.
The investigation of prompt emission in fission is very important in understanding the fission process and to improve the quality of evaluated nuclear data required for new applications. In the ...last decade remarkable efforts were done for both the development of prompt emission models and the experimental investigation of the properties of fission fragments and the prompt neutrons and
γ
-ray emission. The accurate experimental data concerning the prompt neutron multiplicity as a function of fragment mass and total kinetic energy for
252
Cf(SF) and
235
(
n
,
f
) recently measured at JRC-Geel (as well as other various prompt emission data) allow a consistent and very detailed validation of the Point-by-Point (PbP) deterministic model of prompt emission. The PbP model results describe very well a large variety of experimental data starting from the multi-parametric matrices of prompt neutron multiplicity
ν
(
A
,
T
K
E
)
and
γ
-ray energy
E
γ
(
A
,
T
K
E
)
which validate the model itself, passing through different average prompt emission quantities as a function of
A
(
e.g.
,
ν
(
A
)
,
E
γ
(
A
)
,
〈
ɛ
〉
(
A
)
etc.), as a function of
TKE
(
e.g.
,
ν
(
T
K
E
)
,
E
γ
(
T
K
E
)
) up to the prompt neutron distribution
P
(
ν
)
and the total average prompt neutron spectrum. The PbP model does not use free or adjustable parameters. To calculate the multi-parametric matrices it needs only data included in the reference input parameter library RIPL of IAEA. To provide average prompt emission quantities as a function of
A
, of
TKE
and total average quantities the multi-parametric matrices are averaged over reliable experimental fragment distributions. The PbP results are also in agreement with the results of the Monte Carlo prompt emission codes FIFRELIN, CGMF and FREYA. The good description of a large variety of experimental data proves the capability of the PbP model to be used in nuclear data evaluations and its reliability to predict prompt emission data for fissioning nuclei and incident energies for which the experimental information is completely missing. The PbP treatment can also provide input parameters of the improved Los Alamos model with non-equal residual temperature distributions recently reported by Madland and Kahler, especially for fissioning nuclei without any experimental information concerning the prompt emission.
.
A new triangular form of the residual temperature distribution
P
(
T
), entering the prompt emission models in which the sequential emission is globally taken into account (
e.g.
, the Los Alamos ...model of Madland and Nix with subsequent improvements and the Point-by-Point model), is proposed. A deterministic treatment of the successive emission of prompt neutrons, which is based on recursive equations of the residual temperatures, was developed. This modeling was validated by the good description of many and different experimental data of prompt emission (
e.g.
,
ν
¯
(
A
)
,
〈
ν
〉
(TKE),
〈
ɛ
〉
(
A
)
,
〈
ɛ
〉
(TKE),
E
¯
γ
(
A
)
, etc.) and the good agreement with the results of other prompt emission models. To see a possible systematic behaviour of
P
(
T
) as a function of energy and fissioning nucleus, the deterministic treatment of sequential emission was applied to 11 nuclei undergoing fission (spontaneously or induced by thermal and fast neutrons with energies up to the threshold of the second chance fission) for which reliable experimental fission fragment distributions
Y
(
A
,
TKE
) exist. The shapes of all
P
(
T
) distributions for the light and heavy fragment groups and for all fragments resulting from this modeling can be approximated with a triangular form. To make possible the use of this form into the prompt emission models with a global treatment of sequential emission, a connection between the average residual temperature
〈
Tr
〉
and the temperature of initial fragments
〈
Ti
〉
is needed. An important finding of this study concerns the ratio
〈
Tr
〉
/
〈
Ti
〉
, which is
≈
0
.
6
for all studied fissioning systems. This result allows to obtain a new triangular form of
P
(
T
) defined only as a function of initial temperature, which is applicable to any fissioning system at any energy, in the frame of prompt emission models with a global treatment of sequential emission.
To compare two methods of noninvasive assessment: transient elastography (TE) and acoustic radiation force impulse elastography (ARFI).
Our study included 114 subjects: 38 healthy volunteers, ...(considered to have no fibrosis - F 0) and 76 patients with chronic liver disease: 53 who had undergone liver biopsy (LB) (7 with F 1, 24 with F 2, 22 with F 3 Metavir) and 23 previously diagnosed with cirrhosis (F4 Metavir). In each patient we performed a liver stiffness measurement by means of TE and ARFI. ARFI (shear wave velocity quantification) was performed at 3 points: at 0 - 1 cm, at 1 - 2 cm and at 2 - 3 cm under the capsule. For each depth, 5 valid measurements were made, and a median value was calculated, measured in m/sec.
A direct, strong, linear correlation (Spearman rho = 0.848) was found between TE and the stage of fibrosis (p < 0.001). A significant, direct correlation was found between ARFI measurements made 1 - 2 cm and 2 - 3 cm below the liver capsule and the severity of fibrosis (rho = 0.675 and 0.714 respectively). The subcapsularly measured ARFI values showed a poor correlation with fibrosis (rho = 0.469). The best test for predicting significant fibrosis (F ≥ 2) was TE, with the area under receiver-operating characteristic curve (AUROC) 0.908, significantly larger than the AUROCs for ARFI. If only ARFI is considered, measurements made 1 - 2 and 2 - 3 cm below the capsule have the best predictive value, with AUROCs not significantly different from each other (0.767 and 0.731, respectively). For predicting fibrosis (F > 0), TE had the best predictive value: optimized cut-off 5.65 kPa (AUROC -0.898). For ARFI, the cut-offs were: 1.4 m/sec, AUROC -0.747 (1 - 2 cm), and 1.26 m/sec AUROC -0.721 (2 - 3 cm). For predicting cirrhosis (F = 4 Metavir), the optimized cut-offs were: TE -12.9 kPa (AUROC -0.994); ARFI - 1.78 m/sec for measurements made 2 - 3 cm below the capsule, AUROC - 0.951.
At present, liver elasticity evaluation by means of ARFI is not superior to TE for the assessment of liver fibrosis. For ARFI, the most reliable results are obtained if measurements are made 1 - 2 and 2 - 3 cm below the liver capsule. ARFI is an accurate test for the diagnosis of cirrhosis.
A method of total excitation energy (TXE) partition between fully-accelerated fission fragments based exclusively on the systematic behaviour of experimental
ν
(
A
)
(
ν
H
/
ν
pair
as a function of
A
...H
being parameterized) is proposed. This TXE partition method has the advantage to be not dependent on models and assumptions made at scission and in this sense it can be taken as a possible reference method. From this TXE partition applied on many fissioning systems a general parameterization of the fragment residual temperature ratio
R
T
=
T
L
/
T
H
as a function of
A
H
is obtained, giving the possibility to predict prompt fission quantities as a function of fragment. Other TXE partition methods (based on models and assumptions at scission or on equal residual temperatures of complementary fragments at full acceleration) are compared to this one, revealing limits of applicability as well as the sensibility of prompt neutron emission models to the TXE partition. The behaviour of experimental
ν
(
A
)
with the increase of incident energy consisting in the multiplicity increase for heavy fragments only, is argued and entirely supported by the quantitative Point-by-Point model results of
ν
(
A
)
describing very well the experimental
ν
(
A
)
of
237Np(n, f) at 0.8 and 5.5 MeV incident energies.
The experimental data of average prompt neutron multiplicity as a function of total kinetic energy of fragments (TKE) exhibit, especially in the case of 252Cf(SF), different slopes dTKE/dv and ...different behaviours at low TKE values. The Point-by-Point (PbP) model can describe these different behaviours. The results revealed that the slope dTKE/dv does not vary with the incident energy and the flattening of at low TKE values is more pronounced at low incident energies. The average model parameters dependences on TKE resulted from the PbP treatment allow the use of the most probable fragmentation approach, having the great advantage to provide results at many TKE values in a very short computing time compared to PbP and Monte Carlo treatments. This paper talks about point-by-point model description of average prompt neutron data as a function of total kinetic energy of fission fragments.
The Point-by-Point (PbP) model as well as the related computer code is a useful tool to provide different prompt emission data as a function of fragment mass A, fragment charge Z, total kinetic ...energy (TKE), and total average ones. The present work focuses on the sensitivity of prompt neutron multiplicity to different properties of the fission fragments. In the construction of the fragmentation range of the PbP treatment, the use of different Z prescriptions affects the multiparametric matrices of different fragment and prompt emission quantities q(A,Z,TKE). The nonnegligible influence of how the most probable charge is considered (as unchanged charge distribution without or with the charge deviations ΔZ as a function of A or an average ΔZ value), as well as the number of Z taken at each A, is discussed. The calculated average prompt emission quantities as a function of A, as a function of TKE, and total average ones depend on the accuracy of experimental Y(A,TKE) distributions. The prompt neutron multiplicity of complementary fragments v
pair
(A) has a weak dependence on the total excitation energy (TXE) partition between complementary fully accelerated fragments. This assures a good prediction of the average prompt neutron multiplicity as a function of TKE and of the total average one even in the case of a rough or inappropriate TXE partition. The systematic behavior revealed by the experimental ratio v
H
/v
pair
as a function of A
H
together with the weak dependence of v
pair
(A) on the TXE partition can be exploited-in the absence of experimental v(A) information-for an indirect verification of predicted v(A).
The request for new and/or more accurate data of independent fission product yields (FPY) and other distributions of pre- and post-neutron fragments constitutes a priority on an international level. ...The prompt emission model codes nowadays employed are refined enough to answer this request with the condition of using reliable distributions Y(A,TKE) of pre-neutron fragments. Up to now in the majority of cases such distributions were determined by experimental data. Y(A,TKE) from theoretical calculations can extend the use of prompt emission model codes to fissioning systems for which the experimental information is very scarce or completely missing. Such Y(A,TKE), recently obtained from four-dimensional Langevin model calculations in the frame of multi-modal fission, is tested by its use (as input) in the deterministic prompt emission model code DSE, for the case of
239
Pu(n
th
,f). The obtained prompt emission results (e.g. prompt neutron multiplicity distributions ν(A), ν(TKE)) succeed to describe the experimental data and the independent FPY agree with the experimental data, too. Although visible differences between these results and those obtained with a an experimental Y(A,TKE) distribution exist. The present investigations have also emphasized other interesting aspects, e.g. concerning the pre-neutron fragments which contribute to the pronounced peaks and dips in the structure of both the mass yield Y(A
p
) and the isotonic yield Y(N
p
) of post-neutron fragments, in connection with the role played by the even–odd effect in fragment charge, as well as how the position and magnitude of pronounced peaks and dips are influenced by the Y(A,TKE) distribution. Independent FPY separately for each number “n” of emission sequences leading to the last residual fragment Y(A
p
= A-n), reported for the first time, have shown how and which of these components contribute to the structure of total Y(A
p
). The crucial role of the energy partition in fission is revealed again by showing that a good choice of the R
T
parameterization can lead to very close results to those obtained with a TXE partition based on modeling at scission. On the contrary the use of an unique R
T
value for all fragmentations can alter -in some fission cases—the sawtooth shape of ν(A) and its agreement with experimental data, despite the refinement of the prompt emission treatment itself and of a reliable Y(A,TKE) distribution employed in calculations.
Chronic viral hepatopathies can be evaluated through invasive or noninvasive methods. The aim of this paper was to assess the indications and results of transient elastographic (TE) evaluation of the ...liver in patients with chronic viral hepatitis and cirrhosis.
We retrospectively assessed all the liver stiffness measurements (LSM) (FibroScan®) performed over a two-year period (2007 - 2009).
3,459 TE evaluations were made mainly for the assessment of: HCV hepatitis, HBV infection (chronic hepatitis and inactive HBV carriers), biviral hepatitis (B + C or B + D), cirrhosis and in 176 normal subjects (to establish the normal values of LSM). From the 3,459 FS evaluations, we could not obtain valid LSM in 183 cases (5.3 %). 93.9 % of the patients in the failure group were overweight (BMI > 25 kg/m²). In 527 cases (16 %) the SR (success rate = number of valid measurements/total number of measurements) was < 60 %. TE reproducibility was analyzed in 287 cases. The ICCs for the three operators were 0.985, 0.949, and 0.874 respectively, and the overall ICC was 0.982. 596 cases of cirrhosis were evaluated. A cut-off value of 23.3kPa was found to predict the presence of at least grade 2 esophageal varices.
LSM by means of TE is a promising noninvasive evaluation method, which can be used in numerous clinical situations, some in which its value is well established (suspicion of LC, predicting significant fibrosis) and some in which its value is less known (HBV chronic hepatitis, inactive HBV carriers or severity of portal hypertension).
The Large Hadron–Electron Collider at the HL-LHC Aksakal, H; Alekhin, S; Allport, P P ...
Journal of physics. G, Nuclear and particle physics,
11/2021, Letnik:
48, Številka:
11
Journal Article
PDF
