Appendix 8, Decay of Cerium-144

Abstract

As part of an earlier program of investigation in this laboratory, studies were made of the gamma ray spectrum and the beta ray spectrum of cerium-144. In the present work, seme coincidence studies were made on one of the beta groups appearing in the cerium-144 decay and on the gamma rays appearing in the deexcitations from the energy levels of praseodymium-144. Sources of cerium-144 were prepared frcm carrier free radioactive cerium-144 as supplied by the Oak Ridge National Laboratory. The sample material was more than two years old at the time of preparation of sources. No additional chemical purification was attempted. Sources for use in the beta crystal spectrometer were mounted on thin Formvar film on spectrometer ring mounts. The gamma ray spectrum of cerium-144 in the energy range 20 kev to 180 kev is shown in Figure 1. This spectrum was determined using a 2-inch by 2-inch NaI(Tl) crystal. The pulse spectrum was analyzed by a Radiation Instrument Development Laboratory (RIDL) 200 channel analyzer. The spectrum gives clear evidence of gamma ray peaks at 34 {+-} 3 kev and 134 {+-} 2 kev. A rather broad peak at 80 kev is observed. An indication of a gamma ray groupmore » of energy near 100 kev is also shown. The resolution of the detecting assembly was 9.8 percent at 662 kev. The uncorrected relative intensities of the three groups of 34, 80 and 134 kev are 95, 35, and 100, respectively. These intensities are for the gamma radiation exclusive of internal conversion. Gamma-gamma coincidence measurements were made using two of the 2-inch by 2-inch sodium iodide crystals placed at 90 degrees to one another, Ganmma radiation of a particular energy was selected by means of a single channel analyzer and the 200 channel analyzer was used to analyze any coincident pulses frcm detector number two. Insertion of a 1.6 m/sec delay in channel one gave direct observation of random coincidences under identical experimental conditions. Coincidence spectra were taken setting the single channel analyzer for 34 {+-} 2, 80 {+-} 2, 100 {+-} 2 kev gamma radiation. Five hour true and random counts were taken at each setting. Figure 2 shows the spectrum of gamma radiation of cerium-144-praseodymium-144 in coincidence with the 34 kev gamma radiation. There is evidence for coincident radiation of 34, 55, 82 and 101 kev energy with only weak coincidences at 135 kev energy. Figure 3 shows the gamma ray spectrum of cerium-144-prasedymium-144 in coincidence with the 80 kev gamma radiation. Here the expected coincidences with radiation of energy about 35 kev is observed as well as coincidences with gamma radiation of about 54 kev energy. There are no indications of coincidences with gamma radiation of energy greater than 54 kev and less than 180 kev (channels 100 to 199 are not shown). Figure 4 shows the gamma ray spectrum of cerium-144-praseodymium-144 in coincidence with the 100 kev gamma radiation. Here coincidences are observed with radiation of about 34 kev energy (channels 100 to 199 are not shown). No coincidences were observed between gamma rays of 34 kev and gamma rays of energy less than 180 kev (channel 100 to 199 are not shown) except for relatively weak coincidences vith 34 kev.« less