In this chapter we have described how total absorption measurements can play an important role in improving the beta decay data necessary for summation calculations. We have discussed the technique and how its combination with IGISOL and the JYFL Penning trap has allowed us to perform measurements that had a large impact in the decay heat of 239Pu. These measurements can also be relevant for other reasons. The beta feeding distributions can also be used to deduce the beta strength and test nuclear models. This region (nuclear mass ~ 100) is interesting from the point of view of nuclear structure. For example it has been suggested that triaxial shapes play a role in this region of the nuclear chart (Moller, 2006). Most known nuclei have prolate (rugby ball shape) or spherical shapes in their ground state. If triaxiality plays a role in the structure of these nuclei, this will afect the distribution of the strength in the daughter and it may be studied using the TAS technique. Actually, we have previously used the TAS technique to infer shape effects in the A ~ 70 region (Nacher, 2004) and have started recently a related research programme in the lead region (Algora, 2005).

We plan to continue to make measurements using the TAS to obtain data of relevance to decay heat, but it is important to mention that there also similar efforts ongoing in other facilities and by other groups. In Argonne National Laboratory (Chicago, USA), there is a new facility under construction CARIBU, that will allow for the production of neutron-rich species from the fission of 252Cf. Here there are plans to use again the TAS detector employed in the measurements of Greenwood (Greenwood, 1992) and coworkers. Another example is the development of the MTAS detector by the group of Rykaczewski and coworkers, that will be used at the HRIBF facility at Oak Ridge (USA). These new facilities will contribute in the future to improving the quality of beta decay data for the decay heat application.

Our work had a large impact in 239Pu, but there is still a large amount of work to be done for 235U as was mentioned in the previous section. Additionally decays relevant for other fuels like 232Th should be also studied. Recent work by Nichols and coworkers has identified which nuclei should be measured for the 232Th fuel (Gupta, 2010).

Another aspect worth mentioning is the possible impact of these measurements in the prediction of the neutrino spectrum from reactors. In the same fashion as beta and gamma summation calculations are performed, neutrino summation calculations can be done for a working reactor. Because of the very small interaction cross section, neutrinos leave the reactor almost without interaction in the core. They carry information on the fuel composition and on the power level and their flux can not be shielded or controlled. Because of the small

interaction cross section with matter they are difficult to detect (~ 10~43cm2), but they are produced in very large numbers from the fission products. For example, approximately six antineutrinos are produced per fission, and a one GWei reactor produces of the order of 1021 neutrinos every second. The precision of the neutrino spectrum measurements can be important for neutrino oscillation experiments in fundamental physics experiments like Double CHOOZ and for non-proliferation applications (Fallot, 2007). There is presently a working group of the IAEA, which studies the feasibility of building neutrino detectors, which if positioned outside and close to a nuclear reactor can be used to monitor the power level and the fuel composition of the reactor. These measurements, if they reach the necessary precision, can be used to indicate the fuel used and to monitor manipulations of the fuel in a non-intrusive way (Porta & Fallott, 2010). We plan future measurements to address this topic of research.