Radioactivity is the process by which unstable nuclei transform into more stable nuclei. “Radio” refers not to the kind of radio waves we get from a station but to the castoffs---either in the form of particles or electromagnetic waves---radiated by the parent nucleus. Historically the main forms of radioactivity were identified as alpha, beta, and gamma rays (these being the first three letters of the Greek alphabet). An alpha ray or alpha particle is none other than a He-4 nucleus. Beta rays are now known to be electrons. And gamma rays are really just high-energy waves, even more potent than x rays.



The new kind of radioactivity, discovered in an experiment conducted recently at the Istituto Nazionale di Fisica Nucleare, a nuclear laboratory in Italy, consists of nuclear fragments made of two protons. You can think of this as a new isotope of helium. He-2, as it would be called, is highly unstable and very quickly flies apart. Making the unexpected new nuclear species took some ingenuity. First a beam of neon-20 ions was crashed into a foil of beryllium. In this collision some of the neon nuclei suffered a slight robbery: losing two neutons they ended up as neon18 nuclei. Next, these same flying nuclei encountered a foil of lead. This second collision had the effect of exciting the Ne-18 nucleus into a highly unstable condition. The remedy for this instability was for the Ne-18 nucleus to slough off a fragment. There are several ways of doing this. Among the decay options, the Italian physicists found, was a rare, never-before-demonstrated process in which the Ne-18 nucleus turned itself into an oxygen-16 nucleus, plus that He-2 fragment.
According to one of the researchers, Giovanni Raciti at the LNS-INFN lab , the two-proton decay mode was predicted about 50 years ago. A few experiments conducted before this showed ambiguous evidence: two protons emerged from the decay but one couldn’t tell that the protons had not been thrown out one at a time or both at the same time randomly from the whole Ne-18 or from a single lump.The new experiment definitely shows that the two protons come out together from the breakup of a He-2 cluster (see figure at http://www.aip.org/png/2008/302.htm). The new form of helium isn’t good for anything practical since it doesn’t survive even for a billionth of a second. Raciti believes, however, that the observation of this slender isotope of helium will us understand how are built very unstable nuclei with a number of protons exceeding the one of neutrons and, conversely, how heavy nuclei---the cores of the heavier atoms here on earth---are built up in the interiors of stars. (Physical Review Letters, 16 May 2008)






source: http://www.aip.org/pnu/2008/865.html

I have some questions. I wonder how the physicist can notice such a small change with two protons coming out. It seems to me that using microscope is impossible so what measures should the physicist carry out in order to identify it is the proton but no the other particles?


The new helium isotope exists for such a small period of time so how can the physicist notice that?

In many cases particle physicists use a device called a bubble chamber. As they pass through the chamber, charged particles leave behind a track that can be observed. The speed and the charge of the particle can be measured and thus a good idea of what the particle is can be determined. Multiple observations and what you expect to see in the bubble chamber are pretty conclusive means to determine the type of particle.

In the case of the Helium isotope, consider how long the track would be if it existed for 1 billionth of a second if it were traveling the speed of light:
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It is actually hard to measure a track that long as bubble chambers are often about that size in diameter. So a slower particle of that Helium isotope would be even easier to detect.

-Dan

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"I must not fear. Fear is the mind killer. Fear is the little death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain." - The Litany Against Fear, "Dune" by Frank Herbert

I don't want to be off topic, but I won't consider this sentence as entirely true. Atoms up to iron (26 protons if I recall well) are made in the interior of "medium-big" stars. However, to produce all the other elements, till uranium I think, it is made when stars are literally exploding when at the end of their lives. Our lead, uranium, gold, etc. comes from there. A famous astrophysicist who made his doctoral thesis about synthesis of the element in the sun is Hubert Reeves. He explains this process very well.
If you see the "Aston curve" (this : http://fr.wikipedia.org/wiki/Image:Binding_energy.jpg), then you realize that the iron is the more stable element, and therefore is the hardest element to make fusion/fission with. That's principally why the centers of stars aren't able to produce the heaviest elements, but come from another process.

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Isaac
If the problem is too hard just let the Universe solve it.