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Allen, L.S.; Biggers, W.A.; Prestwood, R. J.; Smith, R. K.

doi:10.1103/physrev.107.1363

Cited by 54 publications

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References 6 publications

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“…Values of the ThZ32 (n,2n) Th231 cross sections were calculated froill the observed activities of ThZ3l and P32 corrected to the end of the irradiation and the illeasured cross section for the reaction S32 (n,p) P32, as reported by Allen et al (6). Separate analyses were performed on the two thorium dislrs so that in each irradiation two measurements of the (n,2n) cross section were obtained.…”

Section: Resultsmentioning

confidence: 99%

Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

Butler¹,

Santry²

1961

Can. J. Chem.

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The excitation curve for the reaction Th232 (n,2n) Th23l has been measured by the activation method from the threshold energy, 6.34 Mev, to 20.4 Mev, relative to the known cross section for the S32(n,p)P32 reaction. Monoenergetic neutrons were obtained from the D ( d , n ) He3 and T (d,n) He4 reactions employing a Tandem Van de Graaff accelerator. From threshold to 9.0 Mev, the (n,2n) cross section rises rapidly, reaching its maximum value of 1.88f 0.09 barns in the region of 9.5 to 11.0 Mev. Above 11.5 Mev the (n,2n) cross section decreases due t o competition of the (n,3n) and (n,2nf) reactions and a t 20.4 Mev it has a value of 0.226f 0.01j barns. INTRODUCTIONAlthough many measurelnents of fast neutron cross sections (n,2n), (n,p), and (n,a) have been made with 14-Mev neutrons, relatively few data have beell published over a range of neutron energies for which these reactions have appreciable cross sections. Due to the scarcity of data on neutron cross sections as a function of energy and the lack of agreement among existing results, a program has been initiated to measure fast neutron cross sections from threshold energies to about 21 Mev. These cross sections will be determined whenever possible with a n accuracy of f 5%.The recent development of the Tandem Van de Graaff accelerator now makes it possible to obtain measurements of fast neutron cross sections over a greater energy range.By accelerating deuterons to a precise energy, the reactions D (d,n) He3 and T (d,n) He4 can be used t o produce monoenergetic neutrons a t any energy from about 5 t o 21 Mev.Results have been published on the cross section for absorption reactions of fast neutrons with Th232. T h e (nly) reaction has been measured up to 14 Mev (1) and the fission cross section has been measured by several investigators from threshold energies up to 11 Mev (1, 2) and a t 14.5 Mev (1, 3). However, data on the significant (n,2n) cross section are only available a t a few energies (4, 5). T h e present investigation was undertaken t o determine the cross section for the reaction ThZ3"n,2n) ThZ3l from threshold, 6.34 Mev, to 20.4 Mev. The reaction (n,p) P3? was used to monitor the fast neutron flux. After the irradiation, thorium was purified radiochemically, and the as well as the P32 produced were determined by absolute beta counting. The (n,2n) cross section a t a particular neutron energy was then calculated from the ThZ3l-and Pa?-activity measurements and the lcnown cross section for the sulphur (n,p) reaction (6). E X P E R I M E N T A L METHOD A . Neutron SourcesNeutrons with energies froin 6 t o 11.6 Mev were obtained from the reaction D (d,n) He3 employing the Chalk River Tandem Van de Graaff accelerator. A gas target cell similar to that described by Johnson and Banta (7) and illustrated in the lower part of Fig. 1 was used to contain the deuterium. The bombarding deuteron beam was magnetically analyzed, focused with a set of quadrupole magnets, and collimated by a 0.125-in. gold aperture. Deuterons scattered off the edge of the...

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Section: Resultsmentioning

confidence: 99%

Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

Butler¹,

Santry²

1961

Can. J. Chem.

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“…The table also lists values of the S3? (n, p)P3%ross section used in the calculations (Allen et al 1957;Santry and Butler 1963). The neutron energies were determined from published tables (Fowler and Brolley 1956) relating the incident deuteron or proton energy to the neutron energy.…”

Section: B Cross-section Values and Errorsmentioning

confidence: 99%

“…In the energy range 4.88 to 13.58 Mev the Alu(n, ~t ) N a ?~ and the Mg24(n, p)Naz4 activation cross sections were calculated from the corrected activities of Nax and P32 and the known cross sections for the monitor reaction, S32(n, Values of the cross sections for the reaction S32(n, p)P3' were taken from a smooth curve through the data of Allen et al (1957) and our own data (Santry and Butler 1963). The SY2(n, p ) P 3 k r o s s section was measured (Allen et al 1957) relative to the U238 fission cross section employing a fission ionization chamber containing the same U238 film used in the fission-cross-section measurements.…”

Section: A the Calculation Of Cross Sectionsmentioning

confidence: 99%

“…The SY2(n, p ) P 3 k r o s s section was measured (Allen et al 1957) relative to the U238 fission cross section employing a fission ionization chamber containing the same U238 film used in the fission-cross-section measurements. The U238 fission cross section in turn was determined relative to the (n, p) scattering cross section.…”

Section: A the Calculation Of Cross Sectionsmentioning

confidence: 99%

“…Monoenergetic neutrons were obtained from the T(p, n)He3, D(d, n)He3, and T(d, n)He4 reactions using a Tandem Van de Graaff accelerator or a 125-kev accelerator. The fast-neutron flux was monitored by measuring the amount of P32 formed in the S32(n, fi)P32 reaction so that the cross-section values reported here are relative to the previously determined cross section for the sulphur (n, fi) reaction (Allen et al 1957;Santry and Butler 1963).…”

Section: Introductionmentioning

confidence: 99%

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EXCITATION CURVES FOR THE REACTIONS Al²⁷(n, α)Na²⁴ AND Mg²⁴(n, p)Na²⁴

Butler¹,

Santry²

1963

Can. J. Phys.

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been measured b y the activation method from near threshold energies t o 20.3 Mev. T h e measurements are relative t o the known cross section for the reaction S3?(n, p)P3?. Monoenergetic neutrons were obtained from the D(d, n)He3, T ( d , n)HeJ, and the T(P, n)He3 reactions employing a Tandem V a n de Graaft' accelerator or 125-kev accelerator. Cross sections for both reactions rise above the minimum detectable value o f 0.02 m b near 5 M e v and reach maximum values o f 126 m b for the Al?l(n, cu)NaS4 reaction and 205 m b for the Mg24(n, p)Na?4 reaction a t 13.5 Mev. Above this energy both cross sections decrease. From the excitation curves effective cross-section values for a fission-neutron spectrum have been calculated as 0 . 6 1 f 0.03 m b for the ( n , a) reaction and 1.34f 0.07 m b for the ( n , p) reaction. I N T R O D U C T I O NIn this paper we report on cross-section measurements for two fast-neutron reactions, A127(n, a)Na24 and Mg24(n, p)Na24, which give rise to the same product, 15-hour Na24. This work is part of a research program designed to measure by the activation method complete excitation curves up to 20.3 Mev for fastneutron induced reactions (Butler and Santry 1961). Most of the published data on fast-neutron cross sections are for 14-Mev neutrons and relatively few complete excitation curves are available. In general, previous measurements are characterized by rather large standard deviations and there is a lack of agreement among the existing results. In the present work, however, by a careful choice of irradiation conditions and counting techniques, it has been possible to measure these cross sections with an accuracy of ~4 % over a large energy range. An accurate knowledge of the variation in the cross section with neutron energy for these threshold reactions is essential if these reactions are to be used for fast-neutron monitoring. The A127(n, a)Na24 reaction is of particular importance in this regard inasmuch as it has been used in the field of reactor technology for high-energy neutron monitoring. Furthermore, precise cross-section measurements would also provide the experimental data required to test the predictions of the statistical and direct interaction theories which are being used in the calculation of nuclear reactions. This latter aspect will be dealt with in a forthcoming publication.The A127(n, a)Na24 (threshold of 3.25 Mev) and the Mg24(n, p)Naa4 (threshold 4.93 Mev) reactions were chosen to study neutron interactions in low-Z nuclei. These reactions produce the product nuclide, Na24, which has a convenient halflife and can be easily measured. Monoenergetic neutrons were obtained from the T(p, n)He3, D(d, n)He3, and T(d, n)He4 reactions using a Tandem Van de

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Wirkungsquerschnitte für die Erzeugung von Positronenstrahlern durch schnelle Neutronen

Hertlein

1963

Annalen der Physik

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57Wirkungsquerschnitte fiir die Erzeugung von Positronenstrahlern durch schnelle Neutronen ' 1 Von P r i t z H e r t l e i nMit 10 Abbildungen Inhaltsubersicht Die absoluten Positronenaktivierungsquerschnitte mehrerer (n, 2 n)-Prozesse und der Reaktion NiSs (n, p ) Cob* wurden im ,,weiBen" Neutronenspektrum des Forschungsreaktors Munchen bestimmt. Zur Eliminierung der hohen Untergrundaktivitiit, die vor allem von (n, 7)-Prozessen herriihrt, wurde eine Differenz-KoinzidenzmeBmethode angewandt, bei der die Positronenaktivitiit durch Koinzidenzen zwischen den Vernichtungsquanten in zwei einander gegenuberstehenden Szintillationsziihlern nachgewiesen wurde. Die Ermittlung der totalen Nachweiswahrscheinlichkeit der Anordnung fir Vernichtungsquantenkoinzidenzen erfolgte mit einem kalibrierten NaZz-Priiparat. Als BezugsprozeS zur Absolutbestimmung der Wirkungsquerschnitte diente die Reaktion S32 (n, p) P32, deren energieabhiingiger Aktivierungsquerschnitt bekannt ist.Aus den Messungen laBt sich ein uber den gesamten SpaltfluS gemittelter Reaktionsquerschnitt und ein mittlerer Wirkungsquerschnitt fiir den Energiebereich oberhalb der Schwellenenergie der untersuchten Reaktion herleiten. Letzterer wird mit berechneten Werten verglichen, die sich aus der Kontinuumstheorie von F e s h b a c h und WeiBkopf ergeben. Es zeigt sich eine befriedigende Obereinstimmung zwischen den theoretischen und experimentellen Resultaten. I m Einklang mit einer Hypothese von H u r w i t z und B e t h e ist kein genereller Unterschied im Verlauf der (n, 2 n)-Querschnitte zwischen Targetkernen mit gerader, ungerader und magischer Anzahl der Protonen oder Neutronen festzustellen.

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Cross Sections for theS32(n, p)P32and the

Abstract: The cross section for S 32 (w,^)P 32 has been measured for incident neutron energies up to 15 Mev. The data at high energies differ from previously published measurements. The cross section for S 34 (w,a)Si 31 also has been measured for incident neutron energies up to 14.1 Mev.

Cited by 54 publications

References 6 publications

Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

EXCITATION CURVES FOR THE REACTIONS Al²⁷(n, α)Na²⁴ AND Mg²⁴(n, p)Na²⁴

Wirkungsquerschnitte für die Erzeugung von Positronenstrahlern durch schnelle Neutronen

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Cross Sections for theS32(n, p)P32and the

Abstract: The cross section for S 32 (w,^)P 32 has been measured for incident neutron energies up to 15 Mev. The data at high energies differ from previously published measurements. The cross section for S 34 (w,a)Si 31 also has been measured for incident neutron energies up to 14.1 Mev.

Cited by 54 publications

References 6 publications

Th232 (n,2n)Th231 CROSS SECTION FROM THRESHOLD TO 20.4 MEV

Th232 (n,2n)Th231 CROSS SECTION FROM THRESHOLD TO 20.4 MEV

EXCITATION CURVES FOR THE REACTIONS Al27(n, α)Na24 AND Mg24(n, p)Na24

Wirkungsquerschnitte für die Erzeugung von Positronenstrahlern durch schnelle Neutronen

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Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

Th²³² (n,2n)Th²³¹ CROSS SECTION FROM THRESHOLD TO 20.4 MEV

EXCITATION CURVES FOR THE REACTIONS Al²⁷(n, α)Na²⁴ AND Mg²⁴(n, p)Na²⁴