• Non ci sono risultati.

Reconstruction of solar activity variations in the past by measurement of cosmogenic


Academic year: 2022

Condividi "Reconstruction of solar activity variations in the past by measurement of cosmogenic"


Testo completo


Mem. S.A.It. Vol. 80, 284

SAIt 2009 c Memorie della

Reconstruction of solar activity variations in the past by measurement of cosmogenic

radioisotopes in meteorites

C. Taricco 1,2 , N. Bhandari 3 , P. Colombetti 1,2 , A. Romero 2 , N. Verma 4 , and G. Vivaldo 1,2

1 Universit`a di Torino, Dipartimento di Fisica Generale, Via Pietro Giuria 1, I-10125 Torino, Italy, e-mail: taricco@ph.unito.it

2 Istituto Nazionale di Astrofisica – Istituto di Fisica dello Spazio Interplanetario di Torino, Corso Fiume 4, I-10133 Torino, Italy

3 Basic Sciences Research Institute, Navrangpura, 380 009 Ahmedabad, India

4 Indian Institute of Astrophysics, Bangalore 560 034, India

Abstract. Many reconstructions of solar activity variations in the past are based on the measurement of cosmogenic isotopes (such as 14 C and 10 Be) stored in terrestrial archives.

The concentration of these isotopes is however influenced by terrestrial phenomena. In or- der to avoid this problem our group is studying cosmogenic radioisotopes in meteorites at the underground laboratory of Monte dei Cappuccini in Torino (Italy). Measurement of 44 Ti decay activity in 21 meteorites has revealed a centennial oscillation superimposed on a de- creasing trend of the cosmic ray flux in the last 235 years. The decreasing trend is consistent with some models based on solar open magnetic field variations. We show some prelimi- nary results obtained using a new acquisition system we have recently developed and set up in order to enhance selectivity of 44 Ti detection.

Key words. Sun: activity – Meteoroids – Cosmic rays – Sun: magnetic fields – Techniques:

gamma spectroscopy – Sunspots – Interplanetary medium – Solar-terrestrial relations

1. Introduction

Galactic cosmic ray (GCR) flux in the inter- planetary space is modulated by the solar mag- netic field and therefore an approach to study solar activity in the past is to measure cos- mogenic isotope records. For many years ex- tensive studies on cosmogenic 10 Be and 14 C radioisotopes produced in Earth’s atmosphere and subsequently stored in terrestrial archives, such as ice cores and tree rings, have been carried out in order to deduce information

about solar activity in the past. The measured

records are however affected by terrestrial pro-

cesses such as geomagnetic field variations,

climate-variable deposition rates and exchange

between various reservoirs; on the contrary the

radioactivity produced in meteorites is free of

these interferences. In space, meteoroids are

exposed to both solar and galactic cosmic rays,

but the isotope production is dominated by

GCR particles, as solar particle effects are lim-

ited to the outermost layer (. 5 cm), which sel-

dom survives during the atmospheric transit.


Taricco: Reconstruction of solar activity by meteorite radioactivity measurements 285 (a)





Disk Hard FTP

S.T. 6 µs




OUT PM 5 PM 4 PM 3 PM 2 PM 1

PM 6








from Ge from NaI

PM Plug







BUS Ge signal

NaI signal 3 µs S.T.




Gate Gate Gate


1140 1145 1150 1155 1160 1165 1170

counts / bin

0 20 40 60 80 100

N livetime = 2971808 s

Ge detector energy (keV) 1140 1145 1150 1155 1160 1165 1170

counts / bin

0 20 40 60 80 100

C livetime = 2971808 s


1140 1145 1150 1155 1160 1165 1170

counts / bin

0 100 200 300 400

N livetime = 3251613 s

Ge detector energy (keV) 1140 1145 1150 1155 1160 1165 1170

counts / bin

0 10 20 30 40 50

C livetime = 3251613 s

Fig. 1. a) Block diagram of the detector assembly. b) Detail of detector background for (N)ormally acquired Ge signal and after filtering the data with Ge-NaI (C)oincidence energy windows. c) N and C spectra for Dhajala meteorite (fall 1976, India), showing 1157.03 keV 44 Sc( 44 Ti) prominent γ peak after data filtering.

By measuring radioisotopes having differ- ent half lives it is possible to study GCR vari- ations on different time scales. In particular

44 Ti (t 1/2 = 59.2 years) in meteorites is suitable for studying solar activity variations on cen- tennial scale. This radioisotope is mainly pro- duced in spallation reactions induced by cos- mic ray protons in meteoritic iron and nickel.

Our group has developed γ-ray spectrom- eters to measure the very low 44 Ti activity in meteorites (≈1 dpm/kg). The main challenge is the removal of the strong interference by 214 Bi γ’s from the naturally occurring decay chain of the 238 U. In the underground (70 m.w.e.) labo- ratory of Monte dei Cappuccini in Torino, Italy, we have so far measured 21 chondrites which fell during the last 235 years (Bonino et al.

1995; Taricco et al. 2006). These measure- ments show a linear decreasing trend of ∼43%

in 44 Ti activity (GCR flux) during the past 235 years, superimposed on an ∼87 year os- cillation, with amplitude (peak to trough) of

∼20%. These measurements have also been used to validate different solar activity recon- struction models (Usoskin et al. 2006).

2. New spectrometer: preliminary results

Recently we have set up a new spectrometer using the detectors described in Taricco et al.

(2007): the main detector is a high efficiency and resolution hyperpure Ge crystal (mass

∼3 kg) working in coincidence with a sur- rounding NaI(Tl) umbrella (mass ∼90 kg;

7 photomultipliers). The assembly is housed in a thick Pb-Cd-Cu passive shielding with empty spaces filled with polyethylene to mini- mize radon from ambient air. The cavity for γ counting can accommodate a rock of mass up to ∼1 kg.

We have developed and installed a multiparametric Ge-NaI acquisition system (Fig. 1a), which allows to flexibly filter spec- troscopic information after data acquisition by choosing optimal Ge-NaI coincidence energy windows, crucial for selective 44 Ti activity detection. Moreover, we have de- veloped the managing software embedded in the control electronics in order to allow autonomous acquisition and storage of data for the long-duration meteorite measurements.

Figures 1b,c show some preliminary re- sults, notably the efficient removal of the 214 Bi 1155 keV γ peak in detector background and Dhajala meteorite spectra after filtering the ac- quired data with coincidence windows.

This new γ-ray spectrometer system can possibly be used to measure meteorites which fell even more than two centuries ago.


Bonino, G., Cini Castagnoli, G., Bhandari, N., &

Taricco, C., 1995, Science, 270, 1648

Taricco, C., Bhandari, N., Cane, D., Colombetti,

P., & Verma, N., 2006, J. Geophys. Res., 111,



286 Taricco: Reconstruction of solar activity by meteorite radioactivity measurements

Taricco, C., Bhandari, N., Colombetti, P., Verma, N., & Vivaldo, G., 2007, Nucl. Instrum. Meth. A, 572, 241

Usoskin, I. G., Solanki, S. M., Taricco, C., Bhandari,

N., & Kovaltsov, G. A., 2006, A&A, 457, L25


Documenti correlati

In that case, we could say that the external control, and in particular the accounting control entrusted to the external auditor, should not be mandatory, but it should be quite

plants Location: Solar Batteries Specific Power Solar Radia- tion Specific amount of radiated solar ener- gy per year Specific amount Elec- trical Energy per year with

Time dependence of the cosmic-ray electron and positron spectra measured by PAMELA experiment during the last solar minimum. thesis, Universit`a degli studi di

The present study focuses on the relationship between solar wind MHD turbulence and geomagnetic activity at high latitudes as measured by the AE index, for dif- ferent phases of

The width of the autocorrelation function at mid level (ACFW) is used as a measure of the granulation scale. The im- ages which were taken on the same day or on a few consecutive

The difference between observed behaviour of these three lines at full-disk and the AR contributionm as predicted by the models, correlates with the measured center-disk

To estimate whether this high correlation of the Mn I 539.4 nm line with Mg II index is just result of optical pump- ing, we simulated the change using synthesized profiles of Mn

On the basis of all available global and zonal averages of surface air temperature, as well as measurements in individual stations with long data records we show that the sign of