillan Publishers Limited. All rights reserved