Gamma-Ray Transitions Induced in Nuclear Spin Isomers by X-Rays

• Published in: Hyperfine interactions 2001-01, Vol.135 (1-4), p.51-70
• Main Authors: Collins, C B, Rusu, A C, Zoita, N C, Iosif, M C, Camase, D T, Davanloo, F, Ur, C A, Popescu, I I, Pouvesle, J M, Dussart, R, Kirischuk, V I, Strilchuk, N V, Agee, F J
• Format: Article
• Language: English
• Subjects: Absorption; Bremsstrahlung; Cross-sections; Energy storage; Gamma emission; Gamma rays; Hafnium isotopes; Isomers; Nuclear spin; Radiation; Spontaneous emission; X-rays
• ISSN: 0304-3843; 1572-9540
• DOI: 10.1023/A:1013959015577

Because of the high density of energy storage and the large cross section for its release, nuclear spin isomers have attracted considerable recent interest. The triggering of induced gamma emission from them has encouraged efforts to develop intense sources of short-wavelength radiation. One of the more interesting examples is the 16+ 4-qp isomer of 178Hf which stores 2.445 MeV for a half-life of 31 years meaning that as a material, such isomeric 178Hf would store 1.3 GJ/g. Recently, a sample containing 6.3×1014 nuclei of the isomer of 178Hf was irradiated with X-ray pulses derived from a device operated at 15 mA to produce bremsstrahlung radiation with end point energies set to values between 60 and 90 keV. Emission of gamma radiation from the sample was increased by 1–2% above the quiescent value of spontaneous emission. Such an accelerated decay of the 178Hf isomer is consistent with an integrated cross section of 2.2×10−22 cm2 keV if the resonant absorption of the X-rays takes place below 20 keV as indicated by the use of selective absorbing filters in the irradiating beam. The work reported here describes the current experimental focus and results recently obtained with the use of coincident detection of emitted gamma photons by several detectors.