9 Nuclear Emulsions
419
detector to thermal neutrons at the Kyoto University Research Reactor Institute
(KURRI). The spatial resolution achieved in the measurement of the absorption
point was estimated to be 0.34 μm from the average grain density of the track far
from the end of its range. The detection efficiency was measured by exposing the
detector to a cold neutron beam at BL05 port in the Materials and Life Science
Experimental Facility (MLF) at J-PARC [148]. The measured efficiency of (3.3 ±
0.6)×10 −4 was consistent with the expectation.
The other detector type consists of a 50-nm-thick converter layer made of 10 B 4 C
formed on a 0.4-mm-thick silicon substrate and coated by 10-μm-thick, fine-grained
emulsion [149]. The converter layer was covered by C (50 nm) and NiC (60 nm)
layers. An α particle or a 7 Li nucleus will be detected in the emulsion, as shown
in Fig. 9.23 (right). They are produced via the reactions: 10 B + n → α + 7 Li +
2.79 MeV (6%) or 10 B + n → α + 7 Li + 2.31 MeV (94%). The detector was exposed
to cold and ultra-cold neutrons at J-PARC, and the events of neutron absorption by
10 B were clearly observed. The position resolution of the absorption point in the
10 B 4 C layer depends on the track angle. By limiting the track angle, the expected
position resolution is ∼100 nm [150], which is 1–2 orders of magnitude higher than
that of the conventional detectors used for detecting cold and ultra-cold neutrons.
Further optimisation of the thickness of the converter layer and development of
automatic track reconstruction are explored. The development of these detectors
paves the way to future applications such as the precise measurement of the position
distribution of quantised states of ultra-cold neutrons or neutron imaging with future
neutron sources.
9.6.2.4 Study of Double-Hypernuclei
The knowledge of − interaction is limited as only one out of the nine double
hypernuclei events detected by E373 is fully analysable to extract information of
the interaction (Fig. 9.24). In order to answer questions such as the nuclear mass
dependence of − interaction, the E07 experiment at J-PARC is being carried out,
which is aiming at studying − interactions with 100 double hypernuclei events,
one order of magnitude larger statistics with respect to E373. As schematically
shown in the right side of the Fig. 9.24, E07 uses a 1.7 GeV/c K − beam hitting a
diamond target to produce − hyperons (dss), subsequently stopped and captured
by one of emulsion detector nuclei to produce double hypernuclei. The detector has
a hybrid structure with a silicon strip detector and a spectrometer system for the K +
identification, needed to tag − hyperons. The emulsion detector will be analysed
by an automated scanning system dedicated to this experiment. E07 conducted the
physics runs in 2016 and 2017. The emulsion readout and analysis are in progress.
419
detector to thermal neutrons at the Kyoto University Research Reactor Institute
(KURRI). The spatial resolution achieved in the measurement of the absorption
point was estimated to be 0.34 μm from the average grain density of the track far
from the end of its range. The detection efficiency was measured by exposing the
detector to a cold neutron beam at BL05 port in the Materials and Life Science
Experimental Facility (MLF) at J-PARC [148]. The measured efficiency of (3.3 ±
0.6)×10 −4 was consistent with the expectation.
The other detector type consists of a 50-nm-thick converter layer made of 10 B 4 C
formed on a 0.4-mm-thick silicon substrate and coated by 10-μm-thick, fine-grained
emulsion [149]. The converter layer was covered by C (50 nm) and NiC (60 nm)
layers. An α particle or a 7 Li nucleus will be detected in the emulsion, as shown
in Fig. 9.23 (right). They are produced via the reactions: 10 B + n → α + 7 Li +
2.79 MeV (6%) or 10 B + n → α + 7 Li + 2.31 MeV (94%). The detector was exposed
to cold and ultra-cold neutrons at J-PARC, and the events of neutron absorption by
10 B were clearly observed. The position resolution of the absorption point in the
10 B 4 C layer depends on the track angle. By limiting the track angle, the expected
position resolution is ∼100 nm [150], which is 1–2 orders of magnitude higher than
that of the conventional detectors used for detecting cold and ultra-cold neutrons.
Further optimisation of the thickness of the converter layer and development of
automatic track reconstruction are explored. The development of these detectors
paves the way to future applications such as the precise measurement of the position
distribution of quantised states of ultra-cold neutrons or neutron imaging with future
neutron sources.
9.6.2.4 Study of Double-Hypernuclei
The knowledge of − interaction is limited as only one out of the nine double
hypernuclei events detected by E373 is fully analysable to extract information of
the interaction (Fig. 9.24). In order to answer questions such as the nuclear mass
dependence of − interaction, the E07 experiment at J-PARC is being carried out,
which is aiming at studying − interactions with 100 double hypernuclei events,
one order of magnitude larger statistics with respect to E373. As schematically
shown in the right side of the Fig. 9.24, E07 uses a 1.7 GeV/c K − beam hitting a
diamond target to produce − hyperons (dss), subsequently stopped and captured
by one of emulsion detector nuclei to produce double hypernuclei. The detector has
a hybrid structure with a silicon strip detector and a spectrometer system for the K +
identification, needed to tag − hyperons. The emulsion detector will be analysed
by an automated scanning system dedicated to this experiment. E07 conducted the
physics runs in 2016 and 2017. The emulsion readout and analysis are in progress.