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New isotopes of erbium and holmium
ReactorSciena and Technology(Journalof NuclearEurgy
Parr A/B) 1961.Vol. IS. pp. 229m233. PergamonPress Ltd.
LETTERS
Printedin Northern Ireland
TO THE EDITORS determined from the position of the first two levels; respectively 16.7 & 0.35 and 0.042 $ 0.008.
New isotopes of erbium and holmium* THECONVERSION~~~~~~O~ spectrum of the erbium isotopes formed in the bombardment of tantalum by 660 MeV protons from the synchrocyclotron at the Joint Institute of Nuclear Studies has been studied. A type BPP-1 g&spectrometer was used in this work. The source had dimensions 1 x 30 mm and the solid angle of acceptance was 4 per cent of 4rr. From measurements on the ls7Ba K661.6 line the resolution of the instrument was 0.2-0.25 per cent. A special magnetometer was used to measure the magnetic field which ensured reliable working and permitted us to study conversion lines having half-lives of 15 min or greater. The accuracy of the conversion line energy determinations was 0.1-03 per cent. Amongst the large number of conversion lines (more than 100) belonging to the neutron-deficient isotopes of erbium and holmium,‘al a group of lines was observed with a half-life Tlla = 2.4 hr. From a study of these lines transitions to an isotope of holmium (Z = 67) and also to an isotope of dysprosium (Z = 66) were identified (see Table 1). The holmium daughter product was separated from the erbium fraction within 2 hr of separating the erbium from the tantalum and it was found that the intensity of the lines corresponding to transitions in dysprosium fell to half-value in (28 i 2) min: These facts are consistent with the following decay chain
they are
Acknowledgments-The author takes pleasure in thanking B. S. DZHELEPOVand K. IA. GROMOVfor advice and discussion and 1. A. YUTLANDOVand Y. V. NARSEEVfor undertaking the chemical separation of the samples. I. S. DNEPROVSKII
REFERENCES 1. BEKKERMAN I. M., GUMENIUKB. A. and DNEPROVSKIII. S., The Beta-Spectrometer Type BPP. All Union Institute of Scientific and Technological Information, Moscow (1959). 2. DNEPROVSKUI. S. and KOLESOVG. M., Izv. Akad. Nauk. SSSR (Ser. fir.) 22, 935 (1958). 3. DZHELEPOVB. S. and PEKER L. F., Deformed Region Nd-0s. Dubna (1958).
Nuclei in the
Effect of boron-containing layers on the yield of secondary gamma rays? (Received
3 August
1959)
THE WEIGHTand dimensions of the biological shield of a reactor are usually determined by the hard y-radiation arising from neutron capture in the reactor shell and in the first few layers of the shield. It is therefore extremely important to find ways 27min Er%Ho-Dy of reducing this r-ray flux. The most intense secondary y-radiation arises from the while the relationship between the energies (98.6 and 218.2 keV) radiative capture of the thermal and comparatively low energy and intensities of the transitions implies that these transitions neutrons which have been slowed down in the light materials of take place between levels with energies E1 = 98.6 keV (2+) and the shield. If these neutrons are absorbed in a layer containing E, = 316.8 keV (4+), which correspond to the first rotational boron, fewer of them are captured in the constructional band of an even-even dysprosium nucleus. From the position of materials, particularly steel, which would otherwise have the the first excited level in relation to the number of neutrons”’ it effect of hardirning the y-radiation.“se) Neutron capture in the can be assumed that the mass number of the nuclei in this chain boron gives rise to soft, weakly-penetrating y-quanta with an is A = 158. energy ho.5 MeV and the provision of shielding against these The values of the constants A and B in the expression E = is very much easier. AZ(Z - 1) - BZ2(Z + l)$ giving the energies of these levels were We have studied the effect of boron carbide, inserted between steel and Plexiglas (which was used to simulate water) on the TABLE ~.---GAM~~ATRANSITIONSIN ERBIUM AND DYSPROSIUM intensity of production of y-rays in steel. The geometry of the -experiment is illustrated in Fig. 1. Two kinds of steel were Charge of nucleus T 1/P hv, investigated: ST-3 and IX18N9T, which is a stainless steel. Multipolarity in which transition keV hr The steel and Plexiglas were fitted together to form a prism occus having cross-sectional dimensions 710 x 710 mm. A (Po-a)Be neutron source with an intensity of 2 x 10’ 98,6 2.4 f 0.1 66 E2 neutrons se& was placed inside a water shield in front of the 2.5 f 0.1 218.2 66 steel prism. There were channels in the steel prisfn and Plexiglas E2 or M3 320.5 2.4 * 0.1 66 into which plugs containing detectors could be inserted. and 357.1 2.4 It 0.1 66 between the steel and Plexiglas were filters containing boron, 387.3 2.4 f 0.1 67 which absorbed the thermal and epi-thermal neutrons passing 945.9 2.5 * 0.1 from the water (Plexiglas) into the steel. Three types of filter 2.5 f 0.1 848.5 were used and these are designated II, III and IV in Fig. 1. ??
Translated
by D.
L.
ALLAN
from Atomnaya Energiya 8, 46
(I 960).
6
229
t Translated (1960).
by D. L. ALLAN from Atomnaya Energiya
8, 49
Parr A/B) 1961.Vol. IS. pp. 229m233. PergamonPress Ltd.
LETTERS
Printedin Northern Ireland
TO THE EDITORS determined from the position of the first two levels; respectively 16.7 & 0.35 and 0.042 $ 0.008.
New isotopes of erbium and holmium* THECONVERSION~~~~~~O~ spectrum of the erbium isotopes formed in the bombardment of tantalum by 660 MeV protons from the synchrocyclotron at the Joint Institute of Nuclear Studies has been studied. A type BPP-1 g&spectrometer was used in this work. The source had dimensions 1 x 30 mm and the solid angle of acceptance was 4 per cent of 4rr. From measurements on the ls7Ba K661.6 line the resolution of the instrument was 0.2-0.25 per cent. A special magnetometer was used to measure the magnetic field which ensured reliable working and permitted us to study conversion lines having half-lives of 15 min or greater. The accuracy of the conversion line energy determinations was 0.1-03 per cent. Amongst the large number of conversion lines (more than 100) belonging to the neutron-deficient isotopes of erbium and holmium,‘al a group of lines was observed with a half-life Tlla = 2.4 hr. From a study of these lines transitions to an isotope of holmium (Z = 67) and also to an isotope of dysprosium (Z = 66) were identified (see Table 1). The holmium daughter product was separated from the erbium fraction within 2 hr of separating the erbium from the tantalum and it was found that the intensity of the lines corresponding to transitions in dysprosium fell to half-value in (28 i 2) min: These facts are consistent with the following decay chain
they are
Acknowledgments-The author takes pleasure in thanking B. S. DZHELEPOVand K. IA. GROMOVfor advice and discussion and 1. A. YUTLANDOVand Y. V. NARSEEVfor undertaking the chemical separation of the samples. I. S. DNEPROVSKII
REFERENCES 1. BEKKERMAN I. M., GUMENIUKB. A. and DNEPROVSKIII. S., The Beta-Spectrometer Type BPP. All Union Institute of Scientific and Technological Information, Moscow (1959). 2. DNEPROVSKUI. S. and KOLESOVG. M., Izv. Akad. Nauk. SSSR (Ser. fir.) 22, 935 (1958). 3. DZHELEPOVB. S. and PEKER L. F., Deformed Region Nd-0s. Dubna (1958).
Nuclei in the
Effect of boron-containing layers on the yield of secondary gamma rays? (Received
3 August
1959)
THE WEIGHTand dimensions of the biological shield of a reactor are usually determined by the hard y-radiation arising from neutron capture in the reactor shell and in the first few layers of the shield. It is therefore extremely important to find ways 27min Er%Ho-Dy of reducing this r-ray flux. The most intense secondary y-radiation arises from the while the relationship between the energies (98.6 and 218.2 keV) radiative capture of the thermal and comparatively low energy and intensities of the transitions implies that these transitions neutrons which have been slowed down in the light materials of take place between levels with energies E1 = 98.6 keV (2+) and the shield. If these neutrons are absorbed in a layer containing E, = 316.8 keV (4+), which correspond to the first rotational boron, fewer of them are captured in the constructional band of an even-even dysprosium nucleus. From the position of materials, particularly steel, which would otherwise have the the first excited level in relation to the number of neutrons”’ it effect of hardirning the y-radiation.“se) Neutron capture in the can be assumed that the mass number of the nuclei in this chain boron gives rise to soft, weakly-penetrating y-quanta with an is A = 158. energy ho.5 MeV and the provision of shielding against these The values of the constants A and B in the expression E = is very much easier. AZ(Z - 1) - BZ2(Z + l)$ giving the energies of these levels were We have studied the effect of boron carbide, inserted between steel and Plexiglas (which was used to simulate water) on the TABLE ~.---GAM~~ATRANSITIONSIN ERBIUM AND DYSPROSIUM intensity of production of y-rays in steel. The geometry of the -experiment is illustrated in Fig. 1. Two kinds of steel were Charge of nucleus T 1/P hv, investigated: ST-3 and IX18N9T, which is a stainless steel. Multipolarity in which transition keV hr The steel and Plexiglas were fitted together to form a prism occus having cross-sectional dimensions 710 x 710 mm. A (Po-a)Be neutron source with an intensity of 2 x 10’ 98,6 2.4 f 0.1 66 E2 neutrons se& was placed inside a water shield in front of the 2.5 f 0.1 218.2 66 steel prism. There were channels in the steel prisfn and Plexiglas E2 or M3 320.5 2.4 * 0.1 66 into which plugs containing detectors could be inserted. and 357.1 2.4 It 0.1 66 between the steel and Plexiglas were filters containing boron, 387.3 2.4 f 0.1 67 which absorbed the thermal and epi-thermal neutrons passing 945.9 2.5 * 0.1 from the water (Plexiglas) into the steel. Three types of filter 2.5 f 0.1 848.5 were used and these are designated II, III and IV in Fig. 1. ??
Translated
by D.
L.
ALLAN
from Atomnaya Energiya 8, 46
(I 960).
6
229
t Translated (1960).
by D. L. ALLAN from Atomnaya Energiya
8, 49