187 research outputs found
Advanced simulation code for alpha spectrometry
A Monte Carlo code, known as AASI, is developed for simulating energy spectra
in alpha spectrometry. The code documented here is a comprehensive package
where all the major processes affecting the spectrum are included. A unique
feature of the code is its ability to take into account coincidences between
the particles emitted from the source. Simulations and measurements highlight
the importance of coincidences in high-resolution alpha spectrometry. To show
the validity of the simulated results, comparisons with measurements and other
simulation codes are presented.Comment: 21 pages, 4 figures, to be published in Nucl. Instr. and Meth.
Renormalization of the weak hadronic current in the nuclear medium
The renormalization of the weak charge-changing hadronic current as a
function of the reaction energy release is studied at the nucleonic level. We
have calculated the average quenching factors for each type of current (vector,
axial vector and induced pseudoscalar). The obtained quenching in the axial
vector part is, at zero momentum transfer, 19% for the sd shell and 23% in the
fp shell. We have extended the calculations also to heavier systems such as
Ni and Sn, where we obtain stronger quenchings, 44% and 59%,
respectively. Gamow--Teller type transitions are discussed, along with the
higher order matrix elements. The quenching factors are constant up to roughly
60 MeV momentum transfer. Therefore the use of energy-independent quenching
factors in beta decay is justified. We also found that going beyond the zeroth
and first order operators (in inverse nucleon mass) does not give any
substantial contribution. The extracted renormalization to the ratio
at q=100 MeV is -3.5%, -7.1$%, -28.6%, and +8.7% for mass 16, 40, 56, and 100,
respectively.Comment: 28 pages, 6 figure
Shell-Model Effective Operators for Muon Capture in ^{20}Ne
It has been proposed that the discrepancy between the partially-conserved
axial-current prediction and the nuclear shell-model calculations of the ratio
in the muon-capture reactions can be solved in the case of ^{28}Si by
introducing effective transition operators. Recently there has been
experimental interest in measuring the needed angular correlations also in
^{20}Ne. Inspired by this, we have performed a shell-model analysis employing
effective transition operators in the shell-model formalism for the transition
. Comparison of
the calculated capture rates with existing data supports the use of effective
transition operators. Based on our calculations, as soon as the experimental
anisotropy data becomes available, the limits for the ratio can be
extracted.Comment: 9 pages, 3 figures include
ESTIMATION OF H-p(3) AMONG STAFF MEMBERS IN TWO NUCLEAR MEDICINE UNITS IN FINLAND
The eye lens exposure among 16 technicians in two nuclear medicine departments at university hospitals in Finland was investigated by measuring the operational quantity H-p(3) using EYE-D dosemeters. For all workers, the annual mean H-p(3) was estimated to be 1.1 mSv (max. 3.9 mSv). The relation between H-p(3) to routinely monitored personal dose equivalent H-p(10) was clearly correlated. Considering individual dose measurement periods (2-4 weeks), the H-p(3)/H-p(10) ratio was 0.7 (Pearson's coefficient r = 0.90, p 0.1 mSv vs. <0.1 mSv, respectively), i.e. higher Hp(10) predicts H-p(3) more reliably. Moreover, annual H-p(10) data from national dose register during 2009-2018 were used to derive the annual H-p(3) applying the H-p(3)/H-p(10) ratio. The data from Finnish nuclear medicine departments imply that routine measurements of H-p(3) among nuclear medicine technicians are not justified.Peer reviewe
Towards the solution of the anomaly in shell-model calculations of muon capture
Recently many authors have performed shell-model calculations of nuclear
matrix elements determining the rates of the ordinary muon capture in light
nuclei. These calculations have employed well-tested effective interactions in
large scale shell-model studies. For one of the nuclei of interest, namely
Si, there exists recent experimental data which can be used to deduce
the value of the ratio by using the calculated matrix elements.
Surprisingly enough, all the abovementioned shell-model results suggest a very
small value () for , quite far from the PCAC prediction
and recent data on muon capture in hydrogen. We show that this rather
disturbing anomaly is solved by employing effective transition operators. This
finding is also very important in studies of the scalar coupling of the weak
charged current of leptons and hadrons.Comment: Revtex, 6 pages, 2 figs include
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