36
R. Rüffer and A. I. Chumakov
Time spectra are collected in the traditional ‘start-stop’ technique (see Fig. 1.14).
Normally, the detector signal is the “start” signal whereas the “stop” signal is derived
from the bunch clock, i.e., the reference signal of the rf-frequency of the SR source.
Fast time-to-digital converter and digitizer techniques are under development in
order to improve (i) the response time at early times (< 5 ns) needed especially for
Mössbauer isotopes with short life times, (ii) the throughput, and (iii) to allow for
“multi-hit” operation. The multi-hit option together with high throughput avoids
time gating of the prompt pulse and is mandatory for experiments at the new XFEL
sources [111]. Furthermore, fast position sensitive detectors [112–114] received
attention for applications such as NSAS, TDI, SRMS.
1.6.2.1 Resonance Detector
For some applications such as IXSNRA, SRMS, and RSMR the energy analysis is
carried out with a so-called resonance detector. In principle it consits of an x-ray
detector like an APD with its timing electronics and an absorber or a scatterer, which
contains the Mössbauer isotope for the resonance analysis.
In the simplest case like IXSNRA the APD is covered e.g. by an α−
57 Fe foil.
When the energy of the incident radiation matches the energy of the nuclear transition,
the scattering leads to nuclear forward scattering in the foil of the resonance isotope.
By time discrimination only the (delayed) NFS signal of the time spectrum is taken
and time integrated. This resulting signal measures only “resonant quanta” and is
used for the energy analysis.
For SRMS the details of the detector system are more sophisticated and will be
described in detail in this book by Seto et al. [60]. In case of RSMR (and the SMS)
normally time discrimination is not necessary due to the “100%” resonant beam.
1.6.3 Sample Environment
Versatile sample environment is a prerequisite for a holistic approach of the investigation of novel systems. Nuclear resonance techniques by themselves may contribute in
the study of electric, magnetic, and structural properties, static and dynamic. Combining those techniques with other on-line and off-line techniques such as XRD,
MOKE, transport measurements, etc., will foster a holistic picture. Especially the
small beam size and divergence of synchrotron radiation favours sophisticated experimental environments not feasible in the home laboratories with radioactive sources.
Standard equipment allows for applying e.g. a combination of low temperature, high
pressure, and high magnetic field. Other examples are UHV systems for in situ investigation of surface, interfaces, and nano-structured materials [115]; laser heating system combined with high pressure for in situ investigation of the Earth’s interior and
new materials [116]; pulsed high-magnetic field [117]; combined RAMAN and IR
environment for the investigation of cross-over systems and protein dynamics [118].
R. Rüffer and A. I. Chumakov
Time spectra are collected in the traditional ‘start-stop’ technique (see Fig. 1.14).
Normally, the detector signal is the “start” signal whereas the “stop” signal is derived
from the bunch clock, i.e., the reference signal of the rf-frequency of the SR source.
Fast time-to-digital converter and digitizer techniques are under development in
order to improve (i) the response time at early times (< 5 ns) needed especially for
Mössbauer isotopes with short life times, (ii) the throughput, and (iii) to allow for
“multi-hit” operation. The multi-hit option together with high throughput avoids
time gating of the prompt pulse and is mandatory for experiments at the new XFEL
sources [111]. Furthermore, fast position sensitive detectors [112–114] received
attention for applications such as NSAS, TDI, SRMS.
1.6.2.1 Resonance Detector
For some applications such as IXSNRA, SRMS, and RSMR the energy analysis is
carried out with a so-called resonance detector. In principle it consits of an x-ray
detector like an APD with its timing electronics and an absorber or a scatterer, which
contains the Mössbauer isotope for the resonance analysis.
In the simplest case like IXSNRA the APD is covered e.g. by an α−
57 Fe foil.
When the energy of the incident radiation matches the energy of the nuclear transition,
the scattering leads to nuclear forward scattering in the foil of the resonance isotope.
By time discrimination only the (delayed) NFS signal of the time spectrum is taken
and time integrated. This resulting signal measures only “resonant quanta” and is
used for the energy analysis.
For SRMS the details of the detector system are more sophisticated and will be
described in detail in this book by Seto et al. [60]. In case of RSMR (and the SMS)
normally time discrimination is not necessary due to the “100%” resonant beam.
1.6.3 Sample Environment
Versatile sample environment is a prerequisite for a holistic approach of the investigation of novel systems. Nuclear resonance techniques by themselves may contribute in
the study of electric, magnetic, and structural properties, static and dynamic. Combining those techniques with other on-line and off-line techniques such as XRD,
MOKE, transport measurements, etc., will foster a holistic picture. Especially the
small beam size and divergence of synchrotron radiation favours sophisticated experimental environments not feasible in the home laboratories with radioactive sources.
Standard equipment allows for applying e.g. a combination of low temperature, high
pressure, and high magnetic field. Other examples are UHV systems for in situ investigation of surface, interfaces, and nano-structured materials [115]; laser heating system combined with high pressure for in situ investigation of the Earth’s interior and
new materials [116]; pulsed high-magnetic field [117]; combined RAMAN and IR
environment for the investigation of cross-over systems and protein dynamics [118].