The main experimental difficulty in observing cluster decay comes from the need to identify a few rare events among an enormous number of background alpha particle. The quantities experimentally determined are the partial halflife, Tc, and the kinetic energy of the emitted cluster Ek. There is also a need to identify the emitted particle.
Detection of radiations is based on their interactions with matter, leading mainly to ionizations. Using a semiconductor telescope and conventional electronics to identify the 14C ions, the Rose and Jones's experiment was running for about six months in order to get 11 useful events.
With modern magnetic spectrometers (SOLENO and Enge-split pole), at Orsay and Argonne National Laboratory (see ch. 7 in Ref. pp. 188–204), a very strong source could be used, so that results were obtained in a run of few hours.
Solid state nuclear track detectors (SSNTD) insensitive to alpha particles and magnetic spectrometers in which alpha particles are deflected by a strong magnetic field have been used to overcome this difficulty. SSNTD are cheap and handy but they need chemical etching and microscope scanning.
A key role in experiments on cluster decay modes performed in Berkeley, Orsay, Dubna and Milano played P. Buford Price, Eid Hourany, Michel Hussonnois, Svetlana Tretyakova, A. A. Ogloblin, Roberto Bonetti and their coworkers.
The main region of 20 emitters experimentally observed until 2010 is above Z=86: 221Fr, 221-224,226Ra, 223,225Ac, 228,230Th, 231Pa, 230,232-236U, 236,238Pu, and 242Cm. Only upper limits could be detected in the following cases: 12C decay of 114Ba, 15N decay of 223Ac, 18O decay of 226Th, 24,26Ne decays of 232Th and of 236U, 28Mg decays of 232,233,235U, 30Mg decay of 237Np, and 34Si decay of 240Pu and of 241Am.
Some of the cluster emitters are members of the three natural radioactive families. Others should be produced by nuclear reactions. Up to now no odd-odd emitter has been observed.
From many decay modes with half-lives and branching ratios relative to alpha decay predicted with the analytical superasymmetric fission (ASAF) model, the following 11 have been experimentally confirmed: 14C, 20O, 23F, 22,24-26Ne, 28,30Mg, 32,34Si. The experimental data are in good agreement with predicted values. A strong shell effect can be seen: as a rule the shortest value of the half-life is obtained when the daughter nucleus has a magic number of neutrons (Nd = 126) and/or protons (Zd = 82).
The known cluster emissions as of 2010 are as follows:
|Isotope||Emitted particle||Branching ratio||log T(s)||Q (MeV)|
|114Ba||12C||< 3.4×10−5||> 4.10||18.985|
|28Mg||< 1.18×10−13||> 22.26||74.318|
|28Mg||< 1.8×10−12||> 28.09||72.162|
|236U||24Ne||< 9.2×10−12||> 25.90||55.944|
|237Np||30Mg||< 1.8×10−14||> 27.57||74.814|
|240Pu||34Si||< 6×10−15||> 25.52||91.026|
|241Am||34Si||< 7.4×10−16||> 25.26||93.923|
Read more about this topic: Cluster Decay
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