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Z. Naturforsch. 68a, 610 – 620
(2013)
doi:10.5560/ZNA.2013-0039
Recoil Induced Room Temperature Stable Frenkel Pairs in α-Hafnium Upon Thermal Neutron Capture
1 Universität Leipzig, Fakultät für Physik und Geowissenschaften, Institut für Experimentelle Physik II, Linnéstraße 5, 04103 Leipzig, Germany
2 Variable Energy Cyclotron Centre, Bhabha Atomic Research Centre, 1/AF Bidhan nagar, Kolkata 700064, India
3 Saha Institute of Nuclear Physics, 1/AF Bidhan nagar, Kolkata 700064, India
4 Bose Institute, APC Road, Kolkata 700009, India
Received January 25, 2013 / revised April 24, 2013 / published online July 3, 2013
Reprint requests to: T. B.; E-mail:
butz@physik.uni-leipzig.de
Ultrapure hafnium metal (110 ppm zirconium) was neutron activated with a thermal neutron flux of 6.6E{12} cm−2s−1 in order to obtain 181Hf for subsequent time differential perturbed angular correlation (TDPAC) experiments using the nuclear probe 181Hf(β−)181Ta. Apart from the expected nuclear quadrupole interaction (NQI) signal for a hexagonal close-packed (hcp) metal, three further discrete NQIs were observed with a few percent fraction each. The TDPAC spectra were recorded for up to 11 half lives with extreme statistical accuracy. The fitted parameters vary slightly within the temperature range between 248 K and 373 K. The signals corresponding to the three additional sites completely disappear after ‘annealing’ at 453 K for one minute. Based on the symmetry of the additional NQIs and their temperature dependencies, they are tentatively attributed to Frenkel pairs produced by recoil due to the emission of a prompt 5.694 MeV γ-ray following thermal neutron capture and reported by the nuclear probe in three different positions. These Frenkel pairs are stable up to at least 373 K.
Key words: α-Hf; Frenkel Pairs; Nuclear Quadrupole Interaction.
PACS numbers: 61.66.Dk; 61.80.-x; 76.80.+y